The Application of Thermal Plasma to Extraction Metallurgy and Related Fields

Various applications of thermal plasma to extraction metallurgy and related fields are surveyed, chiefly on the basis of documents published during the past two or three years. Applications to melting and smelting, to thermal decomposition, to reduction, to manufacturing of inorganic compounds, and to other fields are considered

Considerations on Direct Balancing of Ultra-High Power Ac Arc Furnaces in Uneasy State

During the operation of ultra-high-power ac arc furnace the negative effects of unbalance mostly occur in the secondary terminals of the transformer connected to the load. Hence balancing and compensating the furnace at this terminal will not only improve the transformer efficiency but also reduce energy losses that do occur. In this thesis a computer modeling of a reference ac arc furnace in both balanced and unbalanced states were simulated, and the effects of a reactive balancing compensator installed on the secondary side of the furnace transformer was evaluated to see how much delivered energy improvement can be obtained. The balancing compensator used is synthesized using the Currents’ Physical Components (CPC) based power theory, which is also used to evaluate our obtained results. The results obtained provide a platform for developing an adaptive balancing compensator for ac arc furnace operating in uneasy mode, with thyristor switched inductors used for compensator susceptances control

A Study on Reduction of Harmonic Distortion caused by AC Arc Furnaces

In AC arc furnaces, arc ignition is stabilized by inductors which are connected across its supply lines. They cause power factor degradation in the system. When furnaces are modelled as linear RL load, the arc nonlinearity reduces the impact of this degradation to a significant extent. Furnace Power factor is improved by the DC voltage on the arc. In this research study, power factor of AC furnaces is estimated on the assumption that DC voltage on the arc is constant and furnace operates in steady state. Primary objective of this research was to determine the power factor of the furnace in steady state. However, other states of operation such as bidirectional arc and unidirectional arc ignition were also taken into consideration while computing the power factor of the furnace. Secondary objective of this research was to understand the effects of harmonics on arc furnace and design filter parameters to mitigate the impact of harmonics caused by the transient operation of the furnaces. Random extinction and ignition of individual arc furnaces help reduce current distortion of ultra-high-power ac arc furnaces using resonant harmonic filters. This operation can be conducted in condition of fast varying parameters of the furnace. On the other hand, this resonant harmonic filter can be built practically only as a constant-parameters device. Filters built on fixed parameters cannot be well coordinated to the furnace. This discrepancy can cause a decline in the filter’s efficacy of harmonics reduction. A reference model using MATLAB was developed to simulate different conditions on the circuit. Also, use of different resonant filters to reduce these harmonics was performed to find the most efficient filter that will increase the efficacy of this process. This efficiency was investigated, specifically, in a melting mode of an arc furnace operation. A reference arc furnace was used in this study which enabled to draw some qualitative and quantitative conclusions on possibilities of current harmonic reduction at a supply of ultra-high-power furnaces by resonant harmonic filters

Energy and voltage management methods for multilevel converters for bulk power system power quality improvement

Electric arc furnaces (EAFs) are prevalent in the steel industry to melt iron and scrap steel. EAFs frequently cause large amplitude fluctuations of active and reactive power and are the source of significant power quality disturbances. Also EAFs comprise a major portion of industrial loading on the bulk power system. Typically, a static VAR compensator (SVC) or Static Synchronous compensator (STATCOM) are use to provide the reactive power support in order to alleviate the fluctuations in voltage at PCC. Static Synchronous Compensators (STATCOMs) provide a power electronic-based means of embedded control for reactive power support. Integrating an energy storage system (ESS) such as large capacitors with the STATCOM will improve the device performance to have active power controllability as well as the reactive power. A cascaded multilevel STATCOM has been utilized in order to compensate for all the fluctuations caused by an EAF both in the RMS of the voltage at PCC and also the active power generation. Designing a sophisticated controller, it is possible to get the STATCOM track the variations of active power in load. Therefore, the generator does not need to produce the random active power demanded by the load --Abstract, page iv

An Improved Nonlinear STATCOM Control for Electric Arc Furnace Voltage Flicker Mitigation

Electric arc furnaces (EAFs) are prevalent in the steel industry to melt iron and scrap steel. EAFs frequently cause large amplitude fluctuations of active and reactive power and are the source of significant power-quality (PQ) disturbances. Static synchronous compensators (STATCOMs) provide a power-electronic-based means of embedded control for reactive power support and PQ improvement. This paper introduces a new nonlinear control for the STATCOM that provides significant reduction in EAF-induced aperiodic oscillations on the power system. This method is compared with traditional PI controls and has shown to have improved performance

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics