# Why is blocked rotor test done in induction motor?

Contents

## What is the purpose of a blocked rotor test?

This test is performed to determine the short circuit current with normal voltage applied to stator; power factor on short circuit; total equivalent of resistance and Reactance referred to stator.

## Why blocked rotor test is performed at reduced frequency?

In order to obtain accurate results, the Blocked Rotor Test is performed at a frequency 25 percent or less than the rated frequency. The leakage reactances at the rated frequency are obtained by considering that the reactance is proportional to the frequency.

## 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.

## What is the meaning of blocked rotor?

As the name of the test specifies, in Blocked Rotor Test, rotor of Induction Motor is blocked by external means so that it cannot rotate. The Blocked Rotor Test of Induction Motor is similar to the short circuit test of a transformer.

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## 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.

## What causes locked rotor?

Something as simple as a broken wire or weak capacitor can generate a lock rotor condition.

## Why is locked rotor current important?

The locked rotor current (information) is used to choose the overcurrent protection device (circuit breaker / fuse). An electrician has to install the correct breaker, or fuse, to prevent tripping on motor startup, as well as to protect the motor. Knowing the locked rotor current is certainly not useless.

## What information is learned in locked rotor test?

Sometimes it is called as blocked rotor test. This test is similar to the short circuit test in the transformers. In this test only small percentage of rated voltage of the motor is applied to the motor, and full load current is made to flow in the motor.

## 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.

## What information is learned in locked rotor test and no load test respectively?

Locked rotor test – finds the rotor parameters (R2, x2) and stator reactance (x1) . Divide the leakage reactances based on the NEMA design types. Use the following table. No-load Test – Finds magnetizing reactance and combined friction, core and windage power losses.

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