Increasing Voltage Levels Research Articles

Optimized Fabrication Process and PD Characteristics of MVDC Multilayer Insulation Cable Systems for Next Generation Wide-Body All-Electric Aircraft

For wide-body all-electric aircraft (AEA), a high-power-delivery, low-system-mass electric power system (EPS) necessitates advanced cable technologies. Increasing voltage levels enhances power density yet poses challenges in aircraft cable design, including managing arc-related risks, partial discharges (PDs), and thermal management. Developing multilayer multifunctional electrical insulation (MMEI) systems for aircraft applications is a feasible option to tackle these challenges and reduce the size and mass of cable systems. This approach involves selecting layers of different materials to address specific challenges. Our prior research concentrated on the modeling and simulation-based design of MMEI systems for MVDC power cables. Experimental tests are essential for determining the behavior of PDs under varying pressure conditions. Also, the dielectric strength and time to failure of the designs need to be assessed. In this work, the fabrication process of a down-selected MMEI flat configuration is discussed and analyzed. This paper analyzes the fabrication process of power cables employing MMEI configurations and evaluates the PD characteristics of down-selected ARC-SC-T-MMEI cable samples. This study presents a detailed analysis of the characteristics of PD under atmospheric and low-pressure conditions, which will provide essential insights into the design of MVDC cables for future AEA applications.

Effects of Current Filaments on IGBT Avalanche Robustness: A Simulation Study

With the increase in voltage level and current capacity of the insulated gate bipolar transistor (IGBT), the avalanche effect has become an important factor limiting the safe operating area (SOA) of the device. The hole injection into the p/n junction on the backside of the IGBT after avalanche is the main feature that distinguishes the avalanche effect from other devices. In this paper, the avalanche breakdown characteristics of IGBT and the nature of current filament are investigated using theoretical analysis and numerical simulation, and the underlying physical mechanism controlling the nature of current filaments is revealed. The results show that the hole injection on the backside of the IGBT leads to an additional negative differential resistance (NDR) branch on the avalanche breakdown curve. The device’s common-base current gain, αpnp, is a crucial factor in determining the current filament. As αpnp increases, the avalanche-induced current filament becomes stronger and slower, resulting in weaker avalanche robustness of the device.

Partial-Power Conversion for Increased Energy Storage Capability of Li-Ion Battery Energy Storage System

Full-power converters are used in battery energy storage systems (BESS) because of their simple structure, high efficiency and relatively low cost. However, cell-to-cell variation, including capacity, state of charge (SOC), and internal resistance, will decrease the available capacity of serially connected battery packs, thereby negatively affecting the energy utilization rate (EUTR) of BESS. This article proposes a novel BESS scheme that combines a modular converter with partial power conversion architecture to make a modular partial power converter (MPPC) that addresses the issue. The MPPC consists of input-serial and output-paralleled (ISOP) isolated phase-shift full-bridge (PSFB) sub-modules. It processes only the serial compensation power, about 1/3 of the full power. Consequently, the MPPC shrinks the converter capacity, which can reduce the cost and power loss. Furthermore, this article develops a BESS model considering cell-to-cell variations to analyze the energy storage capability of the MPPC-BESS compared with the existing full-power BESS. To test the model, we run a simulation using parameter values from 100 real retired batteries. Our simulation results show that the MPPC can significantly alleviate the reduction of EUTR as the voltage level increase. Finally, we construct a 36V/720W MPPC-BESS prototype with two battery packs and PSFB sub-modules to verify the bidirectional operating stability and energy storage capability.

Influence Analysis of Photovoltaic and Energy Storage Systems in a Distributions System in the Context of Permanent Regime Voltage using the Opendss

This paper presents a study of the reverse power flow and the application of battery banks in the network. Five cases were carried out in which the voltage increase was verified in loads that had no PV connected through the system power flow using OpenDSS software . For this, scenarios with different percentages of distribution generation (DG) were simulated. The use of DG improves the voltage stability in the system when it is decentralized in the network, as observed in case 3. In addition, a set of batteries was inserted to present the increase of the average voltage, and the possible problem that may occur from voltage sinking. This is proven by increasing the batteries in the system, increasing the time lag of the voltage drop. To mitigate the sinking problem, energy storage should be allocated to locations where the voltage drop is greatest, as evidenced by the increased voltage level with the use of only one battery in the system.

