EFFECT UNBALANCE VOLTAGE IN MOTOR

Voltage Unbalance - A motor that gets an unbalanced power supply will cause an imbalance of the current flowing to the motor stator winding. Even though the percentage of voltage imbalance is small (Percent Voltage Unbalance), it can cause a large percentage of the imbalance current flowing into the motor stator winding, so that it can increase the temperature rise of the motor which in turn can cause disturbances to the motor. It is better if the input voltage to the motorbike must be evenly distributed, if the voltage is not balanced (Voltage Unbalance), this will also cause a decrease in motor power which is proportional to the percentage of supply voltage imbalance, such as a graph of the effect of voltage umbalance (unbalanced voltage) on the decrease in motor power below. this:

To calculate the percentage of unbalanced voltage (Percent Voltage Unbalance) you can use the following formula:

Percent Unbalance = 100 x Max. Volt Deviation From Average Volt. / Average Volt.

Example of Percent Unbalance Voltage:

For example, if a three-phase motor with a power of 100 kW operates with input voltages of 380, 372 and 395, the Percent Unbalance of the motor input voltage is:

                   

applied to the running motor terminals:

    ➤ Average Voltage = (380 + 372 + 395) / 3

    ➤Average Voltage = 382 V

    ➤ Max. Voltage Deviation = 15 V

    ➤ Percent Unalance = 100 x 15/382

    ➤Percent Unalance = 3.9%

When viewed from the graph: Percent Voltage Unbalance at the point of 3.9%, it will make the Derating Factor around 0.84 which means about 84 kW against the Rated Power Motor 100 kW. This indicates that with a Percent Unbalance of around 4%, a 100 kW motor can only be charged around 84 kW to prevent damage to the motor. 

Important notes from the chart above:

Do not operate the motor with the Unbalance Voltage Percentage above 5%

Besides the motor experiencing power derating, the voltage unbalance (Voltage Unbalance) will also produce an effect that affects the performance characteristics of the motor, as follows:

Torque Characteristics: Unbalanced voltage will reduce the motor rotor lock value and the motor torque

Characteristics of Full-Load Speed: Unbalanced voltage will result in a slight decrease in the Full-Load - Speed parameter of the motor.

Motor Current: Unbalanced Voltage (Voltage Unbalance will increase the imbalance 6 to 10 times at full load current).

Temperature: From the results of research and experience in the field, the percentage of unbalanced voltage (Percent Voltage Unbalance) up to 3.5% will cause the motor temperature to rise by 25%.