Introduction:- Number of motor burns routinely and reason for motor burning is never very clearly find out. Motor can run without burning for life time of motor if all the reasons for motor burning are avoided.
Main reasons:- Motor winding burnt only because of temperature rise of winding. Reasons of high temperature of winding is heat produced in side of the motor. Heat is produced in winding of motor due to load current flowing in winding, Induced current flowing in rotor bars or winding..Heat generated in lamination due to hysteresis loss and eddy current loss. Some heat is generated in bearings due to friction. All the sources of heat, generate heat but motor dissipate that heat efficiently as all are considered in design.If any of heat source start generating more heat, temperature of motor will increase and ultimately motor will burn.
Motor protection with overload relay- When a motor operates at a higher load than designed it gets heated. The load current increases and thermal overload relay starts working. It takes some time to trip as per current time characteristics of thermal overload relay. By tripping motor it protects motor from burning. But in this way motor gets overheat hence winding wire and stator core starts loosing their properties. After many numbers of tripping winding wire insulation is failed and motor burnt. A better practice of thermal over load setting may be use to set thermal at 90 % of motor full load current. Some person use thermal setting slightly higher then running load of motor.To avoid such failure motor must be operated within there load capacity. In machines like belt conveyor, elevators etc mechanical equipment health must be maintained to reduces unwanted frictional load. Jamming of material near moving parts to be removed to reduce load.
Motor cleaning:-Motor body, cooling fins and cooling ducts are kept clean, All heat generated in motor will dissipated and motor temperature remains in safe limit This will improve motor cooling and hence the life of motor.
Bearings:- Bearing are maintained well lubricated so that bearings will run smoothly and their temperature lies within limit. If a motor run with dry bearing or some what jam or play in bearing, more heat will generate in bearing which will cause over heating of end shied and hence motor stator which will heat winding and ultimate motor burning takes place. Some times due to play in bearings stator core and rotor core starts rubbing each other which increases stator core temperature and hence causing winding burnt out.The load increases because of bearing problems or core rubbing is not too much to operate overload relay that's why in these problems motor does't trips with overload before winding burnt out.
Vibration in motor:- Due to misalignment or unbalance in rotating part vibration generates in motor. Due to vibration a relative motion starts taking place between winding and stator core, between adjacent turns of coils near over hang and between soldered joint and turns of coil. This rubbing of wire results in insulation failure and causing internal short circuit.This problem is also not sense by over load relay. It can be saved by keeping operation of motor vibration free. If any vibration observed, should be rectified by alignment, balancing or some foundation defects correction.
This is what I have seen in my field experience. If some one like to give more reason please feel welcome to comment because I really like to avoid motor burning.
Thanks
Main reasons:- Motor winding burnt only because of temperature rise of winding. Reasons of high temperature of winding is heat produced in side of the motor. Heat is produced in winding of motor due to load current flowing in winding, Induced current flowing in rotor bars or winding..Heat generated in lamination due to hysteresis loss and eddy current loss. Some heat is generated in bearings due to friction. All the sources of heat, generate heat but motor dissipate that heat efficiently as all are considered in design.If any of heat source start generating more heat, temperature of motor will increase and ultimately motor will burn.
Motor protection with overload relay- When a motor operates at a higher load than designed it gets heated. The load current increases and thermal overload relay starts working. It takes some time to trip as per current time characteristics of thermal overload relay. By tripping motor it protects motor from burning. But in this way motor gets overheat hence winding wire and stator core starts loosing their properties. After many numbers of tripping winding wire insulation is failed and motor burnt. A better practice of thermal over load setting may be use to set thermal at 90 % of motor full load current. Some person use thermal setting slightly higher then running load of motor.To avoid such failure motor must be operated within there load capacity. In machines like belt conveyor, elevators etc mechanical equipment health must be maintained to reduces unwanted frictional load. Jamming of material near moving parts to be removed to reduce load.
Motor cleaning:-Motor body, cooling fins and cooling ducts are kept clean, All heat generated in motor will dissipated and motor temperature remains in safe limit This will improve motor cooling and hence the life of motor.
Bearings:- Bearing are maintained well lubricated so that bearings will run smoothly and their temperature lies within limit. If a motor run with dry bearing or some what jam or play in bearing, more heat will generate in bearing which will cause over heating of end shied and hence motor stator which will heat winding and ultimate motor burning takes place. Some times due to play in bearings stator core and rotor core starts rubbing each other which increases stator core temperature and hence causing winding burnt out.The load increases because of bearing problems or core rubbing is not too much to operate overload relay that's why in these problems motor does't trips with overload before winding burnt out.
Vibration in motor:- Due to misalignment or unbalance in rotating part vibration generates in motor. Due to vibration a relative motion starts taking place between winding and stator core, between adjacent turns of coils near over hang and between soldered joint and turns of coil. This rubbing of wire results in insulation failure and causing internal short circuit.This problem is also not sense by over load relay. It can be saved by keeping operation of motor vibration free. If any vibration observed, should be rectified by alignment, balancing or some foundation defects correction.
This is what I have seen in my field experience. If some one like to give more reason please feel welcome to comment because I really like to avoid motor burning.
Thanks
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