Power Quality Measurements Research Articles

Effects of power quality on manufacturing costs in textile industry

This paper reports the effect of electrical power quality on textile industry. For this purpose power quality measurements have been done for six months in two different sector of textile industry. All parameters affecting the power quality have been measured by using ION 7650 Power Analyzer according to the EN 50160 standard. Because of textile industries have high technology machines including electronic control cards and driver controlled motors, poor power quality may damage the system and causes production failure. Measurements showed that the losses caused by electrical power quality were significantly high, being around 15% of the annual net profit of the textile industry. Key words: Power quality, power quality metering, textile industry.

PQONT: A domain ontology for electrical power quality

Electrical power quality (PQ) data is a ubiquitous type of engineering data quantified as a set of PQ parameters, such as frequency, flicker, and harmonics, obtained from electricity transmission and distribution systems. For PQ problems detected as deviations from nominal power system behavior negatively affect the workings of governmental and industrial institutions, as well as the electronic equipment and the psychology of individual humans, several systems of varying complexities to measure and monitor PQ parameters have been developed in order to detect the problems and take the necessary countermeasures. Yet, the domain of PQ data still suffers from the lack of a common vocabulary to be shared by the involved parties. In this paper, a novel domain ontology for electrical PQ, called PQONT, is presented to fulfill this need. Relevant standards and regulations have been utilized extensively during the ontology building process. The proposed ontology also supports linguistic applications by providing a number of linguistic properties applicable to all of its concepts. This facility of the ontology is employed in a multilingual natural language based interface for PQ data collected through a nationwide PQ measurement system so that the data can be queried in a flexible way. The implementation details of the interface is presented with a couple of query examples to illustrate the contribution of the ontology to a real application. The future work includes the extension of PQONT to a more general power system ontology so that it can contribute to a wider range of applications in the power system domain.

New Spectrum Leakage Correction Algorithm for Frequency Estimation of Power System Signals

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A new algorithm for the estimation of the frequency of single-tone signals is presented in this paper. The algorithm works in the frequency domain and is based on best fitting a theoretical spectrum of a single-tone signal that is windowed using a rectangular window on the spectrum of the sampled signal. Using this iterative process, the algorithm compensates the spectrum leakage caused by incoherent sampling and a finite number of samples. Due to leakage compensation, the algorithm provides accurate estimates of the signal's frequency, amplitude, and phase. The influence of noise and harmonic and interharmonic distortions on the proposed algorithm was investigated and is reported here. The algorithm's performance was compared with several other frequency-estimation algorithms (mostly those working in the frequency domain). Since the algorithm is intended for power quality measurements (although it is not limited to this application), it was also tested on signals measured in a single-phase power system. </para>

Synchronized Power-Quality Measurement Network With LAMP

In this letter, a power-quality measurement network for the power system is proposed to integrate electric measurement units with the Internet, global positioning system (GPS), and Linux, Apache, MySQL, PHP (LAMP). A synchronized sensor network is formed to monitor the system's dynamics in a wide-area sense. CompactRIO by National Instruments is used as measurement units to capture voltage at the 110-V outlet and process the signals locally. It has the advantages of ease of portability and standard network communication capabilities. A virtual instrument environment is developed to process measurements and GPS signals. To store and display measurement data over the Internet, a LAMP-based database and Web server are developed. The major advantages of this type of architecture are that they are all commercial-grade software with proven system operation stability and free to use.

Power quality analysis of wind farm connected to Alaçatı substation in Turkey

This paper presents simulation results and power quality measurements of a wind farm. The wound rotor induction generator at 600 kW is employed for power conversion in the wind energy conversion system (WECS). This induction machine is connected to the drive circuit via rotor terminals and speed control is carried out by means of chopper circuit. The model used in the package program is experimentally tested on the single machine drive system at 3.5 kW in the laboratory, after which the power quality issues of the wind farm are investigated by using the same model for 12 wind turbines in PSCAD.

