Primary Conductor Research Articles

In Situ Construction of a Lithiophilic and Electronically Insulating Multifunctional Hybrid Layer Based on the Principle of Hydrolysis for a Stable Garnet/Li Interface

AbstractAdapting solid‐state Li‐metal batteries is an attractive way to pursue higher energy density and safety compared to liquid‐based ones. With high ionic conductivity and excellent stability with Li, Ta‐doped Li7La3Zr2O12 (LLZTO) is an effective option. However, the poor solid–solid interface contact induced by the lithiophobic Li2CO3 layer hinder its practical application. Herein, a versatile strategy is proposed based on the hydrolysis of sodium tetrafluoroborate (NaBF4), aiming to convert the Li2CO3 into multifunctional hybrid layer containing LiF, LiBO2, and NaF. Among them, LiF and LiBO2 serve as the primary Li ion conductors, the introduction of NaF with high surface energy not only enhances the interface wettability, but also further elevates the critical dendrite strength against Li dendrites. All three components serve as excellent electronic insulators, suppressing electron invasion at the interface and preventing Li dendrite growth in the solid electrolyte. As expected, the interfacial impedance of the NaBF4 treated symmetric cell is reduced to 6.0 Ω cm2, the critical current density (CCD) comes to 2.0 mA cm−2, and cycles over 3000 h at 0.3 mA cm−2 and 1500 h at 0.5 mA cm−2 respectively. Besides, the modified SSBs matched with LiFePO4 or LiNi0.6Co0.2Mn0.2O2 cathode show great long‐term cycling and rate performance.

Analyses on an electronic voltage transformer's failure by its resonance with very fast transient overvoltage and suppression

AbstractAs voltage measuring devices are widely used in the high voltage power system with a primary‐secondary‐fusion structure, electronic voltage transformers are directly connected to the primary conductor and would face much more serious electromagnetic environments than general secondary equipment. As a result, they would still experience failures even when general protection measures are adopted to suppress overvoltages' amplitudes. To address this issue, an innovative method is proposed after analyses are conducted on the resonance between a transformer and an overvoltage. Within this method, an air‐cored coil is installed in a transformer to artificially shift its natural frequency and to dodge the high‐frequency dominant component of a transient overvoltage, avoiding the aforementioned resonance and suppressing the secondary overvoltage. In addition, simulations and laboratory tests are conducted to prove this method's validity.

Enhanced proton conductivity of SPEEK membranes by constructing hydrogen bond network through doping ionic liquid and graphene oxide

AbstractSo as to improve proton conductivity at medium temperatures while reducing the loss of ionic liquids (ILs), this article fabricated a series of hybrid membranes with sulfonated poly (ether ether ketone) (SPEEK) as their base material, 1‐allyl‐3‐methylimidazolium chloride ([AMIM][Cl]) as their primary proton conductor, and graphene oxide (GO) as their filler. The characterization results showed that the –SO3H groups of SPEEK formed acid–base pairs with the imidazole ring of [AMIM][Cl] at the interface where electrostatic attraction inhibited the main‐chain migration of the SPEEK. At the same time, the large hydrogen bond network formed between [AMIM][Cl], GO and SPEEK provided more jump sites for proton transfer. Proton conduction of the prepared membranes was enhanced by way of low potential energy barriers. At 120°C, SPEEK/IL/GO‐2% exhibited a proton conductivity of 21.35 mS/cm, and the IL loss rate was 20.17%. The characterization results demonstrated that the prepared SPEEK/IL/GO composite membranes had excellent physicochemical properties, dimensional stability, high proton conductivity, and low IL loss, which were expected to be used in practical conditions at medium temperature.Highlights Large hydrogen bonding network provides additional proton hopping sites. Physical cross‐linking limits the leaching of ionic liquid. SPEEK/IL/GO‐2% membrane achieves a conductivity of 21.35 mS/cm at 120°C.

Разработка и исследование катушки Роговского для работы в условиях эксплуатации открытого распределительного устройства

