Page 773 - Basic Electrical Engineering

or,

K = 1 because full-pitch coil has been used.
p

EMF induced per phase is calculated as

E = 4.44 ϕf T K K V
d
p
Substituting all values

−3
E = 4.44 × 20 × 10 × 50 × 540 × 1 × 0.96 V
or, E = 2301 V

10.9 OPEN-CIRCUIT OR NO-LOAD CHARACTERISTIC
This is the relation between the field current and the induced EMF when the

synchronous generator is run on no load.
When a synchronous machine is driven by a prime mover at synchronous

speed, N , it will generate an induced EMF if its field winding is excited. The
s
field winding is excited by supplying a dc voltage through the brush and slip-

ring arrangement. When the field system is rotated at a constant speed N and
s
the field current, I is gradually increased, keeping the output terminals open
f
as shown in Fig. 10.9, the induced EMF will go on increasing but will have a

saturation effect as shown in Fig. 10.9 (b).
The open-circuit characteristic or OCC as shown in Fig. 10.9 is the

relationship between the field current and the induced EMF when the rotor is
rotated at a constant speed. Since no load is connected across the stator

output terminals, the OCC is also called the no-load characteristic.