Effect of voltage on mechanical properties of carbon fiber reinforced concrete

Under various voltages, the performance variations and compressive and flexural failure modes of carbon fiber concrete were investigated. The findings indicate that while the general concrete will display a cone upon failure, the compressive carbon fiber concrete specimen maintains its integrity under the influence of voltage, displaying a state of surface cracking with similar-sized crack spacing. With an increase in voltage level, the compressive strength of carbon fiber reinforced concrete first rises and then falls. The compressive strength of carbon fiber concrete at a voltage level of 15V is 66% higher than that of carbon fiber concrete without voltage. Similar to the flexural strength test phenomenon of uncharged carbon fiber concrete, the flexural strength test phenomenon of concrete beams when applying voltage is immediate fracture. The maximum strength of carbon fiber reinforced concrete is only 10% higher, and the flexural strength is only marginally improved, fluctuating.

Molecular dynamics simulation of mechanical and thermal properties of nano-zinc oxide modified cellulose insulating paper

With the surge in electrical loads and increasing voltage levels, the mechanical performance and thermal stability of insulating paper are facing severe challenges. However, due to the lack of direct scientific theories or simulation guidance, traditional inefficient “trial-and-error” experiments are difficult to effectively develop new types of cellulose composite insulating papers. For solving this problem, in this work we are to enhance the effects of nanoscale zinc oxide (nano-ZnO) on the mechanical and thermal properties of cellulose through molecular dynamics simulations. Initially, we model the nano-ZnO/cellulose composite material , then carry out a microscopic analysis of the mechanical performance and thermal stability of modified cellulose with varying nano-ZnO content, thus determining the optimal ratio of nano-ZnO to cellulose. The results indicate that compared with the outcomes from the unmodified model, the mechanical performance, cohesive energy density, glass transition temperature, and thermal conductivity of the nano-ZnO-modified cellulose model are all improved, with the highest increase in elastic modulus reaching 45.31% and the highest increase in thermal conductivity attaining 41.49%. The addition of nano-ZnO effectively fills the gaps in the fiber network and enhances the interactions between cellulose chains and thermal conduction channels, thereby improving the thermodynamic performance of cellulose. This work provides valuable theoretical references for rapidly preparing modified cellulose insulating papers with excellent thermodynamic performance.

Research on the Influence of Pantograph Catenary Contact Loss Arcs and Zero-Crossing Stage on Electromagnetic Disturbance in High-Speed Railway

During train travel, various factors, such as body vibration, uneven contact lines, and hard spots on carbon sliding plates and over electric neutral zones, often lead to brief separation between the pantograph and the contact line, i.e., the pantograph catenary contact loss phenomenon. With the continuous increase in train speed and traction power, the probability of pantograph catenary contact loss occurrences rises with a gradual increase in the energy of electromagnetic radiation, making the pantograph catenary arc a primary source of interference affecting the electromagnetic safety of high-speed railways. Understanding the mechanism, characteristics, and influencing factors of electromagnetic interference caused by pantograph catenary contact loss discharges is of utmost importance for analyzing and resolving on-site equipment interference faults. Our analysis of the physical process of pantograph catenary contact loss reveals that when the distance between the pantograph and catenary is significant and the duration is lengthy, high-voltage breakdown occurs within the pantograph catenary gap as it comes close again after the complete extinguishing of the arc. To investigate the electromagnetic radiation characteristics resulting from high-voltage breakdown discharge arcs in the pantograph catenary contact loss process, we established a laboratory test platform for assessing the electromagnetic disturbance characteristics of high-voltage pantograph discharge. We designed a test procedure utilizing fixed-gap breakdown discharge to evaluate the impact of the arc zero-crossing stage on electromagnetic radiation disturbances. Our research indicates that when the pantograph catenary spacing remains constant, an increase in voltage level leads to an elevation in the current within the discharge circuit, resulting in an increased intensity of impulse radiation generated during pantograph catenary contact loss events. During the moment of gap breakdown, the antenna records the highest amplitude of electromagnetic radiation. Also, during the steady-state arc ignition phase of the pantograph catenary gap, the zero-crossing stage generates pulsed discharge currents within the circuit, accompanied by substantial electromagnetic radiation. As the arc current increases, the zero-crossing time shortens, and the pulse current during the zero-crossing process decreases, accompanied by a reduction in the excited electromagnetic radiation. These observations reveal novel characteristics of electromagnetic radiation disturbances during steady-state arc ignition. The outcomes of our study provide valuable insights that can contribute to our understanding of the characteristics and influencing factors of electromagnetic radiation in pantograph catenary contact loss discharges and offer theoretical guidance for the resolution of pantograph catenary contact loss interference faults.

