Breaker panel currently has a double pole 30 amp breaker and it is a replacement for a 30 amp main breaker that had failed. It has tripped when many things in the house were on simultaneously.

You need to replace it with the same size breaker. Breaker size must be determined by the wire size of the circuit. If you have a 60 amp main panel for a house, it's too small. In many cases 100 amp services are too small. A bit more information is needed to evaluate your question and answer accordingly