Single Transformer Research Articles

Blocking Device Placement for Mitigating the Effects of Geomagnetically Induced Currents

Geomagnetically induced currents (GICs) can cause half cycle saturation of transformers and consequently affect the power grid with harmonics and reactive power losses. To effectively mitigate the negative GIC impacts in large-scale power systems, the present paper considers the problem of placing blocking devices in transformer neutrals. The placement problem of multiple blocking devices is first considered by analytically quantifying the associated reactive power losses. A linear sensitivity analysis is further provided for the case of blocking a single transformer, and it has been observed that the effects of blocking transformer neutral currents to be mostly local. This motivates us to propose the scheme that selects multiple substations to block all high voltage level transformers therein, based on a linearized approximation model. The effectiveness of such scheme has been demonstrated using both a 20-bus GIC test case and a realistically sized larger power system.

Materials and Cutting Method Effects of Three Phase Transformer-Core on Magnetization Curve and Inrush Current: Simulation Approach

This paper dealt with simulation approach of the effect of type of material and cutting method of three phases transformer core on magnetization curve as well as inrush current. Different to the one of single phase transformer, flux density affected magnetization curve as well inrush current are change every cycle of three phases sources even in a same point investigated. In fact it is much more complex compared to a single phase transformer. Three kinds of material and two cutting methods were investigated in order to understand how it affect the magnetization curve as well as it inrush current. Investigation done is emphasized on simulation based on finite element method. A simple mathematical approach is also done to obtain the peak value of inrush current. The result showed that material and cutting method affect the magnetization curve and inrush current significantly. The generated inrush current in different cutting method has the difference about 6.8% while ST-37 material has the largest generated inrush current of about 9 times compared to ST-1008 and 4 times compared to ST-1010 material.

18 PULSE UNCONTROLLED RECTIFIER

In this project, a 18 pulse rectifier has been designed for high voltage application. Three 3 -phase are obtained from a single three phase source using zig-zag inter connection of conventional single phase transformer. Thus from the three 3-phase system displaced by 20˚, (obtained using zig - zag connection) 3 six pulse rectifier are obtained that are cascaded to realize a eighteen pulse rectifier. Phase shift of 0˚ and 20˚ are made using star and zig -zag connection and thus finally the addition of relevant line voltage. We can also bring down THD of it up to 5.47%

76–81-GHz CMOS Transmitter With a Phase-Locked-Loop-Based Multichirp Modulator for Automotive Radar

This paper presents the design of a linear frequency-modulated continuous-wave (FMCW) radar transmitter (TX) for automotive radar applications. The TX has a wide operating range from 76 to 81 GHz by employing a frequency-doubling architecture using an LC voltage-controlled oscillator operating at 38–40.5 GHz and a differential frequency doubler using a single transformer. A chirp generator is integrated into the TX, which provides various frequency chirp profiles with programmable chirp slope and sweep duration. The proposed CMOS FMCW TX can be applied to various modulation algorithms for multiple target detection and the avoidance of ghost targets. The TX is implemented using 65-nm CMOS technology. The chip size is 1.48 $\,\times\,$ 1.85 mm $^{2}$ . The measurement results shows a 76–81-GHz frequency range and 3-dBm output power while dissipating 320 mW. The phase-noise density of the TX is ${-}{\hbox{83.33}}$ dBm/Hz at an offset frequency of 1 MHz when the output frequency is 77 GHz.

Model Reduction of Potential Transformer Based on Revised Minimum Information Loss Method

The circuit model of potential transformer (PT) is indispensable in accurately simulating the electromagnetic characteristic under the lightning overvoltage and very fast transient overvoltage in power systems. This paper utilizes a reduction algorithm for potential transformer based on revised minimum information loss method (RMIL). First, we measured a 10 kV single phase potential transformer using the Agilent 4395A network/spectrum/impedance analyzer. Second, we obtained the rational approximation of two-port circuit parameters by vector fitting (VF). At last, revised minimum information loss method is applied to reduction the state equation of circuit parameters. Comparisons between the reduced and original are given to illustrate the approximating performance of RMIL.

