Low Voltage Electrical System Research Articles

Research on the Technical and Economic Development of Large Megawatt Wind Turbines Based on Medium-Voltage Electrical System

INTRODUCTION: With the advent of the "bidding era" and "parity era" in the wind power market, the competition of the whole machine factory is becoming more and more fierce, and the capacity of the single fan is getting larger and larger, which becomes the key to the design of the fan electrical system of the large-capacity unit (5.XMW or more). At present, the low-voltage wind power system (690V,1140V) is the common solution for wind turbines. However, due to the limitation of the cable section of low-voltage electrical system and the increase of the rated current of the generator, the increase of the capacity of a single machine makes more cables from the generator side to the grid, and the cost also increases.
 OBJECTIVES: Aiming at the future large megawatt wind power market, the medium voltage Doubly-Fed electrical system solution is proposed to increase the higher generation and electricity income of wind farms and reduce the manufacturing cost of wind farms.
 METHODS: The technology and economy of medium voltage and low voltage electrical system are compared.
 RESULTS: With the gradual increase of single capacity, the economy of medium pressure wind power generation system is getting better and better, and the higher the height of the tower, the better the economy. At the same time, the reduction of the rated current of the generator brings about the reduction of line loss and the increase of power generation. The number of cables is greatly reduced, and the construction cost and difficulty of cable laying will be greatly reduced.
 CONCLUSION: In response to the technical trend of large-capacity wind turbines in the future, the medium-voltage wind power generation system has a good application prospect, both from the economic and technical point of view.

Proposal of Novel Single-Phase Power Quality Indicators considering subsynchronous frequency perturbations in Voltage and Current under non-sinusoidal conditions.

This work pretends to reconsider power quality (PQ), in AC single-phase low voltage systems, considering perturbation sources with frequency components below the fundamental frequency in voltage and current signals. These perturbations induced by sources like Geomagnetic Induced Currents (GMC), Arc Furnaces, switching VSC, etc. [1]-[2],[30]-[32], can occur in a frequency range comprised between DC and the fundamental frequency of the system. Standard PQ indexes do not characterize properly these subsynchronous frequency perturbations (SFFP), [2]-[3] and this work pretends to analyze the spectra from 0 to 50Hz for voltage and current, proposing new formulation for some PQ as a function of SSFP, with the intention of explaining the observed degradation of the power quality in single-phase low voltage electric systems.

CHARACTERISTICS OF REFUSALS IN LOW-VOLTAGE DISTRIBUTION SYSTEMS

This paper focuses on the determination of the characteristics of refusals in low voltage electrical distribution systems. In order to solve this problem, the phenomena of occurrence of refusals in low-voltage electrical distribution systems, conditioned by different influencing factors, processed and mathematically modelled. The main results of the research consist in establishing the static characteristics of the refusals, the mathematical models that determine the occurrence of the cause phenomena and the parameters that characterize the distributions of the refusals, depending on the occurrence per system, depending on the occurrence per season, depending of interruptions duration and the number of affected consumers. The significance of the results obtained consists in solving a number of problems faced by the operating services of electrical distribution systems, concerning the assurance of reliability of operation, providing the possibility of forecasting and preventing the occurrence of the phenomena of occurrence of refusals, which enable the justified planning of prophylactic measures and ensuring the reliability level.

Mathematical analysis of an electric car in the aspect of the application of renewable energy sources

This paper presents a model of an electric car based on the BMW i3 whose low-voltage electrical system and traction battery were supported by a photovoltaic system installed on the body of the vehicle. The photovoltaic system was installed on the roof, side doors and bonnet. The 350 Wp (Watts peak) system was made of semiflex panels. The input parameters for the model were the measurements taken during the simulated annual operation of the vehicle as driving time, weather conditions and their switching times. During stationary tests, the power of individual electrical consumers was measured and its maximum was 1.1 kW. The model included data on the electricity consumption for driving a given distance. The amount of electricity generated by the photovoltaic system was related to a stationary system of 4 kWp. The degree of shading and curtailment of energy generated by the photovoltaic system was measured during testing on a vehicle driving in urban conditions. In the vehicle under analysis, an additional energy stream supplied the 12 V electrical consumers and recharged the battery. The traction battery used to drive the vehicle during such a power supply scenario may increase the vehicle range by about 16% on average.

