External Overvoltages Research Articles

Experimental Investigation of High-Frequency Effect on Ignition and Damping of Corona Discharges

The impact of high-frequency voltage/current oscillations on the corona discharge’s ignition and damping in electrical networks were experimentally investigated as part of this study. Internal and external overvoltages caused by short-circuit faults or circuit opening/closing in the generation, transmission and distribution lines cause voltage/current oscillations on the lines at different frequencies. At frequencies of 50, 150, 250, 350, and 500 Hz in different electrode systems such as Sphere-Plane and Needle-Plane, the effects of these oscillations at various frequencies in the networks on the ignition and damping of corona discharges on transmission lines have been investigated. The results showed that the ignition and damping voltages of corona discharges are greatly influenced by high-frequency voltage/current oscillations, and that an increase in the frequency value significantly speeds up the corona discharge’s ignition.

Study of the waves propagation of lightning overvoltage impulse in the catenary system of electrified railways

Introduction. The article is devoted to the study of the waves propagation of lightning overvoltage impulse in the catenary system of electrified railways. The purpose of the work is to determine the zone of waves propagation of lightning overvoltage impulse along the catenary system, the degree of attenuation and the influence of the soil condition on the mode of their propagation.Materials and methods. The authors carried out tests on the waves propagation of lightning overvoltage impulse along the catenary system of the 1st (ring) track and the 15th (dead end) track of the Experimental Loop of the Railway Research Institute at the Shcherbinka station using a high-voltage impulse voltage generator.Results. During the tests, the influence of the soil condition on the mode of waves propagation of lightning overvoltage impulse was determined. The degree of attenuation of the lightning overvoltage impulse wave in the catenary system in the looped and dead end sections is determined, considering the influence of the reverse (reflected) overvoltage wave, as well as changes in the voltage level during the wave process occurring in the catenary system. The data obtained during the tests enable to determine the propagation speed of the lightning impulse wave.Discussion and conclusion. The obtained test results will be useful for improving the reliability of lightning protection devices of the catenary system against external overvoltages and can be used to improve insulating elements.

Studi Kemampuan Arrester Untuk Pengaman Transformator Pada Gardu Induk Tanjung Morawa 150 KV

Overvoltage is a voltage that can only be held for a very limited time. Overvoltage that occurs for a time that exceeds the equipment's capacity limit will damage the equipment connected to the network that is subjected to overvoltage. Lightning overvoltage is a periodic overvoltage caused by external overvoltage, both direct and indirect strikes. Lightning overvoltage only lasts a very short time but has a voltage that is so high that it exceeds the operating voltage of the equipment so it is potentially very damaging. Lightning Arrester is an installation safety equipment from overvoltage disturbances due to lightning strikes (Lightning Surge) or by switching surges (Switching Surge). Transformer / power transformer serves to distribute power / electrical power by increasing or decreasing the voltage at the substation. This research focuses on substation equipment, namely Lightning Arrester ASEA type XAR 170A3/144 which is connected to a Power I transformer (transformer) UNINDO 906007289. Good protection is obtained when the arrester is placed as close as possible to the transformer clamp. However, in practice the arrester must be located at a distance X from the transformer being protected. Therefore, the distance must be determined properly so that the resulting protection can be obtained properly. Arrester installation according to theory is 50 meters from the transformer, in practice at the TAMORA Substation the arrester distance is 3 meters from the temporary transformer based on calculations in this final project the best distance is 10.96 meters.

Desain Pemrograman Visual Pengendalian Nomor Urut

Overvoltage is a voltage that can only be held for a very limited time. Overvoltage that occurs for a time that exceeds the equipment's capacity limit will damage the equipment connected to the network that is subjected to overvoltage. Lightning overvoltage is a periodic overvoltage caused by external overvoltage, both direct and indirect strikes. Lightning overvoltage only lasts a very short time but has a voltage that is so high that it exceeds the operating voltage of the equipment so it is potentially very damaging. Lightning Arrester is an installation safety equipment from overvoltage disturbances due to lightning strikes (Lightning Surge) or by switching surges (Switching Surge). Transformer / power transformer serves to distribute power / electrical power by increasing or decreasing the voltage at the substation. This research focuses on substation equipment, namely Lightning Arrester ASEA type XAR 170A3/144 which is connected to a Power I transformer (transformer) UNINDO 906007289. Good protection is obtained when the arrester is placed as close as possible to the transformer clamp. However, in practice the arrester must be located at a distance X from the transformer being protected. Therefore, the distance must be determined properly so that the resulting protection can be obtained properly. Arrester installation according to theory is 50 meters from the transformer, in practice at the TAMORA Substation the arrester distance is 3 meters from the temporary transformer based on calculations in this final project the best distance is 10.96 meters.

