Cable Diagnostic Tests
1.Damped alternating current (DAC) voltage Test:
DAC voltage testing is one of the alternative methods of ac voltage testing and is applicable for a broad range of medium-voltage, high-voltage, and extra-high-voltage cables. Damped alternating current voltages are generated by charging the test object to a predetermined voltage level and then discharging its capacitance through a suitable inductance.
During the discharging stage, a DAC at a frequency dependent on test-object capacitance. and the inductance is present. The capacitance of the test object is subjected to a continuously increasing voltage at a rate dependent on the test-object capacitance and the current rating of the power supply.
Most DAC applications are based on the combination of voltage withstand and advanced diagnostic measurements, such as partial discharge and dissipation factor. DAC testing is an advanced maintenance tool, offering more than a simple "go or no-go" decision.
2.Very Low Frequency Test
Very low frequency (VLF) withstand testing is the application of an AC sinusoidal waveform, generally at 0.01 – 0.1 Hz, to assess the quality of electrical insulation in high capacitive loads, such as cables. During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions. The higher test voltage allows for weak points or pre-damaged areas within the cable to breakdown during the test, rather than while they are in service. Essentially, the VLF withstand test is a “go or no-go” test, otherwise known as a “pass/fail” test