The interest to use Rogowski coils (RC) as current sensors to design secondary systems increases due to application of microprocessor relay protection and automation devices, including those that support the reception and processing of information in a form of a digital code in the format of protocols defined in IEC61850, as well as the disadvantages of traditional electromagnetic current transformers. Despite the popularity of RC, there are many unstudied issues of their functioning under operating conditions of open switchgears of power facilities, especially when operating with modern relay protection and automation devices. The aim of the study is to analyze the effect of ambient temperature on the error of current conversion by Rogowski coils. Studies of Rogowski coils have been carried out using the experimental and industrial samples. During the research modern testing equipment has been used. The equipment is listed on the Unified Register of Measuring Equipment of the Russian Federation and has valid verification certificates. The analysis of the factors influencing the error of metrological channels has been carried out. The analysis is conducted based on traditional current transformers (CT). The factors influencing the measurement error of RC are systematized. Experimental data obtained as a result of the study of the RC conversion error in a wide temperature range are presented. It has been established that due to design solutions, it is possible to neutralize the influence of such factors as the position of the primary conductor, external electromagnetic fields, uneven winding, the number of layers of the secondary winding, and thermal expansion. The use of materials with a low coefficient of linear expansion to manufacture the core of the Rogowski coil makes it possible to obtain the metrological characteristics of the transducer that meet the requirements of normative technical documentation in a wide temperature range. Application of RC as a primary current sensor for relay protection and automation systems is a promising area that requires further comprehensive research, and specifically in the process of industrial operation.

Resolving Current Transformer Partial Saturation Problem: An Analytical Approach to Design the Flux Equalizing Winding

Stray fluxes passing through the current transformer (CT) core produced by adjacent bus-bars and conductors or eccentric installation of primary conductors results in asymmetric magnetic flux distribution along the core. This may lead to exceeding the magnetic flux from its appropriate saturation level in some parts of the core, which is called partial saturation (PS) phenomenon. Under such a condition, CT error increases, and some relays maloperations may take place. This paper proposes a novel analytical approach to design flux equalizing winding (EW) for resolving such a problem. Moreover, PS occurrence in a core balance CT (CBCT) is analyzed using the finite element method (FEM), and its negative influence on a sensitive earth fault (SEF) relay is scrutinized as a case study. Simulation studies reveal that the proposed approach can prevent PS-related undesirable effects in a real power system.

Multipronged Phenotyping Approaches to Characterize Sugarcane Root Systems.

Roots are the primary conductors of water and nutrients and play a vital role in sustaining growth and yield under stressful environments. The study of plant roots poses methodological difficulties in in situ assessment and sampling, which is especially true for sugarcane (Saccharum spp.). Traditional methods during the 1920s documented the genotypic variation in sugarcane root systems, after which few studies were reported on sugarcane root traits per se until recently. In addition to morphology, rhizosphere characteristics, including allelopathic effects and/or affinity for microbial symbiosis, determine plant establishment and survival. Ultimately, root systems define the above-ground productivity of sugarcane. With the impetus for climate-resilient varieties, it is becoming more relevant to explore and utilize the variability in root system traits of sugarcane. This paper describes multipronged approaches for sugarcane root phenotyping, including field excavation by trench sampling, the use of a root core sampler, raised platforms for root sampling, and raising plants under hydroponic culture, employed by a team of scientists at the Indian Council of Agricultural Research-Sugarcane Breeding Institute (ICAR-SBI). Field excavation by trench sampling is imperative to assess the plant roots in their natural growing environment. The use of raised platforms simulating field conditions and a root core sampler are alternative approaches, with a considerable reduction in time, uniform sample size, and less loss of root material. Hydroponic plant culture allows the study of morphology, anatomical features, and rhizosphere biology, including the exudation of organic compounds and microbial interactions. Data generated from different experiments using diverse sampling methods add to the wealth of information on the root system traits of sugarcane.

A Concise Analytical Formula of Mutual Inductance for Circular Rogowski Coil Revealing Spatial Distribution Characteristics of Mutual Inductance Deviation

Mutual inductance between primary wire and circular Rogowski coil varies with the position of primary conductor, the deviation of mutual inductance referred to center of circle causes the measurement error. Usually, the mutual inductance of Rogowski coil can be calculated by the summation of each turn of coil, however the spatial distribution characteristics of mutual inductance deviation has not been revealed. A concise analytical formula of mutual inductance is derived based on the summation form and verified by experiment in this paper, which leads to three characteristics of mutual inductance deviation. The first is the mapping relation of mutual inductance deviation between inside and outside Rogowski coil which established connection between positional accuracy and anti-interference ability. The second is the zero deviation line of mutual inductance deviation given by simple equation, which describes the position of primary wire where the measurement error vanishes. The third is approximate function on turns number, inner and outer radius of Rogowski coil and measurement error, which is easy to calculate and simplifies the design progress of Rogowski coil. Furthermore the formula and characteristics of mutual inductance can be generalized from uniform Rogowski coil and perpendicular primary wire to discontinuous PCB RC, primary conductor with cross section, and inclined primary wire. The mapping relation, zero deviation line and improved formula of mutual inductance deviation are discussed.

