High Voltage Coils Research Articles

Inter-Turn Breakdown Fault Analysis and Winding Structure Optimisation of Winding of Dry-Type Transformers in Wind Farms

To address the problem of winding turn-to-turn breakdown faults in 35 kV dry-type transformers in wind farms under overvoltage conditions, this paper establishes a simulation model based on the structural dimensions and material parameters of the transformer windings. The winding distribution parameters were calculated using the finite element method. The transient processes inside the high-voltage coil were calculated by constructing a multi-conductor transmission line model (MTL) that took into account the influence of the secondary winding. The voltage distribution of the winding was analysed for both lightning shock and extra-fast transient overvoltage conditions. The simulation results show that the maximum overvoltage between turns of the transformer winding under lightning shock is 5.282 kV; the maximum overvoltage between turns of the winding under very fast transient overvoltage is 11.6 kV, which occurs between the first 2–3 layers of the section, close to the insulation breakdown margin. On this basis, the transformer winding structure was optimised and the maximum inter-turn overvoltage after optimisation was 9.104 kV, reducing the likelihood of insulation breakdown by 24.1%. Finally, the accuracy of the winding structure optimisation simulation study was verified by testing the transformer’s impulse voltage before and after optimisation, providing a reference for the stable operation of 35 kV dry-type transformers in wind farm practical applications.

Constant Tension Control System of High-Voltage Coil Winding Machine Based on Smith Predictor-Optimized Active Disturbance Rejection Control Algorithm.

In the production process of high-voltage coils, a constant tension control system is designed to improve the quality of the transformer. The system is composed of a controller, execution structure, detection structure, etc. The active disturbance rejection control (ADRC), optimized by the Smith predictor (SP), is adopted to achieve constant tension control. The experiment results show that the tension control system based on the SP-ADRC has higher control accuracy, shorter stabilization time and stronger anti-interference ability compared with the traditional PID algorithm. The actual experiment shows that the constant tension control system of the high-voltage coil winding machine based on SP-ADRC has a superior control effect and high practical value.

Dielectric barrier discharge analysis from the point of view of supply voltage and reactor topology

This paper aims to provide a comprehensive analysis of the output of DBD reactors considering 2 different power supplies that provide rectangular command voltage with variable duty cycle and frequency. The experiments presented were performed with these power supplies considering four geometries of DBD reactor. At this stage the input parameters of the power supplies are: frequency of control pulses, duty cycle and high voltage level applied on the DBD reactors by choosing a certain number of turns for the primary windings of the high voltage coil. The parameters considered as outputs from the reactor-power supply assembly were: the high voltage output and the electric current from the primary induction coil.

Numerical study on temperature rise and mechanical properties of winding in oil-immersed transformer

In the present paper, the electromagnetic-fluid-thermal-mechanical stress coupling process in an oil-immersed transformer is numerical studied with finite element method. The relationship between electromagnetic force and flux leakage, interaction of losses, temperature and oil flow, and the influence of electromagnetic force and temperature rise on mechanical characteristics of coil are carefully analyzed. Firstly, the leakage flux is mainly generated at the ends of coil and core corner end. The electromagnetic force of B-Phase low voltage coil is the highest due to the leakage flux superimposition caused by A-Phase and C-Phase coils and higher current on B-Phase low voltage coil itself. Secondly, the interaction between losses, temperature and oil flow is remarkable. Compared with the results as heat source is constant, the loss density of high and low voltage coil increased by 18.18% and 14.87%, respectively, and the hot spot temperature increased by 7.06 K. Finally, it is revealed that the coil deformation is mainly caused by thermal load, and little affected by electromagnetic force. The frequency of stress is twice as high as that of energized current. The stress at both ends of the coil is the highest and it would lead to fatigue failures.

Estimation of the eddy current losses in a dry-type 3000 KVA transformer with machine learning

This paper explores the design parameters of high-voltage coils of three-phase transformers and the effects of eddy current losses caused by energy conversion. The commercial software, ANSYS-Maxwell, was employed to conduct the simulation of electrical and magnetic fields. The design parameters of the high voltage coil include the leg distance of core, the height and the block thickness of primary windings, the height of primary coils, and the height of secondary windings. The specification of the three-phase transformer of this study are 3000 kVA with rated voltage of 6600 V and corresponding current of 151.5 A. Base on thirty cases of simulation, machine learning, artificial neural network, was utilized to predict the extra loss due to eddy current in the clamps and the windings. The prediction accuracies are 0.72 and 0.86 for primary and secondary windings, respectively.

