This book covers major components of a high voltage system and the different insulating materials applied in equipment, identifying measurable materials suitable for condition assessment, and also analyses insulation fault scenarios that may occur in power equipment. Suitable for power system engineers, associated with high voltage equipment, students in electrical power engineering, short courses in insulation condition assessment and postgraduates.
Inspec keywords: insulation testing; sensors; condition monitoring; fault diagnosis; high-voltage techniques; insulating materials; artificial intelligence
Other keywords: insulating material; sensor; artificial intelligence technique; fault diagnosis; electrical insulation design; insulation condition monitoring; condition assessment; high voltage insulation; power system equipment; insulation testing
Subjects: Sensing devices and transducers; Insulation and insulating coatings; Transducers and sensing devices; Power line supports, insulators and connectors; Maintenance and reliability; Testing
In this introductory chapter the principle of an AC high-voltage power system is presented together with an indication of the types of equipment involved. The order of magnitude of the operating and associated test voltages are reviewed. The concept of insulation coordination for protecting power equipment insulation from damage due to lightning and switching surges is described. In addition, the developments in HVDC transmission are considered, including recent progress in localized schemes. Appropriate references are given. The need for future insulation assessment and monitoring is emphasized.
In this chapter, the review of insulating materials includes traditional and new forms as applied in power-system equipment. The electrical and physical properties of significance in characterizing and assessing the condition of the materials are introduced. A number of the deteriorative and faiIure mechanisms associated with practical insulating materials are described, including an indication of the magnitude of the electrical breakdown dresses of samples/prototypes compared with the actual operating dresses. An understanding of these various factors and the expected behaviour of the materials enables the mod appropriate techniques for insulation-condition assessment to be selected and assists in interpretation of the complex data recorded by the monitoring systems. The latter are considered in later chapters.
The interpretation of recorded data generated by potential faults and changes in the characteristics of the insulating materials may be aided by analysis of simple electric field configurations representing the original system. For complex arrangements it is often possible to simplify an area of interest to assist with a preliminary analysis. Several simplified cases are described in this chapter. Detailed analyses involve computerized field determinations based on accurate knowledge of the particular design. A special feature of electric field design is the use of stress-control techniques a number of which are listed together with reference to examples included in other chapters. The incorrect application of these methods can result in insulation problems detectable by appropriate monitoring systems.
This chapter discusses insulation configuration of a number of power system components that may be considered as behaving predominantly as capacitances. These components include insulators and bushings, capacitor voltage transformers, power capacitors, surge arresters, circuit breakers, gas insulated systems, and power cables. Descriptions and examples are given of insulation conditions that might result in deterioration and possible failure.
This chapter considers the construction of rotating machines and transformers in sufficient detail to identify a number of possible failure modes.
In this chapter an overview is given of the more important methods employed in the supply industry for assessing the condition of insulation in power system equipment before leaving the factory, on commissioning, during service and when under going major maintenance or repair. The particular requirements for equipment of different insulation structures are described in Chapter 7, including reference to Standards where appropriate. More advanced recently developed methods are presented in Chapters 8-10. The earliest methods for determining whether or not an insulating material was suitable for a particular usage included the application of steady-state voltages for, perhaps, one minute at twice or more the operating stress. Later, this was followed by the development of surge voltage tests to simulate lightning and system switching effects. Much research was necessary in the design and construction of high voltage test equipment and associated test/laboratory areas.
Chapter 7 of the book discusses established methods for assessing the condition of the insulating materials and insulation structures in HVDC power system equipment. Test may be designed as type, sample or routine, depending on the form and number of items manufactured.
There is a pressing need to monitor accurately the insulation condition of HV equipment in the industry. Sensors play an important role in insulation condition monitoring. For different insulation structures and materials used in various equipment, it is necessary to select the most suitable sensors. The environmental noise also affects the selection of the sensor. This chapter presents some advanced sensors recently developed for condition monitoring of electrical insulation..
Offline condition assessment of the insulation in HV equipment is applied extensively in order to minimize the possibility of failure in service. However, the required testing and measurement procedures are sometimes unpractical, costly and not indicative of operating conditions. This chapter considers the alternative of online monitoring by means of which more continuous assessment is possible under operating conditions. Some of the developments during the past decade are discussed, including a number of new techniques aimed at overcoming many difficulties in implementing in-service measurements. The cost, reliability and convenience of the new systems need to be balanced against the savings effected by reduction in outages and the extension of life of the insulating materials.
This chapter concentrates only on some of the techniques and applications developed by the authors. Interested readers can refer to relevant technical papers and books for detailed information.