Winding Turns Research Articles

Electromagnetic Design of Dual Stator-Winding Induction Generator System with Boost Converter

In this paper, the electromagnetic design of dual stator-winding induction generator with boost converter to raise output voltage under the minimum speed is presented. When the output voltage of power winding is very low and the output current very high, the large winding turns ratio between the control winding and power winding is proposed to reduce the current of control winding. The excited capacitor of power winding and filter inductor of control winding can be canceled. With the boost converter adjusting the out put voltage under the minimum speed, the demand of output voltage of the generator can be achieved. Design results show it is much benefit for reducing the dimension ,cost and weight of the system.

Static voltage distribution between turns of secondary winding of air-core spiral strip transformer and its application

The static voltage distribution between winding turns has great impact on output characteristics and lifetime of the air-core spiral strip pulse transformer (ACSSPT). In this paper, winding inductance was calculated by electromagnetic theory, so that the static voltage distribution between turns of secondary winding of ACSSPT was analyzed conveniently. According to theoretical analysis, a voltage gradient because of the turn-to-turn capacitance was clearly noticeable across the ground turns. Simulation results of Pspice and CST EM Studio codes showed that the voltage distribution between turns of secondary winding had linear increments from the output turn to the ground turn. In experiment, the difference in increased voltage between the ground turns and the output turns of a 20-turns secondary winding is almost 50%, which is believed to be responsible for premature breakdown of the insulation, particularly between the ground turns. The experimental results demonstrated the theoretical analysis and simulation results, which had important value for stable and long lifetime ACSSPT design. A new ACSSPT with improved structure has been used successfully in intense electron beam accelerators steadily.

터빈 발전기 회전자 권선의 층간단락 분석

Turbine generator(13.8 ㎸, 137.5 ㎿) has high bearing vibration at rotation speed. Shorted turns in generator rotor windings have strong correlation with increased field current which is thus related to increase in bearing vibration. The recurrent surge oscillograph (RSO) test is performed on the rotor winding in turbine generator to detect shorted turns. The result of the RSO test indicates that shorted turns of rotor winding are generated in two locations. The RSO test was capable of identifying the presence, number, and location of shorted turns in generator rotor windings.

ZVS Resonant Converter With Parallel–Series Transformer Connection

A new series resonant converter with a parallel-series transformer connection is proposed in order to achieve zero voltage switching (ZVS) for all power switching, zero current switching (ZCS) for rectifier diodes at a full load, and less transformer secondary winding with a full-wave rectifier. For high-output-voltage applications, the primary windings of two transformers are connected in parallel in order to share the input current and reduce the root-mean-square rms current on the primary windings such that the copper losses on the transformers are reduced. The secondary windings of the two transformers are connected in series in order to ensure that the primary side currents are balanced and the secondary winding turns are also reduced. Thus, the sizes of the transformer core and bobbin are reduced. The full-wave diode rectifier is used on the output side. Thus, the voltage stress of the rectifier diode is equal to the output voltage rather than being two times the output voltage as that in a center-tapped rectifier topology. Based on the resonant behavior, all switches are turned on at the ZVS, and the rectifier diodes are turned off at the ZCS if the operating switching frequency is less than the series resonant frequency. The laboratory experiments with a 660-W prototype, verifying the effectiveness of the proposed converter, are described.

Characteristics of transformer-type superconducting fault current limiter depending on reclosing in changing the number of turns of secondary winding

The amount of consumed power is increasing with industrial development and rapidly increasing population. In accidents due to increased power consumption, the fault current sharply increases. Superconducting fault current limiters (SFCL) are studied widely to limit such fault currents. In this study, the characteristics of a transformer-type SFCL are analyzed depending on reclosing in changing the number of secondary winding turns. For experiment conditions, the turn ratio of the primary and secondary windings of a transformer-type SFCL was set to 4:2 and 4:4. The voltage was incremented by 80V from 120V for the experiment. The circuit breaker was operated with two open times of CO-0.17s –CO-0.17s –CO seconds (C; closed, O; open), respectively. Comparing the result for the experiment conditions with the case of the turn ratios of the primary and secondary windings at 4:4 and 4:2, the fault current was limited effectively in 4:2 than in 4:4 for the fault current limit ratios. With respect to the result of recovery characteristics, it was examined that the superconducting unit recovered faster when the turn ratio of the primary and secondary windings was 4:2 than 4:4. Comparing the amount of consumed power related to the recovery characteristics of the superconducting element, it was examined that the recovery time was faster in less power consumption for the superconducting unit. As such, since a transformer-type SFCL depending on reclosing in changing the number of turns of the secondary winding controls the turn ratio of the secondary winding to control fault current limiting and recovery characteristics, it can normally operate.

