Power factor is a measure of the power loss through the insulation system to ground caused by leakage current. It is equal to the circuit resistance (R) divided by the circuit impedance (Z).
PF = W / V I or PF = (V I cosθ ) / (V I )
The power factor of insulation is the cosine of the angle between the charging current vector and the impressed voltage vector. In other words, it is a measure of the energy component of the charging current. The amount of charging volt-amperes and the dielectric loss in watts, at a given voltage, increases with the amount of insulation being tested. However, the ratio (power factor) between the charging volt-amperes and watts-loss remains the same regardless of the amount of insulation tested, assuming that the insulation is of a uniform quality. This basic relation eliminates the effect of the size of the electrical apparatus in establishing "normal" insulation values and thus simplifies the problem for the test engineer. Actually, power factor testing is more than just "a" test. It is a series of tests on each part of the insulation system. Insulation power-factor tests can also be made on lightning arresters, air and oil circuit breakers, current and potential transformers, capacitors, cable (500 feet or less) and rotating machinery, such as motors and generators.
What is the purpose of insulation power factor test?
• To determine the relative dryness and material quality of the insulation. It is typically used in conjunction with other dryness indicators, such as insulation resistance and oil dielectric breakdown values, to determine insulation dryness.
• To measure the power loss due to leakage current through the transformer insulation.
• To detect any measurable change in the transformer winding insulation characteristics.
• Gives an overall indication of the condition of the insulating system.
• To measure the power loss due to leakage current through the transformer insulation.
• To detect any measurable change in the transformer winding insulation characteristics.
• Gives an overall indication of the condition of the insulating system.