On-site testing of special transformers

The current differential protection is the most popular protection for transformers, providing good fault sensitivity, selectivity and security. Depending on the application, the transformer size, shape, winding connections vary. Some common power system applications require installation of two- or three-winding conventional power transformers or autotransformers, while others require phase shifting transformers (PST), Scott transformers, LeBlanc transformers, Zig-Zag grounding transformers, or converter transformers. Applying differential protection to conventional type power transformers with “standard” phase shifts of 30 degrees, or multiples of 30 degrees is trivial. However, applying this protection to transformers with non-standard phase shifts is challenging for the protection engineer. Current Transformers (CTs) installed in non-common locations adds even more to the complexity of applying the protection correctly. The later is associated with special CT — relay connections, correct computation of winding currents, phase angles, and selection of protective device supporting such applications. The paper provides essential knowledge on the transformer differential protections throughout theory and application examples. Current transformers and relay connections, as well as computation of transformer setup settings with standard and non-standard phase shift are covered.

A new method is proposed and demonstrated for fabricating phase-shifted fiber Bragg gratings (FBGs) using a variable-velocity scanning UV laser beam in combination with a shielded phase mask. The transmission properties of phase-shifted FBGs were analyzed based on coupled-mode theory and a transfer matrix method. The grating is divided into three parts to allow for easier analysis of FBG properties. These segments included a uniform FBG1 and FBG2 which were separated by a shielded section. A novel phase-shifted FBG was fabricated using this method, in which the refractive indices of FBG1 and FBG2 were different. Transmission properties of these phase-shifted FBGs were simulated numerically using MATLAB, and the experimental results and simulated results are in good agreement. In addition to the length and effective refractive index of the shielded section, the phase shift value of a phase-shifted FBG was also found to be dependent on the lengths and effective refractive indices of FBG1 and FBG2. Moreover, we predicted that changing the scanning velocity for fabricating FBG2 would adjust phase shift value, which exhibits a positive linear relationship with the scanning velocity. These results can provide guidelines for fabricating any phase shift value FBGs. This technique is simple, convenient, and may be developed further for use in fabricating novel tunable fiber filters or DFB fiber lasers.

Objective: Explore the performance of different test methods in detecting COVID-19 antibodies and antigens. Methods: Compare the results of different test methods on samples from novel coronavirus pneumonia patients, and randomly select some of the confirmed samples after gradient dilution to detect the sensitivity of the test products. The sample used for rapid detection of COVID-19 antigen was nasal swab. Three kinds of sample used in the detection of novel coronavirus antibodies were venipuncture/ fingerstick whole blood, serum and plasma. Results: The detection rate of covid-19 antibody increased with the increase of the onset time of patients, while the detection rate of antigen decreased gradually, which was in line with the nature of antigen and antibody in the human body. Conclusion: In view of the advantages of antibody and antigen detection, such as convenient and sample collection, high throughput, low workload, high reproducibility and low cost, we hope to lay a scientific foundation for the horizontal comparison of the data of products (Abbott, Roche, Healgen, AllTest, Citest, Siemens, Lepu, Wondfo) obtained in the research and practical application of epidemic prevention and control of COVID-19.

Three-frame generalized phase-shifting interferometry by a Euclidean matrix norm algorithm

Phase-shift analysis of p-p and n-p elastic scattering at 735 MeV

Under the “weak phase object” approximation, the component of the electron wave scattered by an object is phase shifted by π/2 with respect to the unscattered component. This phase shift has been confirmed for thin carbon films by many experiments dealing with image contrast and the contrast transfer theory. There is also an additional phase shift which is a function of the atomic number of the scattering atom. This shift is negligible for light atoms such as carbon, but becomes significant for heavy atoms as used for stains for biological specimens. The light elements are imaged as phase objects, while those atoms scattering with a larger phase shift may be imaged as amplitude objects. There is a great deal of interest in determining the complete object wave, i.e., both the phase and amplitude components of the electron wave leaving the object.

We report the spectral features of a phase-shifted parity and time ($\mathcal{PT}$)-symmetric fiber Bragg grating (PPTFBG) and demonstrate its functionality as a demultiplexer in the unbroken $\mathcal{PT}$-symmetric regime. The length of the proposed system is of the order of millimeters and the lasing spectra in the broken $\mathcal{PT}$-symmetric regime can be easily tuned in terms of intensity, bandwidth and wavelength by varying the magnitude of the phase shift in the middle of the structure. Surprisingly, the multi-modal lasing spectra are suppressed by virtue of judiciously selected phase and the gain-loss value. Also, it is possible to obtain sidelobe-less spectra in the broken $\mathcal{PT}$-symmetric regime, without a need for an apodization profile, which is a traditional way to tame the unwanted sidelobes. The system is found to show narrow band single-mode lasing behavior for a wide range of phase shift values for given values of gain and loss. Moreover, we report the intensity tunable reflection and transmission characteristics in the unbroken regime via variation in gain and loss. At the exceptional point, the system shows unidirectional wave transport phenomenon independent of the presence of phase shift in the middle of the grating. For the right light incidence direction, the system exhibits zero reflection wavelengths within the stopband at the exceptional point. We also investigate the role of multiple phase shifts placed at fixed locations along the length of the FBG and the variations in the spectra when the phase shift and gain-loss values are tuned. In the broken $\mathcal{PT}$-symmetric regime, the presence of multiple phase shifts aids in controlling the number of reflectivity peaks besides controlling their magnitude.

