ElecPwrPEOct11
Well-known member
This problem specifies a synchronous 3phase generator rated at 50kVA, 230V with per unit reactance of X'd= 0.4. With analysis performed at rated values, what is the magnitude of the transient current?
The solution uses:
Vbase = 230V
Sbase = 50kVA
I base = 50/ (sqrt (3) * V) = 125A
then
1) Vi=I' * X'd.
2) I (pu) = Vi / X'd so = 1 / 0.4 = 2.5 pu
3) On the 50kVA base I actual = Ipu * Ibase = 2.5 * 125 = 312.5A
For these types of problems I've always used the general generator equation Ea = Vt + j*I*X'd
At rated values Vt = 1pu = 230V. We know X'd, but don't know Ea or I. I'm not sure how to solve for I, but don't see how the equation in 1) above is valid. I'm looking to NCEES #135 for guidance but it simply assumes I = 1pu. 2 questions- is the CI answer correct, and if so where does the Vi= I' * X'd equation come from?
The solution uses:
Vbase = 230V
Sbase = 50kVA
I base = 50/ (sqrt (3) * V) = 125A
then
1) Vi=I' * X'd.
2) I (pu) = Vi / X'd so = 1 / 0.4 = 2.5 pu
3) On the 50kVA base I actual = Ipu * Ibase = 2.5 * 125 = 312.5A
For these types of problems I've always used the general generator equation Ea = Vt + j*I*X'd
At rated values Vt = 1pu = 230V. We know X'd, but don't know Ea or I. I'm not sure how to solve for I, but don't see how the equation in 1) above is valid. I'm looking to NCEES #135 for guidance but it simply assumes I = 1pu. 2 questions- is the CI answer correct, and if so where does the Vi= I' * X'd equation come from?