Flux paths and flux transfer mechanism in the T joints of three phase transformer cores

A better understanding of flux behavior within specific regions of a transformer core can lead to improved core design and magnetic efficiency. Flux paths and the flux transfer mechanisms have been determined for two practical T joints of different designs employed in two similar three-phase three limbed transformer cores. Each core was energized at three different core flux densities. The instantaneous flux density patterns both parallel to and perpendicular to the rolling plane of the laminations are presented in graphical and vectorial forms for both types of T joints. By "freezing" the continually changing flux pattern within a T joint, it was possible to trace individual flux paths through the joint and to determine the basic flux transfer mechanism between adjacent laminations. Flux behavior within the joints shows that while its path is dependent on both T joint design and core flux density, the basic flux transfer mechanism remains unchanged in both T joints and at all core flux densities.     

Cavity-enhanced parametric down-conversion as a source of correlated photons

Abstract

The most common way of generating correlated photons is by parametric down-conversion in a nonlinear crystal in free space. However, a drawback of this technique is the extremely low photon flux available. We present a simple analysis which shows that cavity-enhanced parametric downconversion, using an arrangement similar to an optical parametric oscillator and operated well below threshold, can yield a substantially higher photon flux without significantly degrading the correlation between photons.     

Some regulated power supply apparatus using the Morgan circuit

The SCR chopper circuit has a very wide range of application in regulating a dc power, and its merits are universally appreciated. Because of its merits, the circuit is most suitable for a nonfailure power source that supplies power from a set of rectifier-batteries to a communication equipment or any other electronic equipment, which requires a dc power source of several output voltages. For such purposes, the output voltage of the circuit should be smooth, accurately regulated, and should respond quickly; at the same time, the efficiency must be high and reliability excellent. This paper offers, firstly, some improvements on the Morgan circuit in order to make it peculiarly suitable for different kinds of practical applications; namely, the smoothing filter is made as small as possible to make the response of the circuit rapid, while the efficiency is kept high. Secondly, data, obtained through the analysis of the operation in the case of the small filter, are presented. Thirdly, the paper shows, as the result of such analysis, that if a saturable current transformer (SCT) is designed properly, the circuit will behave as a self-regulating constant voltage power source. Lastly, it proposes a practical application which has a suitable protecting circuit composed of some simple circuit elements providing against the failure of commutation which causes a severe overvoltage and overcurrent to the load.     

Design and identification of an equivalent circuit for an LCT component: inventory and representation of losses

A new kind of passive component, the LCT [integrated inductor (L), capacitor (C), and transformer (T)] is becoming very fashionable in the switch mode power supply area. Starting from our knowledge in transformer characterization, we recently elaborated an equivalent circuit for this component. This equivalent circuit is fully deducible from impedance measurements. No dismounting of the component is needed, and no information about its internal design is required. This paper aims mainly to present the new equivalent circuit and the method leading to its identification using a commercial impedance analyzer. The LCT intended to a 300-W power supply working at 200 kHz has been built and characterized between 100 Hz and 40 MHz. Analyzing the frequency dependence of the real part of serial and parallel impedances, several kind of losses rarely taken into account have been identified. Among these losses are those related to the capacitor insulator and those due to the dielectric constant of Mn-Zn ferrite core. Equivalent circuits are supplied to represent every type of loss, and their accuracy is checked.     

Process-induced oscillator frequency pulling and phase noise within plasma systems

Passive radio spectroscopy is employed to examine plasma process instabilities generated by the interaction between the power source oscillator and the plasma load. A fixed frequency of 13.56 MHz and a 170-180 kHz Flyback transformer are considered. The carrier frequencies are interrogated using a resolution bandwidth that constitutes ∼1/7000-1/580 of the target oscillator frequencies with a sweep time of less than 0.06 s across the phase noise disturbance. Within these spectrum analyzer measurement parameters, oscillator phase noise (1/f^n=1-3, discrete spurs and raised noise floor) is shown to be linked to plasma load mismatch and periodic instabilities. In the case of the Flyback circuit, it is found that the oscillator frequency pulling and modulation are linked to the plasma reactance. These results indicate that oscillator phase noise can be used as a non-invasive plasma process metrology tool.     

