Neutral Conductor Research Articles

Control Methods and Compensation Characteristics of a Series Active Filter for a Neutral Conductor

Due to the advance of information technologies, a large number of electronic products such as personal computers have been connected to power distribution systems in commercial buildings. Hence, voltage distortion on utility outlets and excessive neutral current on distribution lines have arisen and lead to a number of serious problems in the distribution system. Two control methods and the related compensation characteristics of a series active filter connected to the neutral conductor are presented in this paper. The distinct functions of the proposed active filter are the mitigation of the third-harmonic voltage and the neutral current in a three-phase four-wire distribution system in a building. The required power of the proposed active filter is less than 10% of that of the harmonic-producing loads. A control method of the dc capacitor voltage on the active filter circuit is also described. It is clarified through experiments that one of the two functions of the active filter can be realized selectively and the dc capacitor voltage of the active filter can be regulated to a desired value

Ampacity of Low-Voltage Power Cables Under Nonsinusoidal Currents

This paper investigates the ac resistance in the presence of harmonics and proposes ampacity derating factors for cables made according to CENELEC Standard HD603. These cables are widely used in low-voltage industrial and building installations. Four-conductor cables of small, medium, and large conductor cross sections are considered. The fourth conductor is used as the neutral conductor. The cables are modeled using finite-element analysis software. The ac/dc resistance ratio is shown to increase with the frequency of the current and the cross section of the conductor, the increase being much larger when zero-sequence harmonics are present. A derating factor is defined and calculated for five typical nonsinusoidal current loads, for example, computer equipment. The derating of the cable's ampacity is shown to be very large when zero-sequence harmonics are present. The cross section of the neutral conductor is shown to be significant only when zero-sequence harmonics are present. The validity of the method is verified by comparison with data given in IEEE Standard 519-1992 and with measurements conducted on a cable feeding a large nonlinear load

Resonance Stabilized Bisdiselenazolyls as Neutral Radical Conductors

An efficient and versatile synthetic route to resonance stabilized bisselenathiazolyl and bisdiselenazolyl radicals 3 and 4 is described. Structural analysis of 3 and 4 confirm that lattice and pi-delocalization energies are sufficient to offset solid-state dimerization of the radicals and that the two selenium-containing radicals are isostructural with the all-sulfur based system 1. Variable temperature conductivity measurements indicate that sequential replacement of sulfur by selenium leads to a progressive increase in conductivity and reduction in thermal activation energy.

Electrostatic internal energy using the method of images

For several configurations of charges in the presence of conductors, the method of images permits us to obtain some observables associated with such a configuration by replacing the conductors with some image charges. However, simple inspection shows that the potential energy associated with both systems does not coincide. Nevertheless, it can be shown that for a system of a grounded or neutral conductor and a distribution of charges outside, the external potential energy associated with the real charge distribution embedded in the field generated by the set of image charges is twice the value of the internal potential energy associated with the original system. This assertion is valid for any size and shape of the conductor, and regardless of the configuration of images required. In addition, even in the case in which the conductor is not grounded nor neutral, it is still possible to calculate the internal potential energy of the original configuration through the method of images. These results show that the method of images could also be useful for calculations of the internal potential energy of the original system.

Study of Neutral Conductor Current in Three-Phase Networks With Single-Phase Converters

In this paper, neutral conductor current in three-phase networks with single-phase ac/dc uncontrolled converters is analyzed, and the influence of the unbalances on neutral conductor current is analytically studied. It is shown that supply-voltage unbalance slightly affects the root-mean-square value of the neutral conductor current and load unbalance can increase it. The obtained results are validated with laboratory measurements.

Control methods and compensation characteristics of a series active filter for neutral conductor

AbstractWith an increase in the number of electronic devices, such as personal computers, connected to power distribution lines in commercial buildings, problems associated with their use, such as voltage distortion on utility outlets and excessive neutral current on the distribution lines, become more and more serious. This paper shows control methods and compensation characteristics of series active filters connected to the neutral conductor. The distinctive functions of the proposed active filter are the mitigation of third harmonic voltage and the reduction of neutral current in three‐phase four‐wire distribution systems. The required kVA rating of the proposed active filter is less than 10% of that of the harmonic producing leads. A control method of the DC capacitor voltage on the active filter circuit is also described. It was experimentally demonstrated that one of these two functions of the active filter (to mitigate harmonics or to reduce the neutral current) can be realized selectively and that the DC capacitor voltage of the active filter can be regulated to a desired value. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 53–63, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20227

The Effect of Selenium Incorporation on the Bandwidth and Conductivity of Neutral Radical Conductors.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

New Family of Aminophenalenyl-Based Neutral Radical Molecular Conductors: Synthesis, Structure, and Solid State Properties

We report the preparation, crystallization, and solid-state characterization of the first members of a new family of spiro-bis-(1,9-diamino-substituted-phenalenyl)boron neutral radicals. The crystal structures show that the three radicals are monomeric and without close contacts in the crystal lattice. In all cases magnetic susceptibility measurements confirm the presence of free radicals with one unpaired spin per molecule. Two of the new radical compounds are among the most highly conducting neutral organic solids, with room-temperature conductivities reaching sigma(RT) = 4 x 10(-2) S/cm. The measured conductivities correlate with the closest intermolecular contacts in the solid state and with the calculated band dispersions, even though the bandwidths are much smaller than those found in other organic conductors.

