Maryam Hajikhani

Considering on the Ground Reflection Effect on the Electromagnetic Fields due to Lightning Channel

Lightning electromagnetic fields are important issues for the evaluation of lightning induced overvoltage on power lines and for setting the appropriate protection level for power networks. Such electromagnetic fields are strongly dependent on lightning return stroke currents at different heights along the lightning channel. On the other hand, the ground reflection factor due to the difference between the return stroke channel impedance and the equivalent ground impedance at channel base can have an effect on the shape of the return stroke currents by entering additional reflected currents into the channel. In this paper, the effect of the ground reflection factor on the return stroke currents at different heights along a channel and the electromagnetic fields associated with the lightning channel at close distances are considered. Moreover, the behavior of the electromagnetic fields versus the reflection factor changes and the radial distance changes are considered and the results are discussed accordingly. The results illustrate that the reflection factor has a direct relationship with the values of the electromagnetic fields while this is usually ignored in earlier studies.

Evaluation of Electromagnetic Fields Due to Inclined Lightning Channel in Presence of Ground Reflection

In this paper, analytical fleld expressions are proposed to determine the electromagnetic flelds due to an inclined lightning channel in the presence of a ground re∞ection at the striking point. The proposed method can support difierent current functions and models directly in the time domain without the need to apply any extra conversions. A set of measured electromagnetic flelds associated with an inclined lightning channel from a triggered lightning experiment is used to evaluate the proposed fleld expressions. The results indicate that the peak of the electromagnetic flelds is dependent on the channel angle, the observation point angle as well as the value of the ground re∞ection factor due to the difierence between channel and ground impedances. Likewise, the efiect of the channel parameters and the ground re∞ection on the values of the electromagnetic flelds is considered and the results are discussed accordingly.

The analytical field expressions associated with lightning channel in presence of ground reflection at striking point

In this paper a general set of field expressions associated with a lightning channel are proposed to evaluate the electromagnetic fields due to lightning in the presence of a ground reflection at the channel base. The ground reflection factor is due to the difference between the channel and ground impedances and can enter additional reflected currents into the lightning channel. The proposed field expressions can support the widely used current functions and current models directly in the time domain without the need to apply any extra conversions. Moreover, the proposed expressions are applied on a sample of lightning current that has been obtained from a triggered lightning experiment and the evaluated electromagnetic fields are compared to the corresponding measured fields and the results discussed accordingly. The results illustrate that the simulated fields based on the proposed method are in good agreement with the measured fields. Moreover, the ground reflection factor can have a great effect on the values of the lightning electromagnetic fields. The proposed field expressions consider all field components directly in the time domain and vary appropriately to join with widely used coupling models to evaluate the lightning induced voltage on power lines without the need to apply any extra conversions.

Evaluation of lightning current using inverse procedure algorithm

In this study an inverse procedure algorithm is proposed in the time domain to evaluate lightning return stroke current based on measured electromagnetic fields at an observation point. The proposed method considers on all electromagnetic fields components and can evaluate full shape of current, velocity and constant parameters of current models in contrast with previous studies. In order to validate the proposed method, a set of measured electromagnetic fields are applied on proposed algorithm and the evaluated currents are compared to the corresponding measured current as well as the results are discussed accordingly. The proposed method can be used for preparing of current data bank that is very useful for considering on lightning effects on the power lines and setting appropriate protection levels on the power systems.

Estimation of Lightning Current and Return Stroke Velocity Profile Using Measured Electromagnetic Fields

Abstract To evaluate lightning current using measured electromagnetic fields, an inverse procedure algorithm is proposed in this article, where the variation of return velocity stroke velocity is considered as opposed to previous methods where the velocity is set at a constant value. The proposed algorithm considers all electromagnetic fields components directly in the time domain without needing to apply any extra conversions. Moreover, it can support the wide range of current models based on the general form of engineering current models. The proposed method is validated using a sample of triggered lightning data and measured electromagnetic fields at two stations with different distances from the lightning channel. The results illustrate that the proposed method could estimate the behavior of current along the channel and can thus be used for preparing a data bank to record lightning current parameters of a wide range of lightning occurrences based on measured fields.

An Algorithm for Evaluation of Lightning Electromagnetic Fields at Different Distances with respect to Lightning Channel

The analytical field expressions are proposed to estimate the electromagnetic fields associated with vertical lightning channel at an observation point directly in the time domain using current and geometrical parameters. The proposed expressions embrace a large number of channel base current functions and widely used engineering current models. Moreover, they can be joined with different coupling models for evaluation of lightning induced voltage when they provide different required field components directly in the time domain. The data from measured fields and simulated fields from previous works were employed to validate the proposed field expressions. The simulated results were compatible with both computed field values from previous studies and the measured fields.

On the Lightning Induced Voltage Along Overhead Power Distribution Line

Lightning induced voltage is a major factor that causes interruptions on distribution lines. In this paper, analytical expressions are proposed to evaluate a lightning induced voltage on power lines directly in the time domain without the need to apply any extra conversions. The proposed expressions can consider the widely used current functions and models in contrast to the earlier analytical expressions which had a number of limitations related to the simplification of the channel base current and the current along the lightning channel. The results show that the simulated values based on the proposed method are in good agreement with the previous studies and the proposed expressions can be used for optimizing the insulation and protection level of existing and new lines being designed.

On the behavior of lightning induced voltage

In this paper, the influence of lightning induced voltages (LIV) on distribution lines (DL) is considered and the effects of channel and also geometrical parameters on the values of LIV are processed and the results are discussed accordingly. The results show that the peak values LIV are more dependent on the current peak, return stroke velocity and the conductor height with a linear relationship. Therefore, in order to design or improve distribution networks, the behaviour of LIV under different channel and geometrical conditions can be useful for setting and optimizing the appropriate protection level on the lines.

On the Lightning Electromagnetic Fields due to Channel with Variable Return Stroke Velocity

Numerical field expressions are proposed to evaluate the electromagnetic fields due to the lightning channel with variable values of return stroke velocity. Previous calculation methods generally use an average value for the return stroke velocity along a lightning channel. The proposed method can support different velocity profiles along a lightning channel in addition to the widely used channel-base current functions and also the general form of the engineering current models directly in the time domain without the need to apply any extra conversions. Moreover, a sample of the measured lightning current is used to validate the proposed method while the velocity profile is simulated by the general velocity function. The simulated fields based on constant and variable values of velocity are compared to the corresponding measured fields. The results show that the simulated fields based on the proposed method are in good agreement with the corresponding measured fields.

The evaluation of lightning return stroke current using measured fields

In this paper an inverse procedure algorithm in the time domain is proposed to evaluate the wave shape of the lightning return stroke current along a lightning channel using measured electromagnetic fields obtained at different distances with respect to the lightning channel. Moreover, the proposed method was applied on an actual sample of lightning current and the results discussed accordingly. The proposed method takes into consideration all the field components which cover the full shape of the current. Thus the method can be helpful for preparing a lightning current data bank and setting a proper protection level for a power system based on local information.