Calculating reactive capability limits 1

[olicg]

I wanted to calculate the Qmax limits for our generator which has following data:

170 MVA, 0.8 lagging to 0.9 leading, 15.5 KV rated terminal voltage. Ifl = 6333 A

While searching on the net found a useful research paper which gives the following equation to be used:

Q max (based on stator current limit) = SQRT(V2 x I2fl - P2 active)
where V2 = square of V and I2 = square of I and P2 = square of P.
My questions are:
Is it a correct formula?
Can we re draw the reactive capability curve at different generator terminal voltage?
What is the (normally or industry practice) stator current limiter operational set point value? we have 1.05 PU. Is there usually a time delay?

 

[ScottyUK]

Reactive power capability is usually defined by the rotor thermal limit below about 0.6pf, so your formula is at best incomplete. The formula is really just telling you what reactive capability you have given unit power output and generator MVA rating.



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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[olicg]

Thanks,


olicg

 

[cuky2000]

Olicg

Enclose are couple basic info associated with generator reactive capability curve that may supplement other references.

Beware that in addition of generator heating limits by the field, armature and the stator_end, there are other limits such as driver capability, stability limits, cooling medium temperature/pressure, AVR limit, etc.

Good luck.

http://cuky2000.250free.com/Gen_Reactive_Cap_Curve__Calc.pdf