变压器空载时投入并联电容器可能发生铁磁谐振

文章论述了空载电力变压器上投人并联电容器时,此一回路可能发生铁磁谐振的原因、条件、可能的危害、防止方法以及处理此类故障的措施等。目的在于提供使用移相电容器单位运行参考。

35 kV电容器组串联电抗器的异常分析及改进

传统的并联电容器具有操作简便、成本低廉的优点,但如果容量选择不正确,可能导致电网中的谐波被过度放大,威胁电网的安全性,因此,电容器串联电抗器非常重要。本文介绍如何通过调整串联电抗器的电抗率来有效抑制谐波,以解决实际工程中电抗率因选择不当而导致的异响问题。

500kV变电站35kV配电装置优化设计研究

在全面调研新型35 kV开关设备及无功补偿设备的基础上,提出将35 kV封闭组合电器(Hybrid Gas Insulated Switchgear,HGIS)、磁屏蔽并联电抗器及紧凑型框架式并联电容器应用于500 kV变电站低压侧的新型应用方案,并对35 kV配电装置进行优化,节约占地面积。

Comparative study of effectiveness of different var compensation devices in large-scale power networks

A comparison of the effectiveness of installing reactive power compensators,such as shunt capacitors,static var compensators(SVCs),and static synchronous compensators(STATCOMs),was presented in large-scale power networks.A suitable bus was first identified using modal analysis method.The single shunt capacitor,single SVC,and single STATCOM were installed separately on the most critical bus.The effects of the installation of different devices on power loss reduction,voltage profile improvement,and voltage stability margin enhancement were examined and compared for 57-and 118-bus transmission systems.The comparative study results show that SVC,and STATCOM are expensive compared to shunt capacitor,yet the effect of installing STATCOM is better than SVC and the effect of installing SVC is better than that of shunt capacitor in achieving power loss reduction,voltage profile improvement and voltage stability margin enhancement.

Power loss reduction of distribution systems using BFO based optimal reconfiguration along with DG and shunt capacitor placement simultaneously in fuzzy framework

In distribution systems,network reconfiguration and capacitor placement are commonly used to diminish power losses and keep voltage profiles within acceptable limits.Moreover,the problem of DG allocation and sizing is great important.In this work,a combination of a fuzzy multi-objective approach and bacterial foraging optimization(BFO) as a meta-heuristic algorithm is used to solve the simultaneous reconfiguration and optimal sizing of DGs and shunt capacitors in a distribution system.Each objective is transferred into fuzzy domain using its membership function.Then,the overall fuzzy satisfaction function is formed and considered a fitness function inasmuch as the value of this function has to be maximized to gain the optimal solution.The numerical results show that the presented algorithm improves the performance much more than other meta-heuristic algorithms.Simulation results found that simultaneous reconfiguration with DG and shunt capacitors allocation(case 5) has 77.41%,42.15%,and 56.14%improvements in power loss reduction,load balancing,and voltage profile indices,respectively in 33-bus test system.This result found 87.27%,35.82%,and 54.34%improvements of mentioned indices respectively for 69-bus system.

Preparation and properties of pitch carbon based supercapacitor

Using the mesophase pitch as precursor, KOH and CO2 as activated agents, the activated carbon electrode material was fabricated by physical-chemical combined activated technique for supercapacitor. The influence of activated process on the pore structure of activated carbon was analyzed and 14 F supercapacitor with working voltage of 2.5 V was prepared. The charge and discharge behaviors, the properties of cyclic voltammetry, specific capacitance, equivalent serials resistance （ESR）, cycle properties, and temperature properties of prepared supercapacitor were examined. The cyclic voltammetry curve results indicate that the carbon based supercapacitor using the self-made activated carbon as electrode materials shows the desired capacitance properties. In 1 mol/L Et4NBF4/AN electrolyte, the capacitance and ESR of the supercapacitor are 14.7 F and 60 mΩ respectively, The specific capacitance of activated carbon electrode materials is 99.6 F/g; its energy density can reach 2,96 W.h/kg under the large current discharge condition, There is no obvious capacitance decay that can be observed after 5000 cycles, The leakage current is below 0,2 mA after keeping the voltage at 2.5 V for l h, Meanwhile, the supercapacitor shows desired temperature property; it can be operated normally in the temperature ranging from -40 ℃to 70 ℃,

Particle swarm optimization algorithm for simultaneous optimal placement and sizing of shunt active power conditioner(APC)and shunt capacitor in harmonic distorted distribution system

Due to development of distribution systems and increase in electricity demand,the use of capacitor banks increases.From the other point of view,nonlinear loads generate and inject considerable harmonic currents into power system.Under this condition if capacitor banks are not properly selected and placed in the power system,they could amplify and propagate these harmonics and deteriorate power quality to unacceptable levels.With attention of disadvantages of passive filters,such as occurring resonance,nowadays the usage of this type of harmonic compensator is restricted.On the other side,one of parallel multi-function compensating devices which are recently used in distribution system to mitigate voltage sag and harmonic distortion,performs power factor correction,and improves the overall power quality as active power conditioner(APC).Therefore,the utilization of APC in harmonic distorted system can affect and change the optimal location and size of shunt capacitor bank under harmonic distortion condition.This paper presents an optimization algorithm for improvement of power quality using simultaneous optimal placement and sizing of APC and shunt capacitor banks in radial distribution networks in the presence of voltage and current harmonics.The algorithm is based on particle swarm optimization(PSO).The objective function includes the cost of power losses,energy losses and those of the capacitor banks and APCs.

