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Recently, several numerical algorithms have been proposed to solve the power flow (PF) problems of islanded microgrids (MGs). However, these algorithms approximate the steady-state model of the distributed generation units (DGs) as linear equations. In some cases, this linear approximation leads to inaccurate PF solutions due to dead-zone and generation limits of the given DGs. To fill this gap, we propose a new non-linear approximation of the steady-state model of the DGs considering dead-zone and generation limits of the DG. Besides, an inversion-free PF algorithm based on the improved Newton-Traub composition (INTC) is proposed for solving PF problems of grid-connected and islanded MGs more robustly and accurately, where the inverse of the Jacobian matrix is updated by using the Broyden’s method. To include the power losses of the neutral conductor and grounding resistance, four-conductor based PF formulation is proposed. The numerical results on several test systems suggest that the proposed algorithm can provide an accurate steady-state solution as compared to other state-of-the-art algorithms.

Load unbalance in an electric power system often occur to meet consumer needs. Distribution of the load that was initially evenly will experience an unbalance when the burdens. As a result, current arises in the transformer neutral, current flowing in the transformer neutral causes losses, losses in the neutral conductor transformer and current flowing to the ground. Technically, if these losses occur continuously, it will be detrimental to PLN and can reduce transformer efficiency. For the supply of electricity to remain stable and continuity, it must be overcome

The use of the AC voltage control method is considered. In this method, the improvement of the current quality of the supply network is achieved by a discrete change of the inductance in the network current flow circuit. In this method, it is proposed to use a circuit with counter-parallel thyristors and the neutral wire. The dependences of the harmonic coefficient and the current distortion coefficient of the electric network on the values of the regulated voltage are constructed. The obtained dependences prove the effectiveness of the proposed regulator. The required number of reactor sections is determined and the proper inductance of their windings to provide the values ​​of the harmonics coefficient that does not exceed 7% while adjusting the voltage depth of 50% on the active-inductive load. References 9, 3 figures 3, table.

The influence of phase current unbalance on the probability of occurrence of fire-hazardous situations in industrial premises that receive power in various power supply systems is considered. The theoretical prerequisites for the occurrence of fire-hazardous situations are described. It is shown that zero-sequence flows flowing through a neutral conductor in an unbalanced mode significantly heat it, which can lead to short circuits and conditions for the occurrence of fires. The results of studies of unbalanced conditions in Russia and abroad are presented. It is shown that the zero-sequence flows resulting from current unbalance lead to an increase in additional losses of active power and electrical energy. It is proved that additional heat losses caused by unbalanced power consumption can destroy the insulation of neutral and phase conductors, which is the main cause of short circuits and, as a result, fires. Based on the use of the Matlab graphical editor, dynamic characteristics of variations in phase and interphase currents and voltages, as well as the power loss coefficient, which characterizes the increase in heat losses, are constructed. The analysis of fires and their consequences for various objects in the Russian Federation is made. A computational unit has been developed in Matlab, which is used for calculating and plotting the dynamics of fires and their consequences over the investigated period of time. It is shown that the occurrence of fires and their consequences due to violations of the rules of operation of electrical installations occurs in any premises and sometimes reaches more than 20% of all possible causes of fires. Methods and technical means of minimizing zero-sequence currents as a means of preventing the occurrence of fire-hazardous situations are considered. The principle of operation of an automatically controlled shunt-symmetric device with a minimum resistance to zero-sequence currents is described.

Conventional power flow algorithms assume that the network resistances and reactances remain constant regardless of the weather and loading conditions. Although the impact of the weather in power flow analysis has been recently investigated via weather-dependent power flow (WDPF) approaches, the magnetic effects in the core of Aluminum Conductor Steel Reinforced (ACSR) conductors have not been explicitly considered. ACSR conductors are widely used in distribution networks. Therefore, this manuscript proposes a three-phase weather-dependent power flow algorithm for 4-wire multi-grounded unbalanced microgrids (MGs), which takes into consideration the impact of weather as well as the magnetic effects in the core of ACSR conductors. It is shown that the magnetic effects in the core can significantly influence the power flow results, especially for networks composed of single-layer ACSR conductors. Furthermore, the proposed algorithm explicitly considers the multi-grounded neutral conductor, thus it can precisely simulate unbalanced low voltage (LV) and medium voltage (MV) networks. In addition, the proposed approach is generic and can be applied in both grid-connected and islanded networks. Simulations conducted in a 25-Bus unbalanced LV microgrid (MG) highlight the accuracy and benefit of the proposed approach, while its computation performance is tested in the IEEE 8500-Node network.

Three-level (3L) converters have been widely used in industry for decades. Compared to the three-phase-three-wire (3P3W) 3L inverter, the three-phase-four-wire (3P4W) one is able to supply the unbalanced loads but has to afford much larger filter inductors because the neutral wire provides a path for high-switching zero-sequence currents. To save filter inductances, a neutral inductor is proposed to insert in the neutral wire. Meanwhile, a complete design methodology is put forward to design the filter inductors and the neutral inductor. With low-frequency zero-sequence currents flowing through the neutral wire, the three-phase load voltages might become unbalanced and/or distorted. To improve the voltage quality, a resonant controller, with the resonant frequency at fundamental output frequency (fo), is presented to add into the zero-sequence voltage loop for balancing load voltages; concurrently, the other resonant controller, with the resonant frequency at 3fo, is presented to insert in the zero-sequence voltage loop or neutral current loop for mitigating voltage distortion. Finally, all of the proposed works are verified on a 3P4W T-type inverter.