An Analysis of Minor Hysteresis Loops Behavior under PWM Voltage - Electromagnetic Device at No-Load and Loaded Conditions

This paper addresses the influence of the primary and secondary resistances on the behavior of minor hysteresis loops when the electromagnetic device is fed by three-level PWM (pulse width modulation) voltage. To study the device transferring energy to a load, the experimental approaches are different of traditional procedures to material characterization, where problems inherent to the process are added. Analytical, FEM and experimental analysis are performed on a toroidal transformer equipped with a flux sensing coil. The leakage fluxes related to the primary and secondary currents are shown to cause errors in the measurement of the core magnetization current. A solution to mitigate this problem is employed, consisting in twisting and winding together primary and secondary conductors. Experimental methodologies for obtaining the value of the iron losses when the device is transferring energy to a load are also performed. The study shown showed that supply voltage with three-level PWM waveform causes minor hysteresis loops and the greater the resistance value of the excitation winding, the larger the areas of the minor hysteresis loops. On the other hand, by increasing the energy transferring to a load the minor loops areas tend to decrease.

Effect of Frequency on the Linearity of Double-Layer and Single-Layer Rogowski Coils

The Rogowski coils are usually used to measure high frequency currents due to their air core. The higher the turn number, the higher the mutual inductance between Rogowski coil and the primary conductor. Performance of Rogowski coil with a high turn number is very difficult to figure out by simulation software. This paper presents an improved lumped parameter model of Rogowski coils. According to the model, the influence of parasitic turn-turn capacitance, turns self-inductance, turn-turn inductance, turn-shielding capacitance, turns resistor, sample resistor and others on the linearity of Rogowski coil with a high turns number at several different frequency ranges are explored. The model is applicable to both double and single layer coils. Three high-turn-number coils of double and single layer are studied and compared in this paper. The improved lumped parameter model is verified by experiments. Five main influence factors on the linearity of the Rogowski coil at a certain frequency range are studied both theoretically and experimentally. The five influence factors include sampling resistors, turns density, shielding layer, positions of the primary conductor, and turns nonuniformity. The numerical and experimental results analyze the influence of the factors on the linearity of the output voltage of the coils at different frequencies quantitatively and qualitatively. The principle of the improved model can be used for multi-layer coils. The model can be a useful guidance in designing coils with suitable structure for special applications at different frequencies.

A Method for Estimating Technical Losses in Primary Feeder Conductors

One of the engineers’ concerns is the loss of energy in the electric power system. Actually, most of the energy losses occur in the distribution system, i.e., about 4-8%. Therefore, efforts should be made in order to improve the performance of the distribution networks. Evaluating losses in the distribution networks should be done in order to reduce losses. The problem is that there are many nodes, several lateral feeders, and the un-uniform current flowing in the feeder so that calculating the losses becomes very difficult. In addition, the big distribution system has so many feeders, generally more than 1000 feeders, with various types. Thus, the calculation of the losses in the distribution system will face very complex and large-scale problems. Therefore, calculating losses for large scale distributed systems that use load flow or measurement methods is not possible. This paper proposes an effective method that uses a lump load model for technical losses in distribution systems. By approaching, the current is proportional to power, the input current into the feeder can be distributed to each lateral feeder. Thus, the current flow in each segment of the feeder can be determined. For typical feeder with the load currents changed linearly by linearity factor, then-current flows of each segment feeder can be easily determined as c function. This function is created as a calculation model of losses with a clear derivative of the mathematical formulations. The results of numerical studies show that this method is accurate enough with the error of 1.26% when compared to the load flow method using an 8-node feeder. The calculation result is based on the IEEE 13-node test feeder; its loss is smaller than 3.86% compared to the load flow method.

Research and Application of Generator Protection Based on Fiber Optical Current Transformer

This paper introduces the basic principle of fibre optical current transformer (FOCT), and explains the advantages of FOCT compared with electromagnetic current transformer (CT). FOCT can be wound around the primary conductor in any shape, has high harmonic accuracy and doesn't suffer from saturation, thus a good solution for generator relay protection. As a common electrical fault within large generators, the inter-turn short circuit in field windings (ISCFW) is likely to cause earth faults between the field winding and the rotor body and magnetization of the main shaft without timely intervention. Steady-state unbalanced currents of even orders and fractional orders related with pole pairs inside phase windings are required to monitor the ISCFW. The inter-turn fault of stator windings may rapidly develop into a phase to phase fault, which seriously threatens the safety of the unit. Split-phase transverse differential current reflects the steady-state current imbalance inside the stator winding. Nevertheless, for most steam turbine generators and some hydro turbine generators, it is unable to obtain phase-segregated transverse differential current due to impossibility of installing branch current transformer in the narrow space inside the generator. However, FOCT which uses fibre optic cable as a sensor is installable within limited space to measure the current of each group of winding branches of each phase. FOCT furthers phase-segregated transverse differential protection, partial differential protection and online monitoring of the ISCFW, thus optimizing the generators protection scheme. In addition, operating speed and sensitivity of generator differential protection are improved based on the reliable measurement from FOCT. The proposed scheme is verified by an application on a 300MW generator at a pump-storage power plant. This is the first attempt of applying FOCT to the relay protection of generator set, which provides reference for further development and application of FOCT in power plant.

