Synchronous generator parameters (units?)

[eeprom]

Hello,
I have the specification parameters for an old GE generators. I am trying to determine the short circuit currents for transient, sub-transient, and synchronous reactances. In my document, I have all the reactances, but no units. I have for example: X'di = 1.64 Rated I. So this is the transient reactance at rated current. Is this value in ohms or per unit? I am assuming these are given as per unit, but I'd like to know for sure, as there is a big difference. Is there a way to tell for sure that the units given for the machine reactances are in per unit?

thanks

 

[lume7006]

Hello,

Typically, generators data sheets are expressed in per unit at rated voltage and power of the unit.

In some cases, mainly for large units, they can also be refered to rated current.

The value you showI believe is too high for X'd, but maybe it is because of the "age of the unit"

 

[ScottyUK]

lume,

We don't know if this is a turbo machine or a salient pole design. X'd might be accurate.


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If we learn from our mistakes I'm getting a great education!

 

[lume7006]

Hello Scotty,

I think you are right, there could be several factors to define the values of the reactances.

thank you for the hint!

 

[eeprom]

FYI,
The reactances are given in per unit. I determined this by a simple sanity check. If I used subtransient wrt v to calculated short circuit current, I get a short circuit something like 25 times the rated FLA. This number is not reasonable. So if I multiply that same reactance value to the Z base, I then get a short circuit current of around 4.5 times the rated FLA. This makes much more sense.