Prolonging the service life of electric motors and generators – generally involved in most industrial processes – can significantly improve their lifecycle cost (LCC) whilst also allowing for operational savings at the production facility.
Sulzer is a 24 hr service provider and repairer of both motors and generators of all sizes. Richard Emery, Head of Technical Services at Sulzer’s Service Centre in Birmingham, has studied issues which may effect the service life of the motors and generators, and has proposed potential resolutions.Since the designs of multi-megawatt motors and generators have many similarities, assessing these allows similar methods to be employed to prolong the service life of both, thus reducing LCC.
Causes of component failure
In order to determine how service life can be improved, it is important to understand the causes of component failure which cause reduced life expectancy.
The biggest concern for both motors and generators is excessive heat, in fact many other issues contribute to this problem. It is, therefore, essential that the optimum operating temperature is maintained and a maintenance regime – that can resolve issues such as dirt build-up, poor ventilation and poor lubrication – is established.
Bearing failure is another major cause of motor breakdown as it can cause overheating, damage to insulation and secondary damage to other motor components. It is important that suitable techniques to maintain and monitor bearing performance are employed.
On larger machines, predictive maintenance methods – vibration monitoring equipment and thermal imaging cameras – can indicate the early signs of a bearing beginning to fail. Equipment performance is unaffected as the machines do not have to be stopped to be able to provide regular data for a preventative maintenance programme.
For small electric motors, a bearing failure and subsequent damage can put it beyond economical repair or, similarly, a winding failure on a medium sized motor can have the same result. For larger motors and most generators, it is usually more time and cost effective to have the windings replaced as opposed to buying a new piece of equipment.
Winding insulation degradation
Voltage imbalance, over and under-voltage, voltage disturbance and temperature contribute to the degradation of the insulation which is applied to motor and generator windings.
Techniques such as partial discharge analysis can provide vital information about the condition of a stator.
Advice from Sulzer
Employing a range of condition monitoring equipment, combined with suitable analysis techniques, can provide an accurate assessment of the status of motors and generators, allowing operators to avoid unplanned downtime and lost production. The use of vibration analysis, combined with thermal imaging, which is used to identify imminent bearing failure, poor electrical connections and the imbalance of phase loadings, can produce an accurate indication of the overall status of the plant.
Additional testing of the electrical windings, especially partial discharge analysis, can also provide useful information on the overall condition and the remaining lifetime for the equipment.