AC Partial Discharge Research Articles

Characteristics of perfluoromethyl vinyl ether: A new eco‐friendly alternative gas for SF6

AbstractThe exploration of eco‐friendly insulating gas to substitute the most potent greenhouse gas sulphur hexafluoride (SF6) has consistently garnered significant attention. Herein, the authors evaluated the feasibility of utilising perfluoromethyl vinyl ether (PMVE, C3F6O) as a new branch of eco‐friendly insulating gas for the first time. The primary dielectric and stability characteristics of PMVE regarding AC breakdown, partial discharge, dielectric recovery, and decomposition properties were revealed under various gas pressure and electrical field conditions. It was found that PMVE demonstrated superior dielectric strength, with the AC breakdown and PD inception voltage (PDIV) 1.10 and 1.14 times that of pure SF6. Furthermore, the dielectric strength of PMVE exhibits stability even after undergoing 100 cycles of AC breakdowns, and there is no observable formation of solid precipitation on the electrode surface. The discharge decomposition of PMVE mainly generates fluorocarbon (CF4, C2F6, C3F6, C3F8, etc.) and CO. Overall, the exceptional insulation stability and no absence of solid precipitation features endow PMVE to be utilised as a new eco‐friendly gas for SF6‐free gas‐insulated equipment.

Long-term AC partial discharge characteristics of a 22 kV cast resin transformer in accelerated tests

Long-term AC partial discharge characteristics of a 22 kV cast resin transformer in accelerated tests

Effect of Conducting, Semi-Conducting and Insulating Nanoparticles on AC Breakdown Voltage and Partial Discharge Activity of Synthetic Ester: A Statistical Analysis.

This paper is aimed at studying the influence of conducting (Fe3O4), semi-conductive (ZnO), and insulating (ZrO2, SiO2, and Al2O3) nanoparticles (NPs) at various concentrations on the AC dielectric strength of MIDEL 7131 synthetic ester (SE) and partial discharges activity. First, a detailed and improved procedure for preparing nanofluids (NFs) in five concentrations ranging from 0.1 g/L to 0.5 g/L is presented, including high-speed agitation and ultrasonication. Then, the long-term stability is checked based on zeta potential analysis. After preparing and characterizing the NF samples, the following step is to measure their AC breakdown voltage (BDV). Due to the limitation of the high voltage supply (Baur system), the tests are performed according to IEC 60156 standard (2.5 mm gap distance) only with ZnO, ZrO2, and SiO2 NPs, and for comparison, tests are executed for all considered NPs with an electrodes gap of 2 mm. It is shown that the addition of Fe3O4 (20 nm), ZnO (25 nm), ZrO2 (20–30 nm), SiO2 (10–20 nm), Al2O3 (20–30 nm), and Al2O3 (50 nm) NPs improves the dielectric strength of synthetic ester upon an optimal concentration which gives the highest AC BDV. SiO2 (10–20 nm) and Al2O3 (20–30 nm) manifest their best improvement at 0.3 g/L, while for the other NFs, the best improvement is observed at 0.4 g/L. Further, the Anderson–Darling goodness-of-fit test is performed on the experimental data to check their conformity with the Extreme value (EV), normal, and Weibull distributions; the normal and EV fit curves are plotted and used to evaluate the breakdown voltages at probabilities of 1%, 10%, and 50%. It is shown that the AC breakdown voltage outcomes for most investigated nanofluids mostly obey the three EV, normal, and Weibull distributions. Then, the best combinations (nature of NP and optimal concentration), namely Fe3O4 (20 nm, 0.4 g/L), Al2O3 (20–30 nm, 0.3 g/L), and Al2O3 (50 nm, 0.4 g/L) NPs, that highly enhance the AC BDV of SE are chosen for a partial discharge activity investigation and comparison with pure SE. It is shown that the addition of those NPs significantly reduces the activity of partial discharges compared to pure SE.