Highly sensitive ultraviolet detector using a ZnO/Si layered SAW oscillator

This study elucidates a highly sensitive ultraviolet light detector using the combination of an oscillator circuit with a high-frequency amplifier, a matching network and a layered surface acoustic wave (SAW) device. In this structure, a ZnO thin film is simultaneously used as an active layer for UV detection and a piezoelectric layer for exciting a high-order surface acoustic wave. The microstructure and crystallization of ZnO films were investigated using the scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SAW oscillator shows a good performance with output power of − 1.14 dBm and phase noise of −94.7 dBc at 100 kHz. Firstly, the frequency shifts of the oscillator exhibit rapid increase with the intensity of the UV light. Then the increased shifts decayed at certain UV intensity due to the saturated photogenerated carriers. An extreme frequency shift of 1017 kHz was obtained as the UV intensity reached 551 μW/cm². The maximum sensitivity of 8.12 ppm/(μW/cm²) can be obtained in this detector.     

SQUID operation with ferromagnetic core superconducting dc transformers

We successfully used ferromagnetic core (Cryoperm 10) superconducting transformers to enhance the transfer of external magnetic flux to a symmetric two-holes rf biased quantum interference device (SQUID). The flux transfer ratio has been enhanced up to a factor of ten in comparison with air core superconducting transformers. It has been observed that the presence of ferromagnetic cores in the holes of the SQUID does not introduce additional noise, while it introduces a reduction in the Q of the 19 MHz tank circuit.The experimental results are discussed in the framework of a detailed analysis of the behaviour of the complete SQUID plus tank circuit plus ferromagnetic core superconducting transformer circuit.     

Circuit co-simulation and measurement techniques applied to voltage-controlled oscillator design

A voltage-controlled oscillator (VCO) was designed for operation in C-band for use in a microwave pointto- point radio system. Microstrip technology was chosen for resonator implementation since it offers ease of manufacturing and frequency adjustment. The design was performed using an electromagnetic harmonic balance co-design technique in conjunction with linear analysis in order to achieve first pass success. Emphasis in this work is the ability to use multiple design approaches and test techniques while validating in advance with co-simulation. The measured frequency against tune voltage data shows excellent agreement with simulation. Maximum deviation of 2% between the two was observed. The VCO tuned from 4.3 to 5.4 GHz as the tuning voltage was varied from 0 to 9 V representing a tuning bandwidth in excess of 20%. Power dissipation is 150 mW. Phase noise over the tune range was better than 2108 dBc/Hz at 100 kHz offset. The oscillator design efficiency, applicable to wider tune range designs, is greater than 2%. The hybrid oscillator figure-of-merit functions evaluated in this work exceeded comparable silicon-integrated implementations.     

Electromagnetic flat-faced robot gripper for handling multipleindustrial transformer core lamination plates

In the industrial transformer core assembly process, significant productivity gains can be achieved by utilizing a robotic gripper that is able to handle, and accurately position, multiple transformer laminations during each pick-and-place cycle. This paper reports on the development of a novel electromagnetic lifter for such applications. The lifter has the unique capability to selectively pick a given number of laminations at a time (the usual requirement is three) from a stack. By considering an analytical model of the magnetic circuit of the electromagnet-lamination stack combination, closed form solutions are obtained for the flux flow pattern and the lifting force on each lamination in the stack which closely agrees with the numerical results obtained using two-dimensional finite element analysis software. Results of experiments conducted on a prototype electromagnet are also presented that validate the analytical model findings     

An accurate AC demagnetizing method using a linear inductance for high permeability cores

A new simple and accurate ac demagnetizing method for high permeability cores is presented. In this method, a linear inductance is connected in parallel with the winding of the core to stabilize the level ofBHminor loops at zero flux level during the whole process of ac demagnetization. The ac demagnetization error is suppressed to less than 0.5% even in 50% Ni-Fe cores. The optimal ac demagnetizing time is longer than 0.5 sec., and the optimal ac demagnetizing waveform of current source is sinusoidal. Experimentally, high demagnetizing accuracy was obtained over a frequency range of 10 Hz-2 kHz. Two cores with the same dimensions and materials are simultaneously ac demagnetized by means of a linear inductance connected in parallel with the primary windings of two cores connected series-aiding, whose secondary windings are connected parallel-opposing and short circuited; thus, the remanent flux level after ac demagnetization is nondestructively detected by destructive readout in other core. This ac demagnetizing method is useful for measuring some magnetic properties such as initial permeability and BH curves and for resetting the small-signal transformer cores and second-harmonic analog memory elements.     

