Coil Parallel Research Articles

Study on the Performance of Distribution Grid System in Different Neutral Grounded Modes

In order to reduce grounded current and restrain arc-grounded over voltage during single-phase grounded faults in transmission line and realize fault-line selection, the neutral grounded mode with Peterson coil in parallel with big reactor is proposed in the paper. The simulation and comparative analysis of the performance of the 10 kV distribution grid systems in different neutral grounded modes have been done. The simulation results have shown that the neutral grounded mode via Peterson coil in parallel connection with big resistances can restrain the fault current effectively and it is the best mode.

MO-F-211-04: Fast Phase Contrast MR Angiography with Simplified Skipped Phase Encoding and Edge Deghosting with Array Coil Enhancement (S- SPEED-ACE)

Purpose: The aim of this work is to investigate the feasibility of accelerating phase contrast MR angiography by the fast imaging method of Simplified Skipped Phase Encoding and Edge Deghosting with Array Coil Enhancement (S‐SPEED‐ACE). Methods: The parallel imaging method of Skipped Phase Encoding and Edge Deghosting with Array Coil Enhancement (SPEED‐ACE) has been simplified with enhanced acceleration for imaging sparse objects and is termed S‐SPEED‐ACE. As demonstrated previously with a computer simulated study, S‐SPEED‐ACE partially samples k‐space with multiple coils in parallel and yields a deghosted image based on a least‐square‐error solution. Without differential filtering and full central k‐space sampling, S‐SPEED‐ACE uses more straightforward reconstruction and achieves further scan time reduction as compared with SPEED‐ACE. In this work, S‐SPEED‐ACE is further developed to accelerate real human 3D phase‐contrast MR angiography. The proposed method was tested with a 3D head PC‐MRA scan, which was acquired using a clinical 1.5T scanner on a healthy volunteer Results: Images are reconstructed by S‐SPEED‐ACE to achieve an undersampling factor of up to 8.3 with four receiver coils. The reconstructed images generally have comparable quality as that of the reference imagesreconstructed from full k‐space data. Maximum‐intensity‐projection (MIP) images generated from the reconstructed images also demonstrated to be consistent as those from the reference images. Conclusions: By taking advantage of signal sparsity naturally existing in the data, SPEED‐ACE was simplified and its efficiency was improved. In this work, the previously proposed parallel imaging method named S‐SPEED‐ACE has been further developed to accelerate a 3D head PC‐MRA scan.

Configuration optimization of magnetostrictive transducers for longitudinal guided wave inspection in seven-wire steel strands

The configuration of magnetostrictive transducers for both transmitter and receiver was optimized for the generation and reception of ultrasonic longitudinal guided waves in seven-wire steel strands in a pitch catch arrangement. Three axisymmetric permanent magnets significantly improved the capability of magnetostrictive transducers compared to two permanent magnets, and effectively increased the amplitude of the longitudinal guided wave mode, L(0, 1) at 160 kHz. Experimental results show that the maximum amplitude of a received guided wave signal could be obtained by using a receiver with a three-layer coil in parallel and a transmitter with a three-layer coil in series. The amplitudes of the defect-reflected signal increased by as much as 50% or more as compared with those when both transducers used a single layer coil. As a result, magnetostrictive transducers with an optimized configuration, including permanent magnet distribution and multilayer coil connection, could be efficiently used for the inspection of seven-wire steel strands by using ultrasonic guided waves in a pitch catch arrangement.

Single-shot dual frequency excitation for magnetic induction tomography (MIT) at frequencies above 1 MHz

In order to make MIT fast it is recommendable to excite several transmit coils in parallel and to acquire all receive channels simultaneously. The separation between the transmit channels can be achieved e.g. by slightly separating the excitation frequencies, so that it is possible to separate their contributions in the receivers by synchronous demodulation. One major problem is the low output impedance of the driver amplifiers so that each transmit coil acts as short circuited when seen from the other transceivers and hence perturbs the primary field. This causes a number of complications both in the reconstruction software as well as from the viewpoint of SNR optimization. Therefore we propose a special passive coupling network which transforms the low driver impedance into a high termination impedance for the coils at two frequencies (1 MHz and 10 MHz). We designed a dual-frequency transformation networks which operates at 1 and 10 MHz and which provides a termination impedance >5kΩ. The feeding current is typically 10mA per Volt driving voltage.

A Loosely Coupled Planar Wireless Power System for Multiple Receivers

Wireless power transfer is demonstrated mathematically and experimentally for M primary coils coupled to N secondary coils. Using multiple primary coils in parallel has advantages over a single primary coil. First, the reduced inductance of the transmitting coils makes the amplifier less sensitive to component variations. Second, with multiple receiving coils, the power delivery to an individual receiver is less sensitive to changes in the loads attached to other coils. By using a 16 cm by 18 cm primary and a 6 cm by 8 cm secondary coil, going from a 1:2 coupling to a 2:2 coupling, we show an increase in received power from 1.8 to 9.5 W, with only a small change in coupling efficiency. The advantages of the multiple primary coil topology increase the feasibility of charging multiple wireless portable devices simultaneously.