Surface Discharge Characteristics of GFRP in GN2and LN2for Designing a Superconducting Coil System

Solid insulation materials used in the application of a superconducting apparatus need to be robust in terms of both mechanical and dielectric performance. The surface discharge characteristics of solid insulation materials are inferior to their penetration breakdown characteristics. Therefore, dielectric accidents in a superconducting appliance can occur as a form of surface discharge rather than as a form of penetration breakdown. In this paper, dielectric experiments on the surface discharge characteristics of glass-fiber-reinforced plastic in gaseous nitrogen (GN2) at room temperature and liquid nitrogen (LN2) at 77 K are conducted to design a high-voltage superconducting coil system with high reliability. As a result, the electric field intensity at surface discharge voltage $V_{\mathrm{SD}}$ under ac and dc voltages is deduced as an empirical formula.

Submersible Dry-Type Transformer

This paper describes the concept and development of dry-type transformers for underground distribution networks, capable of operating in the open air, partially submerged or completely submerged without enclosure and in contact with water. The rating is in the range of 500 kVA to about 2000 kVA and 15- or 25-kV voltage. Immersion depth is limited to 3 m, due to the limits of the plug-in connectors on the high-voltage (HV) side of the transformer. A tap panel is provided on HV coils for $\pm $ 5.0%. Dimensions and losses are comparable to those of liquid-immersed transformers. Electrical insulation is fully solid. The HV coils are shielded and the shield is grounded.

High Voltage Coil Current Sensor for DC-DC Converters Employing DDCC

High Voltage Coil Current Sensor for DC-DC Converters Employing DDCC

National Consultant in Cardiology Experts' Group Guidelines on dealing with patients implanted with some St. Jude Medical Riata and Riata ST leads

In December 2010 St. Jude Medical informed about higher incidence of silicone insulation abrasion in implantable cardioverter-defibrillator leads Riata/Riata ST. The manifestation of this phenomenon is the externalisation of conductors outside the body of the lead, which is visible in a fluoroscopy. The abrasion could also involve an insulation under high-voltage coil and in the worst case could result in a short circuit within high voltage part of the system. The incidence of this phenomenon varies from part of to several dozen percent according to published papers and becomes higher in a longer follow-up. The highest probability of malfunction in 8 F single coil and the lowest in 7 F dual-coil leads is observed. For the needs of this guidelines all Riata/Riata ST leads were divided into: functioning, damaged but active (visible externalisation but electrically functioning), malfunctioning. In the last case the lead should be removed and a new one implanted (class of indication I) ,although only implantation of a new lead with abandoning malfunctioning one is allowed and should be considered (IIa). In patients with functioning lead extraction with a new lead implantation may be considered during elective replacement only in high risk patients (IIb). In case of damaged but active lead its extraction with the implantation of a new lead during elective replacement of the device should be considered in high risk population (IIa) and may be considered in other patients (IIb). The final decision related to Riata/Riata ST should be individualised and undertaken in co-operation with the patient after detailed assessment of the risk related to each treatment option.

Model Based Accelerated Ageing Study of Power Transformer Using UV Spectrophotometer

Power transformers are interface between different voltage levels of essential importance. Because of the long manufacturing processes, transformers are one of the most critical and expensive equipment and so this is one of the reasons why condition monitoring becomes more popular. Monitoring systems as basis for diagnostics open the possibility for expanding the operating time, reducing the risk of expensive failures and allows several maintenance strategies. With different monitoring techniques, detailed information about the transformer condition can be received and helps to minimize the probability of an unexpected outage. In this paper an accelerated study of an oil immersed high voltage coil is carried out using UV-Spectrometry technique under electrical stress i.e. voltage stress & loading beyond current carrying capacity of the model/ test cell under consideration. The results of the study indicate the possibility of assessing the condition of the transformer insulation using UV spectrophotometer

Prospective Evaluation of Defibrillation Threshold and Postshock Rhythm in Young ICD Recipients

