Distributed generators (DGs) within distribution systems can be used as emergency sources to restore critical loads during a major outage caused by extreme events. Since the capacity of DGs is limited, the dynamic performance of DGs needs to be validated by simulations before executing restorative strategies. Currently, many DGs use power electronic converters for grid connection. Therefore, electromagnetic transient (EMT) simulation is needed to study their transient characteristics for feasibility evaluation of service restoration plans. However, the detailed models of converters, which model each individual switch, are time consuming for EMT simulation, unsuitable for the purpose of online validation. This study first develops a simplified model of micro gas turbine (MTG). Then the dynamic average-value modelling technique is used to construct the average-value model (AVM) of grid-connected converters. Finally, the MTG generation system model is integrated into a distribution system model for feasibility evaluation of restoration strategies. A radial test system including three MTG generation systems is utilised to validate the effectiveness of the proposed model. The numerical simulation results indicate that compared with the detailed model, the AVM improves the efficiency of simulation while still accurately predicts the transient behaviours of MTG generation systems. The proposed model is applicable for the online validation of restoration strategies.

Fault characteristics analysis is precondition of relay protection. Theoretical derivation of permanent magnet synchronous generator (PMSG) fault current is necessary. In accordance with the theory that grid-side converter of PMSG is a power balance system under control action, an electromagnetic transient model of PMSG was proposed. Based on it, the active and reactive current was deduced and then the expression of three-phase fault current was obtained and its components, frequency, and attenuation speed of every component and other characteristics were analysed comprehensively. Simulation on PSCAD and field fault recording data as practical analysis verifies that the expressions and the characteristics are correct. The results of this paper are not only important to relay protection, but also are references to transient calculation and transient modelling.

IEC 61850 conformance alone does not necessarily guarantee interoperability of devices from different manufacturers. Achieving full interoperability in a substation protection and control system involving different vendors will increase the confidence of power utilities to deploy digital bays or substations on site. This study presents the development of a virtual site test platform to assess the engineering process and interoperability performance for a fully digital substation with multi-vendor bay solutions. A data monitoring tool has been developed to visualise data flows in IEC 61850 networks, which can help commissioning engineers to intuitively validate signals like they do for conventional schemes. Case studies are presented to investigate the interoperability of sampled values, generic object oriented substation events and manufacturing message specification communication services. The learning from the system integration and testing will help utilities identify potential issues in engineering phases and hence reduce the risks associated with future site tests.

The integration of distributed renewable energy resources in combination with advancements in power electronics make the application of multi-terminal medium voltage DC grids a promising and flexible solution. Fast and selective protection concepts in combination with DC (disconnecting) switches for fault handling are required to ensure high reliability and safe grid operation of these systems. Medium voltage DC grids may be realised based on several converter technologies with different fault clearing capability. Depending on the converter technology, switches for isolating faulted branches or DC circuit breakers (CBs) for fault clearance become necessary. DC medium voltage CB concepts have already been proposed. However, the switching times of these CBs vary significantly depending on the presence or absence of mechanical components resulting in different requirements for fault detection. This contribution evaluates the relations between different converter and DC CB technologies, DC grid topologies and fault detection methods according to selective fault clearing. Transient simulation studies are carried out for the development of protection concepts. Based on the results, reasonable technological combinations of the above-mentioned technologies are identified. Special consideration is given to the dimensioning of series reactors as fault current rise limiting devices.

Correct setting of protection relays are of major importance to the reliable operation of the power system. The root cause of two consecutive blackouts is analysed and shown to origin from a combination of several minor errors which all can be related to an insufficient/wrong setting of the distance relays and their optional functions together with insufficient testing when putting into operation. The learning lessons are discussed and outlined in order to avoid future blackouts having similar origin.

With digital communication technologies continuing to grow in performance and reliability, a fully digital substation automation system (SAS) with a sampled values based process bus has become a realisable prospect in the foreseeable future. This, however, demands additional work in engineering configurations and tightens the existing constraints on multi-vendor interoperability, network performance and time synchronisation. As a result, detailed testing and validation of SASs prior to installation is paramount. Integrated testing is the most comprehensive approach to test a SAS, as it evaluates the performance of multiple aspects of the system simultaneously. Real-time power system simulators can interface with multiple intelligent electronic devices in real-time via IEC 61850 station and process buses, while accurately simulating the electrical substation. Hence, they possess the unique capability to carry out closed-loop, integrated testing of SASs. This study presents a methodology to test a fully digital SAS using a real-time power system simulator. Particular emphasis is given on carrying out integrated system testing of a SAS in a laboratory environment. Example test scenarios are provided to highlight the effectiveness of the proposed testing approach.

When an extreme weather event strikes a distribution system, it is helpful to use microgrids to restore the interrupted critical loads. Due to the relatively small capacity and low inertia of distributed generators (DGs), the switching operations during the restoration process may cause severe fluctuations in voltage, current, and frequency, leading to prime-mover stalling or triggering protection relays. It is essential to investigate the dynamic characteristics of DGs during the restoration procedure. The dynamic models of different types of DGs are developed to analyse the dynamic characteristics. Analytical constraints on the dynamic performance of DGs are obtained from the simulation results, which can be incorporated into the optimisation models of critical load restoration problems. The modified IEEE 32-bus test feeder is simulated to validate the effectiveness of the proposed method.

Fast DC breakers are essential components to realise future high-voltage DC grids. Recent development in the industry shows great feasibility in achieving such DC breakers using various technologies. In particular, hybrid DC breakers with modular design have the potential to operate in fault current limiting (FCL) mode, which can provide added functionalities in DC grid protection. However, the degrees of freedom in breaker design and control, and their impact on the transients associated with the FCL operation has not yet been addressed in the literature. Understanding the characteristics of the FCL operation is crucial to achieve interoperability between various technologies in a multivendor environment. This study investigates the impact of design and control parameters on the transients during the FCL operation. Possible applications of the FCL operation in DC grid protection are discussed and demonstrated in a four-terminal test system.

The short-circuit response of a voltage source converter (VSC) can vary from each other significantly with different control strategies. This study investigates the performance of distance protection under unbalanced faults considering two control strategies during fault-ride-through using hardware-in-the-loop tests. Variations on fault type, converter current limit, fault resistance and pre-fault power flow conditions are also examined. The tests reveal that the error in measured impedance caused by fault resistance will be enlarged in a converter-dominated power system. The first control strategy tends to cause overreach problem while the second can raise both overreach and underreach problems. The indeterminacy associated with the second strategy is jointly affected by control parameters, converter current limit, fault resistance and pre-fault power flow conditions. The findings of this study can help to stipulate grid requirements under unbalanced faults.

The high penetration of distributed generation in distribution grids and the development of microgrids may cause the malfunctioning of the conventional distribution level protection systems. Despite multiple works dedicated to addressing this problem, the development of reliable, high-speed, and cost-efficient protection systems for active grids remains a topical issue. This study proposes a protection system for medium voltage lines that relies entirely on the analytical description of travelling wave transients. This protection uses only local high-frequency current measurements and power-frequency voltage measurements, which potentially makes it a low-cost yet reliable solution. The protection system operates securely by not tripping healthy lines in case of disturbances that do not lead to any faults. The proposed protection is tested on the IEEE 34-bus distribution system with distributed generation.

Introduction of renewable resources into the power system has raised significant challenges to the protection system. Conventional ways of working are deemed insufficient and need to be improved. This study will focus on one subject that has often been overlooked – unbalanced charging current. The application of long high voltage submarine cables to connect a large number of wind turbines to offshore substation has resulted in the considerable unbalanced charging current flowing into the system during earth fault. This study will present a real-life application of differential protection to an offshore wind farm network. It will primarily discuss how the existence of unbalanced charging current affects the sensitivity of the differential protection relays. This discussion is further substantiated with actual fault measurements taken from one of Siemens built offshore wind farms. This study will subsequently recommend ways to improve the sensitivity of differential protection based on Siemens’ experience. As more and larger wind farms are built, this study serves a very valuable experience for offshore wind farm protection.

Conventionally distribution substations utilise hardwires (copper cables) for achieving different operational requirements such as interlocking, inter-tripping and automatic transfer systems. The latest substation communication standard IEC 61850 introduced a new method for horizontal communication of digital and analogue messages between devices in the substation called GOOSE or Generic Object Oriented Substation Event. In addition, IEC 61850 adopted seamless redundancy protocols, namely PRP and HSR, to encourage the utilisation of GOOSE communication in high-dependency applications. Here, the performance of GOOSE communication is assessed under different background traffic conditions in an HSR redundant network. This is achieved by utilising a data quality analyser to inject Ethernet ARP packets simulating background traffic. The network also includes an Ethernet switch, time server, laptop and three IEDs or Intelligent Electronic Devices. The IEDs are natively supporting IEC 61850 with HSR protocol, and configured to exchange GOOSE messages. Test results show GOOSE communication is affected by the traffic, but the severity of the problem, i.e. delays and losses in the communicated messages, depends on the level of traffic, as a percentage of the bandwidth. Tests also show redundancy enhances the overall network reliability via dual paths, limiting the effect of background traffic on the communicated messages..

This study describes an approach for distance protection load desensitisation based on sequence components. Compared to conventional load blinders in the impedance plane, this method allows keeping the necessary sensitivity to high-impedance faults for distance protections, even under high-load conditions. The advantages and drawbacks of this approach are discussed and the results of tests using the algorithm are presented.

