Short Transmission Line Research Articles

A Wideband Scanning Circularly Polarized Array Antenna Based on the Shorted Transmission Line Model

Due to the huge potential of application in the communications, electronic jamming, and radar fields, circularly polarized (CP) array antennas with wide axial ratio (AR) scanning performance at wide frequency bandwidth have received great attention. A wideband scanning CP planar array antenna built by new, tightly coupled dipole array (CP-TCDA) elements, which have achieved promising results in terms of both scanning AR bandwidth and angle range in all scanning planes, is presented in this paper. Based on the shorted transmission line model, a CP-TCDA element arranged along the &#x00B1;45&#x00B0; direction is constructed, which can shift the middle-frequency scanning blind zone out of band and thus obtain a wideband scanning AR bandwidth. Furthermore, the proposed CP-TCDA element adopts four shorting pins and four square parasitic strips, which improve wide-angle CP performance for <i>xz</i>-plane and diagonal-plane scans, respectively. An 8&#x00D7;8 left-handed CP planar array antenna based on the proposed CP-TCDA elements is designed and prototyped. The results show that the array antenna is able to operate over a 3:1 (4&#x2013;12 GHz) overlapping bandwidth, and it meets the requirements of AR &#x003C; 3 dB and active VSWR &#x003C; 2.9 within a &#x00B1;45&#x00B0; scanning angle range.

Optimization of Lumped Parameter Models to Mitigate Numerical Oscillations in the Transient Responses of Short Transmission Lines

The Lumped Parameter Model (LPM) is a known approach to represent overhead transmission lines (TLs), especially when these elements comprehend a few tens of kilometers. LPMs employ a large number of cascaded π-circuits to compute accurately the transient responses. These responses contain numerical spurious oscillations (NSO) characterized by erroneous peaks which distort the transient responses, mainly their peak values. Two modified LPM topologies composed of damping resistances inserted along the longitudinal or transversal branches of the cascaded π-circuits offer significant mitigations in the NSO. In this paper, in an effort to have the maximum mitigation of the NSO and low distortion in the transient responses, two modified topologies with optimized damping resistances are proposed to represent short TLs. Results demonstrate expressive attenuation in the peaks of NSO which reflect good agreement in comparison with the responses computed by the Bergeron’s line model. The mitigation of the NSO is carried out directly in the time domain and it does not require either analog or digital filters.Furthermore, no frequency-to-time transformations are necessary in this procedure. These alternative topologies can be incorporated into any electromagnetic transient program to study switching operations in power systems.

A Python-Based Interface Design for Electric Power System Education.

Python, which is widely used today, is one of the open-source programming languages. In the Python program, its interface is done through the PyQt5 library. With PyQt5, it is possible to develop object-based software that takes up less space on the disk and runs faster. In this study, an educational calculation and analysis program (ITUPSA) was designed for the Electric power systems course using the Python interface. Electric power systems are one of the fundamental courses in electrical engineering. This main course is taught in three sub-course groups as energy transmission-distribution, energy flow and energy economy. The energy transmission-distribution course package constitutes the first and most comprehensive part of the electric power systems group. In the energy transmission-distribution, the creation of the transmission line model and the calculation of the line parameters form an important part of the training. This section contains very detailed mathematical calculations and it is very important that students get the correct result as a result of these calculations. This can be possible with a lot of practice. The interface design was made by students and faculty to teach practical examples correctly. This developed (ITUPSA) python-based interface program is very suitable for calculation and analysis exercises in both undergraduate and graduate courses in the Electrical Engineering department. The purpose of this study is to create a python-based interface in order to solve the problems related to these lines, to make the types of short, medium and long power transmission lines correct and understandable. In the study, after selecting the type of energy transmission line and all parameters related to the line, the necessary mathematical analysis can be made and also the analysis results can be plotted. The analysis program is available in two languages, English and Turkish.

