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VLF insulation testing

 

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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. 

AC is the standard used to transmit power worldwide, usually at a frequency of 50 or 60 Hertz. While supplies to railways and aircraft may use 162/3 of 400Hz, it is still a sinusoidal voltage waveform. A VLF test is ideal for working within these parameters.

Transmitting power with an alternating current is not as efficient as with a direct current however: while all power transmission lines and cable networks do have the side effect of DC resistance loss to the supply voltage, the level of capacitive loss is even higher. This is largely due to the inherent coupling between the phases involved. As a result, generating systems must supply enough energy to meet user demand as well as compensate for the large losses stemming from the transmission process. The small size and high power of the VLF tester helps to solve the practical problem of transmission loss during an AC test on very long sections of cable and apparatus in the field.

This equipment negates the need for on-site generation, large step down transformers or generating company supplies to be employed to power the items under test.

Because VLF testing supplies a working frequency of 0.1Hz as opposed to the 50/60Hz usually required for live transmission, the physical size of the VLF test set is massively reduced. Critically, the test object still receives the Alternating Sinusoidal Voltage that would be supplied through everyday use, but the size of the test equipment is much smaller.