Medium-Voltage Switchgear and Circuit Breakers:Power Factor Testing

Power Factor Testing

The power factor testing of an insulation system is useful in finding signs of insulation deterioration. The absolute values of power factor measured have little significance. However, comparative analysis of values from year to year may very well show insulation deterioration. Therefore, when a power factor test is made, it should be made under the same conditions of temperature and humidity. If differences exist in the temperature and humidity from year to year, this should be taken into consideration when evaluating the test data. Generally, higher temperature and humidity result in higher power factor values. As a general rule, only the air circuit breaker bushing should be power factored, and the arc chutes, operating rods, and so on, should be disconnected when conducting this test. A significant change, especially an increase in watts loss or percent of power factor indicates deterioration, which should be monitored. As a general rule, a power factor below 1% indi- cates good insulation. Any value above 1% warrants investigation. Power factor tests are discussed in more detail in Chapter 3.

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