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The creation of the NPTEL platform in India has led to a vast population of engineering students getting access to quality online content for Signal Processing. These courses are globally accessible, free of cost, and also provide a means of obtaining certificates of proficiency by taking a proctored examination. Recently, a European Union funded project, MIELES, has supported the activity of creating online courses in the fields related to Signal Processing. This paper presents the details and experiences of creating course content and presents guidelines for prospective content creators.

Field observations have shown that the frequency of dangerous lightning events to wind turbines, calculated according to the IEC standard 61400-24:2010, is grossly underestimated. This paper intend ...

Wind turbines are prone to damages due to lightning strikes and the blades are one of the most vulnerable components. Even though the blade tip is usually protected in standard designs, lightning d ...

Attachment of downward subsequent dart leaders has been recently proposed as a possible mechanism of lightning damage of wind turbine blades. Since subsequent dart and dart-stepped leaders propagating after the first lightning discharge are one-to-two orders of magnitude faster than downward stepped leaders, the direct evaluation of the dart leader interception by upward connecting leaders from the turbine has not been attempted before. In this paper, the self-consistent leader inception and propagation model SLIM is used to evaluate the lightning attachment process of subsequent dart leaders by accounting the rapid changing electric fields produced by their fast descent toward the ground. For this, an improved evaluation of the charge per unit length required to thermalize the upward connecting leader is derived. The analysis considers upward connecting leaders propagating along the preheated channel of a prior discharge. Three study cases of lightning attachment of dart leaders and dart-stepped leader reported in rocket-triggered lightning experiments are evaluated. It is shown that reasonable predictions of the length, duration, and velocity of positive upward connecting leaders can be obtained with SLIM in agreement with the experimental results. Further research on upward leader discharges necessary to improve the modeling of attachment of dart lightning leaders is discussed.

Intentional Electromagnetic Interference or IEMI is the result of maliciously created electromagnetic disturbances in sensitive electronic systems. Modern infrastructure such as power supply, wireless communication networks, banking system, and transportation networks are dependent on civilian-off-the-shelf (COTS) equipment for its uninterrupted and reliable operations. Even though COTS equipment are tested for electromagnetic compatibility as per pre-defined un-intentional electromagnetic environment and test methods, intentionally created electromagnetic disturbances creates a lot of uncertainty in the proper functioning of critical COTS elements of the infrastructure. Infrastructure is interconnected widely distributed systems and there are several ports where substantial electromagnetic energy can be coupled intentionally by saboteurs and once coupled these disturbances travel through the interconnected system and cause breakdown at one or more weak links. It is probable that some of these breakdowns may lead to widespread disruption of critical infrastructure, such as power supply blackouts, financial service shutdown or disruption in railway network due to signal failures. Due to its inherent nature, EM attacks to civilian infrastructure may happen anonymously and repeatedly without detection. Protection of civilian critical infrastructure against the effects of IEMI has received a lot of attention recently from the EMC community. This article reviews the work done around the world with special emphasis on the work done in Sweden [e.g; 1–5].

We examined simultaneous measurements of currents and close electric field changes, as well as highspeed video images, associated with pulses superimposed on the initial continuous current (ICC pul ...

We derive electric field expressions, associated with lightning strikes to a tall object, using the monopole (Continuity Equation) technique which is distinctly different from the traditional dipole (Lorentz Condition) technique. Expressions to calculate the charge density along the tall object and lightning channel based on the assumptions of the transmission line model of the lightning strikes to a tall object and a series point current source placed at the object top, are also derived. These expressions are used to calculate the very close-range electric fields in the monopole (Continuity Equation) technique in terms of the retarded current and charge density along the tower and lightning channel and their results are compared with those calculated from the traditional dipole (Lorentz Condition) technique in terms of the retarded current along the tower and lightning channel. Alternative explanations are provided to the inversion of polarity of the vertical electric field at very close range based on distribution of charge density along the tower and lightning channel.

We studied simultaneous electric field changes, microsecond-scale (VLF/LF) magnetic field pulses, and VHF emissions associated with K processes in 37 cloud and 54 cloud-to-ground lightning flashes ...

This study presents a practical method to construct a high-frequency equivalent circuit model for AC motors in Spice-like simulation software. This model can be used to analyse the characteristics of the motor and predict the conducted electromagnetic noise in an adjustable speed drive system. The modelling is based on measured data of the impedance and vector fitting technique. The procedure of the modelling is elaborated in this study and verified by comparing simulated data with experimental data on a 200 kW induction motor in the frequency range from 10 kHz to 10 MHz. This modelling method can be extended to model other types of motors irrespective of the power rating of the motors. Applications of the motor modelling to study common mode voltage in the system and current oscillation in motor winding are presented.

Lightning strikes are a common cause of damage to wind turbine blades. This paper intends to discuss the lightning incidence to wind turbine parks considering both downward and upward lightning discharges. The analysis is based on numerical simulations performed with the Self-consistent Leader Inception and Propagation Model SLIM. It is found that the calculated annual frequency of strikes due to downward lightning is several orders of magnitude smaller than field observations in the Horns Reef 1 wind park. This shows that upward lightning discharges should be considered in order to obtain proper estimates of the lightning incidence to wind turbines. Thus, it is also found that the thundercloud electric field required to trigger upward lightning from wind turbines depends on whether the discharge is self-triggered or nearby-lightning triggered. A discussion about the existing limitations to estimate the upward lightning incidence in wind parks is presented.