Medium Voltage Converter Inductor Insulation Design Considering Grid Requirements

Medium voltage (MV) SiC devices facilitate direct (without 50-/60-Hz transformer) connection of the power electronics converter to the MV grid using simple topology. Compared to the insulation design of MV inductors that have been widely used in the power system, the insulation design of the MV converter filter inductors has new challenges. Particularly, the grid impact on insulation requirements on converter filter inductors is rarely discussed. This article introduces the insulation design of a grid-side filter inductor for a 13.8-kV power conditioning system converter. The grid insulation requirements, including the short-duration power frequency overvoltage and the lightning impulse voltage, are considered in the design. To meet the requirements, the layer-to-layer insulation, winding-to-core/ground insulation, the air gap discharge between the winding and the core, the local electric field, as well as the interturn transient voltage distribution are considered. The designed inductors are validated by the 46 kV (>1 min) dc hi-pot test, 12-kV ac partial discharge test, one-hour single-phase converter full rating test, as well as three-phase converter full rating test.

Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids.

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio.

Comparison of AC and DC Partial Discharge by Monitoring of Vacuum Degree in a Distribution Class Vacuum Interrupter

The vacuum degree of Vacuum Interrupter ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> ) will deteriorate because of gases emitted by arc heat, and leakage through the joints. It is important to select an appropriate maintenance criteria for a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> by monitoring the vacuum degree. However, monitoring of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> installed inside a solid insulation apparatus in a transmission system is impossible. Only studies on the insulation deterioration because of the decrease of the vacuum degree have been conducted, and important factors such as the maintenance criteria have not been investigated. Moreover, most studies have only been performed using AC voltage, not DC voltage. Therefore, in this paper, AC and DC partial discharge were compared by monitoring of the vacuum degree in a distribution class <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> to propose maintenance criteria according to voltage type. Through this, for efficient maintenance, maintenance criteria of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> for each voltage type are presented. The vacuum degree at which the dielectric strength rapidly decreases was confirmed according to voltage type. The coupling capacitor was installed directly on the floating shield of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">VI</i> . Moreover, to measure the pattern and apparent charge of partial discharge according to the vacuum degree, phase resolved partial discharge (PRPD) for AC partial discharge and pulse sequence analysis (PSA) for DC partial discharge were adopted. It is found that maintenance should be performed when the vacuum degree is in the range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-3} \boldsymbol {\sim } 10^{-2}$ </tex-math></inline-formula> torr regardless of the voltage type. Moreover, the usefulness of the technology is higher at AC voltage than at DC voltage.

AC Breakdown Voltage and Partial Discharge Activity in Synthetic Ester-Based Fullerene and Graphene Nanofluids

This paper deals with the study of the AC breakdown voltage (BDV) and partial discharges (PDs) activity of synthetic ester-based nanofluids (NF) with two kinds of carbonic nanoparticles (NPs), namely graphene (Gr) and fullerene (C₆₀); the synthetic ester (SE) being Midel 7131. The BDV measurement was achieved at various concentrations of NPs and different electrodes gap distances, while the partial discharges activity was studied only at the optimal concentration that gave the best improvements of BDV. First, a detailed improved procedure for preparing our NFs is presented. Then, the zeta potential measurements are performed on these NFs, and their stability is checked. After the preparation and characterization of samples, the BDVs and PDs parameters are measured according to IEC 60156 (modified gap distance) and IEC 60270 standards, respectively. Finally, conformity of the experimental data with Normal and Weibull distributions is examined, and the BDV at cumulative probabilities of 1&#x0025; and 50&#x0025; are then deduced. It is shown that BDV outcomes for all studied liquids obey both Normal and Weibull distributions, and the BDVs at cumulative probabilities of 1&#x0025; and 50&#x0025; are improved. Moreover, adding Gr and C₆₀ nanoparticles at different concentrations enhances the BDV values for investigated electrode gaps (0.1 to 2.0mm). The best improvement is obtained with a concentration of 0.4 g/L for 0.5mm and 0.7mm electrode gap with fullerene and Graphene nanoparticles, respectively. For a 2mm gap distance, the best improvements are of about 12.67&#x0025; and 16.64&#x0025; with 0.4g/L of C₆₀ and 0.3 g/L of Gr, respectively. It is also shown that the addition of C₆₀ significantly reduces the activity of partial discharges compared to pure SE, while the addition of Gr destroys the partial discharges resistance of pure SE.

