Investigation the polarity effect and the voltage breakdown in small air gaps (original) (raw)
Related papers
In the present paper the Ground Effect of small rod–plate air gaps, which is observed due to the grounding of one of the electrodes, is investigated. Values of the field strength in the gap are recorded and analyzed for the two different arrangements, with the rod or the plate grounded. The distribution of the field along the axis of the gap is strongly affected by the geometry of the gap, and especially by the electrode chosen to be grounded. The Ground Effect also affects the breakdown voltage of the rod-plate air gaps but in a quite different way than the Polarity Effect does. The values of the breakdown voltage depend on the maximum value of the field strength in the gap, and the corona leakage current through the gap. According to the Polarity Effect the breakdown voltage is considerably higher in the arrangement with negative polarity on the rod because of the intensive corona effects. According to the Ground Effect the breakdown voltage is higher in the arrangement with the r...
Optimization of Corona Effects in Small Air Gaps Stressed by DC Voltages
2012 Sixth UKSim/AMSS European Symposium on Computer Modeling and Simulation, 2012
In the present paper methods of minimizing or maximizing the values of the Corona onset voltage and the Corona current in small rod-plate air gaps are investigated. The geometry and the way of grounding and charging the electrodes, (Ground Effect), the gap length, the existence of barrier in the gap (Barrier Effect), and the conditions of the air in the gap, are some factors, which influence greatly the distribution of the electric field in the gap, and hence the above values. Combining experimental and simulation-theoretical work, it is resulted that: a) the electrode chosen to be ground, strongly influences the distribution of the field and hence the Corona onset voltage and the corona current in rod-plate air gaps. When the rod is grounded the value of the corona onset voltage is higher and the corona current is significantly smaller. b) A dielectric barrier, when placed in specific positions in the gap, increases the Corona onset voltage to a maximum value, and annihilates the Corona Current.
Eurocon 2013, 2013
The present paper aims to the investigation of the methods used to minimize or maximize the values of the Corona onset and Breakdown voltage in small rod-plate air gaps when stressed by dc or impulse voltages. The geometry and the selection of grounding and charging of the electrodes, (ground effect), the gap length, the existence of barrier in the gap (barrier effect), and the Corona effects appearing in the gap prior to the breakdown are the main factors, which influence greatly the distribution of the electric field in the gap, and hence the above values. Combining theoretical, simulation and experimental work, it is resulted that: a) The electrode chosen to be ground, strongly influences the distribution of the field and the Corona effects and hence the values of the Corona onset and breakdown voltage. When the rod is grounded and the plate is negatively charged the value of Corona onset voltage is higher, the corona effects are less intense and dc breakdown voltage, without Corona, is higher. When the plate is grounded and the rod negatively charged the value of the Corona onset voltage is lower, the corona effects are more intense and hence the dc breakdown voltage is higher. b) A dielectric barrier, when placed in specific positions in the gap, decreases the Corona effects and raises the breakdown dc voltage. c) In air gaps stressed by impulse voltages the results are very different. The corona onset and the breakdown voltage are maximum when the rod is grounded and positive leading to more intense Corona effects.
This paper investigates the influence of a resistor on the dielectric behavior of an air gap. The resistor is connected in series with the air gap and the latter is stressed by impulse voltage. Air gap arrangements of different geometry with either the rod or the plate grounded are stressed with impulse voltages of both positive and negative polarity. The resistor is connected in series with the air gap in the return circuit connecting the gap with the impulse generator. The method followed involves the investigation of the graphs of the charging time concerning the air gaps capacitances, in connection to the value of the resistor, the geometry of the gap, the effect of grounding and the polarity effect. It is determined that the charging time of the air gap increases, as the value of the resistor increases. It is also determined that the peak voltage value of the fully charged air gap decreases as the value of the resistor increases. The results of the mathematical and simulation analysis are compared with the results of the oscillograms taken from experimental work. In addition and consequently to the above results it is concluded from the experimental work that the in series connection of the resistor in the circuit has significant influence on corona pulses (partial discharges) occurring in the gap and on the breakdown voltage of the gap. A new method of controlling the corona effects and consequently the breakdown voltage of small air gaps stressed by impulse voltage of short duration in connection to the ground effect and the polarity effect has arisen. Furthermore through mathematical analysis of the charging graphs obtained from simulation and experimental oscillograms there was a calculation of the values of the capacitance of the air gaps in relation to their geometry and the results were compared to the values calculated with mathematical analysis.
