Australia's transmission providers embrace similar strategies for on-line condition monitoring of high-voltage equipment.
The Last 10 to 15 Years have Seen a Significant Increase in the Range of Equipment specifically designed for continuous on-line condition monitoring of high-voltage substation equipment. Today, the opportunity exists for continuous on-line monitoring to assist network providers in meeting new industry demands.
The introduction of electricity markets has imposed operational demands on electricity networks in an environment of cost reduction, coupled with increased risks and liabilities. Utilities are now using several asset-management drivers:
Financial drivers of revenue and cost
Service standards that include voltage quality, system reliability and availability
The minimisation and alleviation of market constraints
Safety and environment.
On the East Coast of Australia, two of the major transmission network service providers (TNSPs) — TransGrid and Powerlink Queensland, whose transmission systems are interconnected — have adopted a similar strategic approach to on-line monitoring in order to realise the potential benefits. Working independently, the two TNSPs — following similar patterns of reviewing existing practices, technology evaluation and field trials in the 1990s — have established asset-management practices that are closely linked to the cost benefits of on-line condition monitoring.
TRANSGRID'S STRATEGY DEVELOPMENT
In 2002, TransGrid formalised its policy regarding on-line condition monitoring for the most significant items of high-voltage substation equipment, namely circuit breakers, power transformers and instrument transformers. TransGrid developed its strategy by relating the justification for installing the on-line monitoring to the cost benefits. This exercise involved assessing potential plant failures, the equipment available on the Australian market and the management of on-line monitoring information. Table 1 offers an example of the rationalised cost-benefit analysis used for each item of equipment identified for possible on-line monitoring.
In addition, TransGrid considered several other factors based on system operational and equipment reliability statistics, experience, geographical location and the cost of on-line monitoring equipment compared to replacing the existing capital asset.
TransGrid initially concentrated its continuous on-line monitoring efforts at new substations, where the technologies could be included in the overall design for the substation and supporting infrastructure such as telecommunications links already existed.
POWERLINK'S STRATEGY DEVELOPMENT
In the late 1990s, Powerlink embraced significant changes to its existing policy by adopting new high-voltage technologies. With the availability of hybrid switching plants and the condition-monitoring technologies that were emerging, Powerlink examined the potential savings plant-monitoring technologies offered. It conducted field trials that incorporated on-line monitoring devices from major plant manufacturers and third-party equipment suppliers.
The range of devices installed included circuit-breaker monitoring, dissolved gas analysis equipment for power transformers and insulation-pollution monitoring. Coupled with a significant investment in the development of an operational wide-area network (WAN), the field-monitoring devices enabled Powerlink to collect a large volume of data for processing and analysis at its remote engineering and operations offices.
However, to maximise the benefits from its investment in technology, Powerlink changed its organisational structure and established an asset-monitoring team (AMT).
Powerlink uses on-line monitoring as both a predictive model and a reactive model, with the former being used to optimise condition-based maintenance and the latter being used to improve post-fault diagnosis to minimise plant outage periods. Using these models for managing real-time faults and long-term plant condition monitoring, Powerlink developed a monitoring standard for use in reactive and predictive modes for all primary plant, secondary system and communication network assets. Table 2 shows the standard that Powerlink developed for its SF6 circuit breakers.
SUBSTATION EQUIPMENT OUTCOMES
After several years of developing their strategies, Powerlink and Transgrid have identified some key outcomes of using on-line condition monitoring for their substation equipment. The substation equipment outcomes fall under three categories:
- Circuit breakers
Circuit-breaker on-line monitors are now available for all forms of monitoring, from basic equipment to multifunctional microprocessor-based monitoring devices, some of which also include control functions. Since 1998, Powerlink has been installing circuit breakers equipped by the manufacturer with either monitoring or control/monitoring devices. To date, 4.5% (39 of 883 units) of conventional air-insulated switchgear (AIS) circuit breakers and 96% (198 of 206 units) of hybrid gas-insulated switchgear (GIS) circuit breakers include some form of monitoring. Presently, Powerlink has decided not to retrofit monitoring devices to older equipment until the economic benefits of on-line monitoring are established.
Similarly, in 1998, TransGrid decided to purchase new circuit breakers with on-line monitoring equipment fitted by the switchgear manufacturer. Today, 7.5% (104 of 1391 units) of AIS and 45% (18 of 40 units) of GIS circuit breakers are fitted with original equipment manufacturer (OEM) monitoring devices.