Joule Heating and Arc-Fault-Induced Electrical Fires for Commercial-Grade Copper and Brass in Low-Voltage Electrical Systems

Electrical fires are usually caused by contact heating, for which the mechanism of heat accumulation is currently not well understood. Previous studies done by many researchers were able to recognize the pattern of the electrical waveform, but the actual mechanism behind such phenomenon is still a mystery. This research focuses on electrical plugs and sockets made from copper and electrical brass, which are the main components where unsupervised electrical fires often occur due to mechanical wear and electrical breakdown. We performed experiments using commercial-grade replacement electrical sockets and plugs made primarily to be compliant with Japan Industrial Standards. Oxides of the materials were formed by subjecting the samples to variable amounts of current and repeatedly making and breaking contact to create an electrical discharge. The copper(I) oxide that formed due to electrical discharge was found to have intrinsic semiconductor properties that played a critical role in electrical fires involving copper components. Poor contacts exhibited distinct behavior, such as contact vibration which also exacerbated the deterioration. From these findings, we concluded that any contact surface made of copper or a copper alloy may have a greater risk of starting an electrical fire than other types of material when a certain arcing condition is met.

A Mixed-integer Linear Programming Model for the Plug-in Electric Vehicle Charging Problem in Unbalanced Low Voltage Electrical Distribution Systems Considering Neutral Conductor

The increasing penetration of plug-in hybrid electric vehicles (PHEVs) imposes new challenges in low voltage distribution networks (LVDNs), due to worsening load imbalance, power losses, and increased probability of blackouts because of the overloads. To overcome these issues, PHEV charging must be performed in a coordinated fashion. In this context, there are several coordinated charging methods in the literature, none of which considers modeling neutral conductors of LVDN.This paper aims to present a mixed-integer linear programming model (MILP) for the PHEV charging problem in unbalanced LVDNs, considering the neutral conductor. In this regard, the main parameters of unbalanced LVDN, such as voltage profile and power loss, are examined with and without modeling the neutral conductor. The results indicate that it is required to consider the neutral conductor to achieve realistic values of the LVDN's parameters. The proposed model is applied to a 449-nodes smart distribution grid consisting of 31 nodes at a medium voltage (MV) level and 418 nodes at a low voltage (LV) level. To verify the performance of the proposed model, it is compared with two uncoordinated charging methods. The results show the effectiveness of the proposed strategy.

Briefly Discussion on the Development and Trend of Low Voltage Electrical System Energy Saving Technology

Briefly Discussion on the Development and Trend of Low Voltage Electrical System Energy Saving Technology

Effects of Demand Fluctuation and Mitigation Strategy in Low Voltage EV Charging Station by Battery Energy Storage System

In this paper, the effects of fluctuating demand on a low voltage electric utility system equipped with electric vehicular charging station have been studied and mitigation strategy has been proposed. By applying Battery Energy Storage System (BESS) and demand management (DMM), the stored electric energy during an off-peak period is controlled to supply the spiky demand during the EV charging period. Employing different approaches of discharging control, the BESS can response and shape the peaky demand into the smoothed one with an elevated load factor. Therefore, the result is that energy cost of EV charging has been reduced by cutting the demand charge during the on-peak period and the power quality of the system has also been improved. These findings are confirmed and illustrated by simulation results.

