For the design and application of a protective scheme, it is very useful to have an idea of the frequency of occurrence of faults on various elements of a power system. Table 1.1 gives an approximate idea of the fault statistics.
Table 1.1 % Distribution of faults in various elements of a power system

From the table, it is evident that 50 % of the total faults occur on overhead lines; hence it requires more attention while planning and designing protective schemes for a power system. Table 1.2 shows the frequency of occurrence of different types of faults on overhead lines.

Table 1.2  Frequency of occurrence of different types of faults on overhead lines

From table 1.2, it is evident that the frequency of L-G faults is more than any other type of fault and hence protection against L-G fault requires greater attention.