Mobile monitoring system to take nationwide PQ measurements on electricity transmission systems

This paper describes mobile power quality monitoring systems developed to carry out extensive power quality (PQ) measurements nationwide, in addition to instrumentation and measurement technologies used in those systems. The developed systems have been used to measure the PQ of the Turkish Electricity Transmission System, which is among the largest transmission systems in Europe. To make trouble-shooting studies at the problematic measurement points in terms of PQ, different measuring instruments and a wide range of PQ analysis methods from raw data acquisition to PQ event detection have been achieved depending on the nature of the problem, thanks to the flexible signal processing algorithms developed. Being an essential issue in the evaluation of PQ at various points of the electricity transmission network, time synchronization of mobile PQ monitoring systems has been applied using different techniques. Electromagnetic immunity of the system has been tested and reported. Based on the proposed instrumentation and measurement technologies, PQ of the 205 measurement points has been assessed all over the country. In order to exhibit the capabilities and usefulness of the mobile monitoring system developed, sample measurement results are given in the paper. Guidelines of instrumentation and measurement technologies are presented for other researchers who would like to build distributed PQ measurement systems.

An efficient approach to detect and classify power quality disturbances

PurposeThe purpose of this paper is to develop a new method for detection and classification of power quality disturbances such as transients, waveform distortions, sags, swells and interruptions.Design/methodology/approachFor the purposes of the proposed method, the power quality disturbances are divided into two groups. Different algorithms are applied to detect and classify the disturbances from each of the two groups. For the processing of transients and waveform distortions, digital high‐pass filter and the mathematical morphology closing are used. Calculation of the RMS value is used for detection of sags, swells and interruptions.FindingsThe proposed method was implemented in a PC‐based measuring setup. The measuring setup was used in a seven‐months‐long monitoring of a single‐phase power system. In the course of the monitoring, the proposed method was verified on over 19,000 transients, 3,500 waveform distortions, 77 sags and 18 interruptions.Research limitations/implicationsThe classification stage of the proposed method does not differentiate between individual types of waveform distortions (harmonics, interharmonics, noise…).Practical implicationsThe described approach is simpler and more reliable than, for example, methods based solely on wavelet transform. The proposed method is suitable for real‐time monitoring of power systems.Originality/valueThe paper describes a new and efficient way of detection and classification of disturbances (especially of transients and waveform distortions). It shows that mathematical morphology operations, which are normally used in image processing, represent a useful tool also in the field of power quality measurements.

Power quality affects teacher wellbeing and student behavior in three Minnesota Schools

Background Poor power quality (dirty electricity) is ubiquitous especially in schools with fluorescent lights and computers. Previous studies have shown a relationship between power quality and student behavior/teacher health. Objectives The purpose of this study is to determine the ability of power line filters to reduce dirty electricity in a school environment and to document changes in health and behavior among teachers and students. Method We installed Graham Stetzer filters and dummy filters and measured power quality in three Minnesota Schools. Teachers completed a daily questionnaire regarding their health and the behavior of their students for an 8-week period. Teachers were unaware of which filters were installed at any one time (single blind study). Results Dirty electricity was reduced by more than 90% in the three schools and during this period teacher health improved as did student behavior in the middle/elementary schools. Headaches, general weakness, dry eyes/mouth, facial flushing, asthma, skin irritations, overall mood including depression and anxiety improved significantly among staff. Of the 44 teachers who participated 64% were better, 30% were worse, and 6% did not change. Behavior of high school students did not improve but elementary/middle school students were more active in class; more responsive, more focused; had fewer health complaints; and had a better overall learning experience. Conclusions Dirty electricity in schools may be adversely affecting wellbeing of teachers and behavior of their students, especially younger students in middle and elementary school. Power line filters improve power quality and may also protect those who are sensitive to this energy. Work on electric and magnetic field metrics with and without Stetzer filters urgently needs to be carried out to determine just what characteristics of the dirty electricity may be interacting with the people.

Feasibility study of the application of optical voltage and current sensors and an arrayed waveguide grating for aero-electrical systems

In this paper we present, for the first time, the hybrid fiber-optic voltage and current sensors interrogated using an arrayed waveguide grating (AWG) device. Due to the excellent dynamic capabilities of an AWG-based interrogator and its improved robustness, the proposed system would be suitable for voltage and current monitoring within an aircraft electrical system. The voltage sensor comprises a multilayer piezoelectric stack, acting as a voltage-to-strain transducer, and a fiber Bragg grating (FBG) used to convert voltage induced strain changes within the stack into wavelength shifts. These wavelength shifts are then analyzed by an AWG. To measure current, the same sensor type is used to monitor a specially designed ferrite-core current transformer. Alternatively, a magnetostrictive transducer is employed instead of piezoelectric stack. It is shown that the system is capable of measuring variable frequency of voltage and current waveforms, typical of those anticipated in the next generation aero-electric power systems. It is also demonstrated that the system can be used for voltage and current harmonic analysis and power quality measurement in such networks.