Analysis of Zig-Zag Transformer Applying in the Three-Phase Four-Wire Distribution Power System

The load unbalance and the nonlinear loads result in a significant neutral current in the three-phase four-wire distribution power system. The Zig-Zag transformer has been proposed to attenuate the neutral current of the three-phase four-wire distribution power system. In this paper, an analysis is carried out and computer simulation is used to evaluate the performance of the Zig-Zag transformer under ideal and nonideal power conditions. The simulation results show that (a) the Zig-Zag transformer can effectively attenuate the neutral current and zero-sequence harmonic currents on the utility side under the balanced utility voltage, (b) the utility side neutral current becomes larger under the unbalanced utility voltage or the distorted utility voltage with zero sequence harmonic components after applying the Zig-Zag transformer, (c) the insertion of an inductor in the utility side of the neutral conductor can alleviate overloading of the neutral current caused by the unbalanced utility voltages and the distorted utility voltages with zero sequence harmonic components.

The effect of selenium incorporation on the bandwidth and conductivity of neutral radical conductors

The first example of an undimerized pi-stacked bis-1,2,3-thiaselenazolyl radical displays improved bandwidth and conductivity relative to an isostructural bis-1,2,3-dithiazolyl.

Overload prevention

This work presents a series active filter system for three-phase, four-wire distribution systems to alleviate the overloading of the neutral conductor. The active filter system employs a voltage sources inverter connected in series with a neutral conductor to suppress the excessive current harmonics. Theoretical analysis shows that series active filter system are more suitable than shunt active filter systems because most of the nonlinear load at low voltage levels are categorized as harmonic voltage source type. Laboratory test results show that the proposed system achieves desired filtering function.

Mitigation of third‐harmonic voltage for three‐phase four‐wire distribution system based on a series active filter for neutral conductor

AbstractThis paper proposes a series active filter for mitigation of the third‐harmonic voltage in a three‐phase four‐wire power distribution system in a building. The active filter which consists of a single‐phase inverter can suppress the harmonic voltage of the system. The active filter is characterized by acting not only as a capacitor but also as a resistor for the third‐harmonic components. A Hilbert transformer is applied to the controller of the active filter in order to realize accurate third‐harmonic detection on a single‐phase active filter. Measurement results of harmonic distortion of source voltage in a building is also shown in this paper. It is clarified in a simulation and experiment that the active filter can suppress the third‐harmonic voltage without increasing neutral conductor current. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 62–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10379

접지 임피던스가 중성선 고조파 전류에 미치는 영향

스위칭 모드 전원 공급 장치와 같은 비선형 부하의 증가로, 3상 4선식 배전계통을 채용하는 중성선에 많은 고조파 전류가 흐른다. 중성선은 접지 시스템과 연결되어 있기 때문에 접지 임피던스는 중성선 고조파 전류에 영향을 끼친다고 알려져 있다. 현장에서 실측한 고조파 전류와 전압으로 고조파 해석용 3상 등가 회로를 구성하였다. 실측한 값과 MATLAB으로 시뮬레이션 한 값을 수치와 파형으로 비교 검토하였다. 또한 본 논문에서는 중성선 고조파 전류와 접지 임피던스와의 관계를 시뮬레이션을 통해 검증하였다.

Neutral Currents in Large Public Lighting Networks

The modern large public lighting networks are characterized by two major aspects that rise problems from both power quality and neutral current point of view in low voltage wye-connected three-phase electrical systems: (i) the supply system is unbalanced loaded; (ii) the presence of discharge sources. It is important to underline that nowadays, these aspects are not taken into account in the proper sizing of neutral conductors. The paper presents a simplified but enough accurate methodology to estimate the RMS value of neutral currents in lighting networks. The theoretical relationships are illustrated for a three-phase public lighting network that contains high pressure sodium lamps.

Synthesis, structure and physical properties of the first one-dimensional phenalenyl-based neutral radical molecular conductor.

We report the preparation, crystallization, and solid-state characterization of a benzyl-substituted spirobiphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state, with the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a pi-step stack. This particular mode of 1-D stacking is forced on the lattice arrangement by the presence of the orthogonal phenalenyl units that were specifically incorporated to prevent the crystallization of low-dimensional structures. The structure shows that this strategy is effective, and neighboring molecules in the stack can only interact via the overlap of one pair of active (spin-bearing) carbon atoms per phenalenyl unit, leading to the pi-step structure in which the remaining four active carbon atoms per phenalenyl unit do not interact with nearest neighbor molecules. The magnetic susceptibility data in the temperature range 4-360 K may be fit to an antiferromagnetic Heisenberg S = 1/2 linear chain model with intrachain spin coupling J = -52.3 cm(-1). Despite the uniform stacking, the material has a room temperature conductivity of 1.4 x 10(-3) S/cm and is best described as a Mott insulator.

