Generator Decrement Curves.

[Russell W. Patterson at T.V.A.]

Dear You-uns:

I'm setting a 51V relay (voltage controled/restrained backup overcurrent)
on a hydro generator. I'm going through the procedure in the Buff book
(ANSI/IEEE Std 242-1986) and am plotting the decrement curves as they did.

My question:

The synchronous portion of my total current curve is higher in magnitude than
the transient current. This may be possible in generators... I don't know
(thats why I'm posting). I would expect the current to go from a high, sub-
transient magnitude to a lower, transient magnitude and go into steady state
at a still lower magnitude (synchronous).

Anyone with generator parameter experience of Std 242-1986 please help.

The equations are:

1) Field forcing 3PU field current

Iac = .953exp-50t - .324exp-.455t + 3 (pu, multiply by 1464 for Amps)

2) Constant excitation (stuck regulator)

Iac = .953exp-50t + 1.676exp-.455t + 1 (pu, bla bla bla as above)

3) DC offset

Idc = sqrt(2.0)*3.629exp-10t

4) Itotal = sqrt(Iac^2 + Idc^2)

You can see that the negative second term in equation 1) is the
reason my curve dips back up in magnitude.

thanks,
russ

p.s.

Generator parameters:
kV = 13.8 kV Td" = 0.02 s
kVA = 35000 kVA Td' = 2.2 s
Xd" = 31 % TA = 0.1 s
Xd' = 44 % IFg = 1 pu
Xd = 100 % IF = 3 pu
et = 1 pu pf angle =23.7943deg

--------------------
Russell W. Patterson, Tennessee Valley Authority
Transmission/Power Supply, System Protection & Analysis
E-mail: rp...@tva.gov
moderator internal newsgroup ----> tva.engineering.relaying
proponent Usenet newsgroup ------> sci.engr.electrical.sys-protection

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