- Instrument transformers
Current-transformer monitoring systems are available for insulation leakage current and tan delta (ä) measurement, the latter of which was installed at six TransGrid substations following a particular type of current-transformer fault. For many years, both TNSPs have installed simple secondary-voltage comparators on capacitor-voltage transformers to monitor the porcelain-insulated high-voltage capacitor stack. Although Powerlink now routinely uses composite insulators for this equipment, the benefits of monitoring are still just as relevant. Powerlink is installing analog-density monitoring on all-new SF6 gas-insulated instrument transformers in addition to conventional alarm switches.
- Power transformers and reactors
Monitoring devices are available for power transformers and reactors to monitor the level and condition of the insulating oil, partial discharge, tap-changer operation and temperature. Both utilities use the full range of devices available with varying degrees of reliability. Dissolved gas analysis, tap-changer performance and tan delta are the predominant characteristics monitored.
Powerlink and Transgrid also have identified some of the key outcomes of using on-line condition monitoring for managing assets. The asset-management outcomes fall under three categories:
TransGrid is introducing a centralised system to manage the information from the on-line monitoring systems installed on the entire transmission system. A Web-based system has been developed that relies on the existing secure WAN infrastructure and is separate from the supervisory control and data acquisition (SCADA) system. The figure on page 46 shows a screen display with monitored trends from four substations.
TransGrid plans on making available to all staff a user-friendly flexible software system designed for future expansion, but redevelopment of the system is needed before this can be achieved in a secure and sustainable manner.
Powerlink also has an operational WAN that is independent of the SCADA system. Data is usually stored on-site with demand-access facilities using systems supplied by the equipment manufacturers. However, users accessing the data through the WAN need specialised training in the use of different software packages.
- Organisational changes
In 2000, Powerlink combined elements of its operations, maintenance and design business units into a single asset-monitoring function, harnessing the necessary skills to process and respond accordingly to the increased volume of information made available from the on-line condition-monitoring systems installed. The AMT was formed to manage condition-monitoring data for fault management and longer-term plant condition-monitoring purposes.
With the passage of time, the AMT has established strong links with the asset manager, which provides real-time fault-management information on transmission system assets. This in turn supports the plant maintenance and refurbishment strategies.
In contrast, TransGrid incorporated on-line condition monitoring into its existing organisational structure. A central asset-management business unit oversees the strategy, and the system will be available to field staff to undertake the interrogation and data analyses.
- Changes to maintenance regimes
TransGrid is considering an alternative maintenance regime specifically for equipment installed with on-line monitoring. The aim is to move to condition-based maintenance to reduce the cost of maintenance, as well as the duration and frequency of maintenance and system outage times.
At Powerlink, where extensive monitoring and remote video surveillance is incorporated in new plant installations, the period between substation inspections has been increased from two months to six months. Significant changes to the existing maintenance policy on circuit breakers or isolated types of equipment are unlikely, because maintenance is scheduled on a complete substation basis, often coordinated with circuit outages on the transmission system.
EXPERIENCE TO DATE
Powerlink and TransGrid have both installed on-line condition-monitoring systems made up of devices, including those with digital monitoring and those with integrated monitoring and control facilities. Hence, both TNSPs now have experience with the technologies available, their application and the data-processing requirements.
Powerlink has gained information on the circuit-breaker travel characteristics for commissioned units; some systems have exhibited hardware and software problems, but the automated data processing of basic information has proven to be beneficial.
TransGrid's on-line monitoring system detected and prevented a current-transformer failure with a known-type fault problem and has been monitoring other types of equipment with known risks.
Both utilities have experienced the same general issues:
Initial lack of understanding of how particular monitoring devices work and how systems should be connected and configured to extract data
Mismatch between utilities and manufacturers on usage of the systems
Lack of understanding within utilities of the end-to-end systems as they cross boundaries that exist between the utility's specialist-knowledge teams
Spurious or low-priority alarms that can generate unnecessary maintenance callouts
Electronic components that are unable to withstand the extreme temperatures prevalent in Australia, particularly when monitoring and control are combined in one device.
Powerlink is not going to install systems with the combined monitoring and control facilities until the electronic-device reliability is greater than the equipment being monitored.
TransGrid is continuing with its planned on-line monitoring strategy and is considering alternative maintenance practices where on-line monitoring systems are installed. Further work is planned to automatically analyse the data collected, combine the data collected from the various systems and evaluate data trends.
Powerlink is moving forward with its strategy, but a review of the benefits of the installed monitoring systems revealed that gas-density monitoring produced the highest cost benefit for circuit breakers. Therefore, the utility is implementing a simple remote monitoring system for gas density on all new circuit breakers.