Pre-charger is a specific DC–DC converter application in the railway propulsion system. This study demonstrates the possible causes for output diode failures in the pre-charger. Overshoot voltage during diode reverse-recovery is a main reason for such failure. A test set-up is proposed to study the influence of reverse bias on the overshoot voltage. The method to mitigate the contact bounce in the control circuit, in the test set-up, is also introduced. The relationship between the overshoot and reverse bias is studied by means of applying different reverse biases. The parasitic capacitance and reverse-recovery characteristic of the diode is changed by the exceeding reverse bias. Reverse-recovery time is reduced when the reverse voltage is beyond a critical level. To overcome the overshoot problem, a snubber is applied, and experimentally verified. Overvoltage is dramatically reduced by applying this snubber. Current and voltage waveforms in different branches are recorded so as to give a better understanding of the working mechanism of the snubber.

In this paper, we discuss two issues related to the measurement and calculation of the horizontal electric fields from lightning. On the one hand, there is an inherent difficulty in measuring the horizontal electric field component from lightning because of the overshadowing effect of the vertical electric field component which, depending on the distance to the lightning channel, the ground conductivity, and the height of the observation point can be one to two orders of magnitude larger than the horizontal electric field component. Consequently, even a small tilt of the measuring antenna would result in a noticeable contamination of the measured horizontal waveform. This may explain the fact that data on horizontal electric fields are very scarce. Numerical simulations show that, for a ground conductivity of 0.0025 S/m, the resulting error for a one-degree sensor tilt in the field peak is about 20% for distances ranging from 60 to 500 m. For strikes to a 100-m-tall tower, the resulting errors are found to be slightly smaller (about 10% to 15% for the first peak). The second issue dealt with in this paper is the computation methods of the horizontal electric field. In this regard, some authors have emphasized the importance of taking into account the so-called conduction current in the calculation of nearby horizontal electric fields. We show in this paper that the conducted contribution is automatically taken into account when using the general solutions of Maxwell's equations or obtained by exact numerical simulations. In this case, there is no need to consider separately any other contributions because the solution yields the total horizontal electric field, taking into account both the radiation from the channel and the current flowing into the ground. However, a “conducted contribution” needs indeed to be taken into account separately when high-frequency approximate solutions are used for the evaluation of the electric field. At very close distances to the lightning strike location, the current distribution in the ground may be highly nonuniform because of surface arcing and plasma channel formations. Given the random nature of these phenomena, it is virtually impossible to gain detailed knowledge of the current distribution and, hence, to evaluate the resulting horizontal electric field near the strike point. Based on the results and discussion presented in this paper, we recommend taking special care when measuring the horizontal electric field from lightning to minimize the contaminating effect of the vertical electric field. It is important that both components (vertical and horizontal) be measured simultaneously to evaluate possible contamination of the horizontal field.

Pantograph arcing in ac traction system generates transients, and causes asymmetries and distortion in supply voltage and current waveforms. These asymmetric voltage and current lead to a net dc component and harmonics that propagate within the traction power and signalling system and cause electromagnetic interference. This problem is enhanced during winter because of the layer of ice/snow on the overhead contact wire. The sliding contact becomes poor and a visible arc moves along with the pantograph. In this paper, it is shown how different parameters like traction current, line speed, power factor, and supply voltage influence the arcing, its characteristics, and the dc components. It is shown that the dc current component increases with increasing train speed and traction current, and reduces at a lower power factor. It is also discussed how the presence of an ice layer influences the arcing and the dc components. It is found that running the trains below the normal operating power factors is an effective choice to mitigate this problem. The findings presented in this paper could be beneficial to estimate the probable limit of the dc component at the planning stage so that proper precautions can be taken at the design stage itself.

Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower. In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.

Power-line networks are promising mediums by which broadband services can be offered, such as Internet services, voice over Internet protocol, digital entertainment, etc. In this paper, an analysis of delay spread, coherence bandwidth, channel capacity, and averaged delay in the frequency bands up to 100 MHz for typical indoor power-line networks are studied. Earlier studies for indoor power-line networks considered frequencies up to 30 MHz only and earlier works have shown that at these frequency bands, the data rates are generally low and are inefficient for digital entertainment in comparison with wireless local-area networks standards, such as IEEE 802.11 n. In this paper, it is shown that at 100 MHz, the average channel capacity for typical indoor power-line networks can be up to 2 Gb/s and it is found that by increasing the number of branches in the link between transmitting and receiving ends, the average channel capacity decreases from 2 Gb/s to 1 Gb/s (when the number of branches was increased by four times for a power spectral density of -60 dBm/Hz). At the same time, the coherence bandwidth decreased from 209.45 kHz to 137.41 kHz, which is much better than the coherence bandwidths corresponding to 30-MHz systems. It is therefore recommended to operate the indoor power-line networks at 100-MHz bandwidths for a wide variety of broadband services.