Electrical distribution network is constantly ageing worldwide. Therefore, probability of cable faults is increasing over time. Fast recovering of damaged networks is of vital importance and a quick and automatic identification of the failure source may help to promptly recover the functionality of the network. The scenario we are taking into consideration is a vast number of recording devices spread across a network that constantly monitor low voltage cables. When the current of a cable reaches a very high value, data is sent to a central server which analyses it through a variant of a Variational Auto Encoder (VAE), a deep neural network. This VAE has been trained by using historical data collected from several hundreds of faults recorded, but in which only a handful of them has been labelled by an on-site analysis of the fault. Data used for training is simply the recorded levels of voltages and currents, after a simple pre-processing step. The final goal is to let the network distinguish if the fault occurred in a point of the cable, on a joint, or at the pot-end located at the termination. A preliminary evaluation of its ability to generalise over the non-labelled samples shows encouraging results.

To achieve a highly reliable data communication network, Future Intelligent Transmission Network Substation (FITNESS) project has considered three different substation data communication redundancy networks. These include two independent parallel star networks, High-availability Seamless Redundancy (HSR) network, and Parallel Redundancy Protocol (PRP) network. This paper presents the assessment and comparison analysis of the data flow performance for these three networks. A typical 275 kV substation with the consideration of three redundancy networks is modelled and simulated using OPNET a communication network simulation tool. The data flow capability performance with respect of the network time delay for the typical protection and control equipment requirements (e.g. IEDs and MUs) in one bay are simulated and analysed. Results show that two independent parallel star networks have the highest data flow capacity. The capacity of PRP network is reduced by a half, while the capacity of HSR network is reduced to a quarter. The results also reveal that Ethernet Switch can consume a part of network bandwidth as well. The work would help power utilities to determine an optimal number of devices to be installed and to ensure highly reliable data communication network for protection and control functions in an IEC 61850 based digital substation..

Time-domain protection relays have gained importance in modern transmission networks since they are able to increase the system stability margins by accelerating the fault clearance procedures. However, as this kind of function is in some aspects new for protection engineers, the modelling and simulation of time-domain relays have been topics of interest to utilities. In this study, a modern time-domain protection relay is modelled and simulated. To evaluate its performance, a wide variety of fault scenarios (882 fault cases) is simulated using the alternative transients program. The obtained results show that the behaviour of the implemented model is very close to that reported by the time-domain relay manufacturer.

Starting synchronous motors connected to high-inertia loads often leads to starting times greater than the synchronous motor locked rotor time. This compromises thermal algorithm capabilities to provide adequate rotor thermal protection under stall and slow acceleration conditions. This study presents a novel slip-dependent thermal model which obtains a slip estimated using stator current modulation caused by rotor saliencies. The proposed algorithm is validated using an OpenModelica model and its performance is compared against the conventional slip-independent thermal model. Finally, the algorithm is implemented in a protective relay and field tested on a 28820HP motor driving a high-inertia gas injection compressor at a natural gas liquids facility.

Within the framework of modernisation of the European electricity grid, multi-terminal high-voltage direct current (HVDC) offshore grids shall be integrated into future transmission systems. An essential aspect of multi-terminal HVDC systems is fast and selective DC-side fault handling and the separation of faulty lines. This study investigates the applicability of different control methods relying on full-bridge-based converters in combination with high-speed switches for a fast and selective separation of faulty line segments in a multi-terminal HVDC cable system in a symmetrical monopole configuration. It is shown that the proposed line current control method can significantly reduce the separation time of a faulty line compared with standard fault control methods. The analysis is based on simulations in PSCAD|EMTDC^™ with a converter model based on the CIGRÉ WG B4.57, which is enhanced for the use of full-bridge converters with fault current control schemes.

Line differential protection is popular for its good selectivity and simplicity as long as there is a dependable communication system between the two ends of the line. However, the sensitivity needs to be compromised when the traditional line differential scheme is applied for ultra-high voltage (UHV)-alternating current lines because of the large charging current. A study of the impact of the UHV transmission line characteristics on line differential protection and a proposed solution based on the compensation of the phase shift that exists between the sending and receiving end currents are presented.

As part of a new Gas Turbine R&D project, there is always a need to test it throughout a wide range of speeds and loads. A generator connected to a load bank has been chosen to be the variable load for the turbine. This poses several challenges from a generator protection perspective. The study addresses these challenges.

A reduction in time required to locate and restore faults on a utility's distribution network reduces customer minutes lost. Detection of repeating transient (self-clearing) faults allows early repair and avoids full faults which reduces the number of customer interruptions. Both these reductions bring improved customer service and direct cost savings from lower regulator penalties. Traditional approaches to fault location involve fault impedance determination from high-volume waveform files dispatched across a communications channel to a central location for processing and analysis. This study describes an existing distributed scheme, where data processing is undertaken locally within substation-based recording instruments thus reducing data volume transmission. Processed events/faults and impedance data are emailed to a central server for entry into the graphical information system, which returns potential fault locations yielding timely repair and restoration of circuits. This study presents a series of fault location case studies based on field experience from the Scottish Power Energy Networks distribution network.

In this study, the development of a wide-area, multi-objective cost function is explained. The cost function is designed for implementation on wide-area phasor measurement unit data. In this study, the cost function was applied to the IEEE 30 and 57 Bus models for monitoring and control purposes. Although the cost function was originally intended as a situational awareness tool that indicated system health; it has now been applied as a control metric for the operation of on-load tap changing transformers on a variety of standard IEEE test systems. The system benefits, relative to conventional local control, are quantified. The primary metrics for testing protection outcomes are maximum voltage deviation and line thermal overload. The wide-area optimisation is assessed from a voltage profile, reactive power demand, and transmission losses. The benefits of this type of wide-area control are demonstrated in a variety of situations and environments.

Explicit current transformers (CTs) are used to measure the currents at power transformers, but these efforts are often saved for the voltage measurements. However, even if there are no dedicated voltage transformers (VTs) attached at the power transformer itself, the voltages at the buses will be measured somewhere. By using Sampled Values, the voltage measurements can be easily delivered to any protection function that requires them. The time synchronised measurements can be simply aligned and processed by the protection algorithms. Transformer differential protection works with Sampled Values just as well as with classical secondary currents. However, with the availability of both the voltages and currents at the transformer, some experiments can be made. Not only Kirchhoff's law for the currents applies, but also the conservation of energy, so the power flow through the transformer must also be balanced. With all the measurements available, the power balance from all terminals is easily observed, vector groups need not be taken into account. In a simulation, the power system quantities are produced as Sampled Values and recorded. Power measurements during the course of power systems faults are compared and the feasibility of such a concept is discussed.

This study reports on experience gained during factory testing on a pilot project digital substation. Testing IEDs in a digital substation is dependent on how test and simulation functionality as defined by the IEC61850 is implemented by the vendors, and also requires a different approach to testing compared to testing on a conventional station. This study highlights limitations imposed on testing due to missing IED test facilities, as well as the need for the end customer to fully specify IED functionality to ensure vendor interoperability.

Current differential protection is one of the major protections for extra-high-voltage/ultra-high-voltage transmission lines, but its performance is severely weakened by the prominent capacitive charging current along transmission lines. Travelling waves take the charging current into account inherently, hence travelling wave-based protection is not impacted by the charging current. Based on the principle of travelling waves, this study proposes the concept of integrated surge impedance (ISI), which is defined as the ratio of the difference of voltage quantities at two ends of a line to the sum of current quantities at two terminals of the same line. The ISI, closely related to travelling wave differential current, can discriminate between internal and external faults clearly. The ISI-based criterion is composed of power frequency quantities in order to ensure the robustness of the protection. The action zone is designed on an impedance plane. EMTP simulation verifies the correctness of the proposed pilot protection.

Voltage source converters (VSCs) are highly vulnerable to DC fault current. Protection methods which can quickly locate and isolate DC faults are necessities in VSC-based multi-terminal DC (VSC-MTDC) systems for its safe and reliable operation. In this paper, a fast and collaborative DC fault location and isolation strategy are proposed. In this strategy, hybrid DC circuit breakers (HDCCBs) are used as the main protection device. The operation control of HDCCB is redesigned and cooperates with fault location results to achieve fast fault isolation. For the fault location method, a fast di/dt criterion is used for fault pretreatment, the transient-voltage energy difference criterion is used to make sure its selectivity. The overall protection strategy is demonstrated in a four-terminal VSC-MTDC system using PSCAD/EMTDC platform. The performances of the typical DC circuit breaker-based strategy and the proposed strategy were compared. Numerous simulation results under various conditions proved its flexibility and validity.

A strategy to evaluate the impact of intermediate sources on the performance of transmission line distance protection is proposed in this study. The influence of an intermediate infeed on the sensitivity of the reach setting and the resulting tripping performance of a distance protection scheme is the main emphasis of this study. The proposed strategy considers the effectiveness of various protection schemes on the protection challenges expected on the National Grid transmission network due to future changes in the generation mix. PowerFactory (DIgSILENT PowerFactory software package) will be used to simulate a double circuit transmission network, when a fault occurs and the strength of the main and intermediate sources change from weak to typical to strong. This study discusses various solutions to the problems observed and a methodology for adapting the grading strategy of distance protection as transmission networks evolve into the future.

The ‘Internet of things’ is the ‘new revolution’. During the past decades, there were major changes in the energy industry: the increased implementation of renewable generation, together with a greater use of electronic power elements in the network such as high-voltage DC links and the use of flexible AC transmission system and new market requirements, introduce new challenges and a need for more intelligent assets monitoring; and additional optimisation with a better balance in the combination of different energy sources and thus guaranteeing the reliability of supply and quality of energy; together with the identification of new business models that allow the integration of new technologies, neutralising cyber threats and ensure an adequate dissemination of knowledge to new generations. Companies are migrating to a more digital model based fundamentally on three pillars: communications, big data and artificial intelligence. The right combination of these three pillars will optimise the operation of the electrical system, reducing costs and polluting emissions, accelerating the adoption of non-polluting energies and renewable energies, while maximising economic performance and a closer way of interacting with users. The industrial Internet of things (IIoT) has been identified as one of the technologies with most potential impact in the next years.

