Basic Electrical Installation Work

| Kategorie: Kniha  |

Strana 102 z 399

Jak získat tento dokument?






Poznámky redaktora
4(b).Basic electrotechnical units and theory 91 The ratio the output power the input power known the efficiency of the machine. The symbol for efficiency the Greek letter ‘eta’ (η). 4.81kW motor driving the mechanical hoist the previous example. Electrical machines Electrical machines are energy converters. the machine input mechan- ical energy and the output electrical energy then that machine genera- tor, shown Fig.3 Simple machine concept. 4. Find the efficiency the transformer. In general, Power output Power input Since efficiency usually expressed percentage modify the general formula follows. Simple a.5, the loop wire will cut the lines magnetic flux Effort Machine Load FIGURE 4.c. generator alternator If simple loop wire rotated between the poles permanent mag- net, shown Fig. The input power the transformer was found 10. 4. % Thus the transformer 90% efficient. The symbol for effi- ciency the Greek letter ‘eta’ (η). Power output Power input 100 Example A transformer feeds the 9. An electrical machine may used motor generator, although in practice the machine will operate more efficiently when operated the mode for which was designed. In general, ␩ Power output Power input . Note that efficiency has units, but simply expressed as percentage.9kW. Power output Power input kW kW 100 9 81 10 9 100 90 . . Definition The ratio the output power the input power known the efficiency of the machine. Alternatively, the machine input electrical energy and the output mechanical energy then the machine motor, as shown Fig.4(a)