Effects of ultrahigh permittivity ceramic on water freezing by high voltage electric field-assisted freezing system

• High voltage electric field-assisted freezing (HVEFF) on water sample was studied. • Ultra-high permittivity ceramic (UHPC) was used for the 1 st time in the freezing. • Decreasing percentage of supercooling degree was 90.3% under UHPC-HVEFF at 9 kV. • UHPC greatly improved water freezing performance when integrated to HVEFF. • UHPC possessed potentials for enlarging the sample-treating capacity of HVEFF. To investigate the effect of ultra-high permittivity ceramic (UHPC) on water freezing, a UHPC-based high voltage electric field-assisted freezing system (UHPC-HVEFF) and a low permittivity acrylic-based high voltage electric field-assisted freezing system (LPA-HVEFF) were developed. The freezing behaviours of water under UHPC-HVEFF and LPA-HVEFF at 0, 3, 6, 9 kV were comparatively studied. Hierarchical cluster analysis (HCA) was used to visualize the difference between UHPC-HVEFF and LPA-HVEFF. COMSOL was used to simulate the distribution of electric field strength in the water sample under HVEF. It was found that the decreasing percentage of the supercooling degree of the water reached 34.9%, 89.2% and 90.3% under UHPC-HVEFF at 3, 6 and 9 kV, respectively, whereas those were only 2.40%, 10.4% and 24.6% under LPA-HVEFF at 3, 6 and 9 kV, respectively. Results from the simulation indicated that the electric field strength in the water under UHPC-HVEFF was on average 11.7-7.5 times that of LPA-HVEFF, thus contributing to the high freezing efficiency of UHPC-HVEFF. This study indicated that UHPC possessed great potential to increase the sample-treating capacity of HVEF-assisted freezing system.

Research on the Application of Intelligent Technology in Low Voltage Electric Automation Control System

Based on the background of intelligent technology, the paper describes in detail the architecture and main functions of the electrical automation control system, including data collection, information transmission, electrical control, etc., based on the principles of stability and scalability in the design of low-voltage electrical automation control systems. Design and implementation of the thesis is to explore the performance of the designed system and select the application examples of the electrical automation control system for analysis. The research results show that the electrical automation control system we designed meets the requirements of artificial intelligence regulation and can effectively improve the safety of the system.

Interline Power Flow Controller with Control strategy to limit Fault Current in Electrical Distribution System

In this article, Interline power flow controller (IPFC) has been recommended to limit the short circuit current (SCC) in low voltage (LV) electrical distribution system. Industrial loads are increasing due to various reasons in the distribution system. It leads to the power requirement at the distribution system level. Therefore, there is a scope for increase in the fault current. Due to the increased fault current, the protection of switchgear is vital. A simple control strategy wth IPFC is proposed in the distribution system to limit the fault current. Low voltage distribution system i.e 800 MW thermal power plant water system LV distribution system is considered for demonstrating the effectiveness of the IPFC. Short circuit analysis is performed without and with the IPFC by applying ETAP and MATLAB (SIMULINK). The simulation results are compared. Further, the effect of different ratings of standard transformers is also analyzed. It is noticed that the control strategy with IPFC can limit the fault current.

Power Quality Investigation of Single Phase Grid-connected Inverter of Photovoltaic System

There is a growing demand for renewable energy resources in countries all around the world. Among renewable energy resources, solar energy is a prominent and promising alternative to meet future electricity needs. Recently, the renewable energy regulations in Jordan have been modified to allow customers to install their own photovoltaic (PV) generators to cover their full energy consumption. This study investigated the power quality profile of single-phase grid-connected PV system in a typical Jordanian low voltage electrical system. The following electrical parameters were monitored: voltage, current, harmonics contents, total harmonics distortion (THD), active power, reactive power, and power factor. Detailed investigations and analyses were made.

Optimal renewable generation and battery storage sizing and siting considering local transformer limits

