ABSTRACT
This chapter covers the power factor (PF) and dissipation factor (DF) tests that are ordinarily conducted in the fi eld for acceptance (start-up) and routine fi eld (maintenance) testing of insulation of electrical equipment and apparatus. The PF and DF tests are conducted using the 60 Hz power frequency voltages, therefore these tests may be referred to as alternating current (AC) voltage tests. The purpose of conducting these tests is to identify if the equipment has been installed properly, determine if corrective maintenance and repair is needed, and/or track the gradual deterioration of the equipment over its life. The question might be asked, why conduct these tests? The answer is obvious because the equipment to be tested is normally energized with 60 Hz AC voltage, therefore testing with the same type of voltage that the equipment sees in service provides the best information on the condition of that equipment. By applying an AC voltage test potential across a series of insulations (insulation system), the voltage drop across each layer of insulation and the resulting measured losses can be equated to true operating conditions. The voltage drop is proportional to the dielectric constant of the insulation layers. There are other AC voltage tests that may be performed along with PF and DF tests. The AC voltage tests can be classifi ed into the categories as listed below:
1. PF and DF 2. AC high potential tests 3. Very low frequency (VLF) 4. AC series resonant 5. Induced frequency 6. Partial discharge (PD) 7. Impulse tests
The AC tests may be classifi ed as destructive and nondestructive tests. The PF and DF tests are considered nondestructive since the test voltages used in
performing these tests do not exceed line-to-neutral voltages of the equipment being tested. The basic principle of the nondestructive testing is the detection of a change in the measurable characteristics of an insulation that can be associated with the effects of contaminants and destructive agents without overstressing the insulation. The AC high potential, VLF, and AC series resonant tests may be classifi ed as destructive since the test voltages associated with these tests are higher than normal operating voltages which may overstress the insulation. The effect of repeated high voltage (HV) tests on insulation are cumulative and therefore thoughtful consideration should be given on the benefi ts of these tests for routine fi eld and maintenance testing, except for special investigations or for acceptance testing. The induced frequency, PD, and impulse tests are primarily conducted at the factory during manufacturing of electrical apparatus and equipment. However, for special investigations these tests may be performed in the fi eld but will require special test equipment and setup. The AC high potential, AC series resonant, VLF, PD, induced frequency, and impulse tests are covered in other chapters under respective equipment category. This chapter is exclusively devoted to PF and DF testing methods.
