Abstract :
The practises of the station operator in regard to circuit breakers are largely governed by his previous experience, his system and conditions on his system. For instance, a very large system may cover a very large area and have a very great capacity connected, but be of such a character that there is very little interconnecting, with very simple switching, and it may have no very great power capacity concentrated at any one point. On the other hand, the system may be very great in power capacity and cover such a small area that the potential of the system is rather low, and on account of the dependability of low potential and the lack of the necessity of numerous ties, the concentration of power is easily limited. In the first case, we find potential so high, and the breaker has to be so large to safely handle the potential, that lightning is not much of a factor, and the current is so small that it is really insignificant in such a large breaker. In the second case, the currents are greater and the breakers of necessity have to be large and substantial to withstand the great magnetic stresses, but such systems generally are confined to a small, closely built area, largely underground, where lightning is a small factor, and they are not interconnected to a great extent on account of the greater reliability of the low potential of the system. The breakers are not subject to such excess capacities, hence the low-potential breaker problem is not such a difficult one.
