Arc Furnace Load Research Articles

Arc Furnace Loads Voltage Stability

The use of the arc furnace and its influence on the power system is being studied. A set of models that allows for the evaluation of the electrical behavior during steady state is presented in this paper. The results are presented and used to validate them. Detection of steady-state voltage instabilities is performed through certain mathematical criteria. Among those arc furnace load criteria (dEs /dVp) criterion, L-indicator criterion, and (ZTh /ZLoad) criterion. The result of those criteria has been checked using the critical voltage value of arc furnace load node, which represents criterion quantities.

실측에 의한 특고압 수용가의 고조파 평가에 관한 연구

전기로를 포함하는 비선형 부하를 가진 규모가 큰 제철소는 특고압 수용가이다. 이득 비선형 부하는 고조파 전류를 발생시키고, 전력계통의 전압을 왜곡시킨다. 고조파 측정결과로 고조파는 시간에 따라 변하는 특성을 가지고 있었다. 시간에 따라 변하는 고조파를 해결하기 위해 쓰이는 가장 보편적인 방법은 누적확률을 사용하는 것이다. 본 논문에서는 전기로 부하의 시간에 따라 변하는 고조파를 국제 고조파 기준인 IEC 61000-3-6, IEEE 519와 JIS C 61000-3-2에 의해 평가하고자 한다.

A Study on the Harmonics Effect of SVC in Electric Arc Furnace Loads

Large steel industries have time-varying nonlinear loads such as electric arc furnaces. These nonlinear loads generate harmonic currents and create distortions on the sinusoidal voltage of the power system. The main objective of the static var compensator is to maintain the rms voltage at the point of common coupling within the limit. In this research, harmonic mitigation studies were conducted with and without the SVC, and time-varying harmonics were evaluated according to the international harmonic standards (IEC 61000-3-6 and IEEE Std. 519) using a cumulative probabilistic approach.

전기로 부하에서 SVC의 플리커 효과에 관한 연구

제철소에서 사용되고 있는 전기로는 전력계통에 전압 변동을 일으키며 시간에 따라 변하는 비선형 부하이다. 플리커는 전압 변동의 크기에 따라 램프의 방출 변화에 의한 인간의 지각 효과로 정의된다. 플리커 레벨은 전압 변동의 크기, 주파수 및 기간에 의해 결정된다. 본 논문에서는 전기로 부하로 인한 154[kV] 시스템에서의 전압 변동 문제를 측정하고, 플리커 저감을 위한 SVC 적용 결과를 분석하고, IEC 61000-3-7에 의하여 플리커를 평가하였다.

전기로 부하의 고조파 측정, 평가 및 동조필터 적용에 관한 연구

규모가 큰 제철소는 전기로를 포함한 비선형 부하를 가지고 있다. 이들 비선형 부하는 고조파 전류를 발생 시키고, 전력 계통의 전압을 왜곡시킨다. 본 논문에서는 전기로 부하의 고조파 현장 측정, 고조파 저감을 위해 수용가 모선에 동조 필터 적용과 국제 고조파 관리 기준인 IEC 61000-3-6과 IEEE Std. 519에 의한 고조파 평가를 심도 있게 분석한다. 고조파 해석 프로그램인 EDSA는 사례연구에 시뮬레이션 도구로 사용되었다.

A Novel Algorithm for Precise Voltage Flicker Calculation by Using Instantaneous Voltage Vector

A novel approach has been presented in this paper to calculate voltage flicker components precisely by using instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the smart discrete Fourier transform can be used to obtain the system frequency and magnitude. Then, the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the fast Fourier transform is used to obtain the voltage flicker components from instantaneous voltage vectors. The flicker components of the other two phases can be calculated by repeating the procedure. The flicker values of three phases are calculated individually and separately. The effects of jump-sampling, harmonics, power frequency shifting, and sampling rates are investigated. The calculation ability of this approach is compared with the traditional indirect demodulation method. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of this approach. From the results, this approach could calculate flicker components accurately with short calculation time by using small size data. It also avoids the frequency leakage effect.

시간에 따라 변하는 전기로 부하의 고조파 측정, 평가 및 시뮬레이션에 관한 연구

Large steel industries have nonlinear loads such as electric arc furnaces. Harmonic field measurements have shown that the harmonic contents of a waveform varies with time. Direct application of the harmonic assessment to the snapshot measurements would result in ambiguous conclusions depending on which instant is sampled. A cumulative probablistic approach is the most commonly used method to solve time-varying harmonics. Harmonic simulations are performed to evaluate the harmonic voltage and current distortions throughout the system. This paper provides an in depth analysis on harmonics field measurement of the electric arc furnace loads, harmonics assessment by the international harmonic standards IEC 61000-3-6 and IEEE Std. 519 and harmonic simulation for the time-varying harmonics. The EDSA program was used as a simulation tool for the case study.