This study evaluates the performance of a permissive overreach protection scheme proposed to ensure rapid fault clearance, in a real example of a medium-voltage (MV) distribution loop by one of the largest European Distribution System Operators. The MV loop and the protection devices including the proposed signal comparison schemes have been modelled in detail in the power system analysis software DIgSILENT PowerFactory. The evaluation has been performed using steady-state short-circuit calculations and electromagnetic transient simulations. This analysis reveals limitations in the permissive overreach scheme based on the zero sequence phase comparison directional logic in the case of cross country faults. Alternative solutions, such as phase, zero sequence and negative sequence magnitude differential protection schemes, have been assessed. A permissive overreach protection scheme based on the negative sequence phase comparison directional algorithm has also been considered.

DC bias can be induced via earth return currents (ERCs) from high voltage direct current (HVDC) systems or geomagnetically induced currents (GICs). However, these currents have different characteristics. This study divides dc bias into ERC and GIC types and separately compares their impacts on current transformers (CTs) performance. This was achieved by simulations using PSCAD/EMTDC. The ERC and GIC were represented by different signatures to describe their characteristics. Transformer differential protection was used as an example to demonstrate how ERC and GIC affect CTs transient performance and protection behaviours. The results show the effects of ERC and GIC on CT performance were similar. Although GIC could introduce more measurement errors than ERC, under a practical level of dc bias current, this difference was negligible. Either ERC or GIC has limited impact on correctly specified CTs during steady state. ERC and GIC can transiently saturate CTs during faults, but CTs can remove the transient saturation inherently. As long as the technical specifications of the CTs were adequate for the application, the impacts of ERC or GIC on CTs and protection behaviour were minor. Consequently, the low-frequency characteristic of GIC was negligible when considering its impact on CTs and protection behaviour.

The demand for accurate time synchronisation available 24/7 increases with the growth of critical substation applications, such as phasor measurement, merging units, travelling-wave fault location and current differential protection schemes. In order to yield the best accuracy and granularity from such applications, the use of a common, reliable and precision-time reference is essential.

Ultra-high-voltage (UHV) transmission lines have a higher requirement for selecting faulted phases fast and reliably. The coupling relationship between the three phases is analysed in detail. On the basis of the coupling relationship, the principle of faulted phase selection (FPS) is proposed, which utilises the time-domain energy of three-phase transient currents. To remove high-frequency noise and preserve the transient current waveform features invariant, a morphological filter with flat structure element is applied in FPS algorithm. The simulation model of Jindongnan–Nanyang–Jingmen UHV transmission project is established in EMTP. The testing results show that the proposed algorithm is feasible and fast (<2 ms) in case of various fault conditions.

The proposed method in this study is a current-restrained DC under-voltage protection for a bipolar HVDC system. In a bipolar HVDC system, the inrush phenomenon of a converter transformer can cause the DC voltage drop of the operating pole due to the sympathetic inrush. In this case, the DC under-voltage protection relay in a bipolar HVDC system may trip the operating pole. Then the bipolar HVDC system cannot transmit any power. In order to block the ignition of an unwanted trip when the converter transformer of the not-operating pole is energised, a current-restrained DC under-voltage protection method for a bipolar HVDC system is suggested. In this method, a DC harmonic current-restraining element is used to detect an inrush phenomenon. The second harmonic component and the fundamental frequency component in the DC-side current are used as a factor to judge the inrush phenomenon in this method. In order to discuss the proposed method, a bipolar HVDC system is modelled with CIGRE HVDC benchmark model by using PSCAD/EMTDC.

This study applies distance protection to real mixed overhead-underground distribution feeders, as an alternative to conventional overcurrent protection schemes. The efficiency of the proposed distance-based protection scheme is examined both in the radial (normal state) and in the looped operation of the distribution feeders. Moreover, distributed generating units of various types are assumed connected to the feeders to investigate their effect on the efficiency of the protection scheme. The latter proved sufficient to coordinate properly with the other protection means in the system, following a fuse-blowing philosophy, providing reliable protection to the lines.

In recent years, different protection strategies for high-voltage direct current (HVDC) grids have been developed by the industry and academia for the reliable and safe operation of direct current grids. The proposed strategies have different impacts on the AC networks where HVDC grids are connected. In the case of embedded HVDC grids embedded in a synchronous AC network, a partial loss of the HVDC grid might cause the desynchronisation of the AC grid. Therefore, it is of utmost importance to assess the impact of those protection strategies into the stability of the whole network. The objective of this study is to propose a methodology for the transient stability assessment of a simple but representative AC grid in case of DC fault. After validation of the methodology, some HVDC link protection criteria are defined in terms of the Critical Time to Return to Operation. These criteria will be helpful for the design of HVDC protection systems or for the sizing of future HVDC links in order to respect the constraints of the existing protection strategies.

Multiple-circuit transmission lines combining different voltage levels in one tower present extra challenges when setting a protection philosophy, as faults between voltage levels are possible. This study analyses faults in multiple-circuit transmission lines that are partly underground cable, by investigating the impact of the cable section on the fault current magnitude and operation of distance protection relays, without pilot scheme. The study shows that a cable's bonding configuration and layout have a small impact on the short-circuit magnitude, whereas the screen's grounding impedance and the presence of an earth continuity conductor impact the fault current magnitude. It was also demonstrated that distance protection relays settings used to protect the higher voltage line against single-phase-to-ground faults are capable of protecting the line against combined faults, for typical line configurations and short-circuit powers.

Since IEC 61850 became the widely used standard for substation communication with a lot of implementations, advanced approaches became applicable. Setting groups (SGs) are such a topic. The concept of SGs is known for a long time and was used in IEC 60870-5-103 already. IEC 61850 extended to approach. This study describes the definitions made within the standard. The SGs services have a relation to another concept in IEC 61850's data model – the logical device hierarchy with its Data Object GrRef. Also, these definitions and their impact on behaviour or IED will be described. The main topic is the practical implementation. Starting with the concept of a utility which will be described the requirements for IEDs and testing equipment will be carved out. Changing and controlling the SGs is a client's task. This study describes the implementation of an IEC 61850 client in testing solutions. An implementation example available in testing software will be presented. Available protection parameters in IED's data model offer a wide range of advanced testing and supervision possibilities. The solution proposed enhances the reliability of the grid and enhances the quality of testing. Implementation of adaptive protection is possible.

High-impedance Earth fault detection is always a topic for any kind of neutral point treatment in electrical power line systems. For compensated networks, it is the disseminated opinion that fault detection is too difficult. The authors aim to show it is simpler and much more sensitive compared with other neutral point treatments. Especially for the sensitivity of classical fault detection methods such as wattmetric (cos ϕ), admittance method and transient method, the question is what sensitivity to expect. This study gives a basic overview of the mentioned detection methods, their achievable sensitivity and the requirements for that. Since the fault detection should work with natural signals only, methods with artificial signal injection during the fault are not included. The necessary measurement accuracy for different detection methods will be considered as well. Basic aspects with practical measurements taken during Earth fault tests in a compensated system with overhead lines are compared. The fault impedance was >5 kΩ in the 10 kV system. The earth fault tests have been undertaken with Energijos Skirstymo Operatorius. The device Erdschluss Ortungs Relais-3D (EOR-3D) has been tested regarding the fault detection sensitivity. They will show that classical methods can achieve high fault detection sensitivity.

This study presents an evaluation of the impact of distributed generation, of varying capacity and connected at different locations, on existing system fault-level estimation algorithms. A number of case studies have been simulated under different scenarios with DGs connected at different points on a 33/11 kV test network. Results show estimation errors when DGs are located downstream the fault-level measurement point and the errors are proportional to the assumed level of fault contribution from the DG. Errors were found to increase when the DGs were located electrically closer to the measurement/fault-level estimation point. Negligible errors were seen with the DG connected ‘upstream’ from the monitoring location. Possible solutions are discussed such as the use of distributed measurements to account for downstream DG fault levels. An approach to peak make fault-level estimation is also described utilising current IEC short-circuit calculation methods.

The increasing number of inverter interfaced distributed generation units in electrical distribution grids can influence the functionality of protective devices in case of grid faults. The result can be an inadmissible delay in tripping time or failure to trip altogether. This study describes a novel approach to identify and amend potentially unreliable protection configurations. Reliance on conservative worst-case approximations of the grid state is avoided by using distribution system state estimation instead. Thereby, protection configurations can be more accurately matched to the specific grids' requirements. The overall computational effort is reduced using methods of regression analysis while maintaining original accuracy.

Environmental incentives to combat climate change are providing the motivation to improve the energy efficiency of power distribution systems and integrate state-of-the-art renewable technologies. Examples include wind/photovoltaic resources, energy storage systems, and electric vehicles integrated via efficient power electronic converters (PEC). Subsequently, DC microgrids (MGs) and distribution systems are receiving considerable attention in the literature because they offer a simple, yet flexible, interface between these modern resources and consumers. However, many technical challenges relating to the design and standardisation of DC protection devices still exist that must be overcome prior to widespread adoption. For example, many protection schemes tailored for DC MGs have been proposed, but few of them have considered the metrology requirements for practical implementation. This study will first review the key features of DC-side fault transients simulated on a DC MG model in MATLAB/Simulink, and analyse the disruptive impact on PEC components. Secondly, a review of newly published DC protection schemes is performed. These protection schemes are classified by their fundamental operating principles and mathematically derived metrology requirements are given.

