Chapter 6, Problem 6.79P

Q34

Q32

Section 15-3 reversing motors using magnetic starters.Section 15-3Use data sheet B on page 383 to draw the wiring diagram. Note: use only the number of contacts required. First 1. Wire the motor to operate in forward and reverse at 115 VAC.

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Use data sheet B on page 383 to draw the wiring diagram. Note: use only the number of contacts required. First 1. Wire the motor to operate in forward and reverse at 115 VAC.

B:A 20 MVA transformer which may be called upon to operate at 30% overload, feeds 11 KV busbars through a circuit breaker: other circuit breakers supply outgoing feeders. The transformer circuit breaker is equipped with 1000/5 A CTS and the feeder circuit breakers with 400/5 A CTS and all sets of CTs feed induction type over current relays. The relays on the feeder circuits breakers have a 125% plug setting, and 0.3 time setting. If 3 ph fault current of 5000 A flows from the transformer to one of the feeders, find the operating time of the feeder relay, the minimum plug setting of the transformer relay and its time setting assuming a discrimination time margin of 0.5 sec. Relays having the following characteristics for TMS=1 PSM T in sec. 2 3.6 5 10 15 20 10 6 3.9 2.8 2.2 2.1

10.34 Determine the power readings of the two wattmetersshown in the circuit of Fig. P10.34 given that ZY = (15− j5) W

10.29 A 208-V (rms) balanced three-phase source supports twoloads connected in parallel. Each load is itself a balanced threephaseload. Determine the line current, given that load 1 is 12 kVAat pf 1 = 0.7 leading and load 2 is 18 kVA at pf 2 = 0.9 lagging.

10.31 A 240-V (rms), 60-Hz Y-source is connected to a balancedthree-phase Y-load by four wires, one of which is the neutral wire.If the load is 400 kVA at pf old = 0.6 lagging, what size capacitorsshould be added to change the power factor to pf new = 0.95lagging?