Low-voltage Power Systems Research Articles

Study on Smart Object-Based Control Model for Cyber-Physical Systems

The cyber-physical systems (CPS) are large-scale intelligent complex systems by the deep integration of technology and the physical systems. The cyber-physical power systems (CPPS) are the key technology to implement the objective of smart grids, by seamlessly integrating the computing, communication and sensing technologies with the power system. The existing research of CPPS is limited to the survey. This paper firstly presents the concept of smart power object applied to CPPS, which often is a power device object adopts RFID technology to identify itself, feeds back its real-time states, and has certain coordination ability. Then, on this basis, the key technical problems of global optimization and local control based on CPPS is further studied, such as control model, construction strategy, coordination control mechanisms, and communication mechanisms. Finally, it is applied to regional voltage optimization control to implement smart optimization control in low voltage power system.

Research on Optimization Design of Low-Voltage Circuit Breaker Power System

A parametric model of a kind of low-voltage circuit breaker was set up by virtual prototyping technology software ADAMS, and the simulation of the low-voltage circuit breaker system’s dynamic characteristics was successfully run to confirm the parametric model. Because it was easy for contact heads to produce arc during closing, the power spring system was designed and researched in order to obtain the parametric sensitivities. Based on the difference of parametric sensitivities, the rotational angular velocity of the moving contact heads was regarded as the objective function, and the optimization design of circuit breaker power system was completed. Optimized system ensured reliable contact and shortened the arc time of the static and dynamic contact heads during closing, avoiding phenomenon as rebound repeatedly beating of the contact heads, continued arcing and temperature sharp rising, etc. The analysis had guide significance for improving the safe reliability and operating life of the low-voltage circuit breaker, and provided a good platform for the further produce development and optimization design.

Active power estimation of photovoltaic generators for distribution network planning based on correlation models

For the last years, PV (photovoltaic) generation has been having an important impact on LV (low voltage) and MV (medium voltage) grids in Spain, due to the increasing number of installations. As power monitoring of the generation is in most cases not required, utilities are forced to make assumptions on PV power generation in order to perform network planning studies for both peak demand and contingency analysis. These assumptions increase errors committed during the analysis, as the number of PV installations increases. This paper presents a methodology for estimating PV active power generation values for planning purposes in MV and LV power systems, from historic generation data, based on the development of correlation models. This methodology is applied to three different examples, using predictors based on real registered data. The methodology was also applied in a typical grid study and it's error was determined.

Extended smart meters‐based remote detection method for illegal electricity usage

Power delivery systems that use power lines can communicate with other electrical systems, monitor the quality of electrical energy and provide an economical solution for automatic meter reading (AMR). Energy meters can be connected to a low-voltage power system by power line carriers for all consumers. Illegal electricity usage in the power delivery system can be easily detected if AMR is installed in the system, which consists of a terminal smart meter (TSM) and a gateway smart meter (GSM). This study proposes a novel remote detection method for illegal electricity usage that uses both TSM and GSM, where the TSM and the GSM are installed on the power system of each consumer and on the node of the power system feeder, respectively. TSM and GSM simultaneously disconnect an electrical source for a very short period of time. After this, the proposed detection method sends a low-voltage signal with a high frequency from the TSM to the GSM during the time of disconnection. Once the signal has passed, the proposed detection method detects illegal electricity usage by measuring the amount of time it was disconnected. This study presents the structure of the proposed detection method as well as the mathematical model, proof, simulation and experimental results.

Modeling and Simulation of All-Electric Ships With Low-Voltage DC Hybrid Power Systems

DC hybrid power systems are of interest for future low emission, fuel-efficient vessels. In spite of the advantages they offer onboard a ship, they result in a complex, interconnected system, which requires effective analysis tools to enable a full realization of the advantages. Modeling and simulation are essential tools to facilitate design, analysis, and optimization of the system. This paper reviews modeling of hybrid electric ship components including mechanical and electrical elements. Power electronic converters are modeled by nonlinear averaging methods to suit system-level studies. A unified model for bidirectional converters is proposed to avoid transitions between two separate models. A simulation platform using the derived models is developed for the system-level analysis of hybrid electric ships. Simulation results of power sharing among two diesel generators, a fuel cell module, and an energy storage system are presented for three modes of operation.

Hardware-in-the-loop simulation applied to protection devices testing

Circuit breakers are ubiquitous elements used for ensuring safe operation of low-voltage power systems. Nowadays the loads supplied by the power systems migrate towards exhibiting significant strong nonlinear behavior accompanied by inrush currents or high-order harmonics that can cause a false tripping of circuit breakers. It is thus necessary to study the interaction between these new loads and the protection devices in order to fully assess their compatibility. Following this context, this paper deals with a new test rig dedicated to protection switching devices, which is based on the hardware-in-the-loop real-time simulation concept. The proposed approach is focused on replicating the tripping conditions of a real circuit breaker coupled to a power system emulated by means of a real-time simulator. The software part of this simulator adds flexibility to the test rig as the circuit configurations and the operating scenarios may conveniently be adapted at lowest cost. The control of the interface between the software simulator and the hardware under test, as well as the closed-loop stability issues, has been thoroughly approached. Experiments carried out on this test rig show the effectiveness of this new test prototyping concept in characterizing real circuit breakers behavior when they protect lighting circuits.

