Estimating X/R Ratio
Estimating X/R Ratio
(OP)
Hi all,
I first want to apologize because I can't imagine that this question hasn't been asked...but nothing turns up in my search for X/R in the key-word...so here goes:
I find that in estimating X/R ratios, I always end up using a graph of typical X/R versus machine kVA from a GE tech paper (or ANSI C37.010). Now those aren't too shabby of resources, but then my estimates are not derived directly from my given info.
Say I was given kW, kVA, rated voltage, stator & field resistance, subtransient, transient, and synchronous d and q reactances, zero seq and neg seq reactance plus all associated time constants with a generator's open circuit and short circuit tests...
I'd guess that coming up with X/R of the source would be a slam dunk...but I can't come up with a number for it even in the ballpark of the ANSI reference - but I have a software package that hits it nearly on the nose (by some type of magic, I presume)...
I'm embarrassed by this...what am I missing (other than an intuitive grasp on the subject)?
I first want to apologize because I can't imagine that this question hasn't been asked...but nothing turns up in my search for X/R in the key-word...so here goes:
I find that in estimating X/R ratios, I always end up using a graph of typical X/R versus machine kVA from a GE tech paper (or ANSI C37.010). Now those aren't too shabby of resources, but then my estimates are not derived directly from my given info.
Say I was given kW, kVA, rated voltage, stator & field resistance, subtransient, transient, and synchronous d and q reactances, zero seq and neg seq reactance plus all associated time constants with a generator's open circuit and short circuit tests...
I'd guess that coming up with X/R of the source would be a slam dunk...but I can't come up with a number for it even in the ballpark of the ANSI reference - but I have a software package that hits it nearly on the nose (by some type of magic, I presume)...
I'm embarrassed by this...what am I missing (other than an intuitive grasp on the subject)?





RE: Estimating X/R Ratio
Your software most likely just has a lookup table based on the ANSI chart you mentioned.
Conrad St. Pierre has some discussion in the Appendix of his book indicating that X/R can be approximated as 2pi times frequency times ta3 (short circuit dc time constant)
You may want to grab a copy of his book "A Practical Guide to Short Circuit Calculations" for more info.
David Castor
www.cvoes.com
RE: Estimating X/R Ratio
RE: Estimating X/R Ratio
Grollor33:
What you mean with X/R ratio? Synchronous machines have reactances like
synchronous reactance Xd and Xq
transient reactance X'd and X'q
subtransient reactance X"d and X"q
and quite a few more.
Regards
Wolf
www.hydropower-consult.com