Power-line networks are proposed for broadband data transmission. The presence of multipaths within the broadband power-line communication (BPLC) system, due to stochastic changes in the network load impedances, branches, etc. pose a real challenge as it affects network performance. This paper attempts to investigate the performance of an orthogonal frequency-division multiplexing (OFDM)-based BPLC system that uses underground cables. It is found that when a branch is added in the link between the sending and receiving end, there is an average of 4-dB power loss. In addition, when the terminal impedances of the branches that are connected to the link between the transmitting and receiving end vary from line characteristic impedance to low-impedance values, the power loss (signal-to-noise ratio) is about 0.35 dB/ Omega. On the contrary, for an increase in the terminal impedances by 100 Omega above line characteristic impedance, the power loss is 0.23 dB//Omega. When the branch terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. It is shown that to overcome degraded network performance, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used, which could be used for an efficient design of the BPLC system that uses OFDM techniques.

Pantograph arcing is a common phenomenon in electrified railway systems. This is also a source of broadband-conducted and radiated electromagnetic interference (EMI) for vehicle as well as traction power and signaling systems. In this paper and the companion paper, experimental analyses of pantograph arcing phenomena are presented for dc and ac feeding systems, respectively. Influences of different parameters on dc traction system, such as supply-voltage polarity, relative motion between pantograph and overhead contact wire, namely, forward motion along the track (longitudinal), and lateral sliding motion of the pantograph (zigzag) are presented here. From the voltage and current waveforms of the test runs, it is shown that pantograph arcing is a polarity-dependent phenomenon. For the positive-fed overhead traction system, where pantograph is cathode, the supply interruptions due to zigzag motion are comparatively less compared to negatively fed traction systems. As a result, the transients, due to pantograph arcing, are more frequent in negatively fed traction systems. It is found that the arc root movement along the electrode surfaces (pantograph-contact wire) is governed by the relative motion and polarity of the electrodes. The analyses presented in this paper also form a foundation to understand the pantograph arcing process and the corresponding influential parameters with the ac supply presented in the companion paper. The findings presented in this paper could be beneficial for coming up with appropriate mitigation techniques from the EMI due to pantograph arcing in dc-fed traction systems.

Transient analysis of lossy multiconductor transmission lines (MTLs) has been studied using the finite-difference time-domain (FDTD) method with lumped loads/devices connected at line terminations. In electrified railway networks, series and shunt devices (whose circuit models are derived either from experiments/borrowed off the shelf), e.g., transformers, converters, switchgear, signal equipments, etc., are found distributed along the MTL system. To simulate such railway systems involving both transmission lines (TLs) and lumped circuits, an interface technique between TL systems, which is solved using FDTD, and all the lumped circuits, which are solved using alternative transients program/electromagnetic transients program software (circuit solver), is proposed. This sufficiently accurate method is simple to apply as only instantaneous voltages and currents are transmitted between the stand-alone FDTD routine and circuit solver. Moreover, the user avoids coding complex circuit models within the FDTD, while at the same time, efficiently uses the potential of accurate frequency-dependent loss models (nonexistent in circuit software) coded in FDTD. The technique is applied on typical electrified railway systems to demonstrate how traction transformers, track circuits, and line interconnections affect the propagating voltages and currents. The method could be beneficial for transient protection and insulation coordination studies in electrified railway systems.

Power-line networks are an excellent infrastructure for broadband data transmission. However, various multipaths within a broadband power-line communication (BPLC) system exist due to stochastic changes in the network load impedances, branches, etc. This further affects network performance. This paper attempts to investigate the performance of indoor channels of a BPLC system that uses orthogonal frequency-division multiplexing (OFDM) techniques. It is observed that when a branch is added in the link between the sending and receiving end of an indoor channel, an average of 4-dB power loss is found. Additionally, when the terminal impedances of the branch change from the line characteristic impedance to impedance of lower values, the power loss (signal-to-noise ratio) is about 0.67 dB/Omega. On the contrary, for every increase in the terminal impedances by 100 Omega, above the line characteristic impedance, the power loss is 0.1 dB/Omega. When the line terminal impedances are close to short or open circuits, OFDM techniques show degraded performance. This situation is also observed when the number of branches increases. In this paper, it is shown that to overcome such performance degradation, the concatenated Reed-Solomon codes/interleaved Viterbi methods can be used. The observations presented in the paper could be useful for an efficient design of a BPLC system that uses OFDM techniques.

Information and communications technologies (ICTs) are gaining importance in developing countries. Power-line network is a potential infrastructure for ICT services provision. Power-lines are highly interconnected network with stochastic variation in number of branches. Under such distributed network conditions the design of a broadband power-line communication (BPLC) system is a challenge. In this paper a case study of an actual power-line network, representative of a low-voltage BPLC channel in Dar es Salaam, Tanzania is considered. We shall investigate the performance of such a low-voltage channel that uses orthogonal frequency division multiplexing (OFDM) technique with binary phase shift keying (BPSK) modulation scheme for communication. For sensitivity analysis, three different transmitter locations were chosen and receiver points were varied to identify the possible degraded performance scenarios. Analysis show that in the frequency bands of 100 MHz, the channel delay spread for such networks is about 4 mus, giving a maximum number of subchannels 4096 with 512 cyclic prefix. To improve the degraded performance scenarios, the concatenated Reed Solomon outer code with punctured convolution inner code was applied to the network. It was found that when the branches were terminated by its corresponding characteristic impedances the performance is improved by 10-20 dB compared to a corresponding uncoded system. On the contrary for a coded system when the branches were terminated either in low or higher impedances compared to branch characteristic impedances the improvement was greater than 2-15 dB. This study demonstrates that the specification proposed by IEEE-802.16 broadband wireless access working groups can be used for performance improvement of distributed low-voltage systems.

