a coil of 12 ohm resistance is in parallel with a coil of 20 ohm resistance. the combination is connected in series with a third coil of 8 ohm resistance. if the whole circuit is connected across a battery having an emf of 30V and an internal resistance of 2 ohm calculate a) the terminal voltage of a battery and b)the power in the 12 ohm coil
Answers
Answer:
Loss [1/36.5/p.1373]
A single-phase motor may be looked upon as consisting of two motors, having a common
stator winding, but with their respective rotors revolving in opposite directions. The equivalent
circuit of such a motor based on double-field revolving theory is shown in Fig. 36.14.
Here the single-phase motor has been
imagined to be made up of (i) one stator
winding and (ii) two imaginary rotors. The
stator impedance is Z=R1+jX1. The
impedance of each rotor is (r2+jx2) where
r2 and x2 represent half the actual rotor
values in stator terms (i.e. x2 stands for
half the standstill reactance of the rotor, as
referred to stator).
Since iron loss has been neglected, the
exciting branch is shown consisting of
exciting reactance only. Each rotor has
been assigned half magnetizing reactance
(i.e. xm represents half the actual
reactance). The impedance of ‘forward
running’ rotor is
( )
( )
2
2
2
2
j x x
s
r
jx
s
r
jx
Z
m
m
f
+ +
+
=
And it runs with a slip of s.
Fig. 36.14
The impedance of ‘backward running’ motor is
( ) 2
) 2
(
2
2
2
2
j x x
s
r
jx
s
r
jx
Z
m
m
b
+ + −
+ − =
And it runs with a slip of (2-s). Under standstill condition, Vf=Vb, but under running
conditions Vf is almost 90 to 95% of the applied voltage.
The forward torque in synchronous watts is
s
I r
Tf
2
2
3 = . Similarly, backward torque
is
s
I r
Tb − = 2
2
2
5 . The total torque is
(2 )
2 ( )
(2 )
(2 )
2
2
5
2
3
2
3
2
2
5
2
3
2
2
2
2 5
2
3
s s
I s I I
r
s s
I s I s
r
s
I r
s
I r
T Tf Tb −
− + = −
− − = − = − = − .
Equivalent Circuit of a Single-Phase Induction Motor with Core Loss