A very low frequency vlf withstand test is an ac withstand test usually carried out at a frequency between 0 1 hz and 0 01 hz.
Vlf cable testing results.
Very low frequency testing for medium voltage and high voltage cables is a method for verifying the integrity of the cable insulation.
If a vlf test is too low in voltage and or too short in duration more harm than good may result.
The major application is for testing solid dielectric cable per ieee 400 2 followed by testing large rotating machinery per ieee 433 1974 and occasionally for testing.
During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions.
The test applies an ac sinusoidal waveform at 0 1 hz frequency and measures the degree of real power dissipation or losses in a dielectric material.
Vlf testing uses very low frequencies as part of an ac cable maintenance routine.
Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
When vlf withstand testing cable the proper test voltage and time duration are critical for the success of the test.
Vlf testing is not only used for testing solid dielectric cable any application requiring ac testing of high capacitance loads can be tested using very low frequency.
Its most frequently used to ac field test medium and high voltage cables and test rotating machinery like motor and generator coils.
Once partial discharge is triggered in a defect under the 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.
The benefits of vlf maintenance testing regular routine maintenance testing of aged cables has been demonstrated to reduce the chance of unscheduled failure to approximately 10 of the failure rate that might be encountered without such testing.
Approximately 12 of cables fail during the test and cable repair can then be done in a planned manner.
Vlf tests at ieee 400 2 test levels do not damage cable systems good insulation but are used to degrade existing insulation defects to failure during the test rather than in service.
The test is conducted on entire drum of cable rather than a test sample length.
Perform the test as instructed to make best use of vlf technology.
This kind of test is suited for testing high capacitance loads such.
Vlf testing is a withstand test usually carried out at a frequency of between 0 1 hz and 0 01 hz rather than 50 60 hz.
Vlf cable testers support iec 60502 and ieee.