This paper presents the influence of line length, number of branches (distributed and concentrated), and terminal impedances on the performance of a low-voltage broadband power-line communication channel. For analyses, the systems chosen are typical low-voltage power-line networks found in Tanzania. The parameters varied were the network's load impedances, direct line length (from transmitter to receiver), branched line lengths, and number of branches. From the frequency responses of the transfer functions (ratio of the received and transmitted signal), it is seen that the position of notches and peaks in the amplitude responses are affected by the aforementioned network parameters and topology. As a result, the time-domain responses are attenuated and distorted. Time-domain responses of power-line channels under various conditions are also investigated for a given pulse input at the transmitter. The observations presented in this paper could be useful for suitable power-line communication system design.

It is argued that it is the intent behind the electromagnetic interference in intentional electromagnetic interference (IEMI) that causes problems to large distributed systems and facilities even if they are designed by traditional zoning concept rules. Hardening such facilities against IEMI requires a correspondence between the electromagnetic zone boundary and the physical access control boundary. The three characteristics of a facility, the accessibility, susceptibility , and consequence, are discussed in the context of vulnerability to IEMI. A methodology for classification of facilities with respect to IEMI is presented.

This paper presents a generalized transmission-line approach to determine the transfer function of a power-line network of a two-conductor system (two parallel conductors) with distributed branches. The channel frequency responses are derived considering different terminal loads and branches. The model's time-domain behavior is validated using commercial power system simulation software called Alternative Transients Program-Electromagnetic Transients Program (ATP-EMTP). The simulation results from the model for three different topologies considered have excellent agreement with corresponding ATP-EMTP results. Hence, the model can be considered as a tool to characterize any given power-line channel topology that involves the two-conductor system. In the companion paper (Part II), the proposed method is extended for a multiconductor power-line system.

In Europe, the railway industry is rapidly getting transformed from traditional mode of public transportation to a very fast, more reliable, long distance and cross country operation. A new concept ...

During a lightning strike to communication tower stroke currents are shared by the tower and by the shields of the cables along the tower. The currents in the tower proceed towards the grounding system (possibly a combination of counterpoises or ring conductors or ground rods or grounding grids) connected to tower legs' foundation. In this paper, lightning strike to communication tower on mount Gaisberg in Austria is considered and measured currents at the tower top and those shared by an instrumented grounding strip connected to one of the tower leg's are presented. The measured currents at different locations on the 70-m long ground strip are compared with the predictions of a frequency dependant lossy transmission line (TL) model and reasonably good agreement was found. From this validation it is claimed that the TL models are appropriate for lightning transient analysis of grounding systems.

A test airport runway lighting system, including a buried cable protected by a counterpoise and vertical ground rods, was subjected to direct lightning strikes, and currents and voltages measured in different parts of the system were reported earlier by Bejleri et al. In this paper, we attempt to model the lightning interaction with this system using the transmission line theory. Lumped devices along the cable such as current regulator and transformers are ignored; possible nonlinear phenomena (arcing) in the system are neglected; the soil is assumed to be homogeneous. The model-predicted currents in the counterpoise, ground rod, and the cable are compared with the measurements, and a reasonable agreement was found for the currents along the counterpoise. It is found that current in the counterpoise is not much influenced by the presence of the cable. Further, vertical ground rods connected to the counterpoise do not have significant influence on the current distribution along the counterpoise. It appears that the model is unable to predict cable currents and voltages in the test system, presumably due to neglecting nonlinear phenomena in the soil and in cable's insulation and electromagnetic coupling with the lightning channel.

In this paper, the propagation of ultra-wideband (UWB) transients through different types of junctions of low-voltage power cables and one real power network of a building were investigated. For the laboratory test, it was seen that the main mode of propagation in the cables and through the junctions tested is transverse electromagnetic (TEM). The received voltage could thus be, within a small error, estimated from transmission-line theory. The main cause for decreased voltage received at the loads of the branches of the junctions is reflections due to impedance mismatch of the junctions. Large voltages can be delivered to many unprotected loads connected to the junctions. UWB transients were also injected into a residential house using a power outlet available on the outside wall of the house. It was seen that the complexity of this network creates deviation from the TEM mode. However, relatively large voltages were still received at the various outlets inside the house. It is recommended that power outlets or lamp sockets outside buildings are controlled from inside using two-pole switches that reduce the received voltage to reduce the risk of conducted intentional electromagnetic interference.

Recently, different models have been proposed for analyzing the broadband power-line communication (BPLC) systems based on transmission-line (TL) theory. In this paper, we make an attempt to validate one such BPLC model with laboratory experiments by comparing the channel transfer functions. A good agreement between the BPLC model based on TL theory and experiments are found for channel frequencies up to about 100 MHz. This work with controlled experiments for appropriate validation could motivate the application and extension of TL theory-based BPLC models for the analysis of either indoor or low-voltage or medium-voltage channels.