IEC 61850 was originally conceived as a communication standard within a substation, but is being extended to cover other areas of the power system such as distribution automation (DA). IEC TC57 Working Group 17 has set up a task force to study the information exchange required for automating the distribution network. A draft technical report IEC 61850-90-6 is available, which presents different use cases of DA, produces the information models and proposes the configuration method. This paper presents one of the use cases which applies distributed control on an open-loop distribution feeder. The system consists of a number of smart terminal units (STUs) to monitor and control substation circuit breakers, sectionalizing switches and tie switches within the feeder. The STUs work together in a distributed manner to achieve fault location, isolation and service restoration (FLISR) of the feeder. The data model for this use case is presented. New logical nodes are introduced. Standardizing the data model allows interoperability between vendors, makes integration of new devices easier, and forms the basis of a smart distribution network. Another important aspect is the configuration of the system. The configuration process of a new DA system is introduced in this paper.

In many recent blackouts and large system disturbances, the performance of protection systems was found to have played an important role in both exacerbating the disturbance and limiting the spread of the disturbance. In the past, protection systems were not widely modelled in transmission planning studies. Instead, the response of protection relays to faults was assumed to follow fixed behaviour based on conservative values for primary and backup protection operating times. For these reasons, the incorporation of more accurate representations of protection systems into planning studies may help identify potential protection misoperations and ensure that protection relay performance is tuned to yield optimum responses to system disturbances. This study begins by discussing how protection relays may participate and respond to cascading tripping, power swings, and other steady-state and transient power system phenomena studied in power system planning. It will then examine how the settings for relays may be populated with conservative ranges where actual settings are not known or difficult to transfer to the planning simulation tool. The paper concludes with an overview of a tool which has been developed to automatically create relay models in planning simulation based on high-level user guidance.

This study presents an assessment methodology of protection strategies for meshed grids. It also proposes the computation of two performance indicators to evaluate protection strategies through a reliability and speed perspective. The Monte Carlo method is used to calculate the two indicators proposed. These two indexes can be used as criteria for comparison between protection strategies. Owing to the increasing debate around the protection for high-voltage DC (HVDC) grids, three proposals of protection of HVDC grids were chosen as application cases.

Multi-terminal high-voltage DC (HVDC) systems equipped with HVDC breakers require that detection and clearing of faults occur within a few milliseconds. Although detection without communication is generally preferred with regard to detection delay and simplicity, detection schemes relying on communication can enhance the overall performance due to their reliability. One such principle is the travelling wave differential protection that is based on the comparison of waves at both ends rather than solely on current. However, as with conventional differential protections, some kind of synchronisation must be applied to properly compensate for the time difference between samples obtained at different geographical locations. In this study, a synchronisation algorithm is presented that applies real-time signal processing to automatically obtain a proper compensation between the signals from both ends. The algorithm is examined by injection of data samples, generated from the simulation of an external fault in a PSCAD/EMTDC model. Additionally, the suitability for a real-time implementation is evaluated by execution time estimation using a simulated DSP. The algorithm is found to perform well, not only in identifying the compensation delay but also in terms of computational efficiency, thus allowing for real-time application.

A three-phase adaptive reclosing scheme using mode current oscillation frequencies is proposed for transmission lines with shunt reactors. Firstly, with phase-mode transformation, the fault boundary conditions are analysed and then the composite mode networks are constructed, respectively, for transient faults and permanent faults. In the composite networks, mode currents of shunt reactors are computed and thus oscillation frequencies are obtained. It is found that in transient fault situations, mode currents oscillate in only one frequency which is the natural frequency of the corresponding mode network. By contrast, the number of frequency components varies in permanent fault situations, depending on the fault type. Based on the frequency characteristics discussed above, a three-phase adaptive reclosing scheme is conceived. In the scheme, the transient fault is identified only if the shunt reactor mode currents contain one frequency which is equal to the natural frequency of the corresponding mode network. Otherwise the fault is taken to be permanent. By simulation, the correctness of the frequency characteristics is verified and the reclosing scheme is validated, hardly affected by fault locations and fault resistance.

The standard impedance protection deployed in distribution networks can malfunction due to underreach errors caused by fault impedances and remote infeed currents from embedded generators (becoming more and more widespread). This paper introduces a compensation method aiming at elimination of these issues and enhancement of relay dependability. As an advantageous outcome, compensated measurements can be utilised for accurate fault location. The method is verified on ABB RED 670 relay in the loop with an OPAL-RT real-time simulator. As the method is based on multi-point measurements, the test setup also contains a communication network emulator for modelling network delays and imperfections. The laboratory tests verify applicability of the method with proper appearance of the tripping signals from the relay. The fault location results based on synchronised data show overreaching inaccuracy rising with fault resistance. Though communication network delays and imperfection of the channels lead to underreaching, it has been revealed that not strict requirements for data synchronisation can be applied to specific measurements.

Life cycles of modern protection IEDs are becoming shorter and shorter. Additionally, the time spans between firmware updates for these devices are decreasing. Therefore, the needs for qualified testing strategies are increasing. The utility needs to verify e.g. the functional requirements, the quality of the new firmware, the correctness of commissioning, the parameter settings and more. This paper focuses on the one hand on the life cycle of a protection device from a utility point of view. The paper classifies the different phases of this life cycle and shows the requirements for testing in different phases. The aspects of testing from first prequalification work to the periodical maintenance tests are discussed. Due to the new approach the testing quality could be increased while the testing time is decreased at the same time. The idea of this method is taken from software development, where a regression test is used to check a new software version. This method requires written definitions describing the various types of tests the IED has to undergo during its life cycle. Due to the high quality of the documentation the utility has a good tool to keep the knowledge in the company.

The study investigates the role of inertial mapping in assessing and preserving frequency stability for grids accommodating greater penetration of low-inertia, intermittent generation, including wind sources. The study considers grid sizing, including large and isolated systems and an approach to limit the excessive rate of change of frequency (ROCOF). Simulation studies using DIGSILENT (Power Factory) and the IEEE 39-bus grid model with nodal phasor measurements have been used to evaluate the work. The proposed approach identifies areas of weak or strong inertial provision and battery energy storage has been used to release active power during disturbances and provide local energy to lessen the impacts of inertia reduction. The study proposes using frequency and ROCOF measurements during system events to map inertia and calculate energy provision. Inertial measurements are used to determine areas where additional generation or storage is required in order to preserve frequency stability and provide contributory counter-measures for grid-level protection.

The detection of high-impedance fault (HIF) on distribution network has been one of the most difficult problems. This study presents a data-driven method for HIF detection by using single-ended micro-phasor measurement unit (µPMU). This approach is based on the two-layer coordination architecture, local side with μPMUs and master station for further analysis. At the local side, the μPMUs gather the synchronous data and achieve feature extraction with k-means clustering algorithm and principal component analysis. For determining the amounts of data categories, the authors adopt a method based on silhouette coefficient. Meanwhile, send the characteristics to the master station, then detect the HIF fault through the support vector machine. Finally, the method was tested on a 34 nodes distribution network in PSCAD/EMTDC. The results justify the effectiveness and the proposed detection scheme has >85% accuracy.

The studies of the performance of feeder distance protection with multiple installations of the static synchronous compensator (STATCOM) are presented. Detailed representation of delta-connected multi-level modular converter (MMC) STATCOM is modelled and its impact on feeder distance protection is analytically studied. A real-time digital simulation (RTDS) based hardware-in-the-loop testing platform is established using practical distance relays, multiple detailed MMC STATCOM models and realistic transmission data. Different types of internal/external faults at varying locations are simulated to investigate the STATCOM's impact on feeder distance protection.

This study presents an evaluation of the influence of mutual coupling modelling on the effectiveness of a distance protection scheme suitable for long parallel transmission lines. Sliding single-line-to-ground fault simulations have been carried out in MATLAB using a phase-domain approach. The output voltage and current signals were applied to the distance relaying algorithm considering exact compensation parameters. It is shown that, for the system considered, assuming parallel transmission lines modelled as a six-phase line, an average relative error of 1.19% is found for the magnitude of the apparent impedances seen by the relay.

The preconditions for dependable overcurrent protection of customer installations are largely unknown in islanded low-voltage (LV) microgrids build by multiple droop controlled and current limited inverters. Consequences may be an islanded operation with limited reliability of supply, investments of uncertain necessity or uncontrolled hazards. Distribution system operators will not opt for intentional islanding until those risks become predictable. Extensive variation studies are therefore performed to screen for decisive influencing factors and to quantify their effect by means of computer simulations in Matlab/Simulink^®. First steps of a standardisation roadmap are drawn that will either enable developing the preconditions for a dependable overcurrent protection or choosing effective alternatives. An initial set of quantitative minimal conditions is given as a basis for further discussions.

Needed new cost-efficient, reliable, standardised and redundant solutions for future resilient smart grids must utilise possibilities of advanced ICT technologies (such as wireless fifth generation and cloud servers with smart big data analytics) and have cyber-security integrated into all solutions. In this study, resilient, future-proof, grid-code compatible combined islanding detection scheme for medium-voltage (MV) and low-voltage network-connected distributed generation units during grid-connected operation is simulated. The utilisation of active network management functionality at the MV level enables to control the reactive power unbalance continuously in order to ensure reliable islanding detection without a non-detection zone. The combined scheme also prevents maloperations due to other disturbances.

Frequency stability in power systems is achieved by active power control, which aims to balance grid generation with load demand. Historically, grid balancing services have been provided by synchronous thermal generating units. As wind penetration levels increase on the power system, it is essential that wind turbine generators (WTGs) provide robust, reliable frequency stability services to grid operators. Like other forms of renewable generation such as solar photovoltaic generation, modern variable speed WTGs are connected to the power system using power electronic converters. This non-synchronous connection decouples the natural inertia of the WTG from the grid frequency. As system non-synchronous penetration levels increase, non-synchronous generation will be required to participate in frequency stability services such as automatic generation control. This study presents a review of WTG frequency response systems that allow WTGs to participate in frequency stability services by emulating the natural inertia and droop characteristics of conventional synchronous thermal generators. Power system simulations performed in MATLAB/Simulink show that the addition of emulated inertia and droop controllers into WTG's power/speed control systems can reduce the rate of change of frequency and increase frequency nadir when the power system is subject to a load/generation imbalance.

