(a) Describe the normal criteria used for setting thermal protection relays and their advantage compared to magnetic types.

(b) Calculate the r.m.s. value, the form factor and peak factor of a periodic voltage having the following values for equal time intervals changing suddenly from one value to next: 0, 5, 10, 20, 50, 60, 50, 20, 10, 5, 0, -5, -10, V etc. What would be the r.m.s. value of a sine wave having the same peak value?