An Electromagnetic Model for the Calculation of Tower Surge Impedance
Based on Thin Wire Approximation
Abstract
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DOI:
10.1109/TPWRD.2020.3003250
Abstract:
When a lightning strikes the top of a transmission line tower or shield
wires, electromagnetic waves propagate through the tower back and forth,
increasing the voltage across insulator strings. ‡is can eventually lead
to a back-flƒashover (BF), which may cause damage to equipment or costly
power outages. To calculate the over-voltages and predict the
probability of a BF, an accurate model of the tower and its grounding
system is needed in electromagnetic transient (EMT) type simulators.
‡There are a number of theoretical models for the equivalent circuit of
a transmission tower. However, they either are not accurate enough or
they are derived for a certain type of transmission tower, which limits
their applicability. Numerical electromagnetic analyses have less
simplifications compared to the theoretical solutions and are by far
less expensive than field measurements. They also have the flexibility
to analyze any type of tower. In this paper, the direct method for the
measurement of tower impedance is implemented by NEC4 and applied to a
400-kV double circuit tower with all its details. Th‡e process of
obtaining the wire network of the tower used in this paper is completely
automated and it can be applied to any other type of transmission tower.
Th‡e results of the numerical simulations are compared to those obtained
with existing tower models. Th‡e developed model in this paper is
capable of considering all the details of the tower and including the
\eurofinite resistance of the ground and grounding electrodes.