Hybrid direct current circuit breakers (DCCB) are the most adopted solution to clear high DC fault currents in short time. Existing literature does not analyse recently validated commercial breakers. This article provides an overview about hybrid DCCB and a list of criteria to evaluate and compare the performance of existing or new DCCB designs. Additionally, general measures are proposed to assess the suitability of the DCCB in a specific grid situation. Accordingly, the fault current evolution under pole-to-pole faults in different parts of a multi-terminal DC grid is analysed by means of mesh analysis with matrix differential equations. Finally, a grid parameter variation analysis is carried out through PSCAD-EMT simulations to compare the presented DCCB concepts.

This study presents a detailed DC-side fault analysis considering inductive termination of lines within a high-voltage multi-terminal direct current (MTDC) grid. The analysis aims to provide design guidelines for DC-side inductors, taking into account important aspects of protection such as the required speed of operation of relays and the performance characteristics of current interruption devices (i.e. of DC circuit breakers). Moreover, the impact of current limiting inductors on the fault signatures is investigated. In particular, it has been found that DC-side inductors not only limit the fault current level, but also the resulting signatures in voltage and current, can assist to enhance the speed of operation, stability and selectivity of protective functions for DC-side faults. The analysis has been extended to include the impact of inductive termination on fast transient phenomena known as travelling waves. Specifically, DC-side inductors can form a significant reflection boundary for the generated travelling waves. A deeper insight into the faults has been achieved by utilising wavelet transform.

This study describes the influence of distributed generation (DG) on a double-ended fault location based on measuring the high-frequency fault transients. The additional non-fundamental frequency current components from DG will influence the accuracy of an impedance-based fault location technique based on non-fundamental frequencies. A double-ended impedance-based fault location technique that utilises the high-frequency content (up to 5 kHz) is studied. This study showed that double-ended method is still able to locate a fault with a maximum error of 4% compared to the case without DG which showed a percentage error up to 2%.

The purpose of this document is to highlight the special treatment or requirements of protection functions when applied to load commutated inverter (LCI) static starter turbogenerators. Static starting of TG's is accomplished by using an LCI, adjustable speed drive system, to motor the synchronous machine and coupled turbine. More specifically, the focus will be on 64B function (busbar earthfault protection) when achieved through 59BN function (neutral overvoltage).

Combined faults occurring between different voltage levels in overhead lines present a challenge for distance protection. Previous work has shown that such faults most often appears as single-phase-to-ground (SPTG) faults in a normal type of overhead line. However, it is not obvious that distance relays will identify and select the correct fault loop according to being similar to SPTG, as all six fault loops get excited when combined faults occur. A study where two distance relays of different manufactures are tested using transient replay and secondary test equipment is presented, in order to reveal which fault loops are activated and whether a safe trip for combined faults happens.

Should a current transformer (CT) secondary winding be left in or inadvertently become open circuited while the primary is energised, then damage may occur to the CT – leaving it inoperable or seriously effecting its measurement accuracy. If the CTs are being utilised in particularly difficult places to access, such as in a gas insulated substation or in a power transformer bushing, this can then lead to an expensive repair to a relatively inexpensive component. To prevent damage occurring to open-circuited CT's, a range of products are available. These devices are based either on a silicon carbide varistor-based technology or on a gas discharge tube-based technology. The purpose of this study is to compare the performance of these devices.

The advantages of a dedicated, standalone DFR are well known: natively synchronised fault records, large record storage capabilities, high sampling rates, numerous types of triggers, and large numbers of analogue and digital recording channels. The main disadvantage to the dedicated DFR is cost: a dedicated DFR must be directly wired to every current, voltage, and status point, resulting in an installed project cost easily ten times the material cost of the DFR itself. However, IEC 61850 process bus makes dedicated DFRs affordable again, by eliminating all field wiring necessary for installing a DFR.

This study presents a software package developed to carry out overcurrent (OC) protection coordination studies for power delivery networks, making use of versatile optimisation models and robust solvers. The problem of setting and coordinating OC functions in modern numerical relays is formulated as a minimisation problem, subject to technical constraints which are relevant to the protection practises applied by utilities. The proposed solution aims to assist protection engineers in calculating optimum OC setting values, which is a labour-intensive task.

Line current differential protection is based on Kirchhoff's current law calculating the vector sum of the currents from each line end to detect faults in the protected zone. For synchronisation of the current vectors, time compensation with a ping-pong measurement of the propagation time delay is used. A new smart multi-ended differential protection is presented in this study, which includes a new capacitive current compensation technique. The protection relay is scalable for any transmission system topology including hybrid lines. The protection is based on RMS values calculated from samples making it immune to frequency variations and the protection operating time is sub-cycle. The protection uses an accurate algorithm for capacitance current compensation with a distributed line parameter model, where only the impedance and admittance per unit are required. This technique has an error <1% even considering transients in the algorithm. The need to provide connections to new renewable generation has increased the need for a multi-ended line differential protection. This new smart protection concept is a step forward in providing reliable, cost effective and integrated protection for these new network topologies.

This study evaluates the travelling wave-based differential protection (TW87) when applied on hybrid transmission lines (HTLs). The TW87 has attracted the interest of utilities due to its high-speed operation and reliability. However, to apply such a function on lines that combine overhead and underground cable sections, additional challenges arise, which must be overcome to guarantee the proper TW87 operation. The goal of this study is to clarify issues related to the TW87 settings and performance when applied on HTLs, highlighting the impact of the used settings on the protection operation. To do so, fault scenarios on a 230 kV/60 Hz test power system were simulated using the alternative transients programme. The obtained results attest the TW87 is able to properly protect HTLs, provided that special requirements are considered.

The aim of this study is to develop a software-oriented framework that will help simulate and study high impedance faults (HIFs) in power distribution systems, as well as design adequate HIF detection techniques. After a thorough literature review, three well-established HIF models have been developed in EMTP-RV, as part of this work. Systematic (black box) modelling is applied so that each developed HIF model can be used in any power system under investigation in the future. An overview of the mostly available HIF detection methods is also included in this study, which subsequently concludes with the development of two proper HIF detection techniques in EMTP-RV/MATLAB environment. A real 20 kV radial overhead distribution line located in Xanthi, Greece is modelled in EMTP-RV and several HIFs at various time and locations are simulated. The simulation results are presented in order to evaluate the accuracy of the developed HIF models and the effectiveness of the developed HIF detection techniques.

Power swings and loss of synchronism are complex events which occur during severe system disturbances. Many protection functions may respond during such events, but not always in an intended, expected, or coordinated manner. This paper aims to present an overview of the scenarios which give rise to power swings, how protection devices response, and how the implementation of protection algorithms by different manufacturers can cause similar relays functions to react in different ways.

With the smart grid development, advancements in deeply integrated information and communication technology (ICT) provide enhanced system awareness, effective decision-making support and high-performance protection and control (P&C) to improve operational reliably and stability of the modern power systems. To manage the risks relevant to the existing industrial P&C systems, it is of high necessity to develop a methodology of cyber security testing for industrial P&C systems. This methodology will be rolled out to continue to evaluate the risks for the next-generation industrial P&C systems when new ICTs are introduced e.g. IEC 61850. This study summarises the main purpose, scope of work of an innovation project in collaboration with National Grid. This on-going project is to develop such a methodology using the state-of-art real-time digital simulation to conduct hardware-in-the-loop testing.

IEC61850 has now been accepted ‘almost unequivocally’ as a preferred standard for substation communications.The extent of utilisation of this standard in a majority of installations around the world is at the ‘station bus’ level. It is foreseen that numerous benefits can be availed if the process values are digitised as close to the source as possible and utilised in a comprehensive automation system. TransGrid carried out an extensive assessment of the substation secondary system design based on the implementation of IEC61850 at the station and process bus level which brought out the business case for full digitisation. The first substation to realise this technology is the Avon 330 kV switching station. At Avon, merging units are installed in outdoor cubicles; digitised signals are then transferred to the substation systems. There has been a special focus on standardisation and re-usable engineering – these are some of the crucial factors to achieve cost reduction. The study describes some of the design principles, estimated cost savings and lessons learnt. The authors envisage that the digital substation technology implemented can bring about substantial cost reduction in green-field as well as brown field builds and paves the way for the efficient integration of asset monitoring systems.

This study describes the main results obtained from the deployment and commissioning of the feeder's protection and measuring system based on analogue and digital acquisitions by concentrator Merging Units. The presented project is installed at the Embu-Guaçu substation, owned by CTEEP, on the AL-60 feeder. The system architecture, protection functions used, network architecture and data segregation strategies, as well as results obtained in the laboratory and in the field from the operating system, are presented. The pilot project deployment experience with Merging Unit acting effectively to generate trip on the system and to act on the circuit breaker is innovative in Brazil.

The increased demand for renewable energy generation requires the higher flexibility of transmission systems. This requirement together with technical progress in high-voltage DC technology has resulted in the ambition to build large-scale multi-terminal DC grids. To achieve this goal, vendor interoperability is considered a key element. Standards exist for AC systems, but not for DC systems. This work discusses and evaluates the suitability of AC standards for DC systems. As a result, a different view on substation architecture is developed and two communication protocols are suggested for further investigation in this context.