Simulation of impulse current generator for testing surge arresters using frequency-dependent models

The object of research is the equivalent circuit of an impulse current generator designed for testing surge arresters. Calculation of the impulse current generator parameters when discharging a capacitor bank to a complex nonlinear load is a difficult task for an analytical solution. Until now, the application of surge arrester frequency-dependent models was limited to the problems of overvoltage computation. Surge arrester frequency-dependent models can predict the residual voltage with high accuracy. This is the reason to consider that surge arrester frequency-dependent models can be used for calculating the main parameters of impulse current generators designed for physical testing of surge arresters.
 The task of determining the equivalent circuit parameters required for getting a discharge current of a given waveform and amplitude in an impulse current generator scheme with a nonlinear load was solved using circuit simulation.
 This article presents the results of studying the processes in impulse current generator equivalent circuit. In the circuit a dynamic model of a surge arrester is used as the load model. For this, an equivalent circuit for the discharge path of the impulse current generator was drawn up. The parameters of the circuit elements (including the required number of capacitors and their charging voltage) are determined, which are necessary for getting a discharge current of a given standardized waveform and amplitude. The parameters of the discharge path are determined for surge arresters of three different voltage classes. It was found that the relative error when determining the residual voltage between the terminals of the surge arrester model does not exceed 3 %.
 The work contributes to the further development of circuit simulation of surge arresters and the expansion of the scope of surge arrester dynamic models. As a result of the research performed, the possibility of using surge arrester frequency-dependent models for determining the discharge current waveform in impulse current generators is shown. The research performed is relevant due to the fact that surge arresters have become a main tool for protecting the insulation of electrical network equipment against external and internal overvoltages

Enhancement of Electro-Thermal Characteristics of Micro/Nano ZnO Based Surge Arrester

Semiconductor ceramics based metal oxide varistors (MOVs) are currently used to protect electrical equipment against internal and external overvoltages without interrupting power supply. The improved protective characteristics of surge arresters helps to reduce the cost with an excellent insulation design for electrical systems. The proper exploration of material with better non-linearity, higher breakdown voltage and lower leakage current is considered as essential parameters for proper design of modern high power, high voltage and gas-insulated substation (GIS). In this paper, varistor samples of Sample 1 (95% Micro ZnO + 2% of Micro Bi2O3 + 2% of Micro Y2O3 + 1% of Micro Sb2O3), Sample 2 (95% Nano ZnO + 2% of Micro Bi2O3 + 2% of Micro Y2O3 + 1% of Micro Sb2O3), Sample 3 (95% Micro ZnO + 2% of Micro SrO + 2% of Micro Y2O3 + 1% of Micro Sb2O3) and Sample 4 (95% Nano ZnO + 2% of Micro SrO + 2% of Micro Y2O3 + 1% of Micro Sb2O3) are prepared through sequential process, which includes ball milling, calcination (700 °C), compression (340 kg/cm2), molding and sintering (1150 °C). The prepared samples are then characterized using SEM, and experimentation is carried out to analyze the various parameters such as non-linearity, permittivity, dielectric loss and thermal conductivity. The SrO included as a principal additive component instead of Bismuth oxide in Sample 3 and 4 makes it with improved surge arrester characteristics. The results revealed that the Sample 4 attained enhancement of 40% in the non-linear characteristics is due to the increase in the active area of grain boundaries in comparison with Sample 1. In addition, the impedance spectroscopy results emphasize that the value of permittivity, resistivity and dissipation factor is better for Sample 4. Thermal analysis concluded that the thermal conductivity enhanced to 0.67 (W/cm K) for Sample 4 by exclusive formation of ZnSrO2 phase.