Effect of O2 on AC Partial Discharge and Decomposition Behavior of C4F7N/CO2/O2 Gas Mixture

This paper focus on the influence of oxygen on the partial discharge (PD) and decomposition characteristics of C4F7N/CO2/O2 gas mixture as eco-friendly gas insulating medium. The PD characteristic parameters and phase resolved partial discharge (PRPD) patterns of C4F7N/CO2/O2 gas mixture are, respectively, extracted and constructed. The influences of oxygen content and applied voltage on the PD and decomposition characteristics of C4F7N/CO2/O2 gas mixture are investigated based on gas chromatography-mass spectrometry (GC-MS). We find that the addition of 2-4% O2 to C4F7N/CO2 gas mixture can significantly inhibit the negative half-cycle PDs and the generation of most by-products (CF4, C2F6, C3F6, CO, C2F6O3, CF3CN, C2F5CN, C2N2). With the oxygen content higher than 6%, the accumulation discharge magnitude and discharge repetition rates of C4F7N/CO2/O2 gas mixture increase sharply, accompanying the intensification of decomposition and deterioration of insulation strength. There is a positive correlation between the mean discharge magnitude and gas mixture decomposition intensity. To avoid the serious impact of PD fault on gas insulated equipment (GIE), the optimal oxygen addition in C4F7N/CO2/O2 gas mixture should not exceed 6%.

Experimental Research on Partial Discharge of High Voltage Direct Current

Under the action of long-term high-voltage DC voltage, the insulation of electrical equipment is inevitably aging, and it is necessary to monitor its insulation status. Since insulation defects of different nature damage electrical equipment to different degrees, the identification of defects is very important. To this end, a DC partial discharge detection system based on AC partial discharge detection equipment was built, focusing on key issues such as the choice of test power supply, the choice of test frequency, and the choice of pressurization methods. The successful completion of the on-site partial discharge test of UHV converter transformers has provided valuable practical experience for the future on-site partial discharge tests of UHV converter transformers, and provided important tests for the establishment of on-site partial discharge test standards for UHV converter transformers. in accordance with.

Classification and comparison of AC and DC partial discharges by pulse waveform analysis

This study aims to classify and compare AC and DC partial discharge (PD) based on PD pulse waveform analysis. To achieve this goal, we designed a testbed that enables precise measurements of individual PD pulses. The testbed is used for collecting data from four different types of PDs including cavity, surface, corona, and floating potential discharges generated by individual PD source samples. All samples were examined under AC, positive DC, and negative DC electrical stresses, through which we captured thousands of PD pulses. We classify the waveforms of each PD type into representative groups associated to their discharge mechanisms. The statistical data of the measured pulses are utilized to identify the differences between AC and DC PDs while the clustered patterns of PD amplitude versus their temporal characteristics serve as a means to classify the types of PDs under AC and DC electrical stresses.

Characteristics of AC PDs on epoxy insulation surface excited by different impulse voltages in SF6 gas

In this paper the behavior of partial discharges (PDs) on epoxy insulation under AC and impulse superimposed voltages are experimentally investigated in SF 6 gas. The lightning impulse (LI) and the switching impulse (SI) voltages with different polarity are superimposed on different phases of the AC voltage. PDs are measured by three sensors, a 50 Ω measurement impedance, an ultra-high frequency sensor and a photomultiplier tube. The max PD amplitude, PD pulse number and PD duration under AC voltage after an impulse voltage are summarized and analyzed. The effect of the impulse superposition phase, the impulse type and the impulse polarity on the characteristics of AC PDs are discussed. Results show that after a positive impulse voltage was applied on the positive semi-wave of AC voltage (0 to 180°), PDs in the negative half cycle of the AC voltage can be remarkably excited. A negative impulse voltage was applied on the negative semi-wave (180 to 360°), AC PDs can be initiated in the positive half cycle of AC voltage. PDs excited by a LI voltage is severe than excited by a SI. PDs excited by a positive impulse is intense than excited by a negative impulse.

Investigations on Novel Carbon Quantum Dots Covered Nanofluid Insulation for Medium Voltage Applications