삼상 분리형 자속커플링 전류제한기의 2차 권선의 턴 수 및 결선 방향에 따른 전류제한 특성

The separated three-phase flux-coupling type superconducting fault current limiter(SFCL) is composed of a series transformer and superconducting unit of the YBCO coated conductor. The primary and secondary coils in the transformer were wound in series each other through an iron core and the YBCO coated conductor was connected with secondary coil in parallel. In this paper, we investigated the current limiting characteristics through winding number of coil 2 and winding direction in the flux-coupling type SFCL. Through the analysis, it was shown that additive polarity condition and lower winding number of coil 2 have advantaged from the point of view of fault current limiting and burned of YBCO coated conductor.

Cryogenic Characteristics of the ATLAS Barrel Toroid Superconducting Magnet

ATLAS, one of the experiments of the LHC accelerator under commissioning at CERN, is equipped with a large superconducting magnet the Barrel Toroid (BT) that has been tested at nominal current (20500 A). The BT is composed of eight race-track superconducting coils (each one weights about 45 tons) forming the biggest air core toroidal magnet ever built. By means of a large throughput centrifugal pump, a forced flow (about 10 liter/second at 4.5 K) provides the indirect cooling of the coils in parallel. The paper describes the results of the measurements carried out on the complete cryogenic system assembled in the ATLAS cavern situated 100 m below the ground level. The measurements include, among other ones, the static heat loads, i.e., with no or constant current in the magnet, and the dynamic ones, since additional heat losses are produced, during the current ramp-up or slow dump, by eddy currents induced on the coil casing.

The Characteristic Analysis Between Flux-Coupling and Flux-Lock Type SFCL According to Variations of Turn Ratios

We have proposed a flux-coupling type superconducting fault current limiter (SFCL) using coils and analyzed its operating characteristics. The SFCL consisted of the primary and secondary coils, which were wound in series each other through an iron core. The superconducting unit, which was based on YBCO thin film, was connected with secondary coil in parallel. Meanwhile, the primary coil and secondary coil with serially connected superconducting unit were connected in parallel in a flux-lock type SFCL, which didn't permit the same inductances between the primary and secondary coils. The short-circuit currents were effectively limited by adjusting the numbers of winding turns of each secondary coil and the winding directions of the coils without a certain limitation in a flux-coupling type SFCL. The flux generated from a coil in normal operation is cancelled out by the direction of windings in the SFCL and the zero resistance behavior of the superconducting unit. In order to compare the influence by turn numbers between coils, the turn number of the secondary coil was varied from 21 to 84 while the turn number of the primary coil was 42 and 63. We confirmed that the flux-coupling type SFCL was significantly efficient in reducing the initial line current after fault initiation. The voltage generated in the superconducting unit was also lowered by reducing power burden of the YBCO thin film in the flux-coupling type SFCL. We considered that this was caused by mutual linkage of the flux between two coils. The current limiting behavior of the flux-coupling type SFCL was more effective for fault current limiting operation.

Synthetic signal injection using inductive coupling

Conversion of MR signals into units of metabolite concentration requires a very high level of diligence to account for the numerous parameters and transformations that affect the proportionality between the quantity of excited nuclei in the acquisition volume and the integrated area of the corresponding peak in the spectrum. We describe a method that eases this burden with respect to the transformations that occur during and following data acquisition. The conceptual approach is similar to the ERETIC method, which uses a pre-calibrated, artificial reference signal as a calibration factor to accomplish the conversion. The distinguishing feature of our method is that the artificial signal is introduced strictly via induction, rather than radiation. We tested a prototype probe that includes a second RF coil rigidly positioned close to the receive coil so that there was constant mutual inductance between them. The artificial signal was transmitted through the second RF coil and acquired by the receive coil in parallel with the real signal. Our results demonstrate that the calibration factor is immune to changes in sample resistance. This is a key advantage because it removes the cumbersome requirement that coil loading conditions be the same for the calibration sample as for experimental samples. The method should be adaptable to human studies and could allow more practical and accurate quantification of metabolite content.

Self-tuning mechanisms of nonlinear split-ring resonators

We study both theoretically and experimentally the dynamic tunability of the magnetic resonance of a single nonlinear split-ring resonator with varactor diode at microwave frequencies. We demonstrate different tuning regimes with and without an inductive coil in parallel with the varactor. We show that the coil changes the sign of the nonlinearity and eliminates the memory effect caused by charge accumulation across the varactor. In addition, at higher powers the nonlinear response of the split-ring resonator becomes multivalued, paving a way for creating bistable tunable metamaterials.

