1. NO LOAD TEST:
1. No load power factor (CosФ0) = W0/ V0I0
Where W0= No load power in watts
V0= No load voltage in volts.
I0= No load current in amps
2.Working component current (Iw) = I0CosФ0amps
3.Magnetizing component current (Im) = I0SinФ0amps
4. No load resistance R0= V0/ Iwohm
5. No load reactance X0= V0/ Imohm
BLOCKED ROTOR TEST:
6.Motor equivalent impedance referred to stator Zsc = (Vsc / Isc) ohm
7.Motor equivalent resistance referred to stator Rsc = ZscCosФsc ohm= Wsc / Isc2ohm
8.Power factor CosФsc = Wsc / VscIsc
9.Motor equivalent reactance referred to stator Xsc = √Zsc 2 – Rsc2ohm
10.Rotor resistance referred to stator R 2’= Rsc – R 1ohm
11.Rotor reactance referred to stator X2’= Xsc / 2 = X1ohm
Where R1= Rac = 1.6 *RdcR 1= stator resistance
X1= stator reactance
12.Magnetizing reactance Xm = 2(Xo –X1– X2’/2)
13.Slip = (Ns-N)/NsNs = synchronous speed in rpm N = speed of the motor in rpm
THEORY:
Theequivalent circuit of a single phase induction motor can be developed by usingdouble field
revolving theory. By using the equivalent circuit the performance of the single phase induction
motor can be obtained.
The single phase induction motor can be visualized to be made of single stator winding and two
imaginary rotors. The developing torques of the induction motor is forwardtorque and backward
torque.
When the single phase induction motor is running in the direction of forwardrevolving field at a
slip S, then the rotor currents induced by the forward field has frequencysf. The rotor mmf
rotates at slip speed with respect to the rotor but at synchronous speed withrespect to the stator.
The resultant forward stator flux and the rotor flux produce a forward air gap flux. This flux
induces the voltage in rotor. Thus due to the forward flux, the rotor circuitreferred to stator has
an impedance of R2’ /2s + jX2’/2.
The backward flux induces a current in the rotor at a frequency (2-s)f. thecorresponding rotor
mmf rotates in the air gap at synchronous speed in the backwarddirection. The resultant
backward stator flux and the rotor flux produce a backward airgapflux. This flux induces the
voltage in rotor. Thus due to backward flux the rotor circuitreferred to stator has an impedance of
R2’/2(2-s )+ jX2’/2

2. An induction motor is simply an electric transformer whose magnetic circuit is separated by an
air gap into two relatively movable portions, one carrying the primary and the other the
secondary winding. Alternating current supplied to the primary winding induces an opposing
current in the secondary winding, when later is short circuited or closed through an external
impedance. Relative motion between the primary and secondary ie, stator and rotor is produced
by the electromagnetic forces corresponding to the power thus transferred across the air gap by
induction.
Equivalent load resistance (RL = R 2’ (1/S -1) in ohm
1 1
V 0 R L R2 1 1
s s
Swinburne’s test theory
The field coil and the armature windings are connected in shunt or parallel across the power
source. The armature winding consists of relatively few turns of heavy gauge wire. The voltage
across two windings is the same but the armature draws considerably more current than the field
coil. Torque is caused by the interaction of the current carrying armature winding with the
magnetic field produced by the field coil. If the DC line voltage is constant, the armature voltage
and the field strength will be constant. The speed regulation is quite good; the speed is a function
of armature current and is not precisely constant. As the armature rotates within the magnetic
field, an EMF is induced in its wining. This EMF is in the direction opposite to the source EMF
and is called the counter EMF (CEMF), which varies with rotational speed. Finally, the current
flow through the armature winding is a result of the difference between source EMF and CEMF.
When the load increases, the motor tends to slow down and less CEMF is induced, which in turn
increases the armature current providing more torque for the increased load.
Motor speed is increased by inserting resistance into the field coil circuit, which weakens the
magnetic field. Therefore, the speed can be increased from “basic” or full-load, full-field value to
some maximum speed set by the electrical and mechanical limitations of the motor. The power
difference between the motor input and the output is dissipated in form of heat and constitutes to
the losses of the machine. These losses increase with load, since the motor heats up as it delivers
mechanical power.

3. D.C. Shunt Motor
H.P Voltage Current Speed Field current Excitation current Winding type
D.C. Shunt Motor
H.P / KW Voltage Current Speed Field current Excitation current Winding type
rating
Sumpners test
The O.C and S.C. tests give us the equivalent circuit parameters but cannot give heating
information under various load conditions. The Sumpner’s test gives heating information also. In
O.C. test, there is no load on the transformer while in S.C. test also only fractional load gets
applied. In all in O.C. and S.C. tests, the loading conditions are absent. Hence the results are
inaccurate. In sumpner’s test, actual loading conditions are simulated hence the results obtained
are much more accurate. Thus Sumpner’s test is much improved method of predetermining
regulation and efficiency than
Scott test
With the help of Scott connection it is possible to obtain 2 – phase supply which is required for
furnaces or even three phase load can be driven from the available 2 – phase supply source.
No load and Blocked rotor test theoy
An induction motor is simply an electric transformer whose magnetic circuit is separated by an
air gap into two relatively movable portions, one carrying the primary and the other the
secondary winding. Alternating current supplied to the primary winding induces an opposing
current in the secondary winding, when later is short circuited or closed through an external
impedance. Relative motion between the primary and secondary ie, stator and rotor is produced
by the electromagnetic forces corresponding to the power thus transferred across the air gap by
induction

4. FORMULAE:
Torque T = (S1 S2) x R x 9.81 Nm
Input Power Pi = VI Watts
2 NT
Output Power Pm= ------------ Watts
60
Output Power
Efficiency % = -------------------- x 100%
1. Ammeter, Voltmeter readings, speed and spring balance readings are noted under no load
condition.
2. The load is then added to the motor gradually and for each load, voltmeter, ammeter,
spring balance readings and speed of the motor are noted.
3. The motor is then brought to no load condition and field rheostat to minimum position,
then DPST switch is opened.
PRECAUTIONS:
DC shunt motor should be started and stopped under no load condition.
Field rheostat should be kept in the minimum position.
Brake drum should be cooled with water when it is under load.