They are in the range of 1 5 u0 to 3 u0.
Vlf cable testing procedure.
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.
We need to apply 1 414 times 11 1 414 15545 volts dc of voltage between phase to phase or between phase to earth.
When vlf withstand testing cable the proper test voltage and time duration are critical for the success of the test.
Thus it is quite natural for utilities to also use withstand and partial discharge tests as commissioning and maintenance tests for cable.
Any one please explain the hi pot pressure test testing procedure for 3 core 70 sq mm copper mv cable.
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.
If a vlf test is too low in voltage and or too short in duration more harm than good may result.
Voltage levels are a multiple of the nominal voltage of the cable.
During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions.
Very low frequency vlf tan delta testing is a precise and non destructive method to provide information on the extent of ageing in cable insulation.
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.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
Perform the test as instructed to make best use of vlf technology.
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.
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.
While the testing procedures of the past dc testing were sometimes actually damaging to the cable insulation modern vlf.
Vlf testers are smaller and more practical than ac testers but output the same amount of power as a 50 hz mains device.
Vlf testing uses very low frequencies as part of an ac cable maintenance routine.
Once partial discharge is triggered in a defect under the test.
The preset test time in the range of 15 to 60 minutes is short and economical.
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 kind of test is suited for testing high capacitance loads such.