Study on a New Low-Voltage Residual Current Protective System

A new theory of leakage protection was presented for the low-voltage power system. The corresponding circuit model was established, then the operational principle was analyzed and the experiment was researched in this paper. The results showed: when the single-phase leakage occurred, the leakage current will be greatly reduced before the protective system shut off the power source. And the power source cannot shut off immediately in the good isolation, which can keep the important load operating normally. At the same time, the protective system can detect the useful signal, which can warn immediately.

An Active Power Filter Controller Based on Dual-DSPs in Low-Voltage Power System

To compensate harmonics from nonlinear load, the controller of Active Power Filter (APF) need to detect harmonic and generate compensation current in high speed. APF controller functions are divided into two parts: outside controller part and inside controller part. Inside controller part detect harmonic current and control the IGBT to generate grid harmonics current. Outside controller part detect common power parameters and generate signal of management in main circuit. An experiment circuit of APF Controller is established. Some experiments are presented here.

저압설비 플리커 특성평가를 위한 국내 저압계통 기준 임피던스 산정 연구

The reference impedances which is about 95% supply impedance value of residential consumers’ supply impedances was published by IEC in 1980. The reference impedances are the standard values for use in determining the voltage disturbance characteristics of electrical equipment like the flicker. In IEC 60725, the reference impedances for premises having service current capacities less than 100A per phase and for service current capacities more than 100A per phase are recommended. And these reference impedances are targeted for the countries using 50㎐ power frequency. Because of the frequency difference, the reactance values of the reference impedances will be increased in 60㎐ power system like Korea, And also the reference impedances are different significantly each other according to declared voltage variation, power consumption and service wire length etc. Therefore It is needed to calculate the reference impedances suitable for domestic low-voltage power system. In this paper, the reference impedances for service current capacities less than 100A in 220/380V, 60㎐ single-phase two wire and three-phase four wire low-voltage system are calculated, And the equations for service current capacities more than 100A to calculate the modulus value of maximum supply impedances are suggested base on IEC 60725 and the reference impedances for those are calculated on service current of 100A per phase.

MEDIDA DE ENERGÍA EN CONDICIONES DE DISTORSIÓN Y DESEQUILIBRIO

Nowadays the study of power quality is a critical issue due to the proliferation of “nonlinear” consumers connected to the grid, most of them electronic loads which produce voltage and current waveforms distortion, causing a worse operation of the power system and leading to higher losses. At present, “bad customers” of power energy are only penalized due to reactive power consumption. The measurement of this consumption is made by using conventional energy meters designed to operate under sinusoidal and balanced systems with parametres within the required limits. In this paper the experimental validation of these devices in low voltage power systems with harmonic distortion and imbalance is carried out. Finally, a new ratio is proposed for the electrical billing, to penalize at the same time the reactive power consumption, the harmonic pollution and the imbalance.

Influence of Combination Wave Generator's Current Undershoot on Overvoltage Protective Characteristics

Evaluation of the ability of equipment to withstand a wide variety of surges that can be expected to occur in low-voltage ac power systems, or of the performance of surge protective devices (SPDs) in dealing with this variety of surges, can be facilitated by a reduction of the database to a few representative stresses. IEEE Std. C62.41.2 and IEC Std. 61000-4-5 define the combination wave surge as a standard surge-testing waveform. However, these standards define different tolerances regarding the waveform undershoot of a short-circuit current surge delivered by the combination wave generator (CWG). In this paper, the influence of CWG short-circuit current undershoot has been analyzed for the case of one-stage protection with SPD located at the service entrance of the building. Simulation results for the model of the observed system in the Alternate Transients Program/Electromagnetic Transients Program and MATLAB, with experimental verification show that the short-circuit current undershoot of CWG has an influence on maximal values of voltages across load and energy deposited in SPDs.

Of International Terminology and Wiring Methods Used in the Matter of Bonding and Earthing of Low-Voltage Power Systems

The worldwide global market requires electrical engineers to have a deep understanding of the bonding and earthing practices adopted in different countries around the world. This knowledge is essential to obtain effective designs and high safety standards and can promote the elimination of technical obstacles that can still create market barriers. The full comprehension of the “grounding” theory requires the command of key technical concepts regarding the earthing methods, which may cause confusion when used in the North American technical realm rather than in the International Electrotechnical Commission (IEC) world. This issue is further worsened by the lack of literature in this matter, as well as of harmonization documents between national codes and international standards. This paper, by analyzing the protection against indirect contact in ac (50/60-Hz) low-voltage power systems by automatic disconnection of supply, seeks to clarify both the terminologies and each type of grounding system adopted in IEC standards, with the intent to create a common reference for practicing engineers in the matter of bonding and earthing of power systems. Major differences encountered between sizing procedures adopted in IEC standards and the North American National Electrical Code are also examined.

