Question

A 3-phase, 220 kV, 50 Hz transmission line consists of 2 cm radius conductors spaced 3 m apart in equilateral triangle form, the air temperature is 20° C. Atmospheric pressure is 75 cm of Hg and irregularity factor is 0.85. If g = 21 kV/cm (rms), then the line-to-line critical disruptive voltage is

• A. 310.86 kV
• B. 240 kV
• C. 179.49 kV
• D. 73.33 kV

Answer 1

The correct option is A 310.86 kV

$V_{a0}=g_0\delta m_{0}rln\left(\frac{d}{r}\right)$

Air density factor, $\delta =\frac{3.92b}{t+273}=\frac{3.92\times 75}{273+20}$

$\delta =1.0034$

$V_{a0}=0.85\times 21\times 2\times 1.0034ln\left(\frac{300}{2}\right)$

$=179.48kV/phase$

Critical disruptive voltage
$=179.48\times \sqrt{3}=310.86kV$