The following maintenance procedure should be performed regularly:- 1) Bearing lubrication 2) Insulation resistance check 3) Cleaning The use of unauthorized parts in the repair/maintenance of the motors, tampering by unqualified personnel, or removal or alterations of guards or conduit covers will result in dangerous conditions which can cause severe personal injury or equipment damage. All safety instructions should be followed.
1.BEARING LUBRICATION: Bearing life is assured by maintaining proper alignment, proper belt or chain tension, and good lubrication at all times. Before dispatch the motor bearings are lubricated with the proper amount and grade of grease, to provide six months of satisfactory service under normal operating conditions. For best results, grease should be compounded from a polyurea base and a good grade of petroleum oil. It should be of No.2 consistency and stabilized against oxidation. Most leading oil companies have special bearing grease that is satisfactory.
Re-lubricate bearings every six months as follows:- 1. Stop the motor. Lockout the switch 2. Thoroughly clean off pipe plugs and remove from housings
2.CLEANING: The motor exterior must be kept free of oil, dust, dirt, water, and chemicals. For fan cooled motors, it is particularly important to keep the air intake openings free of foreign material. Do not block air outlet or inlet. On non-explosion proof motors, a removable plug in the bottom of the motor bearing housing permits removal of accumulated moisture. Drain regularly. During normal operation the slip rings acquire a protective coating that contains copper oxide and graphite with absorbed water as a result of several weeks of operation. This film of coating serves as a lubricant that reduces brush wear. Operating conditions and brush grade affect the makeup and colour of this film from straw colour to jet-black. A good surface film is chocolate brown in colour. Atmospheric pollution has adverse effect on this film and its formation. Softer brushes are used for light loads and help in formation of the protective film. Hard brushes are used for heavy load and oily atmosphere.
Slip rings may be cleaned by a wiper made of several layers of hard woven canvas at the end of a wooden stick. The frequency of cleaning is decided by the atmosphere surrounding the machine. Incase of open slip rings they may be cleaned once after every 24 hours of running. Convas is not abrasive and does not damage the film. For effective cleaning wiper has to be used with sufficient pressure and use of solvents should be avoided.
3.INSULATION RESISTANCE: 1. Check insulation resistance periodically, by a megger. According to the Institute of Electrical & Electronics Engineers the insulation resistance of stator windings at 500n volts D.C after one minute, should not be less than:-
Rated voltage of machine + 1000 = Insulation resistance in Mega ohms 1000 SELECTION
For the selection of a motor for a particular application, the following points should be considered:-
1) Load torque and speed required:- Variable torque with adjustable speed Constant torque with variable speed Constant horsepower with variable speed 2) Starting torque 3) Cost 4) Efficiency 5) Type of enclosure Totally enclosed type forced air cooled (TEFC) Drip proof type 6) Temperature classification Class B motors Class F motors
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