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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

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
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43. Make a sketch showing how to insert three wattmetera in a four-wire three-phase 41. What difficulties exist in the solution of a three-phase three-wire star-connected circuit that is unbalanced? Explain why a solution is facilitated when a star the phase sequence is reversed? Boes - 115. The following unity-power-factor eurrents are phase BN is reversed, i.e., with the arrow in load BN directed from B to N, and power factor of 0.99 (e = 8.1°). Calculate (a) currents INA and IBN, (b) neutral 19. A two-phase three-wire circuit similar to that of Fig. 18-14 is connected so that factor of 0.6 lagging. Calculate the current in each phase and the total power. balanced? Load A consists of lighting circuits (power factor- 1) totaling 4,140 watts, and is an impedance of (9.6 - j7.2); load BA takes a current of 15 amp at a lagging 10. The voltage across each phase of a four-wire two-phase systena (Fig. 18-13) is 115. 11. The following information is given in connection with the two-phase three-wire circuit of Fig. 18-14: EBA = 170; load NA is an impedance of (6 +j8); load BN load B representa lighting and motor circuits totaling 3,105 watta at a power is transformed into an equivalent delta. 42. Describe a four-wire three-phase system. What important advantages do possess? What voltages are generally used for such a system? iystem to measure the total power. Problems 1. The voltage across each phase of Fig. 18-4a is 120. (a) If points a and à a connected what will be the voltage between A and B? (b) If a is joined to 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 kilowatts and kilovolt-amperes, (b) overall power factor, (e) line currents. &.7. A 234-volt three-phase source serves a balanced load consisting of three equal impedances, each of which has a resistance of 3.6 ohms and an inductive resctance of 4.8 ohms. Caleulate the line currents and the total power if the impedances are connected in star. 8. Solve Prob. 7 for a delta-connected load, assuming all other conditions to remain the same. 9. What ahould be the resistance and reactance of each of the impedances of Prob. if, when connected in delta, the line currents and the total pówer are to be t same as for the star connection? %3D current IN, (c) line currents IA and Ia, (d) the total power. has voltages ENA - Exa
Transcribed Image Text:43. Make a sketch showing how to insert three wattmetera in a four-wire three-phase 41. What difficulties exist in the solution of a three-phase three-wire star-connected circuit that is unbalanced? Explain why a solution is facilitated when a star the phase sequence is reversed? Boes - 115. The following unity-power-factor eurrents are phase BN is reversed, i.e., with the arrow in load BN directed from B to N, and power factor of 0.99 (e = 8.1°). Calculate (a) currents INA and IBN, (b) neutral 19. A two-phase three-wire circuit similar to that of Fig. 18-14 is connected so that factor of 0.6 lagging. Calculate the current in each phase and the total power. balanced? Load A consists of lighting circuits (power factor- 1) totaling 4,140 watts, and is an impedance of (9.6 - j7.2); load BA takes a current of 15 amp at a lagging 10. The voltage across each phase of a four-wire two-phase systena (Fig. 18-13) is 115. 11. The following information is given in connection with the two-phase three-wire circuit of Fig. 18-14: EBA = 170; load NA is an impedance of (6 +j8); load BN load B representa lighting and motor circuits totaling 3,105 watta at a power is transformed into an equivalent delta. 42. Describe a four-wire three-phase system. What important advantages do possess? What voltages are generally used for such a system? iystem to measure the total power. Problems 1. The voltage across each phase of Fig. 18-4a is 120. (a) If points a and à a connected what will be the voltage between A and B? (b) If a is joined to 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 kilowatts and kilovolt-amperes, (b) overall power factor, (e) line currents. &.7. A 234-volt three-phase source serves a balanced load consisting of three equal impedances, each of which has a resistance of 3.6 ohms and an inductive resctance of 4.8 ohms. Caleulate the line currents and the total power if the impedances are connected in star. 8. Solve Prob. 7 for a delta-connected load, assuming all other conditions to remain the same. 9. What ahould be the resistance and reactance of each of the impedances of Prob. if, when connected in delta, the line currents and the total pówer are to be t same as for the star connection? %3D current IN, (c) line currents IA and Ia, (d) the total power. has voltages ENA - Exa
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