A highly accurate, hand-held clamp-on current transformer

The design, operation, and performance of a 1000:5 A highly accurate, hand-held, clamp-on-type current transformer are presented. This precision current transformer uses a sensitive magnetic circuit to detect transformer ampere-turn unbalance between the primary and secondary circuits. The unbalance represents an error in the ratio and phase angle of the transformer. The largest of the errors is due to the core magnetization current and magnetic reluctance caused by the cutting of the core material. After sensing the errors, electronic feedback through a magnetic circuit is used to provide an error-correcting current. This reduces the overall errors dramatically. These types of devices are referred to as “active” current transformers because of the use of electronic amplifier and feedback circuits. The device described has a novel feature of an openable, split core. This “clamp-on” capability enables use of the transformer on a bus or cable without the complications or need to open the current-carrying circuit to be measured. Commonly used “clamp-on”-type current transformers generally have uncertainties from about 1 to 5% at full-scale rated current. This paper describes a commercialization of active current transformers having a ratio uncertainty of less than ±0.05% over a current range from full-scale rated to 1% of full-scale. Additionally, this product has a small phase angle which is an important consideration when measuring electric power, energy, and power factor. It is intended to be used by electric utilities, standards laboratories, testing laboratories, and in applications where high measurement accuracy and the split-core, clamp-on feature are attractive considerations     

A parametric quartz crystal oscillator

Parametric oscillators have been well studied but currently are not used often. Nevertheless, they could be a low-phase noise solution, at least outside the frequency bandwidth of the resonant circuit. The theoretical aspect of parametric oscillations is briefly reviewed in this paper. Indeed, the basic theory of a simple resistance-inductor-capacitor (RLC) circuit working in parametric conditions easily can be extended toward a resonant loop that includes a quartz crystal resonator. Then, as an application, this study is transposed to a quartz crystal oscillator that has been modeled and tested as a first prototype. Simulation results are compared with those actually obtained.     

Equivalent circuit for high-voltage partial-core resonant transformers

An equivalent circuit model for the partial-core resonant transformer is presented. A model which omits core losses is first introduced and is verified on a sample air-core resonant transformer. Partial-cores are then introduced into the transformer and the resonant characteristics are re-measured. The model is modified to account for the core losses and then verified against the measured data. Comparisons and transformations between the model and the Steinmetz 'exact' transformer equivalent circuit are given. A procedure for measuring the equivalent circuit inductances is described and then used to investigate the inductance variation with core displacement characteristics of the sample transformer in both axial-offset and centre-gap arrangements. In a capacitive load test the sample transformer was linear to a significantly higher voltage when using the centre-gap arrangement.     

Flux distribution and power loss in the mitered overlap joint in power transformer cores

The design of the joints in a power transformer core has a marked influence on the efficiency of the core as a whole. Two experimental cores have been built such that the lengths of their 45° mitered overlaps could be varied from 0 to 2.0 cm. The larger core, with 1.0 m limbs, was used for investigating flux and loss variations and the second, smaller core was used to study how the results might be affected by changes in dimensions. For the larger core, the power loss was measured in two ways for a range of overlaps: first, using the localized power loss technique, and then by measuring the total power loss with a precision wattmeter. In both cases, a minimum power loss was found when the core was built with an overlap of 0.5 cm. The overlap length was varied in the smaller core and again a minimum power loss was found, but with a 1.0 cm overlap. A change in loss of over 20% was found for the range of overlap lengths used, and the optimum overlap length was independent of flux density over the range from 1.0 T to 1.8 T. The special flux distribution was determined from an array of search coils. The variations in flux distribution enables a qualitative explanation of the occurrence of the minimum in power loss.     

Design of Relaxation Oscillator Based Ultra-wideband SFQ Amplifier for Chip to Chip Interconnection

