Sharif Digital Repository

Power quality has become an increasing concern to utilities and customers. The increased concern has resulted in measuring power quality variations and characteristic disturbances for different distribution companies. This paper explains the results of power quality indexes for 50 customer loads at two voltage levels 20kV and 400v. The measurement period is 7 days with 10 minutes intervals. Also this survey has been presented according to IEC61000 and Iranian Power Quality Standard (IPQS). IPQS has some differences from IEC61000, EN50160 and IEEE standards in power quality indexes, which are investigated in this paper. At the end of paper, individual and global power indicators for all... 

This paper presents a novel flexible control strategy for Unified Power Quality Conditioner (UPQC), which achieves more flexibility in compensation of power quality disturbances as compared to the existing methods. The proposed control strategy provides priority-based compensation as well as full and standard-based compensation considering the rating of series and shunt parts of a UPQC. The priority-based compensation is done based on the compensation priority among different power quality disturbances. In this control strategy, an on-line estimation of different voltage and current disturbances is required. For this purpose, a Unified Adaptive Power Quality Estimator (UAPQE) has been... 

Voltage sags, also known as dips, are important to industrial reliability. This paper presents a Monte Carlo based approach to evaluate the maximum voltage sag magnitudes as well as the voltage unbalance ratio in transmission systems. In this context, investigations have been conducted on a system model taking into consideration the uncertainty in several factors associated with the practical operation of a power system. MATLAB is used in the simulation studies. © 2003 IEEE  

For steel industries optimum operation with high efficiency is of the first importance. On the other hand, extra investments in the supply side of electric arc furnaces may have been seen as redundant cost. Therefore, to improve the system efficiency, devices such as SVCs or STATCOMs can be employed. In this paper, the benefits of dynamic shunt reactive compensation by SVCs in steel industries are investigated. It is shown that this operation leads to optimization in steel production process and is completely beneficial from economic point of view. Supply system of a typical arc furnace is simulated using MATLAB software and the effects of a compensator on the operating characteristics of an... 

This paper presents the results of a thorough analysis of applying power quality standards to a granite factory. It explains the procedure of determining power quality indices in a power system. The paper presents the field data and provides the results of statistical analysis in order to extract power quality indices. A comparison against standard limits is also given. The case study gives an overview of power quality in such customers and brings up some practical limitations when applying power quality standards. ©2006 IEEE  

This paper presents the results of a power quality survey in a distribution system. More than fifty nodes are selected and monitored. Power quality indices are extracted based on IEEE and IEC Standards. The evaluation includes field data collection, extraction of statistical power quality indices and comparing the results against standard limits. Experimental data as well as clarifying tables and graphs are presented. The results are then discussed to evaluate the strength and weaknesses of applying standard limits when real observations are to be performed. Some proposals are also made in order to make standard procedures and limits more effective based on practical observations. © 2007,... 

This paper presents the results of a thorough power quality analysis in order to determine the cause of failure in a Compressed Natural Gas (CNG) distribution transformer. The paper presents the field data and determines power quality indices of such loads based on IEEE/IEC standards. It provides steady state time-series parameters as well as transient waveforms. Different signatures of the voltage and current signals are extracted, and consequences of the distortions are described. The analysis is clarified by presenting both time domain captured waveforms and statistical power quality indices. Optimum solution for improving power quality and prevent component failure is also proposed. ©... 

Conventionally, control system of a static transfer switch (STS) is designed based on the assumption that the STS terminal voltages are in-plane. This paper investigates the impact of phase difference of the STS terminal voltages on the STS transfer time and cross current. The phase difference is assumed to be a result of the difference of the feeder impedances. The paper shows that phase differences of even up to 4.5°, which are accompanied by up to 5% voltage drop at the STS terminal, can noticeably increase the transfer time and the cross current magnitude. The studies are conducted on the IEEE STS-1 benchmark system using the PSCAD/EMTDC software  

Fast (subcycle) bus transfer by means of a static transfer switch (STS) requires short time intervals for detection and transfer process. Due to these time intervals, the load transformer is subjected to a transient process which can be accompanied by large transient current components through the transformer. The transient current, in turn, can cause voltage sag at the load terminal. The STS control logic must be able to distinguish such a voltage sag from those due to the supply disturbances and not disconnect the load. This paper provides simplified analytical expressions to predict F of the load transformer which can be used to estimate the corresponding voltage sag. PSCAD/EMTDC-based... 