The Impact of a 1.1 MWp PV Rooftop Integration in Medium Voltage Distribution Networks

A high penetrating the capacity of Rooftop PLTS has an impact on the performance of distribution network operations and the prior technical studies only using simulation. This paper examines the impact of integrating a 1.1 MWp PV Rooftop into the medium voltage distribution network, involves a comparison between simulation data obtained using the ETAP software, before and after integration, compared with direct measurements. The results indicate improvements in the distribution operating performance. Following the integration, there was a 0.05% increase in voltage levels, a 0.06% increase in short circuit current, a 1.25% reduction in network losses, up to 8.9% harmonics current, up to 0.14% harmonics voltage, and a 0.28% decrease in power factor, as observed at both the substation and the network, they are in accordance with the measurement results.

Comparative Study on Partial Discharge Characteristics of Seven Accessory Defects Under Four On-Site Testing Voltages of a 10-kV Cable Line

Due to the increase in voltage levels and line lengths of power cables, the commonly used alternating current resonance (ACR) voltage is challenging to meet the growth rate of the capacitance of ultra-high-voltage cables for the on-site partial discharge (PD) tests. PD research on power-frequency-like voltages such as damped alternating current (DAC) voltage, very low-frequency sine wave (VLF-Sine) voltage, and very low-frequency cosine rectangular wave (VLF-CR) voltage, has important engineering value for evaluating the cable insulation conditions. In this paper, a PD test and measurement system of a 10 kV XLPE cable line with a 2 km length is established. Seven typical accessory defects are made artificially, including insulation hole, insulation screen tip, ring-cut tool mark, and stress cone installation dislocation defects at the terminals, and connector tip, conductive impurity, and stress cone installation dislocation defects at the joints. PD tests under four kinds of testing voltages of ACR, DAC, VLF-Sine, and VLF-CR are carried out to compare the PD inception voltages (PDIV), phase-resolved PD (PRPD) patterns, and PD location results of various defects. PD equivalence between power-frequency-like voltages and ACR is characterized by PDIV equivalent coefficient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PDIV</sub> , PRPD pattern characteristic quantities and discharge amplitudes. The results show that DAC and VLF-Sine have an outstanding ability to detect and characterize the severity of PD. DAC and VLF-CR have a good ability to recognize the type of PD. And DAC, VLF-Sine and VLF-CR can accurately locate PD. This study provides an important reference for on-site cable defect diagnosis and PD assessment.

Investigating the progression of insulation degradation in power cable based on partial discharge measurements

Assessments of aging and insulation degradation in power components are important to observe and track their condition during operation. Partial discharge (PD) diagnostics is an efficient method for health estimation of the components’ insulation. PD is initiated when the dielectric strength of localized insulation part is decreased. The intensity of PD increases with time, which may lead to insulation failure. This paper investigates the influence of the electrical stresses on the behavior of PD activity in medium voltage (MV) cable containing insulation defects. For this purpose, insulation defects such as internal, surface, and corona are developed in the MV cable environment under laboratory conditions. PD behavior is studied in these defects at gradually increased voltage levels by observing different PD characteristic features including PD inception voltage (PDIV), pulse repetition rate, accumulated apparent charge, average discharge current, discharge power, and quadratic rate. The Tobit regression model is developed for these progressing defects to identify the trends and to predict the behavior based on PD characteristic features. The presented work proposes a framework for the evaluation of the progression of insulation degradation due to increased electrical stress. The study is carried out on XLPE cables, however, the developed approach can be equally implemented on other types of dielectrics and components.

