M. Izadi

Evaluation of lightning current and velocity profiles along lightning channel using measured magnetic flux density

In this paper, an inverse procedure algorithm is proposed in the time domain to evaluate lightning return stroke currents along a lightning channel using measured magnetic ∞ux density at an observation point while the current velocity along a lightning channel is assumed to be a height dependent variable. The proposed method considers all fleld components and it can evaluate the full shape of currents and the current velocity at difierent heights along a lightning channel. Moreover, a sample of measured magnetic ∞ux density from a triggered lightning experiment is applied to the proposed algorithm and the evaluated currents and current velocities are validated using a measured channel base current and magnetic ∞ux density at another observation point.

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.

Analytical fields expressions due to lightning channel considering variation of return stroke velocities along the lightning channel

The return stroke velocity is an important factor for evaluation of lightning electromagnetic fields. Measurements showed that the return stroke velocity is varied at different heights along lightning channel while it is usually entered into field calculations with a constant value in previous studies. This paper presents the analytical electromagnetic fields expressions due to vertical lightning channel where velocity profile along channel is considered. The proposed fields expressions can be used to estimate electromagnetic fields directly in the time domain (without needing to apply any extra conversion to Frequency domain) whereas they are based on Heidler current function and can support widely used engineering current models. Likewise, the proposed field expressions are applied on a typical measured profile of velocity and also a function of velocity profile and the evaluated fields are compared to the corresponding simulated fields based on constant value of velocity and the results are discussed accordingly.

Investigate the effect of variations of ambient temperature on HST of transformer

Temperature, especially the hot spot temperature (HST) and top oil temperature (TOT), have played the most effective factor on the insulation life of the transformer. To determine HST and TOT, ambient temperature enter to equation that show the importance of ambient temperature on hot spot temperature of transformers, and Clause 7 (classic model) has been used as a standard thermal model in this research. In this article has been tried to show the effect of the variations of ambient temperature on a power transformer and at last has been compared by situation that the ambient temperature has been assumed constant.

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.

Influence of air humidity and contamination on electrical field of polymer insulator

This paper presented the simulation results on electric field performances of medium voltage polymer type insulator while its mechanical conditions were reviewed. The purpose of this study is to investigate the electric field behaviour of 33kV polymer type insulator under different weather conditions by mean humidity and pollution. In addition, outdoor service environments of the insulator were reviewed as they are realized to have worldwide issues on degradation of polymeric material. Using 2D simulation, the electric field was found higher nearer to the end fittings whereby increased up to 38.89% under humidity and pollution. Also, the electric field behaviour along the cross section of weathersheds increased up to 661.59% under humidity and 547.30% under pollution. Meanwhile the weak points along the insulator were identified according to the magnitude of electric field strength. This research also verified the sharp edges and the thickness of the material of insulator as one of the factors that affect electric field strength.

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.

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.

Improved algorithm for evaluation of lightning current using measured field at far distances from lightning channel

In this paper, the effect of radiation component of electric field on the total electric field at different distances with respect to lightning channel is considered. Results showed by approximating the total electric field with the radiation component at far and intermediate distances, some percentages of electric fields at different time periods will be neglected and this percentage will be higher when decreasing the distance from lightning channel. Whilst the most common inverse procedure algorithms are based on fields radiation component and the total field as input data, this paper proposed the same procedure that based on measured field with the consideration on the effect of radiation component on the total field in the calculations. The results on the prediction of channel base current illustrated that the proposed method is in very good agreement with real lightning channel base current compared to the corresponding predicted current based on existing methods.

On the consideration of the channel angle effects on the electromagnetic fields associated with inclined lightning channel

In this study, the channel angle effects on the different electromagnetic fields components associated with inclined lightning channel are considered. Furthermore, the effect of channel angle and also observation point angle on different electromagnetic fields are compared to the corresponding fields associated with vertical lightning channel. The results show the channel angle is more effective on the vertical electric field compared to other field components while the vertical electric field has direct relationship with lightning induced voltage for some coupling models.