Automated Complex Determination Indicators of Power Quality

Transcription

1 Automated Complex Determination Indicators of Power Quality 1 Victor O. Mandziy, 2 Volodymyr V. Lypnytskyy, 3 Sergiy M. Babyuk, 4 Ivan M. Sysak 1,3,4 TNTU, Ukraine, 2 TTU, Estonia, 1 vikmand@meta.ua, 2 Lipkav@ukr.net, 3 sermuk@gmail.com, 4 sisak_i@mail.ru Abstract - A device was designed and developed to evaluate the quality of electric power and for a system of control to determine such basic parameters of energy as deviation and fluctuation of voltage, sinusoidal and asymmetrical shape of the curve voltage. Abbreviations PQ - power quality EPS -electric power supply PQI - power quality indices ECM - electronic calculating machine ADC - analog-digital converter PC - personal computer CT - current transformers PSLCU - protection and signal level control unit PCM - pulse-code modulation I. INTRODUCTION The basic factor that defines power consumption quality with non-sinusoidal voltage is the harmonic structure, i.e. the voltage curve form. The evaluation of power consumption quality is complicated in this case because of the absence of universal indices: coefficients and proportions used for the evaluation of a sinusoidal system provide ambiguous results in non-sinusoidal processes and do not characterize the effectiveness as a whole, but show only separate sides of power consumption. To investigate the complex concerning the distortion of current and voltage, it is necessary to find its reasons and characteristics of the sources of that distortion, the way and the degree of its influence on the electrical machinery and power functioning and to provide facilities for neutralization or protection from the distortion. The problem of power quality (PQ) management in a system is directly related to the power supply management. Here the quality of power supply should be characterized as a combination of electric power supply (EPS) reliability and PQ [1]. To normalize power quality, the power quality indices (PQI) hardware control, organizational and economical mechanisms of the impact on the reasons that deteriorate PQ, elaboration of methods and facilities able to reduce distortions are essential. Particularly, if the mutual impact of users on one another is taken into account, it is necessary to formulate the conditions for new user inclusion into the grids correctly. Therefore, it predetermines the methods and programs to be applied for calculation of PQ per electronic calculating machine (ECM) that will allow the electromagnetic situation to be evaluated after such connections. The notion of power quality parameters is defined as the correspondence of energy parameters to its quantity found. The parameters of power quality are the values that characterize power quality on one or more of its parameters [1-4]. Note that the voltage PQI reflect the energy properties of a signal, i.e. characterize the power (energy) of voltage distortion, the scale of the negative impact of power distortions on the system elements and technological processes. For problems of control and measurement the electric power quality often use the following portable devices as: multimeters DIRIS, meters Resurs, registrators and analyzers AKE. In our research we describe a laboratory device designed with a specific software. II. RECENT RESEARCH AND PUBLICATIONS Different sides of power processes are described by various characteristics and parameters of power quality evaluated by two methods [4]. Method 1 oversees the superposition of formal functions into components, each of which is associated with its own integral characteristic. Method 2 that is suitable for simple schemes is based on the choice of power processes proper as the fundamental principle and the analysis of the features of different sides of their passing. The analysis and optimization of power processes in EPS systems based on Method 2 enables reaching the only conclusion about the EPS of different difficulty levels, resulting from system principles, using different degrees of detailing and error processing, if necessary. In this case the characteristics and indices introduced meet the physical processes in EPS and ensure the balance of energy supply, analysis of power efficiency and its conversion, control over PQ and its effectiveness. Depending on the technical conditions, power quality should be characterized by the requirements for the active capacity being consumed, reactive power, pulse or pulse sequence, while 'poor quality' of power will be determined by the reactive power and losses, active power, and distortions. Power quality parameters of electroconsumers according to [5] can be determined as follows: - in power supply from single-phase electric power networks: frequency deviation, voltage deviation, frequency fluctuation range, the scope of voltage change range, and nonsinusoidal voltage coefficient; - in power supply from three-phase electric power networks: frequency and voltage deviations, frequency fluctuation range, voltage fluctuation range, and nonsinusoidal voltage coefficient; - in power supply from direct current power networks: voltage deviation, voltage changes scope, and voltage oscillation coefficient. 95

