Voltage imbalance limit? 1

[pwrtran]

Hello, does anybody know if there is a requirement in North America that sets the voltage unbalance limit for a utility supply?

Thanks in advance!

 

[rbulsara]

A local utility company on their website says we have our own PQ standards and contact our customer engineering department for more info.

That tells me that each utility may have their own standards. At the most each state's DPUC may have something but not sure.

Try asking your local utility company.

Rafiq Bulsara

http://www.srengineersct.com

 

[stevenal]

ANSI C84.1 has a recommended limit of 3% at the meter under no load. Individual state utility commissions may have requirements.

 

[pwrtran]

Thanks rbulsara and stevenal. It seems there isn't a clear cut. I later on digged into IEEE std, a 2% unbalance seems to be a guide line.

 

[dpc]

It also depends on how you define unbalance.



David Castor

http://www.cvoes.com

 

[DRWeig]

Not a standard or rule, but we sell tens of thousands of those small, inexpensive "Motor Saver" 3-phase voltage monitors from several different suppliers. I glanced thru a few at random, and they all have "voltage imbalance" setpoints that are adjustable from 2% to 8%.

As dpc allowed, you have to define your percentage calculation too. There's a NEMA standard somewhere for that on motor loads... I don't know what it is, though. One of the more reputable manufacturers of motor voltage monitors labels the setpoint dial for unbalance trip NEMA %, and you choose something between 2 and 8.

Good on ya,

Goober Dave

 

[dpc]

NEMA MG-1 uses the maximum deviation from the average of the three voltages. I assume ANSI is the same, but I haven't verified.

David Castor

http://www.cvoes.com

 

[pwrtran]

dpc
You are 100% correct, IEEE/ANSI defines in the same way.

 

[sibeen]

For IEC users:

The definition of voltage unbalance is the ratio of negative sequence voltage V2 to the positive sequence voltage V1 and is called Negative Sequence Voltage Unbalanced Factor. This definition is adopted by IEC 60034-26 and is also known as the Voltage Unbalance Factor (VUF) or IEC definition.

 

[busbar]

See ‘Motor Heating’

http://www.eng-tips.com/viewthread.cfm?qid=209235;

in particular elelctricpete’s spreadsheet at

http://home.comcast.net/~electricpete/eng-tips/UnbalanceDerating.xls

 

[stevenal]

C84.1 is actually an ANSI approved NEMA standard, so it is consistent with MG-1.

pwrtran,

Which IEEE standard suggested 2% limit?

 

[pwrtran]

stevenal
IEEE Std1159-1995 Clause 5.5.4 and also Table 2