The extensive use of mineral oil for high voltage insulation applications has directed to widespread research works targeted at improving its dielectric and thermal characteristics. The present study investigates a novel nanofluid insulation prepared using carbon quantum dots (CQD) which is used for the surface treatment of SiO2 nanoparticles added to commercially available mineral oil. The proposed nanofluid referred as CQD–SiO2 nanofluid is tested for its insulation properties such as AC breakdown voltage (BDV), partial discharge (PD), lightning impulse (LI), dissipation factor (Tan-delta), volume resistivity, viscosity and thermal characteristics such as flash and fire point. The tests were conducted for three different nanofluid concentrations, that is, 0.01%wt, 0.05%wt and 0.1%wt. Weibull distribution analysis is carried out for breakdown data of BDV test and LI test. Results of CQD–SiO2 nanofluid are compared with mineral oil with and without SiO2 nanofillers. The results show that inclusion of CQD covered SiO2 nanoparticles have the capability to improve the AC breakdown strength by more than 100%, partial discharge inception voltage by 50%, lightning impulse withstand capabilities up to 20% and volume resistivity by 50%. It has also the tendency to slightly improve the flash point and fire point properties than the mineral oil. Significant reduction of PD magnitude and Tan-delta values are noticed with CQD–SiO2 nanofluid. Such results indicate that the CQD–SiO2 nanofluid can be a suitable candidate for MV insulation applications.

Study on the Influence of Switching Impulse Superposition Phase on AC Partial Discharge of Epoxy Surface in SF6 Gas

In this letter, a test platform capable of generating superimposed voltage with controllable phase is presented. Surface partial discharge(PD) of epoxy insulation was measured and analyzed in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> . The applied voltage is AC and switching impulse superimposed voltage. Results show that only PD of the negative cycles of the AC voltage is excited or accelerated after impulse. With AC voltage at 90% of partial discharge inception voltage(PDIV), AC PDIV is reduced after imposing the switching impulse. When AC voltage is kept at 110% of PDIV, AC PDs are obviously promoted after impulse.

Effect of lightning impulse prestress on AC partial discharge characteristics in cast resin transformer

AbstractIt is crucial for cast resin transformer to detect void and delamination existing in the cast resin because these defects reduce insulation performance of cast resin equipment. Furthermore, defects are likely to be mixed in cast resin because of several surface boundaries between resin and conductor. It is considered that detecting partial discharge (PD) is effective to diagnose equipment of power equipment. However, it is reported that withstand lightning impulse voltage test may give influence on AC partial discharge test, especially partial discharge inception voltage. This paper deals with accumulated charge in a void under AC voltage to investigate the effect of the impulse voltage prestress on subsequent AC PD characteristics in cast resin transformer. AC PD characteristics were compared before and after impulse application. In addition, recovery of PD characteristics was measured to investigate charge decay. As a result, the mechanism of prestress effect is revealed and surface charge density is estimated quantitatively in cast resin transformer.

Cavities in mass-impregnated HVDC subsea cables studied by AC partial discharge measurements

Partial discharge measurements have been used for studying shrinkage voids in the insulation of mass-impregnated high voltage DC subsea power cables. Three 4.5-m long cable samples were subjected to ac partial discharge measurements at different ambient temperatures, both under isothermal conditions and after load current turn­offs. Two distinctly different phase resolved partial discharge patterns were observed, suggesting that two different types of cavities were created. The type causing by far the most powerful discharges appeared a few hours into the cooling period after load turn-off, which coincides in time with when load cycling breakdowns during type testing usually occur. Current loading has a significant effect on the cavities, as it leaves them — at least temporary — with a different dielectric strength afterwards. The mechanisms behind this change are not identified, but the associated time constants are of the order of days and weeks. Consequently, accurately determining the limitations of such cables with regard to their ability to withstand polarity reversals and rapid load changes may be more complicated than previously assumed.

Cavities in mass-impregnated HVDC subsea cables studied by AC partial discharge measurements

Partial discharge measurements have been used for studying shrinkage voids in the insulation of mass-impregnated high voltage DC subsea power cables. Three 4.5-m long cable samples were subjected to ac partial discharge measurements at different ambient temperatures, both under isothermal conditions and after load current turn­offs. Two distinctly different phase resolved partial discharge patterns were observed, suggesting that two different "types" of cavities were created. The type causing by far the most powerful discharges appeared a few hours into the cooling period after load turn-off, which coincides in time with when load cycling breakdowns during type testing usually occur. Current loading has a significant effect on the cavities, as it leaves them — at least temporary — with a different dielectric strength afterwards. The mechanisms behind this change are not identified, but the associated time constants are of the order of days and weeks. Consequently, accurately determining the limitations of such cables with regard to their ability to withstand polarity reversals and rapid load changes may be more complicated than previously assumed.

