When a utility first decides to take partial discharge seriously, the immediate question is what to buy: a portable detector that the crew carries around, or an online monitoring system that stays on the equipment. The honest answer is that most successful programmes end up with both, but in different proportions depending on the asset base. This guide compares the two approaches so the decision is made on evidence rather than habit.
What a handheld detector gives you
A handheld PD detector (for example the HUWOR HMJ9001-Q, which combines TEV, ultrasonic, HFCT and UHF in one instrument) is a patrol tool. The engineer walks the substation, applies the appropriate sensor to each panel, termination or cable, and reads the discharge level on the spot.
Strengths:
- One instrument covers many assets, so the capital cost is shared across the whole fleet
- It reaches every point – including equipment that would never justify a permanent sensor
- It provides immediate localisation: the operator finds the panel, the phase or the joint
- No wiring, no gateway, no software platform to maintain
Limitations:
- The reading is a snapshot. A discharge that appears between patrols is missed until the next visit.
- Results depend on the patrol frequency and on the operator’s consistency
- Trends are only as good as the record-keeping between visits
What an online monitoring system gives you
An online monitoring system installs sensors on the equipment and feeds a platform that records continuously. It answers the questions a patrol cannot: is the discharge growing, and is it growing fast enough to require action now?
Strengths:
- Continuous coverage, including nights, weekends and high-load periods when discharges are worst
- Automatic trend and alarm, so the operator acts on events rather than scheduled inspections
- Better data for diagnosis: phase-resolved patterns, synchronised multi-point measurements and time-of-arrival location
Limitations:
- Capital cost per monitored point (sensor, wiring, gateway, platform)
- The coverage is limited to the points that were equipped; the rest of the fleet is invisible
- It needs configuration, threshold setting and maintenance of its own
How to choose
The decision follows the value of the asset and the failure cost:
- Critical assets where a failure is expensive – main transformers, GIS bays, long cable circuits – justify online monitoring.
- Large populations of similar, lower-criticality assets – distribution panels, RMUs – are best covered by regular patrols with a handheld detector.
- Any asset that a patrol flags as suspect is then a candidate for temporary or permanent online monitoring to confirm and track the trend.
This staged approach keeps the cost proportionate: the handheld detector covers the fleet, and the online system covers the points that the fleet patrol identifies as at risk.
Combining the two tools
In practice the two tools reinforce each other. The online system gives the trend for the equipped points; the handheld detector extends coverage to the rest of the site and localises anything the trend flags. Many HUWOR customers start with a handheld detector for their patrol programme, then add online sensors and gateways on the critical bays as the programme matures – using the same product family and the same platform throughout.
Summary
A handheld detector is the economical way to cover a fleet; an online monitoring system is the reliable way to watch the assets that matter most. The practical programme combines them: patrol with the portable instrument, monitor the critical points continuously, and use the online trend to direct the patrol. HUWOR supplies both product lines, so the two tools share one brand, one platform and one support channel. Contact the HUWOR sales team to plan your programme.