Magnetic Field and Critical Current of a BSCCO HTS Magnet at Various Aspect Ratios

When the length of wire used to make an HTS magnet is fixed, the magnetic properties of the HTS magnet including the central magnetic field and stored energy mostly depend on the aspect ratio of the HTS magnet. This paper presents calculations of the magnetic properties of a BSCCO HTS magnet at various aspect ratios. The HTS magnet was assumed to be made by pancake windings. The total length of the BSCCO wire was varied from 2 to 10 km. For a specific length of the BSCCO wire, the number of pancake windings was varied up to 70. The inner diameter of the HTS magnet was fixed to be 50 mm and 77 K. When the length of the BSCCO wire was 2 km, the central magnetic field was maximum when 34 pancake windings were used. The maximum central magnetic field and the current of the HTS magnet were 859.3 mT and 21.8 A, respectively. The number of turns of a single pancake winding and the aspect ratio of the HTS magnet were 171 turns and 2.54, respectively.

A Theoretical Study on the Transfer Impedance of a Plane Current Probe

This paper theoretically analyzes the transfer impedance of a plane current probe. The plane current probe is an effective device that is used to measure conducted current flowing on the surface of a metal structure. One of the hot topics for plane current probe is to obtain its transfer impedance. Most research concentrates on designing calibration devices and measuring the values of the transfer impedance. However, they all do not carry out theoretical study on transfer impedance. In this paper, the equivalent circuit of the signal detection system of the probe was established based on a transformer model. Furthermore, the expression of transfer impedance was derived from the equivalent circuit. The curve shape of transfer impedance obtained from this study has a good agreement with the measured ones. This fact validates the equivalent circuit and the theoretical formula. Subsequently, influence on the value of transfer impedance was analyzed based on the expression with change of some parameters, e.g., turns of coil winding, dimension of ferrite core, permeability of ferrite core, distributed capacitance. The result gained from the above analysis will provide guidance on the design and application of the plane current probe.

Analysis of the Mutual Inductance in Current Transformers Taking Primary Conductors Eccentricity Into Account

In this work a current transformer (CT) with toroidal core is analyzed from the viewpoint of the eccentricity of the primary circuit where one conductor goes through the core's window and the other is outside the core. The research is focused on the influence of the position of the primary circuit conductors on the evaluation of the mutual inductance between the primary circuit and the secondary winding—an influential factor on the CT's amplitude error. Purely analytical results and closed-form expressions for the mutual inductance are obtained when the core is made of a nonmagnetic material. A finite-element method is also utilized for the numerical computation of the mutual inductance, for nonmagnetic and ferromagnetic cores. Results are cross-validated using both methods. Results are presented and discussed taking into account the system geometry and the number of turns of the secondary winding. This novel contribution shows that the response of nonmagnetic-core current transformers can be significantly affected by the positional eccentricity of the primary circuit, especially when the secondary winding does not possess a large number of turns.

Slimformer—Self-Limiting Transformer Pre-Prototype and Pilot Plant Design, Construction, and Tests

The current limiting or self-limiting transformer, (CLT) is a multifunctional device, which combines the functions of a power transformer with the functions of a current limiter. The investigated SLIMFormer consists of a room temperature primary winding and a secondary high temperature superconductor (HTS) winding (BSCCO 2223) divided into two parts located on different limbs and up to 4 HTS ring (BSCCO 2212). The primary winding is connected to the electrical network, the secondary winding is intended to supply an HTS cable. As a result the SLIMFormer is an inductive terminal between the room temperature network and a projected HTS cable. For investigation of the SLIMFormer a 100 kVA rating experimental device (pilot plant) was designed, built and tested. The design and optimization aspects as well as the construction of the pilot plant will be presented. The present work is based on the previous 20 kVA SLIMFormer pre-prototype device which was tested at Lab of DEPE BME. The SLIMFormer was investigated experimentally for both sudden short circuit and steady-state (transformer) operational modes. The activation currents were determined for both operational modes with the rated secondary winding turn ratio. SLIMFormer work is being performed as part of an EC funded project, project name: acronym SLIMFormer.

Inductance Identification and Study of PM Motor With Winding Turn Short Circuit Fault

A time stepping FEM is performed for study of PM motor with inter-turn fault. The novel analytical expressions are proposed for calculation of faulty machine inductances from healthy machine parameters. The proposed expressions are validated by FEM and can be used in the circuit based fault models. Finally, the FEM is applied for studying the PM machine under various fault conditions.