Characteristics of Indicators for Insulation Deterioration in 26 kV Generator Stator Windings

This study conducted and analyzed the results of non-destructive tests (AC current, dissipation factor, and partial discharge tests) and a destructive test (overvoltage test) on 26 kV-generator stator windings with a ground fault. The target generator was a steam turbine generator in operation for over 30 years, and ground fault in windings occurred because of the rapid and instantaneous temperature rise in the copper conductor owing to the partial loss of generator cooling water. By comparing the non-destructive test data measured during the planned preventive maintenance period two years before the ground fault and the data gathered just after the ground fault, the study conducted an in-depth analysis of the effect of moisture on insulation diagnosis factors. If both the dissipation factor and capacitance data increased when compared to those of previously estimated values at same applied AC voltage level, it represented that the insulation materials absorbed moisture. Moreover, it was further developed that both of the dissipation factor and capacitance surge voltage were detected when the discharge started whereas the concerned surge voltage for AC current was detected when the discharge was proceeded in some extent. It is expected that a wider understanding of insulation diagnosis factors developed from this study will contribute not only to a more reliable diagnosis data analysis but also a stable power supply by preventing accidents in advance.

SF 6 positive DC partial discharge decomposition components under four typical insulation defects

The condition monitoring and fault diagnosis method based on decomposed component analysis (DCA) for SF6 gas-insulated equipment, which mainly aiming at AC SF6 gas-insulated equipment, has become a research hotspot. Therefore, SF6 positive DC partial discharge (PD) decomposition experiments under four typical insulation defects were conducted in this work. The result showed that there is a significant correlation between the generation rules of the five SF6 decomposition components (CF4, CO2, SO2F2, SOF2 and SO2) and the types of defects. The phenomenon was attributed to the variations in the properties of the four insulation defects. In addition, comparing with AC PD experiment, for the protrusion, contamination and gap defect models, the amounts and generation rates of the five characteristic decomposition components under positive DC are less than those under AC by the same defect; however, for the particles defect, it is by contrary. This could be attributed to the essential difference between AC PD and positive DC PD. Therefore, the theory of AC DCA could provide reference to construct DCA diagnostic model for DC SF6 gas-insulated equipment, but cannot be applied mechanically.

Performance of the insulation mock-ups for the ITER PF6 coil

The ITER PF6 coil is manufactured by winding, insulating the superconducting conductors, and further connecting them electrically and hydraulically. To qualify the insulation design and manufacturing process to be applied to the ITER PF6 coil, two beam-shaped mock-ups taking the form of a 3 × 3 array of conductors combined with the same insulation as in the production coil have been tested in simulated Tokamak operating conditions. All the results of the electrical and mechanical tests, including DC and AC high-voltage withstanding at both room and cryogenic temperature, AC partial discharge, Paschen tests, cryogenic compressive fatigue, push-out, and thermal cycling, met the ITER requirements. Performance of the mock-ups confirmed that the insulation design and manufacturing process are suitable for the ITER PF6 coil, based on that the qualification of the insulation manufacturing process for the double pancake can be started.

Study of Breakdown Voltage of Vegetables oil with SiO2 Nanoparticle Additive

&lt;p&gt;This paper investigates the suitability of vegetable oils to replace mineral oil based on its AC breakdown voltage, partial discharge and viscosity. The purpose of the study is to analyze the effect of the nanofluids containing SiO&lt;sub&gt;2&lt;/sub&gt; nanoparticle in vegetables oils; namely, Coconut oil and Palm oil. A nanofluid is a fluid containing nanoparticles. However, the precise effects on the electrical properties is still uncertain. For decades, transformers use petroleum-based mineral oil because of its good dielectric properties and cooling capability. Coconut oil (CO) and Palm oil (PO) are thought to be suitable alternatives to replace mineral oil as transformer oil as they are sustainable and available in plenty as natural resources. It was obtained in this study that the breakdown voltages of these raw oils have fulfilled the standard specifications of good insulating liquid. However, the addition of SiO&lt;sub&gt;2&lt;/sub&gt; did not improve the AC breakdown voltage and viscosity of coconut oil and palm oil at different temperatures. However, the addition of SiO&lt;sub&gt;2&lt;/sub&gt; gave positive results in the values of partial discharges in which the presence of the nanoparticles has greatly reduced the mean volume of partial discharges for both coconut oil and palm oil.&lt;/p&gt;