In response to climate change and sustainability challenges, various incentive programs have increased solar photovoltaic (PV) generation interconnection in the low voltage electrical distribution system. However, electric utility support of PV generation is limited by reverse power flow into the electricity network at high penetration levels. This limits the ability to achieve Zero Net Energy (ZNE) behind individual meters and in whole communities. In parallel, district level energy systems, and Advanced Energy Communities (AEC) that include storage, offer a great prospect for integrating high levels of Distributed Energy Resources (DER) into the built environment. Optimally designing such systems to serve communities, commercial, and industrial loads, while maximizing the penetration of solar PV, has been a challenge to Distribution System Operators (DSO) and city planners. This paper proposes a Mixed Integer Linear Program (MILP) optimization to decide the best DER portfolio, allocation, and dispatch, for an AEC that achieves ZNE and islanding while respecting electrical grid operational constraints, with a focus on distribution transformer overloads. The main strategies to avoid transformer overloads were found to be judicious sizing and siting of battery energy storage and also optimally re-distributing PV throughout the community, which increased the ability of the electric infrastructure to support a PV deployment that is 1.7 times larger than the existing transformer capacity without the need for infrastructure upgrades. This work highlights the importance of including local infrastructure capacities, such as distribution transformer constraints when developing projects that result in high renewable penetration throughout the distribution network.

Estudio y diseño del Sistema de Tierra Integral de la Facultad de Ingeniería de la Universidad Autónoma de Campeche

Nowadays, low voltage electrical systems are more complex due to sensitive non-linear loads to voltage variations due to disturbances or poor quality of power in the electricity supply network, so it is necessary to protect equipment people who use these electrical installations every day. This paper presents a study to design the equipotential grounding system of the Faculty of Engineering of the Campeche´s Autonomous University in order to obtain an earth impedance value that complies with the standards NXM-J-549-ANCE-2005 and NOM-001-SEDE-2012 to provide safety conditions to people and equipment operating in the electrical installation in low voltage, quickly draining the fault, making the value of the voltage with respect to the earth reached in the part failure is equal to or less than the safety value and offer the corrective measures to improve the quality of the energy, which we receive from the supplier company. This study is the basis to implement a model of integral earth system for any type of buildings in our environment to achieve stable voltage levels at a constant frequency.

A cascade-type hierarchical fuzzy system with additional defuzzification of layers for the automatic power quality diagnosis

In general the power quality diagnosis of low-voltage electrical systems is a difficult issue due to the nuances of different power quality standards around the world and the uncertainties characteristics of the evaluation parameters. In this framework, this paper proposes a new methodology for diagnosing the power quality by means of a cascade-type hierarchical fuzzy system with additional defuzzification of layers (C-HFS-ADL), also proposed in this paper, which is able to evaluate the power quality indices in steady-state (total harmonic distortions, power factor, voltage variation, and unbalance voltage) considering several standards and provides a proper and complete diagnosis of the power quality in electrical systems. In the proposed C-HFS-ADL each output of a subsystem is transferred between inner layers of the hierarchical system and a total power quality diagnosis is obtained taking into account a secondary decision-making process with additional defuzzification in order to have a partial diagnosis for each subsystem of the hierarchy. In addition, an algorithm was implemented considering different inference systems for analyzing the behavior of the C-HFS-ADL on a database (power quality indices) obtained from a real electrical substation for observing its advantages and disadvantages.

Calibration of Residual Current Device (RCD) Testers

Residual current devices (RCDs) are commonly used in low voltage electric power systems, including our households, as protective devices against electric shock. They monitor the balancing current b...

A New Approach to Improve PV Power Injection in LV Electrical Systems Using DVR

With increasing photovoltaic (PV) penetration in low-voltage (LV) distribution networks, voltage violation during the peak PV generation period is one of the main power quality concerns. To minimize the PV power curtailment caused by voltage violations, this paper proposes a new approach utilizing one dynamic voltage restorer (DVR) at the secondary of an existing urban distribution transformer as a continuous voltage compensator with an accompanying control algorithm. The voltage compensation algorithm controls the DVR in real-time to prevent over-voltage and under-voltage at all network nodes, thereby maximizing PV injection and preventing equipment damage. The controller uses the equivalent line impedance of network to estimate the average voltage of load points without the need for any communication links for measuring load voltages. In this approach, the fixed tap changer of the distribution transformer is also optimally adjusted to minimize the DVR rating using a proposed offline optimization method. Simulation results on IEEE LV test feeder prove the ability of the DVR in maintaining all network node voltages within the allowable range in peak demand and peak PV generation periods with the benefit of injecting only a small amount of active and reactive power to the system, in contrast to alternative algorithms.