This paper identifies the development of an under voltage and over voltage protection in order to avoid damage in load side. Most of the industries and as well as home appliances are very expensive also more sensitive. This may get damaged due to the instabilities in ac mains supply. It can also lead to losses in the electrical circuit. These losses lead to low power factors and wastage of so much power. The fluctuations can cause great impact to the power quality and many precious and expensive equipment may be damaged. It is therefore advisable to have a tripping mechanism to protect the load. The voltage below the rated value are usually caused under unexpected raise in load due to faults in the system, during short circuit conditions and also rapid increase in source impedance due to lose connection in the circuit. The voltage above the rated values are caused by a sudden decrease in load in a circuit having a poor or damaged voltage regulator. The over voltage may also be caused by a damage in the circuit or loose connections in neutral wire. In this paper, the solution to under voltage and over voltage conditions has been carried out. The proposed circuit will be able to work within the voltage ratings of 195–215 V. Anything below that will be considered as under voltage and anything above that will be considered as over voltage. Thus, we can protect the equipment from damage. By doing this, the proposed circuit is able to protect the electrical appliance. The promising results obtained are presented and discussed here.

The paper presents the results of a theoretical study of safety conditions for various groups of electrical equipment that affect single-phase networks in order to prevent short circuits on the case. The authors analyzed the “PUE” requirement for grounding systems and, as a result, revealed that the “PUE” requirements for grounding systems do not provide sufficient safety and supplements are needed to more clearly regulate the procedure for re-grounding the neutral wire.

During the operation of 0.4 kV electric networks, asymmetry of currents and voltages is unavoidable. As is known, unbalanced operation of 0.4 kV networks is stemming from nonuniform distribution of loads between the phases. This results in that a fundamental frequency zero-sequence current will flow through the neutral conductor in a four-wire three-phase electric network. On the other hand, during balanced operation of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic, higher harmonic currents multiple to three are summed in the neutral conductor. Therefore, it is of relevance to analyze unbalanced operating conditions of a four-wire electric network containing loads with a nonlinear volt-ampere characteristic. The article presents the characteristics of a municipal load for analyzing unbalanced/nonsinusoidal conditions of its operation. For carrying out full-valued assessment of unbalanced operating conditions of a four-wire electric network, a simulation model of a 0.4 kV network section containing a nonsinusoidal load is developed. It is shown that during unbalanced operation of an electric network containing electric loads with a nonlinear volt-ampere characteristic it is recommended to take into account zero-sequence current higher harmonic components that are not multiple to three. An algorithm for calculating the neutral conductor current harmonic component for determining the cable temperature rating is developed.

Energy measurements are done according to the Blondel theorem, which states that in a system containing N conductors, N-1 current sensing elements are needed to measure the energy. In energy metering for billing purposes at residences only the line current is measured. However, in this paper it is shown experimentally that discrepancies can occur, because current can flow through the protective earth. This occurred in a real one-phase low-voltage distribution system where a residual current device was not functioning properly and a leakage current could flow. This resulted in an unbalance between the line and neutral conductor and thus an inappropriate use of the Blondel theorem.

In many wye electrical systems, the function of the ground and neutral conductor is not differentiated because they are incorrectly joined. From a technical point of view, a connection between ground and neutral shall only be made once, at the main electrical panel; otherwise, those conductors should form two different paths. Although the implications of this connection are often seen as shallow and a misinterpretation of the National Electrical Code (NEC) makes it acceptable, this matter is actually very significant when it comes to protecting humans. Thus, it is important to take a deeper look into how to make a suitable ground path, which is the scope of this article.

This paper proposes a comprehensive load flow algorithm for balanced and unbalanced distribution systems considering the effect of a multi-grounded neutral conductor. The method is based on the implicit Z BUS method presenting fast convergence and robustness regardless of the R / X ratio of the lines. Its distinct feature is its ability to handle all network configurations, including highly meshed distribution systems that operate in either islanded or grid-connected mode. Furthermore, an algorithm is proposed for overcoming the limitation of implicit ZBUS method to treat PV nodes. Additionally, the concept of virtual impedance is incorporated into the proposed algorithm to accurately simulate the behavior of distributed generators (DGs) during the islanded operation. Numerical simulations are conducted in 33-Bus and 38-Bus balanced networks as well as in 25-Bus and 30-Bus unbalanced networks to verify the validity of the proposed load flow algorithm.