Both utilities' experience in combined monitoring and control devices has confirmed that such a device can increase system-failure rates and compromise the operation of the main equipment. Therefore, both utilities require the monitoring and control functions to be separate until there are demonstrated improvements in the monitoring reliability of the combined device. This will have significant relevance to any future rollout of IEC 61850-compliant devices at the process-bus level. (IEC 61850 defines the communications protocols for future intelligent electronic devices applied in substations. The process level is the interface between the secondary equipment in the control room and the primary equipment in the switchyard.)
Powerlink and TransGrid have taken advantage of the on-line condition-monitoring technology, installing systems marketed by several manufacturers. Each utility has established its own organisational structure and information systems to collect data, analyse it and respond to it accordingly. Both utilities identified problems with the systems designed with dual monitoring and control functions, and have had reliability issues with electronic devices at high temperatures. Despite these problems, the two utilities are moving forward with their strategies.
On-line condition-monitoring systems are one of several useful tools designed to improve and enhance the performance of a utility's assets and overall system reliability.
Steven Jones (email@example.com), manager of design and construct projects at TransGrid. He has a background in high-voltage equipment and the design of substations, cable, protection and telecommunications systems. With a master's degree in engineering and an MBA degree, Jones has more than 25 years experience in the electricity supply industry. He represents Australia on CIGRÉ's High-Voltage Equipment Committee and has authored a range of international papers.
Andrew Kingsmill (firstname.lastname@example.org) is the performance and compliance manager at TransGrid, where he has worked for 10 years in the design, field asset-management and asset-performance groups. Kingsmill participated in TransGrid's on-line condition-monitoring working group and developed the architecture of the condition-monitoring information system. He holds postgraduate degrees in engineering and engineering management.
Mark Blundell (email@example.com) is a principal consultant of switching technology with Powerlink Queensland. His duties at Powerlink involve investigating new switchgear technologies, investigating failures of circuit breakers and instrument transformers, preparing technical specifications and undertaking technical evaluations of tenders for circuit breakers and instrument transformers. Recently, Blundell was involved in the procurement and application of hybrid GIS circuit breakers with on-line monitoring features and the introduction of point-on-wave switching technology on the Powerlink network.
Jamie Gabb (firstname.lastname@example.org) is the manager of asset monitoring at Powerlink Queensland, where he is responsible for the provision of network-wide asset-monitoring services, including fault management, asset-performance and condition-monitoring services. His background includes 15 years experience in the electricity supply industry across areas of substation maintenance, design, construction and testing, together with international experience in hybrid switchgear development, manufacture and implementation.
Garry Slade (email@example.com) is the asset-monitoring engineer at Powerlink Queensland, where he is responsible for the condition and performance monitoring of plant and equipment, and the coordination of plant failure investigations. Slade was a QUT University Medal winner in 2001 and has more than 20 years experience in the electricity supply industry, in which he commenced his career as an apprentice electrical fitter mechanic in regional Queensland.
Table 1. TransGrid's Cost-Benefit Analysis Form
|Improved efficiency of maintenance practices||$|
|Faster and more-appropriate response to equipment defects||$|
|Improved information for real-time decision making||$|
|Early detection and possible prevention of equipment failure — capital cost||$|
|Early detection and possible prevention of equipment failure — unserved energy||$|
|Long-term data acquisition and improved knowledge of equipment||$|
|Safety (staff and public)||(points)|
|Improved equipment condition knowledge||(points)|
|Cost of capital||$|
|Routine maintenance of on-line condition-monitoring equipment||$|
|Repair of defects on on-line monitoring equipment||$|
|Responses to unreliable readings and nuisance alarms from condition monitoring||$|
Table 2. Powerlink Queensland's SF6 Gas Circuit-Breaker Form
|Fault management||On-line condition monitoring|
|Circuit-breaker pole-position status (for each phase)||Gas-density monitor|
|Hydraulic low-pressure alarm||Spring charge status|
|Hydraulic low pressure — lockout|
|Pump motor failed||Nonstandard features:|
|Pump motor excess run time||Accumulated motor/pump run time|
|Air low-pressure alarm||Motor current profile|
|SF6 gas low-pressure alarm||Trip/close operation times|
|SF6 gas low pressure — trip and/or lockout (selectable)||Contact time/travel characteristic|
|On-board intelligence failed||Primary contact fault current|
|“X” trip circuit faulty||Re-strike detection|
|“Y” trip circuit faulty||Auxiliary contact condition|
|CB controls inhibited||Spring charge time|
|Pole discrepancy operated||Spring energy|
|Trip/close coil current profiles|
|SF6 gas analysis|
|Pole discrepancy operated||Spring energy|
|Trip/close coil current profiles|
|SF6 gas analysis|