efficiency of VFD and asynchronous motor as function of frequency ??
efficiency of VFD and asynchronous motor as function of frequency ??
(OP)
Hello,
I try to get a grip on the advantages of applying a VFD to save energy while driving a pump. Suppliers tend to give the impression, that the efficiency of a VFD and an asynchronous electrical motor remains constant whatever frequency is generated by the VFD and put into the motor. I am not an electrician, but I assume that using a motor with another frequency than the usual 50 or 60Hz is loading the motor in a more inefficient way. In general the nominal power of the motor should be chosen 15% higher, when working in combination with a VFD. Are there any typical characteristics that indicate the efficiency of the VFD and/or the elektrical motor as a function of the relative speed
(compared to the nominal value?). With these graphs I might be able to calculate realistic energy savings instead of the very optimistic tools the VFD suppliers put at our disposal.
I would therefore be grateful if somebody could help me out here!
I try to get a grip on the advantages of applying a VFD to save energy while driving a pump. Suppliers tend to give the impression, that the efficiency of a VFD and an asynchronous electrical motor remains constant whatever frequency is generated by the VFD and put into the motor. I am not an electrician, but I assume that using a motor with another frequency than the usual 50 or 60Hz is loading the motor in a more inefficient way. In general the nominal power of the motor should be chosen 15% higher, when working in combination with a VFD. Are there any typical characteristics that indicate the efficiency of the VFD and/or the elektrical motor as a function of the relative speed
(compared to the nominal value?). With these graphs I might be able to calculate realistic energy savings instead of the very optimistic tools the VFD suppliers put at our disposal.
I would therefore be grateful if somebody could help me out here!
Karel Postulart, The Netherlands
Nuon Power Generation





RE: efficiency of VFD and asynchronous motor as function of frequency ??
But a well designed pump running at the right speed for a constant flow will always be better than a badly chosen pump and motor that have been 'corrected' with a VFD.
The motor runs at its optimum flux at all speeds if the VFD is correctly programmed. Optimum flux usually means optimum efficiency.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: efficiency of VFD and asynchronous motor as function of frequency ??
http://www.eng-tips.com/viewthread.cfm?qid=260203
What I have found is that anytime you vary the pump speed, more energy is used per gallon produced, not less. You are right to suspect the "energy savings" tools supplied by manufacturers. It is more a marketing tool and not realistic data.
RE: efficiency of VFD and asynchronous motor as function of frequency ??
Again to Gunnar's point, if the application is not one that can benefit from variable flow operation, then by all means don't apply a VFD to try to fix other inefficiencies. That is the first step in evaluating the idea.
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RE: efficiency of VFD and asynchronous motor as function of frequency ??
RE: efficiency of VFD and asynchronous motor as function of frequency ??
I suggest you go back and read BigInch's excellent dissertation on the subject. It's about the 6th post down in this thread: thread407-260203: VSD energy savings
Keith Cress
kcress - http://www.flaminsystems.com