9,11 and 13

9. A 100 -watt incandescent lamp produces 1200 lumens at 220 volts. Compute it efficiency and efficacy. 10. A manufacturer requires 1000kW of true electrical power. An electric utility supplies single-phase AC at 12kV and 60Hz. (a) Compute the current required if the power factor is 50%. (b) Compute the current required if the power factor is improved to 95%. (c) How much do the current and line losses decrease for this customer when the power factor is improved from 50% to 95% ? 11. A single-phase AC motor is operated at 120V, producing 5hp with an efficiency of 89% and a power factor of 87%. What is the current through the motor? 2-22 CHAPTER 2. AC POWER SYSTEMS 12. A freight elevator is built to lift a long ton (2200 lb) a distance of 100 feet in 30 seconds. The mechanical efficiency of the gears and cables is 85%. The elevator is to be driven by an AC motor. (a) What power output is required of the motor? (b) A single-phase 220V motor is chosen, having an efficiency of 92%, and a power factor of 70%. How much current must be supplied to the motor? 13. Show how each of the following can be modeled as energy converters: (a) High-voltage transmission line; (b) Transformer; (c) Electric light; (d) AC electric motor