Back Up Protection Scheme for High Impedance Faults Detection in Transmission Systems Based on Synchrophasor Measurements

High impedance faults are rather difficult to detect, due to their inherent characteristics. However, in most cases high-impedance low-current faults evolve to low-impedance high-current faults, thus giving rise to life hazard situations and equipment damage. In this article, a novel back up protection scheme for high impedance fault detection, based on synchrophasor measurement technology, is proposed. In fact, the presented detection method can be thought as the combination of a classic differential and a classic admittance relay. The protection device designated for high impedance fault detection, incorporating the proposed novel protection algorithm, permanently monitors transmission line's shunt admittance thus being able to detect changes-increase in the resistive part of shunt admittance, namely the shunt conductance. Actually, a sudden rise of transmission line's shunt conductance is a strong indicator of high impedance fault inception. Conducted computer simulations confirmed a high degree of selectivity and sensitivity of the proposed method. Moreover, the technical feasibility of the approach was tested considering real-world measurement data obtained for two 220 kV transmission lines. From the acquired data, measurement uncertainties of the monitored parameters in normal operating conditions, were calculated. The results demonstrate excellent sensitivity of the proposed method, even for the case of short transmission lines during low-loading conditions.

Analysis of transient voltages and currents in short transmission lines on frequency-dependent soils☆

Accurate modeling of overhead transmission lines (OHTLs) for transient analysis require that the ground which the phase conductors are suspended be considered on the longitudinal impedance and transversal admittance matrices. In this framework, some models deal with the soil as an ideal conductor (constant resistivity ρg and relative permittivity εr). However, it is known fact that real soils are characterized by frequency-dependent (FD) electrical parameters (ρg(f) and εr(f)). Due to these conditions, different formulations to represent the soil with FD parameters have been developed in the last decades. In order to obtain a precise transient response, these models must be incorporated in longitudinal impedance, as the ground-return impedance, and transversal admittance matrices. In this article, an analysis to compute the impact of some FD soil electrical parameters on transient responses is carried out. These responses are calculated for an energization maneuver and ligtning direct strike on OHTLs with different lengths located above constant and FD soil parameter models of low and high soil resistive values. Results show significant differences between the transient responses obtained with the constant and FD soil models, which these variations are more pronounced for soils of high resistivity and for short OHTLs.

On the Coupling of Power-Related and Inner Inverter Control Loops of Grid-Forming Converter Systems

In the last decade, different control concepts for the synchronisation of voltage-controlled power converters have been proposed in order to form converter-based power systems. The interoperability of these grid-forming power controls is often analysed based on reduced-order models covering only the slow controls or modes. In this article, the coupling of the outer, power-related and inner, inverter output-related control of multiple grid-forming power converter systems is analysed, based on a minimal working example. The elementary study cases each consist of a different grid-forming converter coupled with an external (and passive) grid. Here, the investigated stability problems are already manifested in the simplest possible setup. The analysis of these coupling effects is performed by modelling the system in impedance-based, state-space and phase portrait-based frameworks. In particular, small coupling impedances, like short transmission lines or small short circuit impedances, can be challenging for the controller stability of grid-forming converters while the inner controls can even enhance this issue. The impact of this phenomenon and the participating subsystems are identified in this work. Thus, recommendations concerning modelling techniques and their legitimate assumptions are given. Laboratory experiments validate the performed analysis by indicating a close correlation between analytical models and experimental results.

Análisis de Sobretensiones Resultantes de Descargas Atmosféricas para Suelos Dependientes de la Frecuencia

En este trabajo se presenta un estudio comparativo de la impedancia de un electrodo vertical enterrado en un suelo homogéneo donde los parámetros eléctricos (resistividad y permisibilidad) son dependientes de la frecuencia en relación a los mismos con parámetros constantes. Para su cálculo, es llevado en consideración que el electrodo vertical se puede interpretar como una línea de transmisión (LT) cuyos los parámetros eléctricos son distribuidos por unidad de longitud. Así, la impedancia del electrodo es computada como siendo la impedancia harmónica de LT en función de la frecuencia. Una vez obtenidas las impedancias de aterramiento del electrodo, y empleando una técnica de mínimos cuadrados, se las representan por circuitos eléctricos directamente en el dominio del tiempo. La ventaja de usar este tipo de representación es que el modelo puede insertarse fácilmente en software del tipo EMTP para el análisis de los transitorios electromagnéticos. Así, se calculan las elevaciones de potencial en el aterramiento para una descarga atmosférica incidente en el electrodo. Adicionalmente, una descarga atmosférica es inyectada en el topo de una torre de transmisión aterrada por un electrodo vertical, para evaluar las tensiones en los brazos de la estructura y en su base. Los resultados muestran que las tensiones son significativamente modificadas por la presencia del suelo con parámetros dependientes de la frecuencia, en especial las amplitudes, y que un análisis preciso del transitorio en los sistemas eléctricos debe llevar en cuenta ese fenómeno.

