0195136047.pdf

PROBLEMS 55

ord^2 cmil. The handbook for aluminum electrical

conductors lists a dc resistance of 0.01558per

1000 ft at 20°C for Marigold conductor, whose

size is 1113 kcmil.

(a) Verify the dc resistance assuming an increase

in resistance of 3% for spiraling of the strands.

(b) Calculate the dc resistance at 50°C, given

that the temperature constant for aluminum

is 228.1°C.

(c) If the 60-Hz resistance of 0.0956/mile at

50°C is listed in the handbook, determine the

percentage increase due to skin effect or fre-

quency.

1.2.2MCM is the abbreviation for 1 kcmil. (See Prob-
lem 1.2.1 for a definition of cmil.) Data for com-
mercial-base aluminum electrical conductors list
a 60-Hz resistance of 0.0880/km at 75°C for a
795-MCM conductor.
(a) Determine the cross-sectional conducting area
of this conductor in m^2.
(b) Calculate the 60-Hz resistance of this con-
ductor in/km at 50°C, given a temperature
constant of 228.1°C for aluminum.

*1.2.3A copper conductor has 12 strands with each

strand diameter of 0.1328 in. For this conductor,

find the total copper cross-sectional area in cmil

(see Problem 1.2.1 for definition of cmil), and

calculate the dc resistance at 20°C in (ohms/km),

assuming a 2% increase in resistance due to spi-

raling.

1.2.4A handbook lists the 60-Hz resistance at 50°C of a

900-kcmil aluminum conductor as 0.1185/mile.

If four such conductors are used in parallel to form

a line, determine the 60-Hz resistance of this line

in/km per phase at 50°C.

1.2.5DetermineReqfor the circuit shown in Figure

P1.2.5 as seen from terminalsA–B.

1.2.6Viewed from terminalsA–B, calculateReqfor the

circuit given in Figure P1.2.6.

1.2.7FindReqfor the circuit of Figure P1.2.7.

*1.2.8DetermineReqfor the circuit of Figure P1.2.8 as

seen from terminalsA–B.

1.2.9A greatly simplified model of an audio system

is shown in Figure P1.2.9. In order to transfer

maximum power to the speaker, one should select

equal values ofRLandRS. Not knowing that

A

B

2 Ω

2 Ω

2 Ω

2 Ω

1 Ω

Figure P1.2.5

A

B

4 Ω

5 Ω

2 Ω

1 Ω

1 Ω

3 Ω

3 Ω

Figure P1.2.6