Kamyar Mehranzamir

Statistical analysis of lightning electric field measured under Malaysian condition

Lightning is an electrical discharge during thunderstorms that can be either within clouds (Inter-Cloud), or between clouds and ground (Cloud-Ground). The Lightning characteristics and their statistical information are the foundation for the design of lightning protection system as well as for the calculation of lightning radiated fields. Nowadays, there are various techniques to detect lightning signals and to determine various parameters produced by a lightning flash. Each technique provides its own claimed performances. In this paper, the characteristics of captured broadband electric fields generated by cloud-to-ground lightning discharges in South of Malaysia are analyzed. A total of 130 cloud-to-ground lightning flashes from 3 separate thunderstorm events (each event lasts for about 4–5 hours) were examined. Statistical analyses of the following signal parameters were presented: preliminary breakdown pulse train time duration, time interval between preliminary breakdowns and return stroke, multiplicity of stroke, and percentages of single stroke only. The BIL model is also introduced to characterize the lightning signature patterns. Observations on the statistical analyses show that about 79% of lightning signals fit well with the BIL model. The maximum and minimum of preliminary breakdown time duration of the observed lightning signals are 84 ms and 560 us, respectively. The findings of the statistical results show that 7.6% of the flashes were single stroke flashes, and the maximum number of strokes recorded was 14 multiple strokes per flash. A preliminary breakdown signature in more than 95% of the flashes can be identified.

A Comparative Study on the Positive Lightning Return Stroke Electric Fields in Different Meteorological Conditions

Positive cloud-ground lightning is considerably more complex and less studied compared to the negative lightning. This paper aims to measure and characterize the significant parameters of positive return strokes electric field, namely, the zero-to-peak rise time, 10–90% rise time, slow front duration, fast transition rise time (10–90%), zero-crossing time, and opposite polarity overshoot relative to peak. To the best of the authors’ knowledge, this is the first time such detailed characteristics of positive lightning in Malaysia are thoroughly analyzed. A total of 41 positive lightning flashes containing 48 return strokes were analyzed. The average multiplicity is 1.2 strokes per flash. The majority of positive lightning was initiated from the primary positive charge rather than as a byproduct of in-cloud discharges. The cumulative probability distribution of rise time parameters, opposite polarity overshoot relative to peak, and slow front amplitude relative to peak are presented. A comparison between studies in four countries representing tropic, subtropic, and temperate regions was also carried out. Measured parameters in Florida, Sweden, and Japan are generally lower than those in Malaysia. Positive lightning occurrences in tropical regions should be further studied and analyzed to improve our current understanding on positive return strokes.

Investigation of Short Base Line Lightning Detection System by Using Time of Arrival Method

Lightning locating system is very useful for the purpose of giving exact coordinates of lightning events. However, such a system is usually very large and expensive. This project attempts to provide instantaneous detection of lightning strike using the Time of Arrival (TOA) method of a single detection station (comprises of three antennas). It also models the whole detection system using suitable mathematical equations. The measurement system is based on the application of mathematical and geometrical formulas. Several parameters such as the distance from the radiation source to the station and the lightning path are significant in influencing the accuracy of the results (elevation and azimuth angles). The signals obtained by all antennas were analysed using the LabVIEW software. Improvements in the lightning discharge locating system can be made by adopting a multi-station technique instead of the currently adopted single-station technique.

Comparative study of lightning models with lightning discharges in Malaysia

Cloud to ground flash discharge involves one or more intermittent stages which occur ceaselessly before first return stroke. It starts with preliminary breakdown pulses (PBPs) followed by leaders which cause return strokes (RSs) at the end of a cloud to ground lightning discharge. The pulse trains behaviors are stochastic and vary from a lightning flash to the other flash even in a similar thunderstorm. The variable character of the lightning waveforms effects on the intensity and the duration of the preliminary breakdown pulses. That also causes difficulty to categories the lightning flashes. Several theoretical models for lighting have been introduced by researchers to describe the captured flashes. These models could not be matched to all the recorded waveforms although they are practical and useful most of the time. This paper focuses on the lightning waveforms captured in Malaysia. The compatibility of the BIL model as one the theoretical models with the captured lighting flashes will be investigated during this research.

Modeling of Time of Arrival Method for Lightning Locating Systems

Various methods are used to locate cloud-to-ground lightning flashes. Even though a higher cost is incurred, a network of sensor stations is preferable to a single station due to the improved accuracy. For a single station measuring system, the accuracy of its analyses is mostly based on the chosen mathematical equations which can be solved in either linear or nonlinear mode. The sensitivity of the measuring equipment used is also particularly significant. This paper concentrates on the modelling of time of arrival (TOA) technique for locating a lightning flash by utilizing three broadband antennas. Consequently, by employing the developed model, the influences of geometric parameters on the accuracy of the model are evaluated. Therefore, a Matlab based simulation of the measuring system is developed. In the developed codes, randomly located lightning flash with its corresponding electromagnetic radiation was modelled. Results show that parameters such as lightning path shape, distance of the leader, and leader location can directly affect the accuracy of the TOA technique for extracting the azimuth and elevation.

