22. EFFECTS OF OPERATING CONDITIONS
- Effects of operating conditions are briefly described below:
1. Effect of unbalance supply voltage:
- An unbalance supply voltage produces a rotating field which will move at a non-uniform rate and in a non-uniform strength. It provides unbalanced currents in the stator winding which produce unequal heating.
2. Effect of loading:
- As the load increases, speed falls and consequently torque increases, till a point is reached when the maximum torque will be developed.
- If the load is increased further, there is further fall in the speed and the driving torque decreases and ultimately the rotor comes to standstill.
3. Effects of variation in line frequency and line voltage:
- The variation in supply frequency and supply voltage not only affects the speed and torque of the motor but also the starting current, full-load current, starting torque, maximum torque and operating temperature of various parts of the machine and thus make their operation unsatisfactory.
4. Effects of break in one phase:
- When a polyphase induction motor is in operation and if it’s one phase breaks, may be due to any reason, the motor will continue to operate single phase, provided that load does not exceed 57.7 percent of the normal rating, with about the same temperature rise as when carrying rated load as a 3-phase induction motor. It will not, however, start single phase but if brought upto speed by some external means, such as putting on the belt, it
will continue to operate satisfactorily on load below 57.7 percent of rated one.
- A break in one phase of the rotor of a wound-rotor induction motor may prevent it from starting but if it is brought upto speed before the circuit is opened, it will operate under reduced load but usually with considerable vibrations.