Partial discharge is one of the hidden dangers that accelerate the aging of power cable insulation. Unlike factory laboratory tests, on-site partial discharge detection faces complex interference from surrounding electrical equipment, grounding systems and ambient noise. Many cable faults in 10kV and 35kV distribution networks start from tiny partial discharge defects that are not discovered in time.
What is on-site partial discharge detection for power cables
On-site partial discharge detection is a non-destructive testing method. Inspectors collect discharge signals without cutting off the cable or damaging the cable structure. It can find internal defects such as insulation air gaps, semi-conductive layer burrs, joint poor contact and water tree degradation.
Common detection technologies used in field work
- Ultra-high frequency (UHF) detection: Sensitive to pulse electromagnetic signals generated by partial discharge. It is widely used for cable joints and terminal boxes, and has strong anti-interference ability.
- High-frequency current (HFCT) detection: Installed on the grounding wire of cable accessories. It is easy to operate and suitable for continuous online monitoring.
- Acoustic detection: Capture the ultrasonic sound wave produced by discharge. It helps engineers locate the approximate discharge position on site.
Key challenges of on-site testing
The biggest difficulty comes from external electromagnetic interference. Substation inverters, nearby overhead lines and power equipment will generate a large number of interference signals. Test engineers need to distinguish valid partial discharge signals from noise by comparing phase characteristics and signal waveforms.
Test conditions also affect the accuracy. Humid weather, loose grounding connections and unstable test voltage will cause false alarms or missed detection.
Judgment standards and disposal suggestions
After obtaining valid discharge signals, engineers judge the risk level according to IEC 60270. Low-level stable discharge can be marked for regular recheck. Continuous rising discharge amplitude means high risk, and power outage maintenance is recommended as soon as possible.
If the defect is located inside cable joints, it is usually necessary to disassemble and remake the joint. For water tree defects in cable body, insulation treatment or cable replacement should be evaluated according to the operation age.
FAQ
Q1: Is on-site partial discharge test a mandatory inspection item?
A: It is not mandatory for all cables, but it is strongly recommended for key load cables, old cables and cables that have experienced water ingress.
Q2: Can partial discharge detection replace withstand voltage test?
A: No. Partial discharge test focuses on finding early insulation defects. Withstand voltage test checks the insulation breakdown resistance. They are complementary rather than alternative.
Q: Can we do on-site partial discharge detection when the cable is live?
A: Yes. UHF and HFCT methods support live online testing, which avoids power outage losses for industrial users.
If you are looking for reliable power cables with strict factory partial discharge testing, contact our team for cable specification support and quotation.