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The high voltage direct current transmission system based on modular multilevel converter (MMC-HVDC) technology is now studied and used widely. But traditional half bridge topology of sub module (HBSM) of MMC can't block dc link fault current because of the freewheeling effect of diodes. In order to solve this problem, firstly, this paper improves HBSM topology, a series connected double sub module (SDSM) is designed and dc link fault current blocking capability is realized without tripping ac circuit breaker, so MMC-HVDC with this improved topology can immediately rebuild dc link voltage and resume power transmission. Secondly, the self starting and fault disposing procedure are also designed. At last, simulations in the software PSCAD/EMTDC are carried out to verify its effectiveness and feasibility. [ABSTRACT FROM AUTHOR]

This paper compares how a dc fault affects a multiterminal dc (MTdc) network depending on the HVDC transmission system topology. To this end, a six-step methodology is proposed for the selection of the necessary dc fault protection measures. The network consists of four voltage-source converters converters radially connected. The converters natural fault response to a dc fault for the different topologies is studied using dynamic simulation models. For clearing of the dc faults, four different dc breaker technologies are compared based on their fault interruption time, together with a current direction fault detection method. If necessary, the converters are reinforced with limiting reactors to decrease the peak value and rate of rise of the fault currents providing sufficient time for the breakers to isolate the fault without interrupting the MTdc network operation. The study shows that the symmetric monopolar topology is least affected by dc contingencies. Considering bipolar topologies, the bipolar with metallic return exhibits better fault response compared to the one with ground return. Topologies with ground or metallic return require full semiconductor or hybrid breakers with reactors to successfully isolate a dc fault. [ABSTRACT FROM AUTHOR]

Fractional Frequency Transmission is a competitive technology for offshore wind power transmission. Modular Multilevel Matrix Converter (M3C) plays a key role in a Fractional Frequency Transmission System (FFTS) as the frequency changer. M3C is broadly considered as the AC–AC converter for the future with its attractive advantages in high voltage and high power applications. Due to the lack of a DC link, electrical quantities at different frequencies from two AC systems couple in M3C, resulting in a complex harmonic condition. Harmonics can lead to stability issues and its analysis is of great importance. This paper focuses on the harmonic analysis of M3C. The arm capacitor voltage ripples and the harmonic currents are analyzed at various frequencies. Major factors influencing the harmonics magnitude are discussed. Analysis is conducted on sub-module capacitance and arm inductance selection. A zero-sequence current mitigation controller for M3C is implemented and tested. It is found that for a FFTS, some current harmonics flow into AC systems even though the system is balanced, while the others circulate within the converter. The theoretical harmonic analysis is verified by simulations in Real Time Digital Simulator (RTDS) of a M3C system where each arm consists of forty sub-modules. [ABSTRACT FROM AUTHOR]

This paper presents new series grid interface topologies for enhancing the low voltage ridethrough capability of self-excited induction generator-based wind turbines. Two proposed schemes: static synchronous series compensator (SSSC) and controllable series braking resistor (CSBR) have been designed and simulated. The test system simulated represents a wind turbine connected to an electric grid with alternatively employing SSSC and CSBR. The potential of the two schemes is evaluated and analyzed using positive and negative-sequence reference frames in response to balanced and unbalanced fault scenarios. The simulation results using PSCAD/EMTDC demonstrate the performance of the proposed schemes for improving the fault ridethrough capability and transient stability margin in response to severe symmetrical and asymmetrical grid faults. The schemes have shown successful and fast mitigation of voltage disturbance consequences on the mechanical system. The schemes helped the wind turbine to remain connected with considerable isolation from grid faults. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of dc network topology with respect to two important aspects: the steady-state losses and the transient fault currents. For this, optimal power flow in a combined ac–dc multiterminal HVDC cable system based on voltage–source converters and the development of prospective fault currents during a pole-to-ground fault is simulated. The results prove that an evaluation of grid topologies must include both of the aforementioned aspects and that no network topology can optimize both at the same time. [ABSTRACT FROM PUBLISHER]

In a multiterminal HVDC network, dc circuit breakers (CBs) are required at each end of a line to selectively isolate a fault. Several CB concepts have been implemented in PSCAD, which differ significantly in their structure and performance. This paper describes the interaction of the different HVDC CB topologies with a meshed four-terminal network and assesses their performance in terms of maximum currents and voltages. The tradeoff between network parameters and CB requirements is analyzed. [ABSTRACT FROM PUBLISHER]