Noninvasive Current Sensor for Multicore Cables

Multicore cables are widely used in medium- and low-voltage electric power systems. Current measurement of individual conductors in such cables is especially useful for various advanced applications but technically difficult to implement. Since existing current sensing devices are designed for a single conductor, one has to break the cable enclosure or connector to access individual conductors for current measurement, which is practically infeasible. A noninvasive current sensor for multicore cables is proposed, designed, implemented, and verified in this paper. It is able to measure the magnetic field outside the cable using a sensor array and reversely calculate the currents on individual conductors. It is easy to install and adapt multiple cable specifications. Such a device is able to determine current phasors, perform harmonic analysis, and detect current disturbance with sufficient accuracy. The effectiveness of the proposed approach is validated by both laboratory experiment and field test.

Mitigation Emission Strategy Based on Resonances from a Power Inverter System in Electric Vehicles

Large dv/dt and di/dt outputs of power devices in the DC-fed motor power inverter can generate conducted and/or radiated emissions through parasitics that interfere with low voltage electric systems in electric vehicles (EVs) and nearby vehicles. The electromagnetic interference (EMI) filters, ferrite chokes, and shielding added in the product process based on the “black box” approach can reduce the emission levels in a specific frequency range. However, these countermeasures may also introduce an unexpected increase in EMI noises in other frequency ranges due to added capacitances and inductances in filters resonating with elements of the power inverter, and even increase the weight and dimension of the power inverter system in EVs with limited space. In order to predict the interaction between the mitigation techniques and power inverter geometry, an accurate model of the system is needed. A power inverter system was modeled based on series of two-port network measurements to study the impact of EMI generated by power devices on radiated emission of AC cables. Parallel resonances within the circuit can cause peaks in the S21 (transmission coefficient between the phase-node-to-chassis voltage and the center-conductor-to-shield voltage of the AC cable connecting to the motor) and Z11 (input impedance at Port 1 between the Insulated gate bipolar transistor (IGBT) phase node and chassis) at those resonance frequencies and result in enlarged noise voltage peaks at Port 1. The magnitude of S21 between two ports was reduced to decrease the amount of energy coupled from the noise source between the phase node and chassis to the end of the AC cable by lowering the corresponding quality factor. The equivalent circuits were built by analyzing current-following paths at three critical resonance frequencies. Interference voltage peaks can be suppressed by mitigating the resonances. The capacitances and inductances generating the parallel resonances and responsible elements were determined by the calculation through the equivalent circuits. A combination of mitigation strategies including adding common-mode (CM) ferrite chokes through the Y-caps and the AC bus bar was designed to mitigate the resonances at 6 MHz, 11 MHz, and 26 MHz related to the CM conducted emission by IGBT switching and the radiated emission of the AC cable. The values of Z11 decreased respectively by 15 dB at 6 MHz, 0.4 dB at 11 MHz, and 11.5 dB at 26 MHz and the values of S21 decreased respectively by 8.6 dB at 6 MHz, 7 dB at 11 MHz, and 6.3 dB at 26 MHz. An equivalent model of the power inverter system for real-time simulation in time domain was built to validate the mitigation strategy in simulation software PSPICE.

Czynnik ludzki a skuteczność ochrony przeciwporażeniowej użytkowników prądu elektrycznego w obiektach budowlanych

Opracowanie prezentuje środki ochrony przeciwporażeniowej stosowane w instalacjach elektrycznych niskiego napięcia w aspekcie ich nieskuteczności w odniesieniu do wybranych sytuacji. W pierwszej części artykułu scharakteryzowano powody zapobiegania przepływowi prądu elektrycznego przez organizm ludzki. Jednocześnie opisano sposoby zapobiegania niekorzystnemu oddziaływaniu prądu na użytkownika urządzeń elektrycznych w instalacjach o napięciu do 1 kV. Końcowa część pracy zawiera zestawienie przypadków, w których zastosowane środki stają się nieskuteczne oraz analizę przyczyn powstawania wypadków.