Data Compression Applied to Electric Power Quality Tracking of ARC Furnace Load

The data compression techniques are used to enhance the storage capability of electric power quality instruments in monitoring distorted waveforms of electric arc furnaces. Both voltage flicker in voltage waveforms and harmonic components in current waveforms are major disturbances. The compression approaches by multiresolution analysis developed from the discrete wavelet transform with threshold coding and vector quantization coding are compared. The results from spectrum analysis show high compression ratios while keep low information loss. The error levels between original and reconstructed waveforms are discussed. Field measured waveforms from arc furnace loads are used to show the goodness of the data compression techniques. From the calculation results, the reconstructed voltage waveforms using threshold coding almost keep the same voltage flicker values. However, the vector quantization coding is better for harmonic distorted current waveforms. Thereafter, in the practical application of data compression for arc furnace loads, the threshold coding is used for recording voltage waveforms, and vector quantization coding for current waveforms. For the field measurement voltage and current waveforms, this method can reduce data memory size to 15.11% and 24.51%, respectively, while keep power quality characteristics. This paper provides a good approach to longtime electric power quality tracking of disturbing loads.

Effective voltage flicker calculation algorithm using indirect demodulation method

The voltage flicker is one of the major power quality disturbances in a weak power system. Better measurement and limitation techniques are always desired. An effective and accurate calculation method is presented to obtain the voltage flicker components and the 10 Hz equivalent value. By using the indirect demodulation method, the RMS values of a voltage waveform are calculated cycle by cycle to obtain the envelope. Then the fast Fourier transform (FFT) is used to obtain the flicker components. This method can increase the computing speed and reduce the hardware requirement in a power quality instrument when the FFT is used. The effects of sampling rate, harmonics, and system frequency shifting are investigated. The latter two are common disturbances in addition to the voltage flicker when arc furnace loads are connected in a weak power system. A calibration procedure is used to improve the frequency leakage effect and increase the calculation accuracy. The calculation results from given voltage flicker waveforms and field measured waveforms reveal the effectiveness of the proposed method. It can be used in both 50 and 60 Hz systems.

Adaptive static VAR controller for simultaneous elimination of voltage flickers and phase current imbalances due to arc furnaces loads

Abstract The present paper aims at utilizing the Static VAR Compensator SVC for simultaneously load balancing and voltage flicker elimination due to arc furnace loads. The SVC of thyristor controlled reactor-fixed capacitor TCR-FC type is considered. The effective susceptance of SVC is controlled and adapted by varying the thyristors firing delay angle. The three-phase imbalanced currents of arc furnace load is balanced by adjusting the effective susceptance of SVC Further, at the same time, the voltage oscillations due to arc furnace load currents are eliminated by updating the thyristor firing delay angle of SVC. An equivalent power system comprises a constant voltage source connected to arc furnace load through transmission system and step down transformer. The proposed SVC is connected at the terminal of the arc furnace load. To validate the effectiveness of the SVC in sense of load current balancing, improvement of power factor, and voltage flicker elimination due to arc furnace load, the above power system is simulated digitally over a wide range of arc resistances. The digital simulation results prove the power of SVC in terms of a constant terminal voltage and three-phase balanced unity power factor line currents with varying arc furnace currents.

An adaptive arc furnace model

This paper presents an adaptive arc furnace model. The integrated model is divided into three parts, the supply system model, the nonlinear load model and the controller model. First, the supply system is represented by a set of linear differential equations. Simulation is achieved by a numerical method and the measurements are taken as the control input. Secondly, based on the arc melting process and typical arc furnace V-I characteristic, the arc furnace load is described as a current-controlled nonlinear resistance. The pattern of nonlinear resistance is controlled by the average arc length, which reflects the arc furnace operating condition. Finally, the rectangular approximation of arc voltage is adopted by the controller to generate the arc power-arc length and the arc current-arc length curves. This information combined with the arc furnace operation and measurement information is used for the control scheme to determine the arc length and arc furnace transformer tap. Thus, the proposed adaptive arc furnace model is suitable for different operating conditions. This model is also compared prith the existing arc furnace models, which provides its validity. The effect of arc furnace load on the power system is also studied through the proposed model.

Energy variance criterion and threshold tuning scheme for high impedance fault detection

Summary form only given as follows. This paper presents a new approach to the detection of high impedance fault (HIF). The proposed approach (or detector which implements this approach) has four distinct features. First, the detector input signal is the three-phase unbalanced current (or feeder 3I/sub 0/), rather than the conventional three individual phase-currents. Secondly, the detector is designed by monitoring the energy variance for the second, fourth and sixth harmonics of 3I/sub 0/ individually, and by requiring the increment of randomness of all these harmonics to indicate an HIF. Thirdly, a self-tuning scheme based on the statistical confidence is applied to the automatic setting of threshold level for the energy variances monitored. Fourthly, effective counters are designed to detect both persistent and intermittent arcings. The detector has been tested on 51 staged faults and 8 unfaulted feeders. The test results show that the detector can have 100% fault detection rate so long as the arcing current at fault location is not less than 5 A. As to the dependability tests, no false alarm (or tripping) has happened for all of the unfaulted feeders under test. These feeders either supply special (including arc furnace) load, or have leakage current (referring to the intermittent zero-sequence load due to the feeder location along coast), or are under the normal capacitor or load switchings. The test results and the investigation for the high sensitivity and dependability and for the limitation of proposed fault detection method are presented.

