POWERLINK QUEENSLAND is an Australian government-owned corporation that owns, operates, develops and maintains one of the world's longest and most reliable, extra-high-voltage (EHV) and high-voltage (HV) electricity transmission networks. This sophisticated $3 billion (US$2.3 billion) network extends more than 1700 km (1056 miles) from the New South Wales border in the south to beyond Cairns in the tropical north of Queensland, or over approximately half of Australia's eastern seaboard. This network includes 96 Powerlink substations, all operated from a single control center in Brisbane.

Powerlink traditionally engineered secondary systems for all Powerlink substations until about five years ago when engineering management made a strategic move to install completely integrated systems engineered by major transmission equipment vendors.

The new systems included varying degrees of system integration between primary plant, control, protection and condition-monitoring systems. These turnkey integrated secondary systems were multifaceted with many levels of network connectivity, which made configuration and maintenance activities difficult and complex. The systems were not fully open, so there were limited options for expanding the systems to handle a growing transmission network. In addition, the local staff required extensive training to undertake maintenance and minor modifications. Opportunities for improvements were identified, including performance enhancements, alarming of failure modes, logging of events at times of high system activity, and protocol emulation eliminating single points of failure.

This operational experience resulted in Powerlink pursuing the purchase of a higher level of integration of all substation secondary systems to overcome the identified shortcomings. Primarily, Powerlink sought to reduce the whole-of-life cost of both the substation secondary system, as well as the primary high-voltage plant it controls, monitors and protects. Furthermore, it had to reduce on-site maintenance while satisfying the demanding performance and functionality required for the operation of a sophisticated transmission network.

POWERLINK'S NEW REQUIREMENTS

Powerlink decided the security and reliability of the EHV and HV system should drive the development of a new substation integrated secondary system. The following three guidelines were established to assist in the development.

1. A major requirement was to reduce system maintenance costs for both primary and secondary system equipment. To achieve this, unnecessary routine maintenance practices had to be replaced by condition-based monitoring and maintenance processes.

2. Equipment outage times needed to be kept to an absolute minimum, because the reliability of a substation secondary system directly impinges on the reliability of the primary system. Both are essential to providing a reliable and secure power transmission system.

3. The design had to be as simple as possible, while still meeting all the functionality, security, reliability and performance requirements. Powerlink sought to remove unnecessary transducers, interposing relays and parallel interfaces between items of equipment.

The design brief was to install secondary systems where the design process could be streamlined to allow easy replication for future sites. Powerlink also wanted to reduce on-site installation, testing and commissioning activities, so where feasible, these activities were performed prior to dispatching the system to the site.

SUBSTATION INTEGRATED SECONDARY SYSTEM

Powerlink chose to use standard building blocks from a variety of control, protection and IT equipment suppliers, thus allowing the design to be modular, easily repeatable and not specific to any particular equipment vendor. From these basic building blocks, Powerlink's novel integrated secondary system features several new innovations, including remote-controlled cameras, remote access to secondary system equipment, automation and condition-monitoring facilities, and a reduction in secondary system wiring with serial interfaces to protection relays.

A new and improved secondary system was designed to take full advantage of Powerlink's award-winning Operational WAN (OpsWAN) monitoring infrastructure, as shown in Fig. 1. (OpsWAN won an award at the Institute of Engineers Australia [IEAust] Engineering Excellence Awards in 2001.) OpsWAN provides remote access to substation control, protection and plant monitoring systems, yet does not interfere with the performance or functionality of these time-critical systems. The system facilitates improved fault management because all fault-related data — including analoge event logs — is readily available to those responsible for responding to faults, even though they may well be located 1000 km (620 miles) or more away. Remote-controlled cameras even allow for remote visual inspection of the substation plant.

The secondary system provides advanced automation and condition-monitoring facilities. Condition- monitoring facilities include significant fault diagnosis and alarming features, thereby enabling condition-based-maintenance practices to be established. The demand for scheduled routine maintenance activities is thereby significantly reduced.

Figure 2 shows that implementing serial interfaces to protection relays as well as to some primary plant significantly reduces the substation wiring and complexity. Each item of plant is associated with just two protection relays, which provide duplicate high-speed primary protection of that plant, as well as circuit breaker fail, disturbance recording, event recording and reception relay functionality. Thus, external interposing relays have been entirely eliminated. Each circuit breaker is simply controlled via one bay remote terminal unit (RTU), two protection relays and protection-signalling equipment, all of which are housed in a single swing-frame panel.

Reducing secondary system requirements allows for the implementation of modular, self-contained, demountable secondary system control buildings, offering reduced on-site installation and testing. The majority of testing of the substation secondary system is thus achieved at Powerlink's Virginia complex before being transported to the site for final connection and commissioning. This provides ready access for the relevant design teams during the first stage of testing and significantly reduces the amount of work performed at remote sites.

