N. Rameli

Modelling of lightning current in the case of striking to a tall structure

Lightning current is an important parameter that has to be considered. The different behaviour of lightning current depends on the way the lightning strikes either as a direct or indirect lightning strike. In this paper the modelling of the current as a result of a direct strike of lightning on a tall structure is considered. A few of up-to-date on current models, current functions, reflection factors, the return stroke velocity (RSV), the general equation representation of this case are reviewed. Also, through MATLAB software, the results of a case study are generated. The results show a good agreement with the measured values. In addition, the behaviour of the lightning current is evaluated at different heights of the lightning channel with respect to the top and bottom of a tall structure. Also, the lightning current at the top and bottom of the tall structure are observed for different values of the reflection factor. The results show that the peak of the lightning current along different heights of the channel with respect to the top and bottom of a tall structure decreases with increasing height of the channel. Also there is a time delay during the initial time period. Furthermore, the lightning current at the bottom of a tall structure has a high value of peak current and has an attenuation wave shape of current that compares with the lightning current at the top of the tall structure. As a result, this paper may provide benefit in evaluating the electromagnetic (EM) field since the behaviour of the lightning current on a tall structure is known.

On the influence of inclined lightning channel on lightning induced voltage evaluation

This paper investigates the influence of inclined lightning channel on induced voltage on the line. The angle variations of inclined lightning channel may cause the voltage to be induced at different values for different points along the power line. This behaviour may affect the lines lightning performance if the peak of induced voltage is greater than the critical flashover voltage (CFO) of the line. This induced voltage is expected to be increased when the inclined angle with respect to the observation point is decreased. Appropriate method of induced voltage algorithm with respect to the incline lightning channel will be developed and compared with other method. The outcome of this study would be useful for the utility for their planning and selection of appropriate protection scheme for the line.

On the behavior of lightning return stroke current incidence to tall towers

The return stroke current in the case of a lightning strike on a tall structure is affected by different tower and channel parameters such as the velocity of the return stroke current, the height of the observation point along the structure, the lightning channel and the reflection coefficients at the top and bottom of the structure. This paper will consider all these factors in the behaviour of the return stroke. The current wave shapes at different heights along tower and channel were modeled and the simulated current at tower top was compared to the corresponding measured current. Moreover, the effects of reflection factors and other important parameters on the values of current peak were considered and the results were discussed accordingly.

Effect of the grounding system arrangement on the lightning current along tall structures

The behaviour of lightning current along tall structures is an important case to be evaluated. The behaviour is influenced by a few factors of which one is the ground or earth reflection factor. Previous studies have assumed that the ground reflection factor is a constant value and this value is usually used when evaluating the lightning current along a tall tower. This study presents the behaviour of lightning current along a tower, including variation in the value of the ground reflection factor. The simulation work is done by selecting the sum of two Heidler functions as a current channel base and a distributed source representation current is used to simulate the lightning current along the tower and channel. The ground reflection factor is calculated based on the correlation between tower and ground impedances whereby the ground impedance is dependent on a circle grounding system arrangement. The results indicate that by increasing the length of the rods, the value of the ground impedance decreases, but the peak value of the current along the tower is more dependent on the value of the ground reflection factor. It is shown that by increasing the length of the rods, the current peaks increase. Thus, the outcome of this study may be of benefit to Electrical Engineers to set an appropriate scheme of protection for the equipment which is installed along the tower, based on the effect of the grounding system arrangement for different conditions of soil resistivity.

Evaluation of lightning induced over-voltage due to variations of channel angle

Lightning can create lightning induced overvoltage (LIOV) on a power line. However, detailed considerations are needed concerning the evaluation behaviour of LIOV due to changes in channel angle which is referred to as an inclined lightning channel. The aim of this paper is to evaluate the behaviour of LIOV due to variations of channel angle. The LIOV was generated through the execution of an algorithm in MATLAB. Results indicate that the behaviours of LIOV are direct and show a linear relationship with an increasing channel angle which is an inclined angle and observation point angle. On the other hand, the effect on the LIOV of an increasing channel angle due to the return stroke velocity decreases at the highest velocity. As a result, the outcome of this paper could be useful for electrical power designers for the fast estimation of LIOV peak voltages without recalculation of the LIOV and to assist in the appropriate planning of protection schemes.

