Experiment No.: 11
Aim of the Experiment: –
Applying short circuit (blocked rotor) test on three-phase induction motor.
Apparatus Required: –
| Sl. No. | Name | Specification | Quantity |
|---|---|---|---|
| 01 | Three phase Induction Motor | 400/440V, 50Hz, 6.9 A | 1 nos. |
| 02 | Voltmeter | (0-500)V, MI | 1 nos. |
| 03 | Ammeter | (0-5/10)A, MI | 1 nos. |
| 03 | Wattmeter | (0-750)W, 5/10A, 600V | 2 nos. |
| 04 | Tachometer | Digital Type | 1 nos. |
| 05 | Connecting wire | PVC insulated copper | as per required |
Circuit Diagram: –
Theory: –
Blocked rotor test is similar to the short circuit test on a transformer. It is performed to calculate the series parameters of the induction machine i.e., its leakage impedances. The rotor is blocked to prevent rotation and balanced voltages are applied to the stator terminals at a 25 percent of the rated voltage where the rated current is achieved. Under the reduced voltage condition and rated current, core loss and magnetizing component of the current are quite small percent of the total current, equivalent circuit reduces to the form shown in below.
The slip for the blocked rotor test is unity since the rotor is stationary. The resulting speed-dependent equivalent resistance r2’{(1/s)-1} goes to zero and the resistance of the rotor branch of the equivalent circuit becomes very small. Thus, the rotor current is much larger than current in the excitation branch of the circuit such that the excitation branch can be neglected. Voltage and power are measured at the motor input.
Procedures: –
- Connect the circuit as per circuit diagram.
- Keep the variac to be at zero output.
- First switch on the 3ф supply.
- Now, keeping the rotor still (block the rotor from running), slowly increase the autotransformer output until rated current flows (Typically, this happens at 25% of the rated voltage).
- Take the reading of voltmeter, ammeter ,wattmeter & speed on rated current.
Observation Table: –
| Sl. No. | Vbr ( in volts.) | Ibr (in Amps.) | W1 | W2 | Pbr= W1+W2 |
| 01 |
Calculation:
Conclusion: –
Written by student.