Electrical Machines 2 Lab Experiments
To determine the equivalent circuit parameters of a single phase induction motor by performing the no-load and blocked rotor tests.
Sep 24 2023
Aim
To determine the equivalent circuit parameters of a single phase induction motor by performing the no-load and blocked rotor tests.
Apparatus Required:
S.no |
Equipment |
Type |
Range |
Quantity |
1 |
Voltmeter |
MI |
(0-300)V |
1nos |
2 |
Ammeter |
MI |
(0-10)A |
1nos |
3 |
Wattmeter |
Dynamo type |
(0-300V) LPF (0-10)A |
1nos |
4 |
Wattmeter |
Dynamo type |
(0-150V) UPF (0-10)A |
1no |
5 |
Connecting Wires |
-- |
(0-20)A |
Required |
1 - ɸ Induction motor specifications:
Name plate details:-
1Ф Induction motor
Rated power:2HP
Rated voltage:220V
Current:8A
Speed(RPM) 1500rpm
Cos ɸ (pf) Lagging
Frequency 50Hz
Rotor Squirrel Cage
Circuit Diagram:
Procedure:
No load Test:
- The circuit connections are made as per the circuit diagram.
- Be sure that variac (auto transformer) is set to zero output voltage position before starting the experiment.
- Now switch ON the supply and close the DPST switch.
- The variac is varied slowly, until rated voltage is applied to motor and rated speed is obtained.
- Take the readings of Ammeter, Voltmeter and wattmeter in a tabular column.
- The variac is brought to zero output voltage position after the experiment is done, and switch OFF the supply.
Blocked Rotor Test:
- To conduct blocked rotor test, necessary meters are connected to suit the full load conditions of the motor.
- Connections are made as per the circuit diagram.
- Before starting the experiment variac (auto transformer) is set to zero output voltage position.
- The rotor (shaft) of the motor is held tight with the rope around the brake drum.
- Switch ON the supply, and variac is gradually varied till the rated current flows in the induction motor.
- Readings of Voltmeter, Ammeter, and wattmeter are noted in a tabular column
- The variac is brought to zero output voltage position after the experiment is done,and switch OFF the supply
- Loosen the rope after the experiment is done
Calculation for No-Load Test:
V0I0 Cosɸ= W0
Cosɸ= W0/V0I0
Z0=V0/I0
X0=Z0Sinɸ0
X0=X1 + 1/2 (X2 + XM)
XM=2(X0 - X1)-X2
Calculation For Blocked Rotor Test:
ZSC=VSC /ISC
RSC= WSC/ISC
R1is the DC Resistence of stator of Motor
R2= R SC– r1
X1+ X2= XSC
Since leakage reactance can can’t be separated out, It is common practice to to assume X1= X 2
X1 = X 2=XSC/2 = XSC1/2 √Z 2SC- R2SC
Observations:
For No-Load Test:
S.no |
Voltmeter reading V 0 |
Ammeter reading I 0 |
Wattmeter reading W0 |
cosΦ0= V0I0 |
1 |
220 |
2 |
80*2=160 |
0.3636 |
For Blocked Rotor Test:
S.no |
Voltmeter reading V SC |
Ammeter reading I SC |
Wattmeter reading WSC |
cosΦSC |
1 |
38 |
8 |
130*2=260 |
0.855 |
Circuit diagram for measurement of R 1
Procedure:
- Connections are made as per the circuit diagram
- Initially rheostat is set at maximum resistance position
- Switch ON the supply, and vary the rheostat gradually and note down the readings of ammeter and voltmeter
- For the corresponding values, average of r 1is take
To find stator Resistance:
S.no |
V(volts) |
I(Amps) |
R = V/IΩ |
1 |
5 |
4.76 |
1.05 |
2 |
10 |
9.09 |
1.1 |
3 |
15 |
13.39 |
1.12 |
4 |
18 |
15.65 |
1.15 |
5 |
20 |
18.18 |
1.1 |
Average Value: RDC RACRDC = 1.1
Comments:
- Since IM is not self starting Machine, it is started by placing an auxiliary winding in the circuit.
- Here no-load test is similar to open circuiting the load terminals and blocking the rotor is similar to conducting short circuit on the IM.
Viva Questions:
- Why there is no starting torque in a single phase induction motor
- What are different starting methods employed in single phase induction motors?
- Compare the performance of capacitor-start, capacitor – run, shaded pole single phase induction motors?
- Mention a few applications of single phase induction motors
Precautions:
- Connections must be made tight
- Before making or breaking the circuit, supply must be switched off
Result:Equivalent circuit parameters of 1-Φ Induction motor are determined by using No Load and blocked rotor tests.