Partial Discharge Risks in Switchgear: Causes, Consequences, and Detection
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Switchgear is one of the most critical elements in electrical networks, responsible for protecting, isolating, and routing power circuits. Beginning with medium-voltage levels, typically from 11 kV and upwards, these systems are exposed to conditions that make them vulnerable to partial discharge. Their reliability depends on the integrity of key components such as terminations, bus bars, cables, insulators, and connections. When any of these are subject to defects, contamination, or improper assembly, localized high electric fields can develop and trigger PD activity.
How PD Develops in Switchgear
Inside switchgear, PD can be initiated by several conditions:
- Cables and Insulation – Defects in insulation, voids at terminations, or contamination accelerate degradation and carbon tracking.
- Bus Bars and Joints – Inadequate spacing, loose fittings, or mismatched hardware lead to PD activity.
- Terminations and Connections – Sharp edges, improper torque, or poor surface finishing create points of high stress where corona PD can form.
- Environmental Conditions – Humidity, dust, or residual cleaning agents increase conductivity along surfaces, supporting PD growth.
Once PD occurs, it erodes insulating material, leaves conductive paths, and produces byproducts such as ozone, nitric acid, or white powdering. Over time, this leads to deep carbonization, loss of dielectric strength, and eventually flashover or catastrophic failure.
Case Study: Utility Switchgear Failure
A European utility encountered widespread failures in their switchgear. An extensive inspection using a UV corona camera revealed that approximately 30% of the equipment, around 10 years in service, exhibited PD. As seen in the image, corona activity appeared as bright spots along the center cable, with high PD resulting in repeated line tripping.
The failures were initially attributed to extreme cold weather, but subsequent investigation determined that improper cable installation had induced partial discharge activity within the insulation. This accelerated aging of the dielectric material and ultimately caused insulation breakdown and line tripping.
The Value of PD Detection
Traditional inspections often miss early-stage PD because it is invisible to the human eye. Ultraviolet cameras allow operators to visualize corona activity directly, pinpointing its exact location. By identifying PD at an early stage, utilities can:
- Correct workmanship issues before they escalate.
- Prevent insulation breakdown and unplanned outages.
- Establish a baseline for condition monitoring.
- Extend the service life of critical equipment.
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