A Power-Quality Measure

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A power-quality (PQ) measure is introduced in this paper. The proposed measure, based on the Shannon's entropy, expresses the deviation of the examined voltage cycle from the ideal one. Two entropy concepts are introduced—the spectral and the probabilistic entropy. The two entropies, calculated for every voltage cycle, are properly combined to provide the PQ measure. The PQ measure is represented graphically on a 2-D Cartesian coordinate system. The PQ measure is calculated for the most common PQ disturbances. The graphical representation of the calculated PQ measurements leads to the definition of an area of acceptable PQ on the PQ measure 2-D diagram. The PQ of a power system may be evaluated by the proposed measure, by implementing voltage measurements during predetermined time periods in selected network nodes. The produced electricity price may be configured in terms of the measured PQ. </para>

Wavelet Transform for Processing Power Quality Disturbances

The emergence of power quality as a topical issue in power systems in the 1990s largely coincides with the huge advancements achieved in the computing technology and information theory. This unsurprisingly has spurred the development of more sophisticated instruments for measuring power quality disturbances and the use of new methods in processing and analyzing the measurements. Fourier theory was the core of many traditional techniques and it is still widely used today. However, it is increasingly being replaced by newer approaches notably wavelet transformand especially in the post-event processing of the time-varying phenomena. This paper reviews the use of wavelet transform approach in processing power quality data. The strengths, limitations, and challenges in employing the methods are discussed with consideration of the needs and expectations when analyzing power quality disturbances. Several examples are given and discussions are made on the various design issues and considerations, which would be useful to those contemplating adopting wavelet transform in power quality applications. A new approach of combining wavelet transform and rank correlation is introduced as an alternative method for identifying capacitor-switching transients.

Locating Switched Capacitor Using Wavelet Transform and Hybrid Principal Component Analysis Network

The transient caused by capacitor switching is one of the important power quality (PQ) problems. In particular, switching on the capacitor may result in an overvoltage to a sensitive load, serious disturbance to an adjustable-speed drive or a resonance in the system. This paper presents a new method to locate the positions of the transient sources with the help of the PQ monitoring system. The discrete wavelet transform is used to extract the features of transients caused by capacitor switching. The fuzzy-c-means is then used to determine the placement of PQ measurement facilities. The signal energies attained by wavelet coefficients serve as inputs to the hybrid principal component analysis neural network for locating the transient sources. The simulation results obtained from an 18-bus distribution system show the applicability of the proposed method

The effect of Solar irradiance on the power quality behaviour of grid connected photovoltaic systems

Photovoltaic systems have been increasingly used in the generation of electrical energy, either as a means of providing electricity in areas where there is no grid connection (stand alone systems), or by providing electricity to the grid (grid connected systems). In a deregulated energy market, the cost of energy produced from fossil fuels is rising and the photovoltaic energy becomes a promising alternative source. Yet it still suffers from problems that need to be resolved in order to be widely accepted as an equivalent alternative to fossil fuels. Firstly the more direct problem of efficiency and cost needs to be overcome and secondly the indirect problem of the quality of power provided by photovoltaic technology has to be addressed. In this work 14 different grid connected PV systems have been considered and power quality measurements have been taken. Results for low and average irradiance cases are presented and analyzed in order to determine how power quality quantities are affected by changes in solar irradiance.

Challenges and Trends in Analyses of Electric Power Quality Measurement Data

Power quality monitoring has expanded from a means to investigate customer complaints to an integral part of power system performance assessments. Besides special purpose power quality monitors, power quality data are collected from many other monitoring devices on the system (intelligent relays, revenue meters, digital fault recorders, etc.). The result is a tremendous volume of measurement data that is being collected continuously and must be analyzed to determine if there are important conclusions that can be drawn from the data. It is a significant challenge due to the wide range of characteristics involved, ranging from very slow variations in the steady state voltage to microsecond transients and high frequency distortion. This paper describes some of the problems that can be evaluated with both offline and online analyses of power quality measurement data. These applications can dramatically increase the value of power quality monitoring systems and provide the basis for ongoing research into new analysis and characterization methods and signal processing techniques.

