Abstract

A measurement campaign has been carried out in 400kV air insulated electricity substation to characterise and model radio frequency impulsive noise with a view to assessing its impact on wireless network technologies. The relatively recent availability of new technologies such as WiFi, Bluetooth and Zigbee means that particular emphasis has been put on higher frequency bands (e.g. 2.4, 5 GHz) than have previously been investigated. A detection system to measure wideband noise over a spectrum extending up to 5.1 GHz has been designed, implemented and deployed in a large electricity substation in central Scotland. Results based on a preliminary analysis of the recorded data are reported.


Introduction

A large amount of instrumentation and control equipment is scattered throughout the compounds and control rooms of electricity substations. Information and control signals for both normal and abnormal operation are traditionally connected, using cables or optical fibres, to a SCADA (Supervision, Control and Data Acquisition) system and/or its successor UCA (Utilities Communication Architecture) system. Ethernet local area network (LAN) implementations of such UCA/SCADA systems, which simplify the addition/reconfiguration of instrumentation and the coordination of protection systems, have been proposed and are already being evaluated. Significant flexibility and cost advantages over a wired LAN infrastructure would be gained, however, if signals could be routed around electricity substation compounds wirelessly. Furthermore, wireless communication technologies hold out the prospect of ‘hot-line’, sensors that can be deployed on energized high-voltage (HV) equipment without the inconvenience and costs associated with bridging the system’s primary insulation. Wireless LAN and Wireless Personal Area Network (PAN) technologies represent obvious opportunities to realize these advantages. Whilst the naturally occurring noise environment is relatively benign at Wireless LAN (2.4, 5 GHz) and Wireless PAN (2.4 GHz) frequencies [6], the man-made noise environment within a substation compound is complex and hostile due to (i) partial discharge (PD) arising from imperfect insulation and (ii) sferic radiation arising from switching and fault transients (The term sferic usually relates to radiation from a lightening event but is used here as a shorthand for similar radiation arising from any large current transient). An investigation into the vulnerability of WLAN and WPAN technologies to impulsive noise in electricity transmission substations is currently in progress. One of the primary objectives is the detection and investigation of PD in the microwave bands used by WLAN and WPAN technologies such as IEEE 802.11a/b/g, IEEE 802.15.4 and IEEE802.15.3. This requires investigation of the frequency spectrum up to 5 GHz. PD is an electrical discharge that fails to fully bridge the space between a pair of electrodes. It can occur around an electrode in a gas (corona), within gas bubbles in a liquid or within the space created by voids in a solid. HV plant (transformers, switchgear, cables etc) is especially prone to PD if its insulation is damaged and/or as its insulation ages. If remedial action is not taken the insulation can be seriously compromised leading, ultimately, to catastrophic failure. Energy from PD processes can be radiated whenever spectral components arising from current pulse edges extend into the radio frequency (RF) region. Although the character of PD appears to have some dependence on the size and geometry of plant components (e.g. insulating spacers, L-shaped buses, T-branch buses) damping typically appears to become significant somewhere between 100 MHz and 300 MHz and increases with increasing frequency above this . PD energy in the frequency range 0.5 - 1.2 A large amount of instrumentation and control equipment is scattered throughout the compounds and control rooms of electricity substations. Information and control signals for both normal and abnormal operation are traditionally connected, using cables or optical fibres, to a SCADA (Supervision, Control and Data Acquisition) system and/or its successor UCA (Utilities Communication Architecture) system. Ethernet local area network (LAN) implementations of such UCA/SCADA systems, which simplify the addition/reconfiguration of instrumentation and the coordination of protection systems, have been proposed and are already being evaluated . Significant flexibility and cost advantages over a wired LAN infrastructure would be gained, however, if signals could be routed around electricity substation compounds wirelessly. Furthermore, wireless communication technologies hold out the prospect of ‘hot-line’, sensors that can be deployed on energized high-voltage (HV) equipment without the inconvenience and costs associated with bridging the system’s primary insulation . Wireless LAN and Wireless Personal Area Network (PAN) technologies represent obvious opportunities to realize these advantages. Whilst the naturally occurring noise environment is relatively benign at Wireless LAN (2.4, 5 GHz) and Wireless PAN (2.4 GHz) frequencies, the man-made noise environment within a substation compound is complex and hostile due to (i) partial discharge (PD) arising from imperfect insulation and (ii) sferic radiation arising from switching and fault transients (The term sferic usually relates to radiation from a lightening event but is used here as a shorthand for similar radiation arising