variable frequency drive and and standard epact motor

[sunloco]

In many building cases we supplied HVAC pumps with standard motor though it will be controlled with frequency inverter ,Normally I use standard epact motor to meet variable frequency needs,but I want to know what variable range is frequency for standard normal motor ?

and under what situation we must use variable frequency drive ?

 

[ozmosis]

A practical range for controlling pumps would be to set a minimum frequency of 15~20Hz. I am assuming your pumps are centrifugal and therefore will follow the cubed power to speed profile, this will mean that any increase in speed above the rated speed/frequency of the motor will increase the power consumed by a cubed. So, keep your maximum frequency to 50Hz (I think you previously said you were in China).
This is a practical suggestion. Obviously the frequency inverter will allow the motor to go slower but you may run into motor cooling issues and also the fact that the pump will not be too effective below these suggested frequencies.
I'm not sure that an EPACT motor will have too much difference relating to the speed range, my understanding is that EPACT motors are typically classed as energy efficient (although energy efficient at fixed speed rather than variable speed!).
Your final point "under what situation we must use variable frequency drive ?". I'm not too sure what you mean here. The VFD is intended to control the speed of the motor (and therefore pump) and thus controls the flow/pressure of whatever you are pumping. I think you need to expand on your application to get a more detailed reply to this point.

 

[itsmoked]

sed2developer; Most compressors are positive displacement. What's the power to speed profile on those?

Also for your info most compressors are cooled by the refrigerant flowing thru them so speed isn't going to be cooling related since somewhere else a radiator with fans is actually providing the cooling.

 

[ozmosis]

itsmoked
We can guess on the actual application but the easiest way would be for sunloco to advise what it actually is. If it is a centrifugal pump then I would say follow the info I suggested but if it is a compressor then it depends on the type of compressor: screw, scroll, etc and here other factors come into play such as starting torque, lubrication etc
over to you sunloco...

 

[aolalde]

Hello Sunloco:

EPAC motors (Energy Policy Conservation Act) as it was mentioned above are mainly designed to perform with high efficiency that does not necessarily means they are good for VFD application.
Depending on the VFD design high frequency spikes could reduce the insulation or bearing life of a motor to a few hours in operation. It does not mater the motor speed, operating frequency or power output.
Some standard motors have successfully operated with VFDs but others have had almost immediate failure. If you want to ensure successful operation spend the extra money on a VFD duty motor. Other way, you flip a coin and have good luck.

 

[DickDV]

If your "standard motor" is Insulation Class F and your service is 460V with short drive-motor leads, it will likely be just fine on variable (increasing with speed) torque loads like fans and centrifugal pumps.

On the other hand, if "standard motor" is Insulation Class B, the motor is almost surely not suitable for variable speed applications, the only possible exception being 230V service with very short motor leads.

Today, in my view, your best motor value on fan/pump loads is a high efficiency Insulation Class F motor with MG1 Part 31 Endorsement.

 

[sunloco]

Thanks,all guys

We use the centrifugal pump for HVAC use, the pump will be controlled by frequency inverter.

the motor is from USEM ,380v/3/50HZ,insulation class F,TEFC .

As for what engineer of US motor told me ,the motor can be used in a minimum frequency of 15~20Hz. no necessary to use specical VFD motor.

 

[DickDV]

On a centrifugal pump load, the USEM engineer is correct. In fact, the frequency could probably go a bit lower but there is little point on a centrifugal pump since it isn't pumping anything at those low speeds anyway.

As I said in the earlier post, you would be doing a little better with respect to reliability if the motor had a MG1 Part 31 Endorsement in addition to the Class F insulation but it isn't critical as long as you keep the motor lead length reasonably short.

 

[sunloco]

Could you give me some detail about MG1 Part 31 Endorsement????

 

[CJCPE]

Re: "Could you give me some detail about MG1 Part 31 Endorsement????"

ANSI/NEMA MG 1-2003

http://www.nema.org/stds/mg1.cfm

(purchase)

http://www.nema.org/stds/mg1condensed.cfm

(free download)

Application Guide for AC Adjustable Speed Drive Systems

http://www.nema.org/stds/acadjustable.cfm

(free download)