Intelligent automation functions are performed between RTUs connected in a network arrangement. Some functions require real-time coordination between several RTUs. Substation communications include OptoNet, Ethernet, DNP3, IEC 870-5-101/103 and Modbus Serial. The RTUs calculate voltage, current, megawatts, megavolt-ampere reactive, frequency and phase-angle metering quantities from CT and VT inputs connected directly to the RTU. Circuit breaker synchronizing check functions, from VT inputs to the RTU from either side of the circuit breaker, determine precisely when to issue a close control to the circuit breaker, based on 50-Hz phase and voltage differences. RTU intelligent automation functions include single- and three-pole autoreclosing, primary plant interlocks, maintenance-mode functionality and transformer automatic voltage regulation (AVR) functionality.

Furthermore, secondary system design times have been significantly reduced through the development of “Autobuild” tools, which allow a significant component of the secondary system design process to be automated. Autobuild tools have provided a reduction of 80% in control system design times. (Autobuild also won an award at the IEAust Engineering Excellence Awards in 2003.)

SYSTEM IMPLEMENTATION

With the integrated secondary system scheme development in conjunction with installation in both greenfield and brownfield applications, significant experience has been gained. This combination of design and implementation experience has allowed Powerlink to fine-tune its processes, the net result being a fully engineered and type-tested building block methodology for secondary system design applicable to transmission system substations. By limiting the number of standard panel designs, aspects such as templates for protection-relay settings, configurations and Boolean logic have been established, on again, to ensure a consistent application of type-tested designs.

This innovative process leads to shorter lead times for substation secondary system design, construction, testing and commissioning, all in conjunction with a common application methodology that significantly reduces design errors. In fact, Powerlink has been able to outsource the design of substations by providing the design templates to external contractors who are thus able to provide turnkey solutions identical to those produced in-house, thus eliminating all of the problems identified earlier when turnkey systems are implemented via system vendor proprietary designs and protocols.

HAVE THESE CHANGES BEEN SUCCESSFUL?

To date, Powerlink has installed, tested and commissioned 24 secondary systems based on this design, including OpsWAN facilities at 52 sites. Design for another nine systems is currently in progress. System test results met the targeted goals, satisfying all performance and security requirements. Event time tagging resolution and accuracy requirements have been met. All control and protection functions for each bay reside within a single panel. Full OpsWAN connectivity and condition-monitoring facilities have been provided with access to all control, protection and auxiliary systems, including video cameras.

One of the key successes has been the exploitation of the OpsWAN system. This service aided the response to and diagnosis of system faults in significantly reduced time frames. This has had a marked impact on limiting primary system outage times, and consequently offered an improved service to our customers. The new facilities and the establishment of an Asset Monitoring Team (AMT) have resulted in a reduction in the number of site visits by 16% and immediate callouts by 20%. The AMT has the prime responsibilities of monitoring the condition of all plant and to respond to system faults as reported by control center operations staff. Condition monitoring has facilitated the optimization of primary plant operation, including a reduction in tap changer control for transformers.

Furthermore, with only minor modifications to meet special local requirements, the Transmission Network Service Provider in South Australia, ElectraNet, has elected to implement substation design based on the Powerlink substation integrated secondary system.

The design is currently being rolled out for both new 132-kV and 275-kV Powerlink substations and as a replacement for many existing secondary systems approaching end of life. This is being undertaken in conjunction with Powerlink investigations into new technologies based on IEC 61850, currently under development.

IMPROVED POWER QUALITY

Powerlink's principal objective was to build modular-style substations using new technologies for the same or lower cost than traditional substations. By applying these new technologies, maintenance requirements have been reduced, and reliability and availability has improved, providing economic benefits to customers through improved power quality. The modular design also allows Powerlink to reduce lead times for construction and provides flexibility in response to the demands of the National Electricity Market.

Powerlink's novel integrated secondary system for transmission substation applications has achieved all technical, operational and maintenance targets and, above all, the design has proven to be a minimum-cost solution with low risk. The experience gained over the last five years will also prove invaluable as we move to the next generation of secondary systems that use the IEC61850 standard.

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Len Borowski is principal engineering consultant of automation at Powerlink Queensland, where he is responsible for identifying and evaluating new technology and setting design standards within Powerlink. He also lectures on the subject of SCADA/Automation at the Queensland University of Technology. lborowski@Powerlink.com.au

Barrie Moor joined the successor utility of Powerlink Queensland in 1973, initially employed in the transmission planning and then in substation development. He has been in the Protection Branch since 1981, holding various positions relating to the protection of the transmission plant at 110 kV to 330 kV. Moor represents Powerlink on CIGRÉ committee APB4, Power System Protection & Automation, and also lectures on distance protection and advanced protection at the Queensland University of Technology. bmoor@Powerlink.com.au