Dark solitons and modulational instability of the nonlinear left-handed transmission electrical line with fractional derivative order

This paper unearths solitary wave in a simplified electrical model practical of the nonlinear left-handed transmission electrical line having series capacitance and shunt inductance. The detailed study of the practical model digs out that by taken a good parameter of the lattice, the obtained equation from the evolution of the wave envelope can be reduced to a one-dimensional fractional nonlinear Schrödinger equation, which gives the pipe of the dark solitons propagation. By simulating transient circuits, the evolution of the soliton and modulational instability gain were demonstrated in the areas of perturbation frequency, pulsation, nonlinearity and signal strength with a continuous wave type input signal. It has also been shown that increased perturbation, nonlinearity and signal strength in simplified metamaterial models of short nonlinear transmission lines lead to the formation of Schrödinger dark solitons and increased instability gain in a continuous pulse structure. The establishment of Schrödinger solitons and the progressive distance of a point, i.e. the fractional parameter α = 1, could reduce the width of the signal bandwidth and the breaking of the symmetry of the instability gain in the simplified electrical model practical of the nonlinear left-handed transmission electrical line, so that the evolution of the system cannot be controlled due to the memory effect, which can find important practical applications in communication systems.

Proposing a new method to improve the longitudinal differential relay performance using the Clarke transformation: Theory, simulation, and experiment

Longitudinal differential protection is among the most important protection mechanisms in the short transmission lines. During energization, some factors might disrupt the performance, and on-line fault detection using the longitudinal differential relay might result in an undesired interruption. Therefore, in this paper, a new method is proposed to detect the fault current from the switching currents, and other transient and loading conditions accurately. For this purpose, a new mathematical and performance method is proposed based on the Clarke transformation to extract the features, classification, and instantaneous patterns of the calculations. Therefore, a unique operating characteristic in Iα–Iβ framework is suggested to detect the internal fault from the external fault and other transient conditions by point -to -point checking and tracking the trajectory Iα with respect to Iβ. A typical power transmission network is simulated in the MATLAB software to validate the proposed method. Furthermore, the actual fault on the real transmission line GT918 from Bushehr network in Iran's power grid is analyzed. Simulation and practical test results indicated high speed, stability, reliability, and accuracy of the proposed method in detecting the internal fault in the short transmission lines. The internal fault is accurately detected fewer than 2 ms in all the tests.

NGD Analysis of Turtle-Shape Microstrip Circuit

A negative group delay (NGD) design of a turtle shape circuit topology is developed in this brief. The topology is comprised of two different length transmission lines (TLs) interconnecting two identical coupled lines (CLs). The S-matrix model is established as a function of the TL and CL parameters. The group delay (GD) at the half wave frequency of the short interconnect TL is derived from the transmission coefficient. To verify the relevance of the proposed turtle circuit theory, a microstrip proof of concept was modeled, designed, simulated, fabricated, and tested. The calculated, simulated and measured results are in good agreement and confirm the turtle prototype bandpass NGD function with approximately 1.97 GHz center frequency and NGD level of approximately −1.3 ns. In addition, this passive circuit operates with very low losses less than −2.5 dB over the reflection coefficient better than −14 dB.

Parameter Estimation of Three-Phase Untransposed Short Transmission Lines From Synchrophasor Measurements

We present a new approach for estimating the parameters of three-phase untransposed electrically short transmission lines using voltage/current synchrophasor measurements obtained from phasor measurement units (PMUs). The parameters to be estimated are the entries of the longitudinal impedance matrix and the shunt admittance matrix at the rated system frequency. Conventional approaches relying on the admittance matrix of the line cannot accurately estimate these parameters for short lines, due to their high sensitivity to measurement noise. Our approach differs from conventional ones in the following ways. First, we model the line by the three-phase transmittance matrix that is observed to be less sensitive to measurement noise than the admittance matrix. Second, we compute an accurate noise covariance matrix using the realistic specifications of noise introduced by instrument transformers and PMUs. This noise covariance matrix is then used in least-squares-based estimation methods. Third, we derive different least-squares-based estimation methods based on a statistical model of estimation and show that the weighted least-squares and the maximum likelihood methods, which make use of the noise covariance matrix, produce the best estimates of the line parameters. Finally, we apply the proposed methods to a real data set and show that our approach significantly outperforms existing ones.