This study will present the results of several simulation-based analyses investigating the performance of distribution network protection under a range of future scenarios. It is widely accepted that the integration of a significant amount of distributed generation, often from renewable energy sources and interfaced to the main network via power electronics converters, will be commonplace in the future. Furthermore, at the transmission level, the interconnection of different countries through HVDC links and the decommissioning of many large-scale conventional synchronous generators will result in the power systems becoming progressively weaker in terms of reduced faults level and lower system inertia. This study will, therefore, illustrate and emphasise the challenges and issues that arise in future distribution networks protection due to reduced system strength, fault level and the changing nature of the contribution (both in terms of magnitude and possibly delay in provision) to fault levels and the possible impact this may have on traditional overcurrent-based protection schemes by building a simple model of distribution network in Simulink, MATLAB. In addition to that, the paper will also discuss some potential solutions as novel schemes to tackle the arising protection related problems.

Fault location in power networks is important as accurate information about the faulted line section expedites system restoration following a fault occurrence. A number of fault location methods have been proposed. Methods based on injecting a signal into the network and tracking it along the feeder appear to have received limited attention. In this study, fault location methods based on network signalling are examined. Two different types of approaches are presented. The first one is based on injection on a very low-frequency band, whereas the second one is based on utilising modern modulation technologies on low-frequency band, under 500 kHz, implemented on software-defined radios. The simulation results indicate the capability of the proposed methods in determining the location of a single phase-to-earth fault in medium-voltage distribution networks.

This article focuses on validating a time-domain power system protection solution, based on energy and reactive power algorithms, through simulations using hardware-in-the-loop. The results are compared against a commercial, off-the-shelf, intelligent electronic device. The developed protection algorithms are briefly described, followed by the description of the hardware platform responsible for its practical execution and the description of the applied tests. The obtained results show significant advantages on response times when compared to traditional protection, and the ability to securely identify delicate internal transformer faults, even during inrush condition.

The reflection coefficient of the travelling wave is different with different frequencies because of the inductance and capacitive elements on the boundary of the DC transmission line, which leads to the oscillation of the travelling wave. It is difficult to obtain the wave head's arrival time accurately using travelling wave method to locate fault because of the oscillation. The current travelling wave is the superposition of the incident current travelling wave and the reflected current travelling wave. There is no oscillation in the incident wave. Therefore, a method using incident current wave for fault location is proposed here. The initial current travelling wave and the transmission line boundary function are used to calculate the incident current travelling wave, and the incident wave is used to locate fault. The Prony decomposition algorithm is used to identify boundary function using the initial current travelling wave generated in specific fault condition. PSCAD simulation shows that the influence of oscillations of travelling wave can be eliminated by using incident current wave to locate faults, and the accuracy of fault location is improved.

This study presents a novel concept for a distributed current optical sensing network, suitable for protection and fault location applications in high-voltage multi-terminal direct current (HV-MTDC) networks. By utilising hybrid fibre Bragg grating-based voltage and current sensors, a network of current measuring devices can be realised which can be installed on an HV-MTDC network. Such distributed optical sensing network forms a basis for the proposed ‘single-ended differential protection’ scheme. The sensing network is also a very powerful tool to implement a travelling-wave-based fault locator on hybrid transmission lines, including multiple segments of cables and overhead lines. The proposed approach facilitates a unique technical solution for both fast and discriminative DC protection, and accurate fault location, and thus, could significantly accelerate the practical feasibility of HV-MTDC grids. Transient simulation-based studies presented in the paper demonstrate that by adopting such sensing technology, stability, sensitivity, speed of operation and accuracy of the proposed (and potentially others) protection and fault location schemes can be enhanced. Finally, the practical feasibility and performance of the current optical sensing system has been assessed through hardware-in-the-loop testing.

Ground fault protection is widely used to protect transmission and distribution lines in case of ground faults. Combined with a directional element and used in a teleprotection scheme, ground fault protection can detect and isolate even high resistive ground faults not detected by distance protection. However, there are a lot of maloperations due to the incorrect result of the directional element of the ground fault protection using either zero sequence or negative sequence quantities. After analysing numerous fault records, it seems obvious that these problems with the directional elements cannot be solved using either zero sequence or negative sequence because these quantities are sometimes very small or not related to the fault. This study suggests a new design of ground fault protection using additional information given by numerical relays. With the new design, the ground fault protection takes a lot of advantages regarding phase selection and directional element from the distance protection. The main difference between the distance protection and the ground fault protection remains the different grading. For the distance protection, the sensitivity is limited by the resistive reach. The basic principle for the grading of ground fault protection remains a simple threshold of zero-sequence current.

Sympathetic tripping is a common challenge that affects the proper operation of the earth fault (EF) relays in distribution networks. It likely occurs when healthy feeders are exposed to an unnecessary trip operation in response to an actual fault occurring on an adjacent feeder. The sympathetic tripping phenomena of overcurrent and EF relays in the distribution networks and their causes are studied in this paper. Real recorded data of affected healthy feeder(s) for different sympathetic trip scenarios reported from an Egyptian distribution network are extensively analysed. A custom logic protection scheme is proposed to detect the sympathetic tripping phenomena using the existing features of IED relays without any additional cost. In addition to the captured real disturbance records, simulated scenarios of sympathetic tripping are modelled using MODELS language in ATP/EMTP program to evaluate the proposed schemes. The achieved results ensure the suitability of the proposed protection program in order to avoid the unnecessary false sympathetic tripping for both incoming and outgoing feeders.

As the penetration of Renewable Energy Sources (RESs) increases, the countermeasures are becoming increasingly important because output of the RES is intermittent. Therefore an Energy Storage System (ESS) that can control generation is attracting attention and undergoing various studies in order to stabilize efficiently the output of the RES. The conventional method estimates the capacity of the ESS through error of actual data of the RES's power and reference point using moving average method. However, as the error between reference power and output power of the RES increases, the capacity of the ESS increases. Therefore, in this paper, we propose method for estimating the capacity of the ESS using the improved moving average method.

In this study, the sensitivity of the earth-fault protection (EFP) in medium-voltage distribution networks with a compensated neutral point is investigated. An adaptive residual voltage threshold is proposed as a solution for enhanced EFP sensitivity. The optimal threshold adaptation is based on the horizontal communication between a Petersen-coil (PC) controller and IEDs, utilising IEC 61850 GOOSE messages. The maximum residual voltage information, from a healthy state of the network, is transferred from the PC controller to IEDs, where an optimal residual voltage threshold for the EFP is determined. This adaptation allows maximum protection sensitivity and security to be obtained for each substation and the network state.

This study explains an example where select digital technologies are included to face the challenges related to cybersecurity in a windfarm solution. The network is planned, designed and commissioned by one operator, and will be maintained by two operators – one for generation assets for the windfarm, the other for the grid connection power transmission assets. The topology deployed is shown at a high level, describing how the windfarm offshore and onshore networks will be divided between the operators and the specific requirements of the solution. A more detailed view of the network is shown depicting Ethernet switches, routers and Intelligent Electronic Devices (IEDs); with the services and protocols used are explained and aligned with the challenges that each one represents in terms of cybersecurity, for example interconnections that use Parallel Redundancy Protocol for redundancy exchanging GOOSE interlocking. Each challenge is addressed one at the time and the topology will evolve as the solutions are added, going from a unified network under the control of one operator into two that can be easily split between operators.

This paper analyses the influence of network security measures on the system behaviour of a power system protection device. In this particular case, an IP-based Ethernet protection interface of a line current differential protection system is considered. IPsec has previously been proposed to be part of the security concept of the protection interface. Therefore, the authors conduct a trade-off analysis regarding the influence of IPsec on the protection function and consequently on the system safety. This work shows that the protection function of the relay is not impaired as long as the additional CPU performance for the encryption by the protection relay is available and the necessary bandwidth on the communication channel is provided.

In this study, an optimal protection and control coordination strategy is proposed, which pursues to prevent unwanted protection and control operations caused by wind power integration, as well as adjust the emergency states of the power system to stable operation conditions. Moreover, in order to implement the proposed strategies, a hardware in-the-loop real-time simulation and testing platform is built up to demonstrate those unexpected protective control operations and testify the related solutions in a test distribution network. The related case studies and simulation results can demonstrate the effectiveness of the proposed methods.

This study presents a new protection element that can increase transformer differential sensitivity. The new element, called incremental differential, takes the differential currents, operation and restraint currents and, using a new mathematical approach, it can be more sensitive than the standard differential. The study presents the mathematical calculation and how the incremental differential handles with the errors involved in the differential protection. It also presents the algorithm response for some fault cases, always comparing the element to the standard differential algorithm. As the new element is simple in a mathematical concept, the protection element was developed inside a commercial relay just using the manufacturer programming language and the users’ available programming area. The contributions of this work are the method to increase sensitivity using the same variables already available in differential relays, and the possibility to use the algorithm in a field installed relay.

In future power systems, highly increased renewable integration is expected to meet global decarbonisation targets. The risks and uncertainties brought about by renewable integration will challenge system stability. This study analyses the impact of the increased level of renewable energy sources integration on system transient stability and out-of-step tripping (OST) protection. To this end, the performance of OST protection is assessed in terms of the ability to prevent system instability under different contingencies. A modified two-area test system and Great Britain (GB) 29-zone system integrated with a dynamic model of wind turbines are selected as test systems. A systematic approach is adopted to design a specific OST protection scheme for each test system and to obtain suitable relay settings. An extensive number of simulation studies are carried out using DIgSILENT PowerFactory to assess the performance of the designed schemes under different renewable integration levels. Conclusions are made based on the obtained results, which all imply that revision of the existing OST protection scheme will be inevitably needed.

Substation automation systems are characterised by a high degree of functional integration, which can lead to a centralised substation protection and control (CPC) architecture. Most CPC architectures utilise merging units to interface with current and voltage transformers, which causes a high-communication load on the process bus in case of large substations. This study proposes a CPC architecture based on distributed signal processing units (DSPUs) to overcome those drawbacks by publishing the results of the signal processing algorithms directly. The reduction of the communication load through the usage of DSPUs has been shown in a case study, which uses a 16-bay transmission substation topology as a reference.

