All electric equipment have a life span and motors are no exception. The typical life span of motors stretches from 35,000 to 40,000 hours. However, within this time it is susceptible to breakdowns if subjected to inferior maintenance. General maintenance system may or may not account for motor vibration, however there are a number of other problems which are generally difficult to understand in the first go.
Usually in large organizations, a motor maintenance program is carried out in which the causes of motor failures are identified and some necessary steps are taken to avoid them or lower their impact. Motors need to be inspected regularly, and other maintenance activities need to be performed to ensure efficient operation. Whenever a problem occurs, it should be corrected immediately to avoid further loss.
Here are the major problems faced in motors
- Motor Vibration
Vibrations can be caused due to 2 main reasons, they are:
A. Mechanical Reasons for Motor Vibration
- Neck ellipse or shaft bending.
When the DC motor rotates, the disturbance vibration is caused by rotor gravity, and the vibration frequency is usually twice as high as the DC motor’s working frequency. The bending of the shaft forms an unbalanced weight which rotates around the static equilibrium position at angular velocity with the same result as the rotor unbalance.
- The armature is unbalanced.
Because of the centrifugal force caused by the unbalanced rotation, there is a rotating force on the bearing, which causes the vibration of the DC motor and the foundation. When the air gap is not even, the main pole is not fixed or the rigidity of the seat and the end cover is poor, the vibration will be aggravated. Therefore, when the rotor is found to be unbalanced, the dynamic balance must be balanced.
- Manufacturing error or operating distortion of important supporting parts.
Due to the misalignment error of the main supporting parts of rotor, such as seat, end cap and so on, especially the deformation of the seat, the end cap and other important supporting parts after the large and medium motors run for a longer period of time, the bearing of the DC motor is disturbed by the force of interference when the motor is in operation. Cause motor vibration.
- The radial clearance of the bearing is too large and the outer ring and the end cover are loosened.
The bearings should be tested and qualified at assembly time. The matching of bearing with bearing neck and bearing seat must meet the requirements, otherwise, it must be treated by spraying or brushing technology to avoid vibration caused by poor bearing work. For the wear bearing, the vibration and noise frequency is higher when the DC motor is in operation, so it is easy to judge. It is found that the bearing should be replaced.
B. Electrical Reasons for Motor Vibration
- The air gap is uneven.
Because the disassembly air gap is uneven, the one-sided magnetic pull force occurs when the DC motor is in operation, which is equivalent to the deflection addition of the motor shaft. Therefore, ensuring the average removal of the air gap is a necessary measure to avoid vibration.
- Electromagnetic force
This kind of electromagnetic force is mainly caused by the longitudinal oscillation of the flux under the pole boot and usually has the tooth frequency. Especially when the stator is the opening slot the flux pulse vibration is added and the alternating magnetic pull force is more easily formed.
- Rotor coil damaged.
Because of the rotor coil damage, the rotor radial force is uneven when the DC motor is running, and the result is similar to the rotor imbalance.
Approximately more than 50% of insulating failures in motors occur due to overheating. This can be caused by poor power quality or a high temperature operating environment. For every 10oc that the temperature of a motor rises, insulation life is reduced by half.
Overheating can occur from undersizing the motor, insufficient cooling at low speed when using variable speed drives (VSD), changes to the load on the motor such as jammed equipment and hot ambient conditions.
Shaft misalignment will destroy bearings well before their full working life. The motor shaft must be directly in-line with the shaft it is driving. This minimises the vibration, forces and loads that planetary rotation of one shaft in respect to the other would create.
Dust ingress into the stator coils or the terminal housing leads to short-circuiting. If the motor is to be in a dusty environment keep the immediate area around the motor clean or use dust ingress protection (DIP) methods.
5. Soft Foot
Soft foot occurs when the motor feet are bolted down out of level. If all feet are not in the same plane when pulled down on the base plate the motor housing twists and the bearings are distorted.
The motors face some real challenges in the industry making motor condition monitoring a task, and hence it requires the best care. Preventive measures no longer suffice. Today, we have Smart Motors with in-built Predictive maintenance. IDE (Industrial Data Enabler) attaches to your motors and makes it smart delivering predictive maintenance since the moment you install the equipment.