A Novel Fuzzy Theory-Based Differential Protection Scheme for Transmission Lines

Abstract- Ever-increasing consumption of electrical energy has forced extension of power systems to wider regions, which will augment concerns about the stability and reliability of power systems. Therefore, a special attention has been given to protection systems and protection relays to improve these concerns. By appropriate design of protection systems and proper function of protection relays, it is possible to reduce the adverse effects of undesirable faults. A fuzzy logic-based algorithm is presented to improve differential relay performance. The algorithm is employed for protection of short transmission lines against internal faults with/without resistance. By using fuzzy logic and selecting the best stability characteristics, the possibility of malfunction of protection relays will be negligible. In this algorithm, sensitivity, reliability and speed of the relay performance are preserved at suitable levels. The proposed algorithm is also very beneficial for external faults accompanied with the saturation of current transformers (CTs). The purpose of this study is to present an algorithm based on the fuzzy logic, which can decide on the slope of stability characteristics of a differential relay in the best way during various conditions. The performance of the presented algorithm is analyzed in PSCAD/EMTDC program and compared to conventional methods.

Compact Dual-Band Inverted-Microstrip Ridge Gap Waveguide Bandpass Filter

A compact dual-mode inverted microstrip ridge gap waveguide (IMRGW) resonator and a series of dual-band IMRGW bandpass filters (BPFs) with easily controllable passbands are proposed for the first time in this article. The resonator is embedded into the ridge of the IMRGW without disturbing the placement of the mushroom-type bed of nails. A metalized via-hole is introduced to the center of the IMRGW resonator to ground a central patch, resulting in an inverted microstrip resonance mode and a cavity resonance mode simultaneously. The cavity resonant mode is relatively insensitive to the dimensions of the central patch, while the inverted microstrip resonance is insensitive to the dimensions of the cavity enclosed by electromagnetic band-gaps (EBGs) and two rows of metalized via-holes. Therefore, the resonant frequency of the two modes can be tuned independently. The resonators can be cascaded easily with a short IMRGW transmission line. A series of IMRGW based dual-band BPF with different orders are designed, fabricated, and measured. The third-order BPF’s simulated passbands are 13.07–13.41 and 18.46–18.91 GHz with a fractional bandwidth of 2.5% and 2.3%. Low insertion losses better than 1.7 and 2.1 dB are obtained on the two passbands. The measured passbands are 13.52–13.86 and 18.9–19.34 GHz with a fractional bandwidth of 2.3% and 2.2% while the insertion losses are better than 2.5 and 2.3 dB for the third-order BPF.

High-Order Dual-Port Quasi-Absorptive Microstrip Coupled-Line Bandpass Filters

In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept.

Cyber–physical energy system toward safety in smart grids

The power system operation, stability, and reliability are strongly dependent on the network protection system performance. On the other hand, the penetration of the renewable energy power plants into power grids drastically affects power networks and smart grids’ stability and reliability because of their fast dynamics in comparison to conventional power generators. Hence, power networks are considered as a complex cyber–physical energy system with vast interactions and communications among consumers and generators. In this condition, a reliable monitoring and control system can augment the safety, security, and operation of such an intricate system. Suitable time coordination between the operations of power grids protection relays is one of the most challenging issues to protect the power system properly. In this paper, a reliable supervisor system (RSS) with fast and precise control ability is proposed to improve power systems and smart grids protection system operations. The device utilizes a safe robust communication way which provides a condition for the available relays on two sides of a line to share their data. For this reason, the proposed device is able to diagnose the fault on a short transmission line quickly upon the event occurrence. In other words, fast communication between two sides of a short transmission line helps the protection system to work faster in the presence of a fault. In addition, quick handshaking and data sharing of the network different points provided by the RSS enable grid circuit breakers to disconnect a fault from the system as fast as possible. The proposed system, then, can easily find a defect location and disconnect a faulty line from the grid. According to the experimental results provided in this paper, the RSS can effectively corroborate the network stability.

