the phase sequence is reversed? Dos balanced? 41. What difficulties exist in the solution of a three-phase three-wire star-connected 43. Make a sketch showing how to insert three wattmeters in a four-wire three-phase circuit that is unbalanced? Explain why a solution is facilitated when a star is transformed into an equivalent delta. 42. Describe a four-wire three-phase system. What important advantages dos possess? What voltages are generally used for such a system? iystem to messure the total power. Problems 1. The voltage across each phase of Fig. 18-4a is 120. (a) If points a and i ar connected what will be the voltage between A and B? (b) If a is joined to C and e is joined to b, what will be the voltage between A and B? (e) If a is joined to B, and b is joined to C, what will be the voltage between A and c? 2. The voltage aaross each phase of Fig. 18-46 is 120. If points A and o are con. nected together, what will be the voltage between a and B? 8. The voltage across each phase of a star-connected source is 265. What will be the current in each of the three line wires if a balanced load of 200 kw at a power factor of 0.82 is delivered? 4 What is the voltage of a delta-connected source that delivers an 0.85 power-factor load of 500 kw at 148 amp? 6. A 10-hp 230-volt three-phase motor draws a line current of 25 amp when oper- ating at rated output. If the motor efficiency is 91 per cent, caloulate the power factor. 6. Two balanced loads are connected in parallel to a three-phase 460-volt source. Load A is 900 kva at a power faotor of 0.6 lagging, and load B is 400 kw at a power factor of 0.8 leading. Caleulate (a) total kilowatta and kilovolt-amperen, (b) overall power factor, (c) line currents. A 234-volt the
the phase sequence is reversed? Dos balanced? 41. What difficulties exist in the solution of a three-phase three-wire star-connected 43. Make a sketch showing how to insert three wattmeters in a four-wire three-phase circuit that is unbalanced? Explain why a solution is facilitated when a star is transformed into an equivalent delta. 42. Describe a four-wire three-phase system. What important advantages dos possess? What voltages are generally used for such a system? iystem to messure the total power. Problems 1. The voltage across each phase of Fig. 18-4a is 120. (a) If points a and i ar connected what will be the voltage between A and B? (b) If a is joined to C and e is joined to b, what will be the voltage between A and B? (e) If a is joined to B, and b is joined to C, what will be the voltage between A and c? 2. The voltage aaross each phase of Fig. 18-46 is 120. If points A and o are con. nected together, what will be the voltage between a and B? 8. The voltage across each phase of a star-connected source is 265. What will be the current in each of the three line wires if a balanced load of 200 kw at a power factor of 0.82 is delivered? 4 What is the voltage of a delta-connected source that delivers an 0.85 power-factor load of 500 kw at 148 amp? 6. A 10-hp 230-volt three-phase motor draws a line current of 25 amp when oper- ating at rated output. If the motor efficiency is 91 per cent, caloulate the power factor. 6. Two balanced loads are connected in parallel to a three-phase 460-volt source. Load A is 900 kva at a power faotor of 0.6 lagging, and load B is 400 kw at a power factor of 0.8 leading. Caleulate (a) total kilowatta and kilovolt-amperen, (b) overall power factor, (c) line currents. A 234-volt the
Power System Analysis and Design (MindTap Course List)
6th Edition
ISBN:9781305632134
Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Chapter3: Power Transformers
Section: Chapter Questions
Problem 3.43P: Three single-phase transformers, each rated 10MVA,66.4/12.5kV,60Hz, with an equivalent series...
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