1. Cut costs with an overhaul. Removal of electric motors for timely overhaul can increase the life of the motor and reduce its running costs, and in some instances save a costly failure. For example, the removal of the build-up of foreign matter from the windings and unblocking of cooling airways can extend the life of the motor by reducing the temperature rise.
2. Check the operating temperature. The life of a motor depends on its operating temperature. Any build-up of material on the windings or obstructing airways will be detrimental to the dissipation of heat and result in some inefficiency. The motor’s nameplate gives the highest current and voltage the machine is rated to take without the temperature exceeding a safe value.
3. Check for dust. On slip rings, dust acts as both an abrasive and as an insulator, accelerating wear and restricting full passage of current. Once inside bearings, dust can be as harmful as sandpaper to the highly polished surfaces. Dust holds an even more serious threat to the life of an induction motor, however. If dust is allowed to consolidate in the windings, it turns the winding overhang into a sponge soaking up any harmful moisture, oil or acid fume ingredients in the atmosphere.
4. Remove dust. Regular inspection is recommended with the removal of any accumulated deposits either by hand or by being sucked out using a vacuum cleaner.
5. Check for excess oil and grease. Oil and grease present a particular hazard to motor windings, primarily in their capacity to arrest, absorb and unite other contaminates. This stifling corrosive blanket can seriously impair ventilation and degrade the properties of the electrical insulation of the winding.
6. Remove excess oil and grease. Thoroughly clean windings with an appropriate solvent. Take care in the choice of the solvent, since the use of an improper one can soften or even remove the varnish.
7.Check for moisture and remove. An insulation test will establish whether a motor winding is significantly affected by moisture content. If so, it is preferable to 'dry it out' before attempting to put it into service.
Regular drying procedures are carried out by oven baking the wound stator, or in situ, by forcing a stream of warm air by a fan through the windings, or passing a circulating current through the windings by application of a reduced voltage. A temperature of 90°C should not be exceeded and subsequent application of a coat of insulation varnish to the windings is recommended. For a permanent fix a low wattage heater can be fitted into the motor to keep the windings at an acceptable temperature.
8. Minimise friction. Numerous conditions can lead to generation of unnecessary friction, such as bearings receiving an insufficient supply of oil or grease, application of a totally incorrect lubricant, or contamination of bearing lubricant with solid particles. Due attention should be paid to the manufacturer's lubricating instructions together with use of the recommended type and grade of lubricant.
9. Remedy misalignment. Geometrically incorrect assembly of a driving unit and its driven equipment results in accelerated wear and ultimate failure of a constituent component. Any tell-tale signs - such as overheating, vibration or noise - should be promptly investigated and remedied.
10. Minimise vibration. Vibration can quickly generate problems, such as loose wiring connections or chafing of winding insulation. To trace a vibration source, the most practical procedure is to use a vibration meter but can be achieved often by a process of elimination, checking potential sources in turn until it is located. Disconnect the drive in attempt to isolate source to motor or drive – or, alternatively, eliminate driven equipment. Then follow these stages: 1. Check motor bearings for axial movement; 2. Carefully check motor assembly and all its accessories for rigidity; 3. Check drive alignment; 4. Check drive foundations for solidity.
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