Providing clean, continuous and reliable power to many industrial customers has become a necessity. Where possible, sensitive customers are supplied by two medium-voltage utility feeders one of which is used as back up. Thyristor-based Static Transfer Switches (STSs) are able to provide the loads with a fast transfer to the back up feeder when the main one fails. In addition to being fast, the transfer must be performed with no source paralleling which creates a cross current flowing between the main feeder and the back up one. Due to practical limitations, however, in some cases, cross current cannot be avoided. This paper investigates the performance of thyristor-based STSs with respect to... 

This paper presents a new time domain model for electric arc furnaces using MATLAB, The model can simulate both nonlinear and time varying nature of such loads, which create flicker, harmonics, and voltage/current unbalance. In this model, Cassie and Mayr equations are used in three-phase mode and the effects of arc furnace transformer tap changer and flexible cables mutual inductances are considered. The proposed model takes into account the system inter-relation of parameters and arcing conditions as well  

This paper investigates the harmonic distortion and losses in power distribution systems due to the dramatic increase of nonlinear loads. This paper tries to determine the amount of the harmonics generated by nonlinear loads in residential, commercial and office loads in distribution feeders and estimates the energy losses due to these harmonics. Norton equivalent modeling technique has been used to model the nonlinear loads. The presented harmonic Norton equivalent models of the end user appliances are accurately obtained based on the experimental data taken from the laboratory measurements. A 20 kV/400V distribution feeder is simulated to analyze the impact of nonlinear loads on feeder... 

Distribution system operators that seek operational excellence are supposed to design and implement capable processes throughout their value stream and assess how well their real services match the design specifications. Process capability analysis is a critical stage in systematic and sophisticated quality engineering approaches such as six sigma, which are based on quantitative studies. The capability of a distribution network to maintain the power quality and voltage level within an acceptable range is one of the most important aspects of design and utilisation of electricity distribution network. Capability analysis has been successfully used in the previous studies to assess the quality... 

In recent years, utilizing the electrical propulsion system in the marine industry has become widely popular. Control of the propeller has been a high-priority design challenge in this industry. One of the essential issues in propeller control is the speed control of the ships. A suitable control strategy for the propeller should be economically-efficient while ensuring stability, reliability, and power quality of the ship's power system. This article proposes an improved propeller control strategy for increasing/decreasing the ship's speed. This scheme consists of two strategies: a maximum acceleration strategy and an efficient operation strategy. The maximum acceleration strategy aims to... 

Increase in the number of non-linear loads has increased harmonic pollution in industries, resulting in lower power factor and more losses. Harmonics may also lead to adverse conditions in cases they match a resonance frequency existing in the system. To alleviate the problems of harmonics, tuned harmonic filters are used. However, design and installation of passive elements in power systems or industries requires special attentions due to the possible resonances that may occur. In this paper, a Tire-Rubber company is analyzed for a filter installation. Harmonic analysis is performed, and site measurements are examined. Cautions to be taken for design consideration are then discussed  

This paper presents an investigation of power quality problems arising from electric arc furnace (EAF) operation, and the required compensating system capabilities. It also proposes a compensation system using a shunt active filter and a series inductor. A shunt active filter compensates for the reactive power and the current harmonics of the highly varying load. Reference signals for the compensation logic are obtained from the instantaneous current vector components on a rotating reference frame. Due to noninteger harmonics on voltages at the point of common coupling, conventional methods for the inverter dc bus voltage regulation fail to perform properly. Hence, a new method is introduced... 

This paper discusses the application of unified power quality conditioner (UPQC) for improving power quality of a system supplying an electric arc furnace (EAF). The UPQC comprises a combined series and shunt active filters sharing a common DC link. It is used to mitigate voltage disturbances and compensate for reactive power, harmonics and interharmonics. A novel control strategy of the UPQC is presented. Since voltages at the point of common coupling (PCC) contain low frequency interharmonics, conventional methods can not be used for extracting voltage reference signals. In the proposed method, voltage references are extracted using active power processing to generate sinusoidal waveforms.... 

This paper presents a new unified power-quality conditioning system (MC-UPQC), capable of simultaneous compensation for voltage and current in multibus/multifeeder systems. In this configuration, one shunt voltage-source converter (shunt VSC) and two or more series VSCs exist. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply-voltage imperfections on the other feeders. In the proposed configuration, all converters are connected back to back on the dc side and share a common dc-link capacitor. Therefore, power can be transferred from one feeder to adjacent feeders to compensate for...