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Web-based Power Quality Monitoring System of Smart Transformer Substation RTP-34 MPEI for engineering education. Lev Khruslov, Mikhail Rostovikov, Vladimir Shishov Moscow Power Engineering Institute (MPEI) Moscow, Russia [email protected] , [email protected] www.magistr.tv/demo Abstract—Fragment of an educational program on the basis of online-monitoring of the power quality parameters is discussed. The future of electric power is smart grid, one of it’s main parts is smart substation. To date, there is a decrease in consumption of electricity in three-phase networks with linear loads of 6-10 kV and increased consumption in single-phase 0.4 kV networks. Because the active introduction of power electronic equipment (TV, computers, servers, compact fluorescent and LED bulbs, office equipment, etc.) is the emergence of higher harmonics in the 0.4 kV networks. Higher harmonics cause additional energy losses in distribution transformers and wires. These new trends require innovations in engineering education. On the working distribution transformer substation 7000kVA RTP-34 at Moscow Power Engineering Institute (MPEI), there is a comprehensive system for onlinemonitoring of electric power quality parameters using these parameters in the educational process via the Internet. Remote access via the Internet to the actual industrial equipment has allowed to create a fundamentally new infrastructure of the educational process. Monitoring system provides power quality control and digital fault recording solutions. At common coupling points RTP-34 measure electrical parameters on the high side - 10kV (12 voltages, 42 currents) and low side - 0.4 kV (15 voltages, 99 currents). The measured instantaneous values of voltages and currents of the three phases are calculated values of the total and active power, quality factors and other parameters according to IEC 61000-4-30:2015 standard. Performed spectral analysis of voltage and current harmonics up to the fortieth. Evaluated the contribution of individual harmonics in the level of additional losses in the phase and neutral conductors is done by special “harmonic calculator”. Monitoring system allows us to calculate the additional losses in the power transformer. The effectiveness of the active filter is discussed. Keywords: power quality, web-based internet monitoring, harmonic distortion, additional power losses, active harmonic filter, smart substation. I. INTRODUCTION Currently in the field of traditional electricity there are significant changes. These changes include the active use of power electronics, IT-technologies, increased attention to energy saving, development of approaches to create a "smart grid», the integration of the traditional system of power supply of renewable energy and more. There is a mutual penetration of new concepts in energy, information and telecommunication technologies. It is planned to create the next generation of energy systems - intelligent power networks. Intellectualization of electricity poses problems: • Creating a "smart" instrumentation and devices for substations, providing accounting and energy management in conjunction with non-stop monitoring and control of quality of electric power in stationary and transient conditions. • Develop principles for the organization of intelligent distribution transformer substations of 10 / 0.4 kV. • Formation of the concept and testing of fragments of intellectual energy in the form of Micro Smart Grid on the basis of individual power grid structures, located in a small area around MPEI. • Implementation of the Smart Grid concept in the educational process. New trends in modern electricity require innovations in engineering education, especially in such expensive field as laboratory practice. In MPEI over the past 15 years are working in the direction of energy saving and efficiency of electric power through the introduction of elements of intellectual energy at the facilities of Moscow. We transferred this research experience in electrical engineering education. Developed and produced in small series are two types of smart meters quality control: Magistr DM-306M and Magistr430 PQ. On the basis of these devices implemented more than 20 local power systems «Micro Smart Grid», carried out a pilot project for the creation of smart transformer station RTP-34 MPEI. II. FEATURES OF MODERN ELECTRICITY In world practice, formed two trends related to total consumption of electrical energy: 1. Reducing energy consumption in three-phase networks at a voltage of 6-10 kV and increase the level of consumption in single-phase networks of 0.4 kV. In USA total consumption of electricity 0.4 kV "private and commercial sector" is 73%, and at a voltage of 6-10 kV "industrial sector" 27% (Fig.1) [1]. generally designed for electric power linear loads, provided that the total harmonic distortion THDi does not exceed 3-8%. 