A Compact Four-way Dual-band Power Divider Using Lumped Elements

A compact four-way dual-band microstrip power divider is investigated and demonstrated in this letter. The proposed divider reduces the number of transmission line sections by decomposing a single dual-band transformer into a four-way power divider. The theoretical equations for isolation structures and the design procedures of the power divider are presented. For demonstration, a prototype operating at 1 and 2 GHz is fabricated and measured. Good agreements can be observed between the simulated and measured results.

Low‐power transformer‐based current‐reuse injection‐locked frequency divider

A novel low-power injection-locked frequency divider (ILFD) is proposed, in which a complementary G m -boosted Colpitts oscillator core is employed to improve negative transconductance ( G m ) and the current-reuse technique using a single transformer is applied to reduce the power consumption. The proposed ILFD exhibits a self-resonant frequency of 4.93 GHz with a maximum locking range of 870 MHz at 0 dBm of input power. The phase noises of the input and output signals are -128.54 and -134.53 dBc/Hz, respectively. The ILFD consumes 1.37 and 2.5 mW at 1.15 and 1.3 V, respectively. The chip area is 715.5 × 468 μm 2 in a 0.13 μm CMOS process. To the authors' knowledge, this is the first demonstration of the current-reuse ILFD.

Диагностика однофазного силового трансформатора в рабочем режиме

The use of L-shaped equivalent circuit of the transformer is proposed for the diagnosis of a single phase power transformer. It's required to measure the instantaneous values of the primary voltage, the secondary voltage and secondary current by means of electric power quality analyzer PQA - 824, to measure the temperature of the transformer windings. For active power losses in the windings and the current value of the reduced secondary current to calculate the resistance of the windings. Using the differential equation RL-circuit with constant parameters to calculate the average value of the inductance of the windings on the period. To reduce the error in the determination of changes in the active and inductive reactance of the windings, filtering of the measured signals based on the Fourier transform has been used, as well as the adjustment of the winding resistance according to temperature. Then it's required to determine the relative deviation of the obtained values of resistance and inductance of the windings of the variables defined on a proper transformer, while comparing the obtained deviation to the settings. If deviations obtained more of the defined settings, then it is the failure occurrence of the diagnosed transformer of the windings. A modern mathematical software package MathCad 14 is designed to implement this algorithm. Audited algorithm using this analyzer is tested in the laboratory. The results of the test are verified.

Study on the Characteristics of Low-Frequency Vibration of the Core of Single Phase Transformer Set Caused by GIC

The study on characteristics of transformer vibration caused by GIC is the foundation of studies on transformer noise caused by GIC, location selection of monitoring vibration and noise. In this study, the characteristics of low-frequency vibration of the core of single phase transformer sets caused by GIC have been analyzed through building mathematical models and experimental analysis. The results show that when DC bias occurs the vibration signals contain 50 Hz and 150 Hz vibration. With the degree of DC bias the 50 Hz vibration grows by linear increase and 150 Hz vibration grows by square increase. Affected by GIC, the 50 Hz and 150 Hz vibration waveform’s phase changes with alternate 0 andπ. The characteristics of 50 Hz and 150 Hz vibration discriminate between core vibration caused by GIC and HVDC grounding currents. This study has significance for vibration monitoring of transformer faults, and can assist in determining the level of GIC.

변압기 절연유의 물성치 변화에 따른 온도특성해석

In this paper, the temperature distribution according to the property change of the insulating oil of the power transformer and max temperature were predicted through the ductility interpretation which heat-flow is coupled. By using CFD (Computation Fluid Dynamics) for the interpretation, the temperature distribution of 154kV the class single phase power transformer was predicted. The power loss causing the temperature rise of the transformer was changed to the heat source and we used as the input value for the heat-flow analysis. The temperature distribution was predicted according to the change of the density, specific heat, thermal conductivity and viscosity, that is the ingredient having an effect on the temperature rise of the transformer oil. The mineral oil of 4 kinds used in domestic and international based on the interpreted result was selected and the temperature distribution according to each load and Hot Spot temperature was predicted.