HVDC short-circuit calculation standards will be required to simplify the dimensioning and selection of circuit breakers (CBs) in future HVDC networks. This paper proposes new analytical formulas for the calculation of the ac-side contribution through the blocked half-bridge-based converters during pole-to-ground faults in multiterminal HVDC cable networks. Analytic approximations are derived for the steady-state short-circuit currents and the peak of the transient response for point-to-point HVDC links and extended to multiterminal HVDC cable networks with arbitrary grid topology. The results of the proposed expressions are compared with simulations in PSCAD and provide accurate calculations for the transient peak and steady-state values of the ac-side fault current contribution to the prospective CB current. [ABSTRACT FROM PUBLISHER]

The applications of power semiconductors in circuit-breaker (CB) technology can help achieve considerable improvement in its performance and possible new capabilities. In this paper, new trends in power electronics for the applications in CBs are presented. It also summarizes and reviews the appropriate hybrid mechanical-static CB topologies. Various conventional and derived topologies for ac as well as dc applications are described. Discussions about common and future trends in this technology development are presented. This study will provide a useful framework and point of reference for the future development of hybrid CBs for various different applications. [ABSTRACT FROM AUTHOR]

This paper begins by presenting a generalized methodology for conceptualizing modular multilevel converter (MMC)-based dc–dc topologies, which is predicated on the concept of harmonic power balance. A compelling implication is that MMC-based variants of conventional switched-mode converter structures can be realized. As an example case study, this paper introduces a new dc–dc MMC for HVdc applications, which is derived from the classical buck–boost dc–dc converter. This new topology, which is revealed to be an alternative option to the well-known dual active bridge (DAB) converter with an intermediate transformer, offers buck–boost functionality and bidirectional dc fault blocking, using only two quadrant switching cells. Comparative analysis shows the proposed topology has lower operating losses and a lower total magnetics rating in comparison to an MMC-based DAB solution for dc stepping ratios around unity. A dynamic controller is developed that regulates the converter dc power throughput while maintaining balanced capacitor voltages. The converter operating principle, dynamic controller performance, and dc fault blocking are verified by simulation. [ABSTRACT FROM PUBLISHER]

This paper explains the working principles, supported by simulation results, of a new converter topology intended for HVDC applications, called the alternate arm converter (AAC). It is a hybrid between the modular multilevel converter, because of the presence of H-bridge cells, and the two-level converter, in the form of director switches in each arm. This converter is able to generate a multilevel ac voltage and since its stacks of cells consist of H-bridge cells instead of half-bridge cells, they are able to generate higher ac voltage than the dc terminal voltage. This allows the AAC to operate at an optimal point, called the “sweet spot,” where the ac and dc energy flows equal. The director switches in the AAC are responsible for alternating the conduction period of each arm, leading to a significant reduction in the number of cells in the stacks. Furthermore, the AAC can keep control of the current in the phase reactor even in case of a dc-side fault and support the ac grid, through a STATCOM mode. Simulation results and loss calculations are presented in this paper in order to support the claimed features of the AAC. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter (MMC or M2C) is an emerging attractive multilevel topology for medium-voltage high-power applications. The capacitor voltage balancing control and the improvement of output current rating are two challenging issues of MMC. This paper proposed a new parallel-connected diode-clamped M2C (DCM2C), in which each arm consists of two parallel-connected clusters. In this topology, the capacitor voltages can be balanced automatically without any balancing control algorithms. Theoretically, no voltage sensors are needed to measure the capacitor voltages theoretically. Thus, the control of the converter can be simplified greatly. With a simple current-sharing control, an equal current distribution can be achieved between the two clusters. Furthermore, an extended parallel-DCM2C is proposed for larger current applications, and the corresponding current-sharing control method is developed. Experimental results validated the voltage self-balancing capability of parallel-DCM2C and the effectiveness of the proposed current-sharing control. [ABSTRACT FROM PUBLISHER]

This paper presents an enhanced control for HVDC systems employing hybrid modular multilevel converters (MMCs) during asymmetrical dc voltage faults. The characteristics of pole-to-ground (PTG) fault under different system grounding schemes are analyzed. Then, the principle of enhanced control strategy to deal with the PTG fault is presented for a hybrid-MMC-based HVDC system with symmetrical monopolar configuration. A new control variable is proposed on the arm voltages to distribute the power transmitted from the ac side between the upper and lower arms. By adopting the enhanced control, the overvoltage and the fault current can be eliminated when a PTG fault occurs. Furthermore, the hybrid-MMC-based HVDC system can operate continuously with adjustable active power and controllable reactive power by controlling the upper and lower arms of the converter asymmetrically during a fault period. Finally, the feasibility of the proposed control scheme is verified by simulation results in PSCAD/EMTDC. [ABSTRACT FROM PUBLISHER]