2. Active introduction of elements of power electronics in low voltage caused a sharp increase in the current harmonics and deterioration of electrical energy in the low voltage network, including power transformers. At the present time, more than 95% of the loads of 0.4 kV networks are non-linear (fig.2). Figure.1 Structure of energy consumption in USA Figure 2. The increase of non-linear loads since 1960 Sources of power quality deterioration became institutions, homes, schools, hospitals, etc., mainly because of controlled single-phase rectifiers: compact fluorescent and LED lamps, servers, office equipment, household appliances, switching power supplies installed in the TV , computers etc. It can be argued that the current nonsinusoidality in modern low voltage is mainly determined by the imperfection of the secondary power supply for the equipment. Fig.3 shows the principled model with the idealized electronic key S. Simulation analysis explains the appearance of harmonic currents in power electronics devices with phase control. Depending on the state of the switch S, current in the circuit can take different forms. After Fourier analyze nonsinusoidal load current i(t) is represented as a sum of harmonic currents F r - 1, 3, 5, 7, 9. Figure 3. The emergence of higher harmonics at the phase control. This same condition corresponds to the choice of elements of internal automation: measuring current and voltage transformers, relay protection, etc. Assessing the impact of non-sinusoidal current transformers operating conditions can be produced by various methods, one of which, according to [2], is the K-factor notion load (Fig. 4). K factor I h h 2 2 (1) To facilitate comparison of different forms of the same current selected value of its effective value Irms = 100 A. Despite the absence of reactive elements Fig.3 circuit between the first harmonic of the current i1 (t) and the voltage u (t) phase shift occurs. The shift can be a leading (capacitive), zero (resistive) or lagging (inductive) depending on the switching time key S. In compact fluorescent lamps and LED lamps first harmonic current is usually ahead of the first harmonic voltage. In dimmer devices dimming the first harmonic current lags behind the first harmonic voltage. There are three methods of estimating harmonic load content: the Crest-factor (CF), Harmonic Factor or percentage of Total Harmonic Distortion (THDi) and K-factor. It is known, that the transformer substation 10 / 0.4 kV, are Figure 4. The dependence of the load capacity of the transformer on the value of the K-factor loads. III. WEB-BASED POWER QUALITY MONITORING SYSTEM (WPQMS) OF TRANSFORMER SUBSTATION RTP-34 MPEI. The aim of non-stop monitoring is information about electrical parameters of power supply basic elements. Measuring system consists of decentralized synchronized to external time standard measurement tools with remote access via the Internet to Web-technologies. Methods of measurement of quality of electric energy in the analyzer MAGISTR-430 PQ are going according to IEC 61000-4-30:2015 class “A” [3] and IEC 61000-4-7:2015 [4]. Based on measurements of voltages and currents on the three phases are calculated Online Power Quality Parameters (OPQP) (fig.5): full power, active power, power factor, and a number of other parameters. In accordance with the standard [3] measurement is making always for 10 cycles of fundamental frequency, aggregation is made for intervals of 3 seconds, 10 minutes, 2 hours. For parameters OPQP the word “online” means that the relevant parameters are provided for the last three-second aggregation interval; parameter “PF” means total power factor, parameter “cos(φ1)” means displacement power factor for fundamental frequency. WPQMS provides technical capabilities for the analysis of voltage and current load. For these purposes the harmonic contributions calculator (Fig.6) which makes it possible not only to determine harmonic components and the currents on the neutral conductor, but also to quantify the increase of the cable losses and copper losses in the power transformer. This allows us to estimate (and provide) ELECTROSAVINGS using filters or power supplies with built-in power factor corrector. WPQMS supports various data protocols: CAN, SNMP, ModBus, LonWork etc. In addition the system can be integrated into various devices having a data interface (energy meters, panel meters, PLC controllers, UPS units airconditioning systems, diesel generator, etc.), which provides: • View the measured OPQP in the form of graphs, waveforms, spectra; preservation of information in graphic and text files; counting the number of voltage sags, surges and voltage pulses; • control standard and emergency events, which are displayed on a special screen forms single-line structural schemes using animation and color changes; • viewing parameters measured in real time, including forms of voltages and currents for the three phases (waveform); • Analysis of the harmonic structure of currents and voltages; • archiving (logging) of the measured parameters; • Creation of power quality indices protocol in accordance with Russian Standard RU GOST 32144-2013; • count dips and voltage pulses and their representation in the standard ANSI; • preservation of the graphs in graphic files; • e-mail alerts by e-mail, sms. WPQMS is flexible, scalable, and easily integrated into existing control systems. Structurally complex object is a distributed decentralized network peripheral controllers, combined or fieldbus CAN, or through RS-232, RS-485, Ethernet, through which information is exchanged between controllers and data servers. WPQMS allows the connection of devices from other