To determine the equivalent circuit parameters of a single phase induction motor by performing the no-load and blocked rotor tests.

Aim

To determine the equivalent circuit parameters of a single phase induction motor by performing the no-load and blocked rotor tests.

Apparatus 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:

1. The circuit connections are made as per the circuit diagram.
2. Be sure that variac (auto transformer) is set to zero output voltage position before starting the experiment.
3. Now switch ON the supply and close the DPST switch.
4. The variac is varied slowly, until rated voltage is applied to motor and rated speed is obtained.
5. Take the readings of Ammeter, Voltmeter and wattmeter in a tabular column.
6. The variac is brought to zero output voltage position after the experiment is done, and switch OFF the supply.

Blocked Rotor Test:

1. To conduct blocked rotor test, necessary meters are connected to suit the full load conditions of the motor.
2. Connections are made as per the circuit diagram.
3. Before starting the experiment variac (auto transformer) is set to zero output voltage position.
4. The rotor (shaft) of the motor is held tight with the rope around the brake drum.
5. Switch ON the supply, and variac is gradually varied till the rated current flows in the induction motor.
6. Readings of Voltmeter, Ammeter, and wattmeter are noted in a tabular column
7. The variac is brought to zero output voltage position after the experiment is done,and switch OFF the supply
8. 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 + X_M)

X_M=2(X₀ - X₁)-X₂

Calculation For Blocked Rotor Test:

Z_SC=V_SC /I_SC

R_SC= W_SC/I_SC

R₁is the DC Resistence of stator of Motor

R₂= R _SC– r₁

X₁+ X₂= X_SC

Since leakage reactance can can’t be separated out, It is common practice to to assume X₁= X ₂

X₁ = X ₂=X_SC/2 = X_SC1/2 √Z ²_SC- R²_SC

Observations:

For No-Load Test:

For Blocked Rotor Test:

Circuit diagram for measurement of R ₁

Procedure:

1. Connections are made as per the circuit diagram
2. Initially rheostat is set at maximum resistance position
3. Switch ON the supply, and vary the rheostat gradually and note down the readings of ammeter and voltmeter
4. For the corresponding values, average of r ₁is take

To find stator Resistance:

Average Value: R_DC R_ACR_DC = 1.1

Comments:

1. Since IM is not self starting Machine, it is started by placing an auxiliary winding in the circuit.
2. 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:

1. Why there is no starting torque in a single phase induction motor
2. What are different starting methods employed in single phase induction motors?
3. Compare the performance of capacitor-start, capacitor – run, shaded pole single phase induction motors?
4. Mention a few applications of single phase induction motors

Precautions:

1. Connections must be made tight
2. 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.