커패시터 구동형 단상유도전동기의 권선설계에 대한 연구

This paper is concerned with winding design in capacitor-run single phase motor. Winding design in single phase induction motor is more complicated than that in three phase induction motor, because of using concentric winding in the single phase. Various winding designs are possible, and accordingly layout of the slot is calculated by formula. And then accurate design of winding is available. Using the design process in this paper, we can get the base model with slot layout and turns of windings of 1.12 ㎾ single phase induction motor, and it is verified by finite element analysis. In this paper, winding design and winding layout of single-phase induction motor using concentric winding are suggested.

Detection for Stator Winding Turn Fault by Using Fuzzy Neural Network

A fuzzy neural network based on-line turn fault detection approach for induction motors is proposed in this paper. B-spline membership fuzzy neural network is employed to detect turn fault and a genetic algorithm with an efficient search strategy is developed to optimize network parameters. Based on it, Experiments are carried out on a special rewound laboratory induction motor, the results show fuzzy neural network based diagnosis model determines the shorted turns exactly, and is more effective than the parameters estimation method under the condition of detecting a slowly developing turn fault.

Improved lumped parameter model for transformer fast transient simulations

To accurately simulate fast transient phenomena in transformer windings, a turn-to-turn-based multiple transmission line (MTL) model is regarded as the best approach because it is valid in a wide frequency range and capable to describe discontinuity of capacitive coupling among the turns of a non-uniform winding. However this MTL modelling approach also means that a series of large dimensional equations characterised by fully coupled admittance matrices need to be numerically dealt with, when simulating a winding typically having thousands of turns. In this study an improved lumped Resistor-Inductor-Capacitor (RLC) model is presented, which has lower computational complexity than but almost equal accuracy to the MTL model. Firstly, both the MTL and conventional lumped RLC model were compared and it was concluded that the conventional lumped RLC model is only valid in the frequency range below 2 MHz. Secondly, an improved lumped RLC model was derived in which a negative-value capacitive branch is added in parallel with the inductive branch to compensate the decrease of susceptance with the increase of frequency. Both numerical analysis and laboratory measurements were conducted on large power transformer windings, and it is confirmed that the valid frequency range of the improved lumped RLC model can be extended to about 4 MHz with no significant increase of computational cost.

The Calculation of an Air Gap Between Pancake Windings in a Superconducting Magnet by Using the Response Surface Method

The effects of a gap at a high temperature superconducting magnet which has an insert magnet and an outsert magnet are examined. Both magnets consist of pancake windings. The optimum gap of an insert magnet and an outsert magnet are calculated by using the response surface method. The insert magnet consists of 8 YBCO pancake windings. The number of turns of a pancake winding and the inner diameter of the insert magnet are 60 turns and 40 mm, respectively. The outsert magnet consists of 12 BSCCO-2223 pancake windings. The number of turns of a pancake winding and the inner diameter of the outsert magnet are 100 turns and 115 mm, respectively.

FE-Circuit Coupled Model of Electric Machines for Simulation and Evaluation of EMI Issues in Motor Drives

A new FE-circuit coupled model is proposed to simulate the electromagnetic field interference (EMI) caused by terminal overvoltage and ground current of electric machines connected to driving circuits. The high frequency effects due to the PWM drive were considered in the transient FE-circuit coupled model of the motor using a two-step procedure. First, the resistance in each individual winding turn of a coil is evaluated by time harmonic high frequency FE analysis considering skin and proximity effects. The capacitances of the coil were calculated by an electrostatic FE analysis to form a distributed parameter model of the coil in each conducting region. Second, a lumped parameter model for the coil was obtained through a matrix reduction technique. The lumped models of the different coils were connected in series to form a per phase winding model. The FE-circuit coupled model of the motor is tested in a motor drive to evaluate the terminal over voltages and ground currents. The numerical results were successfully verified by the corresponding laboratory test measurements. The proposed model can be used as a novel computational prototyping tool which would allow the development to design and final product stages to be completed without the need for repeated build and test procedures in an industrial environment.

