Experimental Study on Creeping Flashover Characteristics Along Dielectric Surfaces in Oil‐Filled Transformer Using Electro‐Optic Coupling Method

The growing interest in integrating distributed generation into the existing power distribution grid, the increase in the penetration levels of renewables, as well as the need to achieve a more efficient, reliable, and sustainable grid is leading to the development of new grid-interfaced power converters such as the solid-state transformer (SST). As current and voltage ratings of commercially available power semiconductor devices are normally below power ratings required in distribution systems (e.g., 13.8 kVrms), multiple modules must be connected in cascade configuration at the high-voltage (HV) side to reach higher voltage ratings as well as in parallel at the low-voltage (LV) side to achieve high current levels. A new SST topology consisting of modular boost-based three-level ac–dc converters, medium-frequency transformers with two secondary windings, and four-leg ac–dc converters is presented in this paper. When compared to similar approaches, the proposed topology comprises fewer power conversion stages, lower voltage across the semiconductor devices on the HV side, and lower current flowing through each device on the LV side. These characteristics reduce the number of series-connected modules in the HV side and parallel-connected devices in the LV side. The feasibility of the proposed topology is experimentally validated on a 500 W, 120 Vac/48 Vdc scaled-down prototype.

The advent of Silicon Carbide (SiC) devices has made possible high switching frequency operation of PWM power converters. In this paper, SiC devices are compared in detail with Si devices in a high power (1 MW) DC -DC converter application. The converter is designed as the building block for traction drives which requires it to operate at high power, high input voltage (11 kV) and low output voltage (800 V) levels. A dual active bridge (DAB) and a series resonant converter (SRC) topology are compared to achieve highly efficient operation. The performance and efficiency of these converters are compared by simulations using two different combinations of switches; the SiC combination consists of 10 kV/10 A SiC MOSFET at High Voltage (HV) side and 1200 V/100 A SiC MOSFET at Low Voltage side (LV), and the Silicon combination consists of 6.5 kV/10 A Si IGBT at HV side and 1200 V/100 A Silicon IGBT at LV side. For further understanding, efficiency analysis using the newly developed 15 kV/20 A SiC IGBT on the HV side is also carried out.

A New Adjustable and Rechargeable Induction Power Supply at High Voltage Side

This paper proposes a high-efficiency bidirectional dc-dc converter with high voltage conversion ratio for low voltage energy storage devices. For a step-up operation, the proposed converter operates with a high step-up voltage conversion ratio. It has low voltage stresses of the power switches at the low voltage side. It also has low switching losses of the output diodes at the high voltage side. For a step-down operation, the proposed converter operates with a high step-down voltage conversion ratio. It features zero-voltage switching of power switches at the high voltage side. At the low voltage side, a current doubler rectifier reduces the current ripples. Simulation verifications and experimental results are presented to verify the operation of the proposed converter.

The surface plasmon resonance (SPR)-induced local field effect in Al-Au-Ag trimetallic three-layered nanoshells has been studied theoretically. Because of having three kinds of metal, three plasmonic bands have been observed in the absorption spectra and the local electric field factor spectra. The local electric field enhancement and the corresponding resonance wavelength for different plasmon coupling modes and spatial positions of the Al-Au-Ag nanoshells with various geometry dimensions are investigated to find the maximum local electric field enhancement. The calculation results indicate that the giant local electric field enhancement could be stimulated by the plasmon coupling in the middle Au shell or the outer Ag shell and could be optimized by increasing the Ag shell thickness and decreasing the Au shell thickness. What is more, the local electric field enhancement also nonmonotonously depends on the dielectric constant of the environment; the local electric field intensity will be weakened when the surrounding dielectric constant is too small or too large.

Bidirectional converters are used where bidirectional power flow is required. It reduces the space occupied drastically as compared to the individual converters utilized otherwise. Usually, the system contains a push–pull conversion stage on the lower voltage side (LV) and a full-bridge phase shift conversion stage on the higher voltage side (HV). The transitioning between buck and boost stages in a bidirectional converter is not subject to high currents and voltages which increases the life of the system and its dependability. Bidirectional converters that are isolated in circuit are normally utilized in electric vehicles as well as data storage applications where between the higher voltage side and lower voltage side, power flow is observed. The system execution incorporates the power flow between the higher voltage side and lower voltage side by using a current sustained push–pull conversion stage on the lower voltage side and a PSFB stage that synchronously rectifies the power flow to the lower voltage side. The limitations faced during the implementation of this system are: (1) quick and consistent transition from buck to boost mode and vice versa; (2) during the reverse power in the push–pull converter, the rectification of the high-voltage bridge.

The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.

The effect of inserted gold nanosphere on the local field enhancement of gold nanoshell

This study mentions the problem of determining optimal placements and sizes for capacitor banks by comparing different schemes that allow implemented buses at both high and low voltage side, only high voltage side or low voltage side of transformers in distribution systems. Criterions evaluated for each scheme are active and reactive power losses in whole system, voltage value at all buses, installation and operation cost and accumulative profit saving. Standard with and without transformer branches in distribution systems and Newton-Raphson method are introduced to make clear about the way to analyze power flows in whole system. Optimal placements and sizes for capacitor banks are determined by using a proposed algorithm and optimal capacitor placement tool in ETAP software. Simulation results can help to show the comparisons, evaluations and make decision about optimal capacitor placements and sizes. The contribution shows the best scheme that install capacitors at low voltage side of transformers because it has the lowest implemented capacity, highest economic factors while voltage quality is always in allowable range. Achieved results can be applied in any distribution system, help managers have overall review and decide optimal placements and sizes for capacitor banks. Keywords: Capacitor bank, OCP Tool, ETAP software, Optimal placement, Optimal size, Voltage quality, Optimal cost.