Adaptation of implantable cardioverter defibrillator (ICD) systems to the needs of pediatric and congenital heart patients is problematic due to constraints of vascular and thoracic anatomy. An improved understanding of the defibrillation energy and postshock pacing requirements in such patients may help direct more tailored ICD therapy. We describe the first prospective evaluation of defibrillation threshold (DFT) and postshock rhythm in this population. We prospectively studied patients ≤ 60 kg at time of ICD intervention. DFTs were obtained using a binary search protocol with three VF inductions. Postshock pacing was programmed using a stepwise protocol, lowering the rate prior to each VF induction. Twenty patients were enrolled: 11 had channelopathy, five congenital heart disease, and four cardiomyopathy. The median age was 16 years, median weight 48 kg. Twelve patients had a transvenous high-voltage coil; eight had pericardial +/- subcutaneous coil(s). Median DFT was 7 J (range 3-31 J); 19/20 patients had DFT ≤ 15 J and all patients <25 kg had DFT ≤ 9 J (n = 6). There was no difference in DFT between patients with transvenous versus pericardial +/- subcutaneous coils (median 7 J vs 6 J, P = 0.59). No patient with normal atrioventricular conduction prior to defibrillation required postshock pacing (n = 16). There were no adverse events. These data suggest that many pediatric ICD patients have low DFTs and adequate postshock escape rhythm. This may help determine appropriate parameters for future design of pediatric-specific ICDs.

624 Potential Primary Prevention Implantable Cardioverter-Defibrillator (ICD) Patients Lack Understanding, Want More Information and Are Willing to Reconsider Implant Refusal

cohort had the lead functioning as part of an ICD system and 15 of these patients were using only their high voltage coils. Complication rates for lead extraction vary with the acuity of the procedure with a 2% complication rate for elective procedures (1/50), 10% complication rate for urgent procedures in the setting of lead failure (5/50) and a 28.6% complication rate for mandatory procedures (infected device, 2/7). While the 100 patients that had an elective or urgent lead extraction had a complication rate of 6%, all of these patients were alive, well and had optimally functioning ICD systems at 30 days. CONCLUSIONS: In an experienced surgical based laser lead extraction program, a proactive approach of lead removal has significant advantages. Elective removal carries very low complication rates and this makes early removal of the lead more attractive. At median 5 years post recall this aggressive strategy leaves only 1/3 of the patients with an active recalled lead while minimizing abandoned hardware and still providing excellent 30 day outcomes.

The Implantable Cardioverter-Defibrillator Minimalist

The implantable cardioverter-defibrillator (ICD) was devised to satisfy the unmet need for an effective, instantaneous therapy to prevent sudden cardiac death (SCD) due to ventricular fibrillation (VF) in at-risk, ambulatory patients. That therapy was a high-voltage electric shock delivered directly into the heart muscle. More than 3 decades later, shocks are still the defining operating characteristic of ICDs, and no other instantaneously effective therapy for VF exists. This elite status was clinched by large randomized clinical trials1,2 which demonstrated that ICDs improved mortality in patients with reduced left ventricular ejection fraction, regardless of pathogenesis or accompanying symptoms of heart failure (HF), by primary prevention of SCD due to ventricular tachyarrhythmia (VTA). Like bradycardia pacemakers for asystole, the ICD resides as a therapy genre of one, with no peer, and no competitor on the horizon. These sibling therapies for lethal heart rhythm disturbances will stand prominently among the greatest medical achievements of the 20th century. The ICD is a mature technology, and neither the technique nor the tools have changed much for several decades. Despite a certain evolutionary elegance of the operating system, the ICD is still a blunt instrument. Although it is true that some innovation has occurred, it is still a matter of a shock delivered by insulated metal conductors residing somewhere in direct proximity to the heart. No innovation beyond the fundamental of a timed shock for VF has proven to enhance mortality benefit. The basic design persists simply because no one can think of a suitable alternative and the self-satisfying aphorism that “shocks save lives.” Yet there is a growing intellectual dissatisfaction with the unintended consequences of this powerful, irreplaceable therapy. The stimulus for this self-inspection is an awareness of the very high morbidity risk overhead borne by the primary prevention patient, in particular, …

The Application of the Niching Genetic Algorithm to Optimum Design of the YKK Series Induction Motor

In order to get the YKK series motors to the ultimate purpose of achieving energy-efficient, and to meet the various request constraints set forth in the in the actual production, the paper introduces the niche genetic algorithm to the optimization of the motor design. For the forming structure of medium-sized high-voltage stator coils and the actual situation of three round relative fixed size, this article makes a corresponding improvements to the niche genetic algorithm, the proposed approach surmounts effectively the local convergence problem of standard genetic algorithm. The experimental results demonstrate that: compared with the initial program, the ultimate design results of the electrical motors meet the technical specifications of the proposed efficiency motor. Furthermore, the size of motor has been reduced, which saves the effective materials of the motor. It prove the feasibility and advantages of niche genetic algorithm’ improvement, and more important is, it verify the practical engineering value.