The link between soil water content (SWC) and evapotranspiration (ET) is of great importance in ecohydrology, agroecosystem management, and land-atmosphere interaction of earth-system analysis. There is still a need to understand the key processes linking SWC and ET in different vegetated ecosystems, especially at larger scales. Therefore, in this work, we used wavelet coherence analysis to explore the long-term relationship between SWC and ET among the predominant land use types (cropland, evergreen needleleaf forest, mixed forest, open shrubland, wooden tundra, grassland, and mixed tundra) in Europe during the last four decades (1980-2020). To this end, first a principal component analysis was performed among the SWC and ET data from GLDAS, GLEAM, and ERA5-land, and the first component was then used for further analyses when the target variable was in demand. Using the first component, then, we averaged SWC and ET data over the pixels covered by each land use type. Then, for each land-use types, we averaged the data daily for each decade to account for a representative decadal year of daily data. Then, wavelet coherence analysis was conducted between those averaged data of SWC and ET for each land-use type. The results showed a negative correlation between ET and SWC for all land use types, with ET lagging behind SWC, with an average phase shift value of 134 days for grassland (the minimum) and 168 days for mixed tundra (the maximum). Converting the phase shift values to a time lag [lag = n/2 - phase shift for the case phase shift < -n/4 where n represents the period (1/frequency) of the signals] shows (Fig. 1) that ET controls SWC with a lag of 15 days in mixed tundra (the minimum) and 48 days in grassland (the maximum). Moreover, we applied Mann-Kendall trend analysis test and found that the lag between SWC and ET decreases in mixed and wooden tundras with a slope value of -2.4 days/year, while it increases in cropland and grassland with a slope value of 1.6 days/year. Although there is a significant downward trend in evergreen needleleaf forests (with a slope value of -0.3 days/year) and an increasing trend in mixed forests and open shrublands (with a slope value of 0.4 days/year), the lower slope values in these land use types indicate that the change is slower compared to grasslands, croplands, and tundras. Figure 1- Temporal evolution of the lag between soil water content and evapotranspiration in the annual cycle in different land use types in Europe 

We demonstrate a new full range complex spectral domain optical coherence tomography (FRC SD-OCT) method. Other than FRC SD-OCT systems reported in literature, which employed devices such as electro-/acousto optic modulators or piezo-driven mirrors providing the phase modulations necessary for retrieval of the complex-valued signal, the system presented works without any additional phase shifting device. The required phase shift is introduced by the galvanometer scanner used for transversally scanning the sample beam. By means of a slight displacement of the probe beam with respect to the scanning mirror's pivot axis, the sample arm length and thus the phase is continuously modulated as the beam is scanned in lateral direction. From such modulated spectral data, the complex-valued data yielding a twofold increase of accessible depth range can be calculated using an algorithm based on the Hilbert transform. To demonstrate the performance of our method quantitative measurements of the suppression of mirror images as a function of induced phase shift were performed. In order to validate the FRC SD-OCT technique for high-speed imaging of biological tissue, we present full-range images of the human anterior chamber in vivo.

Power transformer differential protection has been used for decades on standard three-phase power transformers. However, special industrial transformers, such as 24-pulse converter transformers, could not typically be protected easily with the standard power transformer differential relays. The main reason is the nonstandard phase angle shift of 24-pulse converter transformers. Such 24-pulse converter transformers are often used in industrial and railway applications. This paper will show that it is possible to provide differential protection for such special transformers by using standard numerical transformer differential protection relays and external interposing current transformers (CTs). However, the external interposing CTs can be designed in a standardized way. This approach will significantly simplify the application of differential protection for special industrial transformers.

In this paper, a new class of wideband phase shifters on multimode resonator is proposed and developed. Compared with its conventional counterparts, these new phase shifters have a few advantageous features such as simple structure, intrinsic wideband characteristic, large phase-shift value, and easy adjustment in phase shift. The phase properties of multimode resonator are at first studied to derive the quantitative relationship between the phase slope and their respective resonant frequencies. On the one hand, a prescribed wideband phase shift can be achieved by adjusting the impedance ratio $R_{z}$ of the multimode resonator and the electrical length of the reference line. On the other hand, the wide operating band can be intrinsically obtained over a frequency range covered by multiple resonant frequencies in the multimode resonator. In this context, the transmission-line models of the proposed phase shifters are deduced and synthesized to design these phase shifters with a prescribed phase shift value and return loss within the operating band. Moreover, the synthesized model can be directly mapped into all the physical dimensions, thus allowing for a quick design process. Finally, two 180° wideband phase shifters are designed, fabricated, and tested to verify the proposed design method and predicted frequency responses.

