Power Transformer Rated Value and Maximum Value

This depends on specific context. For example, gensets may have a continuous rating and a somewhat higher intermittent rating. Multitap transformers may have several coordinated voltage/current ratings. The maximum KVA rating might be at an intermediate voltage/current combination, and this might be chosen as the nominal transformer rating. However, the maximum voltage might be higher (but with less current and less KVA).

In general maximum values are rated for short durations of time to allow for these possibility's during operation. There should always be a safety factor when considering the design of equipment.

But opposite is the case with circuit breakers?

No, the rated value can never be higher than the maximum.

It depends on the engineer(s) who did the designs on that particular equipment and the type or function the device. If he is experienced and safety is one major factor considered ahead of profit, then he will incorporate a margin of safety into his designs, and that will serve as the maximum rating capacity for that equipment.

On the other hand, the opposite will be true for circuit breakers and other limiting devices, which are meant or intended for safe operation applications. The rated capacity most of the time for this type of applications are and should be the maximum rated capacity the device can safely tolerate just before they interrupt any other form of operations ..

In the case of rated vs maximum supply voltage, it is quite common for the utility to be allowed to have a continuous supply voltage of +-10% from nominal. So 33kV nominal would mean that the utility could supply in the range from 29.7-36.3 kV, and your equipment better be able to handle it. The response on circuit breakers elsewhere is spot on.