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. Note that efficiency has units, but simply expressed
as percentage.
Power output
Power input
100
Example
A transformer feeds the 9. Alternatively, the machine input electrical
energy and the output mechanical energy then the machine motor, as
shown Fig. The symbol for efficiency the Greek letter ‘eta’ (η).
An electrical machine may used motor generator, although in
practice the machine will operate more efficiently when operated the
mode for which was designed.
The input power the transformer was found 10.
Simple a. In
general,
Power output
Power input
.81kW motor driving the mechanical hoist the previous example.4(b). 4.
%
Thus the transformer 90% efficient.
. the machine input mechan-
ical energy and the output electrical energy then that machine genera-
tor, shown Fig. Find the efficiency the
transformer.Basic electrotechnical units and theory
91
The ratio the output power the input power known the efficiency
of the machine. generator alternator
If simple loop wire rotated between the poles permanent mag-
net, shown Fig. 4.c.
Electrical machines
Electrical machines are energy converters. In
general,
Power output
Power input
Since efficiency usually expressed percentage modify the general
formula follows.3
Simple machine concept.9kW.5, the loop wire will cut the lines magnetic flux
Effort Machine Load
FIGURE 4.4(a). The symbol for effi-
ciency the Greek letter ‘eta’ (η). 4
