Effects of opening one line conductor of a 3-phase induction motor

Introduction:
A 3-phase induction motor is a type of motor that operates on a three-phase power supply. It consists of three sets of windings, each placed 120 degrees apart from each other. When one line conductor of a 3-phase induction motor is opened, it will have certain effects on the motor's operation.

Effect:
The correct answer to the question is option 'B': "Motor will run as a single-phase induction motor for some time". This means that when one line conductor is opened, the motor will continue to function but will operate in a different manner.

Explanation:
When a 3-phase induction motor operates normally, a rotating magnetic field is created by the interaction of the three phase windings. This rotating magnetic field induces a current in the rotor windings, which in turn produces a torque and causes the motor to rotate.

However, when one line conductor is opened, the balanced three-phase supply gets disrupted. This leads to several changes in the motor's behavior:

1. Loss of torque: The rotating magnetic field created by the three-phase supply becomes imbalanced. This results in a reduction in the torque produced by the motor.

2. Unbalanced current: As one line conductor is opened, the remaining two lines will continue to supply power to the motor. However, the current in these lines becomes unbalanced, causing an increase in current and resulting in additional heating of the motor windings.

3. Change in direction: Due to the imbalance in the magnetic field, the motor may change its direction of rotation. This can be unpredictable and may vary depending on the motor's design and load conditions.

4. Overheating: The unbalanced current and reduced torque can cause excessive heating in the motor. This can lead to insulation damage, winding failure, and ultimately motor burnout if not rectified promptly.

5. Operation as a single-phase motor: Despite the imbalances and changes in behavior, the motor can still continue to operate. It will function as a single-phase induction motor instead of a three-phase motor. However, the performance will be significantly reduced, and the motor may not be able to handle heavy loads.

Conclusion:
When one line conductor of a 3-phase induction motor is opened, the motor will continue to run but in a different manner. It will operate as a single-phase induction motor for some time, but with reduced torque and increased risk of overheating. It is crucial to rectify the issue and restore the balanced three-phase supply to ensure proper motor operation and prevent damage.