138kV Short Circuit Utility data received looks like absurdly high numbers - explanations ? 1

[bdn2004]

The Utility says the available short circuit energy is 6964 MVA at 138kV at their substation. The 3-phase fault value from the Utility is 29.38kA.
6,964,000,000 / (138,000 * 1.732) = 29,136 Amps ...close to the value given. I'm not used to dealing with transmission voltage levels, but doesn't this number look absurdly high?
What are we doing wrong?

 

[Overvoltage]

Depends on their interconnection, etc, but looks reasonable to me, especially if the line has multiple interconnections nearby.

 

[davidbeach]

That's not a high value. There's a reason that transmission breakers can be had with 63kA and 80kA interrupting ratings.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[bacon4life]

Looks like a typical value to me.

 

[7anoter4]

According to IEC 60076-5/2000 Ability to withstand short circuit
Table 2 – Short-circuit apparent power of the system
Short-circuit apparent power [MVA] for Highest voltage for equipment 145 and 170 kV Current North American practice: 15 000 [MVA]

 

[bdn2004]

Wow... lotta power, did not realize that thanks. We were asked to give the short circuit value from our power software on the 138kV side of a plant regulating transformer - which they want to replace. Does a transformer itself have a maximum short circuit withstand value?

There are multiple 138kV sources including tie lines, grid transmission lines, and two local power plants nearby that can feed it. I don't think our power software that we use for medium voltage coordination and arc flash has any of this modeled accurately. I've suggested they get this information from those responsible for the transmission line protection schemes.

 

[cranky108]

The bracing inside the transformer need to be able to handle it's contribution of fault current.

 

[bacon4life]

Yes the transformer will have a maximum withstand rating. Lower voltage transformers are often designed for an infinite high side bus, but substation transformers per the IEEE standards assume a very small source impedance.