Consideration of Substation

Let us analyze lightning surges at a substation. Assume that the lightning strikes the first tower next to the substation. The refraction coefficient matrix from the line to the substation is given by 

g is the traveling wave on the GW at the tower E,a is the traveling wave on the PW at the tower u t-x) is the unit step function with time delay t 

Calculate the substation entrance voltage under the condition 

The earlier analysis is based on a step function current. In reality, the lightning current has a much slower rise time at the wave front, and thus the lightning overvoltage becomes mush lower. Such an analysis can be carried out considering the wave front but it is quite tedious as hand calculations. 

The earlier analytical results clearly show that the PW voltage in the BFO case is much higher than that in the case of no flashover. This is the reason why the insulation design/coordination of a substation is based on the result in the flashover case. 

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