Low voltage can reduce the capacity of transmission and transformation equipment, lower the charging power of transmission lines, cause large-scale power outages, shorten the service life of equipment, and even burn out electrical appliances.
When the voltage is too low (below 5%), the motor becomes shorter and the square relationship of the voltage decreases, resulting in a significant decrease in starting torque and difficulty in starting the motor (slow or even no starting);
Secondly, if the load of the running motor is constant (under heavy load or rated load), the rotor should maintain the necessary electromagnetic shortening to balance the resistance torque of the load. This forces an increase in rotor current, resulting in an increase in stator current, causing the motor to overheat, increase temperature rise, shorten motor life, and even burn out the motor. There are many situations where the motor starts and runs at low voltage, and the load should be minimized or used intermittently as much as possible. The motor voltage is generally allowed to fluctuate within the range of 10% to -5%. If the power supply voltage is 380 volts, the motor is allowed to run for a long time between 418 and 36 volts.

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