What is Partial Discharge Damage?
Partial Discharge (PD) Damage refers to the progressive physical, chemical, and electrical deterioration of insulation systems caused by localized electrical discharges that do not completely bridge the insulation between conductors. These discharges release energy in the form of electromagnetic waves, acoustic emissions, heat, and chemical byproducts, which over time lead to insulation degradation and eventually catastrophic equipment failure.
The mechanism of partial discharge damage
Electric field concentration or local excessive electric field generated at the insulation defect site
There are defects such as air gaps, cracks, impurities, sharp-angle conductors, and interlayer peeling inside or on the surface of the insulating material.
Under high voltage, the local electric field strength at these locations far exceeds the insulation medium tolerance value and becomes the starting point of discharge.
Local discharge forms a micro discharge channel
When the local electric field exceeds the air gap breakdown field strength, micro discharge occurs at the air gap or weak point in the insulation defect.
This discharge only forms a micro discharge channel near the defect and does not penetrate the adjacent conductor.
Partial discharge releases energy and produces a variety of physical effects
Each partial discharge is accompanied by:
- Local high temperature (instantaneously exceeding 1,000 degrees Celsius)
- Plasma shock
- Electromagnetic wave radiation (TEV, UHF)
- Ultrasonic signal (AE)
- Chemical effect (producing ozone, nitrogen oxides, corroding insulation)
- Local carbonization, dendritic discharge marks
Typical power equipment susceptible to partial discharge
Power Transformers: PD may occur in oil, solid insulation, or winding gaps. It weakens insulation, generates gas, and causes thermal damage.
Gas-Insulated Switchgear (GIS): Defects like floating particles, voids in castings, or surface contamination can trigger PD. It leads to insulation erosion and SF₆ gas decomposition.
High-Voltage Switchgear Cabinets: Surface discharges can happen at insulation supports, cable terminations, and conductor joints, causing thermal and tracking damage.
Power Cables and Accessories: Voids, impurities, or joint defects result in PD, leading to insulation breakdown and cable failure.
Generators and Motors: PD arises from voids, moisture ingress, and insulation cracks, gradually degrading winding insulation and risking machine breakdown.
Consequences of Partial Discharge Damage
Partial discharge (PD) causes progressive deterioration of insulation materials due to localized electrical stress. Over time, this results in erosion, carbonization, and the formation of conductive paths within insulating structures. Continuous PD activity reduces dielectric strength, accelerates insulation aging, and increases the risk of catastrophic insulation breakdown.
In high-voltage equipment, undetected PD can trigger severe faults such as phase-to-ground or phase-to-phase flashovers, leading to equipment outages, costly repairs, and potential safety hazards. In extreme cases, sustained PD activity may result in fire, explosion, or complete asset failure.
Preventive Measures Against Partial Discharge Damage
To mitigate the risks associated with partial discharge, comprehensive monitoring and diagnostic strategies are essential. The partial discharge monitor includes continuous online PD detection using techniques such as UHF, TEV, ultrasonic, and high-frequency current sensors.
Regular insulation testing, dissolved gas analysis (DGA) for transformers, and periodic offline assessments should be integrated into asset management programs. Additionally, improving insulation design, ensuring high-quality installation practices, and addressing identified defects promptly can significantly extend equipment life and enhance system reliability by minimizing PD-induced failures.
