Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | APRIL 2014 | 37 of the load or excessive loads, then check wiring and switches for obvious failures. If the motor is fitted with capacitors, discharge these and check with an ohmmeter. If all of these are OK, then there is probably a problem with the stator or rotor. Dissemble the motor and check for burn marks, failed wiring, loose coils, et cetera. 3. Motor runs but dies down and cuts out A likely cause is an increase in the load. This is fairly obvious, if say, the motor is driving a conveyor that is overfull, but it could also be due to a tightening bearing in the motor or drive train. Another possibility is a voltage drop in the power supply; this could be due to a failing or undersized supply cable, which is easily fixed. If it is the actual supply, other motors will also run slow. 4. Motor acceleration is poor The motor may be undersized, considering the load it is driving; this can be checked with a few fairly easy calculations and addressed. The problem y be mechanical, for example, a tightening bearing, in which case there is likely to be noise, vibration and possibly, local heating. Lubrication and alignment checks may set everything straight. Alternatively, there may be an electrical issue, so check wiring, switches, et cetera. The capacitor may have failed, this will need to be checked with a meter and replaced if necessary. Finally, it may be a supply problem, as above. 5. Motor overload protector continually trips Firstly, the overload protec- tor may not be at fault, but doing its job well. So the first thing to check is the actual load. As previously, check for jamming, excessive load and mechanical problems in the drive line. The protector may also trip if the motor is getting too hot, so make sure the area is well-ventilated and the fan is effective. The stator or rotor may be failing, so check for loose or broken windings or other signs of problems. If the protector is defective, it is relatively easy to replace. 6. Motor vibrates or is noisy A humming noise is likely to indicate an electrical fault such as a failing coil or a loose connection. Vibrations are generally mechanical problems. The simplest mechanical problem is a misaligned load, which is easily rectified. Then there is the possibility of an out-of-balance load, which may suggest a bent motor sha , necessitating a new sha . Vibration may also be introduced if the sha has longitudinal play, in which case its mountings need to be tightened. Bearings are another likely cause, so check their lubrication or if necessary, replace them. If the bearings are fine, it may be that the rotor needs rebalancing. 7. Motor sounds rough at start-up Many motors seem to take a minute or two to settle into a rhythm, and this is indicative of a problem that will get worse if le unaddressed. It is o en the case that some sensible maintenance will sort out the issues. This might include realigning moving parts, lubricating dry bearings, tightening screws, et cetera. 8. Capacitors fail frequently Poor capacitor life may be indicative of an undersized motor or frequent overload of an optimally-sized motor. Other simple problems include a low voltage sup- ply, a failing start switch or overheating due to poor ventilation. Another possibility is stopping and starting too frequently. You may be able to adjust the duty-cycle, add a mechanical clutch to the drive chain or fit a so -start unit to the supply side of the motor. sponsored by Smart liquid lime www.neutralac.co.uk

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