What are the procedures to locate cable faults and Types of cable testing

Why Cable testing is needed

The power supply networks are growing continuously so the quality of power cables is an important factor. Cable testing must be done so that we could determine the condition of the power system, so by this, we could detect cable failures and we can improve the system reliability.

Cable components


Power cable testing

High voltage DC withstand test is the most common method of cable testing, this test can only detect defects which are associated with the conduction, so the defects were detected by the leakage currents

The most common fault in dielectric cables is due to ‘partial discharge’ to perform the partial discharge test the equipment used was very expensive so acoustic equipment are used to do the partial discharge test

Types of cables and their characteristics

Cables can be classified into low, medium and high voltage cables, so according to the cable types the testing and maintenance are done, three-conductor cable has been used in the lower voltage range. Nowadays we use XLPE insulated because of the quality of the insulation material and it is well designed

Due to these features, these cables can be used for extra-high voltage level

What are the procedures for cable fault location

These are the following steps to locate the cable faults

  • Fault indication
  • Disconnecting and Earthing
  • Fault analyses and insulation test
  • Cable fault Pre location
  • Cable route tracing
  • Precise cable fault location
  • Cable identification
  • Fault marking and repair
  • Cable testing and diagnosis

Cable testing

Installation acceptance and maintenance test

  • Installation test is a test which is done after cable installation but it is done before the application of joints or terminations
  • Acceptance test is also a field test which is conducted after cable installation, which is inclusive of terminations and joints before the cable system is commissioned
  • Maintenance test this test is done during the operation life of the cable system

Thermal imaging camera is used for maintenance testing and a Megger for DC high pot testing


Withstand test

This type of test involves the application of a voltage at a nominal level or higher than the prescribed period of time. By doing this test we could determine the cable’s ability to withstand voltage without insulation breakdown

Dielectric response

This kind of test is done to determine the cables dielectric response to the applied electric field, it can be done by measuring properties such as recovery voltage DC leakage current, dissipation factor

This can be done by applying AC or DAC voltage for a prescribed period at a frequency of 20 – 300 Hz


  • An overall assessment of the cable can be done
  • Has the ability to detect the degree of water treeing and conductive type defects

Dielectric response – Dissipation factor

This could determine the loss factor of cables insulation, the loss factor will increase with age, so dissipation factor or Tan delta measurement can be used to determine the cable condition

Dielectric response – DC leakage current

During this test, a DC voltage lower than the withstand voltage is applied between the conductor and the insulation shield. So the leakage current through the cable insulation can be measured

While testing extruded cable system HVDC must not be used leakage current measurement will only take place when the applied voltage reached its steady-state value

Dielectric Response – Recovery voltage

DC voltage is used to charge the cable for a specified time in this test, after that the cable will be discharged to ground through a resistor for short time and then the open circuit voltage is recorded and plotted against time

It is used to determine the level of water tree degradation in extruded insulation

Partial discharge - Acoustic measurements

When a partial discharge occurs energy is released which produces a mechanical wave so the place in which partial discharge occurs acts like an acoustic wave source

Time-domain Reflectometry

This method uses changes in impedance of cable to determine cable imperfections such as faults, open connections, poor neutral, lossy connections, and water ingress