Voltage unbalance - Induction motors are designed to operate at their best with three- phase balanced sinusoidal voltages. When the three-phase voltages are not equal, the losses increase substantially.
- Phase unbalance is normally caused by an unequal distribution of the single-phase loads (such as lighting) on the three phases or by faulty conditions.
- An unbalanced supply can be mathematically represented by two balanced systems rotating in opposite directions. which heat the motor and decrease the torque. Even a modest phase unbalance of 2% can increase the losses by 25%
Distribution Losses
Cable Sizing
- The currents supplied to the motors in any given installation will produce Joule (I2R) losses in the distribution cables and transformers of the consumer.
- Correct sizing of the cables will not only allow a cost-effective minimization of those losses, but also helps to decrease the voltage drop between the transformer and the motor.
- Considering a 2-year payback, it is normally economical to use a cable one wire size larger than the one required by electricity code.
- In most industrial consumers, the main reason for a poor power factor is the widespread application of oversized motors.
- Correcting oversizing contribute improvement of the power factor.
- Reactive power compensation, through the application of correction capacitors, not only reduces the losses in the network but also allows full use of the power capacity of the power system components
Mechanical transmissions - To achieve overall high efficiency it is necessary to use simple, properly maintained transmissions with low losses.
- Transmission types available include direct shaft couplings, gearboxes, chains, and belts.
- Belt transmissions offer significant potential for savings. About one- third of motor transmissions use belts
- Several types of belts can be used such as V-belts, cogged V-belts and synchronous belts.
- V-belts have efficiencies in the 90%–96% range. V-belt losses are associated with flexing, slippage, and a small percentage due to windage.
Maintenance - Regular maintenance (such as inspection, adjustment, cleaning, filter replacement, lubrication, and tool sharpening) is essential to maintain peak performance of the mechanical parts and to extend their operating lifetime.
- Over greasing can cause the accumulation of grease and dirt on the motor windings, leading to overheating and premature failure
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