Periodic inspection of energised substation equipment is the most cost-effective way to find insulation defects early. A handheld partial discharge survey – using TEV, ultrasonic and HFCT sensors – detects activity that visual inspection cannot, without taking equipment out of service. This article sets out a survey plan any utility can run with a small trained team.
What a handheld survey detects
- TEV sensors – surface discharge on switchgear panels and cable boxes, measured in dBmV against ambient background.
- Ultrasonic sensors – surface discharge, tracking and arcing in air-filled compartments, detected as airborne ultrasound in the 20-60 kHz band.
- HFCT clamps – PD pulses on cable earth straps and transformer grounding, indicating internal or termination discharge.
- Infrared acoustic imaging – where available, combines acoustic imaging with temperature data to locate discharge and hot spots in one pass.
Preparing the survey
Background baseline
Record background TEV and ultrasonic levels before starting, so equipment readings are compared with ambient, not against a fixed number. Background varies with weather, load and nearby plant.
Asset list and priority
Survey all switchgear, transformers and cable terminations, but prioritise: critical feeders, equipment near end of service life, and bays with a history of failures or alarms.
Executing the survey
- Switchgear panels – measure TEV on each panel at the cable compartment and busbar chamber, noting the dBmV value and any ultrasound from panel vents.
- Cable boxes and terminations – clamp HFCT on earth straps where accessible; measure TEV at the termination base.
- Transformers – ultrasonic scan of bushings and tank surface; HFCT on the grounding system where permitted.
- Repeat passes – a second pass at different load helps separate load-dependent activity from constant defects.
Interpreting and acting on results
PD activity is evaluated by comparing equipment readings to background and to their own history:
- Elevated but stable readings – schedule a repeat survey within months.
- Rising trends or readings near alarm thresholds – bring the bay into a maintenance plan.
- High readings with audio or thermal confirmation – plan a detailed investigation and consider replacing the survey with permanent monitoring on that bay.
Turning periodic surveys into a programme
Handheld surveys and permanent online monitoring are complementary: surveys find new hotspots across the network; online monitoring tracks the worst ones continuously. Utilities that run both get early warning at network scale and depth on critical assets.
About HUWOR
Zhuhai Huawang Technology Co., Ltd. (HUWOR) supplies handheld PD detectors, TEV and ultrasonic sensors, HFCT clamps, infrared acoustic imagers and online monitoring systems, and offers live-line detection services. The company serves utilities and industrial customers worldwide, with OEM/ODM support. Contact the HUWOR sales team for instrument selection and training.