In low voltage (LV) electric distribution grid, the continuity of power supply service is degraded by various grid faults. Even under single phase to ground faults, the continuous operation capability of healthy phases is also limited. The smart transformer (ST) can establish each phase voltage independently and thus can switch the operation mode from three-phase to two-phase operation during single phase faults, ensuring continuous power supply in two healthy phases and minimizing outage area. However, different from the three-phase operation mode, both high 2nd-order oscillation in dc-link and high current in neutral conductor challenge system performances and reliability under the two-phase operation. Thus, an improved two-phase voltage control strategy is needed either to limit the neutral current amplitude avoiding over ampacity (reducing the power losses and suppressing neutral potential variations), or to suppress dc power oscillation (preventing the lifetime reduction of dc-link capacitors). This paper focuses on the control system design of ST voltage control for the two-phase operation to improve the grid voltage quality. The simulation and experimental results clearly verify the effectiveness and correctness of the proposed strategy.

This paper investigates lightning surges on a distribution line reported using a finite-difference time-domain (FDTD) method. FDTD simulation results show a satisfactory agreement with measured lightning currents when lightning strikes ground nearby a distribution line. The current and voltage characteristics along the line, which were not measured in the test, are calculated by the FDTD simulation. Parametric analysis shows that lightning currents and voltages are dependent on the lightning position, distance from the lightning to the nearest pole, and pole grounding resistance. A large portion of phase-wire voltage is induced by the lightning channel current, and correspondingly, a large portion of phase-wire current is produced by the induced voltage. When the lightning channel is inclined, the peak current and voltage vary by +10% to −10% depending on the inclined angle. The effect of neutral wire position in the line is also investigated, and the induced voltage at the nearest pole to the lightning can be effectively suppressed by installing two neutral wires above and under the phase wires. EMTP simulation results agree qualitatively well with the measurement and FDTD results.

This paper dwells upon identifying the parameters of a four-wire three-phase 0.4-kV distribution grid (DG) using current and voltage vector data as measured by the automation instrumentation system for electricity metering (AIS EM) at the beginning of the DG and at each of its end users. It analyzes an earlier proposed method for identifying the resistance values if inter-user DG segments, which is based on modeling the physical processes in the grid circuits and equivalent transformations of its equivalent circuits. The paper further shows that these proposed transformations are not equivalent. At the same time, the found resistance values do correspond to the phase resistances of the inter-user segments provided that the neutral wire of the DG has resistance values of zero; the found values are not equal to the actual resistances of the four-wire grid. The paper proposes a novel method to solve this problem; the method is based on measuring the current and voltage vectors online in two different DG operation modes. If the current mode of the grid does not change, the AIS EM control unit may command a single temporary disconnection of an end user to invoke a different mode. Research results might be of use for designing AIS EM subsystems tasked to diagnose and control the electrical parameters of the distribution grid mainline as well as to monitor commercial and process-related electricity losses in it online.

In the article the technical analysis of existing constructive decisions concerning use of high-temperature superconducting cables is carried out. The features of the use of superconductors in electrical distribution networks are analyzed. The advantages of using high-temperature superconductors in comparison with low-temperature superconductors are established. It is determined that the use of high-temperature superconductors, due to the increased critical parameters, provides an increase in the power of transmission lines and energy saving. From the analysis it follows that high-temperature superconductor wires of 2G generation have better operational characteristics, respectively, their use is more efficient compared to wires of 1G generation. A scheme of a three-phase high-temperature superconducting power transmission network with a neutral wire is considered. The working conditions of a three-phase power network with high-temperature superconducting cables are analyzed. It is determined that the use of two cores of a high-temperature superconducting cable of a distributed power transmission system provides an increase in the throughput of electric power in distribution electric networks. Accordingly, the efficiency of electric power transmission is increased, as well as the loss of AC power and operating costs are reduced. It is shown that the use of the reactor reduces the requirements for protection devices, facilitates the operation of electrical installations, including generators of power plants, and also reduces the cost of distribution networks equipment. It is indicated that the smallest power loss in a three-phase distributed power transmission system using high-temperature superconducting cables can be achieved with a symmetrical load operation mode. The results of technical analysis can be used to develop recommendations for improving the characteristics of cable power lines.

The flow of a large current in the neutral conductor of a transmission system is one of the major problems caused by harmonic pollution. This current can assume excessive values and even exceed the current flowing in the phases which can be extremely dangerous both for the equipment and the safety of the personnel. Currently, the parallel or shunt active filter (SAF) or parallel active filter is considered as the most effective solution to mitigate harmonic pollution and restore a sinusoidal current waveform in electrical distribution networks. The SAF can be used to compensate for harmonic currents, as well as that of the reactive power. This paper proposes a SAF circuit based on a four-arm inverter topology. The designed SAF is shown to lead to better harmonic compensation with a reduced THD (Total Harmonic Distortion) level in the presence of nonlinear and unbalanced loads in the network. The other goal of this study is to eliminate the neutral current caused by the unbalance in the polluting loads connected to the distribution network, achieve a near-sinusoidal current waveform and protect the electric network equipment.

The paper describes a method for calculation of energy losses in the three-phase four-wire secondary distribution network that allows, based on the measurements of smart meters, determination of losses in the network as a sum of losses occurring during power transmission from the power supply node of the network to every load node. This method for losses determination does not require knowledge of parameters of the network elements and of neutral wire grounding. Efficiency of the method is confirmed by comparison of losses in the main feeder of a real secondary distribution network with the estimates of losses obtained using a non-linear state estimation algorithm based on the simple iteration method with adjustment of voltages of phase wires relative to a neutral wire at each iteration. The possibility of distribution of total energy losses in the feeder between single-phase loads and phases of each three-phase load is shown. The proposed methodology will make it possible to distribute network losses among end users on an equitable basis taking into account contribution to total losses.