Optimal design of single-phase shell-type distribution transformers based on a multiple design method validated by measurements

This paper presents a method for the design of shell-type, single-phase distribution transformers to obtain the manufacturing specifications. The method is simple, efficient and accurate. By an exhaustive analysis, it is concluded that the obtained solution is the global optimum. The following constraints are imposed: excitation current, no-load losses, total losses, impedance and efficiency. The methodology of this paper requires only six input data: transformer rating, low voltage, high voltage, connection of low-voltage coil, connection of high-voltage coil, and frequency. These data are included in the transformer nameplate. In this paper, the minimization of the following four objective functions is considered: total owing cost, mass, total losses and material cost. The consideration of these four objective functions is implemented automatically by running the optimization algorithm four times without intervention of a designer. Consequently, transformer manufacturers save design man-hours and increase capacity. A design example on a 25 kVA transformer is presented for illustration. The optimized solutions of transformer design are validated with laboratory and process measurements.

Electrical AC Loss Measurements on a 2G YBCO Coil

Oak Ridge National Laboratory (ORNL) is collaborating with Waukesha Electric Systems (WES) to continue development of HTS power transformers. Second-generation (2G) YBCO coated conductors will be required for an economically-competitive design. In order to adequately size the refrigeration system for these transformers, the ac loss of these HTS coils must be characterized. Electrical ac loss measurements were conducted on a prototype high voltage (HV) coil with co-wound stainless steel at 60 Hz in a liquid nitrogen bath using a lock-in amplifier technique. The prototype HV coil consisted of 26 continuous (without splice) single pancake coils concentrically centered on a stainless steel former. For ac loss measurement purposes, voltage tap pairs were soldered across each set of two single pancake coils so that a total of 13 separate voltage measurements could be made across the entire length of the coil. AC loss measurements were taken as a function of ac excitation current. Results show that the loss is primarily concentrated at the ends of the coil where the operating fraction of critical current is the highest and show a distinct difference in current scaling of the losses between low current and high current regimes.

Understanding surface partial discharges in HV coils and the role of semi-conductive protection

An electrical insulating system in high voltage rotating machines is subjected to several stresses that cause changes of material properties during its lifetime. This phenomenon reduces progressively ability of the insulation to withstand the service stresses. Internal partial discharges can be located inside the high voltage insulation and usually they are dangerous for life-cycle duration. Surface discharges are generated at the solid/air interface in the gaps of machine stator slots or at the slot exits. Surface discharges can cause more intensive deterioration of the insulation, accelerate aging processes and definitively take aim toward premature failure of the machine. The application of conductive or semi-conductive protection layer provides certain protection for solid insulation from these discharges. Semi-conductive corona protection tapes are used on the coils at the slot exit region to electrical field control and prevent surface discharges. Laboratory measurements of the surface partial discharge quantities in specimens of high voltage coils with mica insulation were performed. The aim of the paper is to describe theoretically the development of surface discharges in rotating machines and to present surface partial discharge development in HV motors when semi-conductive layer protection is missing. The results can be found useful to understand better the surface discharge development and importance of high-quality semi-conductive protection technology.

Management Strategies When Implanted Cardioverter Defibrillator Leads Fail: Survey Findings

Defibrillator implanters have adopted different approaches to managing failures of multicomponent implanted cardioverter defibrillator (ICD) leads. Although recent publications identified single-component failures as common mechanisms of failure, there are no published data regarding how best to manage these failures. An internet-based survey was conducted to identify current management strategies. Questions were asked regarding isolated failure of a high-voltage coil or of a pace/sense electrode, in order to identify the frequency of various techniques to correct these failures. A worldwide query collected strategies from 376 physicians identifying themselves as ICD-implanting physicians. Replies came from 28 countries, with the USA accounting for 83.2%. The survey was completed by 85.6% of respondents. Implant experience was >10 years for 61.1%, 3-10 years for 29.1%, and <3 years for 10.4%. When the right ventricular coil failed, 52% abandoned and 48% explanted the failed lead. In superior vena cava coil failure, 61.2% chose to simply exclude this coil, using the other intact lead components. For pace/sense defects, 53.1% chose to implant a new pace/sense lead or switch sensing electrodes, using the intact lead components. Medical literature (76.1%), personal experience (67.6%), and professional guidelines (63.7%) were strong decision-making influences. (1) Management decisions for single-component failures of ICD leads are complex; (2) Significant differences in management strategy exist among physicians; (3) Medical literature and professional guidelines are strong influences for these decisions; (4) A lead failure registry could help identify reasons for such differences and help guide management.

