Answer Happy

For the electrical installation shown in Figure Q5, it is required to provide time-current grading, using At least 0.4 second as the selectivity margin. Suggest the TMS values of the two DMT relays. Finally, generate a summary table of the approximate tipping times of all the overcurrent protection devices under all the four fault cases, when the DMT relays are set according to your suggestion (13 marks) B c1 C2 Load IDMT #A IDMT #B MCB NC is Type C Figure Q5 Parameters of the electrical installations are given below: IDMT Relay Plug setting CT ratio Fault current at the point at point (PS) (Given) A A 125% 400/5 6000 A A B 100% 20015 5000 A Both DMT relays are “1.33 second" type with a rating of 5A. The IMS can be set to any value between 0.05 and 1.0. Fault curent at points Cl and C2 are (3000) A and (2000+) A respectively. The rating of the Type C MCB is 32 A.