|
| 3 phase motors are not necessarily more efficient at running, though some ancient handbooks and tables make that statement. A 3 phase motor is always more efficient in its use of copper and iron. Its always smaller and lighter for any horsepower and speed rating and smoother running. It gets 3 times the magnetic pulses per revolution than the single phase motor.
Any motor, single or three phase, can be designed for super or for rotten efficiency, in any size. It always costs more copper and iron to design for efficiency, so the lightest and cheapest motor for the load rating is likely to have the poorest efficiency. A 200 to 250 volt rated motor running at 220 volts is likely to have more efficiency than at 208 or 250 volts, motor efficiency is that subtle and to be more efficient than an ordinary motor when that ordinary (not super efficiency) is run at its rated voltage.
A motor's loss depends on voltage and current. A higher voltage reduces the current but increases the iron loss because the iron is driven further into magnetic saturation. A lower voltage increases the current (because the frequency sets the shaft speed and the load sets the shaft power output) that increases the copper loss but reduces the core loss. So the motor rated to work over the wide range of 200 to 250 volts should have a highest efficiency voltage somewhere in the middle of its ratings.
Gerald J. | |
|
Corn Dryers 1 verses 3 phase
