Fully rating

[Ingenieur]

You need to check your math. 27kA sounds reasonable to me.
It would not be unusual for a utility transformer, <300kVA, to be quoted as having an impedance of 1.5%.
The OP said their breakers were rated 10kAIC which is a standard rating for '240V' equipment.

600A / .015 = 40kA

Utilities typically provide available short circuit amps based on the worst case transformer they might ever supply. They want to make sure your equipment does not become overdutied because they had to replace your transformer with 'whatever they had in the yard' during an emergency.

Typical utility data sheet http://www.hydroonebrampton.com/pdfs/2010/standard1950_r8.pdf

not used to seeing 2% ~30 KA at 600 A
wide range

most of the stuff I work with are 1 MVA 5-6% range

Detroit Edison
https://www2.dteenergy.com/wps/port...nbfSavUHiBfvGQ!!/dl4/d5/L2dBISEvZ0FBIS9nQSEh/

learn something every day

 

[Ingenieur]

Pretty useful summary
page 5
util mva vs xfmr kva

http://www.fs.fed.us/database/acad/elec/greenbook/10_shortcalc.pdf

alot higher than I expected