Adverse consequences of marine motors operating at deviations from rated voltage

Any electrical product, including energy-saving motor products, is specified with a rated voltage for normal operation. Any voltage deviation can have adverse consequences on the normal operation of electrical appliances.

For relatively high-end equipment, use necessary protective devices. When the power supply voltage is abnormal, cut off the power supply for protection. For very precise instruments, use a constant voltage power supply for adjustment. For energy-saving motor products, especially industrial energy-saving motor products, the possibility of using constant voltage devices is very small, and there are more situations of power-off protection.

For single-phase motors, there are only two situations: high and low voltage, while for three-phase motors, there is still a problem of voltage balance. The direct impact of these three voltage deviations is an increase in current or an imbalance in current.

The technical specifications for electric motors stipulate that the deviation of the rated voltage of the motor shall not exceed 10%, and the torque of the motor shall be proportional to the square of the terminal voltage of the motor. When the voltage is too high, the iron core of the energy-saving motor will be in a magnetic saturation state, and an increase in stator current will cause severe heating of the winding, even leading to quality problems such as burnt windings; In the case of low voltage, one issue is that there may be problems with starting energy-saving motors, especially for those operating under load. In order to meet the load operation of energy-saving motors, the current must also be increased, and the consequence of increased current is that the winding heats up or even burns out, especially during long-term low voltage operation, which is more serious.

Voltage imbalance in three-phase motors is a typical power supply problem. When the voltage is unbalanced, it will inevitably lead to an imbalance in the current of the energy-saving motor. The negative sequence component of the unbalanced voltage generates a magnetic field in the air gap of the energy-saving motor, which is opposite to the direction of rotation of the rotor. The small negative sequence component in the voltage may cause the current flowing through the winding to be much greater than the current at voltage balance. The frequency of the current flowing through the rotor wire rod is almost twice the rated frequency, so the current squeezing effect in the rotor wire rod causes the loss of the rotor winding to increase much more than that of the stator winding. The temperature rise of the stator winding is higher than that under the equilibrium voltage.

When the voltage is unbalanced, the locked rotor torque and torque of energy-saving motors will decrease. If the voltage imbalance is severe, the energy-saving motor will not work properly.

When the energy-saving motor operates at full load under unbalanced voltage, the slip rate increases with the increase of rotor additional loss, and the speed will slightly decrease. As the voltage (current) imbalance increases, the noise and vibration of energy-saving motors may increase. Vibration may damage energy-saving motors or the entire drive system.

To effectively identify the causes of uneven voltage in energy-saving motors, power supply voltage detection or current changes can be used. Most devices are equipped with voltage monitoring instruments, which can be analyzed through data comparison. In the absence of monitoring devices, regular testing or current measurement should be used; For energy-saving motors with forward and reverse rotation, the two-phase power supply lines can be arbitrarily changed without affecting the dragged equipment, and the current changes can be observed to indirectly analyze the voltage balance. After the problem of uneven voltage is eliminated, it may involve quality issues such as inter turn and inter phase.