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External sensor (patch antenna) for making UHF-method partial discharge measurements on gas-insulated switchgear equipped with observation windows

IP.com Disclosure Number: IPCOM000247308D
Publication Date: 2016-Aug-22
Document File: 4 page(s) / 202K

Publishing Venue

The IP.com Prior Art Database

Related People

ABB Schweiz AG: OWNER

Abstract

The present disclosure belongs to the technical field of gas-insulated switchgear (GIS) in general and to the detection on undesired partial discharges PD in particular. Although many so-called external PD detections devices are known, they often suffer disadvantages. The present approach differs to known devices in that the PD detection device is designed to fit inside the safety cover of an observation window provided in a GIS enclosure anyway. That way, it acts as an extension of the GIS enclosure and provides its shielding effect from external EMI disturbances.

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External sensor (patch antenna) for making UHF-method partial discharge measurements on gas-insulated switchgear equipped with observation windows

Inventors: Glenn BEHRMANN, Roman OBRIST

ABSTRACT

The present disclosure belongs to the technical field of gas-insulated switchgear (GIS) in general and to the detection on undesired partial discharges PD in particular. Although many so-called external PD detections devices are known, they often suffer disadvantages. The present approach differs to known devices in that the PD detection device is designed to fit inside the safety cover of an observation window provided in a GIS enclosure anyway. That way, it acts as an extension of the GIS enclosure and provides its shielding effect from external EMI disturbances.

INTRODUCTION / TECHNICAL BACKGROUND

Partial discharge (PD) is a localized electric discharge, which occurs where the (local) electric field strength exceeds the dielectric withstand strength of the electrical insulation system. PD is often associated with inhomogeneities or defects in the insulation system materials. The electrical discharges produced by PD typically exhibit rise-times <<1 ns; the result is signals whose spectral content extends well past 1 GHz when transformed into the frequency domain. In addition, it should be noted that on-site testing of large, fully erected GIS according to IEC- 60270 ('HIGH-VOLTAGE TEST TECHNIQUES - PARTIAL DISCHARGE MEASUREMENTS', Ref [1]) is not practical due to problems associated with the coupling capacitor in this context. As a result, since the 1980s, workers in the field have applied so-called 'UHF method' techniques to measuring PD in GIS Refs [2-4]. The UHF method (ultra-high frequency method) is based on picking up the PD pulses using near-field radio-frequency (RF) antenna, typically installed within the GIS enclosure. This is done because the PD signals are very weak and the GIS enclosure acts to shield the internal sensors from external electro-magnetic interference (EMI). However, there are often openings of various kinds in the GIS enclosure, which allow the PD signals to leak out; these can be exploited to pick up signals, i.e. in the case that the PD signal(s) sought are very weak and/or in locations far from the next internal sensor.

This document describes an external UHF PD sensor to be applied to observation windows in the GIS, based on the principle of a patch antenna; furthermore, it has been purposely integrated into the safety cover of the observation window (the windows are equipped with safety covers because the intense light output from a switching transient is hazardous to eyesight).

PROBLEMS WITH EXTERNAL UHF PD SENSORS

As explained above in the Introduction, the principal problems with external UHF PD sensors in GIS is that the PD signals are very weak (on the order of nanowatts) and the GIS outer enclosure acts as a partial Faraday shield.

This means that external UHF sensors have both lower sensitivity t...