2 III. PURPOSE OF THE RESEARCH The aim is to analyze the methodologies that define power quality indices in terms of elaboration of an automatic complex. Research objectives: 1. to study the methodology of determination of power quality, 2. to develop a device for determination of power quality, 3. to construct a mathematical model of power quality calculation methods, 4. to design an electrical circuit of PSLCU, 5. to experiment and analyze the results, propose measures for improve. IV. ANALYSIS, RESULTS AND DISCUSSION A. Elaboration of the computer complex 1. The computer complex is demonstrated in Fig. 1. Here are some features of the computer complex that are essential for the implementation of the power audit: - the possibility of energy research in three-phase networks; - the possibility of energy research in single-phase networks; - the possibility of connecting to any computer; - the possibility of the computer functioning both in a complex with 14 - bit ADC and in other complexes. The structure of the device shown in Fig.2 enables a more detailed analysis to be presented. Fig. 1. Illustration of the automated complex. 2. The structure of the computer complex and its role in energy audits. As noted above, all the PQ indices mainly depend on the power supply. The power network itself is characterized mainly by those electroconsumers that are connected to it. Thus, during the implementation of the power audit, i.e. finding out the power quality indices, the given computer complex must be used immediately in the place of electroconsumers connected to the network. The purpose of the energy audit in this direction is to solve the following main tasks: - developing organizational and technical measures aimed at efficient use of electricity; - identifying potential energy savings; - economic grounding of organizational and technical measures. Fig. 2. Structural scheme of the computer complex. This complex includes the following main structural elements: Input device (block) for coordination of the signal level and protection (PSLCU). It is designed to convert current and voltage values into the values "understandable" for an analog-digital converter due to the ammeters connected to this unit for wireless current measuring. Analog-digital converter. ADC is designed to convert analog signals into digital data and provide them for the ECM. Electronic calculating machine. The "heart" of the computer complex, in which real-time PQI values and graphs, data obtained from the ADC and their storage in database are reflected on the monitor. Software. The brain of the mentioned computer complex, which allows data processing according to the PQI processing methodology provided by the user on the program level by means of the program. Database. Its function is to store data obtained from ADC as a separate file, to record the results of processing these data into a separate file for further power audit analysis when defining PQ by means of the computer complex and data analysis in other programs. 96

3 3. Software functioning block diagram. To simplify writing the program and the clear representation of its functioning principle it is reasonable to make up a block diagram. The block diagram of software functioning of the computer complex for exploring power quality and the graphs of the electric loads used in the power audit consists of the following main blocks (Fig. 3): - A block is designated to enter the starting and ending date of the study, the time of the beginning and the end of the study, and continuance of pauses during the periodical investigation; - in B block system, the date and time are read out and compared to the date and time entered at the beginning of the study. If they match, the program will move to the C block; - in C block one selects a certain branch of the program fulfillment depending upon the study algorithm and mode; - in D block we find consistently continuous channel survey in progress. In this case source data comprises the instantaneous voltage values on the three phases, the current values on three phases and zero wire current value. This data is used to make the graph of electrical loads at low duration studies. - in E block the program makes a packet inquiry of each channel for two periods and records the information in the database. These data are used to analyze the power quality. One can find out the maximum effective voltage value divergent from sinusoidality and it is required for the analysis of higher harmonics; - F and G blocks are similar to D and E, but they are used for long-term dimensions. The software for ADC data taking and recording to the database is written in Turbo Pascal 7.0 language. Fig. 3. Flowchart of software functioning. 97