Quench Development in Bi-2212 Bulk Coils During Quenches

We investigated the quench development in resistive superconducting fault current limiters (SFCLs) based on Bi2Sr2CaCu2O8 (Bi-2212) bulk coils. In order to protect them from hot spot formation, the bulk coils were either attached with a metal shunt layer or connected with a shunt coil in parallel. The bulk coils also had a plastic support for enhanced mechanical strength and insulation. The SFCLs were subjected to simulated AC fault currents for quench measurements. They were immersed in liquid nitrogen during the experiment for effective cooling. The resistance of the Bi-2212 bulk coil stayed low for a few milliseconds, until it increased rapidly. The increase was more rapid in the SFCL with a shunt coil than with a shunt layer. Once the quench was completed, the resistance increased at slower rates. The average temperature of the bulk coil reached about 230 K at 3 cycles after quench start at application voltage of 2.4 Vrms/cm with a shunt coil, and at 0.4 Vrms/cm with a shunt layer. The resistance development in Bi-2212 bulk coils could be quantitatively explained with the concept of transfer of heat generated during quenches to the liquid nitrogen as well as within the Bi-2212 bulk. The fault period was divided into three regions: flux-flow region, region prior-to quench completion, and region after quench completion. Resistance was calculated separately for each region and compared with data. The results agreed well with data.

Improvement on Defect Detection Performance of PCB Inspection Based on ECT Technique With Multi-SV-GMR Sensor

This paper describes the improvement on the defect detection performance of printed circuit board (PCB) inspection based on the eddy-current testing (ECT) technique with the multispin-valve giant magnetoresistance (SV-GMR) sensor. To obtain the ECT signal in the same scanning line, SV-GMR sensors are mounted on the exciting coil in the same column parallel with the scanning direction. Harmonic analysis based on the Fourier transform is used to analyze the signal from the SV-GMR sensor in order to increase scanning speed. Then signal averaging is applied to the ECT signal in order to improve the signal-to-noise ratio. Experimental results are performed to verify the inspection performance

Effect of Paralleling the Stator Coils in a Permanent-Magnet Machine

As low-voltage machines require smaller number of turns per phase compared to higher voltage machines, it is normal to connect the various stator phase coils in parallel to form the phase winding. The placement of various coil sides in the slot and the difference in the field produced by different poles of the rotor magnet can influence the induced voltage in various coils and the impedance of the coils. The difference in the induced voltages in the various parallel paths results in a circulating current in the winding and will cause increased losses in the machine. The unequal induced voltage and impedance will cause unequal distribution of stator current in the various parallel paths and will impact the torque-ripple contents. This paper will discuss the effects of these unbalanced parallel paths on the machine performance

Highly accelerated MRI by skipped phase encoding and edge deghosting with array coil enhancement (SPEED‐ACE)

The fast MRI method of skipped phase encoding and edge deghosting (SPEED) is further developed with array coil enhancement, and thus is termed SPEED-ACE. In SPEED-ACE, k space is sparsely sampled with skipped phase encoding at every Nth step using a set of receiver coils simultaneously, similar to SENSE, leading to sensitivity-weighted images with up to N layers of overlapping aliasing ghosts. The ghosted images are edge enhanced by a differential filter to yield ghosted edge maps, in which the ghost overlapping layers are greatly reduced since the sparseness of edges reduces the chance of ghost overlapping. Typical ghosted edge maps can be adequately modeled with a double-layer structure. By using data from at least three coils through least-square-error minimization, a deghosted edge map is obtained and inverse-filtered into a final deghosted image. In this way, SPEED-ACE partially samples k space with a skip size of N by using multiple receiver coils in parallel, and obtains a fairly good deghosted image with an undersampling factor of N. SPEED-ACE is not limited to the double-layer ghost model, but can be generalized to include more layers of ghosts for more flexible and improved performance. As a new parallel imaging method, SPEED-ACE was tested using in vivo data to demonstrate the possibility of achieving undersampling factors even greater than the number of receiver coils, which is so far not achievable by other parallel imaging methods.

Double-Exponential LR Circuit

Simple LR and RC circuits are familiar to generations of physics students as examples of single-exponential growth and decay in the relevant voltages, currents, and charges. An element of novelty can be introduced by connecting two (instead of one) LR coils in parallel with a battery. The resulting circuit can still be treated using little more than the basic tools (Kirchhoff's rules plus a trial exponential solution) employed in the standard LR analysis. But the solution is now a double exponential, as can be verified by constructing such a circuit.

