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Lightning-induced overvoltage in substations is one of the main causes of insulation damage in transformers. As the complexity of power grids is continuing to increase, the existing lightning overvoltage statistical waveform may no longer meet the requirements of modern power systems. It is therefore necessary to obtain the statistical characteristics of lightning-induced overvoltage on transformers. However, the existing devices in current power systems cannot meet the requirements for monitoring of the lightning-induced overvoltages because of their limited bandwidths and sampling rates. This paper proposes a method for monitoring of lightning-induced overvoltages on substation transformers based on the principle of ZnO lightning arrester block voltage division. Consistency testing was performed on the voltage division ratio of a ZnO lightning arrester block in both the linear and nonlinear regions. The experimental results confirmed the feasibility of the proposed method and field applications using this sensor showed that long-term research will be helpful in obtaining the characteristics of lightning-induced overvoltage. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional, stochastic model of a lightning downward leader is proposed. The background electric field in which the downward leader propagates is used to determine the direction of propagation. The critical background electric field for the development of a downward leader was obtained by extrapolating the results of negative long air gap discharge experiments. The distribution of charge in the downward leader was modelled with the charge simulation method. The calculation took into account branching of the leader channel. By choosing a suitable value of the probability exponent, the simulation results of fractal dimension and charge in the downward leader are shown to closely match observational data of lightning. Finally, the model was used to reproduce a negative ground flash. The ground electric field calculated by the model was found to agree well with measurement results from the field. [ABSTRACT FROM AUTHOR]

Research on the attachment processes in competition tests can provide insights into the influencing factors involved in the selection process that determines the lightning strike point. In this paper, a series of competition tests with a rod–rod gap configuration are designed and carried out. The test results indicate that the strike mechanism is decided by two discharge processes, namely the free development of the downward-propagating discharge and the interception process of the upward and downward discharges. If the first process prevails, the strike probabilities for different grounded rods will tend to be equal. For the second process, the strike probabilities reflect the different performances of the grounded rods for intercepting downward discharges. As the scale of the discharge gap increases, the development of the downward leader becomes more and more dominant in selecting the strike point. In natural lightning strikes, the scale of the downward leader is normally more than 90% of the discharge gap, hence the protective effect of lightning rods with different tips will not be significant for low rod heights and small lightning currents. To reflect the effect of the downward leader development on the choice of the strike point, a minimum discharge air gap of 10 m is suggested. [ABSTRACT FROM PUBLISHER]

The transient analysis model of grounding systems is an important tool to analyze the lightning characteristics of grounding devices. When lightning enters the soil through the grounding device, there is a centralized discharge channel. The spatial structure of the discharge channel in the soil has a great effect on the accuracy of the transient analysis model of the soil impulse discharge. In this paper, based on the gray information analysis method, the volume of successive impulse discharge channels in the ground under various currents and soil conditions is calculated, and the changing law with time interval is analyzed. According to the experimental results, an analysis method of the model considering the discharge channel structure is proposed, and an example is analyzed. The results show that the time interval has an effect on the volume of the discharge channel. In a certain range, the volume of the channel increases with the time interval of successive impulse discharges. Taking the critical breakdown electric field strength as the judgment condition and the residual resistivity as the variable, the development process of the discharge channel can be simulated. The calculated results of the model are close to the experimental results. [ABSTRACT FROM AUTHOR]