This paper presents an arc-furnace model consisting of nonlinear, time varying resistance where time-variation laws of arc length are considered. One consists of a periodic, sinusoidal law, the other of a band-limited white-noise law. The arc-furnace model is implemented by EMTP, referring to actual electric-plant configurations. Simulations are reported where the values of flicker sensation and short-term flicker severity P/sub ST/, are determined according to UIE specifications. The results show that the model based on the sinusoidal time-variation law can be useful for worst-case approximations, while the model using white-noise law is able to fit flicker measurements made in electric plants supplying arc furnaces. The models are used to investigate the effect on flicker compensation of the insertion of series inductors at the supply side of the furnace transformer. It is shown that considerable reduction of P/sub ST/ is obtained at the point of common coupling by series inductor installation at constant furnace active power. >

Arc-furnace model for the study of flicker compensation in electrical networks

Global warming is attracting a growing interest worldwide for the generation of large-scale energy from renewable energy sources as it is free from greenhouse gas emissions. Wind energy is one of the most promising renewable energy sources due to its availability and low cost and due to the fact that it is more efficient and advanced in technology. Hence, harvesting of large-scale wind energy is of prime interest today. However, large-scale integration of wind energy sources creates environmental, economic, social and technical impacts that need to be investigated and mitigated as part of developing a sustainable power system for the future. Government, utilities and research communities are working together to increase penetration of wind energy into the power grid and overcome potential barriers associated with this. This paper presents an extensive and useful survey on wind energy technology and associated implementation issues including effects of wind farms on the nearby locality. This paper also reviews the social, environmental and cost-economic impacts of installing large-scale wind energy plants. Finally, potential technical challenges to the integration of large-scale wind energy into the power grid are reviewed in regard to current research with their available mitigation techniques.

Potential challenges of integrating large-scale wind energy into the power grid–A review

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.

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

Thermal and mechanical behavior of ZnO varistors used in surge arresters is simulated for current pulses of various magnitude and duration. Time dependence of the temperature profile and of the distribution of thermal stresses is computed by solving heat transfer equations for varistor disks with nonuniform electrical properties. The simulations identify failure processes and determine energy absorption capability of varistor elements. The results are in excellent agreement with experiment and provide fundamental explanation of the energy handling dependence upon current surge intensity and duration.

Failure modes and energy absorption capability of ZnO varistors

The energy absorption capability is a key parameter for ZnO varistors. This paper discusses the nonuniformity of energy absorption capabilities of ZnO varistors. With experiment results, we show that energy absorption capabilities of ZnO varistors can be highly scattered, for different commercial varistors, and for the same varistors under diverse current waves. We explain this nonuniformity phenomenon through numerical simulations, based on the microscopic circuit and heat transfer models of ZnO varistors. How the applied current, the nonuniformity of microstructure, and the nonuniformity of microstructural electrical and thermophysical characteristics influence the energy absorption capabilities of ZnO varistors is also analyzed.

Discussions on Nonuniformity of Energy Absorption Capabilities of ZnO Varistors

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. >

Development of a model for predicting flicker from electric arc furnaces

Long-term stability of metal oxide surge protectors from four manufacturers has been investigated. Valve elements were energized in ovens at temperatures from 75 to 175 degrees C, and the power dissipation was monitored. The results show the variability in the stability of products available at present. In one case, an observed instability was due to deterioration of the sidewall. The results show that aging can increase or decrease the energy discharge capacity. The findings have application in the selection of arresters and in the development of standards. >

Long-term stability and energy discharge capacity of metal oxide valve elements

The electrical performance of eight metal-oxide valve elements in nitrogen has been examined in an accelerated aging test. Valve elements were energized with AC voltages in air, and later in nitrogen, with and without collars, at 115 degrees C. The performance was based on the change in power dissipation over time. The power-time changes in nitrogen were insignificant for all the valve elements with collars. Some products had little power increase, whereas others had a large power increase. Much of the power increase was found to be reversible on the reintroduction of air. >

C.C. Erven

Papers

Development of a model for predicting flicker from electric arc furnaces

Long-term stability and energy discharge capacity of metal oxide valve elements

The electrical performance of metal-oxide valve elements in nitrogen