Influence of Finite-Length Overhead Conductors on Wave Propagation Characteristics and Transients

This paper investigates the influence of finite length of overhead conductors on wave propagation, characteristics and transients in comparison with those calculated by “per-unit-length (pul)” parameters implemented in existing EMTPs, which are constant everywhere along the conductor. It is shown that the impedances of finite-length conductors are always smaller than the pul impedance and converge to the pul impedance as the conductor length increases. The converging length, i.e. the applicable length of the pul parameters, becomes smaller when the frequency is higher. The admittance of the finite-length conductor is greater than that of the pul admittance. The attenuation is smaller and the propagation velocity is greater in the finite-length conductor. The characteristic impedance shows a similar trend to the impedance. The switching surges on finite length conductors are clearly different from those calculated by the traditional pul approach. A difference between the finite length and pul parameters is less noticeable in a fault surge when the source impedance and/or fault impedance is large.