At a typical vlf frequency of 0 1hz it takes 600 times less power to test the same cable compared to 60 hz.
High voltage vlf testing of power cables.
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 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.
Test sets typically operate at 0 1hz.
Ac high voltage test equipment design vlf operation reduces the power required to load cables which present a capacitive load.
This kind of test is suited for testing high capacitance loads such.
This combination of size and power makes very low frequency cable testing perfect for testing longer sections of cable and apparatus.
Testing of high voltage cables manual horizon power 1st edition february 2013 prepared by field practices safety health.
Ac is therefore recommended in most cable testing standards.
Vlf cable testing very low frequency is a technique for testing of medium and high voltage mv and hv cables.
During the test cables are subjected to a test voltage significantly higher than what they experience during normal operating conditions.
Ac is the standard used to transmit power worldwide usually at a frequency of 50 or 60 hertz.
This publication describes a laboratory test program conducted with the objective to develop a test that would replace the existing dc withstand test.
Power frequency 50 60 hz dielectric.
Vlf ac test voltages with cosinerectangular and the sinusoidal wave shapes are most commonly used.
While supplies to railways and aircraft may use 162 3 of 400hz it is still a sinusoidal voltage waveform.
The most commonly used commercially available vlf ac voltage test frequency is 0 1 hz.
Vlf systems are advantageous in that they can be manufactured to be small and lightweight.
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 ac voltage testing methods utilize ac signals at frequencies in the range of 0 01 hz to 1 hz.
Making them useful especially for field testing where transport and space can be issues.
The selection shall be made after an evaluation of the available test methods and a review of the installed cable system.
Some ofthe available test methods are listed below.
Direct current dc dielectric withstand voltage.
Very low frequency vlf dielectric withstand voltage.
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.
