Partial discharge (PD) is one of the earliest and most reliable indicators of insulation degradation in medium and high-voltage electrical equipment. In distribution switchgear and ring main units (RMUs) operating at 10kV and above, undetected PD activity can lead to catastrophic insulation failure, arc flash incidents, and extended power outages. Understanding how to monitor, detect, and interpret PD signals is essential for modern predictive maintenance strategies in power distribution networks.
What Is Partial Discharge?
Partial discharge refers to localized dielectric breakdown of a small portion of solid or fluid electrical insulation under high-voltage stress. Unlike a complete short circuit, PD only partially bridges the insulation between conductors. Common causes include voids in solid insulation, surface tracking, floating metal particles, and sharp protrusions on high-voltage conductors. In switchgear, common PD sources include deteriorated cable terminations, busbar insulation defects, and contamination on insulating surfaces.
Dual Detection Methods: Ultrasonic and Transient Earth Voltage
Modern online PD monitoring systems for switchgear employ two complementary detection technologies: the Acoustic Emission (AE) ultrasonic method and the Transient Earth Voltage (TEV) method. The AE method uses ultrasonic sensors operating in the 20kHz to 500kHz frequency range to capture the sound waves emitted during discharge events. Because ultrasonic signals are immune to electromagnetic interference prevalent in substation environments, this method provides highly specific PD detection with excellent signal-to-noise characteristics.
The TEV method detects electromagnetic waves in the 3MHz to 100MHz range that propagate through gaps and discontinuities in the metal enclosure of switchgear cabinets. When PD occurs inside the switchgear, the electromagnetic waves propagate outward and induce transient voltages on the inner surface of the metal casing. These signals rise within nanoseconds and decay quickly, requiring high-bandwidth sensors and fast digital sampling circuits for effective capture.
Using dual-mode sensors that combine both AE and TEV detection provides superior diagnostic coverage. The AE channel excels at detecting surface discharge and corona, while the TEV channel is more sensitive to internal insulation defects. By correlating data from both channels, modern integrated online monitoring devices can distinguish genuine PD events from external noise sources with high confidence.
Edge Computing and Real-Time Analysis
A significant advancement in PD monitoring is the integration of edge computing capabilities into the data acquisition units. Rather than streaming raw sensor data continuously to a central server, edge-enabled monitors process PD waveforms locally, performing spectrum analysis, peak detection, and trend calculation on-site. This reduces network bandwidth requirements and ensures continued monitoring even during communication outages. When network connectivity is restored, cached data synchronizes to the cloud, preserving complete historical records.
Integrated Temperature and Leakage Current Monitoring
While PD monitoring detects insulation defects, temperature monitoring identifies loose connections, contact deterioration, and overload conditions in switchgear. Passive wireless temperature sensors powered by electric field induction eliminate the need for batteries and can be embedded directly into insulating plugs within RMU cable compartments. These sensors operate from -30°C to 135°C with ±1% accuracy, transmitting data via 2.4GHz RF up to 100 meters in open environments.
Shield wire leakage current monitoring completes the triad of switchgear condition assessment. Integrated cable sheath monitoring systems track circulating currents in shielded cable grounding wires using closed-type current transformers with local digitization and FFT-based signal processing. Abnormal leakage current patterns often precede insulation breakdown, providing an additional layer of early warning.
Implementation Best Practices
For effective PD monitoring deployment, sensors should be strategically placed at known high-stress locations: cable termination compartments, busbar joints, circuit breaker spouts, and voltage transformer compartments. The monitoring system should be configured with appropriate alarm thresholds based on baseline measurements taken during commissioning. A phased threshold approach—using yellow alerts for trending increases and red alarms for critical levels—allows maintenance teams to schedule interventions before failures occur.
For substations with 110kV and above voltage levels, specialized monitoring is also available for zinc oxide surge arresters and transformer core grounding current, forming a comprehensive condition-based maintenance ecosystem for the entire substation.
Conclusion
Online partial discharge monitoring has evolved from a specialized diagnostic tool into an essential component of modern power distribution asset management. The combination of dual-mode AE/TEV detection, edge computing, and integrated temperature and leakage current monitoring transforms reactive maintenance into proactive, condition-based strategies. As power grids continue to expand with renewable energy integration and increased load demands, continuous insulation condition monitoring will play an increasingly critical role in maintaining reliability and preventing unplanned outages.
Featured Products
- Integrated Online Monitoring Device for Temperature of Partial Discharge and Leakage Current – Comprehensive switchgear monitoring with AE/TEV dual detection and passive wireless temperature sensing.
- SCYC-HLJC2304 Integrated Online Monitoring for HV Cable Sheath and Partial Discharge – All-in-one monitoring for circulating current, PD, and temperature.
- SCYC-PWTM2304 Passive Wireless Online Temperature Monitoring Device – Electric field-powered sensors for RMU and switchgear temperature monitoring.
- DTE2100 Online Monitoring Device for Transformer Core Grounding Current – Real-time monitoring for 10kV+ power transformers.
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
