(a) Determine the time of operation of a IA, 3 s over-current relay h…

Question

(a) Determine the time of operation of a IA, 3 s over-current relay having plug setting of 125 per cent and a time multiplier of 0.6. The supplying CT is rated 400 : 1 A and fault currently is 4,000 A. The relay characteristic curve is given below:

| PSM | 1.3 | 2 | 4 | 8 | 10 | 20 |

|---|---|---|---|---|---|---|

| Time of operation ( in second) | 30 | 10 | 5 | 3.3 | 3 | 2.2 |

(b) Explain rotor fault protection against loss of excitation and rotor earth fault.