Analysis of Overheating Causes of Motor Body in Motor Maintenance

Motor Maintenance - Analysis of Causes for Overheating of Motor Body:

1) Power supply causes motor overheating and malfunctions:

① The power supply voltage is too high. When the power supply voltage is too high, the back electromotive force, magnetic flux, and magnetic flux density of the motor all increase accordingly. Due to the fact that the magnitude of iron loss is proportional to the square of magnetic flux density, the iron loss increases, leading to overheating of the iron core. And the increase in magnetic flux leads to a sharp increase in the excitation current component, causing an increase in copper loss in stator winding 1 and overheating of the winding. Therefore, when the power supply voltage exceeds the rated voltage of the motor, it will cause the motor to 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 constant, the magnetic flux will decrease, the rotor current will increase accordingly, and the load power component in the stator current will increase, causing an increase in copper loss in the winding and overheating of the stator and rotor windings.

③ Asymmetric power supply voltage. When one phase of the power cord is broken, one phase of the fuse is blown, or the corner of the switch starting equipment is burned, causing one phase to not be connected, it will cause the three-phase motor to run single-phase, causing the two-phase winding to overheat and even burn out due to high current.

④  The three-phase power supply is unbalanced. When the three-phase power supply is unbalanced, it will cause the three-phase current of the motor to be unbalanced, causing the winding to overheat.

2) The reasons for motor overheating caused by load are as follows:

① Overloaded operation of the electric motor. 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 operate under overload for a long time (i.e. a small horse pulling a large car), which will cause the motor to overheat. When repairing an overheated motor, it is necessary to first determine whether the load power matches the motor power to prevent blind and aimless disassembly.

② The mechanical load being dragged is not working properly. Although the equipment is matched, the mechanical load it drags is not working properly. During operation, the load varies greatly, such as when the feeding amount of the thresher is too large, the motor is overloaded and heats up.

③ The dragging mechanism is malfunctioning. When the dragged machinery malfunctions, rotates inflexibly or gets stuck, it will overload the motor and cause the motor winding to overheat.

3) The reasons for overheating caused by the motor itself are as follows:

① The motor winding is open circuited. When one phase of the motor winding is broken or one branch of the parallel branch is broken, it will cause three-phase current imbalance and cause the motor to overheat.

② The motor winding is short circuited. When a short circuit fault occurs in the motor winding, the short-circuit current is much higher than the normal operating current, which increases the copper loss of the winding, causing it to overheat or even burn out.

③ The motor connection is incorrect. When the delta connected motor is misconnected into a star shape, the motor still runs at full load, and the current flowing through the stator winding will exceed the rated current, even causing the motor to stop on its own. If the stopping time is slightly longer and the power is not cut off, the winding will not only overheat severely, but also burn out. When a star connected motor is misconnected into a triangle, or when several coil groups are connected in series as one branch of the motor are misconnected into two parallel branches, it will cause the winding and iron core to overheat, and in severe cases, it will burn out the winding.