Unsaturated and saturated subtransient reactance
Unsaturated and saturated subtransient reactance
(OP)
Hi Guys,
I am working on a short circuit study with four generators (range in size from 5MW to 30MW). I have been provided the subtransient reactance, Xd'', however it turns out that all the values I have been given are unsaturated values. There isn't a way to relate unsaturated values to saturated values is there? I was just going to default to IEEE std. 141 if I can't find any type of relation (and my hopes are pretty low on there being a boiler plate relation, given the physical differences from one generator to the next)...
None the less, if anyone knows a place i can look it would be greatly appreciated.
Tim
I am working on a short circuit study with four generators (range in size from 5MW to 30MW). I have been provided the subtransient reactance, Xd'', however it turns out that all the values I have been given are unsaturated values. There isn't a way to relate unsaturated values to saturated values is there? I was just going to default to IEEE std. 141 if I can't find any type of relation (and my hopes are pretty low on there being a boiler plate relation, given the physical differences from one generator to the next)...
None the less, if anyone knows a place i can look it would be greatly appreciated.
Tim





RE: Unsaturated and saturated subtransient reactance
David Castor
www.cvoes.com
RE: Unsaturated and saturated subtransient reactance
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If we learn from our mistakes I'm getting a great education!
RE: Unsaturated and saturated subtransient reactance
Out of curiosity, does anyone have any published information with both unsaturated and saturated reactances? I definitely won't make any conclusion based on your published info, but it is nice to see some actual values for generators. Specifically, salient pole hydro gens.
Thanks for the input
Tim
RE: Unsaturated and saturated subtransient reactance
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Unsaturated and saturated subtransient reactance
AS3851 is based on IEC60909, however section 3.6.1 of IEC60909 does not mention any ratio of X"d sat / X"d unsat to use when only X"d unsat is available.
RE: Unsaturated and saturated subtransient reactance
RE: Unsaturated and saturated subtransient reactance
tricard:
Eddy is right. With an X"d sat = 0.85 * X"d unsat one is on the safe side.
For determining X"d unsat you have to perform a sudden three-phase short test with a terminal voltage as low as possible (10 to 15%). For X"d sat determination a terminal voltage of 100% is required. This is very risky and is therefore done not very often. A test with 40% rated voltage gives you neither a correct "sat" nor a correct "unsat" X"d value.
Regards
Wolf
www.hydropower-consult.com
RE: Unsaturated and saturated subtransient reactance
The actual pu values are
X"dsat = 0.200
X"dunsat = 0.230
X'dsat = 0.270
X'dunsat = 0.300
Xdsat = 1.860
Xdunsat = 2.660
These number vary from one set to the next, but X"d ratio is close to what Eddy has stated.
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