No-Load and Blocked Rotor Test on 3-ф Induction Motor
AIM: To conduct No-Load and Blocked-Rotor Test on 3-ф Induction Motor and determine its
equivalent circuit parameters.
APPARATUS REQUIRED:
SL No.
1
2
3
4
5
6
7
Name
Wattmeter
Ammeter
Voltmeter
Tachometer
3 phase variac
Starter
Connecting Wires
Range
CONNECTION DIAGRAM FOR NO-LOAD TEST:
Figure 1
Name Plate Details:
1. hp/kW rating:
2. Rated Current:
3. Rated Voltage:
4. Rated Speed:
5. Frequency:
Type
Quantity
CONNECTION DIAGRAM FOR BLOCKED-ROTOR TEST:
PROCEDURE:
(a) No-Load Test:
1.
2.
3.
4.
Connect the circuit as shown in the connection diagram in Figure 1.
Start the motor by ensuring the shaft is at no load condition.
For starting, either use autotransformer or starter to reach rated voltage.
Note the readings of voltmeter, ammeter and wattmeter by carefully noting its multiplying
factor.
5. Reduce the voltage using autotransformer to zero and turn the main switch off.
(b) Blocked-Rotor Test:
1.
2.
3.
4.
Connect the circuit as shown in the connection diagram in Figure 2.
Before starting, ensure that the shaft is blocked completely from rotating.
Using the 3-ф variac, increase the voltage to the machine such that it draws rated current.
Note the readings of voltmeter, ammeter and wattmeter by carefully noting its multiplying
factor. Take the readings quickly so that the machine does not heat up due to full load copper
losses taking place at this condition.
5. Reduce the voltage using autotransformer to zero and turn the main switch off.
OBSERVATION COLOUMN:
(i)
SL.
No
Voltage
VNL
(volts)
(ii)
SL.
No
Voltage
VBR
(volts)
No-Load Test:
Current INL
(amperes)
Wattmeter
W1 (watts)
Actual
powerW1act=
W1*M.F.
(watts)
Wattmeter
W2 (watts)
Actual
powerW2act=
W2*M.F.
(watts)
Total No-load
Power
Wo=W1+W2
(watts)
Actual
powerW1act=
W1*M.F.
(watts)
Wattmeter
W2 (watts)
Actual
powerW2act=
W2*M.F.
(watts)
Total Power
WBR= W1+W2
(watts)
Blocked-Rotor Test:
Current IBR
(amperes)
Wattmeter
W1 (watts)
CALCULATIONS:
(i)
From No-Load Test:
No-load power factor, cosфo=
(ii)
→ фo=
√
Iw /ph=Io/ph*cosфo
Iµ/ph=Io/ph*sinфo
Ro/ph=
Xo/ph=
From Blocked-Rotor Test:
WBR= 3*(IBR/ph)2*R01/ph
Z01/ph=
→
→
R01/ph=
X01/ph=√
√