Abstract
Содержание
- Introduction
- 1. Actuality of the task
- 2. The purpose and objectives of the study, the planned results
- 3. Review of research and development
- 3.1 Arc steel-smelting furnace
- 3.2 Non-sinusoidal voltage and current waveforms.
- 3.3 Voltage fluctuation
- Findings
- List of sources
- 3.2 Non-sinusoidal voltage and current waveforms.
Introduction
Arc steel-smelting furnace (DSP) creates a variety of conductive electromagnetic interference (EMC) in the electrical network: deviations, fluctuations, asymmetry and non-sinusoidal voltage, which adversely affect other electrical receivers.
The initial data for estimating EMC are empirically obtained graphs of the effective values of current I for each period of 0.02 s and oscillograms of instantaneous values of current i in three phases, from which the parameters of the EMC are calculated. The exception is current oscillations, which require graphs of actual values over a half-period of 0.01c [2].
The first task is to develop a mathematical model of input processes – currents. They represent random processes for which average values are calculated, correlation functions (QFs), and also the laws of ordinate distribution. The latter are usually approximated by normal distributions. The CF is approximated by exponential and exponentially cosine expressions. The unevenness of the load graphs with the melting time decreases, therefore, the characteristics of the currents are determined within the stationarity sections with a duration of 1 min.
Model of Moore finite state machine (FSM, offered by E. Moore in 1956 and named in his honor), as synchronous sequential circuit, is the part of numerous digital systems and is used in construction of control devices. High complexity of integrated circuits (which is increasing, according to the G. Moore's law) and theoretical basis of automatic calculations make possible the implementation of comprehensive algorithms of processing information. However direct realization of algorithms can lead to inefficient using of crystal's resources and extension of project's cost.
1. Actuality of the task
Compatibility subjects of various activities, processes, populations - this comfortable existence of each of them in the absence of unacceptable influences on other subjects. In power supply systems electrical equipment, devices, apparatus and other devices are located in their common electromagnetic environment, and any of the devices is source (generator) of electromagnetic interference, at the same time electromagnetic interference from other sources. AT In general, electromagnetic interference is characterized as an impact, distorting the main signal and undesirably influencing [4].
Electromagnetic compatibility problem that became relevant in the 1940s years for information transmission systems, is highlighted in all areas of production, transmission and distribution of electricity. The complication of electrical systems, the commissioning of powerful electric drives, valve converters, high degree industrial automation dramatically exacerbate the problem of electromagnetic compatibility. Its significance is commensurate with the importance of problems, energy saving, reliability and energy security.
In the power supply systems of an industrial enterprise, a special Attention is paid to conducted interference, which in three-phase networks AC are determined by various kinds of sinusoidal distortions. voltage and current waveforms and effective voltage values (voltage deviation). This electromagnetic interference does not exhaust all the types of interference indicated in GOST 32144-2013, however they are prevailing since they have the greatest impact on electric receivers Values are called indicators Electromagnetic compatibility or power quality indicators. The problem of power quality is one of the most important components. parts of a common electromagnetic compatibility problem.
2. The purpose and objectives of the study, the planned results
The results obtained will be used to assess EMC for the work of the particle board of a particular enterprise. Static characteristics of the Mode and EMC parameters can be used in the design of new enterprises with the same chipboard.
The main objectives of the study:
1. Development of mathematical models of installations for the study of the impact on the supply network and load.
2. Determining the most rational way to reduce conducted noise generated by arc steel-smelting furnaces in a power supply network together with non-linear load.
3. Investigation of the effectiveness of the adopted circuit solutions to ensure the electromagnetic compatibility of electrotechnical installations with arc steel-smelting furnaces when powered either from the power grid or from an independent power source.
4. Development of methods for calculating special transformers to ensure the electromagnetic compatibility of the steel-arc arc furnace with the network and load.
5. Investigation of the effect of higher current harmonics generated by a non-linear load steel-smelting furnace on an increase in active power losses in the electrical network.
