A fire located in the spare parts room within the complex holding the diesel generators has contaminated and damaged a number of spare parts. These spare parts are required for the power converter.

Historically the mine site was powered by 6 Diesel Generators producing a total power output of 20MegaWatts with an alternating current (AC) frequency of 40 cycles per second (40 Hertz).

In 1986 the decision was made to connect the mine site to the national power grid and to convert the power supply delivered at an AC frequency of 50 cycles per second, to 40 cycles per second required by the mining machinery.

The converter is comprised of four stages:

• Synchronous condenser 
• Rectifier 
• Thyristor Inverter 
• LC Network Filter

Each of these stages is replicated to provide some redundancy with each half capable of supporting 20 Mega Watts.

The synchronous condenser provides a reactive energy reserve that is used to stabilise and buffer the power from the national grid. The rectifier converts the AC input from synchronous converter into a DC supply, which is in turn supplied to the inverter. The Inverter regenerates the AC waveform at 40 cycles per second. This is then filtered through the LC network filter to remove any hazardous spikes and to provide a small reactive load for the system.

Power for the mine is drawn from the national power grid at a frequency of 50 hertz and is reduced to 40 hertz in a converter for the legacy mining equipment. The converter is built as two fully operational halves, one forming a backup to the other. When combined with the ability to produce power locally through diesel generators the risk of loss of mine production beyond 48 hours as a consequence of the fire was considered remote. A number of possible recovery strategies became available by increasing the recovery time period once the low level of risk was understood.