The half-bridge-based modular multilevel converter (MMC) has emerged as the favored converter topology for voltage-source HVDC applications. The submodules within the converter can be constructed with either individual insulated-gate bipolar transistor (IGBT) modules or with series-connected IGBTs, which allows for different redundancy strategies to be employed. The main contribution of this paper is that an analytical method was proposed to analyze the reliability of MMCs with the consideration of submodule arrangements and redundancy strategies. Based on the analytical method, the relative merits of two approaches to adding redundancy, and variants created by varying the submodule voltage, are assessed in terms of overall converter reliability. Case studies were conducted to compare the reliability characteristics of converters constructed using the two submodule topologies. It is found that reliability of the MMC with series-connected IGBTs is higher for the first few years but then decreases rapidly. By assigning a reduced nominal voltage to the series valve submodule upon IGBT module failure, the need to install redundant submodules is greatly reduced. [ABSTRACT FROM PUBLISHER]

The total harmonic current emission in a public low-voltage (LV) network is mainly determined by the large number of electronic devices, which use different circuit topologies with different harmonic emission characteristics. Consequently, the total harmonic current measured at the LV busbar can provide valuable qualitative information, for example, about dominating circuit topologies. This paper describes and applies a methodology to characterize the harmonic current emission of an LV network by a prevailing phasor. Using measurements from 130 German public LV networks, the “prevailing” location of 3rd and 5th harmonic current is analyzed with respect to different types of consumers. The results are compared with initial measurements received from other countries. Based on the prevailing phasor, a simplified method for an approximate estimation of the impact (cancellation potential) of a particular LV network or a new equipment technology (e.g., electric-vehicle charging) on the harmonic levels in a public distribution network is proposed. [ABSTRACT FROM PUBLISHER]

This paper discusses the issues of reliability and real time of information transmission on the communication system of wide-area measurement (CSWAM) from the viewpoint of network architecture. Connectivity and hop count are adopted as the performance indices to build the communication network optimal model that can be satisfied with the requirements of CSWAM. The improved cut saturation algorithm (improved CSA) is used to obtain the optimal network topology in line with network flow and several performance constraints. Under the same conditions, the comparison of the case study showed that it can reduce network costs by nearly 40% with a little deficiency in load balancing compared to the structure of dual directions double ring. It is provided with a new theory basis and is a good reference for the optimal design of network architecture in the CSWAM. [ABSTRACT FROM PUBLISHER]

The directional overcurrent relays (DOCRs) coordination problem is usually studied based on a fixed network topology in an interconnected power system, and is formulated as an optimization problem. In practice, the system may be operated in different topologies due to outage of the transmission lines, transformers, and generating units. There are some situations for which the changes in the network topology of a system could cause the protective system to operate without selectivity. The aim of this paper is to study DOCRs coordination considering the effects of the different network topologies in the optimization problem. Corresponding to each network topology, a large number of coordination constraints should be taken into account in the problem formulation. In this situation, in addition to nonlinearity and nonconvexity, the optimization problem experiences many coordination constraints. The genetic algorithm (GA) is selected as a powerful tool in solving this complex and nonconvex optimization problem. In this paper, in order to improve the convergence of the GA, a new hybrid method is introduced. The results show a robust and optimal solution can be efficiently obtained by implementing the proposed hybrid GA method. [ABSTRACT FROM AUTHOR]

