Partial discharge (PD) is one of the most critical indicators of insulation degradation in medium voltage (MV) and high voltage (HV) electrical equipment. For operators of power distribution systems, understanding PD phenomena and implementing effective monitoring strategies is essential to prevent catastrophic failures, ensure personnel safety, and maintain uninterrupted power delivery.
What Is Partial Discharge and Why Does It Matter?
Partial discharge refers to localized dielectric breakdowns that occur within electrical insulation systems under high voltage stress. Unlike a complete breakdown, PD only partially bridges the insulation between conductors. However, PD activity is both a symptom and a cause of progressive insulation deterioration. Each discharge event erodes the insulating material, gradually creating conductive paths that eventually lead to full dielectric failure.
In medium voltage switchgear—commonly found in industrial facilities, utility substations, and commercial buildings—PD can originate from various sources: voids in solid insulation, surface tracking across contaminated insulator surfaces, corona discharge from sharp conductor points, or floating electrode discharges in loose connections. Left undetected, PD can cause complete switchgear failure within months of onset, resulting in arc flash incidents, equipment destruction, and extended downtime.
Key PD Detection Technologies
Modern integrated online monitoring devices employ multiple complementary detection methods to provide comprehensive PD surveillance:
1. Ultrasonic (Acoustic Emission) Detection
PD events generate acoustic waves in the ultrasonic frequency range (typically 20-100 kHz). Acoustic Emission (AE) sensors mounted on switchgear enclosures detect these pressure waves. Because acoustic signals attenuate rapidly through air gaps, this method excels at locating PD sources with high spatial accuracy and is naturally immune to electromagnetic interference.
2. Transient Earth Voltage (TEV) Detection
When PD occurs within enclosed metal-clad switchgear, electromagnetic waves propagate along the inner surfaces and escape through joints and gaskets. TEV sensors placed on the external metalwork detect these transient voltage pulses. TEV measurement provides a quantitative indication of PD severity and is particularly effective for internal discharge detection in gas-insulated and metal-enclosed equipment.
3. UHF (Ultra-High Frequency) Detection
PD pulses generate electromagnetic emissions across a broad frequency spectrum, including the UHF band (300 MHz – 3 GHz). UHF sensors installed inside switchgear compartments capture these signals with excellent signal-to-noise ratios, enabling reliable PD detection even in electrically noisy substation environments.
Temperature Monitoring: A Critical Complement
While PD detection reveals insulation condition, temperature monitoring identifies another major failure mechanism: contact degradation. Loose or oxidized connections in switchgear busbars, circuit breaker contacts, and cable terminations generate localized heating under load current. Passive wireless temperature sensors—powered by electric field energy harvesting rather than batteries—offer a maintenance-free solution for continuous hotspot detection.
Integrated Monitoring: The State of the Art
Leading-edge systems such as those supplied by Qingdao Britop combine PD detection (AE + TEV), temperature sensing, and leakage current monitoring into a single integrated platform. These smart grid monitoring solutions utilize edge computing to process data locally, transmitting only actionable alerts and trend data to central SCADA or asset management systems. Multi-parameter correlation—for example, comparing PD intensity against load current and ambient temperature—enables accurate distinction between harmless background noise and genuine developing faults.
Applications Across Industries
Utility Substations: HV/MV substations employ online PD monitoring on transformers, GIS, and cable terminations. The DTE2100 transformer core grounding current monitor and DT801 surge arrester monitor form part of a comprehensive substation condition monitoring suite.
Ring Main Units (RMU): RMUs in urban distribution networks are often installed in underground vaults or pad-mounted enclosures where accessibility is limited. Continuous online PD and temperature monitoring transforms these “fit-and-forget” assets into transparent, manageable network elements.
Renewable Energy: Wind farm and solar PV substations face unique challenges—wide temperature swings, harmonic-rich inverter outputs, and remote locations. Integrated monitoring ensures early detection of insulation issues before they force costly turbine or inverter outages.
Industrial Plants: In process industries (oil & gas, chemical, mining), unplanned switchgear failure can halt entire production lines. Predictive maintenance based on PD trending enables planned shutdowns during scheduled maintenance windows.
Best Practices for PD Monitoring Implementation
- Baseline Establishment: Conduct initial PD surveys on all critical switchgear to establish baseline readings. Subsequent measurements are compared against this baseline to identify deteriorating trends.
- Continuous vs. Periodic Monitoring: For critical assets (main incoming breakers, bus section switches), continuous online monitoring is recommended. For less critical feeders, periodic portable PD testing may suffice.
- Multi-Parameter Correlation: Never rely on a single PD metric. Correlate AE, TEV, and UHF readings with load current, temperature, and humidity data for reliable diagnostics.
- Alarm Threshold Setting: Configure multi-level alarms—”warning” for increasing PD trends and “alarm” for levels approaching known failure thresholds.
- Data Management: Integrate PD monitoring data into the enterprise asset management system. Long-term trending enables true predictive maintenance rather than reactive repair.
Conclusion
Partial discharge monitoring has evolved from a specialist laboratory technique to an essential field-deployed tool for switchgear asset management. By combining multiple detection technologies with wireless temperature sensing and intelligent edge computing, modern online monitoring systems provide the visibility needed to transition from time-based maintenance to true condition-based strategies—improving reliability, reducing costs, and most importantly, protecting personnel and assets from catastrophic electrical failure.
Explore Related Products from Qingdao Britop:
- Integrated Online Monitoring for Distribution Switchgear and RMU
- SCYC-HLJC2304 High-Voltage Cable Sheath Monitoring
- SCYC-CW30 Passive Wireless Temperature Monitoring for RMU
- DTE2100 Transformer Core Grounding Current Monitor
Related Products:
Related Products
- Eagle-beak Shear Excavator Attachment – QINGDAO BRITOP QUALITY PRODUCT
- Auger Excavator Attachment – QINGDAO BRITOP QUALITY PRODUCT
- Steel Structure Shear Excavator Attachment – QINGDAO BRITOP QUALITY PRODUCT
- Jaw Crushing Pliers Excavator Attachment – QINGDAO BRITOP QUALITY PRODUCT
- Jaw Crushing Bucket Excavator Attachment – QINGDAO BRITOP QUALITY PRODUCT