Investigation on the Probability of Ferroresonance Phenomenon Occurrence in Distribution Voltage Transformers Using ATP Simulation

Ferroresonance is a complex non-linear electrical phenomenon that can make thermal and dielectric problems to the electric power equipment. Ferroresonance causes overcurrents and overvoltages which is dangerous for electrical equipment. In this paper, ferroresonance investigation will be carried out for the 33kV/110V VT at PMU Kota Kemuning, Malaysia using ATP-EMTP simulation. Different preconditions of ferroresonance modes were simulated to ascertain possible ferroresonance conditions in reality compare with simulated values. The effect of changing the values of series capacitor is considered. The purpose of this series of simulations is to determine the range of the series capacitance value within which the ferroresonance is likely to occur.

Return Strokes Measurements of Electric Field Produced by Lightning Discharges in Malaysia

The physics of cloud discharges have not been known completely yet. The cloud to ground discharges is divided by researchers into several stages to make the analyses of lightning flash easier. The first step is preliminary breakdown which is called to pre-starting process prior to leader initiation within the clouds. The leader initiation precedes return strokes in continuing the cloud discharges. The time and amplitude of lightning waveforms differs in each flash with the other ones due to the stochastic characteristics of lightning flashes. This research tries to add more analyses to few previous researches done in tropical regions. On the other hand, observations of this study is compared with those obtained in Sweden to show the differences between statistics of return strokes in Malaysia and Sweden as a temperate region. A broadband antenna and a buffer system for amplifying input signal and also impedance matching is used in this study for capturing electric field of lightning waveforms to carry out statistical analyses on them in Johor, Malaysia. The percentage of single stroke flashes was 18% in Sweden and 12.1% in this study which shows single strokes happens more in temperate regions rather than tropical regions. Total number of 568 subsequent return strokes out of 271 flashes shows a Mean number of 3.4 strokes per flash in Sweden compared with 184 subsequent strokes out of 58 flashes in this study which presents 4.1 strokes per flash in average.

Study on the Vertical Component of Lightning Electric Field during Monsoon Period in Malaysia

The most recognized and powerful demonstration of electrostatics in the natural world is a lightning discharge. The misoperation of several equipment and circuits would not only be caused by a direct contact with the lightning flash, but also by an indirect effect of a lightning channel. Appropriate information about lightning signature parameters can provide precise knowledge of lightning discharge that can be essential for the design of more improved detection and protective system. In this paper, the preliminary breakdown pulse train and the first return stroke of cloud to ground lightning discharge signatures observed in south of Malaysia are analyzed. Statistical analyses of the ratio between the maximum preliminary breakdown pulse trains amplitude and the first return stroke amplitude (BP/RS ratio), and the time duration between the high active part of the pulse train, and the return stroke (BP/RS separation) are presented. Observations on the statistical analyses show that about 94% of lightning signals have detectable breakdown pulses. The arithmetic means of BP/RS ratio and the BP/RS separation are 36.3% and 26.4ms, respectively.

Observation of Isolated Breakdown Lightning Flashes in a Tropical Region

The impact of lightning on humans and its threats on life and structures have encouraged the scientists to pursue study in this field. Lightning flash is a high current electric discharge that can be classified into five categories which are intra-cloud discharges, cloud to cloud, cloud to air, ground to cloud and cloud to ground discharges. Intra-cloud discharges have the main portion of the lightning flashes. The most damages and disturbances of lightning flashes are due to cloud to ground and ground to cloud flashes. The discharge phenomenon has various behaviors even in the same thunderstorm. The cloud to ground lightning discharge starts with preliminary breakdown pulses followed by leaders which cause return strokes. The subsequent strokes happen after the first return stroke in a typical lightning flash, but in few flashes the discharges do not lead to any subsequent strokes. This research investigates on these types of flashes which are called isolated breakdown lightning flashes, in Malaysia. The isolated breakdown flashes have rarely been seen in tropical regions compared with temperate areas. Among 150 selected waveforms on 9th May 2013 in our measurement station, only 10 isolated lightning flashes were observed in our dataset, which make up less than 7% of total flashes in one thunderstorm.

Effect of shunt capacitance on ferroresonance model for distribution Voltage Transformer

This paper presents a study of the ferroresonance phenomena occurring on Voltage Transformer (VT) of 132 kV substation at PMU Kota, Malaysia. Ferroresonance is a complex non-linear electrical phenomenon that can make dielectric and thermal problems to the electric power device. It causes overcurrent and overvoltage that is harmful for electrical apparatuses. The analysis is made by The Alternative Transients Program (ATP) which is a version of Electromagnetic Transients Program (EMTP) simulation compare with experimental events. The impact of changing the values of shunt capacitor (Cshunt) has been considered. The purpose of these kinds of simulations is to determine the range of the shunt capacitance value within which the ferroresonance is likely to occur.