Question

4.

(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.

DIE FIG. 1

Answer 1

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