a) A lightning strikes a 30-m unshielded over-head transmission line tower which has the following parameters: Surge impedance of the tower = 100 12 Surge impedance of lightning channel at tower top = 500 12 Tower-footing resistance = 10 12 Tower height = 30 m Cross-arm height = 27 m The lightning strike current is assumed to be a constant 30 kA for a duration of 20 us. The traveling wave propagation speed in the tower is 1.2 x 108 m/s. i) Determine the voltage reflection coefficients at tower top and tower foot. (ii) Determine the time of travel from tower top to tower foot. (iii) Determine the time of travel from cross arm to tower foot.
a) A lightning strikes a 30-m unshielded over-head transmission line tower which has the following parameters: Surge impedance of the tower = 100 12 Surge impedance of lightning channel at tower top = 500 12 Tower-footing resistance = 10 12 Tower height = 30 m Cross-arm height = 27 m The lightning strike current is assumed to be a constant 30 kA for a duration of 20 us. The traveling wave propagation speed in the tower is 1.2 x 108 m/s. i) Determine the voltage reflection coefficients at tower top and tower foot. (ii) Determine the time of travel from tower top to tower foot. (iii) Determine the time of travel from cross arm to tower foot. (iv) Draw the voltage lattice diagram with proper labels of the time. (v) Ignoring the phase voltage, determine the insulator voltage after 2 us. The insulator voltage approaches a constant value after 2 us. If the basic impulse insulation level (BIL) of the insulator for phase conductor is 150 kV, evaluate the condition of the insulator and conclude the type of power quality problem that will occur for an end-user facility connected to the transmission line. Assume that the surge arresters and circuit breakers at the end-user facility are working properly.
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