This paper presents the fault detection and alarm processing in loop system with fault detection system (FDS). FDS consists of adaptive architecture with probabilistic neural network (PNN). Training PNN uses the primary/backup information of protective devices to create the training sets. However, when network topology changes, adaptation capability becomes important in neural network applications. PNN can be retained and estimated effectively. With a looped system, computer simulations were conducted to show the effectiveness of the proposed system, and PNN's adapt network topology changes. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive autoreclosing concept for HVDC transmission systems with modular multilevel converters in full-bridge topology for single pole-to-ground faults. Since HVDC transmission will be used in the German energy transmission system to support the heavily loaded ac grid for energy transport over far distances, the interruption time has to be kept as short as possible to preserve system stability. Within the presented autoreclosing concept, the necessary interruption time is determined adaptively. After fault detection, the converter control drives the fault current to zero and injects a low-level ac current. The nonlinear interdependence between the fault arc resistance and the current is used to detect the final arc extinction and to start the voltage recovery, enabling a fast resumption of the power transmission. PSCAD|EMTDC is used to model the electric arc behavior and the dielectric recovery inside an exemplary point-to-point HVDC grid model as an evaluation of the concept. The minimum required ac current is identified related to the used fault detection method. Additionally, the influences of fault position, line length, and fault resistance on fault detection are investigated. The results show that the required interruption time can be determined adaptively for transmission line length up to 400 km. [ABSTRACT FROM PUBLISHER]

The main motivation for this paper was to investigate certain asymptotic properties of impulse response in periodic tree-type distribution networks owed to the network topology alone, regardless of ohmic losses or material dispersion normally present in practical situations. The research was performed using theoretical analysis of Dirac impulse propagation through a model network, with a focus on topology-related features. Several numerical examples were designed to illustrate the meaning of the main conclusion, namely that the very topology of any tree-type network leads to an impulse response in which amplitudes of individual pulses decay rapidly with their respective delays after the leading impulse. On the other hand, it was not a goal of this research to design any practical tool for network-response calculation. The very fact that impulse response decays rather quickly after the train of the first few impulses does not mean that the calculation of these first few is by any means simple. The frequency-domain network-analysis methods in case of a complex distribution network with a tree-like topology seem to have practical advantages over the impulse-response calculation techniques, especially because the effects of ohmic losses and material dispersion would have to be included in any model constructed for realistic simulations, and in the authors' experience, this can be done more easily in frequency-domain-based models. [ABSTRACT FROM AUTHOR]

It has been shown that coordination between protective devices in distribution systems in the presence of significant distributed generation (DG) will be disrupted. With the recent trend of adopting and integrating renewable resources and microgrids with distribution systems, it is probable that distribution systems will have significant and arbitrary penetration of DG in the near future. This will change the distribution systems to multisource unbalanced systems where protective devices may not coordinate. The fault location in this type of system will be a challenge. This paper describes a general method to locate faults in this type of system. The method uses synchronized voltage and current measurements at the interconnection of DG units and is able to adapt to changes in the topology of the system. The method has been extensively tested on a 60-bus distribution system for all types of faults with various fault resistances on all sections of the system, with very encouraging results. [ABSTRACT FROM AUTHOR]

This paper introduces a dual genetic algorithm (DGA)-based approach for a fast screening process for distributed generations (DGs) connected to a distribution network. The existing deterministic approaches overlook some operation conditions that may give rise to incorrect results and lead to wrong decisions in practical applications. The DGA is an extension of a traditional single genetic algorithm (GA). Owing to complicated distribution system operating states, such as the actual topologies and features, and the load states, it is hard to take all uncertainties into account when the latter is used. Hence, an improved GA—DGA—is proposed to deal with these kinds of uncertainties. The outcomes are of value for a fast screening process for grid interconnection applications in DGs. [ABSTRACT FROM AUTHOR]

In real power systems, the network topology is subjected to uncertainty due to single-line outage contingencies, maintenance activities, and network reconfigurations. These changes in the network topology may lead to miscoordination of directional overcurrent relays (DOCRs). To overcome this drawback, corresponding to each primary/backup relay pair, a set of inequality coordination constraints which is related to different network topologies should be satisfied. In this paper, a new approach based on the interval analysis is introduced to solve the DOCRs coordination problem considering uncertainty in the network topology. The basic idea is to convert the set of inequality constraints corresponding to each relay pair to an interval constraint. In this situation, the DOCR coordination problem is formulated as an interval linear programming (ILP) problem. Using well-known mathematical theorems, the obtained ILP problem, which has no equality constraints, can be converted to standard linear programming (LP). As a result, the number of coordination constraints is significantly reduced in the proposed methods. The application of the proposed method to the IEEE 14- and 30-bus test systems proves the ability of the interval method in modeling topology uncertainty in the large-scale coordination problem. [ABSTRACT FROM AUTHOR]

