Why is blocked rotor test done in induction motor?

A blocked rotor test is normally performed on an induction motor to find out the leakage impedance. Apart from it, other parameters such as torque, motor, short-circuit current at normal voltage, and many more could be found from this test. Blocked rotor test is analogous to the short circuit test of transformer.

What is blocked rotor test in induction motor?

A blocked rotor test is conducted on an induction motor. It is also known as short circuit test, locked rotor test or stalled torque test. From this test, short circuit current at normal voltage, power factor on short circuit, total leakage reactance, and starting torque of the motor can be found.

What is the purpose of no load and blocked rotor test?

1. To obtain the variation of no load power and current and blocked rotor power and current with changes in the applied voltage to the stator. 2. To determine the equivalent circuit parameters of an induction motor.

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How do you test an induction motor rotor?

HIGH CURRENT ROTOR TEST – This test is performed by applying high current through the shaft of the rotor (rotor out of stator) and thermally scanning (infrared or thermoscan) the rotor O.D. searching for shorted laminations. These shorted laminations cause localized hot spots which cause uneven heating of the rotor.

How does a locked rotor test conducted?

The Blocked Rotor Test of an induction motor is similar to the short circuit test of a transformer. In this test, the shaft of the motor is locked so that it cannot move and the rotor winding is short-circuited. In the slip ring motor, the rotor winding is short-circuited through the slip rings.

Why is blocked rotor test performed at reduced frequency?

Thus, the blocked rotor test should be performed at a reduced stator frequency because the effective resistance and the leakage reactance of the rotor at the reduced frequency may differ considerably from their values at the rated frequency.

When the rotor of an induction motor is blocked the slip is?

When rotor of three-phase induction motor is blocked, the value of slip is. When rotor of three-phase induction motor is blocked, the value of slip is: 0.1.

Why Blocked Rotor Test is called as short circuit test?

It is also known as short-circuit test (because it is the mechanical analogy of a transformer short-circuit test), locked rotor test or stalled torque test. From this test, short-circuit current at normal voltage, power factor on short circuit, total leakage reactance, and starting torque of the motor can be found.

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What will be the efficiency of the induction motor under no load and blocked rotor condition?

Since the power factor of the induction motor under a no-load condition is generally less than 0.5, one wattmeter will show a negative reading. Therefore, it is, necessary to reverse the direction of current-coil terminals to take the reading.

How can the Blocked Rotor Test be performed to obtain induction motor characteristics in synchronous speed?

As in Transformer short circuit test, we apply a voltage which can circulate rated current in the winding, likewise in Blocked Rotor Test we apply a Voltage to the Stator winding of an Induction Motor by using VARIAC so that rated current flows through the stator winding.

How do I test my rotors?

The AC impedance test is used to find indications of shorted rotor turns. The test is performed by means of applying an AC voltage across the field winding and raising it in 10-volt steps up to 100-120 volts, or till the current supply gets maxed out.

What is pi test of motor?

Polarization index (PI) testing is an extension of the insulation resistance test and is designed to check specific issues in a motor such as moisture and insulation deterioration.

What is load test of induction motor?

The load test on induction motor is performed to compute its complete performance i.e. torque, slip, efficiency, power factor etc.

What is locked rotor power factor?

You mean power factor of induction motor when rotor is blocked. Under such condition, the motor behaves as a transformer with its secondary short circuited. Therefore the power factor is near zero because current is limited mainly by stator and rotor leakage reactances.

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What is locked rotor torque?

The locked rotor torque is the torque the electrical motor develops when its starts at rest or zero speed. The magnitude of the locked rotor current is determined by motor horsepower and design characteristics. Normally, it will be six to seven times of the motor full-load current.