A 400 MVA, 22 kV synchronous generator is tested for OCC and SCC. The following data are obtained from these characteristics extrapolated where needed. If = 1120 A, VOC = 22 kV, ISC = 13.2 kA At If corresponding to ISC = Irated it is found that VOC (air-gap line) = 24.2 kV (line). (a) Determine

Question

A 400 MVA, 22 kV synchronous generator is tested for OCC and SCC. The following data are obtained from these characteristics extrapolated where needed.

[latex] I_{f}=1120 A , \quad V_{O C}=22 kV , \quad I_{S C}=13.2 kA[/latex]

At [latex] I_{f}[/latex] corresponding to [latex] I_{SC} = I_{rated}[/latex] it is found that [latex] V_{OC}[/latex] (air-gap line) = 24.2 kV (line).

(a) Determine [latex] X_{s}[/latex] (saturated) in ohms and in pu.

(b) Determine SCR.

(c) Determine [latex] X_{s}[/latex] (unsaturated) and [latex] I_{f}[/latex] corresponding to [latex] V_{OC} = 22.4 kV[/latex] on air gap line.

(d) The generator when operating on no-load rated terminal voltage, find the value of the generator current if it is short circuited.

Accepted Answer

Base [latex] ( MVA )_{B}=400,( kV )_{B}=22[/latex] (line) or 12.7 (phase)

[latex] I_{B}=\frac{400}{22 \sqrt{3}}=10.49 kA[/latex]

[latex] ( Ohm )_{B}=\frac{22 \sqrt{3}}{10.49}=1.21 \Omega[/latex]

(a) [latex] I_{f} = 1120 A[/latex]

[latex] V_{O C}=V_{ ext {rated }}=\frac{22}{\sqrt{3}}=12.7 kV[/latex] (phase)

[latex] I_{S C}=13.2 kA[/latex]

Then [latex] X_{s}( sat )=\frac{12.7}{13.2}=0.962 \Omega[/latex]

Or [latex] \frac{0.962}{1.21}=0.795 pu[/latex]

(b) [latex] S C R=\frac{1}{X_{s}( sat )( pu )}=\frac{1}{0.795}=1.258[/latex]

(c) [latex] I_{S C}=I_{ rated }=10.49 kA[/latex]

[latex] V_{O C} ext { (air gap line) }=24.2 kV[/latex] (line)

= 13.97 kV (phase)

[latex] X_{s} ext { (unsat) }=\frac{13.97}{10.49}=1.33 \Omega=\frac{1.33}{1.21}=1.1 pu[/latex]

For finding [latex] I_{f}[/latex] [latex] SCR =\frac{o f^{\prime}}{o f^{\prime \prime}}[/latex] (Fig. 8.15)

[latex] 1.258=\frac{o f^{\prime}}{1120}[/latex]

Or [latex] I_{f}=o f^{\prime}=1120 imes 1.258=1409 A[/latex]

Question 8.44: A 400 MVA, 22 kV synchronous generator is tested for OCC and...

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