SUMMARY We performed pumping tests with a periodic succession of injection and production intervals in a field of three shallow boreholes penetrating a jointed sandstone formation. Tests were conducted at periods ranging from 10 to 5400 s and pumping rates between 5 and 20 l min−1. Two types of analysis for the periodic pumping tests are presented. Injectivity analysis rests on the determination of the amplitude ratio and phase shift between the periodic flow rate and pressure records from the pumping well. Interference analysis is based on an evaluation of attenuation and phase shift between the periodic pressure signals at the pumping and monitoring wells. A periodic excitation permits to employ standard signal processing tools, such as fast Fourier transformation, facilitating the evaluation of weak signals. The observed amplitude ratio and phase shift values are compared to analytical predictions of 1-D and radial flow models. Results of interference tests are particularly diagnostic for the applicability of a subsurface model. Our test results do not fully agree with any of the considered analytical models suggesting a heterogeneous subsurface. We suppose that the two analysis methods yield averaged hydraulic properties of different volumes of a heterogeneous subsurface. Periodic injectivity tests screen the subsurface to increasing penetration depth if pumping period is systematically increased, while the subsurface volume between pumping and monitoring well dominates the outcome of an interference test at all periods. Periodic pumping provides several operational advantages compared to conventional testing, such as drawdown, pulse or shut-in tests. Periodic testing can be superposed on a long-term operation reducing operational conflicts and permitting continuous monitoring of changes in subsurface properties. Processing of periodic signals provides results even in a field with strong transient changes in fluid pressure related, for example, to operations in nearby wells. Periodic pumping can be performed in a closed loop minimizing the total fluid volume involved.

This paper introduces a high-efficiency high-power-density single-stage isolated 48V-to-1.8V point-of-load (PoL) converter. This converter achieves large step-down with high efficiency using a distributed transformer and a resonant immittance network. The high efficiency is maintained across variations in input voltage and output power using an impedance control network (ICN) based high-frequency inverter structure, which enables zero-voltage and near-zero-current switching across wide operating ranges. High power density is achieved by utilizing rectifier phase-shift control that eliminates the need for bulky electrolytic capacitors, and by implementing the converter's inductors and transformer as planar integrated magnetic structures. The design of the magnetic structures is optimized using 3D finite-element analysis. A prototype 90-W 1-MHz PoL converter utilizing PCB-integrated planar magnetics, designed to operate over an input voltage range of 36 V to 60 V and an output voltage of 1.8 V is built and tested. The prototyped converter achieves a peak efficiency of 92.6%, maintains full-power efficiencies above 88.9% across its nearly 2:1 input voltage range, and achieves a power density of 314 W/in3.

A new class of wideband differential phase shifters employing two distinctive multimode resonators both in main and reference lines is presented. Compared with their counterparts, the proposed phase shifter firstly can achieve wideband phase shift and good filtering function with controllable same insertion loss (IL) bandwidth in main and reference lines as required. To design two phase‐shifting elements with design indices (phase‐shift value, return loss, and operating bandwidth), an effective synthesis method is presented and sets of design curves are graphically demonstrated. Prototype phase shifters are then fabricated and measured. Finally, the design approach is validated experimentally. It is shown that the proposed phase shifters achieve 90° ± 2.3° and 45° ± 2.0° over the prescribed band 2.26–3.72 GHz (48%) and 2.04–4.03 GHz (66%). The good frequency selectivity with the same IL bandwidth is obtained and out‐of‐band rejection is >30.2 and 26.4 dB up to 7.0 GHz.

Hybrid on‐load tap changers (OLTCs) are attractive solutions for the smooth change in voltage without current interruption in the converter transformer. This paper proposes a systematic topology derivation method of hybrid OLTC. To begin with, the topology derivation principle of OLTC is studied according to graph theory and equivalent electrical network theory, and the basic structure of OLTCs is constructed. Based on the topology derivation and optimization method, some hybrid OLTC topologies are derived. Particularly, a new hybrid star‐type parallel three‐switch OLTC topology with independent intellectual property rights is investigated in detail. Then, the optimal timing control is designed to reduce the time of current flow and shorten the overall switching time. Circuit simulation results show that arc‐free and reliable switching can be realized in the new topology. In addition, the losses and the heat generated during the switching process are calculated, and the impact of the phase between the stage voltage and system current on the loss and electrical stress is studied. Furthermore, the comparison between the proposed topology and other topologies is carried out to show the advantages of the proposed topology. Finally, Saber circuit simulation will be carried out to verify the theoretical and numerical analysis results.