Effect of soil resistivity on the lightning current along tall towers

A direct lightning strike on a tall structure may result in damage to the equipment that is installed along the tower. This may be caused by the behaviour changes of the lightning current value and wave shape along the tall structure. The influence of this behaviour change may be contributed to by the ground reflection factor. Previous studies have assumed that the ground reflection factor is a constant value. However, this factor depends on the correlation between the tower and ground impedance. Thus, the aim of this paper is to evaluate the behaviour of the lightning current along the tower and channel with respect to the variation of the ground reflection factor. The lightning current along the tower and channel are modelled by selecting the distributed current source model whereby the sum of two Heidler current functions is used as a channel base current. Also, the value of the soil resistivity is included in the circle electrode grounding arrangement in order to determine the variation value of the ground impedance. Thus, the results of this paper may be of benefit for the maintenance of telecommunication towers in order to set an appropriate protection level based on the soil resistivity and also when considering the installation of such telecommunication towers.

Characterization preliminary breakdown in the measured lightning electric fields

In this study, characterization of measured electric fields due to lightning channel was done. Likewise, previous studies on this case were reviewed and discussed accordingly. Furthermore, preliminary breakdown was done in detail and it was indicated on the real measured electric fields and the results were discussed. The behavior of preliminary breakdown signal was observed. This study shows that it will be easier to design filtering of the preliminary breakdown. The result show compelling agreement with theoretical predictions and significant improvement over previous effort by Clarence and Malan, Weidman and Krider and Rakov, et al. the work presented here has profound implications for future studies of Preliminary Breakdown and may one day help solve the problem of designing protection level for Electrical Engineers. The results show that the occurrence of PBP is in between 2 to 10 milliseconds before return stroke as agreed with Clerence and Malan.

Effect of soil resistivity on magnetic field in the case of lightning strike to a tall structure

When a tower is struck by lightning, an induced voltage can generate in conducting objects within its vicinity. This phenomenon is due to the interaction between the electromagnetic field of the lightning with the object. The magnetic field is part of this field. Previous studies have shown that the magnetic field is affected by ground reflection coefficient factors that are usually taken as constants. However, the ground reflection coefficient factors have correlation with tower and ground impedance whereby the ground impedance can be determined based on soil resistivity and grounding system. This paper investigates the effect of soil resistivity on the value of magnetic field for a case of lightning strike on tall structures. Lightning current has been modelled accordingly and a set of equations is proposed to evaluate the magnetic field. Also, the effects of soil resistivity on the value of ground reflection coefficient factor consequently of the magnetic peak have been investigated. The results indicate that the magnetic field changes substantially with a variation of the soil resistivity. The magnetic field peak also has a strong correlation with the changes of soil resistivity as well as the fast front time of the channel base current. The outcome of the result of this paper will be beneficial to utility companies in determining the appropriate level of lightning protection since the magnetic field will be a result of induced voltage when have interaction with power lines.

Variations in return stroke velocity and its effect on the return stroke current along lightning channel

A direct lightning strike to a tall structure can impart high impact damage to electrical equipment that may be installed within and around the structure. This is due to the behaviour of the lightning return stroke current which generates a lightning electromagnetic field (LEMF) and consequently creates an induced voltage (LIV) on the electrical equipment. The lightning return stroke current along the channel is influenced by the parameters of the return stroke velocity (RSV). The return stroke velocity can be determined by measurement. Mostly, this value is considered as the average value in the range c/2 to 2c/3 for the first hundred metres of channel height, which should be taken into account when calculating the LEMF. Hence, the result of the evaluation of lightning return stroke current behaviour will inherently influence the evaluation of the lightning protection that is required for the electrical equipment surrounding the tall structure. However, when performing measurements, the return stroke velocity shows a changing trend value for different channel heights. In this paper, this trend will be used to evaluate the return stroke current at different heights along a channel. Thus, modelling of a lightning current along a channel was undertaken. Also, the return stroke velocity for different channel heights was calculated by considering the initial delay time. The results indicate that the lightning current along the channel has a significant effect on the changes in the return stroke velocity profile.

Characterization Preliminary Breakdown in the Measured Lightning Electric Fields on Malaysia Data

This paper presents a characteristic of lightning electric fields. The lightning electric fields were captured by two parallel plats sensor and the characterization for preliminary breakdown pulse (PBP) was studied. A total of 207 data were recorded and 10 data are selected and been utilized in this paper accordingly. In PBP signal data, time before return stroke, ending time and maximum peak of PBP were analyzed. The time duration between the PBP and the occurrence of return stroke was obtained as 0.64 ms and 4.05 ms and then compared with results from other researchers.