Underground power cables carry an enormous share of urban load, and most of that cable is out of sight in tunnels, ducts and shafts. When cable insulation ages, overheats or develops a defect, the first warning is often not electrical at all – it is chemical. Insulating materials break down and release characteristic gases, and those gases accumulate in the confined space around the cable. Measuring them is one of the fastest and most reliable ways to catch a developing cable fault before it becomes a fire or an outage. This article explains the technology behind cable gas monitoring and the HUWOR cable gas sensor (model HMJ1012-WLQ).
Why cable gas monitoring works
Different cable systems produce different warning gases:
- Oil-filled cables: overheating and partial discharge decompose the insulating oil, generating hydrogen (H2) and, in more severe cases, acetylene (C2H2).
- Cross-linked polyethylene (XLPE) cables: thermal ageing and treeing release hydrogen, methane (CH4) and other hydrocarbons, with carbon monoxide (CO) appearing when the insulation burns or carbonises.
- In all cable systems: a sustained fault or a burning joint produces CO in quantities that are easy to detect long before smoke reaches a human patrol.
Because the gases appear before the fault current flows, gas monitoring gives the operating team a lead time that electrical protection alone cannot provide. In a cable tunnel, even a single gas sensor per section can flag the zone that needs attention.
What the HMJ1012-WLQ measures
The HUWOR HMJ1012-WLQ is a cable gas online monitoring sensor designed for cable shafts, tunnels and ducts. It detects hydrogen, acetylene, methane and carbon monoxide in the air around the cable circuit, and reports the measured values continuously to a monitoring platform. According to the published specification, the detection accuracy is ±1 ppm, measured under the reference conditions stated in the product datasheet.
The sensor is compact and installed directly in the cable shaft or tunnel wall. It is built for the harsh environment of a cable trench: it has to tolerate humidity, dust and temperature swings while keeping its calibration stable. The output connects to the cable monitoring system or to an IoT gateway, so the values can be logged, trended and alarmed in the control room.
Turning a gas reading into an alarm
An individual gas reading is only useful when it is compared with a threshold. The HUWOR monitoring platform raises an alarm when a measured value crosses the configured warning or alarm level, so the operating team can investigate before the condition worsens. In practice, the strongest signal is usually the trend: a slowly rising hydrogen concentration in an oil-filled cable circuit is typical of thermal ageing, while a sudden jump in acetylene suggests an electrical fault is developing.
For new installations, the threshold levels are set during commissioning based on the cable type, the tunnel ventilation and the utility’s operating rules. For existing tunnels, the system can first run in monitoring mode to establish a baseline, and the thresholds are then set relative to that baseline to avoid nuisance alarms.
Where to install cable gas sensors
The sensor should be placed where the gas actually collects:
- Cable shafts and manholes, especially at the highest point where lighter gases such as hydrogen accumulate
- Long tunnel sections at regular intervals, typically at the ventilation low points for heavier gases and at high points for hydrogen
- Joint bays, because joints are the most common failure location on a cable circuit
- Duct ends and transition chambers where oil-filled cable circuits terminate
A typical city project combines gas sensors with cable PD monitoring (HFCT or oscillating-wave testing), temperature sensing and, in critical tunnels, video and smoke detection. The gas layer is the chemical early warning; the PD layer is the electrical early warning; together they cover both failure paths.
Integration with the monitoring platform
The HMJ1012-WLQ feeds the same platform that collects PD sensor data, so the operator sees chemical and electrical indicators on one screen. In a HUWOR architecture, the sensors are connected through the HMJ1020-WJM485 IoT gateway, which aggregates the data, applies edge logic and forwards alarms. For utilities that already operate a scada or asset-management platform, the sensor data can be exported through the standard interfaces of the gateway.
Summary
Cable gas monitoring converts the chemistry of cable ageing into a measurable, alarmable quantity. Hydrogen, acetylene, methane and carbon monoxide are the four gases that give the earliest and most specific warning of cable insulation breakdown, and a sensor such as the HUWOR HMJ1012-WLQ measures them continuously with ±1 ppm accuracy in the harsh environment of a cable tunnel. For utilities planning a new tunnel or hardening an existing one, adding a gas-monitoring layer is a low-cost complement to PD and temperature monitoring.
Zhuhai Huawang Technology Co., Ltd. (HUWOR) supplies cable gas sensors, cable PD monitoring systems, IoT gateways and complete online monitoring solutions, with OEM/ODM support. Contact the HUWOR sales team for a cable monitoring proposal.