This paper presents a new method for an optimal measurement placement of phasor measurement units (PMUs) for power system state estimation. The proposed method considers two types of contingency conditions (i.e., single measurement loss and single-branch outage) in order to obtain a reliable measurement system. First, the minimum condition number of the normalized measurement matrix is used as the criteria in conjunction with the sequential elimination approach to obtain a completely determined condition. Next, a sequential addition approach is used to search for necessary candidates for single measurement loss and single-branch outage conditions. These redundant measurements are optimized by binary integer programming. Finally, in order to minimize the number of PMU placement sites, a heuristic technique to rearrange measurement positions is also proposed. Numerical results on the IEEE test systems are demonstrated. [ABSTRACT FROM AUTHOR]

This paper presents a method for calculating zone-2 setting of distance relays without causing coordination problems. The proposed method is based on the impedance seen by distance relays when faults are simulated on the reach of zone-1 of primary relays for the maximum and minimum generation outputs of the power system. It is shown that the proposed method increases the reach of zone-2 relays without causing coordination problems. The proposed method is modified for use in an adaptive protection system. It is shown that further improvements can be achieved when settings are calculated using the proposed method and the prevailing system conditions. Measures to alleviate the impact of communication failure are discussed. The proposed method and its adaptive version were applied to an existing power system and some results are reported in the paper. [ABSTRACT FROM AUTHOR]

An improved explicit estimation algorithm is proposed for reliability estimation of the distribution network. Firstly, hierarchical clustering is used to identify and cluster typical feeders based on the topology structure. Secondly, the explicit formula of reliability index under each typical feeder topology is derived by regression analysis, to establish the model for network reliability estimation. Numerical simulations show the suitability of the proposed method in obtaining accurate reliability index for diversified network topology. [ABSTRACT FROM AUTHOR]

This paper presents a field-validated load model for the calculation of the energy conservation gains due to conservation voltage reduction (CVR) in highly meshed secondary networks. Several networks in New York City are modeled in detail. A time resolution of one hour is used to compute the energy savings in a year. A total of 8760 power flow runs per year for voltage reductions of 0%, 2.25%, 4%, 6%, and 8% from the normal schedule are computed. An equivalent ZIP model is obtained for the network for active and reactive powers. The most important finding is that voltage reductions of up to 4% can be safely implemented in the majority of the New York City networks, without the need of investments in infrastructure. The networks under analysis show CVR factors between 0.5 and 1 for active power and between 1.2 and 2 for reactive power, leading to the conclusion that the implementation of CVR will provide energy and economic savings for the utility and the customer. [ABSTRACT FROM AUTHOR]

A directional comparison bus protection unit (DCBPU) can provide a high speed bus fault clearing in the IEC61850 process-bus environment. This technique is based on superimposed fault direction for each circuit connected to the protected bus. In this paper, the implementation and testing of a superimposed directional comparison technique for bus protection based on an IEC61850 process bus is investigated. Design, hardware implementation, and related issues of DCBPU are described. A unique test setup is proposed and developed for testing DCBPU, including merging unit simulator, traffic generator, prototype DCBPU, and Ethernet switches to simulate the real IEC 61850-based substation automation process bus. Test results are reported. [ABSTRACT FROM AUTHOR]

The operation of photovoltaic (PV) units connected to the grid is characterized by several uncertainties due to the number of currently operating units, the points where these units are sited, the exported power, and the injection of harmonic currents. The objective of this paper is to investigate the impact of the penetration of PV units in the low-voltage (LV) network. Thus, a model has been developed for the computation of load flows, harmonics, and voltages in the feeders. A PV panel is modeled as an irradiance-driven current generator, with an embodied maximum power point (MPP) tracking algorithm; it is connected to the network via electronic switches that represent the PV inverter. Simulations are performed with PSIM and Harmoniques simulator packages. Results from the simulated model are validated with data acquired from field measurements and bibliography. Finally, the acceptable penetration level of PV systems is investigated for several scenarios, depending on the topology of the LV network, the number, size, and locations of loads and PV units. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach to statistical modeling of power-line channels is illustrated and its application to low-voltage indoor power networks is analyzed in the bandwidth 1-30 MHz. The proposed approach is based on the well-known bifilar model and on a generalization of the so-called N-branch network topology. It is shown that our model can be exploited to devise an efficient channel simulator predicting the mean impedance matrix and transfer function between an arbitrary couple of plugs in a class of indoor networks sharing multiple parameters (e.g., number of branches, minimum and maximum cable lengths, power-loading conditions). Finally, it is shown that Monte Carlo results generated by our simulator are in good agreement with a set of experimental data acquired in a measurement campaign. [ABSTRACT FROM AUTHOR]