4 4. Circuit diagram and its description. Circuit diagram is implemented as the protection and signal level control unit. PSLCU is a part of the computer complex for the implementation of the power audit. It serves as the current and voltage measurer, chooses their form and protects ADC from overload in case voltage and current exceed the admissible limits (Fig. 4). Fig. 4. Circuit diagram. PSLCU consists of current transformers (CT), which are the constituent part of the current measure tongs (ammeters for wireless current measuring). They transform large current values into those admissible for ADC measurement range. The current which passes through the linear conductor A is transformed by the CT1 current transformers and goes to the ADC input through the R1 resistor. After the R1 resistor there is a protective zener diode turned on between the common wire and the alarm wire. It limits the voltage value by increasing current value above limits, and resistor R1 limits the latter. When increasing the current the voltage increases proportionally. If the current value starts to exceed the upper limit, the zener diode VD1 is opened and it starts to limit the voltage level on the stabilization level. Thus, if the current continues to grow, the voltage grows as well until it decreases on the R1 resistor and it will not enter the ADC input. Similarly, the restrictions of current and voltage in the phases B, C and 0 take place. Current measuring on the wire 0 is necessary to determine the phase distortion, to define possible grounding of the 0 wire, which can lead to power despoilment. To measure the voltage at the phases voltage dividers R4 and R5 are used. Zener diode should be switched on in parallel to the voltage divider output to prevent overtention. It will protect ADC from the breakdown. Also, PSLCU has the control indicators turn on for each phase. They consist of the LED (light-emitting diode) and the resistor connected in series circuit. They enable one to ascertain visually the correctness of the connection settings. The structural setting is constructed as a device connected to the ADC by a special flex. The scheme is assembled on the printed board placed in a plastic case. 5. ADC description used in the setting. There are many ways to convert the analog signal, i.e. voltage or current that varies smoothly and continuously, into the stream of digital data representing the discrete coded sequence of pulses. In practice analog-digital conversion by means of pulse-code modulation (PCM) is most commonly used. In this case the process begins with the representation of a continuous signal as a sequence of readings taken after a specified period of time (i.e. a defined discretization frequency). This function is performed by the scheme which is called a selective device. By remembering the instantaneous value of the input signal (often at a capacitor), this device ensures the preservation of the reading value taken during the time of digitization summed into the represented amplitude of each reading in the form of binary code word with a definite number of digits. Therefore, the method used to perform such a digitization determines the possibilities, the complexity and the cost of the analog-digital converter. ADC is designed to work in automated measuring systems for control and research on the basis of IBM PC/AT type of PC. The ADC module used in our computer complex enables: - random measurement of the voltage (or current) values on 32 channels with a common 'ground' wire by means of switching the amplification factor by electrically separated jumpers from computer circuits; - ADC performance starting on the signal installed on the board timer on the previously installed channel number. 98

5 B. Experimentation and data analysis 1. Results obtained. The records of voltage and current curve forms are given by means of the complex. The actual voltage values, voltage deviation values are provided on the basis of the data received (Fig. 5). Similarly, the actual current values in three phases are provided (Fig. 6). Fig. 7. Pulse power supply model. Fig. 5. Curve graph form of actual voltage and voltage deviation values. Fig. 8. Pulse current form. Fig. 6. Graph of the actual current values in three phases. 2. Data analysis. As seen from the graph, network voltage is non-sinusoidal. This is caused by the non-sinusoidal current consumption shown in Fig. 6. Also, this figure shows the uneven phase load. Powerful users are concentrated on the only phase this is the A phase. The loading mode was analyzed. As a result, the computer technology proved to be the source of electricity load. As is known, there are pulse power supplies on the computer input that consume pulse current from the network. The power supply model shown in Fig. 7 was built up. Modeling of the working process showed that the pulse current was actually consumed from the network, which is depicted in the oscillogram of Fig Measures to improve power quality are as follows: 1. to distribute the electric load equally into three phases; 2. to equip the computer lab UPSs with a built-in power factor corrector, provided that it consumes the network with sinusoidal current. CONCLUSIONS With the developed laboratory automated complex determination indicators of power quality with specific software we have the new device which has the following advantages. We can in real time to observe, record and analyze the current and voltage curves with EOM. Also we can immediately see the changes after applied actions Based on the records of the current and voltage curve forms, the actual network voltage values, voltage deviation and current graphs in three phases were built up. The charts reveal that the non-sinusoidal network voltage is caused by nonsinusoidal current consumption. Also, the graphs show that the loading phase is uneven, and the most powerful users are focused on the A phase. As a result of the analysis of the loading mode it was found that the computers created the main electric load, on the input of which pulse power supplies exist that use the pulse current from the network. The pulse power supply model proved the assumptions mentioned. Some measures to improve power quality were proposed. REFERENCES 1. Soldatkina A. A., Electrical Networks and Systems: Manual for HES. Moscow: Energiya, p Ovcharenko A. S., Rosinskij D. I., Improving the electricity supply efficiency of industrial enterprises. Kyiv: Tehnika, p Fedorov A. A., Ristheyn E. M., Electrical supply of industrial enterprises.: Textbook for high schools. Moscow: Energiya, p Zhezhelenko I. V., Rabinovich M. L., Bozhko V. M., The quality of electricity on the industrial enterprises. Kyiv: Tehnika, p Bibliogr.: pp GOST