[原创]电气英语原文3 Substation The purpose of a substation is to transform the characteristics of of the electrical energy aupplied to some form suiteble foe us, as for example, a conversion form alternating current to direct currect for the use of city railway service, or a chang form one voltage to another, or one frequency to another tTheir functions include. Tap.—To be economical, transmission of larger amounts of power pver long distance must be done at voltages above 110,000 volts. Substations for supplying smail smounts of power form such highvoltage lines are not satisfactory form the standpoirt of operation and are also uneconomical. It is, therefors, common practice to intall a few subtations at advantageous points along the high-tension lines and step down the high-transmission voltage to a lower secondary-transmission voltage form whice numerous small loads may be supplied. Distribution.—Any substation that is used to transform electrical to a potential that is low enough for general distribution and utilization is a distributing receive its energy over a few comparativefy high-teision lines and distribute it over a large number of low-voltage lines. Industrial.—When fairly large block of power are reqoired by industrial plants, it often becomes necessary and advisable to install an individual substation ti supply such a load directly form the main high-volatige line or secondary line of lower voltage. Its simplest form would comprise only switching equipment, there being no voltage transformation. In most cases a voltage transformation is probably needed; hence transformer equipment is inclded. Sectionalizing.—In very long high-volitage large-capacity lines, particularly when several circuits sre run in parallel, it is often nrcessary to split the lines into section s,inorder that proper protection to the line and servicce can be obtained. Such a substation is, therefore, helpful in sectionalizing damaged section of a line, provding continuity comprise only switching equipment. In long lines it may also serve to supply power-factor-correcting equipment. Transmission-line Supply.—It is becoming more and more common to install the high-tension equipment of a power plant outdoors, the installation becoming nothing more than a step-up substation receiving its power at generetor voltage, then stepping up its voltage and finally sending it out over high-voltage transmission lines. Such a substation is nothing more than an outdoor distributing substation turned around, the voltage being stepped up instead of stepped down. Power-factor Correction.—The voltage at the end of long lines tends to increase as the load supplied is decreased , while on the other hand it tends to the inductance and the load is increased. Owing to the inductance and capacity effects, this variation in voltage is accompanied by a wide variation in power factor of a line, it is necessary to use synchronous condensers at the end of the line, To supply such a machine the transmission-line voltage must be stepped down, hence a power-foactor-correcting substation will include switching equipment., transforms, and all equipment necessary for the operation of synchronous condensers. Frequenency changer.—To interconnect two systems of different freqiencies it is absolutely necessary that frequency changers be used. Invariably a station of this type will necessitate transformers to step down or step up the voltage supplied to or delivered from the frequency changer, since the highest voltage that is normally feasible for rotating machinery has been found to be zbout 13,200 volts. Railway.—Substations supplying railways may be generally classified under two heads, namely, as alternating current and as direct current. In the cases of alternating-current substations the problem is generally one of voltage transformation and of supplying single-phase power to the train. It is, howere, possible to supply single-phase to there-phase insind the locomotive by the use of a phase converter. In the case of direct-current railways, the substations are generally supplied with there-phase power and converted to direct current by means of rotary converters, motor-generator sets, or rectifiers. Direct current for Light and Power.—There are still a few sections in some of out large cities which are supplied withdirect-current there-wire systems. Such a supply is invariably obtained from synchronous converters. There are also certain types of motor loads in industrial plants which require direct current; these are as a general rule supplied form rotary converters. For electrolytic work, low-voltage direct current is absolutely essential, hence motor generators or rotery converters are also applicable. ----------------------------------------------