Power frequency 50 60 hz dielectric.
High voltage vlf testing of power cables.
Vlf systems are advantageous in that they can be manufactured to be small and lightweight.
The most commonly used commercially available vlf ac voltage test frequency is 0 1 hz.
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.
A vlf test.
Making them useful especially for field testing where transport and space can be issues.
The fundamental difference between ac and dc high voltage testing is the avoidance of space charge effects.
This kind of test is suited for testing high capacitance loads such.
Vlf cable testing very low frequency is a technique for testing of medium and high voltage mv and hv cables.
Ac is therefore recommended in most cable testing standards.
The article describes the methodology used to establish the voltage duration and magnitude of vlf 0 1 hz high voltage field tests suitable for crosslinked polyethylene xlpe insulated power cable.
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.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
This publication describes a laboratory test program conducted with the objective to develop a test that would replace the existing dc withstand test.
The increased load capability in field applications in which 60 hertz is too bulky and expensive making it nearly impossible to test a cable of considerable length.
Vlf ac voltage testing methods utilize ac signals at frequencies in the range of 0 01 hz to 1 hz.
Very low frequency is the preferred method over 60hz for two reasons.
Direct current dc dielectric withstand voltage.
Vlf ac test voltages with cosinerectangular and the sinusoidal wave shapes are most commonly used.
At a typical vlf frequency of 0 1hz it takes 600 times less power to test the same cable compared to 60 hz.
Some ofthe available test methods are listed below.
The selection shall be made after an evaluation of the available test methods and a review of the installed cable system.
Test sets typically operate at 0 1hz.
While supplies to railways and aircraft may use 162 3 of 400hz it is still a sinusoidal voltage waveform.
During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions.
Testing of high voltage cables manual horizon power 1st edition february 2013 prepared by field practices safety health.
