At the same time, a thermographic inspection was performed to see the physical effect of the overload on the weak conductor. The maximum operating temperature (corresponding to its rating) from the manufacturer for the three-phase line with 7#12 copper conductor is recommended as 75°C. On-site inspection revealed that the conductor was visibly sagging due to the overload, while the thermograph indicated that the conductor temperature was around 112°C, considerably higher than the recommended maximum operating temperature.

The time at this stage was only 5:15 p.m., and this portion of conductor had already exceeded its recommended maximum overload. However, the previously generated trends indicated that the evening peak would occur around 6:30 p.m., which meant loads were still due to increase and further pressure the conductor. Western Power decided to start shedding load from COL 302 immediately to save the conductor from failing and to minimize the possibility of more customers being without power.

The feeder had not quite reached its HiHi alarm limit when it was decided that COL 302 should shed some load. Approximately 3% of the CL load was shed to keep the three-phase line with 7#12 copper conductor from failing. If an offload had not taken place at this point, the rapidly growing evening peak would have led to an almost certain failure of the copper conductor, which would have left far more customers without power. This scenario also would have posed a safety risk to the public if the overhead conductor failed and fell to the ground.

Without the use of DPA and its provision of vital extra knowledge for decision-making, load may not have been shed when required. This would have almost certainly led to a failure on the three-phase line with 7#12 copper conductor and a fault. Conversely, without being able to see trends for the expected loading on the feeder and without the use of DPA, a cautious approach could have been taken where the shedding of load would have been performed too early, resulting in customers being without power unnecessarily.

The estimated customer impact of a failure of the three-phase line with 7#12 copper conductor can be illustrated using the performance metric of customer interruption minutes (CIM). By comparing the actual CIM due to events over the two days with the estimated CIM that would have resulted if a conductor had been lost, the true benefits of using the network management system are evident: an extra 31% above the actual CIM would have been incurred with a conductor failure. CIM for conductor failure would have approached 3.1 million instead of the actual 2.3 million.

The use of ENMAC DMS proved invaluable in efficiently managing key aspects of the control center operations. This was especially apparent during the outage and restoration scenario. The various functions conveyed vital information to the controllers to improve and streamline decision making under pressure. The effective use of DPA during the CL Substation fault enabled Western Power to safely restore power to its customers as soon as possible, minimizing the impact on sensitive customers, curtailing load only when absolutely necessary and avoiding the failure of critical conductors.

Janica Lukas is a graduate electrical engineer with Western Power. She holds a double degree in electrical and electronic engineering (with honors) and commerce from the University of Western Australia. Since joining the Western Power Graduate Rotation Program in February 2005, she has worked in the areas of network access, transmission networks, distribution design and network operations. She is also a committee member of the WA Engineers Australia Young Engineers and is a Young Engineers WA Electrical Panel representative. janica.lukas@westernpower.com.au

Tim de Grauw is a network engineer involved with the operational capacity and reliability of the distribution network. He holds an electrical engineering degree from Curtin University of Technology (with honors), and his area of speciality is power system analysis. These skills assisted de Grauw in the successful implementation of ENMAC DPA since he became involved in the project. He has also worked in the areas of planning, protection, design and project management in both the power utility and mining sectors. tim.degrauw@westernpower.com.au

Shane Duryea is manager network operations with Western Power and is responsible for the operation of the distribution network including outage management. He holds an electrical engineering degree from Curtin University of Technology. Since joining Western Power in 2000, he has worked in the areas of power quality, asset management, and network data management and operations, and was part of the implementation team for the distribution management system. shane.duryea@westernpower.com.au