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.

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.

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.

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..

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.