Shining Light on the Doble Test

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Doble Power Factor is a test done to transformers or motors to measure the effectiveness of the insulation. It’s not an actual type of test but rather slang used to refer to the procedure of measuring power-factor. It is called a Doble test because most of the test equipment used in measuring power-factor is made by Doble Engineering. 

The so-called Doble test measures the effectiveness of the insulation on transformers and DC motors. In this procedure, the test equipment applies an alternating current to the test conductor and measures the power-factor in the insulator. The power-factor is the ratio of capacitive and resistive currents in the insulation of the test conductor. A good insulator has only capacitive current and zero resistance leakage current. However, if the insulator is degraded or wet, current will flow through it and will be detected. This increases the power-factor reading. A Doble test may also refer to the timing test for a circuit breaker with a shunt trip. Doble Engineering manufactured the first equipment that tests the time a breaker opens its contacts the moment the signal was initiated.

Doble equipment has become the standard in power-factor testing in transformers and motors. That’s why it is sometimes referred to as the Doble test. Protec has a complete line of Doble equipment for power-factor testing. Visit Protec’s website for more information about Doble test equipment.