What is a Partial Discharge Test ?

What is a Partial Discharge Test ?

Discover What is Partial Discharge Testing in Depth:

  • The importance of proper and adequate maintenance of electrical equipments cannot be over-emphasised in an industry.
  • This is because it ensures the longevity of the equipment and allows for optimal functionality to produce reliable results.
  • Also, a system comprising of multiple equipments, each with its own specifications and conditions of operating needs proper looking after.
  • As such, it becomes necessary that adequate technologies are put in place to perform comprehensive test and maintenance checks.
  • Partial discharge testing is a type of comprehensive testing carried out on electrical systems to ensure insulation failures are avoided.

What is Partial Discharge (PD)?

  • Partial discharge is an electric spark found, anywhere, within an electrical equipment’s insulation.
  • This occurs because the dielectric material’s strength is weakened to contain the electric field that is generated.
  • As a result of this, the electric spark is able to bridge the gap between the conductors in the casing.
  • Hence, a connection of the conductors occurs.
  • The weakened dielectric material’s strength, also referred to as breakdown strength is an indication of the insulation’s condition.
  • The reason for this is due to the presence of cracks, defect in dielectric material and possibly cavities.
  • Likewise, for these to be present, it is also indicative of wear and tear or aging of the material.
  • In situations whereby these defects are not noticed and repairs made, the insulation can get eroded resulting in sudden outages.
  • This is because the discharges can have a minimum voltage rating of 2kV and bring about failures in MV/HV equipments.

Partial Discharge Testing from theory to practical

Usually, partial discharges which occur are only around for a few nanoseconds as they are just a tiny electric spark.

Hence, to test for PDs, analogue capacitive and inductive sensors are used for detection of the discharges.

The signals obtained are filtered to eliminate noise then, amplified before being converted to digital data for analysis and interpretation.

Partial Discharge Solutions

Whilst there are a number of partial discharge testing solutions available to choose from, listed below are a few.

Offline Partial Discharge Testing of Medium Voltage Equipment:

This involves performing the partial discharge test on a new equipment as a form of acceptance test hence, being done offline.

Usually, this test is done to check for specific conditions such as

  • Determining stress levels when subjected to varying voltages without a fault being triggered.
  • Detection of fault and its location in an equipment

Online Partial Discharge Testing of Medium Voltage Equipment

This test is one that is performed on equipments while they are undergoing normal operations, voltages and stress.

Advantages of this testing solution include

  • It is non-destructive
  • It is non-intrusive
  • Non-exposure to unnecessary voltage stresses

Continuous Partial Discharge Monitoring of Medium Voltage Equipment

This testing solution involves having to record and analyse data obtained while the equipment is undergoing operation.

This solution finds application in unmanned systems and helps to provide an accurate, real-time data.

Also, it shows if there are any failures that might occur before it happens so it is addressed.

What are the applications of Partial Discharge Testing ?

  1. Whilst partial discharges can largely be an indication of age and wear and tear, it is limitless.
  2. Performing a partial discharge test on equipments or electrical systems before being installed and after installation is highly recommended.
  3. This helps to detect, if there are, any points of breakdown before installation and those brought by faulty installation.
  4. Also, scheduled partial discharge checks can help detect any breakdown due to conditions of operations or faults in design.
  5. Performing routine partial discharge tests on electrical equipments is very important because it applies to all types.
  6. As long as the electrical equipment operates on medium to high voltages, a partial discharge test should not be overlooked.

Examples of some equipments are:

  • Transformers
  • Motors
  • Generators
  • Bushings
  • Switchgears
  • Cables, splices and terminations

On most occasions, cables are not usually included in the lists of items to undergo routine maintenance checks.

Though unacceptable because they are an integral part of electrical systems but adequate tests to ascertain their condition are lacking.

Recent technological advancements have made partial discharge testing more effective in checking the capability and conditions of cables.

This determines how effective an insulation material is in eliminating occurrence of insulation failures as part of an electrical system.

Also, electrical installations become more reliable when maintenance checks have PD tests included in addition to other tests like IR imaging.

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