Single-phase Lines Research Articles

State-of-the-Art Power Factor Correction: An Industry Perspective

On 1 January 2001, the IEC 61000-3-2 regulation became effective. Since then, mitigating current harmonics has been essential to ensure that electronic equipment connected to single-phase power distribution lines conforms to electromagnetic compatibility directives. Today, high-quality rectification, commonly known as power factor correction (PFC), is a well-established technique widely adopted by the industry for powering various devices from the ac line. The topic has been studied by academia and industry since the mid-1980s; thus, an enormous amount of research has been published and countless solutions have been proposed since then. However, only a few of those solutions have encountered wide industrial usage. So, it is not the authors’ intention to provide a comprehensive review, but to take stock of the most used PFC techniques from an industry perspective. This paper will review the power factor theory with non-sinusoidal currents, the practical and regulatory aspects of using PFC, and the most common industry solutions for power factor correction in equipment operated from the single-phase, public, low-voltage supply system, with a special focus on boost PFC pre-regulators, their control methods, design procedures, and issues.

Electric grid resilience: The effects of conductor coverings, enhanced tree trimming, and line characteristics on tree-related power outages

Tree damage is a major cause of storm power outages in forested regions of the world which results in substantial economic losses each year. Utilities must understand the effectiveness of resilience programs to make the best use of limited resources. Our study evaluated the effectiveness of covered conductors and enhanced tree trimming (ETT) in reducing tree-related outages during storms for an electric overhead distribution system. Our study area was the Eversource Energy service area in Connecticut which has heavy forest cover coinciding with areas of high population density. We controlled for the effects of confounding factors including weather, power line phase, and tree canopy cover. Covered conductors and ETT were similarly effective in reducing power outages with median rate reductions of 0.19 - 0.29 outages/km/year. When used in combination, covered conductors with ETT had a significant additive effect with median reductions of 0.29 – 0.33 outages/km/year compared to bare conductors with no ETT. Multiphase power lines had median outage rates that were 0.17 – 0.37 outages/km/year lower than outage rates for single-phase power lines. Our findings will help utilities select and justify their choices of resilience strategies and more accurately predict outage locations in advance of approaching storms.

Development and implementation of a PQ analyser to monitoring public lighting installations with a LoRa wireless system

In smart cities, public lighting installations have a significant consumption of electrical energy. In order to measure this consumption, it is necessary to install sensors capable of obtaining electrical parameters in real time. In this way, the installations are monitored and energy saving and efficiency measures can be implemented. In this sense, this research has developed a PQ analyser meter with Long Range wireless communications technology (LoRa). This technology allows coverage of up to 5 km, which makes it ideal for public lighting applications. PQ Analyser with LoRa (PQAL) has been developed to achieve a fully functional prototype. PQAL comes in two versions for single-phase and three-phase street lighting lines, so that it adapts to any type of installation. PQAL uses the open-source Arduino platform which allows it to adapt to the monitoring needs of every installation. PQAL can monitor installations up to 100 A and 23 kW per phase. The use of non-invasive current sensors allows this device to be installed without modifying the installation to be monitored. Due to the long range of the LoRa network, it can be installed in locations far from the gateway without the need for additional cabling or Internet connection.

The device for monitoring the insulation breakdown zone of power cable lines in distribution networks with isolated neutral system during high-voltage diagnostic

The article considers an electrical device designed for diagnostic work in distribution networks of 6-10 kV, namely, the determination of damage zones in case of failure of insulating materials of cable lines during high-voltage diagnostics with a rectified voltage of negative polarity. The novelty of the developed device is its ability to connect directly to a high-voltage cable line without additional matching devices. The device is capable of detecting damage zones in lines up to 10 km remotely with an error of up to 0.2% of the cable length. The prefix allows you to fix any variants of damage to single-phase and three-phase cable lines with high transient resistance at the site of damage without the operation of “burning” insulation, which significantly reduces the time of repair work at the controlled facility.