Hybrid continuous circuit‐trapezoidal integration method analysis of multi‐cross structure of grounding system

An essential requirement to improve the lightning performance of transmission line is the achievement of low impulse impedance of grounding system, which diminishes the occurrence of the external overvoltages. In this study, for the first time, a multi-cross structure used as transmission line tower-footing grounding system is investigated by means of hybrid continuous circuit-trapezoidal integration method (HCCTIM). It is discovered that the angle of minimum impulse impedance or the optimal structure of multi-cross grounding system is mainly dependent on the branch length compared to the effective length of a single horizontal conductor. Furthermore, in the current work, the trapezoidal integration method is used to solve the continuous circuit equations which elements are extracted from electromagnetic integral method, called HCCTIM. Coupling elements and soil ionisation are considered in this model. This method is an accurate, simple, and less time-consuming computational method. The comparison of the results with measurements, other recent simulations and CDEGS software, satisfactorily validate the proposed method.

Superfast Thyristor-Based Switches Operating in Impact-Ionization Wave Mode

The process of triggering thyristors by an overvoltage pulse with a short rise time was investigated. Low-frequency commercial thyristors of tablet design with diameters of silicon wafers of 32-56 mm and an operating voltage of 2-2.4 kV dc were used in the experiments. An external overvoltage pulse was applied across the thyristor main electrodes, which ensured a voltage rise rate from 0.5 to 6 kV/ns within a few nanoseconds. Under such conditions, the thyristor closing process occurred due to initiation and propagation of a fast ionization front across the semiconductor structure. The time of switching the thyristor from the blocking state to the conducting state was within 200-400 ps. The thyristor-based switches operated in this mode were tested in two discharge circuits. In the first circuit, an assembly of nine 2-kV and 40-mm thyristors connected in series switched a 2-μF capacitor, which was charged to a voltage of 20 kV and to a resistive load of 0.17 Ω. The following results were obtained: discharge current amplitude of 45 kA, maximum current-rise rate of 134 kA/μs, current rise time (0.1-0.9 level) of ~0.4 μs, pulse duration (FWHM) of ~1 μs, and switching efficiency of 0.85. In the second circuit, the switch contained two 2.4-kV and 56-mm thyristors connected in series. A 400-μF capacitor, which was charged to a voltage of 5 kV, was switched to a resistive load of 0.026 Ω. The following discharge parameters were obtained: discharge current amplitude of 114 kA, maximum current-rise rate of 32 kA/μs, current rise time (0.1-0.9 level) of ~5 μs, pulse duration (FWHM) of ~20 μs, and switching efficiency of 0.96.

A thyristor switch with a subnanosecond switching time

The possibility of triggering thyristors by an overvoltage pulse with a short rise time was investigated. Low-frequency thyristors of pellet design with diameters of semiconductor structures of 32 and 40 mm and an operating voltage of 2 kV were used in the experiments. An external overvoltage pulse that increased from 2 to 5–8 kV within a time of 0.8–1 ns was applied to the thyristors. Under such conditions, the time of switching a thyristor into a conducting state was no longer than 200 ps. An assembly of six thyristors connected in series switched a capacitor with a capacitance of 2 μF, which was charged to a voltage of 13 kV, to a resistive load of 0.25 Ω. The following results were obtained: a discharge-current amplitude of 27 kA, an initial current-rise rate of 110 kA/μs, a FWHM pulse duration of 1 μs, and a peak power in the load of 190 MW. The circuit diagram of the experiment and the obtained results are described.

Effect of the grounding resistance to the behaviour of high‐voltage transmission lines’ surge arresters

External overvoltages constitute a typical cause of faults, damages and interruptions in the electrical networks’ high-voltage transmission lines. In order to protect the lines and their equipment against lightning, overhead ground wires in combination with surge arresters are installed, improving the lightning performance of the system and reducing the annual failure rate. The achievement of low values of earth resistance is an essential requirement, since a good grounding system reduces considerably the corresponding insulation breakdowns. However, the behaviour of surge arresters in relation to the grounding resistance is different, as it depends on the position of the lightning hit. The current work is devoted to the sensitivity analysis of the failure probability of surge arresters with relation to the grounding resistance, investigating concurrently the effect of the arresters’ installation interval and the energy absorption capability.