Axially Displaced Research Articles

Method of Evaluating Probability of Pressboard Failure in Power Transformer with Disc‐Type Winding Due to Electromagnetic Force by External Short Circuit

The evaluation of the failure probability is essential in the reliability‐centered and risk‐based maintenance of power transformers. The breakage of the pressboard in disc‐type transformers is one of the critical factors determining the lifetimes of power transformers. In this paper, a hierarchical method for evaluating the probability of pressboard failure, which is the breakage of the pressboard, in power transformers that considers the axial displacement of the winding is introduced. In the method, the diagnosis of the axial displacement is classified into three distinct classes. In class 1, no diagnosis is implemented, and the probability of failure is evaluated with the maximum possible axial displacement. In class 2, the diagnosis determines whether the winding is axially displaced. When the winding is diagnosed to be displaced, the probability of failure is evaluated with the maximum possible axial displacement. In class 3, the axial displacement is diagnosed quantitatively, and the probability of failure is then evaluated using the diagnosis result. Examples of the evaluated probabilities of pressboard failure are introduced, and the extension of the evaluated lifetimes of power transformers via the diagnosis of winding axial displacement is demonstrated. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Detection and quantitative diagnosis of axial displacement of transformer winding by frequency response analysis

Transfer functions of a transformer whose winding is axially displaced are measured in several connection schemes of frequency response analysis (FRA), and the sensitivities of the measured transfer functions in these connection schemes to the axial displacement are evaluated. For the objective evaluation, some numerical indices are employed, and it is found that the inductive inter-winding measurement is the most sensitive to the axial displacement. Furthermore, a simple circuit model is proposed to reproduce the measured transfer functions. All the parameters of the proposed circuit model can be determined from the measured transfer functions in FRA. The proposed model can also reproduce the measured transfer functions with the axial displacement by varying one parameter. The variation of the parameter in reproducing the transfer function with the axial displacement show good linear relation to the amount of the axial displacement. This indicates the possibility of a quantitative diagnosis of the axial displacement by FRA.

The curve shape of a bent ruler—analytical, numerical and experimental studies

A ruler, where one of its ends is axially displaced a known distance, is studied using analytical, numerical and experimental methods. The exact nonlinear differential equation for the bent ruler is derived and solved numerically. This exact differential equation is then simplified to a fourth order differential equation using a small angle approximation. Using this equation together with appropriate boundary conditions, an approximate curve shape for the ruler is determined, which turned out to be a sine function with no dependence on material parameters or cross-sectional data. An expression for the length of the bent ruler is derived and using the constraint that this length is constant, an equation for determination of a relationship between the midpoint transverse displacement (deflection) and the known axial displacement is obtained. This equation is solved numerically. In addition a simple algebraic relationship between the midpoint deflection and the axial displacement is derived. A comparison between measured data for a bent ruler, the numerical solution of the exact differential equation, the numerical solution of the approximate equation and the algebraic expression is presented. It is found that the algebraic sine-shaped solution gives reasonable results for moderate axial displacements. The experimental investigations, the algebraical expressions and the numerical simulations can be useful in high school teaching and at undergraduate university level.

Axial Magnetic Fields, Axial Force, and Losses in the Stator Core and Clamping Structure of a Synchronous Generator with Axially Displaced Stator

Axial displacement of the stator in a synchronous machine gives rise to axial magnetic field both at the ends and deep inside the stator. The axial magnetic field causes losses. This article contains results from two studies with an axially displaced stator. In the first study, axial magnetic leakage fields in the ends of a small synchronous generator at load and no load were measured and simulated. In the second study, axial force and iron losses at no load were calculated with non-linear materials and a three-dimensional, time-stepped finite element method. For some machines with vertical shafts, the sum of iron losses and thrust bearing losses can be reduced if the rotor is lowered or the stator raised, whichever is best.

