As the world moves towards S F6-free insulation technologies, understanding the dielectric behaviour of alternative gas mixtures is becoming increasingly important. Detailed characterization of partial discharge (PD) behaviour within conventional measurement circuits is constrained by distortion of the fast transient signal, limiting the effective measurement bandwidth. This study presents a novel measurement circuit that omits the traditional coupling capacitor and instead leverages the inherent capacitance of the gas-insulated structure to establish a more compact and sensitive detection path. The improved setup enables detailed time-domain acquisition of fast-rising PD pulses using a high-frequency current transformer (HFCT). Using this system, the corona discharge characteristics of a CO2 / O2(7 0 % / 3 0 %) gas mixture are experimentally investigated at pressures of 0.2,0.3 and 0.4 MPa. Phase-resolved PD patterns are analysed to assess the influence of gas pressure on PD inception voltage, charge magnitude, and pulse repetition behaviour. ... Read more

Accurate and reliable characterization of current transformer (CT) performance is essential for maintaining grid stability and power quality in modern electrical networks. CT measurements are key to effective monitoring of harmonic distortions, supporting regulatory compliance and ensuring the safe operation of the grid. This paper addresses a method for the characterization of CTs across an extended frequency range from 50 Hz up to 150 kHz, driven by increasing power quality issues introduced by renewable energy installations and non-linear loads. Traditional CT calibration approaches involve measurement setups that offer ppm-level uncertainty but are complex to operate and limited in practical frequency range. To simplify and expand calibration capabilities, a calibration system employing a sampling ammeter (power analyzer) was developed, enabling the direct measurement of CT secondary currents of an unknown CT and a reference CT without any further auxiliary equipment. The resulting expanded magnitude ratio uncertainties for the wideband CT calibration system are 10 ppm (k=2) up to 10 kHz and less than 120 ppm from 10 kHz to 150 kHz; these uncertainties do not include the uncertainty of the reference CT. Additionally, the operational conditions and setup design choices, such as instrument warm-up duration, grounding methods, measurement shunt selection, and cable type, were evaluated for their impact on measurement uncertainty and repeatability. The results highlight the significance of minimizing parasitic impedances at higher frequencies and maintaining consistent testing conditions. The developed calibration setup provides a robust foundation for future standardization efforts and practical guidance to characterize CT performance in the increasingly important supraharmonic frequency range. ... Read more

This paper presents a future-proof switching procedure for the switching of increasing electrostatic (e.s.) and electromagnetic (e.m.) induced currents with a line side earthing switch. The induced currents are becoming much higher than stated by IEC-standards due to increasing line current and the use of combined (un-transposed) overhead lines. Notorious are overhead lines with different voltage levels combined at single pylons. This adapted switching procedure becomes even more important due to the increasing amount of Gas Insulated Switchgear (GIS) being introduced in the grid. ... Read more

Due to climate change more power converters are installed in the grid resulting in the injection of (supra-) harmonic currents and voltages in the grid. As part of a larger research, the impact of harmonic frequencies on insulation materials is studied. This paper discusses the results of breakdown voltage tests of synthetic ester liquid with varying frequency and electrode distance. A test cell according to IEC 60156 is used with electrode distance varying from 0.5 mm to 0.1 mm and the frequency is varied from 50 Hz to 2000 Hz. The results indicate a dependency on both electrode distance and fundamental frequency. ... Read more

In the 1960’s, gas insulated switchgear (GIS), gas insulated busbar (GIB) and other gas insulated substation components were developed to overcome several disadvantages of air insulated substations. Gas insulated substations, although more expensive than the air insulated counterparts, are almost insusceptible to atmospheric conditions such as precipitation, pollution and ice formation. Moreover, the surface area of gas insulated substations is significantly smaller than that of air insulated substations at the same voltage level and power rating. The direct influence of gas insulated substations on the environment is also small compared to air insulated substations because of the lack of corona and thus audible noise and radio frequency interference, especially in wet weather conditions.
From the above mentioned advantages it seems that gas insulated substations are advantageous with respect to air insulated substations. However, the main disadvantage, next to the construction costs, is the fact that almost all GIS is filled with sulphur hexafluoride (SF6) as an insulation gas, which has a very high global warming potential of roughly 23,000 times that of CO2. The global warming potential of SF6 has resulted in strict governmental regulations on the usage and storage of SF6. Therefore, the urge from the industry to replace SF6 with a more environmentally friendly insulation gas has become very strong over the past years.
Unfortunately, most readily available and environmentally friendly insulation gases have a relatively low electrical breakdown strength, which would require the operating pressure or the dimensions of GIS to be significantly increased. Increasing the operating pressure or the dimensions of GIS would be unfeasible. Therefore, the main challenge in the field of GIS is to improve the electrical breakdown strength of GIS without increasing the size or raise the operating pressure above the current design limits.
The investigation into the improvement of the breakdown strength of GIS has taken two main paths. Firstly, ongoing research is being conducted to develop a new replacement gas which has a breakdown strength comparable to that of SF6. This research has recently led to several replacement candidates. Secondly, research has shown that the breakdown strength of GIS can also be improved by the introduction of a dielectric coating layer on the electrodes inside GIS. This thesis focusses on the improvement of the breakdown strength of GIS with the application of a coating layer.
In this thesis the lightning impulse breakdown voltage of gas-coating insulation systems is evaluated with the use of lightning impulse breakdown tests on a rod-plane electrode configuration. These tests include a wide variety of coating materials with a wide range of material properties and are mainly conducted in dry air as an insulating gas. Next to the breakdown tests, a range of material characterisation experiments are performed to obtain more information on the coating material structure and to find a relation between the coating material parameters and the breakdown strength of the gas-coating insulation system. The material characterisation experiments include dielectric spectroscopy, surface roughness measurements, conduction current measurements, electrical breakdown tests and optical microscopy... ... Read more

The design constraints of gas insulated switchgear(GIS) are changing due to an increasing power demand and decreasing available floor space for substations. Ideally, new GIS should operate at a higher nominal voltage with a minimal or no increase in size. Another ongoing development in the power industry is the desire to replace SF6 by an environmentally friendly gas which is preferably readily available and has relatively low production costs. Unfortunately these gases show a breakdown strength which is significantly lower than SF6. Coatings can prove to be a possible solution to this problem. The breakdown strength of GIS can be improved with the application of a dielectric coating on the electrode surfaces. In this paper, the influence of thick coatings on the breakdown strength of GIS is evaluated with negative lightning impulse breakdown tests. The tests are performed on a rod-plane electrode arrangement in which the rod electrode is coated. The coatings consist of a 10mm thick layer of epoxy or an epoxy based nanocomposite. ... Read more

In gas insulated switchgear(GIS) SF6 gas is widely in use because it has good electrical insulation and arc interruption capabilities. Due to environmental constraints the desire to use alternative gases is continuously growing. This paper focuses on dry air as an alternative gas which unfortunately has a breakdown strength which is lower than the breakdown strength of SF6 at equal gas pressure. To improve the breakdown strength of dry air filled GIS, dielectric coatings can be applied to the electrodes. In this paper, the performance of GIS with thin coatings is evaluated through breakdown tests in a rod-plane electrode arrangement. Negative lightning impulse voltage is applied on the rod electrode and the gas pressure is kept constant at 0.9 MPa. ... Read more