The availability of the power station depends mainly on the reliability of the house-service power, which is also a determining factor in the power supply from the whole system. The house-service supply must therefore be ensured at any time i. e. when starting up, in normal operation and in case of breakdown. For this reason certain requirements are set for the reliability of the house-service supply, the controllability and the back-up of block units, the switch-over arrangements in the power stations and the set-up of the switchgear. Corresponding to the wide range of power-station designs, various different circuits have been introduced for the house-service supply when the required high availability is achieved by intrinsically safe circuits or by the possibility of switching over to a reliable outside supply. All the various circuits are based on the attempt to ensure safe supply for house service optimally matched to the paricular power-station conditions, which avoids damage to the power station, especially in case of breakdown, and makes the power-station block unit available again in the shortest possible time.
