When replacing a motor, its exact dimensions, as well as speed, hp, and torque characteristics should be determined and duplicated if the same performance is desired. When replacing a motor, the entire system should be inspected for internal and external degradation. Neither the motor mounting nor the mechanical coupling should exhibit signs of wear.

The power supply and connections should not be damaged. These should be frequently checked for proper frequency, voltage, and voltage balance between phases. Poor and broken connections of one of the supply lines are a major cause of voltage unbalance. Overload relays for each phase should protect against extreme (greater than 5%) voltage unbalance.

Misalignment between the motor and the driven machine (e.g., centrifugal pump ) can cause bearing failures and shaft breakage. Excessive vibrations frequently indicate misalignment. All motor feet must be fastened to a flat, preferably machined, surface. Otherwise, the frame can bend when the motor is tightened down, which twists the motor frame and causes misalignment. Care should be taken to evenly tension mounting bolts. If torque values are specified, follow the manufacturer’s recommendations. The mounting should be inspected frequently. If necessary, retighten bolts with the proper torque. If vibration is detected, one or more of the motor feet may have to be shimmed. A few thick shims are preferable to many thin shims if it is necessary to align motor and machine (pump) shafts. Misaligned couplings create bearing loading in both the motor and the machine, causing high-speed distortions and also increasing power consumption.

Motor should be greased using manufacturer’s specified greases in concert with manufacturer’s specified lubrication frequency and quantities (sealed ball bearings cannot be lubricated after manufacture). Relubrication is necessary to replenish grease that has broken down by oxidation or been lost by evaporation and centrifugal force.

Inspect and keep cooling and ventilation vents clear of obstructions.

If a motor burns out, the windings should be inspected for signs of single phasing, short circuiting, overloading, and voltage unbalance. Any cause of winding damage should be identified and corrected. If a motor burns out, the circuit supplying the voltage should also be inspected for broken or shorted wires, burnt contacts, or voltage unbalance.


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