中性線用アクティブフィルタの制御法と補償特性

As a large number of electronic products such as personal computers are now connected to power distribution lines in commercial buildings, the serious problems such as voltage distortion on utility outlets and excessive neutral current on the distribution lines have arisen. This paper shows control methods and compensation characteristics of a series active filter connected to the neutral conductor. The distinctive functions of the proposed active filter are the mitigation of 3rd-harmonic voltage and reduction of neutral current in a three-phase four-wire distribution system. The required kVA rating of the proposed active filter is less than 10% of that of the harmonic producing loads. A control method of the dc capacitor voltage on the active filter circuit is also described. It is clarified through experiments that one of those two functions of the active filter can be realized selectively and the dc capacitor voltage of the active filter can be regulated to a desired value.

Spin crossover of spiro-biphenalenyl neutral radical molecular conductors.

We present ab initio molecular and solid-state calculations at the level of density functional theory (DFT) for the ethyl-substituted spiro-biphenalenyl neutral radical organic conductor. We find that the phase transition of this material is accompanied by a spin crossover (low-spin, LS, to high-spin, HS), and consequently a different band becomes the conduction band. The energy gap (Eg) increases from 0.12 eV of the low-temperature polymorph to 0.23 eV of the high-temperature polymorph corresponding to a different occupancy causing a change in the number of the available charge carriers, explaining the change of conductivity by 2 orders of magnitude at the phase transition. These gap values are also consistent with structural, IR, electrical conductivity, and magnetic susceptibility data of Itkis et al. The proximity of the monomers in the stacking dimers is closely related to the spin crossover in this material.

Measurement of the division of lightning return stroke current among the multiple arresters and grounds of a power distribution line

A triggered-lightning experiment was conducted during Summer 2000 at the International Center for Lightning Research and Testing (ICLRT) in north-central Florida for the purpose of studying the lightning current division in an 829-m-long, 18-pole, three-phase plus neutral, unenergized, overhead distribution line equipped with six arrester stations. Eight lightning flashes containing a total of 34 recorded return strokes, as well as low amplitude, long duration steady currents, were artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique, and the flash currents were directed to phase C (one of the two outer conductors of the three-phase cross-arm-configured line). Six of the eight triggered lightning flashes caused damage to one of the two closest phase C arresters. In the case when no arrester was damaged or was not yet damaged by current in the flash, it is inferred that about 40% of the return stroke peak current and about 25% or more of the return stroke charge transferred in the first millisecond passed to the neutral conductor through each of the two closest arresters located about 70 m away on either side of the strike point. The bulk of the peak current then flowed from the neutral conductor to ground through the groundings of the two closest arresters. The charge transferred in the first millisecond from the neutral to the eight system groundings, six at arrester stations, and one at each of the two line-end poles, appears to be distributed inversely to the low-frequency, low-current grounding resistances. From our measurements of return stroke current division and in view of the available data on the currents of first strokes in natural lightning, we estimate that over half of natural first strokes would result in an arrester failure in our test distribution line, which is representative of some distribution lines in service, within about 450 /spl mu/s of the initiation of the first return stroke current flow, in the absence of flashovers and other alternative current paths that might be provided by transformers or underground cable connections to allow the stroke current to bypass the arrester. Additional first stroke current flow beyond about 450 /spl mu/s and currents associated with subsequent strokes and potentially other processes should further increase the likelihood of arrester damage.

Analysis of the neutral conductor current in a three-phase supplied network with nonlinear single-phase loads

This paper describes what factors (i.e., load and supply) have an important effect on the neutral conductor current. It is shown that an asymmetry up to 10/spl deg/ or an unbalance of 10% in the power supply has only a minor effect on the RMS value of the neutral conductor current. An unbalance in load conditions increases the neutral conductor current. Harmonics in the power supply voltage highly affect the RMS value of the neutral conductor current.

Characterization and modeling of in-building power lines for high-speed data transmission

This paper analyzes the characteristics of power lines in Singapore residential network in order to develop a channel model suitable to simulate its behavior for high-speed data transmission. The channel model, which describes the transfer function and noise characteristics of typical in-building power line channels in a frequency band from 1 to 10 MHz, is developed and tested through software simulation and hardware implementation. The transfer function is described by an echo model and the noise spectrum is derived statistically from measurements on actual power lines. Some measurement results on power line impedance, noise and attenuation are presented. The results are based on measurements between line and neutral conductors in a 230-V power line network. From the results obtained so far, the impedance, noise and attenuation of power lines exhibit variations with frequency, time and location.