The Diseases Of Electrical Machinery

ELECTRICAL MACHINERY. 63 Synchronizing.—Where two or more alternators are to be operated in parallel on the same ’bus-bars, it is necessary to provide synchronizing arrangements, so that the attendant on the switch board may not throw into Circuit an alternator that is not already in step with those that are already on the circuit. Acci- dents of a serious nature have arisen from generators being switched in when not in step. To avoid acci- dents, the generator that is to be thrown in should be brought up to the proper voltage and to the proper speed, but must not be switched in until, by gentie adjustment of the speed up or down, the electromotive force has been brought into precise phase with that of the circuit. The synchronizing apparatus for indi- cating this usually consists of a lamp, fed through a small differential transformer, which lamp does not shine with a steady brilliance unless synchronism has been attained. Cleaning Alternators. — Alternators must be cleaned from time to time from dust or dirt. A biast of high-pressure air is very convenient for this pur- pose ; or, for small stations, a hånd air-pump, made of wood, having a barrel 2 feet long and 4 inches wide, is useful. In foundries and factories, where iron scale or iron dust is in the air, the magnet-wheels of alter- nators are sometimes found to collect fringes of dust on their poles, which ought to be cleaned off every day.