Transformer IV is one of the 20 kV distribution transformers found at the Sukamerindu Bengkulu Substation (GI). The transformer has a power rating of 30 MVA. In distribution transformers, inter-phase load balancing is needed. If the load is not balanced between the phases, current will flow in neutral wire. In this study the effect of unbalanced load on neutral current in transformer IV Sukamerindu Bengkulu is analyzed. The load is analyzed every hour of the day by observing the amount of current and voltage in each phase. From the results of the analysis it was found that the highest neutral current loss value was 1306.25 watts or 1.30 kW and the lowest was 0.724 kW, with an average neutral current loss that occurred in the IV unit transformer Sukamerindu at 639 watts.

The increase in electric energy tariffs in conjunction with social and cultural aspects often leads electric energy consumers to tamper with electric energy meters, as a means to decrease the reading for consumed energy at their respective residencies. One form of meter tampering that is very difficult to detect is the removal of the neutral conductor, which goes on to produce an effect where the meter registers a consumption that is lower than the real consumption. The identification of this fraud is difficult due to the fact that the readings are scheduled, and as such the fraudulent consumer needs only to reconnect the neutral conductor at the time of the meter reading. This article presents a device developed for identifying and registering this type of theft, thus making it more difficult to practice. Laboratory tests and simulations have shown that the lower the power factor of an installation in low voltage, lower will be the reading registered on the meter when this type of fraud arises. This newly developed device has shown itself to be robust, with a low cost as well as efficient in performing to its proposed intent.

A four-leg distribution static compensator (FL-DSTATCOM) has been employed for improving the quality of power in electric distribution system using field-programmable gate array (FPGA). A predictive current control technique without any modulation scheme is utilised to generate switching pulses for FL-DSTATCOM using a cost function defining the preferred system behaviour. This technique makes the supply current as balanced and sinusoidal by exactly tracking the reference current, compensating the reactive power, maintaining near unity power factor and nullifies the current flow in neutral conductor during steady and dynamic state conditions. Synchronous reference frame theory is effectively implemented for extracting the reactive and harmonic part of load current which are the primary components in the evaluation of reference currents. The predictive current control scheme implemented in FPGA has been deployed to evaluate the behaviour of the FL-DSTATCOM under multifarious loading conditions.

A multi-phase losses allocation method is proposed to provide explicit information about losses allocated to the neutral conductor. This information from the proposed methodology can be utilized by distribution system operators in the identification of highly unbalanced nodes in a network and consequently, allows them to implement suitable unbalance compensation schemes at these nodes in order to improve network balancing. The newly developed approach, based upon neutral losses allocation factors, reduces the unbalance in a network by switching single-phase loads across phases of highly unbalanced nodes. Two-phase switching algorithms, based upon individual and combined load commutation, are proposed to achieve this objective. The developed technique is implemented on a real LV Italian distribution network by adopting real customer’s power profiles. Results indicate a significant improvement in network balancing and losses reduction, which clearly represent the positive active role that neutral losses allocation factors can play in the assessment and management of distribution networks.

This paper presents an approximate formula for the peak-value of the lightning overvoltages induced on aerial lines installed over high resistivity ground, which is valid up to 10 kΩ m. The formula is validated by comparing its results with results obtained from more accurate techniques. The formula is then applied in a Monte Carlo code to assess the effect of high-resistivity ground on the lightning performance of distribution lines without grounded neutral conductor. The results show that, for good conducting ground (e.g., 100 Ω m), indirect flashes are relevant for the 100 kV CFO lines, but they are not relevant for the 170 kV CFO lines. For poorly-conducting ground (e.g., 1000 Ω m), indirect flashes are relevant for 170 kV CFO lines, but they are not relevant for the 300 kV CFO lines. Indirect flashes become relevant for the 300 kV CFO lines only for very poor-conducting ground (e.g., above 2000 Ω m). The paper results also show that using a grounded neutral conductor improves significantly the indirect lightning performance of distribution lines.

The Neutral to Earth Voltage (NTEV) rise are categorised one of power quality (PQ) problems in the commercial building. Usually, the NTEV rise occur due to the neutral conductor problems. Theoretically, the neutral problems give an adverse effect to the network system where the phase voltage and harmonic distortion become more imbalance, heating on the conductor cable, and the electrical appliances prone to damaged. This paper presents a novel technique to identify the source location of NTEV rise in the commercial building due to the loose and open neutral conductor. The proposed technique able to identify the problems that occur either on the upstream or downstream location which respected to the measurement points. In addition, the characteristics of neutral problem due to the loose termination and open conductor are also explored based on the 13-nodes distribution system. The results show the source of NTEV rise can be correctly identified. Keywords: Power quality (PQ), Neutral to Earth Voltage (NTEV), Loose termination, Open conductor

