The installation has eliminated frequent and lengthy power outages from affecting the entire network.Conditions are now reduced to short outages in isolated areas of the network allowing the mine to operate efficiently with minimum interruptions.
The central cause of all this fuss was the extremely large population of bats living in the immediate vicinity. Before the reclosers were installed they would fly into the lines, causing a fault that would trip the circuit breaker back at the substation resulting in the loss of an entire feeder. This feeder not only supplied parts of the mine, but also the accommodation village nearby.
Mines are generally temporary constructions, and the cost of running feeders underground for any significant length of time cannot be justified. On the other hand, the bats are protected and cannot simply be culled to reduce the problem. Kimberley Nickel Mines looked into the problem and decided to install two reclosers on the sections most affected by the bat strike problem.
Automatic circuit reclosers (ACR) are essentially circuit breakers designed to re-connect power after detecting and interrupting a fault. If the fault is temporary the reclose operation will succeed allowing power to be restored instantly without human intervention.
Bats are usually incinerated when they come into contact with voltages of this level (11kV). When the recloser detects the fault it opens and lets the bat fall to the ground. This removes the fault and the reclose operation is generally successful. If a permanent fault is on the line, the recloser will open and close a number of times, depending on how it has been programmed and eventually isolate the section of network if the fault is of a permanent nature.
The worst case now is that a small portion of the network may lose power while the fault is restored. In most cases, however, the interruption will only last a few seconds.
Installation of the reclosers was undertaken by an electrical contractor. Kimberley Mine's electrical coordinator, Peter Jensen, then contacted NOJA Power directly to help with commissioning. Although reclosers are a common sight in electrical utility networks, they are not so common in small privately owned networks.
NOJA Power pride themselves on superior service and support and are always ready to help customers who need to properly commission their new recloser. Due to the remote location of the mine, all training and commissioning advice was delivered over the phone and online using email.
NOJA Power's service manager, Oleg Samarski, was supplied Information on the substation circuit breaker settings, transfomer sizes and other network Information. From this he calculated appropriate settings that accounted for proper protection coordination and transformer inrush currents. These were delivered to Peter Jensen as a downloadable configuration file.
"Commissioning a recloser as flexible as ours can be difficult if you have never worked with one before," Oleg said."We are always happy to help customers get the most out of our reclosers for their particular situation. In this situation we were able to solve a considerable technical issue without the need to visit the site ourselves."
All NOJA Power reclosers have extensive configuration settings, data logging and measurement capabilities. These can be viewed locally at the control cubicle attached to the recloser, or on a PC using a software package called TELUS which is supplied free of charge. Peter Jensen used this tool to load the new configuration into the recloser.
After the recloser had been in service for a while the data log was downloaded and analysed. It was discovered that the recloser had cleared many temporary faults due to bat-strike. In order to reduce the number of interruptions, it was decided to further fine-tune the protection settings to coordinate even closer with the main substation circuit breaker.
Reviewing the protection coordination based on actual in service data proved to be invaluable in improving the overall reliability of the power supply. By raising the phase to phase fault current pick levels to just below the substation settings allowed a greater number of bats to hit the lines and fall off without having the recloser interrupt the fault at all.
The settings have now been adjusted so finely that interruptions have been reduced to the absolute minimum possible given the circumstances.