Civilian handheld global positioning system receivers were tested for their susceptibility against radiated electromagnetic disturbances of different characteristics and field levels. This susceptibility data were compared to the existing electromagnetic compatibility (EMC) immunity requirements for electronic devices. Some of the receivers were disrupted by continues waves at in- as well as out-of-band frequencies, at field levels far below the existing EMC requirements. The possible reason for this is discussed. In general, due to the ever-growing use of commercial-off-the-shelf equipment even for critical functions, certificates of conformity to current EMC requirements may be inadequate.

In this paper, the vulnerability of the future electrified railway system in Europe from a high-power microwave (HPM) source is investigated. The scenario of in-band disturbances radiated toward a GSM-R antenna and damaging the connected communications system is evaluated for different classes of HPM sources and situations. The minimum realistic distances for the different HPM sources from the antenna to cause permanent damage is shown, and the severity of threat from the different sources is discussed.

An underground cable power transmission system is widely used in urban low-voltage power distribution systems. In order to assess the performance of such distribution systems as a low-voltage broadband power-line communication (BPLC) channel, this paper investigates the effects of load impedance, line length, and branches on such systems, with special emphasis on power-line networks found in Tanzania. From the frequency response of the transfer function (ratio of the received and transmitted signals), it is seen that the position of notches and peaks in the magnitude are largely affected (observed in time-domain responses too) by the aforementioned network configuration and parameters. Additionally, channel capacity for such PLC channels for various conditions is investigated. The observations presented in this paper could be helpful as a suitable design of the PLC systems for better data transfer and system performance.

Estimation of electromagnetic (EM)-fleld emissions from broadband power-line communication systems (BPLC) is necessary, because at its operating frequencies, the radiated emissions from BPLC systems act as sources of interference/crosstalk to other radio-communication systems. Currently, the transmission-line (TL) system used for BPLC is complex, involving arbitrarily/irregularly distributed branched networks, arbitrary termination loads, varying line lengths, and line characteristic impedance. In order to study the electromagnetic-compatibility (EMC) issues associated with the radiated emissions of such complex BPLC networks, knowledge of current and voltage distributions along the length of the power-line channels is needed. This paper attempts to derive and present generalized expressions for either the current or voltage distribution along the line (whose TL parameters are known) between the transmitting and receiving ends for any line boundary condition and configuration based on the TL theory. The expressions presented in this paper could be beneficial for direct calculation of EM emissions from BPLC systems.

The power line has been proposed as a solution to deliver broadband services to end users. Various studies in the recent past have reported a decrease in channel capacity with an increase in the number of branches for a given channel type whether it is an indoor or low-voltage (LV) or medium-voltage (MV) channel. Those studies, however, did not provide a clear insight as to how the channel capacity is related to the number of distributed branches along the line. This paper attempts to quantify and characterize the effects of channel capacity in relation to the number of branches and with different terminal loads for a given type of channel. It is shown that for a power spectral density (PSD) between 90 dBm/Hz to 30 dBm/Hz, the channel capacity decreases by a 20-30 Mb/s/branch, 14-24 Mb/s/branch, and a 20-25 Mb/s/branch for an MV channel, LV channel, and indoor channel, respectively. It is also shown that the channel capacity is minimum when the load impedance is terminated in characteristic impedances for any type of channel treated here. It is shown that there could be a significant loss in channel capacity if a ground return was used instead of a conventional adjacent conductor return. The analysis presented in this paper would help in designing appropriate power-line communication equipment for better and efficient data transfer.

This paper investigates the importance of a follow-on buried bare earth wire for the lightning protection of buried shielded cables. The use of follow-on bare wires for lightning protection of communication towers was suggested as a recommendation in certain standards, without being complemented either by theory or experiments. When lightning transients couple to the cable shields, it induces large currents (depending on the type of coupling) causing transient overvoltages between the inner conductors and the shield. It is shown by simulations based on multiconductor transmission line theory that if the follow-on bare earth conductor is placed in parallel with the shielded cable with the bare earth wire connected to the shield at the current injection end, then the shield current, and thereby, the internal transient voltages of the cable are reduced considerably.

This paper presents the effects of load impedance, line length and branches on the performance of an indoor voltage broadband power line communications (BPLC) network. The power line network topology adopted here is similar to that of the system found in Tanzania. Different investigations with regard to network load impedances, direct line length from transmitter to receiver, branched line length, and number of branches has been carried out. From the frequency response of the transfer function (ratio of the received and transmitted signal), it is seen that position of notches and peaks in the magnitude and phase responses are largely affected by the above said network parameters/configuration, mainly in terms of attenuation and dispersion. These effects are observed in the time domain responses also. The observations presented in the paper could be helpful in the suitable design of the BPLC systems for a better data transfer and system performance.

It is a usual phenomenon that lightning strikes tall communication towers. Some of the questions about lightning interaction with communication towers are dealt with in this paper. Can tall towers influence the incidence of lightning in the area where the tower is situated? Are the parameters of lightning, such as peak currents, influenced by the presence of the tower where lightning strikes? What would be the difference in the electric and magnetic field environment in the near vicinity of the tower and far from the tower when compared to the corresponding values with lightning striking level ground? Are lightning protection methods designed primarily to protect the communication equipment sufficient to prevent lightning surge transfer to nearby local networks? This paper addresses the above issues based on the analysis, models and observations made in the recent past and also using some simple calculations by the authors.