Temperature and concentration fields in a generator integrated to single stage heat transformer using Water/Carrol mixture

The generator is the starter device of single stage heat transformer (SSHT) and its characteristics have main effects on the overall efficiency of this kind of absorption machines. This article reports a study of the generation of steam and changes in the concentration of the working solution (Water/Carrol mixture) into a plate heat exchanger as a function of its horizontal and vertical position by gravity effect. It is considered the analysis of six experimental tests; two were evaluated in a plate heat exchanger in a horizontal position and four in a vertical position (90 degree inclination). The generation of steam and increased concentration of the working solution are more sensitive to the vertical position of exchanger than in horizontal position. The results of numerical-experimental analysis indicates that a heat exchanger in horizontal position, the steam generation and the change in the concentration of the working solution occurring in the middle of the plate (or at greater distance depending to the thermodynamic conditions) and instantly in vertical position (at the input of the plate).

New Wilkinson Power Dividers and Their Integration Applications to Four-Way and Filtering Dividers

This paper involved developing two (Type I and Type II) equal-split Wilkinson power dividers (WPDs). The Type I divider can use two short uniform-impedance transmission lines, one resistor, one capacitor, and two quarter-wavelength ( \(\lambda/4 \) ) transformers in its circuit. Compared with the conventional equal-split WPD, the proposed Type I divider can relax the two \(\lambda/4 \) transformers and the output ports layout restrictions of the conventional WPD. To eliminate the number of impedance transformers, the proposed Type II divider requires only one impedance transformer attaining the optimal matching design and a compact size. A compact four-way equal-split WPD based on the proposed Type I and Type II dividers was also developed, facilitating a simple layout, and reducing the circuit size. Regarding the divider, to obtain favorable selectivity and isolation performance levels, two Butterworth filter transformers were integrated in the proposed Type I divider to perform filter response and power split functions. Finally, a single Butterworth filter transformer was integrated in the proposed Type II divider to demonstrate a compact filtering WPD.

An Isolated Resonant AC-Link Three-Phase AC–AC Converter Using a Single HF Transformer

An isolated three-phase ac-ac converter with a high frequency (HF) ac link, soft switching operation, high input power factor, and bidirectional power flow is introduced. The galvanic isolation is attained by a single HF transformer, which is substantially smaller than the line-frequency transformers. Moreover, the magnetizing inductance of this transformer and two small ac capacitors form the convertor's HF ac link; no bulky short-life electrolytic capacitor is used. The magnetizing inductance is the main component for transferring power, and the link capacitors provide partial resonance to achieve zero voltage switching for the power switches in all operating modes. The basic operation of the topology is composed of 16 modes and is described. The detailed analysis of the proposed topology is carried out to reveal further the converter's behavior in different operating conditions. The simulation and experimental results are also provided to demonstrate the effectiveness of the proposed power converter.

A new low cost cascaded transformer multilevel inverter topology using minimum number of components with modified selective harmonic elimination modulation

In this paper, a novel cascaded transformer multilevel inverter is proposed. The number of the switching devices is reduced in the proposed topology. This topology comprises of a DC source, several single phase low-frequency transformers, two main power switches and some bidirectional switching devices. In this topology, only one bidirectional switch is employed for each transformer. However, in conventional cascaded transformer multilevel inverter, four switching devices are required for each transformer. Therefore, more output voltage levels can be obtained using fewer switching components. Reduction in the number of switching devices which also means reduction in the number of gate drivers results in smaller size and low implementation cost. Switching power losses are also reduced in this topology. Selective harmonic elimination (SHE) technique is applied to the proposed inverter to obtain a high quality output voltage. Simulation and experimental results are also provided to verify the feasibility of the proposed converter.

