 also need to be connected to the standby system as opportunity. necessary. Matching modular plant designs to provide equipment cooling are increasingly seen as efficient and cost effective systems, and can be integrated into the main power system design to ensure 24.14 Future developments overall high reliability targets can be achieved (Allen, 1990). In broad terms, power systems may be divided into the two basic groups of a.c. and d.c. plant, and this format is like to continue for 24.13 Reliability and cost the future. The trend for a.c. plant is likely to be for the mains equipment such Terms such as reliability, failure, defect, mean- time to repair and SO as transformers, switchgear, cabling etc., to retain its robust con- on and SO forth, need adequate definition to have real meaning in a struction. Similarly, the standby engine-generating plant, whilst given situation. Failure may be defined as a complete loss of the achieving modest increases in efficiency and reduced fuel consump- mains supply, or it may be defined as the system voltage reducing tion, will continue to be the most cost effective solution to providing to a level whereby equipment malfunctions start to occur, perhaps longer term reserve a.c. power supplies. What will change, and when the voltage becomes some 90% of the nominal value. This sort dramatically in some cases, will be the increasing use of electronics of analysis may then be continued for all aspects of a total communi- and the microprocessor to monitor and control the supplies; re- cations scheme, of which power and cooling etc., form part. An motely if required, bringing in its train the more efficient utilisation operator must therefore define the acceptable limits or parameters of the facilities both operationally, and in maintenance terms. of a given system for any meaningful consideration of reliability The changes in d.c. plant have already been reflected in Section standards to be produced, and hence allow performance targets to 24.3.3.6 which dealt with distributed pow