The operation of a resonant-grounded network during an earth-fault condition depends on the three basic parameters: damping, detuning, and unbalance factor. These parameters are influenced by the environmental conditions (e.g. humidity, temperature, and pollution), and the network topology. Accurate values of these parameters during an earth-fault condition are required to examine the operation of the compensation system. The fault records could be used for that purpose. The recorded neutral-to-ground voltage signals have been paraineterized (using damping and detuning as parameters) according to the mathematical model of the transient process. Iteratively reweighted least squares algorithm has been used to fit the model. This algorithm is the major improvement over the classical least squares approach. It is able to filter out noise more efficiently. As a direct result, very accurate parameter identification has been achieved. This paper concludes with the practical examples. [ABSTRACT FROM AUTHOR]

We propose a new graph theory-based algorithm for the determination of the minimum breakpoint set of meshed systems. We show that if there is a k-tree in the graph G(V,E) associated with the system, then the minimum breakpoint set has a cardinality of \vert E\vert -\vert V\vert +k. The proposed algorithm implements an iterative procedure to identify such a k-tree and having minimum k. It is found that the cardinality of the minimum breakpoint set is 9 for the IEEE 14-bus system and 16 for the IEEE 30-bus system. These minimum values are smaller than the previously best reported results of 10 and 18 for the same systems. [ABSTRACT FROM AUTHOR]

We propose an efficient bottom-up power-line communication (PLC) channel simulator that exploits transmission-line theory concepts and that is able to generate statistically representative in-home channels. We first derive from norms and practices a statistical model of European in-home topologies. The model describes how outlets are arranged in a topology and are interconnected via intermediate nodes referred to as derivation boxes. Then, we present an efficient method to compute the channel transfer function between any pair of outlets belonging to a topology realization. The method is based on a systematic remapping technique that leads to the subdivision of the network in elementary units, and on an efficient way to compute the unit transfer function referred to as the voltage ratio approach. The difference from the more conventional and complex ABCD matrix approach is also discussed. We finally show that the simulator can be configured with a small set of parameters and that it offers a theoretical framework to study the statistical PLC channel properties as a function of the topology characteristics, which is discussed in Part II of this work. [ABSTRACT FROM AUTHOR]

In recent years, impedance-based methods have been widely used to analyze the stability of grid-connected converters. However, the impedance models in three-phase AC systems are 2 × 2 matrices and a strict stability analysis is based on the generalized Nyquist criterion, which involves eigenvalue computation. Hence many methods only study the diagonal elements of the impedance matrices, but the neglect of the non-diagonal elements may bring hidden dangers to the stability of the system. This letter proposes a stability criterion for grid-connected converters based on impedance models and Gershgorin's theorem. The effect of the non-diagonal elements is considered and the criterion is a strictly sufficient condition of stability, which is conservative but can guarantee the stability of the system. [ABSTRACT FROM AUTHOR]

We develop a general channel model in broadband power-line communications (BPLC) network using infinite geometric series and the description matrices. The developed general channel model can handle arbitrary PLC channel links easily; thus, we can calculate accurate channel characteristics without increasing computing complexity. For considering the effect of the various branches of the network, we investigate the characteristics of the channel links with adjacent nodes composed of multiple branches. We conduct the simulations by varying the degree of distantness of the adjacent nodes and the number of branches at the nodes. Our simulation results suggest that we should consider adjacent nodes with a degree of distantness up to one for the arbitrary channel links; these were not considered in previous studies. This enables us to calculate accurate channel responses of the arbitrary channel links of indoor BPLC networks. [ABSTRACT FROM AUTHOR]

The asymmetry phenomenon observed during the load-loss test of three-phase transformers is rigorously analyzed. The transformer is represented as a three-port impedance network despite its six-port network nature, making any formal study more tractable. The analytical restrictions required for such a representation are derived. As a result, it is possible to mathematically prove (and understand) the asymmetrical behavior of a three-phase transformer subjected to the load-loss test. Only two circuit-field simulations or tests (single-phase load-loss tests) are required to obtain the impedance system of the six-winding transformer. A 3-D finite-element (FE) model of a transformer is used here to obtain its short-circuit impedances, exemplifying the use and extent of the analytical results. The eddy currents generated at the transformer tank and frame are properly taken into consideration. The short-circuit impedance model is validated with the 3-D FE model and with a six-port network approach that has been previously verified. [ABSTRACT FROM AUTHOR]