from any large current transient). An investigation into the vulnerability of WLAN and WPAN technologies to impulsive noise in electricity transmission substations is currently in progress . One of the primary objectives is the detection and investigation of PD in the microwave bands used by WLAN and WPAN technologies such as IEEE 802.11a/b/g, IEEE 802.15.4 and IEEE802.15.3. This requires investigation of the frequency spectrum up to 5 GHz. PD is an electrical discharge that fails to fully bridge the space between a pair of electrodes. It can occur around an electrode in a gas (corona), within gas bubbles in a liquid or within the space created by voids in a solid. HV plant (transformers, switchgear, cables etc) is especially prone to PD if its insulation is damaged and/or as its insulation ages. If remedial action is not taken the insulation can be seriously compromised leading, ultimately, to catastrophic failure. Energy from PD processes can be radiated whenever spectral components arising from current pulse edges extend into the radio frequency (RF) region [8]. Although the character of PD appears to have some dependence on the size and geometry of plant components (e.g. insulating spacers, L-shaped buses, T-branch buses) damping typically appears to become significant somewhere between 100 MHz and 300 MHz and increases with increasing frequency above this . PD energy in the frequency range 0.5 - 1.2 . A large amount of instrumentation and control equipment is scattered throughout the compounds and control rooms of electricity substations. Information and control signals for both normal and abnormal operation are traditionally connected, using cables or optical fibres, to a SCADA (Supervision, Control and Data Acquisition) system and/or its successor UCA (Utilities Communication Architecture) system . Ethernet local area network (LAN) implementations of such UCA/SCADA systems, which simplify the addition/reconfiguration of instrumentation and the coordination of protection systems, have been proposed and are already being evaluated . Significant flexibility and cost advantages over a wired LAN infrastructure would be gained, however, if signals could be routed around electricity substation compounds wirelessly. Furthermore, wireless communication technologies hold out the prospect of ‘hot-line’, sensors that can be deployed on energized high-voltage (HV) equipment without the inconvenience and costs associated with bridging the system’s primary insulation . Wireless LAN and Wireless Personal Area Network (PAN) technologies represent obvious opportunities to realize these advantages. Whilst the naturally occurring noise environment is relatively benign at Wireless LAN (2.4, 5 GHz) and Wireless PAN (2.4 GHz) frequencies , the man-made noise environment within a substation compound is complex and hostile due to (i) partial discharge (PD) arising from imperfect insulation and (ii) sferic radiation arising from switching and fault transients (The term sferic usually relates to radiation from a lightening event but is used here as a shorthand for similar radiation arising from any large current transient). An investigation into the vulnerability of WLAN and WPAN technologies to impulsive noise in electricity transmission substations is currently in progress . One of the primary objectives is the detection and investigation of PD in the microwave bands used by WLAN and WPAN technologies such as IEEE 802.11a/b/g, IEEE 802.15.4 and IEEE802.15.3. This requires investigation of the frequency spectrum up to 5 GHz.
PD is an electrical discharge that fails to fully bridge the space between a pair of electrodes. It can occur around an electrode in a gas (corona), within gas bubbles in a liquid or within the space created by voids in a solid. HV plant (transformers, switchgear, cables etc) is especially prone to PD if its insulation is damaged and/or as its insulation ages. If remedial action is not taken the insulation can be seriously compromised leading, ultimately, to catastrophic failure. Energy from PD processes can be radiated whenever spectral components arising from current pulse edges extend into the radio frequency (RF) region. Although the character of PD appears to have some dependence on the size and geometry of plant components (e.g. insulating spacers, L-shaped buses, T-branch buses) damping typically appears to become significant somewhere between 100 MHz and 300 MHz and increases with increasing frequency above this . PD energy in the frequency range 0.5 - 1.2 GHz, however, is readily radiated from apertures formed, for example, by insulating spacers or bushings [13]. PD current pulses in strong insulators (e.g. SF6) can have risetimes as short as 50 ps and may contain significant energy at frequencies up to 3 GHz .
Several methods and systems for detection of very-highfrequency (VHF, up to 300 MHz) and ultra-high-frequency (UHF, up to 3 GHz) PD in GIS have been investigated . These are intrusive techniques, however, in which VHF or UHF couplers are mounted directly onto items of plant. A non-intrusive PD measurement system based on RF technology has been shown capable of detecting energy at frequencies up to 1.2 GHz . The authors are not aware, however, of any non-intrusive measurements of PD at frequencies up to 5 GHz. In this paper we describe a system to monitor impulsive noise in the general electricity substation environment and present preliminary measurement results.

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