Effects of Supply Voltage on Motor Current

Voltage is a very important performance parameter of motor products; in order to ensure the normal operation of the motor, the power supply voltage of the motor should meet the requirements of the rated voltage of the motor, otherwise it will cause the motor to fail to output normally, and even the winding will be burned. Serious consequences.

The range of motor voltage deviation is usually based on national standards and manufacturer technical documents. For AC motors, such as induction motors and synchronous motors, the allowable voltage deviation is generally controlled between ±5% and ±10% of the rated voltage. When the voltage deviates for a long time, different states of the motor will correspond to different consequences. When the motor is in the no-load operation state, the no-load current of the motor is positively correlated with the voltage, that is, the higher the input voltage of the motor, the greater the corresponding no-load current. It can be directly verified in the inspection test of the motor that the increase in the no-load current is greater than the increase in the voltage; the most common is that when the star-connected motor is powered by the triangle connection method, the no-load current becomes larger and the motor is accompanied by a dull “buzzing” sound, and the winding will burn down in a short time.

When the motor is running with load, if the input voltage of the motor is low, in order to drive the load to run, especially when the rated power is running, the stator current and rotor current of the motor will increase, resulting in increased losses; at the same time, the speed of the motor will decrease to varying degrees. For self-fan-cooled motors, due to the dual adverse effects of reduced motor speed and increased winding temperature, the motor temperature rise is too high and the winding insulation is aging and burned. For power-frequency motors that start directly, a lower voltage will cause the motor to fail to start.

The same is for on-load operation. If the input voltage of the motor is higher than the rated voltage, the stator current will decrease. This can be qualitatively compared with the relationship between the stator current of the high and low-power motor; however, the higher voltage input will increase the inter-turn voltage of the motor winding, which directly threatens the insulation performance of the winding, and the motor winding will heat up or even burn down because of the breakdown of the inter-turn insulation.

Therefore, relative to the rated voltage, regardless of whether the input voltage is high or low, there are greater hidden dangers of failure for motors running on load. When applying motors, special attention should be paid to the compliance of the basic parameters of the rated operation of the motor.