Dielectric Strength of Polymeric Solid–Solid Interfaces under Dry-Mate and Wet-Mate Conditions (original) (raw)
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On the tangential AC breakdown strength of polymer interfaces considering elastic modulus
2017 IEEE Conference on Electrical Insulation and Dielectric Phenomenon (CEIDP), 2017
The interfacial breakdown between two dielectric surfaces was reported to represent one of the leading causes of failure for power cable joints and connectors, in which elastic modulus of the dielectric material plays a key role. The primary motivation of this paper is to study the influence of the elastic modulus of the polymer insulation on the tangential AC breakdown strength (BDS) of polymer interfaces experimentally. In the experiments, four different materials with different elastic moduli were employed under various contact pressures: polyether ether ketone (PEEK), cured end product of epoxy resin (EPOXY), cross-linked polyethylene (XLPE), and silicone rubber (SiR). The BDS of each interface increased as the contact pressure was augmented. As the contact pressure became threefold, the interfacial BDS rose by a factor of 2.4, 1.7, 1.8, and 1.4 in the case of the PEEK, EPOXY, XLPE and SiR interface, in a sequence following the decrease of the elastic modulus. Under the same contact pressure, it was observed that the lower the elastic modulus, the higher the BDS.
Proceedings of the Nordic Insulation Symposium, 2017
This paper examines the influence of the elastic modulus of the polymer insulation on the tangential AC breakdown strength (BDS) of polymer interfaces theoretically and experimentally. In the experiments, four different materials with different elastic moduli, namely crosslinked polyethylene (XLPE), cured end product of epoxy resin (EPOXY), polyether ether ketone (PEEK) and silicone rubber (SiR) were employed under various contact pressures. The BDS of each interface increased as the contact pressure was augmented. As the contact pressure became threefold, the interfacial BDS rose by a factor of 2.4, 1.7, 1.8, and 1.4 in the case of the PEEK, EPOXY, XLPE and SiR interface, in a sequence following the decrease of the elastic modulus. Under the same contact pressure, it was observed that the lower the elastic modulus, the higher the BDS. The employed contact theory also suggested a decreasing BDS as the modulus was augmented; however, the experimental results tended to deviate widely ...
Effect of elastic modulus on the tangential AC breakdown strength of polymer interfaces
IEEE Transactions on Dielectrics and Electrical Insulation
Solid-solid interfaces between insulating materials dictate the long-term electrical properties of the complete insulation system. This paper presents theoretical and experimental investigations aiming to address the impact of the material elasticity on tangential AC breakdown strength (BDS) of interfaces between polymers. Four different polymers with different elastic moduli were tested using: Cross-linked polyethylene (XLPE), filled epoxy resin (EPOXY), polyether ether ketone (PEEK) and silicone rubber (SiR). The interfaces were formed between identical specimens and were breakdown tested at various contact pressures. It was found that elastic modulus and contact pressure had pronounced effects on the BDS of interfaces. Higher elastic modulus correlated with decreased BDS by a factor of 1.6 at the same contact pressure. On the other hand, the increase of contact pressure by a factor of 3 elevated the interfacial BDS by a factor of 1.4 in the case of the lowest elastic modulus (SiR-SiR) whereas that for the highest modulus (PEEK-PEEK) was about 2.4 times higher. Using the proposed theoretical approach, we postulated that discharged cavities govern the interfacial BDS at the interface together with the electric treeing resistance of contact area between the cavities. Although the electrical treeing resistance increases with a higher modulus, local field enhancements due to discharged cavities also increase significantly. Therefore, the observed reduction of the BDS with the increase of the elastic modulus is ascribed to the larger cavity size and hence the smaller contact area. It is concluded that increased elastic modulus reduces the dominance of the discharged cavities over the interface breakdown and increase the governance of the electrical treeing resistance of the contact spots.
