Pavilion C-5, premises 108
1. Algorithms and measuring instrument to assess the variability of transmitted electro-energy parameters
Contemporary electro-energy systems are increasing due to non-linear loads of electricity supply, including a wide range of frequency components adversely affect on consumers, therefore it is necessary to control the parameters of electro energy and the state of the power system. Such control allows the measurement parameters of transmitted electro-energy and electro-energy networks to perform with sufficient accuracy. The basic definitions of parameters related to electro-energy networks and electro-energy are provided by a number of standardization documents. These parameters describe the state of the network and the phenomena that may occur in the time or frequency domain. Performing measurement instruments based on the definitions given in the standards and recommendations are now being built using a variety of hardware and software solutions.
Problems related to the structure of such instruments can be divided into two groups:
Within the framework of the project, for measurement devices performing measurements ofpower quality will be developed (Harmonic Levels and interharmonics, subharmonics content, asymmetry, asymmetry voltage, THD, RMS voltage and currents, the instantaneous active power, frequency, as proposed by the authors measurement of voltage fluctuations and flicker-free light ratio) and analysis of electro-energy system (backup energy system impedance and load, the newly proposed by the authors, the measurement of vulnerability of the electro-energy system to interference). These parameters will be measured taking into account the inevitable nonstationarity current and voltage signals. The device will be implemented in an advanced signal processing algorithms voltages and currents. In particular, nonlinear dynamic model of voltage processing, resampling algorithm of rendering recorded signals measurements as a frequency function of the changes of fundamental frequency as well as the replacement algorithm for estimating the network impedance measurement uncertainty and orthogonalization algorithm for voltage and current signals based on the discrete Hilbert transform will be used. The authors based on their experience are planning to build a measurement system performing: auto-calibration, measurement of parameters, long-term recording and transmission of measurement results using standard interfaces and using a mobile phone network. The basis of equipment will track measured electrically isolated analog signals, the band anti-alias filters and sample-and-remember system independently for each input channel, high-resolution digital converters analogical-floating TMS320C6xxx series signal processors and programmable structure XILINX SPARTAN Company.
The authors plan to create a prototype, which should have a measurement uncertainty of selected parameters of less than 2%. In the case of the parameters that describe the state of electro-energy system measurement uncertainty, depend on the current volatility of the current and voltage signals, it will be estimated and recorded. To meet the estimated measurement uncertainty is necessary to use A / D converters with a resolution of 16 bits or more. Galvanic isolation circuit design, with low noise generation, is no less important. Measurement methods and processing algorithms also should ensure established measurement uncertainty and speed. High speed operation allows to determine the parameters measured in real time. In addition, the measurement system will allow long-term measurements of aggregate registration for observation times of 30 days. Built measurement system will enable the development of effective methods of diagnosis of the energy system and the impact assessment of its reconstruction or expansion.
2. Development of impedance measurement replacement electro-energy networks based on the natural variability of the load
Currently, electro-energy quality one of the major technical and economic problems in the European Union. This is due firstly to the growing amount of non-linear loads of energy, which degrades the quality as well as the huge financial losses resulting from poor power quality. The poor quality of electro-energy causes: damage to electricity consumers, affects the health and quality of life of people, and generates energy transmission losses. Electro-energy quality is described by a number of parameters such as: the level of voltage and current harmonics (talking about disturbances at frequencies higher than the basic), the rate of flicker (talking about low-frequency disturbances), the frequency dips and power outages, voltage and current unbalance, etc.
The first two indicators are saying about deformation passes currents or voltages which goes beyond the allowed in the standards. Deformation of the sine current is generated by non-linear and/or nomadic receivers. Unfortunately deformation generated in one point in the network does not have local coverage. Through finite (non-zero) impedances electro-energy supply lines these disorders are moved to other points in the network, in the form of so-called the voltage drop in the supply lines. The result is the deformation not only electricity, but also tension in other points of the network, as well as damaging the electro-energy network operating in a non-linear receiver and restless working on the same network, if only the disturbances caused by the receiver in restless was big enough at workplace of damaged receiver.