This paper investigates the propagation of subnanosecond rise time (ultra wideband) voltage transients in low-voltage installation power cables. Experimental results are compared to simulations. It is concluded that the main mode of propagation of differentially injected transients in low-voltage installation power cables is transverse electromagnetic mode. Also, such transients would spread relatively unattenuated to any load or junction in the power system, received power primarily only limited by the impedance mismatches causing reflections. The effects of different types of bends in the cable have been studied. The study was conducted as a part of an assessment of the susceptibility of civilian facilities to intentional electromagnetic interference.

The paper investigates the applicability of some closed form expressions for the ground impedance and ground admittance of buried horizontal wires (bare and insulated) for lightning or switching transient analyses based on transmission line (TL) theory. In view of the frequency contents that typically characterize such transients, the behavior of the ground impedance and admittance is studied for a wide frequency range up to 10 MHz. Low frequency approximation of the ground impedance is not always appropriate for transient analysis. Sensitivity analyses show that, unlike overhead wires, the ground impedance for buried wires is little sensitive to the ground conductivity. On the other hand, the ground admittance varies strongly with the ground conductivity. The paper also discusses the results of transient analysis of buried cables performed by means of electromagnetic transient programs (EMTP) that neglect the ground admittance. The limits of such an approximation are discussed in order to evaluate the applicability of EMTP-like programs to the transient analysis of buried conductors. Transient pulse propagation in time domain based on finite difference time domain (FDTD) method of solution of TL equations is also discussed for a future inclusion of non-linear phenomena, like soil ionization and arcing/breakdown mechanisms, in the soil. The analysis presented could be useful in estimating surge propagation characteristics of buried wires for appropriate insulation coordination and transient protection. © 2007 IEEE.

Transient surges in one of the overhead conductors, due to direct lightning strikes, causes crosstalk [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992] in other adjacent conductors. It is a common electromagnetic interference (EMI) phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multiconductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, heights of the receptor conductor and the terminal loads. For receptor conductor close to the ground, compared to the emitter conductor [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992], the decrease in ground conductivity increases the crosstalk peak currents at near end (end near to the source in the emitter conductor) of the receptor conductor, but at the far end it could either increase or decrease depending upon the line height and ground conductivity. It is found that the ground impedance [J.R. Carson, Wave propagation in overhead wires with ground return, Bell. Sys. Tech. J. 5 (1926) 539–554; Y.J. Wang, S.J. Liu, A review of methods for calculation of frequency dependant impedance of overhead power transmission lines, Proc. Natl. Sci. Conc. ROC (A), 25 (6), (2001) 329–338; E.D. Sunde, Earth conduction effects in transmission systems, 1st ed., Dover Publications Inc., New York, 1968; A. Deri, G. Tevan, A. Semlyen, A. Castanheira, The complex ground return plane a simplified model for homogenous & multilayer earth return, IEEE Trans. PAS 100 (8) (1981) 3686–3693; K.C. Chen, K.M. Damrau, Accuracy of approximate transmission line formulas for overhead wires, IEEE Trans. EMC 31 (4) (1989) 396–397; A. Semlyen, Ground return parameters of transmission lines an asymptotic analysis for very high frequencies, IEEE Trans. PAS 100 (3) (1981) 1031–1038; E.F. Vance, Coupling to Cable Shields, Wiley Interscience, New York, 1978; J.R. Wait, Theory of wave propagation along a thin wire parallel to an interface, Radio Sci. 7 (6) (1972) 675–679; R.G. Olsen, J.L. Young, D.C. Chang, Electromagnetic wave propagation on a thin wire above earth, IEEE Trans. Anten. Propag. 48 (9) (2000) 1413–1418; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. I. Single conductor configuration, IEEE Trans. EMC 38 (2) (1996) 127–138; M. D’Amore, M.S. Sarto, Simulation models of a dissipative transmission line above a lossy ground for a wide-frequency range. II. Multiconductor configuration, IEEE Trans. EMC 38 (2) (1996) 139–149; F. Rachidi, C.A. Nucci, M. Ianoz, C. Mazzetti, Influence of lossy ground on lightning induced voltages on overhead lines, IEEE Trans. EMC 38 (3) (1996) 250–264; F. Rachidi, C.A. Nucci, M. Ianoz, Transient analysis of multiconductor lines above a lossy ground, IEEE Trans. Power Deliv. 14 (1) (1999) 294–302; F.M. Tesche, M.V. Ianoz, T. Karlsson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997; A.K. Agrawal, H.J. Price, S.H. Gurbaxani, Transient response of multiconductor transmission lines excited by a nonuniform electromagnetic field, IEEE Trans. EMC 22 (2) (1980) 119–129] has profound influence in all the crosstalk cases studied here. Hence, a brief review and comparison of different closed form ground impedance expressions under the limits of transmission line approximation [F.M. Tesche, M.V. Ianoz, T. Karlsson, EMC Analysis Methods and Computational Models, John Wiley and Sons Inc., 1997] and its behavior at both high and low frequencies is presented. It is shown that low frequency approximation of ground impedance is not sufficient for lightning transient studies involving ground conductivities lower than 10 mS/m. The observations presented in the paper have important implications in EMI studies of large distributed outdoor systems, such as the railway network, subjected to lightning strikes.

