How do you calculate motor current imbalance?

There are three steps in the calculation:

1. Determine the voltage or current average.
2. Calculate the largest voltage or current deviation.
3. Divide the maximum deviation by the average voltage or current and multiply by 100 % unbalance = (Max deviation from average V or I/average V or I) x 100.

What causes current unbalance in motors?

Current unbalance can be due to the motor or the supply line. If the high current and low current readings follow the same line leads, the supply is the cause of the problem. If the high and low readings follow the motor leads, the motor is the source of the problem.

How do you test a motor drive?

Tests

1. Check the output of the drive focusing both on voltage to frequency ratio (V/F), and voltage modulation.
2. Check for voltage modulation using phase-to-phase measurements.
3. Check the steepness of the switching impulses indicated by the drive reading.
4. Test the switching frequency with phase to DC.

What is the maximum allowable current imbalance?

NEMA MG1 standard gives a maximum allowable voltage imbalance of 1%. If current imbalance exceeds 10%, the motor must be derated.

What are the disadvantages of an unbalanced power supply?

Vibration of Motor: The negative-sequence voltage caused by voltage imbalance produces opposite torque and leads to motor vibration and noise. Severe voltage imbalance may even result in motor collapse. Reduce Motor Life: Heat generated by Unbalance Voltage may also reduce the Motor life.

What will happen if motor runs in an unbalanced voltage?

A small amount of voltage unbalance may increase the current an excessive amount. The effect on the motor can be severe and the motor may overheat to the point of burnout. The voltages should be evenly balanced as closely as can be read on the usually available commercial voltmeter.

What is the first thing you should do when troubleshooting a motor?

For the supply, test first with the motor disconnect open and locked out. Use your megohmmeter to test the insulation resistance to ground….Final tests and procedures.

1. Listen for unusual noises.
2. Smell for smoke or hot insulation.
3. Feel the motor for excessive heat or vibration.
4. Look for possible obstructions.

What happens if phases are not balanced?

If the reactance of three phases is not same, it will result in varying current flowing in three phases and give out system unbalance. A current leakage from any phase through bearings or motor body provides floating earth at times, causing fluctuating current.

What is acceptable voltage imbalance?

Generally, the difference between the highest and the lowest voltages should not exceed 4% of the lowest voltage. Greater imbalances may cause overheating of components; especially motors; and intermittent shutdown of motor controllers.

What is the maximum allowable of current imbalance in a 3 phase system?

RE: Acceptable current unbalance in three-phase motor NEMA MG1 standard gives a maximum allowable voltage imbalance of 1%. If current imbalance exceeds 10%, the motor must be derated.

Can a motor be unbalanced at full load?

Yes, at full load. At no load current unbalance can be up to 20 times voltage unbalance. A common cause of current unbalance on a perfectly balanced supply is a slight eccentricity of the rotor. In practical terms, I would be happy to see the currents match so closely on a motor in the field.

What happens when there is a voltage imbalance in a motor?

What this means to technicians is that when there is excessive current draw caused by a voltage imbalance, the end result is that the motor will operate at a higher-then-normal temperature, which can lead to premature failure.

How to measure the unbalanced current in a circuit?

Then connect A to 1, B to 2, and C to 3, operate the motor, and measure the current in each line. Next, de-energize the motor and connect A to 3, B to 1, and C to 2, operate the motor, and again measure the current in each line.

What causes three phase imbalance in induction motor?

Three Phase Imbalance. When line voltages applied to a poly-phase induction motor are not exactly the same, unbalanced currents will flow in the stator winding, the magnitude depending upon the amount of unbalance. A small amount of voltage unbalance may increase the current an excessive amount.