Implementation of wireless intelligent street lighting with phase-detection system

The advancement of technologies in wireless communication has led to several engineering designs for human requirements to solve a country’s problems. Ghana as a country has issues with power instability on domestic, single-phase lines, to monitor some of these line faults “example when an area power outage occurs is a problem for the power distribution company to be aware of this fault ”, this intelligent wireless street lighting with a phase-detection system is to solve this problem by automatically switch power sources to the battery which powers the streetlight when the national gridline is off, for temporal light at the location or area and also send a monitoring notification to the fault monitoring office, with the fault code for feather investigation. The project consists of a battery, inverter circuit, microcontroller, LCD, and current sensor. The system power battery stores a current of 9Ah (Ampere-hour), which means the battery can provide 9 amperes of current in one hour which can sustain three light units to the next morning. Since the system uses a 3.3 ampere the lamp, the battery can produce power within 6 hours before the power supply will be switched to the power grid for charging or for the fault to be rectified. From the data gathered, we can say that it is possible to use a streetlight to monitor line faults and also produce a two-way powering street light. The system is proven to be effective and operational.

Analytical-Numerical Approach to the Skin and Proximity Effect in Lines with Round Parallel Wires

Power and communication lines with round wires are often used in electrical engineering. The skin and proximity effects affect the current density distribution and increase resistances and energy losses. Many approaches were proposed to calculate the effects and related quantities. One of the simplest approximate closed solutions neglects the dimensions of neighboring wires. In this paper, a solution to this problem is proposed based on the method of successive reactions. In this context, the solution with substitutive filaments is considered as the first approximation of the true solution. Several typical arrangements of wires in single-phase communication lines or three-phase bus ducts are considered to detect the limits of applicability of the first approximation. The error of the first approximation grows with wire radius to skin depth ratio and wire radius to wire spacing ratio. When the wire radius to skin depth ratio is up to 1, and the gap between the wires is above the wire radius, the error is at a level of 1%. However, lowering the distance and/or skin depth leads to a much larger error in the first approximation.

Cálculo de parámetros eléctricos en líneas de transmisión de alta tensión

This article aims to determine the electrical parameters of the transmission lines, it will focus on the calculation of geometric inductance and capacitance. For this, the cases of the single-phase and three-phase lines with equilateral spacing are studied. The COMSOL Multiphysics program is used to obtain the parameters of the lines. The simulation results are compared with the classic basic equations.

Transient analysis of compact distribution lines with dielectric-coated phase cables

This paper studies wave propagation characteristics and the transient response of single-phase and three-phase compact distribution lines. Although compact line configurations present bare and dielectric-coated cables in relative proximity, it is shown that their external per-unit-length parameters can be calculated using simplified expressions valid for widely-spaced cables. An attempt is made to identify whether the insulating layer surrounding the phase cables must be included for an accurate simulation of switching and lightning transients on compact distribution lines. The results show that the dielectric coating reduces the propagation velocity of certain modes to values slightly below the speed of light. However, this reduction does not have a significant influence on the initial peak values of the calculated switching and lightning overvoltages. Only the wave tails of the resulting voltage waveforms are more strongly modified depending on the terminal conditions of the line.

SPECIFIC FEATURES OF POWER CONSUMPTION OF LED DEVICES AND ACCOUNTING THEM IN CALCULATION OF ELECTRICAL NETWORKS

The indicators of power consumption of lighting devices based on LEDs are studied depending on the supplied voltage. For the lamp and floodlight with LEDs active and reactive power, current and power factor as a function of voltage (which value changed in the range 200–245 V) were experimentally determined. The analysis of experimental data demonstrated that due to the drivers in the specified voltage range the active power consumed by light devices remains practically unchanged. The reactive power of LED devices depends on the supplied voltage and is capacitive in its nature. In contrast with gas-discharge light sources the LED devices under study do not consume reactive power, but generate it. With the change of the supplied voltage from 200 to 245 V the value of the generated reactive power increases to 60 % for the floodlight and 50 % for the lamp. The LED floodlight has a low coefficient of active power. The current consumed by the floodlight has increased by 22 %, and by the lamp – by 13 %. The formulas for determining the maximum value of the length of the calculated section of single-phase group lines were developed, taking into account specific source data. LED light sources tend to feed by electric power by single-phase group lines. The number of lamps connected to single-phase lines is regulated by normative documents. Bearing this in mind as well as the small power of LED sources single-phase group lines are usually performed with conductors of the smallest possible cross section. The limit values of the length of the calculated section that correspond to a predetermined loss of voltage in line with ambient temperature from 15 to 60 °С were determined for them. The calculations demonstrated that for group lines that feed the LEDs, the choice of conductor cross-sections in accordance with permissible voltage loss is not critical. The determinant factor for the choice of the cross-section of the conductors of group electrical networks is the calculation of acceptable heat with respect to temperature of the environment.