Hydro Generator High Voltage Stator Windings: Part 2 - Design for Reduced Copper Losses and Elimination Of Harmonics

Hydro generator stator winding design is one of the key factors when considering machine upgrades and uprates. The hydro generators built 30-50 years ago employed stator insulation systems with lower voltage stresses and correspondingly larger insulation allowances. Modern insulation systems use thinner, more homogenous insulations, which permit higher voltage stresses, while providing much improved thermal conductivity and better heat dissipation. There is therefore quite a scope for the high voltage (HV) stator winding designer to increase overall coil copper content by between 20-40%, which often provides copper losses at increased output not much higher than the losses produced by the existing winding at pre-uprate machine rating. In conjunction with the new insulation improved thermal dissipation, it is possible to design uprated windings with temperature rises similar to the existing ones. The main focus of the HV coil design for hydro generator upgrades and uprates is therefore reduction of copper losses, and optimisation of thermal characteristics for best dissipation of heat losses. The loads connected to the hydro generator terminals (transformers, transmission lines, switchgear, etc.) are all designed to operate with pure sinusoidal EMF (Walker, 1981). The purity limits of the generators’ open circuit wave are prescribed by the standards (AEMC, 2008). Given the salient pole construction of hydro generator rotor with large variation of magnetic permeance in direct and quadrature axes, and the concentrated nature of rotor field pole windings, special measures are implemented on the geometry of rotor pole face. They include pole face shaping for sinusoidal approximation of rotor MMF, and adjustment of damper winding geometry relative to the slotted periphery of stator bore for reduction of the slot ripples (Walker, 1981). Given the relatively slow hydro generator operational speeds and necessarily large number of poles, the stator winding consists of large numbers of pole phase groups having only a few coils (typically 1 to 3). The stator winding MMF will therefore be rather coarse, and special measures must be implemented to achieve the output waveform as close to a pure sinusoid as possible. This second of four papers on hydro generator stator windings (refer to Znidarich, 2008a, Znidarich, 2009b, and Znidarich, 2009c) describes some tools at the hydro generator stator winding designer’s disposal for effective reduction of harmonics and optimisation of output waveform purity. They include skewing of stator core slots, fractional (short) pitching of stator winding coils and fractional slot windings.

Covering sleeves can shield the high-voltage coils from lead chatter in an integrated bipolar ICD lead

Integrated bipolar implantable cardioverter-defibrillator (ICD) leads use the distal high-voltage coil as both the ventricular sensing anode and the distal shocking electrode. Mechanical interactions between the distal ICD coil and other intracardiac leads have been reported to result in electrical oversensing and inappropriate ICD therapies. We sought to determine whether covering sleeves over the high-voltage coils of an integrated bipolar ICD lead could prevent sensed artefact from mechanical lead interactions. Endotak Reliance 0157 and Endotak Reliance-G 0185 leads, the latter with expanded polytetrafluoroethylene (ePTFE) sleeves covering the high-voltage coils, were connected to ICD generators and the leads were submerged in saline. Device programmers were used to communicate with the ICD generators, providing real-time electrogram recording throughout testing. A series of mechanical interactions were performed with the ICD leads, including sliding and striking each distal coil against metal and non-metal components of other ICD and pacemaker leads. All direct metal-metal interactions resulted in sensed electrical artefact, including interactions between the bare ICD coil and another bare ICD coil or metal pacemaker ring. Identical mechanical interactions where metal-metal contact was prevented due to an interposed ePTFE covering sleeve were electrically silent with no sensed artefact. A covering sleeve over the distal high-voltage coil of an integrated bipolar ICD lead can mechanically shield the lead from metal-metal interactions, which might otherwise result in sensed artefact and inappropriate ICD therapies or withholding of pacing output. This finding has implications for lead selection when a new ICD lead is to be implanted adjacent to abandoned intracardiac leads or lead fragments.