Blocked Rotor Test
Blocked Rotor Test:
Blocked rotor test is also known as locked-rotor or short-circuit test. This test is used to find–
1. short-circuit current with normal voltage applied to stator
2. power factor on short-circuit. Both the values are used in the construction of circle diagram
3. total leakage reactance X01 of the motor as referred to primary (i.e. stator)
4. total resistance of the motor R01 as referred to primary.
In this test, the rotor is locked (or allowed very slow rotation) and the rotor windings are short-circuited at slip-rings, if the motor has a wound rotor. Just as in the case of a short-circuit test on a transformer, a reduced voltage (up to 15 or 20 per cent of normal value) is applied to the stator terminals and is so adjusted that full-load current flows in the stator.
As in this case s = 1, the equivalent circuit of the motor is exactly like a transformer, having a short circuited secondary. The values of current, voltage and power input on short-circuit are measured by the ammeter, voltmeter and wattmeter connected in the circuits as before.