Fault Ride-Through Enhancement of PMSG Wind Turbines with DC Microgrids Using Resistive-Type SFCL

Integrating permanent magnet synchronous generator (PMSG) wind turbines with DC microgrids have attracted a great attention due to the inherent merits of DC systems. However, under the fault conditions, the excessive energy during fault will be reflected on PMSG rotating parts causing overspeed, mechanical stresses, and fast aging. Also, large fault currents will force generator-side converter to disconnect making it not complied with grid codes. Accordingly, this paper aims to apply superconducting fault current limiter (SFCL) to enhance the performance of PMSG wind turbines with DC microgrids under the fault conditions. PSCAD/EMTDC software is used to build the system under study that includes PMSG, controlled AC/DC converter, SFCL, and DC bus. The behavior of SFCL in enhancing the DC output of the converter is first studied. Then, the impact of using SFCL on the speed, torque, and output current of PMSG is investigated and discussed. Finally, the suitable current limiting resistance is adopted considering DC output as well as PMSG speed

Hybrid Grey Wolf Optimizer for Transformer Fault Diagnosis Using Dissolved Gases Considering Uncertainty in Measurements

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New technique for using SMES to limit fault currents in wind farm power systems

This paper introduces a new scheme, which uses a multifunctional superconducting device that can be used as an energy storage and as a fault current limiter. It is denoted as a superconducting magnetic energy storage - fault current limiter (SMES-FCL) and is modeled as a number of pancakes. It is connected to a wind turbine power system via tertiary transformer and power converters. A complete control scheme is built to achieve effective power transfer between the superconducting coil and the power system during normal operation to smooth the wind turbine output power. The fault current limiting function is implemented using a new technique that inserts a few pancakes from the whole SMES coil into the main electrical system during the fault and isolates the remaining pancakes. The number of pancakes used to limit the fault is quenched and operates as a resistive fault current limiter. The whole system including the wind turbine, the SMES-FCL model, and the interface circuit are implemented using PSCAD/EMTDC computer package. Also, the control scheme of SMES-FCL is built based on a feedback current signal to enable its operation into the two modes

Investigation of the dielectric and thermal properties of non-edible cottonseed oil by infusing h-BN nanoparticles

Vegetable oils have emerged as insulating fluids in transformer applications and as a prominent and effective alternative for traditional dielectric fluids. However, most of vegetable oils are edible causing their application on a large scale to be limited. In the present work, a novel non-edible vegetable oil is developed as an insulating fluid. The developed oil is oxidation-inhibited cottonseed oil (CSO) based nanofluids. Tertiary butylhydroquinone was used as antioxidant. The concept of nanofluids was used to overcome the limited dielectric and thermal properties of cottonseed oil. Hexagonal Boron Nitride (h-BN) nanoparticles at low weight fractions (0.01 - 0.1 wt%) were proposed as nanofillers to achieve adequate dielectric strength and improved thermal conductivity. Stability of prepared CSO based nanofluids was analyzed using Ultraviolet-visible (UV-Vis) spectroscopy. Then, the prepared nanofluids were tested for dielectric and thermal properties under a temperature range between 45 °C and 90 °C. The dielectric properties include breakdown strengths under AC and lightning impulse voltages, dielectric constant, dissipation factor, and resistivity, while thermal properties include thermal conductivity and thermogram analysis. The dielectric and thermal properties were significantly improved in CSO based nanofluids. The creation of electric double layer at nanoparticle/oil interface and the lattice vibration of nanoparticles were used to clarify the obtained results. The proposed CSO based h-BN nanofluids open up a great opportunity in both natural ester insulating fluid applications and thermal energy management systems

Recent Advances in Polymer Nanocomposites Based on Polyethylene and Polyvinylchloride for Power Cables

Polymer nanocomposites used in underground cables have been of great interest to researchers over the past 10 years. Their preparation and the dispersion of the nanoparticles through the polymer host matrix are the key factors leading to their enhanced dielectric properties. Their important dielectric properties are breakdown strength, permittivity, conductivity, dielectric loss, space charge accumulation, tracking, and erosion, and partial discharge. An overview of recent advances in polymer nanocomposites based on LDPE, HDPE, XLPE, and PVC is presented, focusing on their preparation and electrical properties

Condition Assessment of Natural Ester–Mineral Oil Mixture Due to Transformer Retrofilling via Sensing Dielectric Properties

Funding Information: This paper is created upon work supported by Science, Technology & Innovation Funding Authority (STIFA), Egypt, under a grant (31292). Publisher Copyright: © 2023 by the authors.Mineral oil (MO) is the most popular insulating liquid that is used as an insulating and cooling medium in electrical power transformers. Indeed, for green energy and environmental protection requirements, many researchers introduced other oil types to study the various characteristics of alternative insulating oils using advanced diagnostic tools. In this regard, natural ester oil (NEO) can be considered an attractive substitute for MO. Although NEO has a high viscosity and high dielectric loss, it presents fire safety and environmental advantages over mineral oil. Therefore, the retrofilling of aged MO with fresh NEO is highly recommended for power transformers from an environmental viewpoint. In this study, two accelerated aging processes were applied to MO for 6 and 12 days to simulate MO in service for 6 and 12 years. Moreover, these aged oils were mixed with 80% and 90% fresh NEO. The dielectric strength, relative permittivity, and dissipation factor were sensed using a LCR meter and oil tester devices for all prepared samples to support the condition assessment performance of the oil mixtures. In addition, the electric field distribution was analyzed for a power transformer using the oil mixtures. Furthermore, the dynamic viscosity was measured for all insulating oil samples at different temperatures. From the obtained results, the sample obtained by mixing 90% natural ester oil with 10% mineral oil aged for 6 days is considered superior and achieves an improvement in dielectric strength and relative permittivity by approximately 43% and 48%, respectively, compared to fresh mineral oil. However, the dissipation factor was increased by approximately 20% but was at an acceptable limit. On the other hand, for the same oil sample, due to the higher molecular weight of the NEO, the viscosities of all mixtures were at a higher level than the mineral oil.Peer reviewe

Physical Mechanisms of Partial Discharges at Nitrogen Filled Delamination in Epoxy Cast Resin Power Apparatus

For proper insulation design of epoxy cast resin power apparatus such as molded transformers, it is important to consider the criticality of defects that might exist into the dielectric material. One of the most important defects is the delamination defect at the interface between resin and conductor. Accordingly, this paper aims to investigate partial discharge (PD) characteristics and to clarify their mechanisms for micro gap delamination defect of epoxy cast resin power apparatus. An experimental model simulating delamination defect was built. Nitrogen gas at atmospheric pressure was used as a typical filled gas inside the delamination of epoxy cast resin power apparatus. Simultaneous measurements of PD light emission intensity, PD light emission image and PD current pulse were carried out. PD inception voltage was measured for different delamination depths. PD generation characteristics were recorded. It was found that multiple PD events were detected only by PD light emission images and could not be detected by their current pulses as a result of very small magnitudes of PD current pulses. Time transition of PD activity for 10 minutes were obtained and analyzed using the captured light emission images. Based on the obtained results and comparing with SF6 gas filled delamination, physical mechanisms behind PD activity could be discussed