Why Cable Partial Discharge Testing Matters
Underground cables are the backbone of urban distribution networks, and their weakest points are the joints and terminations. Moisture ingress, installation defects, and ageing of insulation materials all generate partial discharge (PD) long before a cable fails. Because a cable fault is expensive to locate and repair â excavation, re-jointing, and prolonged outages â detecting PD early is one of the most cost-effective condition monitoring investments a network operator can make.
Cable partial discharge testing identifies developing insulation defects in service, so repair work can be planned during scheduled outages instead of after a forced failure.
PD Detection Methods for Cables
| Method | Principle | Application | Best Fit |
|---|---|---|---|
| HFCT (high-frequency current transformer) | Clamp sensor on cable earth lead or screen detects PD current pulses | Live testing at joints, terminations, and link boxes | Routine screening of in-service cable circuits |
| OWTS / damped AC (oscillating wave) | Offline damped AC voltage excites the cable; PD measured and located | Offline, after switching or for commissioning | Accurate PD location along the cable length |
| Tan delta (loss angle) | Dielectric loss measurement indicates overall insulation condition | Offline, periodic | Global ageing assessment rather than local defect location |
| Acoustic / UHF | Secondary confirmation at joints and terminations | On live accessories | Confirmation and localisation at specific points |
In practice, utilities combine HFCT screening while live with periodic offline tests (OWTS or tan delta) on circuits flagged as at risk.
HFCT Cable PD Testing in the Field
- Sensor placement. The HFCT clamp is placed around the cable earth conductor, screen, or link box connections where PD pulses return to earth.
- No outage required. Screening is performed on energised circuits, making it ideal for routine patrols of cable feeders, substation exits, and joint bays.
- Pattern recognition. PRPD patterns distinguish cable PD from switching noise, corona, and interference â critical to avoid false alarms.
- Trending. Repeat measurements at fixed intervals reveal whether discharge activity is stable or growing.
HUWOR Cable PD Testing Solutions
HUWOR (Zhuhai Huawang Technology Co., Ltd.) supplies HFCT sensors for cable PD monitoring projects, portable multi-function partial discharge detectors such as the DAC-M30 for live screening, and online cable PD monitoring systems with IoT data concentrators. HUWOR’s products are engineered to the requirements of standards it participates in drafting, including Q/GDW 12082-2021 for wireless sensors in the power IoT.
- View the HUWOR PD detection product range
- Transformer PD online monitoring guide
- Live-line portable PD testing guide
- Download HUWOR white papers
Frequently Asked Questions
Can partial discharge in cables be tested while the cable is live?
Yes. HFCT clamps around the cable earth lead or screen measure PD pulses on energised circuits, so routine screening can be performed without taking the feeder out of service.
What is the best method to locate PD in a cable?
For accurate location along the cable length, offline methods such as OWTS (damped AC) are the standard choice. For quick screening of many circuits, HFCT measurement at joints, terminations, and link boxes is the most practical first step.
What causes PD in cables?
Common causes are moisture ingress at joints and terminations, installation defects, mechanical damage, and ageing of the insulation. All of these create local electric field stress that produces detectable partial discharge.
How often should cable PD testing be done?
Many utilities screen critical cable circuits annually or half-yearly with HFCT, and perform offline tests (OWTS or tan delta) every 3â5 years or after significant events such as repairs or flooding.
For cable testing guidance, a demonstration, or white papers, contact us at hezhiqiang@huwor.com.cn.
Related Reading
Cable Online Monitoring System
Transformer Partial Discharge Online Monitoring: Methods, Sensors and System Design
HUWOR Cable Testing Instruments
HUWOR supplies the Cable Oscillating Wave Partial Discharge Tester (OWTS/DAC) and the Portable Integrated Cable Tester for cable acceptance testing and field PD surveys. OEM/ODM supply is supported for contractors and utilities.