Analysis of a Liquid Metal Current Limiter

A liquid metal fault current limiter (LMFCL) was investigated as a tool for improving the power quality and reliability of power service. The LMFCL is a newly developed current limiter for low-voltage power systems. It can effectively limit the fault current by taking advantage of the pinch effect and arcs in the LMFCL. A multiphysics simulation of magneto-fluid in the LMFCL was performed based on the 3-D finite element method for analysis of the pinch effect. The magnetic forces were calculated, and the turbulence driven by the magnetic forces was simulated. The results of the turbulent simulation coincide with those of the experiments. Several characteristics of the LMFCL are described based on analysis of the results of experiments with single-phase power sources of 253, 440, and 725-V.

Influence of line routing and terminations on transient overvoltages in LV power installations

AbstractIEC 62305‐4 gives the rules for the selection and the installation of surge protective devices (SPDs), where the maximum enhancement factor is considered to be equal to 2 in the worst case of open‐circuit condition. The objective of the present paper is to check this relation for equipment connected to low‐voltage (LV) power system. The LV power system is considered as TN‐S system with different routings in three‐ and six‐storey buildings. The terminals of apparatus are substituted by a variety of different loads, namely, resistances, inductances, and capacitances. All Maxwell's equations are solved by the method of moments (MoM) and the voltage is calculated at the apparatus terminals. The SPD itself is simulated by a voltage source at the ground floor. The results reveal that the voltage at the apparatus terminals may overshoot the SPD protection level by a factor of 3 irrespective of the number of floors and loops. Copyright © 2008 John Wiley & Sons, Ltd.

Higher voltage aircraft power systems

Modern aircraft designs are focused on minimising the use of engine bleed air, eliminating gearboxes, and reducing the reliance on hydraulic systems. Instead, many of these mechanical systems will be replaced with electrical versions. The increasing amounts of electrical power that will be shipped through an aircraft means that it is increasingly difficult to rely on low voltage power systems owing to voltage drop and weight constraints. This discusses the challenges that relate to the safe use of higher voltage systems within aircraft.

Implementation and Performance of an Anti-Resonance Hybrid Delta-Connected Capacitor Bank for Power Factor Correction

This paper presents a new three-phase anti-resonance hybrid delta-connected capacitor bank for power factor correction in low-voltage industrial power systems. In general, shunt capacitors connected in series with reactors should be designed carefully before installation in order to avoid series and/or parallel harmonic resonance between the capacitors and system inductances. However, the system parameters vary dynamically according to the power system configurations and loads. Consequently, harmonic resonance might occur after the capacitors have been installed. The main objective of the proposed hybrid capacitor bank is to compensate for reactive power without any harmonic resonance. The hybrid capacitor bank is a combination of delta-connected capacitors connecting in series with three small-rating single-phase inverters without any matching transformer. The inverter is used to improve the characteristics of the capacitors. This paper deals with the implementation and control of the hybrid capacitor bank. Experimental results verify the viability and the effectiveness of the proposed anti-resonance hybrid delta-connected capacitor bank for reactive power compensation.

Enhancement of the SPD Residual Voltage at Apparatus Terminals in Low-Voltage Power Systems

Surge protective devices (SPDs) are installed at the boundaries of lightning protection zones to damp the surges to the protection level of the SPD. If the circuit between the SPD and the apparatus to be protected is too long, the propagation of the surges leads to oscillation phenomenon. In this case, the overvoltage can be increased at the apparatus terminals. The increase is taken into account by an enhancement factor which gives the ratio of the maximum overvoltage at the apparatus terminals to the SPD protective level. According to IEC 62305-4, the maximum enhancement factor is considered to be equal to two in the worst case of the open-circuit condition. The objective of this paper is to check this relation for equipment connected to low-voltage (LV) power systems. The LV power system is considered as a TN-S system with different routings in three- and six-story buildings. The terminals of apparatus are substituted by a variety of different loads. All Maxwell's equations are solved by the method of moments and the voltage is calculated at the apparatus terminals. The SPD itself is simulated by a voltage source at the ground floor of the building. The results reveal that the voltage at the apparatus terminals may overshoot the SPD protection level by a factor of 3.

Power anomaly effects and costs in low-voltage mobile power systems

Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales.

각종 시설물 전원계통의 전압과 전류고조파 실태

This paper presents the actual conditions and reform measures of voltage and current harmonics being made in low-voltage power systems supplying various loads. The measurements were carried out at the secondary output terminals of 22.9[kV]/380[V]220[V] customer`s transformers, and the results were discussed on the basis of the comparison with IEEE and IEC harmonics control standards. The voltage THDs of the power systems employed in this survey were less than that is considered to be acceptable. On the contrary, the current distortions were significantly greater than the voltage distortions, and the current THDs were distributed over the wide-range from 15.7 to . In particular, the current distortion on the low voltage power lines of office buildings in which many PC and fluorescent lamps are used is remarkably more serious than that of factory facilities. As a result, the voltage distortion factors are observed within the range of its allowable level or less than the limits, but the current distortion factors are significantly greater than the limits of IEEE and IEC standards.

Analysis and design of low-voltage power systems: an engineer's field guide

Analysis and design of low-voltage power systems: an engineer's field guide