Figure 1 – Chipboard power supply diagram
3. Conductive noise overview
3.1 Arc steel-smelting furnace
The nonlinearity of the current-voltage characteristic of the arc leads to the generation furnaces of higher harmonic currents. The shape of the furnace current curves to a large extent depend on the mode of combustion of the arc in different periods of melting. In the initial period melting the furnace current fluctuates between the currents of the idle mode and short circuit, the shape of the curves of the currents is significantly different from sinusoidal. With the advent of liquid metal, melting is carried out at a short arc, the current fluctuation is relatively less. The shape of the current curves improves and approaching a sinusoidal [3].
Compared to valve converters of the same power levels The harmonics generated by arc furnaces are 3 times less. This refers to the period of melting, therefore, for practical purposes it is important to know the harmonic levels for the period of melting.
Level 5, 7, 11 and 13th harmonic current generated by electric arc ovens are relatively small. The equivalent effective value of them is not exceeds 10% of the 1st harmonic current. The currents of electric arc furnaces contain also abnormal 2, 3, 4, 6th harmonics. The main reasons for the appearance abnormal harmonics are continuous changes in the conditions of arcing furnaces and incomplete alignment of the resistance of the short network. Equivalent current value of high harmonic currents in current due to abnormal harmonics increases 1.8 (2 times).
Animation (13 frames, 562 kb, repeat constantly) – Principle of electric arc steelmaking furnace
Arc vacuum furnaces are powered by valve converters that are switched in a 6-phase circuit with equalizing reactor. The mains current curve is the same as the bridge current. electric drive converters. The level of abnormal current harmonics it turns out to be much more significant than I2 (8%), I3 (6%).
Single-phase electroslag remelting furnaces are practically linear load, since the remelting of the electrode is due to heating the ingot in a layer of molten electrically conductive slag.
Rudyothermic furnaces work with shunted arc, thanks to this nonlinearity of the arc is almost not manifested. Harmonic content in current furnaces slightly; Levels 2, 3 and 5 of the current harmonics do not exceed 1.5%, the remaining harmonics are much less.
Installation of electric arc and resistance welding. For installations electric arc welding as a power source are used semiconductor rectifiers. High harmonic currents generated by welding rectifiers are different for individual modes of operation of welding installations.
Depending on the load, the rectifier can operate in one of three modes: intermittent current mode at low loads, which corresponds to two-valve switching A; medium loads B; mode three-valve switching with large loads With [1].
Mode A has no practical value. In mode B levels 5th and 7th current harmonics are very unstable. Harmonic Level current in mode C is significantly lower than in mode B.
Electrical welding installations are included in the network using thyristor keys. For smooth control of welding current valve The devices are supplied with phase control systems. Phase application regulation leads to a distortion of the form of current consumed by welding by cars. The decisive harmonics for current decomposition are 1.3 and 5th. In addition to the odd harmonics, there are also even harmonics. Appearance Even harmonics are explained by the scattering of the valve control angles. Influence even higher harmonics on non-sinusoidal currents of welding machines is small.
Figure 2 – Electric arc furnace
3.2 Non-sinusoidal voltage and current waveforms.
In modern industrial enterprises, a significant spread Got loads whose current-voltage characteristics are non-linear. K them The number includes thyristor converters, installations of arc and contact welding, electric arc steelmaking and ore-smelting furnaces, gas discharge lamps, etc. These loads consume current from the network, the curve which turns out to be non-sinusoidal, the result is non-linear distortion of the mains voltage curve or non-sinusoidal modes.
Non-sinusoidal regimes adversely affect the work of power electrical equipment, relay protection systems, automation, telemechanics and communication. Economic damages arising from this are mainly due to deterioration of energy performance, reduced reliability operation of electrical networks and reduced service life electrical equipment [5].
The main range of issues that make up the content of the problem non-sinusoidal, reduced to the following:
- evaluation of the electromagnetic compatibility of higher harmonic sources and other loads;
- quantification of the higher current harmonics generated various non-linear loads, and predicting the values of higher current and voltage harmonics in electrical networks.
- lower harmonic levels
It is known that any non-sinusoidal periodic function f ((t) with period 2) satisfying the Dirichlet condition can be represented as the sum of constant and infinite series of sinusoidal variables with multiples frequencies. Such sinusoidal components are called harmonics.
A sinusoidal component, the period of which is equal to the period non-sinusoidal periodic value, called the main harmonic. The remaining components of the sinusoid with frequencies from the second to the n-th are called higher harmonics.