Removal of free cyanide in dry-milled cassava flour using atmospheric nonthermal plasma treatment

The primary concern for the cassava industry is reducing hydrogen cyanide (HCN) in the final product to a level that meets the Codex standard. Wet milling and drying to produce cassava starch can reduce cyanide compounds to levels that are safe for human consumption and meet international regulations, but at a high cost in terms of water. The purpose of this study was to investigate the effect of atmospheric nonthermal (ANT) plasma treatment on the removal of free cyanide from dry-milled cassava flour, as well as other physical and chemical properties. To generate cold plasma, helium was used as the feed gas in a dielectric barrier discharge reactor. The results show that the first-order kinetic model can explain the fraction degradation of cyanide by ANT plasma. The rate of HCN fraction removal increased from 0.0116 min−1 to 0.0453 min−1 and 0.0119 min−1 to 0.0349 min−1 with increasing voltage level (10–20 kV) when the initial HCN were 143 ± 7 and 233 ± 5 mg kg−1 dw, respectively. The 20 kV-15 min ANT plasma treatment of cassava flour containing 143 ± 7 mg kg−1 dw reduced 35.7% of HCN without affecting starch crystallinity, protein, fiber, fat, or moisture content, but significantly changed the pasting properties (P < 0.05).

Smart inverter and battery storage controls to reduce financial loss due to overvoltage-induced PV curtailment in distribution feeders

The rapid growth of rooftop solar photovoltaic (PV) systems in low-voltage distribution networks has caused reverse power flow leading to voltage rise. As the voltage level increases, PV inverters first reduce the output power to regulate the voltage and may eventually shut down if the voltage level remains above the permissible limit. When this happens, the PV output power is curtailed, leading to financial loss. This paper examines two control strategies to reduce PV curtailment: (1) smart PV inverters and (2) residential battery storage system optimally sized to reduce the cost of household energy. Smart PV inverters can reduce the voltage level by absorbing reactive power at the expense of curtailing its active power output. Residential battery storage can reduce the voltage level by storing excess PV power instead of exporting it to the grid Using these two strategies, a systematic approach is presented to reduce PV curtailment and the associated financial loss. Three types of electricity tariffs are used, namely, electricity market pool price, and retail flat and time of use tariffs for household customers. An 11-kV distribution feeder in South Australia is analysed with the prevailing feeder and inverter voltage limits per Australian regulatory standards. The results demonstrate that installing 100% of PV systems with smart inverters and optimally sized battery storage can reduce the PV curtailment and the corresponding financial losses by 47%.

Study on the Interference Law of AC Transmission Lines on the Cathodic Protection Potential of Long-Distance Transmission Pipelines

Through inductive coupling, AC transmission lines can generate large amounts of voltage to buried oil and gas pipelines in areas with common corridors, posing a threat to the cathodic protection effect of pipelines. Therefore, this paper investigates the effect of AC transmission lines on the cathodic protection of long-distance pipelines through inductive coupling. COMSOL Multiphysics finite element simulation software is used to calculate the distribution of cathodic protection potential of long-distance pipelines under different voltage levels, parallel spacing, conductor-to-ground height, conductor arrangement and pipeline burial depth for normal operation of AC transmission lines. Comparison and analysis of the AC transmission line on the pipeline cathodic protection potential interference law is conducted. The results show that: 1. AC transmission lines cause serious electromagnetic interference with the pipeline cathodic protection system, which will cause the pipeline cathodic protection potential to shift out of the effective protection area. 2. The maximum value of the induced voltage of the pipeline will appear at the two ends of the pipeline, and the induced voltage of the pipeline in the middle position is 0. 3. The shift of the pipeline cathodic protection potential increases with the increase of voltage level and decreases with the increase of parallel spacing, conductor height and burial depth. The pipeline cathodic protection potential shift is highest when the wires are arranged horizontally and lowest when they are arranged in an umbrella shape.

