Repair And Rewind Electric Motor & Generator
Most of the motors in the ship’s engine room are continuous running motors connected to a pump or compressor or some other machinery. Like any other mechanical machinery, motors also have their own running hours, after which, the complete overhauling of the motor is to be done to ensure efficient working and performance.
Also, if any other parameters such as voltage, current or insulation resistance is abnormal or the motor came in contact with water (due to flooding or water leakage), the overhauling of motor is to be performed ( Repair And Rewind Electric Motor & Generator) .
In motor construction, the air gap between the stator and the rotor is very less. If there is a little deviation in the shaft rotation, the rotor will slowly start touching the stator (In this condition, you can feel much more vibrations in the motor), which can lead to short circuit and burning of windings.
The scheduled maintenance of motor should be carried out in such a way that the motor does not reach this stage. Thus, proper overhauling of the motor is of great importance.
Before overhauling the motor, rotor running hours should be calculated, along with the lifetime of the bearing (running hours). The bearing must be renewed if required. In the motor, bearings are most susceptible to damages from friction during transmission.
In the event that an electric motor has been accidentally fooded with salt water,proceed as follows :
- Do not attempt to start it
- Disaaemble it and clear it with abundnat fresh water in order to eliminate salts residus
- Clean it with a chemical approved for this purpose.
- Dry it in a furance , or using lamps or heating elements.
- Check the insulation .
- Install and Star it .
How To Do Motor Overhauling?
1/ Insulation test:
Checking the insulation of the stator winding is very important before and after the overhaul procedure. Multimeter is used for this purpose, with its one probe connected to the winding and other to the earth with switch selected in the resistance knob.
2/ Dismantling:
Note: Before dismantling any part of the motor or motor connection, marking of both motor housing and connection wires is very important. This will ensure that the boxing back procedure is smooth and there is no mismatch of parts. Also check the direction of the motor rotation before stopping the motor for overhauling.
Before overhauling the motor, pre-planning of removing and fixing back the motor safely in place must be discussed and implemented (depends on place where it’s fixed and also on the size of the motor) otherwise the load side (for e.g. Pump connected to motor) will be damaged by the motor shaft. The motor can be connected to the load as vertically coupled load and horizontally coupled load.
Clean the shaft on both ends and heat the new bearing up to 70 deg. C to avoid tight insertion of the bearing in the shaft. Do this for both sides.
Wait for 20 minutes, let the bearing cool down, and after that insert the bearing housing cover from one side.
4/ Box back the motor
Before boxing up the motor, do the insulation test again to compare with previous values. If the values are on higher side, start boxing back, otherwise heat up the winding for some more time with Halogen light.
Box up to be done as per the markings
Take up the rotor with one side cover (If bearing locking nut were there in one of the sides, prefer that to be the first to assemble) and push it inside the stator
Lock with one side nut bolts, slowly insert the other side cover, do the hammering slowly by wooden hammer,insert and lovk with nut and bolts,and the rotor will now apply load on the bearing. Gently tighten the bolts using opposite tightening method . Insert the colling fan and protection cover , and once again verify the tightness of the bolts .
Fix in place the motor as per the marking and give the connections accordingly.
Try out and check the Amperage. Compare with rated amperage and before overhaul amperage.
Note: Check the direction of rotation after overhauling. If it indicates opposite direction, it means the connection done is wrong.