Longitudinal AC breakdown voltage of XLPE-XLPE interfaces considering surface roughness and pressure
IEEE Transactions on Dielectrics and Electrical Insulation, 2017
The interfacial breakdown between two dielectric surfaces has been reported to represent one of the principal causes of failure for power cable joints and connectors; thus, a better understanding of interfacial breakdown mechanisms is vital. The primary purpose of this paper is to investigate the influence of the surface roughness and interfacial pressure on the tangential AC breakdown strength (BDS) of solid-solid interfaces experimentally. The three-dimensional surface texture parameters are utilized to characterize the morphology of the surfaces. Experiments were performed using samples made of cross-linked polyethylene (XLPE) at three different contact pressures. The surface roughness was varied by polishing the surfaces using four different sandpapers of different roughness. Each surface topography was then assessed using a 3-D optical profilometer. Next, the samples were assembled under ambient laboratory conditions. The experimental results showed a good correlation between the tangential BDS and the surface roughness. The results suggested that reducing the surface roughness resulted in decreased mean height of the surface asperities by nearly 97% and increased the real contact area of the interface considerably. As a result, the tangential BDS rose by a factor of 1.85-2.15 with increasing pressure. Likewise, the increased contact pressure yielded augmented tangential BDS values by a factor of 1.4-1.7 following the decrease of the roughness.
Factors influencing the tangential AC breakdown strength of solid-solid interfaces
IEEE Transactions on Dielectrics and Electrical Insulation, 2016
The combination of two solid dielectrics (interface) increases the risk of formation of microscopic cavities reducing the breakdown strength (BDS) of the interface considerably, particularly when the electric field has a tangential component. The main purpose of this paper is to investigate the impact of the applied contact pressure and composite elastic modulus on the tangential ac BDS of the solid-solid interfaces experimentally. In the experiments, three different contact pressures were applied using different mechanical loads with two different materials having different elastic moduli, i.e. cross-linked polyethylene (XLPE) and silicon rubber (SiR). Two rectangular prism shaped samples were placed between two vertical Rogowski shaped electrodes either in air or oil. The type of the interface (air/oil) is highlighted duly upon showing the results. Increase in contact pressure caused relatively higher increase in the tangential BDS of dry SiR-SiR (assembled in air) than that of XLPE-XLPE, revealing that elastic modulus facilitated significantly to reduce the mean void size in SiR that in turn improved the tangential BDS. Likewise, the tangential BDS of hybrid interfaces formed by XLPE-SiR specimens increased by 43% compared to that of XLPE-XLPE interface at the same pressure. Additionally, the same set of experiments assembled in oil reveals that the presence of oil enhanced the tangential BDSs around 2-3 times for all three-interface cases. Moreover, with the increase of applied pressure the tangential BDS of air-filled and oil-filled cavities tended to get significantly higher.
Effect of material elasticity on the longitudinal AC breakdown strength of solid-solid interfaces
IEEE Transactions on Dielectrics and Electrical Insulation, 2019
Solid-solid interfaces between insulating materials dictate the long-term electrical properties of the complete insulation system. This paper presents theoretical and experimental investigations aiming to address the impact of the material elasticity on tangential AC breakdown strength (BDS) of interfaces between polymers. Four different polymers with different elastic moduli were tested using: Cross-linked polyethylene (XLPE), filled epoxy resin (EPOXY), polyether ether ketone (PEEK) and silicone rubber (SiR). The interfaces were formed between identical specimens and were breakdown tested at various contact pressures. It was found that elastic modulus and contact pressure had pronounced effects on the BDS of interfaces. Higher elastic modulus correlated with decreased BDS by a factor of 1.6 at the same contact pressure. On the other hand, the increase of contact pressure by a factor of 3 elevated the interfacial BDS by a factor of 1.4 in the case of the lowest elastic modulus (SiR-SiR) whereas that for the highest modulus (PEEK-PEEK) was about 2.4 times higher. Using the proposed theoretical approach, we postulated that discharged cavities govern the interfacial BDS at the interface together with the electrical tracking resistance of contact area between the cavities. Although the electrical tracking resistance increases with a higher modulus, local field enhancements due to discharged cavities also increase significantly. Therefore, the observed reduction of the BDS with the increase of the elastic modulus is ascribed to the larger cavity size and hence the smaller contact area. It is concluded that increased elasticity reduces the dominance of the discharged cavities over the interface breakdown and increase the governance of the electrical tracking resistance of the contact spots.