There are various definitions for effective length/area of grounding wire/grid for lightning transients [A.S. Farag, T.C. Cheng, D. Penn, Grounding terminations of lightning protective systems, IEEE Trans. Dielectics, Elect. Insul 5(6) (1998) 869-877; B.R. Gupta, B. Thapar, Impulse impedance of grounding grid, IEEE Trans. Power Apparatus Syayem PAS-99(6) (1980) 2357-2362; Y. Liu, N. Theethayi, R. Thottappillil, An engineering model for transient analysis of grounding system under lightning strikes: non-uniform transmission line approach. IEEE Trans. Power Delivery 20 (2) (2005) 722-730; M.I. Lorentzou, N.D. Hatziargriou, Modelling of long grounding conductors using EMTP, in: IPST'99, International Conference on Power System Transients, Budapest, 20-24 June, 1999; L.D. Grcev, M. Heimbach, Frequency dependent and transient characteristics of substation grounding system, IEEE Trans. Power Delivery 12 (1997) 172-178.]. The present work investigates and discusses the validity of those existing definitions. Further, practical methods for estimating the effective length/area of different grounding structures are proposed for engineering applications. The calculations for effective length/area based on non-uniform transmission line approach (Liu et al., 2005) show that, for a single grounding wire, the empirical equation for effective length in Farag et al. (1998) is not valid when the injection current has very fast rise time. Also, the empirical equation for effective length of grid edge in Gupta and Thapar (1980) is not applicable for grids with large inner mesh size.

It is a common practice that the unused pairs (inactive conductors) in shielded cables are left open (open circuited at the terminal block) in telecommunication systems. In this paper, it is shown by both theory (based on transmission line analysis) and experiments that if those inactive conductors are shorted to the cable shield, then the transient voltages on the other active conductors (conductors in service) can be reduced when external transients/faults due to lightning or switching couple to the shield. This could be a good EMC practice for transient voltage reduction in telecommunication systems.

Experiment and simulation results of conventional transformer design have shown that there are considerable differences in the characteristics of the surge voltages that are important in deciding the transferred voltages, depending on whether it is from primary to secondary or vice versa. Dryformer is a new technological advance of dry power transformer, which is constructed from XLPE insulated high voltage cables as its winding, and is designed to provide a direct link between ultimate customers and transmission systems in one step transformation [Leijon M, Andersson T. High and dry—dryformer, an innovative high-voltage transformer design that, eliminates the need for oil, promises a host of performance and environmental benefits. IEE Rev 2000:9–14. [1] ; Leijon M, Dahlgren M, Walfridsson L, Ming L, Jaksts A. A recent development in the electrical insulation systems of generators and transformers. IEEE Electr Insulat Mag 2001;17(3):10–15. [2] ]. It is important therefore to have a better understanding of Dryformer behaviour in regard to transient surge voltage transfer between its circuits. This paper presents the application of a high frequency model for the study of transient surge voltage transfer between the Dryformer circuits due to surges having various steepness, amplitude and duration characteristics, which are expected in practise. The model is based on the creation of an RLCG network that gives the same admittance function as that obtained experimentally at the transformer terminals [Manyahi MJ, Leijon M, Thottappillil R. Transient response of transformer with XLPE insulation cable winding design (Dryformer). ELSEVIER Electr Power Energy Syst 2005;27(1):69–80.]. The validity of the formulated model has been verified by comparing the model predictions with experimentally obtained voltage transfer function. The model is successfully applied in estimating the threat levels posed to Dryformer winding and customer connected equipment due to transient overvoltages.

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5 m (tracks) to 10 m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance that has better early time and late time behavior. The main interconnection between the conductors and the flashover strength of the supporting insulators is included in the simulations. A simple model for the arc channel during flashover of the insulators and the ionization of the soil around the pole foundations is also included in the model to assess the possible realistic surge voltage distribution in the system. It is shown in the paper that finite ground conductivity, interconnections between the conductors, arcing phenomena of insulation flashover and grounding of the poles decide the voltage/current distribution in the conductors. Simulations have been also carried out to determine the voltages on the lines and across the rails as function of distance from the point of strike as it could be a necessary data for deciding the possible future protection schemes. It was found that for a lightning stroke of 31 kA peak, large common mode and differential mode surges exist on the lines which could create excessive voltages between the line and neutral of the transformer and might pose a threat to the various low voltage equipments used for telecommunication, signaling and control.

