The claim that motor repair cuts down the efficiency of motors is purely mythical. Most of the time, the failures in motors occur due to winding problems which means rewinding is the only available alternative in getting a new motor to resume seamless operations. Some studies have established that the efficiency of motors reduces by up to 5% when rewound. Is that’s the case ,then why are motors repaired and not replaced?
Repairing failed motors costs far less than replacing them, but efficiency degradation is an important factor that is to be considered when motors are repaired. Although, it has been noticed that motor repairs reduce the efficiency of motors by up to 2%, but motor repair can also preserve the efficiency, if repaired correctly. Reduced efficiency results in greater energy consumption as well as increased operating costs. The effects of repairing on the efficiency of motors may vary from one vendor to another yet could be identified by taking the efficiency measurements before and after the repair.
To determine what level of damage can be restored to the original motor state, the following levels are defined:
Level 1: Basic reconditioning such as replacing lubricant, cleaning all parts, replacing bearings, adding seals and other accessories as told by the client.
Level 2: Includes Level 1 plus straightening of bent shafts, repairing of damaged fits and varnish treatment of stator windings.
Level 3: Includes Level 1 plus replacing winding and insulation of the stator.
Level 4: Includes major repairs such as rewinding of stator, shaft replacement, and of stator lamination replacements. These repairs are costly and reduce the efficiency of the motor as well. Therefore replacement option is better in such cases.
Level 5: Replacement option is better than repairing if the spare parts are not available or if the operator does not have adequate time for the repairing of motor.
Because of irreparable damage, all motors cannot be restored to their original level of efficiency. Motors that require level 1, 2 and 3 repairs, as discussed previously, can be repaired without damaging the efficiency of motors, yet the motors that need level 4 and 5 repairs should be evaluated separately depending on the damage that is impossible to repair completely. Therefore, the level of reduction in motor efficiency depends on the milestones of motor damage, and on the number of times a motor is subjected to the same damage over a period of time.