Answer to Question #95486 in Electrical Engineering for Fantahun

Question

A single and loss transmission line receives at x=0 a lighting stoke corresponding to a normalized waveform 1.2/50µs. that is an impulse current from a perfect current source with
io(t)=Io(exp(-v/τ2)-exp(-t/τ1)).The line is open at the final end ,that is at x=l,the resistances R1 is infinite. let us call τ=l/u0 the travel time (forward or backward) along the line.
a) Both time constant are associated with the raising and decreasing phases of the lightning stock.which of them is associated to the raising step and what is its value?Idem for the one associated to the falling step?

Answer 1

As you can see in a common graph taken from [1] and representing the impulse current from a lightning stroke below, the notation 1.2/50 µs means that the raising step lasts for 1.2 µs, while the falling step is always slower and lasts (50-1.2)=48.8 µs. 50 µs is the total duration of the impulse.

References:

[1] Deepak Subedi, Matti Lehtonen. (2017). Lightning Induced Over-voltages in Power Transformer and Voltage Spikes in Connected Load