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X/R Ratio of Large Generators

X/R Ratio of Large Generators

X/R Ratio of Large Generators

(OP)
Hello to all,

After reading an article on generating stations some time ago, I thought of getting some first hand information from our learned members.

As you all know during a short circuit the magnitude & shape (current zero crossings) of the asymmetrical current wave depends on the relevant X/R ratio at the fault location. High X/R ratio results 1) high peak 2) non current zero crossings at least on one phase 3) etc. Normally ANSI & IEC recommends to watch about existence of non current zeros if X/R > 17 (60 Hz) or 15 (50 Hz) when specifying circuit breakers especially for generators. As a result we have to device some method to obtain current zeros by introducing resistors on the breakers during a short circuit or intentionally delaying the breaker contact parting time (in IEC terms opening time) etc. etc.

I understand that in off shore oil platforms gas turbine generators with very high MVA ratings are being used for oil production. That means obviously they must be having very high X/R ratios.

Therefore could any member from large generating stations, kindly furnish the following data (I believe that they are not secret data) taken from existing generator data sheets so that a simple short circuit calculation can be performed to sketch the current waveforms of all three phases?

1)Generator nominal MVA & kV rating?
2)X/R ratio?
3)Resistance Rg?
4)Time Constants Td”, Td’ and Tg (some say Ta)?
5)Reactances Xd”, Xd’ and Xd?
6)Do the circuit breakers on the generator bus (or any
  other Bus) have any special method for current breaking
  due to possible existence of non-current zeros?
7)Breaker type (Vacuum, SF6, Air Blast) & Contact
  parting   time (ANSI)/ Opening time (IEC)?
8)Any other relevant data?

Thanks in advance!
Kiribanda  

RE: X/R Ratio of Large Generators

If you provide a size or two (MVA, Voltage) of generators of your interest,I may be able to provide you data that the program I have spits out as 'typical' values.  

RE: X/R Ratio of Large Generators

(OP)
Hi rbusara,

The ratings must be in the range of 200 to 300 MVA/ 11 kV. Large generators fall into that range I guess. Even ETAP/ SKM software programs have got typical values-which have been copied from old handbooks - which I also tried.

But at this moment I am really interested in "existing values" rather than "typical values" of large generators.

Thanks for your effort!
Kiribanda

RE: X/R Ratio of Large Generators

Hello,

You may visit some generator manufacturer web sites for example:

www.solar.com
www.wartsila.com

They may have what you are looking for.

In a private email I may send you one or two data sheet of some generators

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