Kiribanda
Electrical
- May 6, 2003
- 697
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
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