The Pirate Henry Hotel at Port Royal has a chilled water AC system. At the Chiller room of the hotel the following loads are connected: Z1 = 6 ∠300 Ω, Z2 = 8 ∠450 Ω, Z3 = 10 ∠600 Ω each connected between the red phase and neutral, yellow phase and neutral, and blue phase and neutral respectively. A 3-phase 60 Hp induction motor 90% efficiency and operating at 85% power factor lagging. A 3-phase 100 Hp induction motor 85 % efficiency and operating at 80% power factor lagging.

Choosing a suitable 3-phase, 4-wire, voltage system (as used in Jamaica) to supply these loads and assuming all the phase to neutral voltages are the same, and a RYB Phase sequence:

a. Calculate the line currents supplying loads.

b. Calculate the current in the neutral wire to the loads.

c. Calculate the positive, negative and zero phase sequence components of the currents determined in (a) above.

d. Use the sequence components determined in (c) above to calculate the line currents.

e. Calculate the overall power factor of the system.

Answer rating: 100% (QA)

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