Phase-to-neutral voltage or neutral-to-virtual neutral voltage zero-crossing points (ZCPs) detection method is usually used for sensorless brushless dc motor commutation control. Unfortunately, neither of them can be realized in lower speed range. In this paper, a simple commutation point detection method is proposed based on detecting inactive phase terminal to dc-link midpoint voltage. It eliminates the requirement of neutral wire or virtual neutral voltage and provides an amplified version of back electromotive force at the ZCPs which makes the lower speed range detection possible. As the speed increases, commutation point error is enlarged due to the low-pass filter. Utilizing the symmetry of the terminal to midpoint voltage, the phase error can be corrected. However, due to the nonlinear relationship between the detected voltage difference and phase error, it is difficult to regulate the error fast and robustly. Therefore, a novel phase regulator based on fuzzy neural network is proposed in this paper with simple structure and learning ability. The validity of the proposed ZCPs detection method and commutation instant shift correction method are verified through experimental results.

Downed distribution conductors in overhead distribution systems may not be a concern for equipment but greatly challenge the safety of persons, as well as the integrity of properties. Standard overcurrent protective devices may not be able to detect the magnitudes of currents resulting from high-impedance ground faults. Sophisticated relays able to detect high-impedance ground faults have been available to electric utilities. However, their implementation is rather uncommon, especially in developing countries, most likely due to their costs. In this paper, the authors formalize the problem, and propose a possible cost-effective solution for low-voltage overhead lines with neutral wire. This solution consists of a metal hook underneath the line conductors, attached to the pole and connected to the neutral wire. In the case of a falling line, the hook would be contacted and a line-to-neutral short circuit would occur; this would positively activate existing standard overcurrent devices, which can therefore disconnect the supply. Costs related to the installation of the device to existing overhead lines are herein analyzed. The effectiveness of the proposed solutions for two different voltage levels (400 V in European countries and 240 V in the USA) is also discussed.

A modification of the CPC power theory to four-wire power systems with non-sinusoidal and unbalanced voltage supply is presented. The reasons behind the introduced modification are thoroughly explained by referring to Buchholz's apparent power definition. By applying Cauchy-Schwarz-Bunyakovsky inequality it is proved that the differences between the corresponding power quantities given by the original and proposed CPC definitions depend on the presence of voltage unbalance. In the case of load compensation to unity power factor the presented theory gives the smallest possible line losses for the same active power transferred to the load. In order to determine where the proposed definition stands among other power definitions, quantitative differences between the corresponding power quantities for the cases of different harmonic and unbalance levels in power system voltages are investigated by means of numerous computer simulations. This analysis includes also the definitions given by the IEEE and DIN standards, and Conservative Power Theory. Finally, the proposed CPC theory is extended for the cases when the supplying line has neutral conductor which resistance differs from the resistance of phase conductors.

Three-phase four switch (TPFS) inverters are an effective solution to reduce the size and cost of the distribution STATic COMpensator (DSTATCOM). The performance of TPFS inverter is identical to three-phase four leg, three-phase split capacitor inverter topologies during balanced load conditions. During unbalanced load conditions, the absence of the neutral wire in TPFS topologies does not allow the DSTATCOM to compensate the unbalance in load currents. To overcome this limitation, a special purpose transformer is connected across the load along with the DSTATCOM. This special transformer provides a path for neutral current, reduces the cost and rating of the inverter, improve the performance under stringent unbalanced currents generated by computer loads and also improves short duration overloading capability. In the proposed work, two different TPFS topologies namely four switch one capacitor and four switch split capacitor are proposed along with two special purpose transformers which include zigzag and T-connected for three-phase four-wire distribution systems. The combination of TPFS inverter and special transformer can achieve power factor improvement, harmonic elimination, neutral current compensation and load balancing. The evaluation of the proposed method has done using simulation and experimental investigations.

Theoretically this paper will explain the formation of higher harmonic components in the electricity network, their causes, consequences on consumers and the ways of their elimination. Transformer role in the Dyg connection will be explained on the concrete example. For a specific example the waveform of primary (R) phase at 10 kV voltage level, the current of the secondary (r) phase and the neutral conductor at the 0.4 kV voltage level will be determined as shown in the concrete example in the work. Harmonic content will be determined up to 15 harmonics and the effective value of all these currents (phases R and r). THD for current of primary (R) phase and secondary (r) fase will be calculated. In this paper, the dimensional three-phase filter is set to eliminate the maximum harmonic component of current of the primary (R) phase on the 10 kV side of the transformer. The waveform, the corresponding harmonic content for the current and THD of primary (R) phase will be determined. Additional measures have been proposed to reduce the THD. Another parallel filter has been realized to eliminate the second by size harmonic components of primary (R) phase current. It will also compare THD for primary (R) phase as in the previous cases. For the total duration of the simulation, the used time is Tstop = 0.1 sec. All of the above simulations will be realized in the MATLAB/PSB program package and simulation models will be displayed.