Volt/var optimization of unbalanced distribution feeders via mixed integer linear programming

The paper presents a Mixed Integer Linear Programming (MILP) model for the solution of the three-phase volt/var optimization (WO) of medium voltage unbalanced distribution feeders. The WO of a distribution feeder is aimed at calculating the most efficient operating conditions by means of the scheduling of transformers equipped with an on-load tap changer and distributed reactive power resources (such as embedded generators and switchable capacitors banks). The proposed model allows the representation of feeders composed by three-phase, two-phase, and single-phase lines, by transformers with different winding connections, by unbalanced wye- and delta-connected loads, by three-phase and single phase capacitor banks and embedded generators. The accuracy of the results is verified by using IEEE Test Feeders.

Transfer characteristics of electric-power lines passing through urban and suburban areas

Distribution systems consist of single-phase, two-phase, and/or untransposed three-phase lines serving unbalanced loads. Because of that during normal operating conditions of a distribution line, unbalanced currents flow through the ground and neutral conductor(s). Also, a fluctuating magnetic field exists around and along the line and it interacts with the surrounding metal installations. Currents induced in these installations reduce the part of the current returning through the ground and neutral line conductor(s). Thus, for determination of the actual values of series impedance of distribution lines it is necessary to take into account the existence of surrounding metal installations. Independent of their basic function, these installations spontaneously form a large network of different mutually connected elements that are in direct or indirect contact with earth. Also, this network is mainly under the surface of the earth and it has structure and topology that cannot be visually determined or verified. However, from the standpoint of the influence on distribution line parameters all these, known and unknown, metal installations can be substituted by only one equivalent conductor. The favorable effects of this conductor on the series impedance of different types of distribution lines are evaluated.

Evaluation of Lightning-Induced Voltage on Overhead Lines With Nonlinear Load Using the Scattering Theory

In order to evaluate the effects of indirect lightning return stroke on overhead lines, a solution of the electric-field integral equation (EFIE) in the time domain is adopted to describe the electromagnetic transients from lightning. The resolution of (EFIE) by the method of moment (MoM) in the time domain by introducing the antenna theory model (AT) of the lightning channel conducts to a precise evaluation of the coupling mechanism between the lightning channel and overhead lines. This method is applied to single-phase and three-phase overhead lines located above a perfectly conducting ground. By solving EFIE with MoM in the time domain, not only is it possible to evaluate the induced overvoltage more accurately, but it is also possible to apply nonlinear protective devices, such as surge arrester, in the overhead lines and simulate the effects of these devices. The proposed method will provide an outstanding view on the protection scheme to protect overhead lines against lightning.

Approximate analytic solutions to Radulet equations for the analysis of electromagnetic transients in single-phase power transmission lines

In this work, an analytic development for a transmission line with a corona effect for simulating an electromagnetic transient is presented. The asymptotic solution for the Radulet equations in which a nonlinear term is presented is obtained. The study is carried out for a single-phase transmission line. The electrical parameters for an overhead line are defined and several formulations for their calculation are presented. The frequency dependence of the electrical parameters is considered. In the first part, the linear problem solution is found; the Fourier and Laplace transforms are applied with respect to distance and time respectively. After finding the solution in the Fourier–Laplace domain, which is expressed in terms of a Green’s function integral, an approximate analytical solution is obtained in the distance–time domain by means of asymptotic methods. Finally, the nonlinear solution is found using as a first approach the linear solution. The results obtained show an attenuation in the voltage wave due to the corona effect.

Unbalanced Model and Power-Flow Analysis of Microgrids and Active Distribution Systems

This paper presents a three-phase power-flow algorithm, in the sequence-component frame, for the microgrid (μgrid) and active distribution system (ADS) applications. The developed algorithm accommodates single-phase laterals, unbalanced loads and lines, and three/four-wire distribution lines. This paper also presents steady-state sequence-component frame models of distributed energy resource (DER) units for the developed power-flow approach under balanced/unbalanced conditions. The DER models represent the synchronous-generator based and the electronically-coupled DER units. Both constant power (PQ) and regulated-voltage (PV) modes of operation of DER units are considered. The application of the developed power-flow method for two study systems is presented. The study results are validated based on comparison with the detailed solution of the system differential equations in time domain, using the PSCAD/EMTDC software tool.

