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Abstract-Vertical ground rods have been used extensively from the early days of electrical engineering for earth termination of electrical and lightning protection systems. They are usually represented with equivalent circuits with lumped and distributed parameters based on quasistatic approximation, which limits the upper frequency of their validity domain. However, lightning-related studies often require modeling in the megahertz frequency range. Also, emerging technologies, such as power-line communications, require analysis in frequency ranges even up to a few tens of megahertz. The rigorous electromagnetic (EM) field theory approach may be used for such frequency ranges, but equivalent circuits are needed for the usual network analysis methods. In this paper, we look at possibilities to construct simple equivalent circuits that can approximate or match results from the EM model. In particular, we compare a usual homogenous distributed parameter circuit with a nonhomogenous one determined by curve matching with results from the EM model. The analysis is illustrated using numerical simulations.

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The algorithm uses a modified continuous Fourier transformation that provides an accurate time domain computation. As an example, the interturn voltage distributions for two 500-kV autotransformers are computed and compared with measurements provided by other publications.

When an unloaded transformer or motor is switched under certain conditions, the circuit breaker can be exposed to a re-strike effect that leads to voltage escalation. The effect of reignition depends not only on the Qpe of circuit breaker, but also on the surrounding network.In this paper we describe a detailed model of all system components, which is extended where necessary, for the calculation of transients caused by the vacuum circuit breaker switching surges. Especially the transformer modelling is explained in detail for n broad frequency range because of a very complex transient behaviour. The system confguration consisting of a circuit breaker, a cable, a transformer and arresters is observed and modelled by means of some provided measured data. The results of some models are compared with measurements. The models have been imbedded into the Alternative Transient Program (ATP). The program developed here can be widely used for studies of transient recover?, overvoltages caused by interruption of transformer steady-state and inrush currents i f the measured data and parameters for the system components are known.