manufacturers under the relevant protocols. Figure 5. Online Power Quality Parameters (OPQP) WPQMS is addressed to six major categories of professionals: duty electricians; engineering staff service; scientific and engineering staff of specialized organization that helps in the analysis of emergency situations; managers (not electricians) secondary and primary level; students of higher and specialized educational institutions; researchers. By providing non-stop monitoring of the quality of electrical energy is proposed to use a visual representation as in fig.5. Online monitoring is supported by records and retention of basic quality parameters of electricity each day in a journal. Direct measurement and archiving OPQP correspond to the current trend of continuous monitoring of the main parameters of electric power, similar to the system of monitoring the leading Russian TV and Radio centers. Figure 6. Harmonic Contribution Calculator Technically WPQMS allows for multi-parameter analysis of modes of load and mains. Additional tool for monitoring computer is the contribution of harmonics, which allows not only to evaluate the currents in the neutral conductor, but also to quantify the increase in cable loss and copper loss of the power transformer. This allows you to define (and provide) the effectiveness of power management when using active filters or power supplies with built-in power correctors. Fig.7 shows the screen form regime suppress current harmonics active filter designed to reduce harmonic distortion of the current in the cable and power transformers. Source THDi determined by the type of real load section 2, and is approximately 20%. Active filter reduces the level of THDi to 2-3% (fig.8). The current in the neutral conductor depends on the imbalance of the first harmonic and on the presence of harmonics especially that are multiples of three. Fig.7 data show that in the two main power elements - a transformer and power cable between the transformer and the filter - THDi decrease for each phase is about 7 times and the power factor PF increase from 0.97 to 1. OPQP are continuously stored in the archive in the form of daily graphs of the main parameters. Archival data and the online power quality parameters are used in the educational process. From archival data students determine loss parameters according to time of day, the level of current harmonics and the transmit power level. It identifies additional power losses in the power transformer (fig.9), cable and active filter. From analyzing OPQP students determine the first harmonic imbalance, the share of for different harmonics in neutral current, assesses harmonic current compensation for active filter (fig.6). All calculations are done for real loads at the time of measurement. Real power and harmonics level differs each day and doesn’t depend on professor. Figure. 9. Active power losses in T2, MPEI RTP-34, 22.04.2015. Figure 7. Active Filter ABB. Fig. 9 shows the changes in active power in the power transformer T2 during the day. Active power on the high voltage side (PHV) and on the low voltage side (PLV) of transformer are measured and averaged each hour from 8:00 am to 8:00 pm. Power losses are calculated as the difference between PHV and PLV. Educational structure "Distribution transformer substation 10 / 0.4 7000 kVA with internet access" is the development of the Department of Electrical and Electronic devices MPEI and is designed to prepare specialists in the fields: electrical engineering, electric power supply, electromechanics, industrial electronics, electrotechnology and several others [5]. Internet access to the web-resource WPQMS RTP-34 is available free of charge and is documented on the use in the educational process, with specific forms of application: http://www.magistr.tv/demo REFERENCES [1] [2] Figure 8. THDi levels before and after active filter during 29.04.2015. For demonstration filter was off from 16:00 to 18:00. IV. CONCLUSION. It has been found, that students who are faced with principles of power quality have problems in understanding, when their course does not include laboratory exercises. WPQMS set of parameters can be considered as an additional tool for the analysis of inpatient and emergency processes of distributed energy systems. For example, WPQMS enables the evaluation of real losses in power lines and power transformers and instrument control to ensure energy efficiency. [3] [4] [5] T.Heidel, J.Kassakian, R.Schmalensee "Policy challenges and technical opportunities on the U.S. electric grid" IEEE Power & Energy magazine, may/june 2012, pp30-37. ANSI/IEEE C57.110-2008. Recommended Practice to Establish Transformer Capability when Supplying Non-Sinusoidal Load Currents. IEC 61000-4-30:2008. Electromagnetic compatibility (EMC) – Part 4-30: Testing and measurement techniques – Power quality measurement methods. IEC 61000-4-7:2008. Electromagnetic compatibility (EMC) – Part 4-7: Testing and measurement techniques – General guide on harmonics and interharmonics measurement and instrumentation, for power supply systems and equipment connected thereto. L.Khruslov, M.Rostovikov, V.Shishov “Web-based Power Quality Monitoring System at RTP-34 MPEI”. Conference “Metrology and metrology assurance 2014”, September 7-11, 2014, Sozopol, Bulgaria.