Improved Characterization of Polyphase Induction Motor Losses: Test Standards Must Be Modified to Improve Efficiency Optimization

For many years, industry standards, including IEEE Standard 112, have characterized the component losses of three-phase induction motors as primary and secondary conductor or (I2R) core, friction and windage, and stray load loss (SLL). The definition of each, as epitomized by IEEE 112, guarantees that part of the losses will be characterized as SLL. It also ensures that the secondary I2R loss will be underestimated and that the core loss associated with field distortions resulting from load current are not properly identified. This article provides the opportunity to further optimize motor efficiency by discussing issues with existing test-standard loss models and describing model methods that better characterize motor losses.

NSGA-II+FEM Based Loss Optimization of Three-Phase Transformer

In order to obtain a good optimization method for the electrical transformer design with optimal selection of parameters, performance evaluation of three evolutionary algorithms (EAs), namely, genetic algorithm (GA), differential evolution algorithm, and nondominated sorting GA (NSGA-II), is carried out. The aim of this paper is to optimize parameters of transformer design (core thicknesses, primary-turn number, secondary-turn number, primary conductor area, and secondary conductor area) for minimization of total power losses (no-load losses and load losses) in three-phase transformer topology while maintaining high efficiency and low cost. The method used for this optimization scheme combines the finite-element method (FEM) and EAs to provide an accurate selection of parameters together with the optimized magnetic flux density and decreased loss. Experimental results show that NSGA-II+FEM model successfully provides a global feasible solution by minimizing total loss and related cost while improving the efficiency of three-phase transformer, rendering it suitable for application in the design environment of industrial transformers.

Modeling and Analyzing the Mutual Inductance of Rogowski Coils of Arbitrary Skeleton.

There are Rogowski coils of various shapes in the on-site measurement, and it is difficult to calculate the electrical quantities of Rogowski coils of curved skeleton and circular cross-section by simulation software. This paper proposes a theoretical derivation to calculate the mutual inductance between the conductors of any shape and Rogowski coils with skeletons of any shape. Based on the derivation, the influence of four skeleton shapes of Rogowski coils and four shapes of the primary conductors on the mutual inductance of Rogowski coils are studied by the comparison between the ideal cases and some non-ideal ones. The gap and gap compensation of the openable Rogowski coils are also considered. Experiments verify the numerical results according to the derivation. It is shown that to reduce the errors of the measurement the circular skeleton deformation should be avoided, the coil’s skeleton should be with curved angle, the primary conductor should be as straight as possible and should go through the center of the skeletons vertically. Furthermore, for the Rogowski coils of the rectangular skeleton, we propose a new skeleton structure to reduce the deviation influence of the primary conductors.

Performance Enhancement of Rogowski Coil Through an Additive Manufacturing Approach

The Rogowski coils, along with the amperometric clamps, are probably the most widespread current transducer when measurements must be performed on electrical circuits and/or systems that cannot be interrupted. Thanks to their flexible shape and a suitable closing mechanism, they can be easily installed around the primary conductor without interrupting the electric current that must be measured. Although their operating principle is very simple, the practical realization is far from the transducer model and, therefore, particular attention must be paid to geometry, orientation and positioning with respect to the primary conductor in order to reduce the uncertainty associated with measurement. To overcome this problem, the authors propose hereinafter a coil support realized in additive manufacturing technology capable of granting that (i) the Rogowski coil maintains a circular shape, (ii) the primary conductor passes in the coil center and (iii) the primary conductor is orthogonal to the surface defined by the coil itself. Thanks to 3D printing approach, the support can easily be adapted to coils of different circumference by simply rescaling its dimensions during the printing phase.To assess the performance improvement brought by the proposed support, several tests have been conducted in operating conditions involving different values of nominal current; in particular, the difference between the nominal current and that measured by the coil mounted on the proposed support was measured and compared with that associated with the coil characterized by one or more of the considered problems. The results obtained showed limited and systematic differences, which can then be compensated through a preliminary calibration operation in the laboratory.