Low voltage cable faults are frequently associated with arcing at the fault which creates 2 high frequency transients which propagate away from the fault towards opposite ends of the cable and whose difference in arrival times can be used to determine the fault's location using the Type D method. A variant of the Type D method, known as the Transient Recording System (TRS) using asynchronous data acquisition units (ADAU) has been used successfully in situations where multiple branches on a cable have precluded the use of other travelling wave methods. The range, and precision of location, of the TRS method is extended by the use of a Marker Unit (MU) which allows the distance and direction to a fault to be determined relative to the point of connection of the MU. The asynchronous data acquisition units operate in ‘listening’ mode and are triggered by the arrival of the transients created by the fault arc. Prior to triggering, the ADAUs continuously (over)write all received data into their cyclic buffers, including the low amplitude MU pulses. Shortly after triggering the (over)writing of the cyclic buffer stops and earlier (pre-trigger) data retained – including the received MU pulses.

Whole-line quick-action protection utilising single-end electrical parameters has been studied and verified in alternating current and direct current power systems. This study analyses the origin of fault generated high-frequency harmonics based on the properties of boundary elements and power source during the fault, creating the possibility for the distribution network to achieve single-ended protection. Based on the non-loss transmission line model, the differences of transient harmonic characteristics are explained by the comparison of the stabilisation process of the power system with boundary elements and the one without. It is revealed that the source generated specific high-frequency harmonics and energy storage elements generated high-frequency harmonics contribute to single-ended protection criterion during the fault. As the protection scheme only relying on the source generated specific harmonics is hard to take effect for all segments of the distribution network, the travelling wave generated harmonics ought to be utilised to distinguish between internal and external faults for each segment by adding a proper boundary element in the line.

This study presents a methodology that allows examining the differential protection of power transformers through computational simulations and numerical relay tests. Using that purpose, the alternative transient program (ATP) was used as a computational tool to perform several different events, which the power transformers are submitted to, and that can cause mal-operation of its differential protection, such as: external and internal faults, inrush current and saturation of current transformers (CTs). A testing system was implemented in laboratory, which consisted in simulating the power system in ATP (power transformer, CTs and faults modes) and applying the simulated signals through a programmable test set to a commercial relay to evaluate their response to these events. The main results of the behaviour of transformer protection relay under the tested transients are presented and discussed in this work.

Variability of the available short-circuit power also implies variation of the fault level, which can potentially cause several protection problems in the electric networks. In this study, a novel protection method that is insensitive to the fault level changes caused by variable short-circuit power is presented. It relies on utilisation of symmetrical components of the short-circuit currents and on communication between the protection relays. The proposed method addresses the single phase to ground (SPG) faults occurring in directly grounded distribution networks, with focus on closed-loop medium voltage (MV) feeders. Case studies are presented, which demonstrate that the proposed protection scheme is capable of effectively detecting the SPG faults in closed-loop feeders with variable short-circuit power.

This study sets out requirements for a tool to automatically evaluate protection relay coordination and assess, track, and visualise protection coordination results for large grid areas. The tool requirements include the selection process for which fault types, fault locations, contingencies, and generation dispatch should be studied, how the relay performance could be assessed, and how the large datasets produced by such analysis could be stored and visualised. Using these requirements, add-on tools were developed for two popular commercial short-circuit analysis programmes and tested and validated using network models from a number of real transmission and distribution grids.

The behaviour of today's installed interfaced distributed generators (IIDGs) during grid faults in German low-voltage grids is regulated in the valid guideline VDE-AR-N 4105. Presently, a new revision of this guideline is discussed, defining a higher voltage threshold of 0.85·V_N and requiring the IIDG to remain synchronised for a given period of time during low-voltage dips. An analysis of IIDG using a CIGRE LV benchmark grid shows the possibility of an increase in minimum short-circuit currents, following the new guideline. Nevertheless, there are still cases in which the behaviour of NH fuses as feeder protection is tempered up to an uncertain tripping behaviour, leading to possible threats for persons and equipment. Furthermore, the used CIGRE LV benchmark grid does not cover all worst-case scenarios for the analysis of blinding of protection in German grids. It is shown that the usage of digital (directional) overcurrent detection can be a proper solution to cope with the lower short-circuit currents. The combination of a fuse link allowing the triggered disconnection in the overcurrent range can be a promising solution, especially regarding the retrofit of existing feeders. Laboratory tests with a prototype show a reliable tripping with tripping times of <300 ms.

Fault discrimination and protection design for bipolar high-voltage direct current transmission solutions based on modular multilevel converters (MMC-HVDC) links are of significant importance for a reliable and resilient power transmission. If full-bridge submodules are utilised, fault-dependent handling concepts considering the location of an event are enabled. This study presents a comprehensive approach to differentiate and deal with internal converter and dc side faults. While a multitude of measurements inside and at the clamps of each converter is usually only used for simple threshold-based hardware-related protection, additional differential and derivative criteria may further improve selectivity. However, this requires careful configuration to avoid improper reactions. To highlight the coordinated manner of the proposed concept, various faults are analysed and selected examples are explicitly investigated and visualised using the PSCAD EMTDC software.

This study presents a novel time-domain protection technique for application to DC grids. The technique utilises the power developed by the forward and backward travelling waves produced by a fault to distinguish between internal and external faults. For an internal fault, the calculated travelling wave power must exceed a predetermined setting; otherwise the fault is external. The ratio between the forward travelling wave power and the backward travelling wave power provides a directional comparison. For a forward directional fault, this ratio is less than unity, whereas the ratio is greater than unity for reverse directional faults. To improve the sensitivity of the protection scheme for long-distance remote internal fault, a second element utilising the concavity of the forward travelling wave power is proposed. The proposed technique is time domain based and does not require complex mathematical burden; moreover, as such can be easily implemented since it will require fewer hardware resources. Simulations were carried out in power systems computer-aided design/electromagnetic transient simulations, and the results presented considering wider cases of fault scenarios including 500 Ω remote internal fault shows the suitability of the proposed scheme as all fault scenarios indicated were identified within 500 µs following the application of the fault.

An overcurrent relay analyses and processes the secondary currents from a set of current transformers (CTs) and if the currents exceed the operating threshold initiates the tripping of a circuit breaker after an appropriate time. An important issue for a protection relay is how it responds when the steel core of the CT is saturated. The exact behaviour of a CT depends on various factors such as core size, CT ratio, primary current magnitude, DC offset, secondary burden resistance and remnant flux. The aim of this study is to investigate the impact of CT saturation on overcurrent relays using both a physical relay test bench that includes actual protection CTs, and a modern relay test set configured to simulate the test bench and its CTs. The relay operating times, obtained under similar fault conditions using both the test bench and the test set, will then be compared. The results obtained will then be used to determine how different levels of CT saturation affect different generations of an inverse time overcurrent relays. The final section of this study will explain how CT saturation affects an overcurrent grading study involving a mixture of electromechanical, static and numerical relays.

Various papers and professional literature describe plenty of methods of locating the exact place of the earth fault in a compensated medium-voltage (MV) network. However, the usability of these methods is very polemic – from the perspective of achieved accuracy, as well as extreme investment demands. Information on practical experience and results from the actual operation are rarely published at all. Handheld earth fault location finder (device) is an innovative and highly functional alternative to static earth fault locators for overhead MV lines. The device enables a contactless determination of the relative earth fault location in relation to the specific place of measurement. With sequential measurements in right positions, it is possible to get to the fault location very quickly. This study describes the function and possibilities of the handheld device, as well as practical experience with locating both the actual and the experimental earth faults in the MV network.

The overcurrent protection on the traditional distribution system uses local measurements and settings as a basis for decision-making. However, connection of multiple distributed generators with different short-circuit characteristics makes the local measurements unpredictable, leading to possible loss of protection coordination. In order to solve this problem, this study proposes an algorithm that achieves its protection function through load flow and sensitivity calculations based on voltage measurements. The algorithm is built on a modelling approach that splits the distribution network into a series of overlapping protection zones. The overlapping feature is realised logically through peer-to-peer communications between intelligent agents located in adjacent zones. A sensitivity-based electrical signature was identified that is generated when a fault occurs within a zone. Simulation results show that the proposed protection algorithm is able to identify the zone in which the fault has occurred and the specific faulted node or line section in that zone. The fault current contributions, or no contributions, of the distributed generators (DGs) do not impact the operation of this algorithm.

This study explores how protection systems affect the design of a medium-voltage (MV) flexible AC/DC link (FDCL). To show this impact, two FDCL designs are analysed. The first designed before considering protection and the second created specifically to solve the protection issues realised in the first. One of the main aspects of the FDCL is to be placed into an existing network, reuse existing equipment, and not require any changes outside of the substations of installation. In this way, the converters must be sized in such a way to retain selectivity of the lower network as well as be able to secure a continuous supply of power through the link even in the case of a DC-side fault. How this is performed and the converter overrating requirements are determined for a 10 kV MV link.

Time-domain protection relays have increasingly attracted the attention of electrical power utilities. These relays speed up the tripping process of traditional protection schemes, increasing the stability margins of high-loaded power grids. Among the existing time-domain protection functions, the travelling wave (TW)-based differential protection TW87 has shown to be promising. However, as such a function is relatively new in the relay market, studies on the TW87 performance have been of interest to protection engineers. Thus, this study presents a parametric analysis of the TW87 performance. To do so, massive fault simulations are carried out, considering different fault scenarios and protection settings. From the obtained results, important issues related to the TW87 performance are addressed.

