how to calculate the short circuits currents
how to calculate the short circuits currents
(OP)
I got a question about the calculation of shrt circuit current, I got a salient poles generator with X`d and X`q, how i could use it.. in example: the reactance base is 18 ohms, and X`d is 20% and X`q is 25 %, the voltage is 6000 V, how do you take into account the reactances. Do you sum?






RE: how to calculate the short circuits currents
RE: how to calculate the short circuits currents
if i write it i think its
Xtotal transient= X`d+ jX`q is this true?
RE: how to calculate the short circuits currents
The Xd is the reactance for current 90deg out of phase with the no-load generated voltage. Xq is the reactance for current that is in phase with the no-load generated voltage. Short circuit current is usually close to 90deg out of phase with the voltage, hence the reason direct axis components are normally used for fault calculations.
You might want to take a look at a couple of references listed in the FAQ238-1287: What are good references for a Power Engineer? for this forum -
Elements of Power System Analysis by William Stevenson
or
IEEE Red Book - Industrial Power Systems
RE: how to calculate the short circuits currents
Thank you for your post and link really nice info.
RE: how to calculate the short circuits currents
RE: how to calculate the short circuits currents
thanks a lot for your answers
RE: how to calculate the short circuits currents
You need calculate not only short circuit current.
In your case for example, you need use Xq for calculate underexcitaton ( or min. reactance) setting.
Regards.
Slava
RE: how to calculate the short circuits currents
I agree with Slava:
The transversal reactance[xq,xq',xq"] is used to calculate other important parameters as for instance:.
Synchronizing power Ps is defined as the power per electrical radian of rotor displacement; in other words = ?P/??
For steady-state[ very small changes] :
Ps=Eo*U1/xd*cos??U1^2*(xd-xq)/xd/xq*cos2?
Were ? is the internal angle from Eo to U1
The synchronizing torque Ts is given by
Ts=Ps/?s
where ?s is the synchronous angular speed of the machine.
From Eq. (8), it is clear that the synchronizing power is a maximum for no load (? = 0) and decreases as the load on the machine increases.
For a load angle of 90 electrical degrees, the synchronizing power is zero, meaning that the machine is on the verge of instability.
The larger the load angle, the less stable the synchronous machine becomes.
The output power per phase is also[for steady state]:
Pa=Eo*U1/xd*sin?+U1^2/2*(xd-xq)/xd/xq*sin2?
The are a lot of other application also.
Best regards
RE: how to calculate the short circuits currents
Find pls. a jpeg attached, better.
RE: how to calculate the short circuits currents
Attached is the correction.
RE: how to calculate the short circuits currents
thanks to all of you for your time and hope all of you got a happy entering on the new year.....
RE: how to calculate the short circuits currents
Again mix of terms.
I wrote about underexcitaion/min. reactance/loss of excitation setting for the electrical protection 40, where for the silent gen. possible used Xq instead Xd.
You ask about excitaion current limit. This Q for the genrator mnf. only.
Regards.
Slava