what about single phasing?? 1

[ELECTRICALCHOICE]

Hi i like to know where can i find some information about the single phasing condition in induction cage rotor machine( 3 phase). if anyone know the park's transformation aplied to the same induction motor.

thanks in advance

 

[busbar]

Can’t address Park transformation, but there’s this from ABB IL 41-171:

“An open-phase condition, caused by blown fuse or an open winding, produces a negative-sequence component, I2 equal to the running current before the open occurred..."

Since the negative-sequence impedance of a motor is so low, by a factor equal to the starting–to-running current ratio, a 5% voltage unbalance causes typically 30% negative-sequence current. This condition should be detected quickly since the negative-sequence component causes disproportionate overheating.”

See: hread237-23710

 

[ELECTRICALCHOICE]

Thanks Busbar, but also i ask you, how can i deduce the relation between Line Voltage Unbalance Rate (LVUR) and the magnitude of the negative sequence current. I know that this is a unsupporting condition, but stabndstill time is very low, enought ato remove a transient's earth to ground fault (monophase recloser). anyone know something about this???

once, thanks in advance

 

[electricpete]

The approach that busbar suggests is supported by other documents. The negative sequence impedance is approximately equal to the locked rotor impedance according to: 1- IEEE C37.96-2000 page 51, 2- EPRI 5036V4.

NEMA MG-1 has some discussion. They derate along a simpler approximate principle which I think estimates the negative sequence component of the "voltage imbalance"... which is computed as maximum deviation from the average of the three phase voltage magnitudes.

What is Voltage Unbalance Rate (LVUR)

I'm pretty sure the motor textbook by Krauss has some very detailed discussion of induction motor behavior in presence of unbalanced condition. Do you have that?

 

[ELECTRICALCHOICE]

THANK YOU ELECTRICPETE

the LVUR is defined by NEMA.

LVUR=(maximum voltage from average line voltage magnitude *100%)/average line voltage magnitude


average line voltage mag= (Vab+Vbc+Vca)/3.

this formulae looks PVUR(phase voltage unbalance rate) defined by IEEE Std. 141.

With regard the Krauss's book no, dont'n have it, please where i may find it?, do you have an electronic version?.

thanks in advance

 

[electricpete]

That quantity defined by NEMA is supposed to be an approximation of the negative sequence component.

I have only hardcopy of Krauss' Analysis of Electric Machinery 1986 McGraw Hill ISBN 0-07-035426-7. Chapter 9 is 34 pages on the subject of Unbalanced Operation of Induction Machines, primarily using reference frame theory. Unfortunately I don't understand it well enough to describe it to you. And since it's copyrighted I can't really give it to you. Sorry I can't be of more help on this one. But if you can locate a colleague to borrow the book from I'm sure you'll find what you need.

Unless anyone else on the forum has the same book and wants to describe it? jbartos?