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Intro to Power Systems Rodney Lucas Chapter 2 (2.3-2.7)

13-31 odd

13. In a single-phase ac circuit, for a general load composed of RLC elements under sinusoidal-steady-state excitation, the average reactive power is given by B –Vrms Irms sin Ф

15. With load convention, where the current enters the positive terminal of the circuit element, if Q is positive then positive reactive power is absorbed A- True

17. Consider the load convention that is used for the RLC elements shown in Figure 2.2 of the text If one says the inductor absorbs zero real power and positive reactive power is it A-(TRUE). If one says that a capacitor absorbs zero real power and positive reactive power or delivers positive reactive power is it. B-(TRUE). If one says that a positive valued resistor absorbs positive real power and zero reactive power is it A- (TRUE)

19. The admittance of the impedance –j 1/2Ω is given by A- -j2s

21. The three phase source line to neutral voltages are given by Ean= 10< 0o Ebn = 10 < +2400 Ecn = 10 < -2400 is the source balanced. A – YES.

23. In a balanced system the phasor sum of the line to line voltages and the phasor sum of line to neutral voltages are always equal to zero B – TRUE

25. For a balanced delta load supplied by a balanced positive sequence source the line currents into the load are √3 times the delta load currents and lag by 300 A- TRUE.

27. When working with balanced three phase circuits per phase analysis is commonly done after converting delta loads to Wye load, thereby solving only one phase of the circuit. A – TRUE.

29. The total instantaneous power absorbed by a three phase motor (under balanced steady state conditions) as well as a balanced three phase impedance load is A – Constant

31. One advantage of balanced three phase systems over separate single phase systems is reduced capital and operating costs of transmission and distribution. A- TRUE.

Intro to Power Systems Chapter 2(2.3-2.7) Problems 20,26,31,48,49,50

20). A circuit consists of two impedances, Z1 = 20 < 300Ω and Z2 = 25 < 600 in parallel supplied by a source voltage V= 100 < 600 volts. Determine the power triangle for each of the impedances and for the source. 1 V1 100 Vrms 0 Hz 60°

Z1 0Ω 20