Web based Partial Discharge Monitoring
A web based non intrusive partial discharge alarm is used in a field trial to show a reduced failure rate of medium voltage (MV) switchgear, reduced supply disruptions and increased longevity of MV plant equipment functionality. The benefits of using a web based non-intrusive partial discharge alarm are demonstrated by the case study of two failures that were prevented by use of the equipment.
By Simon GOLDTHORPE, EA Technology – UK; Charles WILLIAMSON, EA Technology Australia; and Simon HODGSON, Nortech – UK
This article is based on a paper presented to CIRED 2009 in Prague. Partial Discharge (PD) is accepted as being one of the major causes of Medium Voltage (MV) switchgear failure [1 &2]. Over recent years non-intrusive partial discharge measurements have become an effective tool for network operators to assess the condition of their switchgear without taking it out of service [3].
Utilising commercially available, small, handheld PD detection instruments, during routine maintenance visits, it is now both quick and simple to assess the condition of equipment. However, getting the right information to the right people at the right time is often a challenge, which is solved by the new EA Technology UltraTEV Alarm with a web-based remote monitoring capability.
challenge, which is solved by the new EA Technology UltraTEV Alarm with a web-based remote monitoring capability.
THe PD AlArm SOluTiOn
The EA Technology UltraTEV Alarm is a semi-permanently installed partial discharge alarm system. It consists of multiple sensor devices (nodes) connected in a ‘daisy-chain’ to a single device (hub) that collects and interprets data from the nodes. The standard node combines transient earth voltage (TEV) and ultrasonic sensors. The TEV sensor will detect internal discharges such as voids in cast resin insulation whilst the ultrasonic sensors can detect surface discharge such as in air-insulated cable boxes or tracking in circuit breaker spouts. Using these two detection methods, the UltraTEV Alarm can be used to monitor a wide range of MV assets. Other sensor nodes can be added to provide monitoring of cables and further ultrasonic monitoring points, in order to match the requirements of the substation.
There are many benefits to using an alarm type system as opposed to a complete measuring and monitoring system. The UltraTEV Alarm system will only generate alerts when there is significant discharge activity for a period of time. This allows the system to ignore any activity caused by short transients or switching events. As the device does not require all the measurement circuits of a monitoring system the cost of monitoring an entire substation is substantially reduced. This means that it becomes cost-effective to install at a larger number of sites than would be possible if purchasing permanent monitoring equipment. This can remove the need for routine site visits with handheld PD equipment.
The UltraTEV Alarm is especially useful at high risk sites, those with a history of PD or that either have intermittent activity or insignificant activity where there is a risk it will worsen. The system will only alert when the PD activity goes above the threshold. These alarms can be sent through a SCADA system to a control centre via the in-built interface on the hub. Recording this information, analysing and relaying it from the control centre to the correct field personnel or technical support staff can often be a problem. Migration to a web based solution allows easy and practical implementation of these systems.
Web-based Monitoring The Nortech iHost is a web based SCADA platform already in use within the U.K. power industry for a variety of applications including power outage detection, fault passage indication, load and temperature monitoring, distance to fault location, circuit breaker control, meter reading and cable pressure monitoring. Support for new devices and features are being added continuously.
iHost provides a unified method of collecting data for a variety of different applications as it supports a wide range of device types and protocols. The web interface allows access to data direct from any desktop PC with an internet connection. iHost can also be easily and quickly integrated with control room systems as it provides a consistent interface to the control room system regardless of the type of device being used. However, the web-based monitor can also be interrogated directly by the asset manager, rather than being routed through the normal control room, which is often busy with daily network management priorities.
RTUs and Devices in the field using different communications hardware and protocols to connect and communicate with iHost CSM modules.
Integrating the UltraTEV Alarm with a Nortech embedded Remote Terminal Unit (RTU) allows the UltraTEV Alarm to communicate with the i-Host system. This allows continuous remote monitoring anywhere in the world. The system logs alarms when partial discharge events are detected. It continuously monitors the ambient temperature and humidity of the site. It allows the remote reset of the visual/audible alarm on site.
The RTU’s communicate to the server using GPRS as the primary communications channel. This means that there are no international call costs to bear, allowing the UltraTEV Alarm to be deployed worldwide with minimal operating costs.
The i-Host server provides a web based user interface that can be accessed by engineers in the field, control centre staff and experts at EA Technology if required. This gets the right information to the right people when and where they want it. Users are also able to configure iHost to send SMS and e-mail notifications when a discharge has been detected. This ensures that the appropriate persons are notified when problems arise. Such a direct line of communication from substation to field engineering staff may greatly reduce response times for dealing with partial discharge before further damage takes place, consequently improving network reliability.
Field Trails IFI (Innovation Funding Incentive) is a U.K. Government incentive allowing companies to recoup a proportion of their research and development costs. As part of an IFI project, a trial of partial discharge monitoring equipment was installed at a number of primary substations on switchgear with a known history of partial discharge activity.
Figure 2 Ultrasonic discharge alarms as an association with humidity and temperature at one site
Figure 2 shows correlation between PD activity and humidity detected at one such site using the UltraTEV Alarm. The site has now been fitted with dehumidification units and the switch room sealed. The UltraTEV Alarm will be used to allow the identification of a humidity threshold necessary to minimise the PD activity. Similar measures are being implemented by an Australian utility.
The switchgear at two other sites was investigated, with deterioration of the insulation and associated equipment at advanced stages due to partial discharge activity. If the partial discharge had been left to develop unchecked then it is possible that the switchgear could have failed.
Ongoing Monitoring of SwitchgearImplementing a strategy to install permanent Partial Discharge monitoring equipment on plant in service is potentially very expensive, and such equipment is often difficult to retrofit to old plant.
A non-intrusive partial discharge monitoring system such as the UltraTEV Alarm has the benefit of having known reliability. It is non-intrusive, and does not interfere with the normal operation of the switchgear. Being easily portable and easily installed, the system may be relocated to a higher-priority substation once a PD problem has been eliminated at a site.
The local indication of PD activity alerts field staff in the substation, while the remote indication via iHost provides up to date information round-the-clock on PD activity at multiple sites, resulting in saving regular visits to download this information. It is immediately available to key technical staff responsible for asset management.
In the longer term, remote PD monitoring using a web-based interface such as iHost may correlate any detected PD events with external system activity or changing environmental conditions. This will allow beneficial modifications to operational practices or substation building requirements (e.g. dehumidification levels).
Conclusion PD monitoring techniques have considerable potential for the early identification of faults in HV electrical plant, allowing proactive investigations to be considered with consequential improvements in employee safety and equipment integrity.
This trial of the non intrusive partial discharge alarm in routine use suggests that early warning of emerging PD activity will lead to increased life expectancy of MV switchgear with a reduction in equipment failure, resulting in improved network performance and maintenance costs.
References - IEEE Standard, 1998, IEE Recommended Practice for Design of Reliable Industrial and Commercial Power Systems – Gold Book, IEEE, New York, USA , 493 - 1997
- C.J. Lowsley, N. Davies and D.M Miller, 2006, “Effective Condition Assessment of MV Switchgear”, 21st AMEU Technical Convention
- N . Davies, J. Tang, P. Shiel, 2007, “Benefits and experiences of non intrusive partial discharge measurements on MV Switchgear”, CIRED 19th International Conference on Electricity Distribution, Paper 0475
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