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The improvement of the lightning performance of overhead distribution lines, hit by direct strokes, is investigated considering the use of additional shield wires beneath the phase conductors. The frequency-domain theory of multiconductor transmission lines with periodical grounding is adopted permitting a rigorous evaluation of the phase and shield wire currents and of the overvoltages across insulators. These can be minimized by careful positioning of the underbuilt shield wires. A sensitivity analysis on the overvoltages is conducted by varying either the position of the underbuilt shield wires and the grounding impedance.

We present an efficient procedure for the calculation of the characteristic impedance matrix of a lossless multiconductor transmission line with one or more conductors periodically grounded. This matrix can be used to properly simulate power transmission or distribution lines with shield wires periodically grounded and, also, distribution lines with grounded neutral. The presented procedure can be applied to an arbitrary number of ungrounded and grounded conductors. Numerical results are shown for practical cases. Finally, an equivalent circuit of the impedance matrix is derived for the simulation in the time domain.

The paper presents analytical formulas for computation in the time domain of electromagnetic (EM) fields generated by tortuous cloud-to-cloud (CC) lightning channels over a perfectly conducting ground. For the first time, the study was not limited to a horizontal lightning path but was extended to take into account the natural, tortuous geometry of the lightning channel. After the calculation of the step response, a convolution integration was applied for the computation of the fields generated by an arbitrary current source. The produced electric and magnetic fields were then compared with the fields generated by a horizontal channel. The method can be of primary importance to evaluating the hazards for electric and electronic systems of flying aircraft, estimating the voltages induced on overhead transmission lines by CC lightning, and, in general, evaluating the induced effects on sensitive electric and electronic components. Moreover, it may represent a simple, robust, and time-saving tool for estimating important physical parameters that characterize lightning phenomena.

The paper deals with the evaluation of the characteristic impedance of a multiconductor transmission line with one conductor periodically grounded. The topic, even if not adequately discussed in literature, has a relevant application in the analysis of the role of the shield wire in power lines, in order to quantify the mitigation of induced overvoltages. The problem is here modelled, leading to a nonsymmetric algebraic Riccati equation, that is solved with both a factorization and an iterative method. The solution is presented in a practical case and the efficiency of the methods are discussed.