Local electric field enhancement in a long cylindrical Au nanohole with Pt coating has been theoretically studied based on quasi-static model. Calculation results show that both the peak wavelength and local field factor in the nanohole are greatly dependent on the Pt coating thickness. Because of the Pt coating, a new local surface plasmon resonance (LSPR) band takes place in the ultraviolet wavelength below 400 nm, which also results in intense local electric field enhancement in the nanohole. As the Pt coating thickness is increased, the local field factor peak corresponding to the Pt shell red shifts and gets intense rapidly, which is much greater than that of Au shell. However, the increasing Pt thickness can also leads to the decrease of the local field factor when the dielectric constant of inner hole is much greater than that of outer environment. The local field factor in Pt shell is also sensitive to the Pt thickness and local dielectric environment. At the inner surface of the Pt shell, the increasing Pt thickness results in non-monotonic change of the local field factor when the dielectric constant of inner hole is equal or smaller than that of outer environment. Whereas at the outer surface of the Pt shell, the increasing Pt thickness always results in monotonic decrease of the local field factor, which is independent on the difference of the dielectric constant between inner hole and outer surrounding. This Pt coating-controlled local field enhancement in cylindrical Au@Pt nanohole presents design criteria and synthetic strategies toward local field effect-induced surface-enhanced Raman scattering (SERS), surface-enhanced fluorescence, and biosensing applications.

Design and research of fiber optically powered Rogowski coil current transformer

In this paper, partial discharge inception voltage (PDIV) and partial discharge (PD) characteristics of mineral oil compared with natural ester were studies. Three typical PD types, corona discharge of the liquid insulations, surface discharge and internal discharge of the liquid impregnated pressboards were investigated. In case of corona discharge, both corona discharges from high voltage side and from low voltage side were simulated by using the needle-plane electrode configuration. The needle with the tip radius of 10μm, 20μm, 40μm respectively was used as high voltage electrode while the brass plane electrode with 45 mm diameter was used as the grounded electrode for simulation the corona discharge at high voltage side, and vice versa, for simulation corona discharge at low voltage side. The gap distance was fixed for 30 mm. Moreover, the mineral oil and natural ester were used to impregnate the pressboards which were 1.6 mm thick. Then, the impregnated pressboards were selected to experiment for surface discharge and internal discharge respectively. The surface discharge experiment was performed with the 40μm tip radius needle as high voltage electrode put on the ten pieces of 12 hour impregnated pressboards stuck together as a single insulation and the plane electrode with 45 mm diameter as grounded electrode. In case of the internal discharge, ten pieces of 6 hour impregnated pressboards were stuck together as a single insulation. A cylindrical void with 5 mm diameter and a height of 3.2 mm was simulated at the middle of the insulation. Then, the insulation was placed between the mentioned plane electrodes for the internal discharge experiment. PD test circuit was prepared following to IEC 60270. PDIV was examined by applying the step voltage to the high voltage electrode with the increase rate of 1 kV per step for the step duration of 1 minute until observing the PDIV. Then, PD activity was examined and recorded for 1 minute at 110% PDIV level. Form the test results, the natural ester and pressboards impregnated with natural ester provide higher PDIV than mineral oil and the mineral oil impregnated pressboards. Consequently, the PD amplitude at 1.1 PDIV of natural ester and natural ester impregnated pressboards are higher than that of mineral oil and mineral oil impregnated pressboards.

Sweep Frequency Response Analysis (SFRA) is a technique which is recently used to detect the malfunction operation of electrical power transformers. This paper suggested three diagnostic techniques used to interpret SFRA for power transformer fault turn to turn identification. Namely they are Chinese standard DL-911/2004, Cross-Correlation Coefficient Factor technique (CCF) and R2 relative factor technique. The diagnostic techniques are used to identify the transformer turn to turn short circuit faults at high voltage and low voltage sides. The results of diagnostic techniques used in power transformer fault identification; indicate that the used method can accurately identify the transformer faults.

ABSTRACTA soft-switching bidirectional DC–DC converter is presented herein as a way to improve the conversion efficiency of a photovoltaic (PV) system. Adoption of coupled inductors enables the presented converter not only to provide a high-conversion ratio but also to suppress the transient surge voltage via the release of the energy stored in leakage flux of the coupled inductors, and the cost can kept down consequently. A combined use of a switching mechanism and an auxiliary resonant branch enables the converter to successfully perform zero-voltage switching operations on the main switches and improves the efficiency accordingly. It was testified by experiments that our proposed converter works relatively efficiently in full-load working range. Additionally, the framework of the converter intended for testifying has high-conversion ratio. The results of a test, where a generating system using PV module array coupled with batteries as energy storage device was used as the low-voltage input side, and DC link was used as high-voltage side, demonstrated our proposed converter framework with high-conversion ratio on both high-voltage and low-voltage sides.

In recent years, energy storage systems assisted by super capacitor have been widely researched and developed to progress power systems for the electronic vehicles. In this paper, a full-bridge/push-pull circuit-based bidirectional DC-DC converter and its control methods are proposed. From the results of detailed experimental demonstration, the proposed system is able to perform adequate charge and discharge operation between low-voltage high-current super capacitor side and high-voltage low-current side with drive train and main battery. Furthermore, conduction losses and voltage/current surge are drastically reduced by ZVS operation with loss-less snubber capacitor in high voltage side as well as the synchronous rectification in low-voltage high-current super capacitor side.