Why Live-Line Partial Discharge Testing?
Taking high-voltage equipment out of service to run insulation tests is expensive and, in modern networks, often impractical. Live-line partial discharge (PD) testing lets maintenance teams detect developing insulation defects while the asset stays energised, which means faults can be found and planned for instead of discovered through an unplanned outage.
A portable partial discharge detector is the workhorse of this approach. It is carried from bay to bay, used during routine patrols, and can be deployed in GIS substations, air-insulated switchgear rooms, transformer yards, and cable terminations without modifying the installation.
How Portable PD Detectors Work
Portable detectors sense the energy released by a discharge and convert it into measurable patterns. The main sensing technologies are:
- UHF probes and couplers pick up the electromagnetic pulses radiated by discharges, offering high sensitivity and good defect-location capability in GIS and switchgear.
- Acoustic (AE) sensors detect the ultrasonic pressure waves generated by discharges in SF6 gas, air, and solid insulation. They are fast to deploy and excellent for locating the source once activity is found.
- HFCT clamps measure high-frequency current pulses on earth straps and cable screens without breaking the circuit, making them convenient for cable and transformer checks.
- Phase-resolved PD (PRPD) analysis in the instrument firmware then classifies the discharge source: corona, surface discharge, internal void, floating electrode, or free particle. This pattern recognition is what turns a raw signal into a diagnosis.
Live-Line Testing vs Outage-Based Testing
| Dimension | Live-line (portable) testing | Outage-based (offline) testing |
|---|---|---|
| Availability impact | None; asset stays in service | Requires a shutdown window |
| Typical use | Routine patrols, screening, trend tracking | Acceptance tests, commissioning, major repair verification |
| Detection focus | Active PD under real operating voltage and load | PD at controlled test voltage |
| Cost per test | Low; one instrument covers many assets | Higher; outage scheduling and test setup dominate |
| Coverage | Quick sweep of many bays in one visit | Deep, repeatable measurement on a single asset |
Most asset owners run both: portable detectors for regular live-line screening, and offline testing for commissioning and after major work.
What to Look for in a Portable Partial Discharge Detector
- Sensitivity and bandwidth. The instrument should resolve small discharges (from a few pC) across the frequency range of the method you use.
- Built-in PRPD analysis. On-screen phase-resolved patterns and automatic defect classification save hours of expert interpretation in the field.
- Interference rejection. Substation environments are noisy; proven noise-gating and pattern-based discrimination prevent false alarms.
- Practical field design. Battery life, weight, glove-friendly controls, and readable display matter when the detector is used outdoors or in confined switchgear rooms.
- Reporting and data export. Automated reports with PRPD screenshots and trend history make it easy to document findings and compare visits.
- Training and support. PD interpretation has a learning curve; a supplier that provides training and application support is worth more than marginal hardware differences.
HUWOR Portable PD Detection in Practice
HUWOR designs and manufactures portable live-line detection instruments including the DAC-M30 partial discharge detector, used for substation patrols across GIS, switchgear, transformers, and cable terminations. The product line also includes permanent online monitoring systems and passive wireless temperature monitoring for joints and contacts.
HUWOR participates in drafting utility and industry standards â Q/GDW 12082-2021 for wireless sensors in the IoT of power transmission and distribution equipment, the DL/T specification for 35 kV and below high-voltage ceramic capacitance sensors, and T/EPTC 002-2022 for 10 kV intelligent distribution transformers â and applies those requirements directly to its portable and online instruments.
- Explore the HUWOR portable partial discharge detector range
- Handheld live-line testing and detection services
- Download white papers on PD monitoring and live-line testing
- How to choose a partial discharge detector for GIS substations
Frequently Asked Questions
What is live-line partial discharge testing?
Live-line partial discharge testing detects and measures insulation discharge activity while the equipment remains energised and in service, using portable or permanently installed sensors. It allows defects to be found during routine patrols without an outage.
Can partial discharge testing be done without taking equipment out of service?
Yes. Portable detectors with UHF, acoustic, or HFCT sensors are designed for live-line work: they couple to the equipment from outside or via existing access points and do not interrupt operation.
What equipment is needed for portable PD testing?
A typical kit combines a handheld detector with interchangeable UHF, acoustic, and HFCT sensors, plus analysis software for PRPD patterns and reporting. The exact configuration depends on the asset type: GIS, switchgear, transformer, or cable.
How often should substation PD testing be performed?
It depends on asset criticality and age. Many operators screen critical bays quarterly or after any significant switching event, with annual or biennial coverage for the wider fleet. Continuous online monitoring is reserved for the most critical or failure-prone assets.
For application advice, a product demonstration, or a copy of our white papers, contact us at hezhiqiang@huwor.com.cn.
Related Reading
How to Choose a Partial Discharge Detector for GIS Substations
Online Monitoring vs Portable PD Testing: Which Should a Utility Invest in First?
All-in-One PD Testing System: UHF, TEV, AE & HFCT Methods Explained