Every partial discharge detection technology sees part of the picture. Transient earth voltage (TEV) picks up the electrical pulse that a discharge couples into the earthed metalwork of a switchgear panel. Ultrasonic (acoustic emission, AA) picks up the sound the discharge makes. A discharge deep inside a vacuum interrupter may show almost no TEV while producing a clear ultrasonic signature; a bushing defect may show in TEV while staying acoustically quiet. In real switchgear, the two technologies find different defects – which is why the two-in-one sensor has become the standard building block for switchgear and ring main unit monitoring. This article explains the HUWOR HMJ1010-AT.
What each technology catches
TEV sensors measure the transient voltage pulse on the outside of the panel caused by an internal discharge. They are easy to retrofit – the sensor is bonded to the panel surface – and they are the most economical way to cover every panel of a switchboard. Their limitation is that electrical pulses travel through the earthing system, so a discharge in one panel can appear on its neighbours; TEV alone is good at flagging activity but less precise about the exact source.
Ultrasonic sensors detect the airborne ultrasound generated by the discharge, typically in the range above human hearing. They are immune to electrical noise, which makes them valuable in rooms where electrical interference is heavy, and they naturally localise the source because the sound is strongest closest to the discharge. Their limitation is that the sound attenuates through solid barriers – a discharge inside a fully enclosed compartment may be inaudible from the outside.
Combined in one housing, the two technologies cross-check each other: a TEV reading that also has an ultrasonic confirmation is a genuine internal discharge, not a disturbance from elsewhere, and a defect that only one technology sees is still caught rather than missed.
The HMJ1010-AT at a glance
The HUWOR HMJ1010-AT is an intelligent two-in-one partial discharge sensor integrating ultrasonic (AA) and transient earth voltage (TEV) detection in a single unit. It is widely used in substations, switching stations and other power facilities for monitoring partial discharges in ring main units, switchgear panels and cable termination compartments.
The sensor is surface-mounted on the panel, connected to the monitoring system by a single cable, and reports both channels to the platform. Installation does not require an outage in the normal case, because the sensor is bonded to the outside of the enclosure.
Where the two-in-one sensor is the right choice
Typical deployments of the HMJ1010-AT:
- Ring main units in distribution networks, where the compartment is compact and a single sensor covers the whole panel
- Air-insulated switchgear rooms, one sensor per panel, feeding a multi-channel diagnosis system
- Cable termination chambers, where both electrical and acoustic signatures are relevant
- Industrial switchboards where electrical noise makes ultrasonic confirmation valuable
For a standard switchroom project, one HMJ1010-AT per panel plus a multi-channel unit (such as the HUWOR HMJ9041) gives complete online coverage at a modest cost per panel.
Working with temperature and humidity sensing
Where switchgear operates in hot, humid or polluted environments, the same monitoring point can also carry temperature and humidity sensing. The HUWOR HMJ1010-WAT adds these channels to the TEV and ultrasonic pair in the same housing, so one installation point measures discharge activity and the environmental stress that accelerates it. The two-in-one HMJ1010-AT remains the economical choice where climate is not a dominant factor.
Summary
No single PD technology covers every defect, and the two-in-one sensor is the practical answer for switchgear and RMU monitoring: TEV for the electrical pulse, ultrasonic for the acoustic signature, one housing, one cable, one channel on the monitoring platform. The HMJ1010-AT brings this combination to substations and switching stations with surface-mount installation. HUWOR supplies the sensor with OEM/ODM support. Contact the HUWOR sales team for a panel-by-panel monitoring proposal.