Power management related to the application of power system islanding is investigated. In an islanded power system, without the utility grid to regulate the island voltage and frequency, distributed generations (DGs) must switch their control tactics to maintain these parameters within the permissible ranges. Generation–load balance is a vital criterion that needs to be ensured, which requires the island DGs to properly share the load demand. Conventional DG coordination strategies cannot deliver high power quality and utilise full island generation capacity at the same time. To address this issue, an adaptive multiple-master strategy is proposed. This strategy requires neither communication infrastructure nor extra control system, and thus it is immediately applicable to the current network. In addition, this strategy can improve the system transient performance and maximise the economic and environmental benefits. Through simulations conducted on an islanded system consisting of both synchronous and inverter-based DGs, the effectiveness of the proposed strategy is validated. This strategy also performs well for the islanding events initiated by permanent grid faults.

With the advent of wide area monitoring protection and control, the new wide area control and protection applications emerge that require the identification of zones or islands in the network subject to certain specific requirements. The requirement of retaining certain buses in the same network zone or island appears in several power system protection applications, including intentional controlled islanding and parallel power system restoration. This study describes a new algorithm to define islands in power networks with respect to the specified bus grouping constraints. The method is based on the construction of tree subgraphs spanning the buses of each group, and its superior performance is demonstrated by a comparison with the two state-of-the-art methods from the literature.

This study demonstrates the capability and performance of the developed state-of-the-art hardware-in-the-loop (HIL) testing platform based on the real-time digital simulator (RTDS). The evaluations of (i) the effects of thyristor-controlled series compensation (TCSC) on the feeder protection first main (unit protection) and (ii) the performance of feeder protection second main (distance protection) of multi-ended transmission circuits with adjacent TCSC are carried out. Realistic parameters of transmission lines and TCSC are used for system modelling, and practical physical relays are used for the testing. The potential impacts of TCSC on both unit protection and distance protection are analysed based on the simulation results and relay measurements from the developed RTDS-based HIL testing platform.

A modular protection system was developed for DC radial microgrids. The novelty of the realised protection system is based on the combination of different fault detection, characterisation and localisation criteria. The protection system was developed based on real-time monitoring of voltages and currents at different positions within smart modular switches in the DC system. Intelligent modular DC switches were developed for the setup. On the basis of fault detection criteria, protective measures are initiated and appropriate switching signals are sent to the appropriate switches in order to isolate the faulty part. Different fault locations and types have been tested in the laboratory for a 24 V DC test setup. Hence, the selectivity of the new protection concept has been verified.

Fault location in distribution systems is difficult for multiple discontinuities, such as branch and junction points on feeders. This paper proposes a scheme for fault location in distribution systems using network topology information and circuit breaker reclosure-generating travelling waves. Based on the topology information, the circuit breaker closure-generating travelling waves can be got through analysis. When a permanent fault occurs, the circuit breaker reclosure-generating travelling waves contain the information on fault position. In this paper, the difference between the pre-fault travelling waves and post-fault travelling waves induced by the breaker reclosing in a feeder, defined as reclosing superimposed travelling waves, is calculated. For the reclosing superimposed travelling waves, the initial travelling wave reflects the fault distance. Subsequently, wavelet transform is applied to extract the travelling wave reflected from the fault point. Finally, the time difference between the reclosing instant and the arrival instant of the reflected travelling wave is employed to calculate the fault distance. In order to verify the effectiveness of the proposed scheme, several simulations were carried out using ATP-EMTP software. The simulation results indicated that the proposed scheme can be effective in fault location for distributed feeders, regardless of grounding system type.

This study describes a new differential protection algorithm for power transformers, which is not affected by transient conditions. The proposed algorithm uses the statistical second central moment, statistical variance, to characterise the signal waveform. The goal is to obtain the variance from each differential current after a pre-processing filter stage and to compare it with a threshold. The event will be identified as an internal fault, or otherwise as an inrush current. The algorithm was implemented in MATLAB, and a broad array of cases was carried out using the electromagnetic transient software PSCAD. All results show the algorithm successfully differentiated inrush from the internal fault conditions in over 2000 cases.

This study presents the methodology, experience and practical outcomes of the risk assessment-based revision of loss-of-mains (LOM) protection settings in the NIE Networks' distribution system. An investigative project has been undertaken by the authors to revise the current LOM practice as recommended by the G59/1/NI regulation and to propose the settings which would meet the all-Ireland transmission system stability criteria. It is also important to ensure that any increased personal risk is realistically quantified and satisfies the health and safety requirements. Both aspects (i.e. LOM protection stability and sensitivity) are covered in the study. The results and observations included in the study aim to provide the means and supporting evidence for achieving the best compromise in the revision of LOM protection settings.

During the commissioning of the substation automation systems (SASs) with protection, automation and control traditionally the main focus of testing is on testing the protection system and its settings. Protection testing uses established methods. When looking at the time spent during commissioning, testing the automation and communication system nowadays consumes even more time than testing the protection. Automation systems became increasingly complex and the efforts for testing communication and proper operation of all signals transmitted to the supervisory control and data acquisition (SCADA) systems grew dramatically. This study describes a new approach to be used in all phases of the lifecycle of SAS. By utilizing the data available in substation configuration description (SCD) files it is possible to introduce new and more efficient methods for factory acceptance testing (FAT) and site acceptance testing (SAT). The approach identifies potential signals to be tested in the SCD file. Communication links and the used IEC 61850 services are recognized, documented and can be used for generating test plans. These test templates can be created during the specification phase, adapted for FAT and subsequently reused during SAT. Requirements for test equipment will be identified. An example of technical realization will be presented.

IEC 61850 is the established standard for substation communication. Since the standard describes different stages of lifecycle of Substation Automation Systems the demands for specification, testing, and especially simulation differ. The approach described in this study can be used in the different stages and fulfil practical requirements. It describes the requirements for simulation and proposes an implementation applicable. If a single Intelligent Electronic Device (IED) and its data model to be simulated in technical investigation phase is sufficient at Factory Acceptance Testing and Site Acceptance Testing multiple IEDs and utilised services as GOOSE and reports will be needed. In addition, the methods described for indicating test mode/behaviour and simulation indication become important. The simulation has to be embedded in testing environment and interact with tools to be used for visualisation of changes in IED's data model. Advanced services in IEC 61850 like setting groups control, switching device control and file transfer have to be added. The requirements will be discussed from a utility's perspective. The method described can be extended for routine testing and maintenance testing, e.g. after firmware upgrades. An outlook develops a vision to be utilised for automation and control testing.

As the ability of DC circuit breaker is limited, transmission line protection has to identify the fault and inform the DC circuit breaker to cut off fault current as quickly as possible after a fault occurs on the transmission line of modular multilevel converter-based high-voltage direct current (MMC-HVDC) grid, in order to prevent the fault current from exceeding the ability of the DC circuit breaker. MMC-HVDC grid requires the speed of transmission line protection to be extremely fast. Travelling wave protection utilises the fault-induced travelling waves to construct protection criteria. As fault information firstly propagates in the form of travelling waves in the grid after a fault, travelling wave protection can achieve the fastest operation speed in theory, so it is an ideal choice for MMC-HVDC grid. This study analyses the characteristics of fault-induced travelling waves in the MMC-HVDC grid and the results can be the foundation of travelling wave protection of transmission line in MMC-HVDC grid.

This study presents the application of single-phase and three-phase adaptive reclosing method for transmission lines using a commercial protection relay. The method ensures the application of the automatic reclosing just after the extinction of a transient fault, the blocking of the automatic switching and, subsequently, the three-phase tripping for permanent faults. The study describes the proposed method implementation in a commercial relay. To represent both transient and permanent faults, oscillograms of real cases were used. The contributions of this work are the method to test the new algorithm in a commercial hardware, the distinction between transient and permanent faults and the detection of transient fault extinction through adaptive algorithms using commercial equipment.

Here, the use of incremental currents in time-domain phase comparison (PC) line protection schemes is evaluated. The incremental currents have been applied in modern high-speed protection relays, showing to be suitable for protection functions based on time-domain analysis. To carry out the proposed studies, the alternative transients programme was used to simulate a wide variety of fault scenarios in a 500 kV/60 Hz test power system, considering different fault features (distance, resistance, and inception angle), source-to-line impedance ratio values, and system loading conditions. In each case, the tripping times of the time-domain PC protection when implemented using traditional phase currents, sequence currents, traditional incremental currents, and incremental replica currents are compared. The obtained results show the use of incremental currents improves the PC protection reliability, speeding up the protection operation times.

Network Rail is currently electrifying one of the world's oldest main line railways, the Great Western main line between London and Cardiff. The traction system substations will incorporate full IEC 61850 functionality including the Rationalised Autotransformer Scheme: the world's first wide-area traction protection scheme operating using GOOSE messaging. The design and construction elements of a wide-area IEC 61850 system have been considerable. However, attention now focuses on future management of the IEC 61850 assets including the Substation Configuration Language files associated with the scheme. This study considers the IEC 61850 scheme of Network Rail from an asset owner's perspective. It sets out a structure for system modification and renewal which can be implemented by the in-house substation maintenance organisation for a complex IEC 61850 architecture. The system modelling and configuration control systems are described, along with a detailed examination of the management processes associated with future changes to IEDs and wide-area tripping logic.

This study proposes a non-selective protection strategy for multi-terminal high voltage direct current grids based on resistive-type superconducting fault current limiters (SFCLs). Located at the output of AC/DC converters, the SFCL limits the current contribution from the AC grid in case of DC fault. With this approach, the fault clearing time constraint is relieved allowing the use of mechanical DC circuit breakers for fault current interruption. Furthermore, the breaking capability and energy dissipation requirements of the breaker are greatly reduced. To achieve a fast restoration of the DC grid, a redundant SFCL is introduced in parallel to those in operation, bypassing them when the fault is effectively suppressed. In addition, primary and back-up protection schemes are described and tested using a three-terminal bipolar high voltage direct current (HVDC) grid based on half-bridge modular multilevel converters and cable transmission. Simulations are implemented in EMTP-RV^® to analyse and discuss performances of the proposed fault clearing strategy.