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VLF Testing for MV Cables

Very Low Frequency testing for Medium Voltage and High Voltage cables is a method for verifying the integrity of the cable insulation. VLF testing is a withstand test usually carried out at a frequency of between 0.1 Hz and 0.01 Hz rather than 50/60 Hz. The test is conducted on entire drum of cable rather than a test sample length.

Although the frequency is very low, it is an alternating current with polarity reversals every half cycle. At 0.1 Hz output, it takes 600 times less current and power to apply an AC voltage to a capacitive load.

VLF testing for MV Cables


VLF testing of solid dielectric cable is supported in IEC 60502 (up to 35kV) and in IEEE 400.2 (up to 69 kV). Acceptance test voltages are generally 2.5-3 times the line to ground system voltage. VLF tests should last between 15 and 60 minutes with a recommended minimum duration of 30 minutes.

The tested MV or HV cable must withstand an AC voltage for the specified testing time without flashover. VLF cable testing  on MV and HV cables uses different wave shapes, typically sine and square, so care must be taken when describing the voltage to be used. RMS and peak voltages have different relationships to each other depending on the wave shape - IEEE 400.2 uses the peak voltage level to equate the wave shapes.


VLF testing in MV facility


IEEE 400 embraces VLF testing as a viable alternative to DC testing. It is testing methodology widely adopted by Distribution Network Operators (DNOs) as it exposes serious cable defects, thus preventing in-service failures, while not harming healthy insulation or aggravating minor defects.

MV Cable Test Facility for VLF Testing

VLF Testing on MV and HV cables is undertaken in our specialist MV test facility, under strictly controlled test conditions. As with all testing undertaken within The Cable Lab, our technical experts precisely match proscribed test methodology with results recorded impartially and automatically within our systems.

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The Cable Lab®

UKAS-accredited specialist cable testing laboratory

About Eland Cables

The Cable Lab® our in-house cable testing facility, is UKAS-accredited to ISO 17025, which is the single most important standard for calibration and testing laboratories around the world. Accreditation to this international standard demonstrates our laboratory's technical competence and the accuracy of its results.

For our customers, it means peace of mind. They can have full confidence in the quality of our products and can demonstrate due diligence in selecting their cable supplier.

Our customers can also rely on the Cable Lab's services for an independent, objective and comprehensive quality assessment of cables procured from third parties.


About Eland Cables

About Eland Cables

Established in 1975, Eland Cables is a supplier of power, data, instrumentation and control cables and cable accessories to the world's most demanding industries and to some of its most prestigious projects. Our reputation is built on an unswerving focus on quality, technical expertise and customer service.


Our focus on quality has resulted in our in-house specialist cable testing facility securing the ISO 17025 accreditation. This certifies the competence, impartiality and performance capability of our laboratory and its evaluations. In turn, it means peace of mind for our customers with regard to the quality of the cables they source from us.

Expert tecHnical support

Our highly-qualified technical team is on hand to provide technical support with all aspects of cable selection, technical specification, regulatory requirements, and bespoke cable design and manufacture.

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We are a key contributor to projects in over 100 countries every year, adding value through comprehensive technical support, reliable logistics, innovative solutions, and a customer-centric approach.