# A three-phase underground distribution line is operated at 23 kV. The three conductors are… 1 answer below »

A three-phase underground distribution line is operated at 23 kV. The three conductors are insulated with 0.5-cm solid black polyethylene insulation and lie flat, side by side, directly next to each other in a din trench. The conductor is circular in cross section and has 33 strands of aluminum The diameter of the conductor is 1.46 cm. The manufacturer gives the GMR as 0.561 cm and the cross section of the conductor as 1.267 cm2. The thermal rating of the line buried in normal soil whose maximum temperature is 30°C is 350 A. Find the dc and ac resistance at 50°C and the inductive reactance in ohms per kilometer. To decide whether to consider skin effect in calculating resistance, determine the percent skin effect at 50°C in the ACSR conductor of the size nearest that of the underground conductor. Noie that the series impedance of the distribution line is dominated by R rather than XL because of the very low inductance due to the close spacing of the conductors.

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