ations tend ing more stringent, and Recommendation G5/3 of the Electricity to be intermediate repeater stations in chains of land-line or radio Council requires the total harmonic distortion to be limited to 5%, links, and almost by definition, they are in environments of near and individual harmonics limited dependent on the type of plant and desert (Lee, 1986), subject to ice and snow (Gahrn, 1987; Kolousek, its size. This means that in particular, larger thyristor controlled 1986), in mountainous terrain, or subject to tropical and damp (high rectifiers must be carefully designed to take due account of any humidity) conditions (Olden, 1983) and have power demands of just constraints imposed by particular supply authorities. a few kilowatts, or even watts. Where equipment is connected to such a supply without interven- Diesel-generator sets still have a part to play, either as the prime ing power conversion plant, it is possible that electro-mechanical or power source, or in combination with other systems, for example, a electronic voltage regulators may be required if voltage variations wind generator (Grant, 1983; Akerlund, 1983). But clearly, if access 24/4 Telecommunication power systems is a major problem, the difficulties of getting fuel (diesel oil or some 24.2.4.3 Petrol engines form of bottled gas) to site, are significant. There are, therefore, advantages in the employment of wind and solar energy, but such Petrol engines are not normally used for fixed installations because systems have the disadvantage of being weather and time depend- of their limitations in the automatic starting mode. They are of ent. Hence they must always be associated with another power relatively low ratings not readily adapted to fixed industrial appli- source to bridge the gap arising from windless or sunless conditions, cations, and the fuel itself presents significant hazards in handling a battery of secondary cells for instance. For situations where the and large scale storage. However the very small sets are sometimes e