Please explain why you chose the values you did. 14.4 A lightning stroke which r

Question

Please explain why you chose the values you did. 14.4 A lightning stroke which reaches a peak current of 35 kA in 1 us strikes a 20 m tower on a 345 kV transmission line. The line has a ground wire joining the tops of the towers; its surge impedance is 520?. The tower surge impedance is 90? and the ground footing resistance is 40? Determine whether the line insulators will flashover as a con- sequence of the surge, assuming that their impulse flashover strength is 1050 kV. A coupling factor 0.3 with the phase conductors can be assumed; the impedance of the stroke channel can be ignored; a wave velocity on the tower of 2.98 x 10 m/s can be assumed

Explanation / Answer

Impulse flashover strength should be high. It will be in the range from 1000kV to 25000kV. Our assumed strength is slightly greater than minimum range.

The coupling factor for line insulators should be less than 0.5. Our assumption is 0.3 which satisifies the criteria.

And the wave velocity is approximately equal to light velocity which is 3*10^8 m/s

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