How is the generator sizing with driving VFD

[ilkerkgulle]

I have 2750kw 6,3kV motor for process and driving this motor with variable speed drive at the 6,3kV , and also , I want to supply this motor with generator sets , but How can I calculate what about generator sets we need , Please could you help

 

[itsmoked]

Using a drive on the motor will greatly ease the demands on the generator.

As for the generator, we can't answer that question without a ton more info.

What you should do is find all the generator companies around you that could support you locally, and start talking to them. They will all be happy to analyze your situation and give you advice using the necessary details.

You can then run the designated solution by us for an experence based check.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[jraef]

Using a drive on the motor will greatly ease the demands on the generator.

That's right. Remember, you cannot just compare the running condition of the motor for generator sizing, you must always consider how you are going to start the motor. A VFD is the best way to start that motor as far as stress on the generator is concerned. Some people even go so far as to use VFDs as starters even though they run at fixed speed just to avoid having to oversize the generators any more than necessary.

The main trap to watch out for is that the VFD manufacturers will try to sell you on how the VFD presents a .95 power factor to the system, but this is disingenuous. The displacement power factor may be .95, but the distortion power factor is usually much worse; .75 or lower. This is often unimportant to utility supplies (at least as far as rate penalties go), but is critical when you are running on a fixed source such as a generator. Your generator will need to supply ALL of that power.

 

[ScottyUK]

Make sure the generator manufacturer has full knowledge of the load characteristics. Rectifiers and other highly non-linear loads can cause problems with a generator's AVR. Correct specification underpinned by a well-written contract should prevent you seeing any problems of this nature but in the first instance you must ensure that the generator manufacturer has all the data they need.


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If we learn from our mistakes I'm getting a great education!

 

[gepman]

jraef
Is there a definition for displacement and distortion power factor?

 

[jraef]

Specifically, I don't recall the exact definitions; the terms came to me in a course I took on power factor control and correction a long time ago. But this paper does as good a job of explaining the issue as I have seen.
LM Photonics Power Factor paper
Scroll down (if you don't want to read the whole thing) to the section on Inverters, then again to the very end.

Displacement PF would be the "normal" pf we think of, i.e. cos phi of the angular difference between voltage and current. Distortion pf is the result of harmonics in non-linear loads and can be crudely defined as kW/kVA regardless of what you think you see on a meter not designed to react to harmonics.

 

[jraef]

Follow up for gepman:

http://en.wikipedia.org/wiki/Distortion_power_factor

JRaef.com
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[gepman]

jraef
Thanks for the information. It will help me in my work. If I understand both links correctly, Power Factor would be kW/kVA as measured by a True RMS Power Meter. Displacement Power Factor is the cosine of the angle between the voltage and the current (which would be equal to the Power Factor for a sinusoidal system). Distortion Power Factor = Power Factor/Displacement Power Factor.

 

[ScottyUK]

Displacement power factor is the cosine of the phase angle between the fundamental frequency components of both voltage and current. Normally voltage is sinusoidal (or pretty close) so the calculation is simplified when doing it manually. A decent power analyser will extract the fundamental of both voltage and current and use these values in its calculation.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

Yes, but that's not what the utilities use to bill you for poor pf! ;-)