In this work a simplified procedure for the formulation of distribution transformer model for studying its response to lightning caused transients is presented. Simplification is achieved by the way with which the model formulation is realised. That is, by consolidating various steps for model formulation that is based on terminal measurements of driving point and transfer short circuit admittance parameters. Sequence of steps in the model formulation procedure begins with the determination of nodal admittance matrix of the transformer by network analyser measurements at the transformer terminals. Thereafter, the elements of nodal admittance matrix are simultaneously approximated in the form of rational functions consisting of real as well as complex conjugate poles and zeros, for realisation of admittance functions in the form of RLCG networks. Finally, the equivalent terminal model of the transformer is created as a π-network consisting of the above RLCG networks for each of its branches. The model can be used in electromagnetic transient or circuit simulation programs in either time or frequency domain for estimating the transfer of common mode transients, such as that caused by lightning, across distribution class transformer. The validity of the model is verified by comparing the model predictions with experimentally measured outputs for different types of common-mode surge waveform as inputs, including a chopped waveform that simulate the operation of surge arresters. Besides it has been verified that the directly measured admittance functions by the network analyser closely matches the derived admittance functions from the time domain impulse measurements up to 3 MHz, higher than achieved in previous models, which improves the resulting model capability of simulating fast transients. The model can be used in power quality studies, to estimate the transient voltages appearing at the low voltage customer installation due to the induced lightning surges on the high voltage side of the transformer. The procedure is general enough to be adapted for any two-port devices that behaves linearly in the frequency range of interest.

A nonuniform transmission line approach is adopted in this paper for modeling the transient behavior of different types of grounding systems under lightning strikes in time domain by solving Telegrapher's equations based on finite-difference time-domain (FDTD) technique. Electromagnetic couplings between different parts of the grounding wires are included using effective per-unit length parameters (l, c, and g), which are space and time dependent. The present model can predict both the effective length and the transient voltage of grounding electrodes accurately, while, an uniform transmission line approach with electrode length dependent per-unit length parameters fails to predict the same. Unlike the circuit theory approach , the present model is capable of predicting accurately the surge propagation delay in the large grounding system. The simulation results for buried horizontal wires and grounding grids based on the present model are in good agreement with that of the circuit and electromagnetic field approaches , . From an engineering point of view, the model presented in this paper is sufficiently accurate, time efficient, and easy to apply.

Significant advances in XLPE insulation cables that have higher electric field strength withstand capability have made it possible to apply these high voltage (HV) cables as windings in generators and transformers. Therefore, the recent advent of HV generator (Powerformer) that can be connected directly to the power transmission line has motivated the design of HV transformer (Dryformer) that performs one step transformation from transmission to distribution voltage levels. Since the dryformer will be connected directly to transmission lines, they will be subjected to transients resulting from direct and indirect lightning strikes as well as fast switching surges from Gas insulated circuit breakers. This paper presents the results of experimental studies on the cable winding power transformer (Dryformer) to study its response to various transients. Experimental investigations have been carried to obtain the transformer model parameters based on terminal measurement of admittance functions using Network Analyser, and hence for comparing the model predictions with experimentally obtained responses. The model has been successfully used in estimating the dryformer transient responses at its terminals due to surge application of various front times and peak amplitudes that are representative of lightning and switching caused transients. Experiment and simulation results show that there are considerable differences in the transient response characteristics of dryformer windings as compared to that of transformers with traditional winding design. These differences on transient responses are discussed in perspective of their basic difference in winding design features.

Railway overhead traction system is a classic example of scattered conductor configuration, where tracks and other wires form multi-conductor transmission lines (MTLs) with large variation in conductor heights above ground and they are spread across regions having different soil conditions. Lightning transient analysis in such systems has not received much attention earlier. Here we analyze the influence of conductor heights and lossy ground on the induced voltages in a two conductor MTLs for the case of a direct lightning strike. For transient analysis, modified time domain transient ground impedance expressions having better early and late time behavior was used. The dependence of transient ground impedance on conductor heights and ground resistivity are presented and discussed. The early time transient ground impedances are unaffected by ground resistivity but their decaying nature is highly dominated by ground resistivity. It is found, if one of the conductors is close to ground (a rail) and if it is at large vertical distance from struck conductor (an auxiliary power line), then with increasing ground resistivity the peak induced voltages in the conductor close to ground initially increase, then decrease and finally tend to remain constant (within 100–10,000 Ω m). This phenomenon is opposite to that compared to conductors that are close to each other with minimum vertical separation (two auxiliary power lines), where the peak induced voltages increase with increasing ground resistivity. The study focuses mainly to access when a mutual coupling due to system geometry or due to ground losses becomes dominant in determining induced effects from lightning in MTLs, which could be an important contribution to the lightning interaction studies for electrified railway systems.

The electric and magnetic field structures around a semi-infinite thin-wire antenna vertically placed above a perfectly conducting ground plane are investigated when the antenna is supporting two different types of sources. It is shown that when the wire is carrying a uniform line charge, the electrostatic potentials are equal on the surfaces of imaginary cones of fixed cone angles with axis along the wire and apex at the conducting plane. The electrostatic field vectors are shown to be perpendicular to the imaginary cones and tangential to the meridian lines of half-spherical shells centered at the base of the line charge. The vertical components of the electrostatic field on the surface of these imaginary half-spherical shells of a given radius are constant, except at the wire itself. The magnetic field structure associated with a constant current in the semi-infinite antenna is that of an infinite wire. The electric and magnetic fields due to a time-varying charge or current pulse propagating with the speed of light along the vertical thin-wire antenna have a spherical transverse electromagnetic (TEM) field structure, identical to that for the case of a uniform line charge and a uniform current. The connection between the static and dynamic solutions is derived mathematically using two different approaches.