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Connection is best made at a point at or near the incoming supply point. Where a full system is not being covered by the generator, then the connection should be made at an appropriate point to cover only the necessary loads.
It is important to ensure that there is adequate electrical protection to disconnect the supply in event of a fault on the system. Applying a generator to a board where there are loads that are greater than the rating of the generator could lead to overload conditions, with the frequency dropping and the generator tripping out. Whilst a control system could be arranged to prevent this happening, it is far preferable to have a dedicated emergency services board.
Switching the power source between mains and generator is another important consideration. Automatic transfer switching with mechanical interlock will enable the power to be safely changed over to the generator supply automatically on loss of mains, and then back again when the mains returns. For commercial installations an automatic changeover switch will normally be fitted, especially if an UPS system is provided.
For diesel generators that require to be paralleled with the grid, it is necessary to have appropriate synchronising facilities in place to ensure that the voltage, frequency and phase are all matched before the generator circuit breaker is closed.
When paralleling with the grid, the Distribution Network Operator will provide the correct metering to monitor any export of power. In the event of loss of grid elsewhere in the local network, there will need to be the necessary protection in place to rapidly disconnect the diesel generator so as to avoid possible damage to other equipment on the network.
Permanent generators are best connected through a fixed arrangement, while smaller temporary generator connections can be made via plug and socket arrangement.