When a long marshaling high-speed train (HST) with two raised pantographs passes an articulated split-phase region, there will be eight electromagnetic transient processes along with pantograph arcing. These transients cause over-voltage in the train body (TB), which can have a negative effect on the train's electronic equipment. In view of this issue, this paper closely analyzes the different transient processes generated by an HST passing a split-phase region. The analysis focuses on identifying the root causes and influencing factors relating to each transient process, examining, in particular, the capacitive coupling between TB and overhead contact system and the capacitive coupling between TB and the neutral wire. The results of this analysis are then used to establish Bergeron mathematical models that can be used to derive and study the eight independent transient processes. This leads to the generation of more detailed models that can be used to accurately simulate the phenomenon according to different variables, such as the phase difference of feeders, with Electromagnetic Transients Program (EMTP) software. The analysis results demonstrate that the hazardous PH over-voltages and TB over-voltages are easily generated. This paper concludes by drawing upon the simulation results to discuss possible over-voltage suppression measures, such as phase and grounding optimization for the pantograph and TB.

The influence of phase load asymmetry on power losses in electric lines is investigated. The influence of phase load redistribution on power losses in three-phase three-conductor line with the insulated neutral is analyzed. It is demonstrated that additional power losses occur in this line which are in quadratic dependency on the relative change of phase loads. The influence of neutral conductor resistance in the four-conductor three-phase electric network on power losses in different asymmetry modes is investigated. It is shown that power losses in this network are much larger than in three-conductor network with identical phase load asymmetry and depend on the neutral conductor resistance. Significant economic effect can be obtained by increasing the cross-section of neutral conductor. At the same time, the simultaneous decrease of power losses and increase of the operational reliability of electric network are observed.

The article deals with the issues of electricity quality in power supply systems. The quality of electrical energy is often determined not only by energy supplying organizations, but also by electricity consumers. A significant decrease in the quality of electricity inevitably leads to negative impacts on the electrical equipment of both energy enterprises and the consumers of electrical energy, providing these conditions for the occurrence of both technological and electromagnetic damage. Ultimately, it leads to financial losses and other undesirable consequences from violations of the electricity quality. The results of parameters measurements of the LED lamps modes operating obtained by the authors of the article are presented. The presence of electronic converters in these luminaires leads to the appearance of higher voltage and current harmonics. These results show that the massive use of LED lamps and other nonlinear consumers leads to a decrease in the quality of electricity in 0.38 kV electrical networks. On a computer model of the simplest power supply system with nonlinear consumers it is shown that constant monitoring of the values of load currents and voltages can be used to identify the causes of the appearance of current and voltage significant higher harmonics. Nonlinear resistances of load receivers or the sources of these harmonics are located in the electrical networks of power supply organizations. The use of resistance values monitoring in combination with monitoring the current with a frequency of more than 50 Hz in the neutral wire allows to determine with sufficient accuracy the cause of the distortions of the voltage and current curves sinusoidal shape.

Orlando Utilities Commission (OUC) discovered that even one seemingly small error could produce an 18.5% deviation in calculated zero sequence impedance value. The utility began measuring transmission line impedance to analyze different scenarios including underground cable sections, mutually coupled lines, and neighboring utility distribution lines. By comparing values from the collected field-tested impedance data, OUC and Leidos improved the 18.5% zero sequence impedance error between OUC’s CAPE model and actual transmission line field measurements. The error was corrected when the neutral conductor on an offset distribution line near the 230kV transmission line was modeled. This paper discusses how utilities can identify and measure assets that can impact their zero sequence impedance the most. Accurate data results in more effective relay operation, and overall improved relay settings. A conference attendee will take away a better understanding of the impact different parameters have on calculating zero sequence impedance and how to get an accurate zero sequence impedance in the models. Topics include how engineers can calculate zero sequence line impedance, determine the highest priority parameters, and using transmission modeling software to model a variety of parameters including standard tower designs, conductor types, temperature, and distribution lines. Many times, the distribution system is not accounted for even though it has a significant impact on zero sequence impedance.

Uninterruptible Power Supplies (UPS) play a key role in feeding a wide range of critical applications such as high-tier datacenters and medical facilities. Given the variety of loads that typically exist in such applications, UPS systems should be able to correctly operate under highly unbalanced load conditions and to simultaneously supply single- and three-phase loads. On the other hand, UPS systems are usually parallel-connected in order to improve the overall system feasibility and/or to increase the overall installed power capacity. In this paper, a system topology based on two paralleled UPS systems with neutral wire at the load-side is proposed. Moreover, a new Finite Control Set Model Predictive Control (FCS-MPC) strategy is also proposed to control all converters of the paralleled systems. The proposed technique permanently ensures: the generation of a high-quality load voltage waveform; elimination of the undesired circulating current that can flow between both UPS systems; a fully controlled load power distribution. Simulation results are presented, demonstrating the effectiveness of the proposed strategy even under highly unfavourable load conditions.

This paper presents a comprehensive study of peak-to-peak and root-mean-square (RMS) values of AC current ripples with balanced and unbalanced fundamental currents in a generic case of three-phase four-leg converters with uncoupled AC interface inductors present in all three phases and in neutral. The AC current ripple characteristics were determined for both phase and neutral currents, considering the sinusoidal pulse-width modulation (SPWM) method. The derived expressions are simple, effective, and ready for accurate AC current ripple calculations in three- or four-leg converters. This is particularly handy in the converter design process, since there is no need for heavy numerical simulations to determine an optimal set of design parameters, such as switching frequency and line inductances, based on the grid code or load restrictions in terms of AC current ripple. Particular attention has been paid to the performance comparison between the conventional three-phase three-leg converter and its four-leg counterpart, with distinct line inductance values in the neutral wire. In addition to that, a design example was performed to demonstrate the power of the derived equations. Numerical simulations and extensive experimental tests were thoroughly verified the analytical developments.

