AN ASSESSMENT OF THE HARMONIC POLLUTION DUE TO LINE CORONA

Abstract

This work deals with the phenomenon of corona on high voltage overhead transmission lines as a possible source of harmonic pollution. Starting with a validated method for simulating corona by means of distributed nonlinear shunt resistors, the distorted current waveforms for different locations on a long line could be determined. The location-dependent frequency spectrum of the line longitudinal current could be obtained through numerical Fourier analysis. It is shown, that under some operating and weather conditions, the harmonic content of the line current can attain technically unacceptable values.     

ELECTROMAGNETIC TRANSIENTS ON COMPENSATED LINES UNDER CORONA

ABSTRACT

The purpose of this paper is to present a digital computational method for the determination of the fast electromagnetic transients propagating on compensated overhead power lines, evoked by internal or external over voltages, as effected by corona discharges. The approach enables the consideration of series capacitor and shunt reactor compensation. The line model is based on time-domain solution using the Runge-Kutta-Verner numerical technique to solve a set of simultaneous differential equations, whose number depends on the assumed number of line sections, as derived from the line equivalent circuit. The increase of the location-dependent conductor effective radius due to corona is considered as one of variable sets, using an iterative solution procedure. To avoid the parasitic Gibbs-oscillations due to the finite number of line sections (which are superimposed on the actual solutions, a set of properly chosen damping resistors is added to the line model, yielding a frequency-dependent damping. The simulation of the corona discharge uses a model derived from an experimentally measurable voltage-charge hysteresis loop relationship of a line test length. As far the input voltage stimuli are concerned, so the model can consider any voltage-time function (step, ramp, double-exponential, sine waves...etc), or even be in the form of tabulated numerical data. The validity of the model is checked by comparing its results to corresponding measurements.     

OPTIMAL COMPENSATION OF NONUNIFORMLY LOADED RADIAL FEEDERS,WITH APPLICATIONS

ABSTRACT

This paper presents a generalized mathematical model for assessing the loss reduction in nonunlformly loaded radial feeders by capacitor shunt compensation. The model allows for the simultaneous presence of linearly increasing feeder load density in addition to a concentrated load at the feeder end. Any number of compensating capacitors can be included in the analysis. The model is then applied to study the effect of the number of feeders on the achieveable optimal reduction in the feeder copper loss. The paper also gives the optimal size and locations of these capacitors, for any number of radial feeders eraenatlng from a distribution substation to serve a certain total load.     

EFFECTS OF NISIN AND MODIFIED ATMOSPHERE PACKAGING (MAP) ON THE QUALITY OF EMULSION‐TYPE SAUSAGE

ABSTRACT

The aim of this work was to study the effects of nisin (30 ppm) and modified atmosphere packaging (MAP) on the chemical, microbial and sensory properties of emulsion‐type sausage stored under two different atmospheres (%CO₂/%N₂/%CO/%O₂): 39.5/60/0.5/0 and 39.5/20/0.5/40. The samples were stored at 3 ± 1C for 42 days. Microbial count, values of pH, CIE L*, a* and b* color parameters, lipid oxidation, production of nitrosomyoglobin and sensory properties were assessed throughout the storage period. The data showed that nisin was able to reduce the growth of mesophilic, psychrotrophic and lactic acid bacteria. In addition, the MAP did not show any significant effects on microbial growth. However, free O₂ MAP, in combination with nisin, reduced the growth of yeast and mold. MAP could produce a stabilized red color and minimize the oxidative reactions in the samples. Packaging conditions had no significant effect on pH and sensory properties.

PRACTICAL APPLICATIONS

The results of this study confirmed that nisin can reduce the growth rate of lactic acid bacteria, psychrotrophic and mesophilic bacteria in emulsion‐type sausage, and free O₂ MAP, in combination with nisin, inhibits the growth of yeast and mold. The use of 30 ppm nisin, in combination with MAP containing 39.5% CO₂ and 0.5% CO gases, can lead to better quality preservation of the emulsion‐type sausages stored at low temperature and can extend their shelf life.