(a) What is meant by time grading in protective systems?
(b) In FIGURE 1, time graded relays control the circuit breakers. Which will have the shortest delay in operating for a fault at the location shown
(c) A voltage transformer for use on an 11 kV system has a star connected primary. If the turns ratio is 100/1 what will be the residual voltage of the open delta winding?
(d) A 1 A electromagnetic relay has 80 turns on minimum setting. If the settings are from 50% to 200% in 25% steps, calculate the plug bridge turns for each setting. If the relay presents a burden of 3 VA determine the number of turns required if the relay was to operate at 12 V.