inverter system For telecommunications purposes, no-break power loads tend to be in the kilowatts range, and in general terms there is little to choose between the two technologies of static and rotating plant, although there is inevitably much debate between the competing manufacturers. However, the transient response of the former may well have the edge. To counter balance this however, the rotary Figure 24.6 Standby or 'hot' standby inverter system systems seem to have a rather better ability to cope with overload, as well as giving complete electrical separation stemming from the mechanical coupling of a motor generator set. It has also been machines on a single shaft, plus a flywheel to provide carry over argued that the static plant is more complex in its technology and energy. A diesel engine is provided as part of the set and this is hence is not SO readily maintainable, but this is an issue rather brought into operation on mains failure via forms of magnetic clutch conditioned by the viewpoint of the user, and the ready availability (Dolezal, 1987) or induction coupling (Beems, 1981) to continue of suitably trained staff and spares. the drive to the generators. There is an increasing use of switched mode power supplies for a.c./d.c. conversion, and this gives rise to the drawing of current from the a.c. supply for short periods of time, centred about the peak 24.3 D.C. systems of the voltage waveform. The peak may be of the order of three to five times the r.m.s. current and can present problems where the In the final analysis most communications equipment use d.c. power equipment is fed from a UPS, (or indeed a standby generator set), at a multiplicity of voltages, the value being dependent on the type D.C. systems 24/9 of component. In the past (Pine, 1971) this has resulted in all manner Engine Control And of different power plants supplying loads, typical of which were a Automatic Change-Over nominal -28 volts for transmission equipment, or +80 volts for System Rectifier telegraphs. However, exchange