GBM asked in Science & MathematicsEngineering · 7 years ago

# Y connected Sync Generator reactance Xs resistance?

A 3MVA, 11kV three phase Y connected generator has no load voltage of 12488V (Eo). At the rated voltage and apparent power conditions, the load power factor is 0.8 lagging.

Q. Determine the sync reactance Xs neglect the armature resistance?

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• UJ
Lv 6
7 years ago

S = 3 x 10^6 VA

E(no-load) = E(line-line) = 12488 V

Solving for I:

I = S/V(phase) = (3 x 10^6)/(11,000/sqrt(3)) = 472.377 A

By using phasor diagram:

pf = cos(THETA) = 0.8

THETA = arccos(0.8) = 36.87 degrees

rf = sin(THETA) = sin(36.97 deg) = 0.6

[E(line-line)]/sqrt(3) = SQRT[((V(terminal)/sqrt3)*(cos(THETA)))^2 + ((I)*Xs + (V(terminal)/sqrt3)*(sin(THETA)))^2]

12488/sqrt(3) = SQRT[((11,000/sqrt3)*(.8))^2 + ((472.377)*Xs + (11,000/sqrt3)*(.6))^2]

Solve for Xs:

Xs = 2.763 ohms => answer!

Source(s): Electrical Technology Volume II by B.L. and A.K. Theraja
• Rick
Lv 7
7 years ago

I can't answer this, because you haven't told us what current and PF apply at a generator terminal voltage of 11 kV. Are you saying the terminal voltage is 11 kV at a load of 3 MVA and a load R and L that give a PF of .8?