Enhancement of static excitation system performance for generators near electric arc furnace loads

The tuning of static excitation systems (SESs) to enhance the performance of six gas turbine (GT) generators near an electric arc furnace (EAF) feeder has been successfully accomplished. The operation of these EAFs causes severe and long duration voltage fluctuations at the generator bus. Frequent generator tripping was reported when the adjacent EAFs were in operation. Preliminary field measurements and computer simulations indicated that the SESs did not have sufficient damping under this type of voltage fluctuation. By the adjustment of the SES gains and time constants according to the guideline set by the IEEE Standard 421.2, the SES damping can be greatly improved. This has been verified by additional field tests on six GT generation units. Now these generators can be operated very well although the EAFs still cause voltage fluctuation.

98/02153 A flexible ac transmission system (FACTS) for balancing arc furnace loads

98/02153 A flexible ac transmission system (FACTS) for balancing arc furnace loads

A flexible ac transmission system (FACTS) for balancing arc furnace loads

A flexible AC transmission system (FACTS) is a proposed new technique for balancing unbalanced three phase arc furnace loads. Although reactances of conductors can be balanced by traditional methods, the method proposed here is a unique method for balancing inevitably unbalanced arc resistances. Compensator controller elements and relations between their variables and the actual firing angles are derived. The influence of furnace load balancing on its characteristics is discussed. The inherent improvement of input power factor to unity is highlighted.

A new frequency domain arc furnace model for iterative harmonic analysis

This paper presents a new frequency domain arc furnace model for iterative harmonic analysis by means of a Newton method. Powerful analytical expressions for harmonic currents and their derivatives are obtained under balanced conditions of the power system. The model offers a three-phase configuration where there is no path for homopolar currents. Moreover, it contemplates continuous and discontinuous evolution of the arc current. The solution obtained is validated by means of time domain simulations. Finally, the model was integrated in a harmonic power flow where studies have been performed in a network with more than 700 busbars and 7 actual arc furnace loads.

A new time domain voltage source model for an arc furnace using EMTP

This paper presents a new time domain controlled voltage source (CVS) model for an arc furnace using the Electro Magnetic Transients Program (EMTP). The developed model is based on a piecewise linear approximation of the V-I characteristic of the arc furnace load. In addition to this, the novelty of this simulation technique lies in the fact that the active power consumed by the load is also considered in the proposed load model, thus making the proposed load model dependent on the operating conditions of the load. Dynamic variation of the arc is incorporated through sinusoidal and band limited white noise variation of the arc resistance in the V-I characteristic of the arc furnace load. Depending on the variation of the arc resistance, the developed load model accurately represents both static (deterministic) and dynamic (random) arc characteristics. While static arc models are useful for harmonic studies, dynamic models are useful for power quality studies and in particular, the study of voltage flicker. The results are compared with actual voltage measurements taken from a local utility to prove the validity of the proposed load model.

Virtual instrument measures harmonic filter duty

Harmonic filters for a static VAr compensator (SVC) suppress power frequency harmonics generated by the nonlinear characteristic of the thyristor controlled reactors and electric arc furnace loads. SVC filters also provide the 60 Hz capacitive current needed by the SVC to reduce bus voltage flicker. Following reactor and capacitor failures the reliability of the SVC filter was improved. The first step was to measure the SVC filter stresses which was performed using a virtual instrument. The measurement equipment consisted of a personal computer equipped with two analog-to-digital (4/D) input boards, two signal conditioning input boards, and commercially available instrument and control software capable of configuring these basic hardware components for user defined instrumentation and analysis. Virtual instruments were used to sample, store, analyze, and display 32 channels of high speed data for 55 minutes of the combined furnace heat cycle. The author discusses the virtual instrument software, measurement and analysis technique, and statistical analysis. >

Performance comparison of single-phase active power line conditioners for harmonic suppression and reactive power compensation

Use of an active power line conditioner is a new solution for power system harmonic and reactive power compensation. In this paper, the performance of a proposed single-phase and four typical single-phase power line conditioners is simulated and compared under arc furnace, half-wave rectifier, and full-wave rectifier loads. Their performance under a distorted mains voltage is also discussed. The simulation results show that the performance of the proposed active power line conditioner is superior to that of the conventional ones. A prototype of the proposed active power line conditioner is implemented and tested to verify its performance.

Development of a model for predicting flicker from electric arc furnaces

Owing to the characteristics of electric-arc phenomena electric arc furnace loads can result in serious electrical disturbances on a power system. Low level frequency modulation of the supply voltage of less than 0.5% can cause annoying flicker in lamps and invoke public complaints when the frequency lies in the range of 6-10 Hz. There is a need therefore to develop better techniques to predict flicker effects from single and multiple arc furnace loads and the effects of compensation schemes. The authors discuss the nature of arc furnace loads, and describe the instrumentation, field measurements, and signal analysis techniques which were undertaken to develop an arc furnace model. A single-phase furnace model is proposed suitable for use on digital simulation programs such as the EMTP or other appropriate commercial software simulation programs. Representative results based on actual furnace input data are included to show the validity of the model. >