Home Health Case Studies in Maintenance and Reliability: A Wealth of Best Practices
We selected the following projects based on the criteria discussed earlier. A brief description of the work is given along with its justification and timing. 
preferred they decided themselves, as it would minimize arguments. The project was justified as an HSE item.
The public electricity supply system was unreliable, due to a serious mismatch between supply and demand. There were frequent power cuts; to overcome this difficulty, the company had installed four 350 kW diesel generators, with a fifth on order. These worked as stand-alone units, supplying isolated sections of the factory. This limited our flexibility to provide power where it was needed to suit the (variable) production demand. With stand-alone units, we could never load the machines fully. To overcome these limitations, we planned to synchronize the generators and connect them to the distribution network. The latter was currently not a ring main; this was another shortcoming needing correction.
This project required major investment in new transformers, circuit breakers, and feeders. Due to the lead time required for procuring the hardware, this project was phased over three years. The cost of the project was high, but so were the expected returns. We expected to reduce the value of lost production due to electrical supply problems by 50-60%, giving a benefit-to-cost ratio of 5:1.
A different issue related to the cost of electricity purchased from the public supply system. The electricity supplier applied a three-part tariff, with charges for the connected load (kW), energy consumed (kWhrs), and a surcharge for power factor below 0.96 (kVA charge). In addition to the thousands of induction motors in service, there were large induction furnaces in the factory. Without correction, the power factor could drop as low as 0.91. We already had a number of power factor correction capacitor banks, which brought it up to 0.94-0.95. We planned a separate project to increase the power factor to a maximum of 0.98. This upper limit was set by the possibility of a large induction furnace trip when we could end up with a leading power factor. The new capacitor banks would be brought into service or disconnected so that the power factor never exceeded 0.98 or went below 0.96. The project was phased over two years, based on hardware availability. The costs were relatively low and the expected benefit-to-cost ratio was 5:1.
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