Experimental heat transformer monitoring based on linear modelling and statistical control process

In this paper the Statistical Process Control (SPC) methodology is used for first time to analyse the data obtained from an Absorption Heat Transformer (AHT), the aim in here is to define if the system was operated under statistical control using a Carnot Coefficient of Performance (COP) equal to 0.7 as an established specification. Data of a 10 kW prototype Single Stage Heat Transformer (SSHT) were analysed. Carrol/water mixture was used as a working pair in the thermodynamic cycle. The operating conditions of the SSHT under steady stated conditions show an energy recovery between 352.9 and 366.0 K, while waste energy is added from 339.1 to 361.9 K. Condenser temperature shows a process under statistical control; its Process Capability Ratio (Cp) is 1.15 dimensionless, and the Actual Process Capability Index (Cpk) is 1.11 dimensionless, as well. A linear modelling technique was used to control the SSHT. Finally, the COP variation is expressed as the absorber and generator linear functions, and evaporator temperatures are shown as techniques for SSHT control. The Cpk value indicates that the Condenser process has the ability to perform the specified operation of the SSHT.

Photovoltaic Power Generation System with Extended Boost Quasi-Z-Source Inverter

This paper proposes a extended boost quasi-Z-source inverter (qZSI) which is used as power conditioning unit for residential solar powered system .The proposed topology used is extended boost quasi Z source inverter and implemented using three phase induction motor. The cascaded qZSI is derived by the adding of one diode, one inductor and two capacitors to the conventional qZSI. The proposed two-stage qZSI has all the advantages of conventional qZSI such as voltage boost and buck functions, continuous input current, improved reliability and a new feature such that it reduces the shoot-through duty cycle by over the 30% for the same voltage boost factor qZSI. The main focus of this paper is to generate residential power using low power input of renewable energy like solar along with two stage qZSI (cascaded qZSI), single phase isolation transformer, and a voltage doubler rectifier and three phase induction motor. Two- stage qZSI in shoot-through and non-shoot-through operating modes is analysed theoretically. The simulation and experimental results are also discussed and presented using MATLAB/simulink. Index Terms— Quasi-Z-source inverter(qZSI),Power conditioning unit(PCU),Voltage doubler rectifier(VDR), photovoltaic system (PV),Maximum power point tracking(MPPT).

Simulation Research on Variable Frequency Flash Based on Blind Source Separation

This dissertation proposes a method of constructing a delay matrix using the output signal sequence of single voltage transformer instead of the multiple sensor output signal arrays. The matrix satisfies the basic requirement of BSS so that each frequency component is separated from flicker,harmonics and inter-harmonics which contain a number of frequencies.

Special issue on selected papers from NORCHIP 2013 conference

This special issue of Analog Integrated Circuits and Signal Processing presents the extended versions of selected papers from the 31th NORCHIP conference which was held in Vilnius, Lithuania, November 11–12, 2013. The 31th NORCHIP conference had 56 registered participants and 45 papers were presented during the 2 days the conference lasted whereof 30 papers were presented in 10 oral lecture sessions in two tracs, 12 papers were presented in two poster sessions, the 3 presentation, in session on Education and Training. The 3 invited presentations (first—Romualdas Navickas, ‘‘Self-formation in high speed integrated circuits’’, second—Petar Popovski, ‘‘Wireless technologies competing for a seat in the 5G bandwagon’’, and third—Ville Eerola, ‘‘Correlator design and implementation for GNSS receivers’’) were given. However, more submissions are originating from the local area of the conference (only one accepted paper was from a non-European country). From the contributed papers nine papers have been selected for this special issue. The selection of the papers for this special issue is based on quality criteria and they reflect the topics in analog circuit design highlighted during the conference, the feedback of the session chairs and the selected papers all contain contributions that will be of interest to the reader. The papers are briefly introduced below. The two first papers present two RF amplifiers. In the first paper ‘‘Triple Cascaded Current-Reuse Low Noise Amplifier’’ Muh-Dey Wei, Sheng-Fuh Chang, Renato Negra present a triple cascaded current-reuse CMOS low noise amplifier (LNA) for 3.5 GHz WiMAX application. Three commonsource amplifiers are stacked and reuse the same current. This triple cascaded topology is able to enhance power gain but needs two coupling networks which costs enormous chip size. In order to have reasonable chip size, two coupling methods are investigated. For obtaining simultaneous input and noise matching, an additional capacitor is employed to adjust quality factor and reduce the gate induced current noise. The proposed chip is implemented in 180 nm CMOS technology. The measurement results show a maximum power gain of 21.7 dB and minimum noise figure of 3.11 dB. The chip size is 1.05 9 0.93 mm including all pads and the power consumption is 5.16 mW with a supply voltage of 1.5 V. In the second paper ‘‘A 1 V Power Amplifier for 81–86 GHz E-band’’ authors Tobias Tired, Henrik Sjoland, Carl Bryant and Markus Tormanen describe the design and layout of a two stage SiGe E-band power amplifier using a stacked transformer for output power combination. In EMsimulations with ADS Momentum, at E-band frequencies, the power combiner consisting of two individual single turn transformers performs significantly better than a single 2:1 transformer with two turns on the secondary side. Imbalances in the stacked transformer structure are reduced with tuning capacitors for maximum gain and output power. At 84 GHz the simulated loss of the stacked transformer is as low as 1.35 dB, superseding the performance of an also presented alternative power combiner. The power combination allows for a low supply voltage of 1 V, which is beneficial since the supply can then be shared between the power amplifier and the transceiver, thereby eliminating the need of a separate voltage regulator. To improve the gain of the two-stage amplifier it employs a capacitive cross-coupling technique not yet seen in mm-wave SiGe Pas. Capacitive cross-coupling is an effective technique for gain enhancement but is also sensitive to process variations as shown by Monte Carlo simulations. To mitigate this two R. Navickas (&) Department of Computer Engineering, Vilnius Gediminas Technical University, Naugarduko str. 41, r. 437, 03227 Vinius, Lithuania e-mail: romualdas.navickas@vgtu.lt

Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain

After the good results obtained from an assessment of geomagnetically induced currents (GICs) in a relatively small subset of the Spanish power transmission network, we now present the first attempt to assess vulnerability across the entire Spanish system. At this stage, we have only included the power grid at the voltage level of 400 kV, which contains 173 substations along with their corresponding single or multiple transformers and almost 300 transmission lines; this type of analysis could be extended to include the 220-kV grid, and even the 110-kV lines, if more detailed information becomes available. The geoelectric field that drives the GICs can be derived with the assumption of plane wave geomagnetic variations and a homogeneous or layered conductivity structure. To assess the maximum expected GICs in each transformer as a consequence of extreme geomagnetic storms, a post-event analysis of data from the Ebre Geomagnetic Observatory (EBR) during the 2003 Halloween storm was performed, although other episodes coincident with very abrupt storm onsets, which have proven to be more hazardous at these mid-latitudes, were analyzed as well. Preferred geomagnetic/geoelectric field directions in which the maximum GICs occur are automatically given from the grid model. In addition, EBR digital geomagnetic data were used to infer statistical occurrence probability values and derive the GIC risk at 100-year or 200-year return period scenarios. Comparisons with GIC measurements at one of the transformers allowed us to evaluate the model uncertainties.

A 1 V power amplifier for 81–86 GHz E-band

The design and layout of a two stage SiGe E-band power amplifier using a stacked transformer for output power combination is presented. In EM-simulations with ADS Momentum, at E-band frequencies, the power combiner consisting of two individual single turn transformers performs significantly better than a single 2:1 transformer with two turns on the secondary side. Imbalances in the stacked transformer structure are reduced with tuning capacitors for maximum gain and output power. At 84 GHz the simulated loss of the stacked transformer is as low as 1.35 dB, superseding the performance of an also presented alternative power combiner. The power combination allows for a low supply voltage of 1 V, which is beneficial since the supply can then be shared between the power amplifier and the transceiver, thereby eliminating the need of a separate voltage regulator. To improve the gain of the two-stage amplifier it employs a capacitive cross-coupling technique not yet seen in mm-wave SiGe PAs. Capacitive cross-coupling is an effective technique for gain enhancement but is also sensitive to process variations as shown by Monte Carlo simulations. To mitigate this two alternative designs are presented with the cross coupling capacitors implemented either with diode coupled transistors or with varactors. The PA is designed in a SiGe process with f T = 200 GHz and achieves a power gain of 12 dB, a saturated output power of 16 dBm and a 14 % peak PAE. Excluding decoupling capacitors it occupies a die area of 0.034 mm2.