another decrement curve question

[robeward]

I have been trying to teach myself some more about generators and decrement curves the last couple days. I wanted to attach a few images and see if any of the results appear off. i am using Power Analytics DesignBase.

225 KVA gen. attached is alternator data sheet(split for size). the highlighted yellow is the one in question.
the hand written numbers are for the my application
x''d = .104 pu
x'd = .339 pu
xd = 3.974 pu
x2(neg) = .104 pu
x0(pos) = .01 pu

Gen FLA = 225KVA/(208*1.732) = 624 A

the image attached is the input screen for gens in designBase. disregard the library as they do not have this small of a gen. i have changed all numbers. i don't know if it causes other issues beyond the values seen here but don't believe so.

my first question is on the x/r ratio. the gen data sheet does not have one and from what i have see it is not common for that to be given. if i enter the armature short circuit time the program estimates the x/r to 3.39 seen.

i believe it is doing this based on the approximation of x/r = 2*pi*f*Ta3

i am going to post the decrement curve also. i am just looking for a sniff test here. not trying to get someone to hand jam out everything. i am just trying to get more familiar with what all these numbers mean and how they affect the results.

 

[LEO2854]

I have been trying to teach myself some more about generators and decrement curves the last couple days. I wanted to attach a few images and see if any of the results appear off. i am using Power Analytics DesignBase.

225 KVA gen. attached is alternator data sheet(split for size). the highlighted yellow is the one in question.
the hand written numbers are for the my application
x''d = .104 pu
x'd = .339 pu
xd = 3.974 pu
x2(neg) = .104 pu
x0(pos) = .01 pu

Gen FLA = 225KVA/(208*1.732) = 624 A

the image attached is the input screen for gens in designBase. disregard the library as they do not have this small of a gen. i have changed all numbers. i don't know if it causes other issues beyond the values seen here but don't believe so.

my first question is on the x/r ratio. the gen data sheet does not have one and from what i have see it is not common for that to be given. if i enter the armature short circuit time the program estimates the x/r to 3.39 seen.

i believe it is doing this based on the approximation of x/r = 2*pi*f*Ta3

i am going to post the decrement curve also. i am just looking for a sniff test here. not trying to get someone to hand jam out everything. i am just trying to get more familiar with what all these numbers mean and how they affect the results.

What are decrement curves?

 

[Phil Corso]

Robeward, Leo2854,

Decrement curves depict how AC machines react with respect to time for specific operations. Most transient conditions can not be desribed wih a single "fault" impedance. Instead, the values you list, plus several others, are used to determine the fault-current decay-rate thru several time-periods, usually identified as, fault-initiation, sub-transient, transient, and steady-state!

The X/R value you mentioned represents that part of the process involving Armature-Reaction which is non-linear during transients! It is not derived from any of the values listed!

To continue your quest for knowledge I suggest you procure a good reference, such as Prof. J. Lewis Blackburn's, "Symmetrical Components!"

Regards, Phil Corso (Cepsicon@aol.com)