Distributed generation (DG) allows the production of renewable energy where it is consumed, avoiding transport losses. It is envisioned that future DG units will become more intelligent, not just injecting power into the grid but also actively improving the power quality by means of active power filtering techniques. In this manner, voltage and current harmonics, voltage unbalance or over-voltages can be mitigated. To achieve such a smart DG unit, an appropriate multi-functional converter topology is required, with full control over the currents exchanged with the grid, including the neutral-wire current. For this purpose, this article studies the three-phase four-wire split-link converter. A known problem of the split-link converter is voltage unbalance of the bus capacitors. This mid-point can be balanced either by injecting additional zero-sequence currents into the grid, which return through the neutral wire, or by injecting a compensating current into the mid-point with an additional half-bridge chopper. For both methods, this article presents a discrete time domain model to allow controller design and implementation in digital control. Both techniques are validated and compared by means of simulation results and experiments on a test setup.

Distribution transformer 8 at PPSDM Migas Cepu has a capacity of 500 kVA with load connected to boiler and refinery. The loading connected to the distribution transformer 8 is the majority of the 3-phase motor pump load and some 1-phase pump motors. In this case study measurements were made using the ampere pliers as the hypothesis of the current of each phase. From the measurement result there is imbalance of load between channel and also there is current value of neutral conductor side. And to know the content of harmonics on the distribution transformer, then measured with a power quality analyzer.The result of measurement with fluke quality 436 type fluke quality got result of measurement that current value at neutral conductor side equal to 14A. The value of load imbalance between conductor obtained by value of channel current R equal to 346A, in channel S equal to 306A, and in channel T equal to 318A. The THD value of the current obtained from the measurement with the power quality analyzer on the conductor side of R is 3.4%, on the conductor side S of 3.0%, and on the conductor side of T is 3.0%, and in the neutral channel is the greatest value of 29%. In the analysis of this chapter we get the result of imbalance loads of 4.6%, with the average loading of 45% of the total capacity of the transformer

This work presents a power grid reduction method that allows the accomplishment of several study cases with different loading conditions regarding the same system by performing a single reduction process. In particular, this technique presents robustness for radial and meshed power grid topology and unbalanced systems modeled with neutral wire, which are not available in related existing publications. Equally important, the evaluation metric employs the phasors voltages instead of just the magnitude itself, as normally seen in the literature. In this fashion, the proposed technique shows the capability to remove more than 2000 buses from a benchmark EPRI feeder with phasorial voltage accuracy of 99% and to speed up 67% its power flow simulation time. Moreover, this paper also exposes a meshed grid reconfiguration and an evaluation of losses from the reduced IEEE 123 buses feeder with photovoltaic distributed generation through a QSTS simulation with a maximum of 1.8% relative losses errors.

Three-phase-four-wire (3P4W) three-level (3L) inverters are widely used for feeding unbalanced ac loads. Because of the neutral wire, however, the size and volume of the ac filter inductors and dc-link capacitors are much increased, leading to reduced power density. This paper discusses the way of reducing ac filter inductances and dc-link capacitances in the 3P4W 3L inverter. To save the total ac inductances, a neutral inductor is proposed to insert in the neutral wire, and closed-form formulas are derived for guiding the ac filter design. To minimize the dc-link capacitances, a neutral module is employed to bypass part of the midpoint current and neutral wire current. Finally, the proposed works are verified on a 10-kVA 3P4W 3L inverter.

Neutral wire is used in multiple active front-end application. Some of these applications are single phase loads and maintaining system stability in case of emerging unsymmetrical components, which can lead to malfunction and device failure. In such cases neutral wire potential can be middle point of DC-link, what leads to capacitor separation, but also can be implemented as additional arm, leading to full DC-link voltage utilization and additional control channel for zero symmetrical component in case of unsymmetrical load. In order to perform control system synthesis for such a complicated object, knowledge of its complex mathematical model is required. Four arms active front-end mathematical model is developed for analysis and control system development, featuring phase-coordinates usage and taking into account multiple peculiarities of this converter. Diagrams of main voltages and currents components are derived from model research.

This paper presents distributed power quality conditioning system to compensate current and voltage distortions in three-phase four-wire networks caused by unbalanced non-linear single-phase loads. The proposed conditioning system consists of several hybrid filter units installed in various nodes for compensation of excessive neutral currents and voltage distortions in a selected area of the distribution network. The system is open and it can be easily modified by installation of new filter units. A novel hybrid filter design procedure based on filter frequency characteristics optimization in the parameters of passive and active parts is presented. A digital system of control signal computation for active filters based on the use of modern methods of spectral analysis is considered. The proposed digital control system enables selective compensation of fundamental and harmonic components. The mathematical model of the proposed power quality conditioning system is developed in the MatLab software. The simulated results show that the presented conditioning system reduces the level of neutral conductor currents and the voltage unbalance as well ensures harmonic compensation in three-phase four-wire networks.

