WAZIPOINT Engineering Science & Technology: Partial Discharge in HV & EHV Power Lines

Wednesday, May 8, 2024

Partial Discharge in HV & EHV Power Lines

A video clip for Brug cable PD Measure

Partial Discharge in High and Extra High Voltage Lines

Partial Discharge (PD) is very important for Underground Power Cables. If you work with Power Cable, you must know why and where Partial Discharge is present. It will help to take action at the right place at the right time. 

  1. In electrical engineering, partial discharge (PD) is a localized dielectric breakdown of a small portion of a solid or fluid electrical insulation system under high voltage stress, which does not bridge the space between two conductors.
  2. Partial discharges are small electrical sparks that occur within the insulation of medium and high-voltage electrical assets. Each discrete partial discharge is the result of an electrical breakdown of an air pocket within the insulation. These discharges erode insulation and eventually result in insulation failure.
  3. Partial discharge (PD) is a phenomenon that can occur in high voltage (HV) and extra high voltage (EHV) power lines and equipment. It is an electrical discharge that only partially bridges the insulation between conductors and occurs within voids, impurities, or imperfections in the insulation. PD can lead to deterioration of the insulation over time and, if left unaddressed, may result in complete insulation failure and subsequent equipment breakdown.
  4. Partial discharge testing results can help predict future performance and reliability of critical assets, including:

    • Cables, splices, and terminations
    • Power transformers and bushings
    • Switchgear
    • Motors and generators

Partial Discharge in HV and EHV power lines

Causes of Partial Discharge:

Insulation Defects: PD is often caused by localized defects in the insulation, such as air voids, impurities, or moisture.

Voltage Stress: High voltage stress on the insulation can initiate partial discharges.

Impulse Voltage: Rapid changes in voltage, such as lightning or switching operations, can trigger PD.

Aging: Insulation materials can deteriorate over time, leading to increased susceptibility to partial discharges.

Detection and Monitoring:

PD Measurement: Various diagnostic techniques are used to detect and monitor PD, including high-frequency current transformers, ultrasonic sensors, and radio frequency (RF) sensors.

Partial Discharge Testing: Periodic testing is conducted to assess the condition of insulation and identify potential PD issues before they escalate.

Consequences of Partial Discharge:

Insulation Degradation: Continuous partial discharges can cause progressive deterioration of insulation, reducing its effectiveness.

Equipment Failure: If left unchecked, PD can lead to complete insulation breakdown and equipment failure.

Mitigation and Prevention:

Regular Maintenance: Scheduled maintenance and inspections are crucial to identify and address potential PD sources.

Insulation Design: Proper design of insulation systems, including material selection and configuration, can minimize the risk of partial discharge.

Monitoring Systems: Continuous monitoring systems help detect and analyze partial discharges in real time, allowing for timely intervention.

Safety Considerations:

Fire Hazard: PD can lead to localized heating, posing a fire hazard.

Personnel Safety: Unchecked PD can result in equipment failure, posing risks to personnel working in the vicinity.


Standards and Regulations:

IEC 60270: International standard for the measurement of partial discharges.

IEEE Standards: Various IEEE standards address partial discharge testing and monitoring.


In summary, understanding, detecting, and mitigating partial discharge is essential in maintaining the reliability and safety of high-voltage and extra-high-voltage power systems. Regular monitoring and appropriate maintenance practices play a crucial role in identifying and addressing partial discharge issues to prevent equipment failures and ensure the integrity of the power infrastructure.


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