Reactive Power Compensation of Non-linear industrial loads

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Date
2012
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Publisher
MPUAT, Udaipur
Abstract
Application of non-linear loads such as adjustable speed drives, electric arc furnaces and power conversion devices in power system results in power quality problems such as harmonics, inter-harmonics and voltage fluctuation that force the utilities and consumers to take countermeasure actions. Worldwide steel production by means of electric power has been rising. Despite the various advantages of electric arc furnace over conventional blast furnace, this type of electrical load produces voltage disturbances which affect adversely to other loads in the electric network. Arc furnace is a non-stationary electric load. This fact gives rise to voltage fluctuation which produces the effect known as flicker. Also the arc furnace is a highly non-linear load, which produces current harmonics. This current harmonics will give rise to high voltage harmonics depending on the impedance of the electric network. In order to estimate the stochastic characteristics of the arc furnace, it is necessary to accurately simulate the arc furnace behaviour. For this purpose, an arc furnace model, which can simulate all the mentioned power quality indices, is developed based on Hyperbolic-Exponential model (V-I model). Electric arc furnace present rapidly varying, largely unbalanced, poor power factor loads to the utility power transmission network. The large and erratic reactive current swings cause corresponding voltage drops across the impedance of the ac system, resulting in fluctuating terminal voltage. Therefore an equally rapid compensating device is required to remedy and prevent the spreading of the power quality problem caused by electric arc furnace. Passive filters used in conjunction with thyristors have been successful in correcting the power factor and compensating the harmonics. But, these methods are unable to supply any portion of the fluctuating real power drawn by the furnace. Therefore in this study, by considering the high changes of reactive power and voltage flicker of non-linear furnace load, a model UPFC connected to an arc furnace is designed and modelled using MATLAB/Simulink block-set. The UPFC with active compensation capability behaves as a positive or negative resistance opposing to variation of the arc resistance and suppress voltage flicker at the source. The power fluctuation which causes the voltage drop can be separated in two parts: Mean reactive power absorbed by the furnace, which could be compensated by fixed shunt-capacitor, and the instantaneous variation of the reactive power around its mean value which can only be compensated with a dynamic device. The instantaneous Variation of the reactive power can be cancelled by means of several solutions. Two compensations can be distinguished: - Shunt compensation: the reactive power consumed by the arc furnace must be kept constant. This type of compensation does not protect the arc furnace, consequently, in case of short-circuit the installation of the furnace undergoes high currents. A shunt compensation of active power does not seem very interesting because of the inductive nature of the feeding system. - Series compensation: two types of compensation can be achieved by this structure: active and reactive compensation. UPFC can control real and reactive power consumed by the arc furnace by injecting series voltage of the appropriate magnitude and angles.
Description
Reactive Power Compensation of Non-linear industrial loads
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Citation
Paliwal and Macherchandani, 2012
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