Lightning arresters protect the most valuable equipment in a substation, and they are among the least monitored. They have no moving parts and no obvious external symptom of ageing, yet a varistor that has absorbed moisture or aged thermally will eventually fail – usually during the next overvoltage event, which is exactly when it is needed most. The way to see the deterioration coming is to measure the leakage current through the arrester and, in particular, its resistive component. This article explains the HUWOR lightning arrester leakage current monitor (model HMJ1011-WBJ).
The resistive current tells the story
Under normal operation, a metal-oxide varistor conducts a small leakage current dominated by its capacitive component. As the valve blocks age or absorb moisture:
- The resistive component of the leakage current rises, often before any change is visible in the total current.
- The temperature of the varistor may begin to rise under stress, accelerating the ageing.
- The arrester becomes progressively more likely to fail at the next surge.
This is why the HMJ1011-WBJ is described as a precision sensor for monitoring leakage current and resistive current components: the resistive component is the sensitive early indicator of ageing and moisture, and tracking it over time converts a hidden process into a maintainable trend.
What the HMJ1011-WBJ provides
The HMJ1011-WBJ is designed to monitor the leakage current and resistive current components of lightning arresters. According to the published specification, the total current range is 100 uA – 5 mA, measured under the reference conditions stated in the datasheet. The sensor also features a lightning strike counter, so the operator sees both the condition trend and the stress history of the arrester.
Installation is in the earthing conductor of the arrester, which keeps the high-voltage side untouched. The readings are reported continuously to the monitoring platform, where thresholds are set for warning and alarm.
Using the data in maintenance
In practice, the operator watches two signals:
- The trend of the resistive current – a slow rise over months suggests ageing; a sudden step suggests moisture ingress or a developing defect.
- The strike count – an arrester that has absorbed many strikes, or a cluster of recent strikes, deserves a closer look even if the resistive current is still normal.
When both signals move together – rising resistive current after a series of strikes – the arrester should be scheduled for testing or replacement before the next storm season.
Where arrester monitoring is most valuable
The HMJ1011-WBJ is deployed on substation arresters, line arresters and the arresters protecting capacitor banks and transformers. It is especially valuable where arresters are numerous and visually identical, where inspection intervals are long, and where an arrester failure takes a bay or a transformer out of service.
Integration with the platform
The monitor connects to the HUWOR online monitoring system alongside the partial discharge sensors. The platform logs leakage current, resistive current and strike counts, displays them per phase, and raises alarms on the configured thresholds. Because the sensor family shares the same gateway architecture, a substation project adds arrester monitoring to the PD monitoring system without a second platform.
Summary
Lightning arresters fail silently unless their leakage current is tracked. The HMJ1011-WBJ monitors the total and resistive components over a 100 uA – 5 mA range, detects the ageing and moisture that raise resistive current, and counts every lightning strike. Installed in the earthing conductor and feeding the monitoring platform, it gives the operator the trend that precedes the failure. HUWOR supplies the monitor with OEM/ODM support. Contact the HUWOR sales team for specifications.