We need to look at two things: Art 450 for transformer protection and Art 240.21 for conductor protection.
With a 60 amp breaker you are well within the allowed 125% of the primary current and that can be as much as 250% IF you have proper secondary protection.
Likewise you are below the allowable secondary over current protection with your 100 amp breaker.(I normally see 125 amp or 150 amp on a 45kva)
You wire size are correct for the over-current protection you describe. (The secondary could possibly have been a #3).
As far as what you stated, you are Code compliant provided the length of your secondary conductors must meet one of the 250.21(C) rules.
You did not mention how you handled your system bonding jumper, grounding electrodes, etc.[/QUOTE
The only thing that one should be cautious about when selecting a primary MCCB protective device is to make sure that the instantaneous pickup is greater than the transformer's inrush when energizing the transformer. A 150deg C rise 45kva transformer customarily will have 11x or greater inrush. When considering 115, 80degC and K-factor transformers the inrush will be even greater. As such my suggestion would be is to select the highest rating OCPD that is allowed by the NEC. There really is no reason to do otherwise. Basically, when secondary protection is required and/or provided go with the 250% rule for primary protection. The sec. oCPD is the device that protects the secondary conductors as well of the transformer for overload.
The Pri. Device simply provides short circuit protection should the there be a transformer failure which often is commonly an internal fault. The goal is to take that transformer off line before it affects the upstream dist. system.
The most difficult application is the 3ph 480D-208y/120 75kva transformer with a 90fla primary. I have have countless call regardind nuisance tripping when energizing the transformer. All too often the panel being used to feed thevtrasformer is limited to a maximum of a 100a frame breaker. Pointing out what that issue is not a pleasant task.
