3450 RPM Motor at 1750 RPM
3450 RPM Motor at 1750 RPM
(OP)
Is there any long term problem running a 3450 rpm submersible motor permanently at 1750 rpm with a VFD, so long as sufficient water is moving to cool the motor?
2 Pole motors are much less expensive than 4 Pole.
I have to have the VFD anyway, why not save money on the motor?
2 Pole motors are much less expensive than 4 Pole.
I have to have the VFD anyway, why not save money on the motor?
PUMPDESIGNER





RE: 3450 RPM Motor at 1750 RPM
At 30 Hertz you will only have 50% horsepower and 50% voltage.
You best be is to ask the pump manufacturer and motor manufacturer if reduced speed running will impair anything. There are likely some people who are running their submersible pumps variable speed to reduce water hammer when starting and stopping and to reduce the number of on/off cycles.
Mike Cole mc5w at earthlink dot net
RE: 3450 RPM Motor at 1750 RPM
HP= T*rpm/5250
If a pump demands 50 HP at 1750 rpm, a standard 50 HP, 4 Poles, design B, induction motor, 60 Hz will handle that load; however you will need 100HP, 2 poles, 60 Hz to provide those 50 HP with 30 Hz.
I think you will not save a penny.
RE: 3450 RPM Motor at 1750 RPM
RE: 3450 RPM Motor at 1750 RPM
Did you reduced the voltage proportional to frequency?
example; if the original motor was 460 Volts- 60 HZ
at 41 HZ Vn = 460 *41/60 = 314.3 Volts
Other way the magnetic circuit reaches saturation increasing the magnetizing current and finally the total current increases too.
RE: 3450 RPM Motor at 1750 RPM
RE: 3450 RPM Motor at 1750 RPM
Better check the instruction book.
RE: 3450 RPM Motor at 1750 RPM
The input to the motor for 10 HP:
I ~ 10*746/(1.732*314.3*.8) ~ 17 amps at the motor input.
(+/- 1 or 2 amps due to harmonics)
The input to the driver, considering driver EFF*PF= 0.95, should be around:
I1 ~ 10*746/(.89*1.732*460*0.95) = 11.07 Amps at 460 V, 60 HZ
RE: 3450 RPM Motor at 1750 RPM
At half speed the torque is one-quarter that of full speed and the horsepower has dropped to one-eighth of full speed.
The bigger question is whether the pump and motor package is designed to operate at half speed. That info must come from the pump manufacturer.