Two IDMT type relays have to be coordinated for a fault current of 10,000 amps with a coordination interval of at least 0.3 seconds. The downstream relay is designated as A and the upstream relay as B.
Calculate the TMS setting (to two decimals) of B to achieve coordination based on the data given below.
Both relays have characteristics defined by the IEC operating curve for Normal inverse type of protection.
A is connected to a CT of 600/1 ratio and has a pick-up setting of 0.7 pu TMS of 0.20.
B is connected to a CT of 1200/1 ratio and has a pick-up setting of 0.9 pu.