In the last decade, mainly due to political incentives towards energy efficiency, the share of lamps with power electronic interfaces, like Compact Fluorescent Lamps (CFL) and Light Emitting Diode (LED) lamps, has significantly increased in the residential sector. Their massive use might have a substantial impact on harmonic currents and, consequently, on the current flowing in the neutral conductor. This paper analyzes the impact of modern energy-efficient lighting technologies on the neutral conductor current by using a synthetic Low Voltage residential grid. Different load scenarios reflecting the transition from incandescent lamps, via CFL, to LED lamps are compared concerning the neutral conductor current at different points in the network. The inherent randomness related to the use of lighting devices by each residential customer is considered employing a Monte Carlo simulation. Obtained results show that the use of CFL has a greater impact on the neutral conductor current of Low Voltage (LV) residential grids and that, with increasing use of LED lamps, a decreasing impact can be expected in the future. Fil: Hernández, Jairo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina Fil: Romero Quete, Andrés Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Energía Eléctrica. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Energía Eléctrica; Argentina Fil: Meyer, Jan. Technische Universität; Alemania Fil: Blanco, Ana María. Technische Universität; Alemania

The problem of ensuring the proper quality of electricity does not lose its relevance, since many electrical appliances are used in production and at home, which are extremely sensitive to voltage deviations from acceptable values specified in GOST 32144-2013 "Electric energy. Electromagnetic compatibility. Quality standards for electric energy in general-purpose power supply systems." The increase in electricity consumption in the domestic sector is associated with the widespread use of various types of electrical appliances, as well as with the intensive introduction of new consumers, which in many cases leads to unacceptable voltage deviations. Power lines designed according to the norms of power consumption of the 80-90s no longer have the necessary bandwidth. Deviations of voltage beyond the permissible values lead to a malfunction and a decrease in the service life of electrical appliances. The insufficient pace and high cost of reconstruction of distribution electric networks with a considerable length, combined with an increase in energy consumption lead to a deterioration in the quality of electricity, which in many cases no longer meet regulatory requirements. An important factor affecting energy saving is the asymmetry of the load of distribution electric networks on the side of 0.4 kV, which causes additional losses of electricity both in phase wires and in the neutral wire.

In the three phase four wire applications, three phases and neutral, often the loads are not well balanced; hence there is a flow of current through neutral conductor. In these applications, the voltage source converters have to handle return or neutral currents into the DC link. This paper presents analysis of the RMS current stress on the DC link capacitors of the four leg 3L T-type voltage source converter caused by unbalanced loads.

The main objective of this study is to offer an approach to analyze the performance of different three-phase four-wire residential rooftop photovoltaic system topologies. Among different photovoltaic system topologies, this work focuses on the two most used. These two photovoltaic topologies have different design regarding the neutral wire. The first topology includes a DC-link neutral point and the second one incorporates a Delta/Star grounded transformer. Authors conduct a comparative study of both topologies based on the following criteria and constraints: (1) the battery and the DC link capacitors lifetimes; (2) the impact of non linear load on the neutral current; (3) the power quality; (4) the cost of the photovoltaic system topology and (5) voltage and current total harmonic distortion. Analyses are supported by simulation results performed under PSIM software.

The quality of electrical power is a common condition that describes the characteristics of the parameters of electrical quantities. This study aims to determine the power quality profile that includes current, voltage, active power , reactive power , apparent power, frequency , harmonic current and voltage harmonics. Power quality profile is done by measuring for 24 hours to determine the characteristic qualities of the object of research in Balai Latihan Pendidikan Teknik (BLPT) Yogyakarta. Measurements were taken at each of output transformer 250 kVA at BLPT Yogyakarta . Based on the measurement results , the total peak load for loading in BLPT Yogyakarta is 129.242,45 VA or equal to 51.70% of the installed transformer capacity. The most prominent conditions of measurement results are any indication of the current flow in the neutral wire is high enough, ie 103,05 amperes, which will impact on the value of the energy loss in the neutral wire and losses in the transformer.

3- phase distribution transformers generally have a Delta (Triangular) connected primary winding and a Star (Wye) connected secondary winding. The secondary Star configuration allows for a 3-phase and Neutral, Dy1 supply providing line and phase voltages and currents. Commonly the Neutral and Earth connections which provide a 5-wire (3-phases + Neutral + Earth) TN-S (separate Neutral and Earth) supply to homes and buildings are connected together at the star point of the three secondary winding, thus the Neutral and Earth are effectively bonded together and remain at the same zero or Earth potential. However, with a TN-C (combined Neutral and Earth) 4- wire (3-phases + Neutral) supply the Neutral wire also acts as the Earth wire, but the neutral wire is still bonded along with a separate Earth electrode to the star point of the secondary winding to provide the required phase voltages and currents. TT and IT configurations have different Neutral and Earthing arrangements. Being a Delta connected Primary winding and therefore a balanced load for the supplying network, there is no Neutral or Earth connection to the three primary winding, (Earthing is done at the generator source) but it is possible that the physical metal casing of the transformer has been bonded to the secondaries Earthing bar for safety.