In Rapid Signal Flux Quantum (RSFQ) logic circuits, on-chip interconnects and multichip module implementations for nearby distances have already been established. However, the flexible interconnection of two distant chips is still not achieved reliably due to impedance mismatching and attenuation. In this work, we propose a circuit that allows the usage of Passive Transmission Lines (PTLs) to transfer single-flux-quantum (SFQ) pulses between two distant chips which are separated by a distance greater than 10 cm by using 50 ?? transmission lines. For this purpose, we design an SFQ amplifier circuit to deal with impedance mismatch and attenuation problems. The circuit consists of two main parts: a relaxation oscillator (RO) circuit and an impedance transformer. The RO circuit utilizes relaxation oscillations occur in the underdamped Josephson junctions. The impedance matching circuit is an 8-section Chebyshev quarter-wave transformer and it eliminates impedance mismatching problem between the amplifier circuit and PTL. We performed circuit simulations and obtained voltage amplitude of about 600 ??V at the output of the circuit. The transformer has a broadband impedance matching with a fractional bandwidth (ratio of the bandwidth of a device to its central frequency) of 1.4 and a maximum Voltage Standing Wave Ratio (VSWR, the maximum voltage divided by minimum voltage on the transmission line) of 1.5.     

Oscillator Circuit for a Vibrating Capacitor Driven by an RF Electric Field

The vibrating capacitor to be discussed consists of a metalized membrane, clamped at its edges, between two electrodes. The membrane is driven by an RF electric field (309 kHz), which is amplitude modulated at the natural frequency (6 kHz) of the membrane. This RF field is caused by a voltage applied to one of the electrodes, which, together with the membrane, forms the driving capacitor. The other electrode, and the membrane, constitute the vibrating capacitor. A special RF oscillator has been designed, of which an essential part is the driving capacitor. This capacitor causes the RF voltage to be amplitude modulated at the natural frequency of the membrane. The oscillation conditions of this electromechanical system are derived from the equation of motion of the membrane and the electrical properties of the driving circuit. An oscillator circuit with optimum performance is designed with the aid of a computer. Finally, the computed results are verified by measurements.     

Magnetic hysteresis model

A dynamical model is described which permits calculation of the excitation currentIas a function of time in a laminated grain-oriented (G-O) steel transformer core. The independent variable is the magnetic flux density or, equivalently, the coil voltage less theIRdrop associated with the resistanceRof the windings. Recent observations on flux reversal mechanisms in GO steel indicate that, in the range of magnetic field intensities typically present in transformer cores, the important reversal processes are the motion of long 180° domain walls continuous across grain boundaries and the motion of 90° walls within individual grains. These processes are represented in the model by two subcircuits connected in series. Each subcircuit consists of an inductive element in parallel with a linear resistor which accounts for the eddy current losses accompanying the flux change. The properties of each inductive element (flux vs. current) reflect the two wall motion mechanisms, respectively, in the limit of zero frequency. This model is capable of faithfully simulating minor loop behavior as well as the response to complex waveforms; e.g., the superposition of two or more frequencies. The circuit equations are solved, and some results of computer calculations using a program that implements this model are presented.     

基于可编程片上系统的宽频带超声波电源系统设计

针对当前超声波处理装置的频率单一、专机专用等问题,提出了一种基于可编程片上系统(System-On-aProgrammable-Chip,SOPC)的新型宽频带超声波电源系统。该系统基于现场可编程门阵列(Field-Programmable Gate Array,FPGA)可编程逻辑及数学运算等方面的优势,移植了NIOS II软核作为主控制器,移相脉宽调制(Phase-Shifted Pulse-Width-Modulation,PS-PWM)用于调频调功,正交相关电路检测输出电压与电流间的相位差。实验结果表明,该方案能在指定带宽范围内(20~40 k Hz)使超声波振子工作状态趋近于谐振状态。     

The geometry of regulating transformers

Ferroresonant, ballast, and current-limiting transformers are similar in geometxy. Optimization of weight, losses, or cost can result in different choices for the shape (core or shell) and proportions of the lamination. In the ferroresonant transformer, the problem of saturation losses, noise and stray flux can be alleviated by altering the geometry to produce a magnetic circuit with nonuniform flux density.     

Flux-locked current source reference

The quantization of flux in a closed superconducting circuit is used to provide a stable reference current. A 10-mA current source is coupled through a toroidal transformer to a DC superconducting quantum interference device (SQUID) input, and the resulting signal is fed back as an error current. The result is a net flux linkage that exhibits short-term stability of 1 part in 10⁹/h. The net current is quantized with a step size of 59.4 nA, and it will exhibit the same stability as the flux provided the mutual inductance of the transformer remains constant. This current is passed through a precise 100-Ω resistor and compared against Zener diode references. The observed temperature coefficient for the flux transformer is 28.5±3 ppm/K at 4.2 K. Possible sources for the temperature dependence are discussed