er supplies. Increasingly, be set. Table 24.1 gives a typical example of assumptions and power conversion units will be capable of being embedded in the definitions which can be used to assess the mean time between equipment it immediately serves, together with its reserve battery. failure of an a.c. supply when an engine generating plant is available New cell couples will undoubtedly be fully developed and pro- with a given failure to start rate. Other analysis can be repeated for duced, the lithium polymer type for instance, and perhaps, after SO all aspects of any system (Banfield, 1982; Banfield, 1984). many false dawns, the fuel cell will come into its own. Cost is not an aspect against which a simple formula can be The capability to build in the d.c. power conversion system will, ascribed. First capital cost is not the sole arbiter; rather the whole therefore, greatly enhance an operator's ability to introduce new life cost for a complete scheme must be considered. This can then communications systems as required, without limitations arising be set against the cost of failure within the costing period, not the from the use of centralised, or quasi centralised, power plant. 24/16 Telecommunication power systems There are, nevertheless, dangers arising from this fragmented Coppinger, J.M. (1987) Telecommunications power systems - approach to overall power system design, that is the homogeneous the operations and maintenance perspective. In Proceedings of nature of a.c. and d.c. systems, particularly the loss of the co- INTELEC, Stockholm. ordinated consideration of other services such as cooling; which are Dolezal, H. (1987) UPS: Dynamic-Rotary systems with flywheel essential to the operational capability of a communications system. and diesel engine. In Proceedings of INTELEC, Stockholm. Lack of foresight in the co-ordination of all the power and building Eoolley, J. (1986) A.C. power systems - operational experience service systems, based on the outmoded concept of their being out at satellite earth station