전기철도 차량기지 변전소의 실시간 무효전력/역률 보상설비 적용에 따른 전력품질 개선에 관한 연구

In this paper, real-time reactive power/power factor compensating equipment is suggested for improving power quality at electrical railway's substation in marshalling yard and designing optimal capacity of compensating equipment for actual apply at current marshalling yard. For this purpose, several kind of real-time reactive power/power factor compensating equipments are introduced and SVG(Static Var Generator) as optimal compensating equipment that is suitable for load characteristics of substation in marshalling yard is suggested. This paper shows proper simulations by suggested equipment using PSIM software and describe basic compensating principle and simulation results. Optimal capacity design for applying current marshalling yard is based on real measured power quality data. Power quality improvement that is performed by SVG as real-time reactive power/power factor compensating equipment is estimated at electrical railway's substation in marshalling yard. As reference, real-time reactive power/power factor compensating equipment is composed by voltage source inverter and DC capacitors.

Development of a network-based power quality diagnosis system

This paper presents a network-based power quality (PQ) diagnosis system. In accordance with the IT development, PQ monitoring networks are prevalent in many existing systems because such networks can provide system-wide insights to users. The developed PQ management system of this paper also consists of network-based devices such as PQ monitoring systems (PQMS), the PQ Server, and the PQ diagnosis system (PQDS). PQMSs measure power quality data at various points in the power systems and send them to the PQ Server through the Ethernet. The PQDS diagnoses the PQ data stored in the PQ Server in order to provide various diagnosis functions to the users. However, in many existing PQ monitoring networks, it is still difficult to pin-point the event location and to find appropriate solutions. The developed PQDS focuses on identifying power quality events, especially on finding the fault location and the type of faults as well as various statistical and stochastic analyses. Therefore, it can help users cope well with power quality problems with the right measure in the right place. The PQ diagnosis system also provides event trend diagnosis, stochastic diagnosis, and PQ indexing functions for user convenience.

Analysis of state of MV distribution system before and after connection of small wind farm Ravna1

In the last two decades, the number of installed wind turbines has grown rapidly all over the world. This was due to the huge improvement in technology and increased interest in using wind energy as an important energy source in the future. Following this worldwide trend, the first small wind farm in Croatia named Ravna1 was installed on the Pag Island. To check its influence on local distribution network, power quality measurements have been made in different points in the network before and after the connection of the small wind farm. In parallel, simulation of the distribution network with its connection to 110 kV network was made, and power flow and voltage analysis were made for cases of network with and without wind farm connected. Analyses were made to check the influence of the connection of the wind park on the relatively weak island network, and were made with different power outputs of wind turbines. Calculated values of power flows and values of voltages in the network match very well with measured ones. Also, measurements show that connection of small wind farm does not affect power quality on the Pag Island distribution network.

Measuring electric power quality: Problems and perspectives

The proliferation of non-linear and time-variant loads is causing a number of disturbances on the electric network, from a more and more significant distortion of both currents and voltages, to transient disturbances on the supply voltage. In this respect the electric network behaves as an “healthy carrier” of disturbances, so that a disturbance generated by one customer can be distributed to other customers, causing possible damage to their equipment. The measurement of the quality of the electric power in a network section is therefore becoming an impelling need, especially in a deregulated electricity market, where each actor can be responsible for the injection of disturbances. However, there are still some respects of power-quality measurement, from both the methodological and instrumental point of views, that are still unsolved and require to be carefully analyzed. The paper gives a survey of these problems and some indications about the present trends of the research work in this field.

Power-Quality Measurements in an Autonomous Island Grid With High Wind Penetration

Autonomous power systems, such as those existing in small and medium-size islands, typically consist of medium voltage networks fed by conventional power stations and present characteristics not typical for large interconnected grids. In this paper, results are presented and analyzed from a power-quality measurement campaign, conducted in a diesel-powered island system with significant wind penetration. Emphasis is placed on the voltage flicker, which was found quite increased under all operating conditions. It is shown that the diesel engines of the conventional power station are the main source of flicker in the system, due to the pulsed variation of their torque. The operation of the wind farms, on the other hand, does not result in any notable deterioration of the voltage quality level in the system.

A Comparative Analysis of the Statistical and Random-Fuzzy Approaches in the Expression of Uncertainty in Measurement

The present practice for uncertainty expression and estimation in measurement, endorsed in the IEC-ISO Guide to the Expression of Uncertainty in Measurement, is based on a statistical approach, which is also the basis for the Monte Carlo method generally employed to overcome the problems met in the strict application of the guide. More recently, methods based on the fuzzy theory have been proposed too, with encouraging results. This paper compares the results obtained, in the expression of uncertainty, by the use of the Monte Carlo method and the random-fuzzy variable method. Both methods are applied to a real, digital signal processing-based instrument for electric power quality measurement, and the obtained results are compared and discussed.