High harmonic currents, passing through the network elements, cause falls voltages in the resistances of these elements, which are superimposed on the main sinusoid voltage, lead to a distortion of the shape of the curve voltage.
3.3 Voltage fluctuation
During the work of power consumers with sharp alternating shock load in the power grid there are sharp jolts of power consumption. It causes mains voltage changes whose sweeps can reach large values. These phenomena take place during the operation of rolling electric motors, electric arc furnaces, welding machines, etc. Specified circumstances extremely adversely affect the work of all electrical receivers, connected to the network, including the power consumers causing these changes.
For example, the welding time for contact machines ranges from 0.02 to 0.4 s, then voltage fluctuations of even short duration affect quality of welding [6].
With voltage fluctuations, as a result of which the voltage decreases more than 15% below the nominal, it is possible to turn off the magnetic starters operating electric motors.
In enterprises with significant synchronous load fluctuations voltages can cause the drive to fall out of sync and process breakdown.
Voltage fluctuations adversely affect the work of lighting receivers. They cause the lamps to flash, which when exceeding the threshold irritability can affect long-term perception of people.
Voltage fluctuations that occur when large synchronous operation engines with highly variable load, are determined taking into account the transient processes, because at the same time the power consumed by the electric motor, significantly different from the power of the steady state.
The resistance of all network elements, except cables significantly less inductive. But in the factory networks of large enterprises with widespread introduction of 6-10 kV conductors and 110-220 kV deep bushings. They become very short and their share decreases sharply. Therefore they do not have a big impact on the resulting value of the ratio r/x as a whole on the enterprise. This will simplify the calculation of voltage fluctuations at highly variable shock loads [7] .
Based on the above, it can be concluded that given in the P and Q outline, the oscillation value is determined by the power of k.z. feeding network and the latter is higher, the less fluctuations.
The second significant source of voltage fluctuations are arc steelmaking furnace (chipboard). When working chipboard there are frequent outages the number of which reaches 10 or more during one heat. Heaviest conditions are obtained during the melting of the metal and at the beginning of the oxidation. At This causes operational shocks of the current. Jog Current depends on the capacity of the furnace, the parameters of the furnace transformer, full short network resistance.
Figure 3 – DSP curves: 1 – voltage, 2 – first harmonic, 3 – interference
Conclusions
Asymmetry has the most effect on engines. Therefore, the dynamic model includes a block that simulates the motor current, and a quadratic inertial smoothing link that simulates the additional heating of the voltage sensing motor. The first block corresponds to the replacement circuit of the motor according to the reverse sequence current.
Non-sinusoidality greatly influences capacitor installations and insulation of the network and all electrical equipment. Here the dynamic model has the same structure, but in the first block of actions, the current is simulated in accordance with the equivalent circuit of capacitors and insulation.
Since the time constants for heating capacitors and motors are large, in the second block, it is sufficient to calculate the effective values of the currents from which the maximum superheat temperatures are calculated, the additional losses of active power, and the reduction in service life is estimated.
The results obtained will be used to assess EMC for the work of the particle board of a particular enterprise. Static characteristics of the Mode and EMC parameters can be used in the design of new enterprises with the same chipboard.
List of sources
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- Основные показатели, определяющие качество электроэнергии. – [Электронный ресурс]. – Режим доступа: свободный. https://bobych.ru/...
- И. В. Жежеленко, А. К. Шидловский, Г. Г. Пивняк, Ю. Л. Саенко, Н. А. Нойбергер Электромагнитная совместимость потребителей. – [Электронный ресурс]. – Режим доступа: свободный. http://ir.nmu.org.ua/...
- И. В. Жежеленко, А. К. Шидловский, Г. Г. Пивняк. Электромагнитная совместимость потребителей.2012 г. – [Электронный ресурс]. – Режим доступа: свободный. http://eom.com.ua/...
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- Оценка и нормирование несимметрии напряжений в системах электроснабжения общего назначения Э. Г. Куренный, Е. Н. Дмитриева, А. П. Лютый, О. А. Сидоренко – [Электронный ресурс]. – Режим доступа: свободный. http://masters.donntu.ru/...