A compact high-voltage pulse generator based on pulse transformer with closed magnetic core

A compact high-voltage nanosecond pulse generator, based on a pulse transformer with a closed magnetic core, is presented in this paper. The pulse generator consists of a miniaturized pulse transformer, a curled parallel strip pulse forming line (PFL), a spark gap, and a matched load. The innovative design is characterized by the compact structure of the transformer and the curled strip PFL. A new structure of transformer windings was designed to keep good insulation and decrease distributed capacitance between turns of windings. A three-copper-strip structure was adopted to avoid asymmetric coupling of the curled strip PFL. When the 31 microF primary capacitor is charged to 2 kV, the pulse transformer can charge the PFL to 165 kV, and the 3.5 ohm matched load can deliver a high-voltage pulse with a duration of 9 ns, amplitude of 84 kV, and rise time of 5.1 ns. When the load is changed to 50 ohms, the output peak voltage of the generator can be 165 kV, the full width at half maximum is 68 ns, and the rise time is 6.5 ns.

Study on Axial Flux Hysteresis Motors Considering Airgap Variation

Axial flux hysteresis motor (AFHM) is self-starting synchronous motor that uses the hysteresis characteristics of magnetic materials. It is known that the magnetic characteristics of hysteresis motor could be easily affected by air gap and structure dimensions variation. Air gap length plays an important role in flux distribution in hysteresis ring and influences the output torque, terminal current, efficiency and even optimal value of other structural parameters of AFHM. Regarding this issue, in this study effect of air gap variation on performance characteristics of an axial flux hysteresis motor and effect of air gap length on hysteresis ring thickness and stator winding turns is investigated. Effect of air gap length on electrical circuit model is perused. Finally, simulation of AFHM in order to extract the output values of motor and sensitivity analysis on air gap variation is done using 3D-Finite Element Model. Hysteresis loop in the shape of an inclined ellipse is adopted. This study can help designers in design approach of such motors.

Summer monsoon onset in the subtropical western North Pacific

Monsoon onset in July over the subtropical western North Pacific (SWNP, 15–25°N; 130–150°E) is investigated by focusing on the westward movement of cloudy region east of the SWNP, which is associated with high vorticity in the upper troposphere. At least in seven of the 22 years between 1985 and 2006, the arrival of clouds at the SWNP from the east coincides with a significant change in the upper tropospheric circulation and a rapid northeastward extension of strong convections from the tropical western North Pacific, which essentially is monsoon onset. Before the monsoon onset, the sea surface temperature (SST) increases, but winds remain divergent over the SWNP. Right after the monsoon onset, winds turn convergent and convections enhance, leading to a rapid decrease of surface heating and SST. It is suggested that westward‐moving upper‐level disturbances might trigger onset of monsoon in July when low‐level atmospheric conditions favor development of deep convections.

Leakage magnetic flux density in the vicinity of induction motor during operation

In this work, the low frequency electromagnetic flux density around induction motors is studied; the main objective is to provide safety regions for humans in the vicinity of these motors, especially in electrical vehicles, where high currents and hence high flux density emissions are expected. A new equivalent magnetic circuit which accounts for stray magnetic fields is developed. The analysis shows that the emission of the stray field in the radial directions depends on the permeability of the stator body as well as the ampere turn of the stator winding. Small values of stator body permeability may result in very high stray flux emissions at levels that may require shielding to protect passengers just above the motor. Relatively far away from the stator (e.g., 50 cm for the tested motors), the flux is normally of low level and may not represent an exposure threat.

Role of Air–Sea Interaction in the Long Persistence of El Niño–Induced North Indian Ocean Warming*

Abstract El Niño induces a basin-wide increase in tropical Indian Ocean (TIO) sea surface temperature (SST) with a lag of one season. The north IO (NIO), in particular, displays a peculiar double-peak warming with the second peak larger in magnitude and persisting well through the summer. Motivated by recent studies suggesting the importance of the TIO warming for the Northwest Pacific and East Asian summer monsoons, the present study investigates the mechanisms for the second peak of the NIO warming using observations and general circulation models. This analysis reveals that internal air–sea interaction within the TIO is key to sustaining the TIO warming through summer. During El Niño, anticyclonic wind curl anomalies force a downwelling Rossby wave in the south TIO through Walker circulation adjustments, causing a sustained SST warming in the tropical southwest IO (SWIO) where the mean thermocline is shallow. During the spring and early summer following El Niño, this SWIO warming sustains an antisymmetric pattern of atmospheric anomalies with northeasterly (northwesterly) wind anomalies north (south) of the equator. Over the NIO as the mean winds turn into southwesterly in May, the northeasterly anomalies force the second SST peak that persists through summer by reducing the wind speed and surface evaporation. Atmospheric general circulation model experiments show that the antisymmetric atmospheric pattern is a response to the TIO warming, suggestive of their mutual interaction. Thus, ocean dynamics and Rossby waves in particular are important for the warming not only locally in SWIO but also on the basin-scale north of the equator, a result with important implications for climate predictability and prediction.