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Medium Voltage Cables - Onsite Diagnostics


Cable capacitance and dissipation factor (tan δ) measurements

The Tan Delta can be used to help determine the insulation quality of cables and other capacitive loads. It is used in conjunction with a Very Low Frequency (VLF) AC Power Supply to measure the loss angle or Tan Delta of the insulation. These measurements can be used to track the deterioration of service aged cable and establish baseline readings on new cable installations. Changes in Tan Delta measurements can indicate degradation of the insulation, which can be used to make engineering decisions about decisions about the service life of the cables.

Test Description 

test according to

  • IEEE   400.2


The Tan Delta is a bridge for use with a sinusoidal high voltage VLF power supply. High voltage is applied to the test specimen through the measuring unit. The control unit compares the phase angles of the voltage and current waveforms to give a loss angle of the insulation.

Cable Tand test set (High Voltage Inc.)

Tan δ measurements in medium voltgae cable  - phase L2 insulation deteriorated