VFD Motor Types for pump application ( Constant vs Variables)
VFD Motor Types for pump application ( Constant vs Variables)
(OP)
I would like to know how we determine the application pf the pump is variable or constant torque ?
Under what circumstances that inverter duty motor os selected ?
Is standard VFD motor is capable to run under constant torque application ?
Is there a rule of thumb or guide to set motor range, assuming 4 poles ?
Eg: 4 poles at 50 Hz which is 1500 rpm is it capable to be run at below 1450 rpm or lower. How low it could be stretched ?
My understanding is that standard VFD is also capable of lowering the speed (50%) of 1450 rpm. Will the motor burn if using the stdrd VFD to drive at lower speed and high torque ?
I encountered a formula : rpm =120 x hz / pole. DOes this formula determine the minimum the motor could run assuming the Frequency is 30-50 Hz.
Does the VFD vs inverter duty, inverter"s benifit exceeded standard VFD ?
Under what circumstances that inverter duty motor os selected ?
Is standard VFD motor is capable to run under constant torque application ?
Is there a rule of thumb or guide to set motor range, assuming 4 poles ?
Eg: 4 poles at 50 Hz which is 1500 rpm is it capable to be run at below 1450 rpm or lower. How low it could be stretched ?
My understanding is that standard VFD is also capable of lowering the speed (50%) of 1450 rpm. Will the motor burn if using the stdrd VFD to drive at lower speed and high torque ?
I encountered a formula : rpm =120 x hz / pole. DOes this formula determine the minimum the motor could run assuming the Frequency is 30-50 Hz.
Does the VFD vs inverter duty, inverter"s benifit exceeded standard VFD ?





RE: VFD Motor Types for pump application ( Constant vs Variables)
RE: VFD Motor Types for pump application ( Constant vs Variables)
Is this called a constant torque ?
If regardless any poles I could varies the frequency from 50 to 5 Hz, is that means the lowest speed is = 5 hz * 120 /4 = 150 rpm
I doubt it can be tuned down to this for standard vfd motor ?
Is all motor could be driven by VFD ?
RE: VFD Motor Types for pump application ( Constant vs Variables)
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: VFD Motor Types for pump application ( Constant vs Variables)
Ted
RE: VFD Motor Types for pump application ( Constant vs Variables)
Except the torque does actually vary with speed (because of increased mechanical and fluid friction losses at higher speeds) and it also varies with viscosity (again because of increased churning losses with the thicker fluids).
By the way Ted, can I take this opportunity to wish you and yours a happy Christmas and a peaceful new year. I've very much enjoyed contributing to the same questions as you - but you usually get there first and beat me hands down on brevity.
DOL
RE: VFD Motor Types for pump application ( Constant vs Variables)
I enjoy and appreciate your more detailed responses.
Ted
RE: VFD Motor Types for pump application ( Constant vs Variables)
Would motor manufacture specify the stdrd VFD frequency ? Assuming it could be VFD driven at 30-50 Hz.
Am i right to say, i cant drop the motor below 30 Hz ?
RE: VFD Motor Types for pump application ( Constant vs Variables)
You can, subject to the limitations of the driven pump, run the motor down to a virtual standstill. To do this you'd need a separately cooled motor. In small sizes these are typically provided with a small fan mounted on the NDE cowling and which runs from a permanent auxiliary supply. To know the lower speed limit for a standard motor you would need to know details of the load, and then consult the motor manufacturer, not the VFD manufacturer.
RE: VFD Motor Types for pump application ( Constant vs Variables)
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: VFD Motor Types for pump application ( Constant vs Variables)
Operation?.
RE: VFD Motor Types for pump application ( Constant vs Variables)
Regardless what other valued members say I still say that you should look for a constant torque drive for a PD pump. The terms "constant torque" and "variable torque" are related to the drives and have something to do with the speed torque characteristic which can vary with the square of speed.
RE: VFD Motor Types for pump application ( Constant vs Variables)
RE: VFD Motor Types for pump application ( Constant vs Variables)
The drives are no different - it's a sales 'trick' to allow you to buy, say, an 11kW drive and use it to run a 15kW centrifugal pump. The drive can do this by giving up most of its overload margin, in the reasonable assumption that a centrifugal pump or fan load is not going to suddenly increase. The drive is not built differently - the 'quadratic' drives are just working a lot closer to the edge of their safe operating area. Some drives are dual-rated, one being the continuous capability with only 10% overload capability and the other being the continuous capability with 50% overload capability.
Merry Christmas!
RE: VFD Motor Types for pump application ( Constant vs Variables)
RE: VFD Motor Types for pump application ( Constant vs Variables)
http://www.motorsanddrives.com/cowern/motorterms7....
Constant torque means the torque required by the load is independent of speed. The particular torque for a particular fluid would be constant over a range of speeds. Change the fluid and the required torque may change but remain at the new constant at various speeds.
Ted
RE: VFD Motor Types for pump application ( Constant vs Variables)