Thermal sensing capability and current–voltage–temperature characteristics in Pt/n-GaP/Al/Ti Schottky diodes

We have discussed the thermal sensing capability under a constant current level and current versus voltage (I–V) traces by measuring the temperature of high series resistance Pt/n-GaP/Al/Ti Schottky structures in the 100−320 K range. The Rs values of 35 Ω and 4.50 × 103 kΩ for the device have been determined from I–V traces at 320 and 100 K, respectively. The thermal sensing (V–T) curves are expected to give a straight line at each current level. However, the V–T curves have deviated upward from linearity due to the high Rs value of the device after a certain temperature. The deviation point from linearity in V–T traces shifts to higher temperatures with an increase in bias voltage and current level. Thereby, the straight-line interval portion of the V–T curve has become too small with an increase in the current value. The thermal sensing coefficient α changed from 2.49 mV/K at 10 μA to 3.21 mV/K at 0.50 nA. Therefore, it has been concluded that the Pt/n-GaP/Al/Ti Schottky barrier (SB) is preferable for thermal sensor applications at the small current levels of 0.50, 1.0, 2.0, and 10.0 nA with high sensitivity up to a minimum temperature of 100 K. From I–V curves, qΦb0 and ideality factor values have ranged from 1.200 eV and 1.066 at 320 K to 0.854 eV and 1.705 at 100 K. It has been reported in the literature that the large SB height leads to a better temperature response.

Low-Pressure Optical Detection, Location, and Quantification of Electrical Discharges in Aircraft Wiring Systems

Strict regulations issued by international administrative bodies limit the CO2 equivalent emissions for new aircraft, while increasing efficiency requirements. To reach this goal, next generations of aircraft will use more electrical power than their predecessors, so distribution voltage levels will inevitably increase to limit the weight of the electrical wiring interconnect system (EWIS). However, such increased voltage levels generate higher electric stresses in insulation materials as well as in electric and electronic components; thus new failure modes triggered by electrical discharges will appear, their effects being aggravated by harsh environments typical of aircraft systems. The combined effect of higher electrical stresses, compact designs, and low-pressure operating conditions greatly intensifies the risks of premature insulation failure due to electrical discharge activity. This paper shows that by using image sensors, it is possible to detect, localize, and quantify the intensity of electrical discharges occurring in aircraft environments. Through experiments carried out in a low-pressure chamber using an image sensor, this work detects and determines the intensity of electrical discharges generated in electrical wires in their initial stage, long before major faults develop. This paper also shows that the intensity of the discharges calculated from the digital images obtained with the image sensor is directly proportional to the electrical energy involved in the discharge process and increases linearly with the applied voltage. Due to the difficulty of detecting these failure modes at a very early stage, this strategy could potentially facilitate predictive maintenance tasks while contributing to increased levels of aircraft safety.

Condition Assessment of HVDC Cables during their Lifecycle

Recent market developments towards power generation in remote renewable power plants such as concentrated solar power plants in deserts or large off-shore wind parks, raise an interest for long distance power transmission via extruded HVDC cables. HVDC cables require quality assurance during the complete product lifecycle, mainly: a) R&amp;D activities for design verification and - validation b) routine tests in the factory for confirmation of proper manufacturing c) acceptance test after erection and commissioning to exclude defects caused during transport and installation d) ageing monitoring and quick fault detection and location detection during service life. Considering increasing voltage levels, increasing cable lengths and ground or even offshore installation, the dielectric testing of extruded HVDC cables in the factory and on site remains challenging. The long-term validation of insulation coordination requires high voltages for quality assurance tests which represent typical expectable stresses during service. Typical examples are wave shape, partial discharge behavior and dielectric field stress in the insulation medium. Hence, different technical solutions are available to generate these required high voltages for testing of HVDC cables. This paper discusses essential technical and commercial aspects of HVDC cable quality assurance and presents suitable methods for HVDC cable testing.

