Vlf Cable Testing Procedure

When vlf withstand testing cable the proper test voltage and time duration are critical for the success of the test.

Vlf cable testing procedure. 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. Once partial discharge is triggered in a defect under the test. High voltage withstand tests are used in conjunction with partial discharge measurements on solid dielectric cable and accessories within manufacturing plants to ensure the quality of completed cable system components from mv to ehv. Perform the test as instructed to make best use of vlf technology.

Voltage levels are a multiple of the nominal voltage of the cable. Any one please explain the hi pot pressure test testing procedure for 3 core 70 sq mm copper mv cable. 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. We need to apply 1 414 times 11 1 414 15545 volts dc of voltage between phase to phase or between phase to earth.

While the testing procedures of the past dc testing were sometimes actually damaging to the cable insulation modern vlf. They are in the range of 1 5 u0 to 3 u0. In accordance with respective standards sine wave voltage is used for vlf testing. 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.

Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device. The most widely accepted test frequency is 0 1 hz however frequencies in the range of 0 0001 1 hz may be useful for diagnosing cable systems that exceeds the limitations of the test system at 0 1 hz. This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus. This kind of test is suited for testing high capacitance loads such.

Vlf testing uses very low frequencies as part of an ac cable maintenance routine. Approximately 12 of cables fail during the test and cable repair can then be done in a planned manner. The procedure for vlf testing is nearly identical to that of dc hi pot testing and is also conducted as a go no go test. 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.

If a vlf test is too low in voltage and or too short in duration more harm than good may result. The preset test time in the range of 15 to 60 minutes is short and economical.