A Parallel Approach for Real-Time Power Flow in Distribution Networks

The new reality of smart distribution systems with use of generation sources of small and medium sizes brings new challenges for the operation of these systems. The complexity and the large number of nodes requires use of methods which can reduce the processing time of algorithms such as power flow, allowing its use in real time. This paper presents a known methodology for calculating the power flow in three phases using backward/forward sweep method, and also considering other network elements such as voltage regulators, shunt capacitors and sources of dispersed generation of types PV （active power and voltage） and PQ （active and reactive power）. After that, new elements are introduced that allow the parallelization of this algorithm and an adequate distribution of work between the available processors. The algorithm was implemented using a multi-tiered architecture; the processing times were measured in many network configurations and compared with the same algorithm in the serial version.

Harmonic Filter Design to Mitigate Two Resonant Points in a Distribution Network

This paper investigates the usage of passive harmonic filters to mitigate harmonic distortions when two resonant points are present in a system caused by shunt capacitors used for power factor correction and bus voltage regulation. Six scenarios were investigated using DIgSILENT 14 power factor）＇ software. The investigations are with and without power factor correction and capacitors used to increase bus voltage. Passive harmonic filters are designed to reduce harmonic distortions at the PCC （point of common coupling） to fall within the IEEE 519 harmonic voltage and current limits caused by parallel resonance. The results of the case studies are analysed to evaluate the effectiveness of the filter design.

A New Configuration for Planar Magnetic Elements to Reduce Capacitive Couplings

This paper presents an analysis of planar magnetic element configurations in order to reduce capacitive couplings between the windings. The capacitive couplings between layers of planar magnetic elements introduce a stray capacitor which can conduct high frequency currents when high dv/dt voltage is applied. High frequency current may cause electromagnetic interference （EMI） and harmonic problems. The investigation and simulation results, both 2D and 3D Finite Element （FE） show the effect of shifting the planar layers in reduction of the capacitive couplings. The simulation results are compared with test results to validate the proposition.

High Speed Column-Parallel CDS/ADC Circuit with Nonlinearity Compensation for CMOS Image Sensors

A high speed column-parallel CDS/ADC circuit with nonlinearity compensation is proposed in this paper.The correlated double sampling (CDS) and analog-to-digital converter (ADC) functions are integrated in a threephase column-parallel circuit based on two floating gate inverters and switched-capacitor network.The conversion rate of traditional single-slope ADC is speeded up by dividing quantization to coarse step and fine step.A storage capacitor is used to store the result of coarse step and locate the section of ramp signal of fine step,which can reduce the clock step from 2 n to 2 (n/2+1).The floating gate inverters are implemented to reduce the power consumption.Its induced nonlinear offset is cancelled by introducing a compensation module to the input of inverter,which can equalize the coupling path in three phases of the proposed circuit.This circuit is designed and simulated for CMOS image sensor with 640×480 pixel array using Chartered 0.18μm process.Simulation results indicate that the resolution can reach 10-bit and the maximum frame rate can reach 200 frames/s with a main clock of 10MHz.The power consumption of this circuit is less than 36.5μW with a 3.3V power supply.The proposed CDS/ADC circuit is suitable for high resolution and high speed image sensors.

Comparison of Optimal Place and Size of TCSC and SVC for Maximum Available Transfer Capability

This paper deals with power transfer capability enhancement using two common Flexible Alternating Current Transmission Systems （FACTS） devices, Thyristor Controlled Series Capacitor （TCSC） and Static Var Compensator （SVC）. For this purpose, at first the optimal place of TCSC and SVC is investigated and the optimal size is determined. At the end, a comparison is made between the two FACTS devices. For calculating Available Transfer Capability （ATC）, Repeated Power-Flow （RPF） rule used, and the network limitations such as voltage, stability, thermal capacity, and power generation limits are taken into consideration. The proposed algorithm is run on a sample network. Results show effectiveness of TCSC in situations where the thermal limit is the dominant limitation of the network. In such situations, SVC is almost useless. It was also seen that under conditions of voltage limitations, both elements are helpful for the enhancement of ATC.

Fault component integrated impedance-based pilot protection scheme for EHV/UHV transmission line with thyristor controlled series capacitor(TCSC) and controllable shunt reactor(CSR)

This paper analyzes the fundamental frequency impedance presents a novel transmission line pilot protection scheme characteristic of a thyristor controlled series capacitor （TCSC） and based on fault component integrated impedance （FCII） calculated for a transmission line with TCSC and controllable shunt reactor （CSR）. The FCII is defined as the ratio of the sum of the fault component voltage phasors of a transmission line with TCSC and CSR to the sum of the fault component current phasors where all the phasors are determined at both line＇s terminals. It can be used to distinguish internal faults occurring on the line from external ones. If the fault is an external one the FCII reflects the line＇s capacitive impedance and has large value. If the fault is an internal one on the line the FCII reflects the impedance of the equivalent system and the line and is relatively small. The new pilot protection scheme can be easily set and has the fault phase selection ability and also it is not affected by the capacitive current and the fault transition resistance. It is not sensitive to compensation level and dynamics of TCSC and CSR. The effectiveness of the new scheme is validated against data obtained in ATP simulations and Northwest China 750 kV Project.