Why the 3 phase squirrel cage induction motors burned when running at low voltage?

As a professional 3 phase squirrel cage induction motor manufacturer and repairer, Shandong Langrui Motor Factory has many years of industry experience. It once received an inexplicable customer, of course because the motor repaired by Shandong Langrui Motor Factory is good. He said that the three phase squirrel cage induction motor burned out after a long time. He found someone to repair it locally, and it burned up after a short time. Later, he heard from friends that the motor repaired by Shandong Langrui Motor Factory will not break. Here it comes. We opened the motor for inspection and the winding appeared to be overloaded. As soon as the customer was unhappy, the voltage there was about 340V, and the 380V motor could not be burned; our maintenance engineer explained patiently and made a more appropriate analogy: it will be tiring to carry a sack with a hungry stomach dead! We can repair the three-phase squirrel-cage induction motor, but if the voltage is not adjusted, it will soon be broken. After the motor is repaired, the customer solves the voltage problem, and we boast that the motor repaired by our motor factory is good.

About The Rated Voltage and Frequency

Any kind of electrical appliance will have the requirement of rated voltage. During the actual operation, the electrical appliance will work normally within the normal fluctuation range, otherwise it will cause failure. The power supply frequency used in China is 50Hz, and the frequency deviation range is generally specified as ± 0.5Hz. Another example is the heat radiation light source. If the voltage is too high, its service life will be greatly shortened; if the voltage is too low, the light source illumination will be significantly dimmed, which seriously affects work efficiency and human vision health. It can be seen that grid voltage fluctuations will affect the normal operation and service life of electrical equipment. Therefore, the continuous, reliable voltage, frequency and power supply are the basic indicators of the power quality.

All electrical equipment in a power system has a rated operating voltage and frequency. The electrical equipment works best at its rated voltage and frequency. For example, A 3 phase squirrel cage induction motor, if the voltage is too high, although the torque increases, the current also increases, and the temperature increases, which will seriously damage the motor insulation and shorten the service life.

If the voltage is low, the torque will be reduced according to the voltage quadratic. When the load torque is required, the winding current will increase, and the motor insulation will be damaged, which shortens the service life. Low, it will also seriously affect the torque and service life of the three-phase squirrel cage induction motor.

Consequences of Voltage Failure

Changes in the power supply voltage that is too high or too low have an adverse effect on the three-phase induction motor. When the voltage is too high (more than 10%), the core magnetic circuit is saturated (because when the squirrel cage induction motor is designed and manufactured, the magnetic circuit at the rated voltage is generally near the saturation point). Therefore, the main magnetic flux the increase causes the exciting current to increase sharply (several times the value of the applied voltage), thereby increasing the stator current, and the 3 phase squirrel cage induction motor is overheated, causing the temperature rise to exceed the allowable value and burn out.

When the voltage is too low (below 5%), the torque of the three-phase squirrel-cage induction motor dropped in a voltage-squared relationship. One reduces the starting torque a lot, making the motor difficult to start (slow start or even start); two for a running motor, if the load is constant (during heavy or rated load operation), the rotor must maintain the necessary electromagnetic torque to balance the resistance torque of the load. This forces the rotor current to increase, which causes the stator current to increase, causing the motor to overheat, increasing the temperature rise, shortening the motor life, and even burning the squirrel cage induction motor.

When the voltage is too low (less than 5% or less), the motor torque dropped in a voltage-squared relationship. One causes the starting torque to decrease a lot, making the motor difficult to start (slow start or even start); the second is the running motor. If the load is constant (during heavy or rated load operation), the rotor must maintain the necessary electromagnetic torque to balance the load's resistive torque. This forces the rotor current to increase, which causes the stator current to increase, causing the motor to overheat, increasing the temperature rise, shortening the motor life, and even burning the motor.

Three-phase squirrel cage induction motors often start and run at low voltage. At this time, the load should be reduced or used intermittently. Generally, the voltage of squirrel-cage induction motors can fluctuate within the range of + 10% to -5%. If the power supply voltage is 380 volts, allow the motor to run for a long time between 418-361 volts.