PMU–Based fault location method for Three–terminal transmission lines with outage of one line branch

This paper proposes a fault location method for three-terminal double-circuit untransposed transmission lines with outage of one line branch utilizing the synchronized voltage and current measurements obtained from both ends of in-service line branches. The proposed method is applicable for short, medium, and long transmission lines as it is based on a distributed line model parameters considering the mutual couplings between all phases. Initially, the faulted phases are identified and the fault location for in-service line branches is determined adopting previously proposed two-terminal fault location technique. In addition, a fault location method is introduced for out-service line branch. This method is based on the resistive nature of the fault impedance. The three calculated fault distances corresponding to each line branch are compared with each other to determine the faulted line branch and the fault location. Simulation studies implemented using DIgSILENT Power Factory software and MATLAB environment show that the proposed method has acceptable performance for different fault resistances, types, and inception angles.

General Analytic Solution of the Telegrapher’s Equations and the Resulting Consequences for Electrically Short Transmission Lines

Based on classical circuit theory, this article develops a general analytic solution of the telegrapher’s equations, in which the length of the cable is explicitly contained as a freely adjustable parameter. For this reason, the solution is also applicable to electrically short cables. Such a model has become indispensable because a few months ago, it was experimentally shown that voltage fluctuations in ordinary but electrically short copper lines move at signal velocities that are significantly higher than the speed of light in a vacuum. This finding contradicts the statements of the special theory of relativity but not, as is shown here, the fundamental principles of electrical engineering. Based on the general transfer function of a transmission line, the article shows mathematically that an unterminated, electrically short cable has the characteristics of an ideal delay element, meaning that an input signal appears at the output with a slight delay but remains otherwise unchanged. Even for conventional cables, the time constants can be so small that the corresponding signal velocities can significantly exceed the speed of light in a vacuum. The article also analyses the technical means with which this effect can be conveyed to very long cables.

Modal analysis for selection of DFIG‐based wind farms for damping and reduction of the risk of SSR

The rapid growth of non-conventional energy sources makes it important to identify the sub-synchronous oscillation-damping capacity of generating systems such as doubly fed induction-generator-based (DFIG) wind farms under the IEEE-first benchmark model (FBM). In this study, a system, in which the FBM is augmented to include DFIG generation was evaluated at various compensation levels, wind speeds, and DFIG ratings. On the basis of this analysis, the authors propose a basis for the selection of an accurate configuration of wind farms penetration at a given compensation for damping and reducing the risk of sub-synchronous resonance (SSR) in the FBM-DFIG augmented system. It is also demonstrated that, with a suitable DFIG rating, carefully choosing the gains of the DFIG inbuilt converter controllers and an acceptable distance of connected short transmission line between the DFIG and the synchronous generator can suppress induced SSR at 60% compensation, eliminating the need for a damping controller. To obtain higher ranges of compensation level, a corresponding DFIG wind farm asset is suggested for reducing the risk of SSR. The proposed model was validated using eigenvalue analysis, calculation of the participation factor, and time-domain simulation.

Origin of pseudo-dispersion in non-dispersive media by terahertz time-domain spectroscopy.

We report the false appearance of dispersion in non-dispersive materials when measured by terahertz time-domain spectroscopy. This occurs when the material is measured in reflection geometry and has a bulk metal interface opposite to the incident interface, for example, when a substrate is supported by a metal stage with the THz light incident on it from above. We explain this effect in terms of the frequency-dependent response of the material when it is represented by a shorted transmission line model.

Development and optimization of RF MEMS switch

Isolation and actuation voltages are important parameters in micro-electro-mechanical switches. These parameters can be destroyed by the effect of creating bulge and erosion in the surface of the beam. In this paper, a fabrication method is proposed to create a smooth and flat beam. Additionally, using two short high impedance transmission lines, the destructive effects on the input/output matching have been reduced. S-parameters and mechanical parameters of the proposed switch are calculated by the network analyzer and laser Doppler vibrometer. According to the results obtained from the proposed switch in the C–K band, the return loss, which is less than − 20 dB, and the highest isolation value, which is equal to − 20 dB, occur at the frequency of 21 GHz. Furthermore, the insertion loss is better than − 1 dB in the full frequency band, which is very desirable. The actuation voltage and resonance frequency were obtained at 18 V and 164 kHz, respectively. Finally, four steps are proposed to optimize the actuation voltage, isolation, stress and switching time, which results in reducing the actuation voltage by 37% and the isolation will increase by 46%. Maximum stress in the initial state is 25 MPa, and decreases to 10 MPa after optimization, which increases the lifetime of the switch.