Contents
How do you calculate current imbalance?
There are three steps in the calculation:
- Determine the voltage or current average.
- Calculate the largest voltage or current deviation.
- 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 a current imbalance?
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.
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 is the maximum allowable current imbalance in a three phase supply?
2 percent
Voltage unbalance exceeding more than 2 percent in three-phase systems can cause current unbalance among the windings. These, in turn, can cause an increase in winding temperature and an overheating problem that can be harmful to the motor.
How to calculate voltage unbalance on an amp?
We could also estimate it from current measurements. For purposes of estimating voltage unbalance, it is conservative to assume that all current unbalance results from voltage unbalance. Given that your current is on the order of 75% full load current, using the figure at the bottom here (looking between the no-load and full-load regions)
Can a voltage drop cause an unbalanced current?
Unbalanced loads can result in unbalanced voltages, which are causal factors for unbalanced currents. Voltage drop across contacts typically does not result in voltage unbalance exceeding the action level of 1% for motors. How about an article about “Sustained Overvoltage Conditions”?
What is the unbalance of a full load amp?
Given that your current is on the order of 75% full load current, using the figure at the bottom here (looking between the no-load and full-load regions) … we estimate voltage unbalance would be a factor of 10 less than current unbalance or approx 0.5%.
Is there a limit to current imbalance on NEMA?
Yes. NEMA limits voltage imbalance, not current imbalance. They suggest derating the motor above 1% voltage imbalance (derating is not a problem as long as motor is not operating near full load). They suggest not operating the motor above 5% voltage unbalance.