2013
In the present paper methods of controlling Corona and breakdown in small rod-plate air gaps are investigated. Combining experimental and simulation-theoretical work, it is resulted that when the rod's diameter is bigger, the gap length larger and the rod is grounded the field is less inhomogeneous. Therefore the value of the dc breakdown voltage without Corona is higher. If Corona occurs then the values of the Corona onset voltage are higher, and the corona effects are not intense. The Corona effects, lead to a rise of the value of the dc breakdown voltage especially when the rod is negatively charged. Moreover an insulated thin barrier, when positioned near the rod increases the breakdown dc voltage to a maximum value, and minimizes the Corona effects. Especially for gaps stressed by impulse voltage the Corona effects, appearing with the form of electric current pulses, are influenced by the same factors with a different way. The values of the breakdown voltage in contrast to what happens with dc voltage are higher when the Corona effects are weaker, depending on the influence of the field's inhomogenity (geometry and effect of grounding). It is also resulted that a resistor connected in series with the gap decreases its maximum charging voltage and increases the value of the breakdown voltage.
The influence of the Ground Effect to the corona leakage current in small air gaps
Proceedings of The IEEE - PIEEE, 2007
The Ground Effect is the phenomenon that occurs due to the different way an air gap is grounded while stressed by high voltage. This phenomenon influences the distribution of the field in the gap, the corona onset voltage and the breakdown voltage in small gaps. In longer air gaps, the Ground Effect influences the Corona Effects and consequently the values of the Corona Current through the gap. The corona leakage current is higher in a rod-plate air gap with the plate grounded, because in such an arrangement the electric field is more inhomogeneous. This is valid for both polarities of DC voltage and AC voltage as well. In a rod- rod air gap the values of the corona current appear differences between the two polarities of DC voltage. When the corona current becomes high enough it decreases the inhomogeneity of the field and influences the values of the breakdown voltage. The principle of action-reaction is valid. "The corona current reacts against the action of the field to pro...
The rod - plate air gaps are of great importance in High Voltage applications. The rod - plate air gap with the plate grounded has been investigated enough, while a study of the case with the rod grounded is missed. In the present paper both arrangements of a rod - plate air gap with the rod or the plate grounded are experimentally investigated and analyzed with the aid of special simulation software, using the Finite Element Method. Values of the field strength in the gap when stressed by the breakdown voltage are recorded and analyzed. The results show that the distribution of the field in the gap axis is strongly affected by the geometry of the electrodes and the arrangement of the gap, while the values of the breakdown voltage are strongly related to the maximum values of field strength in the gap, as well as the leakage corona current. A dielectric plate, called barrier, placed between the electrodes, influences analogically the distribution of the field and the breakdown volta...
Onset voltage of negative corona on dielectric-coated electrodes in air
This paper describes theoretical and experimental investigations of the effect of an electrode coating on the onset voltage of a corona on negatively stressed electrodes. Dielectric-coated hemispherically-capped rod-to-plane gaps positioned in air are investigated. The onset voltage is calculated based on the self-recurring single electron avalanche developed in the investigated gap. Accurate calculation of the electric field in the vicinity of a coated rod and its correlation to the field values near a bare rod of the same radius are obtained using the charge simulation method. The calculated field values are utilized in evaluating the onset voltage of the corona. Also, laboratory measurements of the onset voltage on bare and coated electrodes are carried out. The effects of varying the field nonuniformity, the coating thickness and its permittivity on the onset voltage values are investigated. The results show that coating the electrodes with a dielectric material is effective in increasing the onset voltage of the corona on its surface. The calculated onset voltage values for coated and bare electrodes agree satisfactorily with those measured experimentally.
Mathematical Modelling of Engineering Problems
The stable corona discharge is widely used in filtration and electrostatic separation in recent years, and several models have been used by researchers to analyze one of its most important properties which is the current-voltage characteristic. The aim of this paper is to investigate the influence of ambient temperature and electrodes’ gap on negative DC discharge using rod-plane geometry, and the Townsend formula was found to be most appropriate model (I=K.V.(V-V0)). The experimental results show that for the same voltage level applied to the high voltage electrode, the discharge current rises with increasing temperature and decreases as the electrodes’ gap increases. Using curve fitting, it was proven that the geometric factor K is proportional to temperature and to the power of the distance between electrodes independently, and the threshold voltage V0 is proportional to the product of the temperature reciprocal and the power of the inter-electrode spacing. From these results, a n...