The Doble power factor test is a diagnostic test done in motors, transformers and other high voltage devices to test how good the insulator is in isolating the conductors. This is done to ensure the safety of the devices while it is operating.
In order to conduct a power factor test, a high voltage alternating current is passed through the conductor by the tester while the capacitive current and the resistive current flowing through the insulator is measured. A good insulator should only allow a very small capacitive current to flow through the insulator. The resistive current flowing should be minimal. If the resistive current is slowly rising as the test voltage is increased, there may be moisture or contamination between the insulator and the conductor.
Capacitive current can flow because the device tested acts like a capacitor. The conductors act as the poles of the capacitor and the insulator acts as the dielectric. When AC current is applied, the conductors are charged and then reversed on the next cycle.
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