Modern approaches for protection of series compensated transmission lines

Series compensation has been employed to improve power transfer in long-distance transmission systems worldwide. However, this in turn introduces problems in conventional distance protection. The complex variation of line impedance is accentuated, as the capacitor's own protection equipment operates randomly under fault conditions. This paper proposes two approaches based on travelling waves and artificial neural networks (ANN) for fault type classification and faulted phase selection of series compensated transmission lines. A modal transformation technique, which decomposes the three-phase line into three single-phase lines, is used for this purpose. Algorithms based on two different modal transformations are developed for phase selection and fault classification. Each algorithm is derived from a corresponding truth table. The truth tables are constructed for different types of faults with different faulted phases and different transformation bases. The proposed ANN topology is composed of two levels of neural networks: In level-1, a neural network (ANN F) is used to detect the fault. In level-2, four neural networks (ANN A, ANN B, ANN C and ANN G) are used to identify faulted phase(s), and activated by the output of ANN F if there is a fault. System simulation and test results, which are presented and analyzed in this paper indicate the feasibility of using travelling waves and ANN in the protection of series compensated transmission lines.

Optimal Planning of Unbalanced Networks Using Dynamic Programming Optimization

This paper presents a method based on dynamic programming optimization to design distribution and industrial networks with unbalanced customers. Low-voltage and medium-voltage network customers can be three-phase (i.e., industrial and commercial) and single-phase (e.g,. residential and rural areas). Moreover, American medium-voltage distribution networks have single-phase lines (rural areas) and three-phase lines (urban and primary feeders). Optimization of an unbalanced network implies optimal assignation of single-phase customers to each phase. This works considers different conductor types, tapering, power losses in lines, capacity and voltage drop constraints and deterministic loads, all employing single-phase and three-phase lines. The necessary modifications to apply it by single-wire earth return systems is presented.

Induction generators for small hydro schemes

In developing countries, small hydro projects producing power outputs in the range 1-10 kW are gaining popularity, particularly as isolated power supply schemes for village electrification. These small generating plants supply power to remote locations where utility power is well out of reach. Consumer loads connected to these small hydro schemes are normally single-phase lighting loads. Therefore generators that produce single-phase output are used, partly due to the lower cost of single-phase distribution lines.

CIRCUITRY INNOVATION FOR THREE-PHASE MOTOR OPERATION ON SINGLE-PHASE POWER

Power companies restrict the largest single-phase motors that they permit on their single-phase power distribution lines because of the high starting current of ordinary single-phase motors. These ordinary single-phase motors have low efficiency and power companies routinely restrict motor power to 7.5 horsepower (hp) or less without special permission. The operation of higher-power three-phase motors connected to a single-phase line have been previously inconvenienced by the need of a phase converter. This need has been overcome by the use of an Enabler™ circuit that connects the three-phase motor to the single-phase line. High-efficiency three-phase motors of 10 hp and 40 hp have now been running for several years on single-phase distribution lines. The starting currents are low and acceptable for the single-phase distribution lines. The running currents are high power-factor. The currents are balanced in the windings of these three-phase motors connected to the single-phase lines by capacitors in the Enabler circuit. Motor performance has been reliable.

Calculation of the effective magnetic field under high-voltage power lines

The calculation of the rms magnetic field due to several out-of-phase AC parallel currents involves some simple but instructive vector algebra. In the present paper the expressions of the magnetic field under single-phase and three-phase lines are derived. The analytical results are discussed and compared with measurements performed under a six-wire, high-voltage power line and near some electrical appliances.

Tree Growth Regulators Reduce Line Clearance Trimming Time

Untreated silver maples (Acer saccharinum) and trees that were trunk injected with the tree growth regulator (TGR) paclobutrazol in northern Indiana were matched according to crown size, trim type, and number of overhead conductors. Trim time and total job site time for TGR-treated and untreated trees within four trimming regimes (single phase side trim or V-trim and three phase side trim or V-trim) were recorded for each tree. Trim time for TGR-treated trees side trimmed was not significantly reduced for either single phase or three phase lines. Trim time for V-trimmed TGR-treated trees was reduced significantly for both single phase and three phase lines (36% and 48%, respectively). Total job site time was not reduced significantly for TGR-treated trees either side trimmed or V-trimmed around single phase lines. However, total job site time for side trims and V-trims of TGR-treated trees was reduced significantly (25% and 58%, respectively) for trees associated with three phase lines.