B–H Curve-Based Model for CT Error Evaluation

Current transformers (CTs) of the bus bar type are widely used in ultrahigh voltage power systems for monitoring and protection. This paper presents a mathematical model to predict the measured current error caused by tilting and position eccentricity of the primary conductor of a bus bar in a CT. The model is based on actual B–H curve characteristics and is verified by comparing the model predicted results to corresponding 2-D and 3-D transient finite-element model results.

Mutual Inductance Between Arbitrary Conductor and Rogowski Coil With Circular Skeleton and Gap Compensation

To study the influence of the shape and position of the primary conductor on the Rogowski coil, this paper presents a theoretical derivation of mutual inductance between Rogowski coil and conductors with any shape and any position. Based on this, we study a gap compensation method for openable Rogowski coil with a gap. The validity of the compensation method is verified by comparing the theoretical and experimental results after compensation with those for the no-gap case. To verify the theoretical results of the derivation, we carry out experiments with three Rogowski coils and five common shapes of primary conductors in several representative positions. The three Rogowski coils include cases of with and without a gap, and with and without gap compensation. The five kinds of primacy conductor include straight, tilted, curvilinear, D-shaped, in and out the hole of Rogowski coil. The numerical calculations and experiments are both carried out and verify the theoretical results of the calculation method.

An Improved Analysis Method of Irreversible Demagnetization for a Single-Phase Line-Start Permanent Magnet Motor

This paper presents an effective analysis method of irreversible demagnetization for a line-start permanent magnet (PM) motor considering the magnetic field produced by secondary conductor bars. The magnetic field produced by the secondary conductor bars opposes the variation of the magnetic field caused by the primary part, and these result in the reduced magnetic field acting on the PM. By using finite element analysis in the transient magnetic field, currents in the primary and secondary conductors are estimated and used for demagnetization analysis of the magneto-static field. Therefore, conditions closer to actual situations can be achieved. Both the general demagnetization analysis method, using only primary currents, and presented analysis method are compared and the results are verified by experiments. General demagnetization analysis leads to over-estimation of the magnetic field acting on the PM, and results in excessive PM usage.

Behavior of an Inductive Loop Sensor in the Measurement of Partial Discharge Pulses with Variations in Its Separation from the Primary Conductor.

Ideally, an insulation system must be capable of electrically insulating the active components of a machine or device subjected to high voltages. However, due to the presence of polluting agents or imperfections inside or on the surface of the insulation, small current pulses called partial discharges (PDs) are common, which partially short-circuit the insulation and cause it to lose its insulating properties, and thus its insulation capacity, over time. In some cases, measurements of this phenomenon are limited by the type of sensor used; if it is not adequate, it can distort the obtained results, which can lead to a misdiagnosis of the state of the device. The inductive loop sensor has experimentally been demonstrated to be capable of properly measuring different types of PDs. However, because of its current design, there are several practical limitations on its use in real devices or environments. An example is the presence of a primary conductor located at a fixed distance from the sensor, through which PD pulses must flow for the sensor to capture them. In this article, the sensor’s behavior is studied at different separation distances from the line through which the PD pulses flow. In addition, the measuring capacity of the sensor is tested by removing the presence of the primary conductor and placing the sensor directly over the line through which the PD pulses of a real device flow.

Fabrication and characterization of transparent conducting reduced graphene oxide/Ag nanowires/ZnO:Ga composite thin films on flexible substrates

In recent years, flexible transparent conducting films (TCFs) have attracted considerable research interest because they are essential materials in flexible optoelectronic devices, which are still limited by the lack of suitable electrode materials. In this study, a highly stable, transparent, and a flexible composite electrode was developed using reduced graphene oxide (rGO)/silver nanowires (AgNWs)/Ga-doped zinc oxide (GZO) composite thin films. The rGO film was the first spin coated on flexible substrates and used as an adhesion enhancement layer. The AgNWs, which were used as a primary conductor, formed a random percolating network embedded between the rGO and GZO films. The GZO film was sputtered on the surface of the AgNWs and was used as a protective layer to prevent the oxidation of the AgNWs. The rGO/AgNWs/GZO composite thin film exhibited excellent electrical conductivity and superior stability to a monolayer or a bilayer TCF. The sheet resistance of the composite film (5.45 ± 0.41 Ω/□) slightly increased to no more than 5% when exposed to the atmosphere for 60 days. The rGO/AgNWs/GZO composite film exhibited an optical transmittance of approximately 85% at a wavelength of 550 nm. A bending test was conducted for 600 cycles with a curvature radius of 1 cm, and the test results revealed that sheet resistance of the composite film varied by less than 10%. The developed rGO/AgNW/GZO transparent conducting thin films have potential for use in future flexible optoelectronic device applications.