'What will the value of the short-circuit current be?'. The short-circuit current value on the first circuit breaker depends on the size of the transformer and the length and size of the cable from the transformer to that Circuit Breaker. Here is a document explaining how to calculate the short-circuit current.
Do not simply replace an MCCB with one that has the same rated current. The most important consideration is the Ultimate short-circuit breaking capacity (Icu). Incorrectly replacing MCCB will result in dangerous consequences. In this video, we will guide you through the step by step process to do this.