What is Partial Discharge in Transformers?
Partial Discharge (PD) is a localized electrical discharge that occurs within the insulation system of a transformer. It does not completely bridge the space between conductors but indicates early-stage insulation deterioration. Over time, these discharges can cause insulation breakdown, resulting in power failure or costly transformer damage.
The Partial Discharge Test is a diagnostic technique used to detect and measure such discharges — helping identify insulation defects before they lead to failure.
Why is Partial Discharge Testing Important?
The insulation system of a transformer is crucial for its reliable operation. Any minor defect—like voids, cracks, moisture, or contamination—can trigger PD activity. Detecting PD at an early stage ensures:
Early detection of insulation defects
Prevention of unplanned outages
Increased transformer lifespan
Improved system reliability and safety
Reduced maintenance and repair costs
Types of Partial Discharge in Transformers
Internal Discharge – Occurs inside insulation material due to air pockets or voids.
Surface Discharge – Appears along the surface of insulation when moisture or contamination exists.
Corona Discharge – Happens in gaseous insulation near high-voltage points or sharp conductors.
Treeing Discharge – Progressive electrical breakdown forming tree-like structures inside insulation.
Partial Discharge Test Methods
1. Offline Partial Discharge Testing
- Performed when the transformer is de-energized.
- Uses IEC 60270 standard measurement techniques.
- Detects PD inception voltage (PDIV) and extinction voltage (PDEV).
- Helps identify insulation defects under controlled lab conditions.
2. Online Partial Discharge Monitoring
- Performed while the transformer is in service.
- Uses sensors like UHF, acoustic, and capacitive couplers.
- Continuously monitors PD activity in real-time.
- Ideal for critical transformers in substations and industrial plants.
3. Acoustic Emission Method
- Detects ultrasonic signals produced by PD activity.
- Sensors placed on transformer tank surfaces pinpoint PD location.
4. Electrical Pulse Analysis
- Measures electrical signals generated by PD using coupling capacitors.
- Helps estimate PD magnitude and location.
Benefits of PD Testing in Transformers
Detects insulation aging before catastrophic failure
Ensures transformer reliability and efficiency
Reduces maintenance costs and downtime
Improves power system safety
Extends equipment lifespan
The Partial Discharge Test of Transformers is one of the most effective diagnostic tools for assessing insulation health. Regular PD monitoring allows early detection of faults, ensuring long-term reliability and performance of electrical power systems.
Investing in PD testing not only prevents unexpected transformer failures but also supports a proactive maintenance strategy for industrial and utility networks.
Contact GK Expertise today for trusted and professional transformer service that ensure peak performance and long-term reliability.