Several situations where the motor current is too high

When the motor current is high, it is often manifested in the serious heating of the motor. The following 7 points basically summarize the reasons for the excessive motor current, let us learn from it.

National standard motor power supply problem

1. The power supply voltage is too high

When the power supply voltage is too high, the motor back electromotive force, magnetic flux and magnetic flux density will increase accordingly.Since the size of the iron loss is proportional to the square of the magnetic flux density, the iron loss increases, causing the core to overheat.The increase in magnetic flux also causes a sharp increase in the component of the excitation current, which increases the copper loss of the stator winding and causes the winding to overheat.Therefore, when the power supply voltage exceeds the rated voltage of the motor, the motor will overheat.

2. The power supply voltage is too low

When the power supply voltage is too low, if the electromagnetic torque of the motor remains unchanged, the magnetic flux will decrease, and the rotor current will increase accordingly, and the load power component in the stator current will increase accordingly, causing the copper loss of the winding to increase, resulting in the stator and rotor The winding is overheated.

3. Asymmetrical power supply voltage

When one phase of the power cord is broken, the fuse is blown in one phase, or the corner of the knife starting device is burned and one phase is blocked, it will cause the three-phase motor to go single-phase, causing the running two-phase winding to overheat through high current and even burn out.

 

 

Therefore, fuse protection is generally not suitable for three-phase motors.

4. Unbalanced three-phase power supply

When the three-phase power supply is unbalanced, the three-phase current of the motor will be unbalanced, causing the winding to overheat.

It can be seen from the above that when the motor is overheated, the power supply should be considered first (soft start, frequency converter, and servo drive can also be regarded as power supply).After confirming that there is no problem with the power supply, then consider other factors.

Power problem

1. Motor overload operation

When the equipment is not matched and the load power of the motor is greater than the rated power of the motor, the motor will be overloaded for a long time (that is, the small horse-drawn cart), which will cause the motor to overheat.When repairing an overheated motor, you should first find out whether the load power is consistent with the motor power to prevent blind and unintended disassembly.

2. The dragging mechanical load is not working properly

Although the equipment is matched, the mechanical load to be driven is not working properly, the load is sometimes large and sometimes small during operation, and the motor is overloaded and heats up.Three-phase asynchronous motor When the three-phase stator windings of the motor (each phase differs by 120 degrees in electrical angle), after the three-phase symmetrical alternating current is applied, a rotating magnetic field will be generated. The rotating magnetic field cuts the rotor winding, thereby generating an induced current in the rotor winding ( The rotor winding is a closed path), the current-carrying rotor conductor will generate electromagnetic force under the action of the stator rotating magnetic field, thereby forming an electromagnetic torque on the motor shaft to drive the motor to rotate, and the direction of the motor rotation is the same as the direction of the rotating magnetic field.

3. The dragging machinery is faulty

When the machine being dragged is faulty, inflexible in rotation or stuck, it will overload the motor and cause the motor windings to overheat.Therefore, when the motor is overheated, the load factor cannot be ignored.

Problems with the motor itself

1. Open circuit of motor winding

When one of the windings of the motor is open, or one of the parallel branches is open, it will cause the three-phase current to be unbalanced and cause the motor to overheat.

2. Short circuit of motor winding

When the motor winding has a short-circuit fault, the short-circuit current is much larger than the normal working current, which increases the copper loss of the winding, and causes the winding to overheat or even burn.

3. Wrong connection of motor star angle

When the delta connection motor is wrongly connected in a star shape, the motor is still running with full load, and the current flowing through the stator winding will exceed the rated current, and even cause the motor to stop by itself. If the stop time is a little longer and the power supply is not cut off, the winding is not only serious Overheating, it will burn.When a star-connected motor is wrongly connected to form a triangle, or a motor with several coil groups connected in series into a branch is connected to two branches in parallel, the winding and the iron core will be overheated, and the winding will be burnt in severe cases.

4. Wrong connection of motor coil

When a coil, coil group or one-phase winding is connected reversely, it will cause serious imbalance of the three-phase current and overheat the winding.

5. Mechanical failure of the motor

When the motor shaft is bent, the assembly is not good, the bearing is defective, etc., the motor current will increase, copper loss and mechanical friction loss will increase, and the motor will overheat.

Ventilation and heat dissipation problems

1. The ambient temperature is too high, making the inlet air temperature high.

2. The air inlet is blocked by debris, which makes the air inlet difficult, resulting in a small amount of air inlet.

3. Excessive dust inside the motor affects heat dissipation.Compared with single-phase asynchronous motors, three-phase asynchronous motors have better running performance and can save various materials.According to different rotor structures, three-phase asynchronous motors can be divided into two types: cage type and winding type.

4. The fan is damaged or installed reversely, resulting in no wind or small air volume.

5. There is no wind shield or no wind baffle in the motor end cover, resulting in the motor without a certain air path.

other problems

 

　　1. 

Repair motor problems

The starting current of the repaired motor is more than 66%, and the frequent operation of the motor will also cause the current to be high and cause the motor to overheat.

 

　　2. Series resistance problem

Wound-type motors do not match with series-connected resistors. At the same time, frequent operation of the motor will also cause high current and cause the motor to overheat.

 

　　3. Motor vibration problem

Excessive motor vibration may also cause high motor current. Reasons and treatment methods:

1. Rotor unbalance-leveling balance

2. Unbalanced pulley or bent shaft extension-check and correct

3. The axis of the motor and the load are not aligned-check and adjust the axis of the unit

4. Improper installation of the motor-check the installation situation and foot screws

5. Suddenly the load is too heavy-reduce the load