 D.C. Systems 24/8 Battery systems 24/12 Power supply distribution 24/13 Power for computer systems 24/14 Customer systems 24/14 Power management systems 24/14 24.9 Maintenance and costs 24/14 24.10 Mobile power plant 24/14 24.11 Power plant accommodation 24/14 24.12 Building engineering services 24/15 24.13 Reliability and cost 24/15 24.14 Future developments 24/15 24.15 References 24/16 24.16 Acknowledgement 24/17 This page intentionally left blank Introduction 24/3 24.1 Introduction are unacceptable. Typically, in the U.K., plant would have to be able to cope with voltage supply limits of +6% to -6%, and, of course, transients of short duration. Power systems are a crucial element of any communications net- work, be the latter large or small, and they are one of the few elements capable of causing a total failure or malfunction of even 24.2.2 Local power supplies the most sophisticated network. Hence the definition of the supplies, and their required level of reliability, has to be decided at an early In some locations site generation may be appropriate, based either stage of design. Neglect of this seemingly self evident fact, all too on economic considerations, or in the case of remote installations, often results in a poor standard of service of the switching equip- out of sheer necessity. ment etc., which will be difficult if not impossible to retrospectively put right in a cost effective manner. In general there are no wholly defined international standards for 24.2.2.1 Site generation complete power systems for any given communications service. These tend to be set by individual companies, or national adminis- In the U.K., a major telephone exchange at Cardiff was designed to trations, although they inevitably follow a trend. This section there- work on a total energy scheme, using natural gas or diesel dual fuel fore, sets out the principles of those most commonly employed in prime mover engines driving medium voltage generators. This plant major networks, and not the least, those which have been, and a