6th Edition

ISBN: 9780078028229

Author: Charles K Alexander, Matthew Sadiku

Publisher: McGraw-Hill Education

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Alternating Current (AC) is a type of electric power in which the electric current changes, both in magnitude and direction, at regular intervals. This AC Circuits can deliver power in either a Single Phase system or a Three Phase system.

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Textbook Question

Chapter 12.10, Problem 14PP

Let the line voltage V_L = 208 V and the wattmeter readings of the balanced system in Fig. 12.35 be P₁ = −560 W and P₂ = 800 W. Determine:

(a) the total average power
(b) the total reactive power
(c) the power factor
(d) the phase impedance

Is the impedance inductive or capacitive?

Answer: (a) 240 W, (b) 2.356 kV AR, (c) 0.1014. (d) 18.25 Chapter 12.10, Problem 14PP, Let the line voltage VL = 208 V and the wattmeter readings of the balanced system in Fig. 12.35 be , example 1 , inductive.

Chapter 12.10, Problem 14PP, Let the line voltage VL = 208 V and the wattmeter readings of the balanced system in Fig. 12.35 be , example 2

Figure 12.35

Two-wattmeter method applied to a balanced wye load.

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Chapter 12.10, Problem 13PP

Chapter 12.10, Problem 15PP

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Problem 2 For the system shown in Figure 12.5: a) Find Is. b) Find the average power delivered to each element. c) Find the reactive power associated with each element. d) Find PT, QT, and ST. e) Find the power factor seen by the source E. R₁ ww 392 + E = 50 V/60° R3 ww 492 R₂ 12 Ω Χ 16Ω Xc 802 Figure 12.5

12. A certain load takes 300 kW at 400 V. A three phase capacitor bank rated 15 kVA per phase is connected in parallel with the load to raise the power factor of the system to 90% lagging. What is the power factor of the load before correction? c. 92% d. 88% a. 99% b. 95% 13. A 132 kV line three phase system delivers 70.7 MVA on a balanced delta connected load of a power factor 70.7% lagging. Determine the reactance necessary to attain unity power factor. a. 1 092 ohms c. 1142 ohms d. 1 045 ohms b. 965 ohms 14. A 150 kVA transformer bank will serve a load expected to draw 135 kW at 0.80 lagging power factor. Solve for the size of the capacitor bank needed to be added in order to prevent overloading of the transformer bank. a 40.391 KVAR d. 28.266 KVAR a. 32.506 KVAR b. 35.866 KVAR

1. What is the main direct cause of reactive power in AC system? A. Resistance of transmission lines B. Inductance and capacitance in the loads C. Ideal transformer connected in the system D. Power produced by generator 2. "Reactive power in a system is dissipated generally as thermal energy?" A. TRUE B. FALSE 3. Which of the following statements are correct for three phase circuit: A. Sum of all the three phase currents is zero in unbalanced network B. Total power transfer to load is constant with time C. Neutral conductor is same size in terms of material used as in single phase conductors D. Net apparent power consumed is equal to real power

Chapter 12 Solutions

Fundamentals of Electric Circuits

Ch. 12.2 - Given that Vbn=22030V, find Van and Vcn, assuming...Ch. 12.3 - A Y-connected balanced three-phase generator with...Ch. 12.4 - One line voltage of a balanced Y-connected source...Ch. 12.5 - A positive-sequence, balanced -connected source...Ch. 12.6 - In a balanced -Y circuit, Vab=44015 and ZY = (12 +...Ch. 12.7 - For the Y-Y circuit in Practice Prob. 12.2,...Ch. 12.7 - Calculate the line current required for a 30-kW...Ch. 12.7 - Assume that the two balanced loads in Fig....Ch. 12.8 - The unbalanced -load of Fig. 12.24 is supplied by...Ch. 12.8 - Find the line currents in the unbalanced...

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Solution Summary: The author analyzes the two-wattmeter method applied to a balanced wye load.

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