A stochastic model for contact surfaces at polymer interfaces subjected to an electrical field
Tribology International, 2018
Morphology of the contact area between solid insulation materials ultimately determines the long-term electrical properties of the complete insulation system. The primary purpose of this paper is not only to propose a statistical model to scrutinize the real area of contact between solid dielectric surfaces but also to verify and correlate the model outputs with experiments. The model computes real area of contact, number of contact spots and average cavity size at the interface as a function of elasticity, contact force and surface roughness. Then, using the average cavity size and the Paschen's law, cavity discharge inception field (PDIE) is calculated. In the experiments, AC breakdown strength (BDS) testing of solid-solid interfaces was carried out, where cross-linked polyethylene (XLPE) samples with four different surface roughnesses were subjected to various contact pressures. Following the increased contact force, the calculated average cavity size decreased by a factor of 4.08 − 4.82 from the roughest to the smoothest surface, that in turn yielded increased PDIEs by a factor of 2.01 − 2.56. Likewise, the experimentally obtained BDS values augmented by a factor of 1.4 − 1.7 when the contact pressure was elevated from 0.5 MPa to 1.16 MPa. A linear correlation between the PDIE and BDS was assumed, yielding a correlation coefficient varying within 0.8−1.3. When the 90% confidence intervals were considered, the range reduced to 0.86 − 1.05. This close affinity suggests that interfacial breakdown phenomenon is strongly governed by the cavity discharge. Hence, the proposed model is verified with experiments.
Longitudinal Breakdown Strength of Wet-mate Solid-Solid Interfaces at VLF and 50 Hz AC voltages
Proceedings of the Nordic Insulation Symposium
The 50 Hz AC breakdown strength of dry interfaces is known to strongly depend upon the mechanical properties, contact pressure, roughness of the surfaces, and the type of lubricant used at the interface. This paper aims to experimentally examine how these factors affect the longitudinal AC breakdown strength of interfaces assembled in water, so-called wet interfaces. The main aim is to obtain data relevant to the design of power equipment operating at very low frequency (VLF) or DC voltages.Experiments were conducted using identical specimens made from 4mm thick plaques of PMMA and plane sections cut from XLPE cable insulation. The findings were discussed with respect to expected dimensions of interface voids and contact regions, considering tribology-based contact theory, including the impact of surface roughness, modulus of elasticity, and applied mechanical interface pressure. The longitudinal 50 Hz AC breakdown strength values of wet samples were typically as low as 80 % of sam...
Breakdown strength of solid|solid interface
2010 10th IEEE International Conference on Solid Dielectrics, 2010
Interfaces between solids are generally considered weak regions in electrical insulation systems. This is particularly so if the electrical stress is applied parallel to the interface. Important parameters, affecting the breakdown strength, are interface pressure, humidity, presence of liquid dielectric and the surface roughness of the solid in contact. The main aim of the work presented here is to examine, theoretically and experimentally, the effect of interfacial pressure and roughness on the tangential breakdown strength. The size and gas pressure of enclosed surface voids were estimated using mechanical contact theory. The dielectric 50 AC tangential strength of XLPE|XLPE interface was investigated for various values of pressure and roughness. The increase in breakdown strength due to increased pressure was largest in case of surfaces with the high degree of roughness. As expected the highest breakdown strength was observed in case of the smoothest surfaces. The estimated results of void size and gas pressure were found to be in good agreement with the experimental observations.
Impact of Contact Pressure on Breakdown Strength of Solid-Solid Interfaces
Solid-solid interfaces are considered as weak points of the insulation since combination of two solid dielectrics increases the risk of cavities and moisture at the interface against the tangential component of the applied electrical stress. The main objective of this paper is to investigate the impact of the applied contact pressure on shrinkage of the size of cavities on the interface that leads to enhancement in the breakdown strength. Experimental measurements of AC 50 Hz breakdown voltage of solid-solid interfaces assembled under standard laboratory conditions were conducted using two different specimens, namely XLPE and silicon rubber. For the same applied contact pressure, breakdown strength of XLPE-XLPE and silicon rubber-silicon rubber interfaces were also analyzed to yield the influence of elasticity modulus (softness) of the solid material on the effectiveness of the applied pressure. Two different levels of contact pressures were applied for each type of interface and hi...