Parameter that indicates the ability to carry interference - disorders of measuring point until it reaches the end of the network (in the direction of electricity supply) is equivalent impedance seen from point of measurement. Acquaintance of this parameter allows to assess the condition of the power system when the latter is viewed from the point where the measurement is carried out, as well as it allows to make decisions about changes in the structure of the network, for example joining at a given point of additional receivers. Moreover, knowing the impedance as a function of system replacement frequency, it is also possible to identify sources of harmonics and their percentage in the deterioration of energy at the point of the joint connection. These facts make the replacement measurement impedance of electro-energy system is one of the critical research issues that need to be taken.
It is proposed to develop a method to measure the equivalent impedance of the power network based on the observation of network load variation. This is possible through the development of algorithms for the processing of voltages and currents observed in digital form that can be repeatable implementations in measuring instruments based on signal processors. Digital realization largely eliminates the uncertainty arising from the implementation of the definition of impedance measurement and does not depend on measurements results of scattering parameters of the measuring system components. The proposed method allows continuous monitoring the impedance of the network, which is not available in existing solutions.
3. Development of methods for measurement and analysis of non-stationary low-frequency spectral interference in electro-emery networks in real time
Electro-energy Quality is understood as a set of values of certain parameters which can be changed, due to the disruptive effects manures and power grid only at certain, usually small limits. These parameters are defined in standards documents. They are also defined the ranges of their changes. To assess the quality of electricity, it is necessary to determine the values of these parameters through the measurement, recording the results and their analysis. The range of acceptable parameter changes of electricity for less than the base frequency band (50 Hz) usually it is a few percentage, and the uncertainty of the popular measuring instruments can not be greater than 5%. Reference devices should be characterized by the measurement uncertainty of less than 1%. Even a cursory analysis of measurement uncertainty limits the designers of measurement systems and signal processing algorithms for measuring the search for solutions in the A / D converters with a resolution of 16 bits or more. Methods for measuring and processing algorithms should also ensure the proper measurement uncertainty, and characterize the corresponding speed.
Within the framework of the project, the authors intend to develop a data acquisition systemdesign based on the latest design A / D converters which allow to obtain the necessary measurement resolution both in amplitude and in real time. For this purpose, it is necessary to synchronize the measurement with respect to the fundamental of the spectrum, so that the variation in the spectrum of the low frequency would only associated with the observed phenomena without overlapping operation results derived from the measurement system. The synchronization is intended to carry on the way of digital signal processing in the digital programmable structure. Input circuits used in such a system must provide two basic functions: separation from the mains with a high rate of CMMR, and a sufficiently wide range of input signals. It is assumed that the low-frequency analysis is sufficient to ± 35Hz around the carrier. The proposed measurement system will be based on processors and operating systems with the possibilities of the implementation of DSP instructions in order to achieve high computational electro-energy.
Modeling studies will be carried out to develop methods of analysis, and in the final phase of testing on a real object with the prototype of the measurement system. It is intended to use the dedicated DSP resources associated with addressing (circular buffers) and floating-point calculations and registers with increased precision.
4. Medium and high voltage measurement electro-energy on the basis of electric field observations
Measurement of voltage in power networks of medium and high voltage is possible only through indirect systems: transformers or dividers. This means that it is possible for such a voltage measurement to perform only in places where measurement systems are constructed. These are very important elements of the power system for the diagnosis, control and economic settlement. Currently, a major focus in the design and manufacture of voltage transformers is to build them so that the fundamental of 50Hz would transfer to the primary side with the least uncertainty, both in amplitude and phase. At present, the result is estimated from the uncertainties over 10% of the amplitude characteristics and basically unknown phase characteristics for higher frequencies - up to 40 harmonics.
Work on the field of observation under the overhead high voltage line at various centers iscarried out for many years 90 XX centuries. The results of this work show that such a measurement is possible. It is proposed to measure voltage potentials by observing an electric field under overhead line or in the rails switchgear. This measurement will be carried out by means of miniature sensors recording the instantaneous values of the potentials, then the calculations are performed - the solution of the inverse problem to determine the instantaneous values of observed lines. This measurement requires the selection of sensor placement and knowledge of the geometry system. If the geometry of the sensor arrangement is simple to determine this for overhead line, distance determination is difficult, and it is possible that during the measurement variables changes due to changes in weather: wind, temperature. The introduction of procedures for the variation analysis of electric field distribution and the sensitivity of the measurement algorithms allows to propose such a measurement methodology to reduce the negative aspect.
prof. dr hab. inż. Paweł Gryboś
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