Alternator in parallel new critical clearing time

[jaus tail]

Homework Statement

Homework Equations

critical clearing time proportional to square root of (H / (P times frequency) ) equation 1
Power remains same as alternator at 1p.u
Frequency is also same
H will increase.
It's not given so we can assume machines swing together, so H = H1 + H2 = 2H since they are identical.
If machine wouldn't swing together it'd be H1. H2/ (H1 + H2)

The Attempt at a Solution

So now we get from equation 1 time(clearing) proportional to Square root of H
So 0.4/(new tcr) = (square root of (H/2H) = 0.707
So new tcr = 0.567sec
Answer is D
Book answer is B
How?

 

[anorlunda]

There's an ambiguity in the problem statement. Are the two generators the same size as the original generator, or are the two both half the size (rating) as the original one? It also doesn't say what the per unit base the 0.5 power is based on, system or generator? System is the usual base.

But with the most likely interpretations, I agree with you: D.