Ghost artifact removal using a parallel imaging approach

Parallel imaging techniques, which use several receive coils simultaneously, have been shown to enable a significant scan time reduction by subsampling k-space. Nevertheless, the data acquired with multiple coils in parallel exhibit some redundancy if the number of receive coils exceeds the subsampling factor. This redundancy leads to an overdetermination of the reconstruction problem, which is generally used to optimize the signal-to-noise ratio (SNR). However, it can yield further information about the quality of the reconstructed image, and can thus be used to identify and correct image artifacts. While some known approaches try to solve this problem in k-space, this study addresses it in the spatial domain and uses a modified SENSE reconstruction to reduce or completely remove ghost-type artifacts arising from processes such as motion or flow during data acquisition. Phantom and in vivo studies show significant improvements in image quality after correction, and serve as a basis for the discussion of the performance and limitations of this new approach.

Predicting the effects of inhomogeneities in resistive superconducting fault current limiters

This paper describes a fully functional computer model which we have created based on E– J data which includes provision for the effects of substrate heating, film boiling etc. In this model the superconductor is modelled as a grid of squares each of which can have its properties set independently, thus the effects of inhomogeneities, weak links cracks etc. can be included. In addition the model allows the effects of magnetic field (either fixed field or coil in series or parallel) to be considered. The model is written in Delphi and employs an extensive GUI which includes both graphical and pictorial representations of the output. This paper describes both the model itself and includes case studies which we have prepared using the model.

Sensitive high-T/sub c/ SQUID magnetometers for unshielded operation

We have developed sensitive highly reliable high-T/sub c/ SQUID magnetometers a reproducible SNS junction fabrication process. In order to enable unshielded operation in the earth's field, we have incorporated flux dams into direct-coupled SQUID magnetometers. By using up to four pickup coils in parallel, each with its own flux dam, an effective area of 0.57 mm/sup 2/ has been achieved on 24 mm/spl times/24 mm substrates using 100 /spl mu/m wide pickup coils. We have demonstrated a magnetic field noise sensitivity of 80 fT//spl radic/Hz 10 Hz and 77 K in an externally applied field 60 /spl mu/T. This magnetic field sensitivity unchanged from the zero-field measurement.

A new principle for fast DC-sensitive potential-independent current comparators

A new principle of operation makes feasible small, cheap potential-independent current comparators whose performance reaches or exceeds the best properties of bulky magnetic amplifiers of the second-harmonic type. Connection of a ferrite-core coil in parallel with a suitable negative resistance generates relaxation oscillations g(t) . Inherently, at large oscillations the coil ( i,\phi )- characteristic is perfectly symmetric about the origin: \phi(-i) = -\phi(i) . Provided that the negative-resistance ( i,u )- characteristic has the same symmetry: i(-u) = -i(u) , the oscillations g(t) are perfectly symmetrical in the sense that g(t+T/2) = -g(t) . Here g represents either the coil flux φ, the current i or the voltage u . The time is t and T the oscillation period. External magnetomotive force shifts the coil ( i,\phi )-characteristics, invalidating (1) and therefore (3). Consequently, the deviation from 50% duty-ratio of the oscillating q(t) is a sensitive and extremely stable measure of this MMF. Neither core temperature, pressure nor magnetic creep cause any zero drift. Orders of magnitude reached experimentally are: Short-time zero instability and noise: \leq 10^{-5} ampere-turn, time resolution: \leq 10^{-4} s, zero drift from -70 to +100°C: ampere-turn.

Induction‐Tuned Method to DetermineCasing Lengths in Hydrogeclogic Investigations

AbstractAn induction‐tuned device was designed and tested under a variety of well casing conditions. It can detect casing lengths to within 0.4 to 2.0 inches for casing ranging from 2 to 14 or more inches in diameter which are made of either magnetic or nonmagnetic metals. A casing separation as small as one inch is detectable for 12‐inch diameter casing and a four inch or more separation is detectable for 4‐inch I.D. casing. These values indicate the range in sensitivity expectable when determining casing separations.Dial readings in microamps are indicated as the ptobe is raised or lowered within a well bore. Readings vary depending whether the probe is centrally located or located to one side. The maximum and minimum dial reading is established for a given casing diameter at the start of a survey. A consistent change in dial reading from previous valves indicate a casing diameter change.The sensing element is a coil whose inductance is changed by varying its proximity to any metallic conductor. A coil and capacitor in parallel make a tuned circuit resonant at 3 K.C. The device includes a transistor in a phase shift oscillator, and a second transistor which acts as a current amplifier, a 0–100 μa d. c. meter driven through a bridge rectifier, capacitors, and other elements. Twelve to 14 volts at 4 to 6 milliamperes or less than 0.1 watt is sufficient to power the device.A maximum meter reading is obtained by adjusting an oscillator to the resonant frequency of the probe. Lowering the probe into a well casing detunes the probe, changing its impedance and the meter reading.All electrical elements are standard except the probe and all materials can be purchased for about $40.00 exclusive of the reel and cable assembly.