An experimental device for measuring the internal temperature and pressure of rock for rock breaking by pulsed discharge in petroleum exploitation

In order to measure the variation of temperature and pressure inside rock subjected to pulsed discharge, a device for measuring the temperature and pressure inside rock is designed in this work. The device is composed of an excitation module and a signal module. Based on the analysis of pulsed discharge process, the structure of key components of the device was designed. The experiment of rock breaking by single pulsed discharge was conducted. The peak values of temperature and pressure inside sandstone rock samples of 20 cm*20 cm*20 cm were measured when they were broken at 8 different voltage levels in the range of 2.5 kV–20 kV. It was found that with the increase of voltage level, the temperature and pressure inside the rock were also significantly increased when the rock was broken. At the maximum 20 kV voltage, the temperature peak inside the rock is 398 °C and the pressure peak is 2.4 MPa. The temperature and pressure inside the rock rose dramatically as it broke. This device can monitor temperature and pressure inside rock during the rock breaking process, and its embedded computer can construct time-varying temperature field and pressure field with transmitted temperature and pressure signals. This technically supports theoretical research on rock breaking by pulsed discharge.

Motion characteristics and distribution of metal particles in insulating oil under DC voltage

Studying the dynamic behavior of metal particles in insulating oil in case of flow-electric field coupling is important to fully understand the insulation mechanism in transformers, such as partial discharge and insulation deterioration of contaminated insulating oil. In this paper, through experiments, the particle image velocimetry (PIV) technique is applied to study the motion of metal particles in the oil flow under direct current (DC) electric field. According to the observation results of flow field, the effects of voltage level, electric field non-uniformity, and oil flow velocity on the motion and distribution of particles are analyzed in detail. The obtained results show that the applied voltage has an obvious effect on the motion of metal particles in oil flow, and it causes the formation of wavy trajectories of particles, where such effect becomes more obvious as the voltage level increases. Moreover, it is observed that the increase of flow velocity can weaken the influence of electric field, and the electric field non-uniformity affects the trajectory of particles mainly by changing their velocity component in the vertical direction. In addition, the concentration of particles group in the oil flow is sensitive to the external electric field, where the concentration decreases with the increasing electric field. Certainly, the results reported herein are effective in further revealing the effect of impurity particles on the insulating oil.

Nonthermal atmospheric plasma reactors for hydrogen production from low-density polyethylene

Hydrogen is largely produced via natural gas reforming or electrochemical water-splitting, leaving organic solid feedstocks under-utilized. Plasma technology powered by renewable electricity can lead to the sustainable upcycling of plastic waste and production of green hydrogen. In this work, low-temperature atmospheric pressure plasma reactors based on transferred arc (transarc) and gliding arc (glidarc) discharges are designed, built, and characterized to produce hydrogen from low-density polyethylene (LDPE) as a model plastic waste. Experimental results show that hydrogen production rate and efficiency increase monotonically with increasing voltage level in both reactors, with the maximum hydrogen production of 0.33 and 0.42 mmol/g LDPE for transarc and glidarc reactors, respectively. For the transarc reactor, smaller electrode-feedstock spacing favors greater hydrogen production, whereas, for the glidarc reactor, greater hydrogen production is obtained at intermediate flow rates. The hydrogen production from LDPE is comparable despite the markedly different modes of operation between the two reactors.

Using CMOS Image Sensors to Determine the Intensity of Electrical Discharges for Aircraft Applications

The development of more electric aircrafts (MEA) and all electric aircrafts (AEA) inevitably implies an increase in electric power and a consequent increase in distribution voltage levels. Increased operating voltages coupled with low pressure in some areas of the aircraft greatly increase the chances of premature insulation failure. Insulation failure manifests itself as surface discharges, arc tracking, arcing, and disruptive or breakdown discharges, in order of increasing severity. Unfortunately, on-board electrical protections cannot detect discharges at an early stage, so other strategies must be explored. In their early stage, insulation faults manifest as surface and corona discharges. They generate optical radiation, mainly in the near-ultraviolet (UV) and visible spectral regions. This paper focuses on a method to detect the discharges, locate the discharge sites, and determine their intensity to facilitate predictive maintenance tasks. It is shown that by using small size and low-cost image sensors, it is possible to detect, locate, and quantify the intensity of the discharges. This paper also proposes and evaluates the behavior of a discharge severity indicator, which is based on determining the intensity of digital images of the discharges, so it can be useful to apply predictive maintenance tasks. The behavior and accuracy of this indicator has been tested in the laboratory using a low-pressure chamber operating in the pressure range of 10–100 kPa, which is characteristic of aircraft applications, analyzing a needle-plane air gap geometry and using an image sensor. The proposed method can be extended to other applications where electrical discharges are an issue.