Motor Repair ‘Half Life?’ Reality or Myth?
It actually depends on the quality of the repair. A quality repair process can provide an average life of 20 to 25 years, as with a new electric motor. Motors that do not survive that long normally have some type of some issue such as contamination, operation, too many starts, electrical or mechanical anomalies, and other issues that reduce their life.
As was determined in the Canadian Electrical Association study, “Evaluation of Electric Motor Repair Procedures,” a quality motor repair process will maintain the original efficiency of the motor. In particular, rewinding using a mechanical process will maintain the losses of the stator whereas higher temperature processes, such as burnout, increase the eddy-current (stator) losses. Increased losses result in reduced efficiency (an average of an increase of 0.5 to 1% per rewind) in which the losses are seen as higher operating temperatures. The higher temperatures, or even hot spots in the stator core, reduce the insulation life at that point. To check for core damage, a before and after core loss test should be performed on all motors that are burned out, or the core is damaged, and there should be no change in the core loss with an upper limit of about 6 Watts per pound.
Additional issues include that 81% of motor repair facilities modify your windings through the repair process with 73% of those modifications for the convenience of the repair facility. Improper modifications to windings will result in changes to the efficiency of the motor and may result in increased stator I2R losses and possibly even rotor losses, depending on the result of the modification. These changes also increase operating temperature, also resulting in a reduced thermal life of the motor.
The results may be seen as slight increases in operating current under the same load conditions, hotter running motors, reduced efficiency, the motor tripping upon return from repair, reduced mean time between failures, and other anomalies, including significant changes to soft foot due to mechanical changes in high temperature ovens.
For more information on the impact of improper motor repair practices, go to http://www.motordiagnostics.com/presentations.htm. A number of papers can be found on the electrical and mechanical impacts of motor repair.
As was determined in the Canadian Electrical Association study, “Evaluation of Electric Motor Repair Procedures,” a quality motor repair process will maintain the original efficiency of the motor. In particular, rewinding using a mechanical process will maintain the losses of the stator whereas higher temperature processes, such as burnout, increase the eddy-current (stator) losses. Increased losses result in reduced efficiency (an average of an increase of 0.5 to 1% per rewind) in which the losses are seen as higher operating temperatures. The higher temperatures, or even hot spots in the stator core, reduce the insulation life at that point. To check for core damage, a before and after core loss test should be performed on all motors that are burned out, or the core is damaged, and there should be no change in the core loss with an upper limit of about 6 Watts per pound.
Additional issues include that 81% of motor repair facilities modify your windings through the repair process with 73% of those modifications for the convenience of the repair facility. Improper modifications to windings will result in changes to the efficiency of the motor and may result in increased stator I2R losses and possibly even rotor losses, depending on the result of the modification. These changes also increase operating temperature, also resulting in a reduced thermal life of the motor.
The results may be seen as slight increases in operating current under the same load conditions, hotter running motors, reduced efficiency, the motor tripping upon return from repair, reduced mean time between failures, and other anomalies, including significant changes to soft foot due to mechanical changes in high temperature ovens.
For more information on the impact of improper motor repair practices, go to http://www.motordiagnostics.com/presentations.htm. A number of papers can be found on the electrical and mechanical impacts of motor repair.
posted by MotorDoc at
7:28 PM
0 Comments:
Post a Comment
<< Home