Today, in all countries in the world that utilise electricity as an efficient source of light and energy, some form of a transmission and distribution system exists. Both systems carry electric current, albeit at different voltages and they are connected to each other. They are part of the bulk transport and distribution system that essentially delivers and distributes the electrical energy, converted from primary energy sources, to the end users. The only clear differences between the two systems is based on the perception of their end use and functionality. Transmission systems provide the bulk transport paths for electrical energy from generation centres located close to the primary energy sources to the major load centres within a large geographical area, thus facilitating economic and efficient bulk power transfer. On the other hand distribution systems are concerned with the delivery of electrical energy to individual customers within a smaller geographical area. In this respect a distribution system may have a number of delivery points to its major load centres, from one or more transmission systems and/or elements of a transmission system, the final shape of the system structure being dependent on the magnitude and the pattern of demand within its geographical area. It is also usual for transmission systems to be interconnected to enable shared economic benefits and operational access to generating capacity.

This chapter introduces the subject of gaseous insulation and provides information relating to the application of gaseous insulants to high voltage systems. It examines atmospheric air, compressed gases and illustrates how, by linking available experimental test data from such sources with a knowledge of the 'effectiveness' of various practical gas-gap clearances, the designer can achieve reliable insulation design. The chapter also briefly discusses the need for high voltage and extra high voltage (UHV) test areas or laboratories. Evidence is presented of how laboratory studies, on representative insulation systems and electrode arrangements, provide the designer with choices relating to electrical stresses, clearance levels, service performance and testing procedures. Gas insulated substations (GIS) using sulphur hexafluoride (SF₆) gaseous insulation have been used in transmission systems worldwide for more than 35 years. The service reliability of this class of equipment is of paramount importance. In addition, the chapter presents a large amount of experimental breakdown information on SF₆ and briefly reviews the application of field computation strategies in support of GIS and other equipment designs. Several of the major factors influencing the insulation design and in-service behaviour and reliability of SF₆ gaseous and epoxy resin support insulations, as used in GIS equipment, will also be considered.

The purpose of this chapter is to provide an overview of the design, manufacture, construction, testing and maintenance of the various components which go to make up overhead transmission and distribution lines. The transmission of electrical energy is carried out over long distances at voltages of 66 kV and above, whereas distribution is carried out over short distances at voltages of between 11 and 66 kV using the same technology.

The interruption of current in a network cannot meaningfully be considered in isolation from the operating voltage of the system and the nature of the system components and structure. The operating voltage itself affects the type of interrupter chosen for duty whilst the system components and structure (e.g. the extent to which the network is induct ive etc.) will influence the detailed design of the interrupter unit because of the voltage transients produced during the current interruption process. It is for these reasons that a discussion of current interruption in electric power systems is appropriate in a book on high voltage technology. The fundamental principles of current interruption as governed by high voltage considerations are therefore described with respect to both system based effects and the characteristics of circuit-breakers. Various types of SF₆ interrupters are considered and different factors which limit their performance are explained. Some possible trends in future developments are indicated.

The function of a substation in a transmission system is to provide a switching node through which circuits, generating units and step-down transformers can be interconnected. Substations are critical to the safety, reliability and availability of the network and should be carefully planned with both current and future system requirements in mind.

This chapter reviews the circuit-breaker designs which are type tested to IEC 60298 and IEC 62271-100 for use on distribution voltages up to 52 kV. The design and service experience of different types of commercially available circuit-breakers are considered. The chapter also discusses some special switching duties and focuses on aspects which are necessary for the selection of circuit-breakers for various duties: for example, for switching capacitor banks, capacitive and inductive currents, generators, reactors and synchronised switching of transformers with reactors on the secondary side.

This chapter discusses the design of high voltage power transformers.

The measurements of voltage and current in high voltage tests are difficult because the amplitudes are high and they cannot be measured directly with conventional measuring and recording systems. Further more, not only the peak value but also the shape of the signal, particularly for impulse voltage and current, should be measured and evaluated, and this requires an adequate recording system using either an oscilloscope or a digital recorder.

The partial discharge measurement is a typical nondestructive test and it can be used to judge the insulation performance at the beginning of its service time taking into account the reduction of the performance during the service time by the ageing, whereby the ageing depends on numerous parameters like electrical stress, thermal stress and mechanical stress. Depending on the kind of insulating material, different limits for the allowed partial discharge value at a given stress are defined in the rele vant recommendations. In particular, for solid insulation where a com plete breakdown seriously damages the test object the partial discharge measurement is a tool for quality assessment.

Traceability is defined as an unbroken chain of comparisons (calibrations), each having a stated uncertainty, which relates the result of a measurement or the value of a standard to stated references. Wherever practical the maintained electrical standards are taken as such references. A chain of measurements can be extended from any convenient reference point in such a chain, providing the route to a primary standard of measurement can be traced. An accredited calibration laboratory provides a widely accepted point of reference in the chain of traceability. Although in many countries traceability through accredited calibration laboratories for a range of measurements (mass, temperature, low voltage) is readily available, a similar service for high voltage measurements is not so common. The concept of the approved measuring system introduced in IEC Publication 60060-2:1994 helps to redress that deficiency. The concept regards the complete measuring system as an entity in the traceability chain, and it includes the voltage divider (or other converting device), lead from the test object, lead damping resistor, low voltage transmission system, attenuator, recording instrument and earthing cables.

The scope of optical fibre sensing for high voltage equipment and systems monitoring has been illustrated with respect to circuit-breaker applications. The techniques are equally applicable to other high voltage equipment such as transformers. Already the use of optical fibre distributed sensors for monitoring temperatures and hot spots is apparent in relation to the windings of transformers. A number of extension of the fibre sensor types described above for circuit-breakers are possible to other equipment. For instance, the optoacoustic fibre dyne interferometer has been deployed for monitoring partial discharges in gas insulated systems and in power cables. Modified forms of the chromatic particle monitor have already been utilised for oil monitoring in the semiconductor industry and for kerosene monitoring in the nuclear industry and have the potential for application to transformer oil monitoring. The chromatic approach to optical fibre sensing is synergetic with the broader issue of intelligent monitoring discussed via the utilisation of the chromatic processing for extracting information about complex systems operation. The methodology therefore permeates through the intelligent monitoring system illustrating how intelligence may be distributed therein.

Plant reliability is essential to the overall reliability of the power system. Therefore this chapter starts by considering sources of information on reliability and how this will help the user and manufacturer. Examination of system reliability data will enable the user to make further improvements on system reliability, to look for requirements for new plant, and to help towards planning and prioritising an asset replacement strategy for the existing plant.