A Vector-based Approach to Discriminate Radial Deformation and Axial Displacement of Transformer Winding and Determine Defect Extent

The transfer function is a well-known method to detect mechanical defects of transformer windings. After measurement of transfer functions, they must be evaluated to detect any anomaly in transformer windings. One of the main problems in this stage is lack of transparency. This article tries to solve this problem through a vector space-based perspective to diagnose radial deformation and axial displacement of transformer windings. To determine the severity of the winding deformation or displacement, the angular proximity index is used. The measurement results show the effectiveness of this index. Based on the verified model of the transformer, a dimensionality reduction technique is applied to transformer's transfer function to map it from its original high-dimensional vector space to a lower-dimensional one. It is shown that transfer functions of radially deformed and axially displaced windings are well separated visually in the reduced space.

Investigation of Axial Carrying Capacity of Radial Hybrid Magnetic Bearing

This paper investigates the axial carrying capacity of a new radial hybrid magnetic bearing (RHMB) using experimental, finite element, and magnetic circuit methods. The thrust bearing of traditional structures is not included because an axial resilience is generated by this new RHMB when the rotor is axially displaced. The relationship between axial resilience and displacement is tested, from which the axial passive stability stiffness is derived. The passive stability stiffness linearly decreases with increased displacement. Based on the 2-D and 3-D finite element models of RHMB established with AYSYS software, the axial resilience is calculated and compared with the experimental results, which shows that the numerical results are fully consistent with the experimental ones. The influence of structural dimensions to the axial resilience, including air gap length, permanent magnet sectional area and height, and magnetic pole board height, are analyzed in detail based on the 2-D model. The formula to calculate the axial resilience suitable for different lengths of air gap is deduced by the magnetic circuit method. Theoretical results calculated by this formula are in good agreement with the experimental and numerical results. The conclusions are helpful in designing and controlling RHMB.

Performance of an Electrically Small Aperture, Axially Displaced Ellipse Reflector Antenna

This work reports the performance of an axially displaced ellipse (ADE) antenna with an electrically small aperture. The diameter of the antenna is about 20¿ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , which is considerably smaller than the ADE antennas already reported. This antenna provides a measured peak gain of 33.3 dBi at 8.484 GHz, which corresponds to an overall efficiency of 55%.

Spatially integrated speckle intensity: maximum resistance to decorrelation caused by in-plane target displacement

Laser speckle produced from a diffuse object can be used in determining the angular position of a rotating object. When the object rotates the backscattered speckle pattern, which changes continuously but repeats exactly with every revolution, is sampled by a suitably positioned photodetector. The photodetector output signal is periodic, and one period is stored in the memory as a reference. Shaft position can then be determined by the comparison of this stored reference signal with the current photodetector output signal. When the shaft is axially displaced, for example, by vibration, the backscattered speckle pattern changes on the photodetector and the similarity between the reference signal and the current signal is reduced. We examine the cross correlation of the real-time photodetector output signal and the stored reference signal as a function of axial shaft position. Use of a rotating shaft when collecting data is shown to be an efficient means by which to make effectively several thousand independent estimates of the maximum axial displacement tolerable before decorrelation of the photodetector output. Theoretical results and experiments conducted show that the decorrelation displacement varies, according to optical configuration, to a maximum value of 0.7 of the beam diameter. This has important implications for a proposed laser torquemeter as well as additional applications in which changes to the sampled speckle pattern, including decorrelation, are either desirable or undesirable.

A new technique for increasing the gain of the log periodic dipole antenna †

Abstract A technique for increasing the gain of the log periodic dipole antenna is presented. An axially displaced half-wave dipole antenna provides a narrower half-power beam width and gives slightly increased gain as compared to the conventional half-wave dipole antenna. Using this fact it is theoretically shown that the gain of the log periodic dipole antenna can be increased by axially displacing the feed points of the constituent dipoles of the log periodic dipole antenna. Typical theoretical results are given for different values of the axial feed displacement.

A Beam Compression Technique for Log Periodic Array

A new technique for compressing the beam of the log periodic dipole antenna with Ψ-0° is presented. An axially displaced half wave dipole antenna provides a narrower half power beam width as compared to the conventional half wave dipole antenna. Using this fact it is theoretically shown that the beam of the log periodic dipole antenna can be compressed by axially displacing the feed points of the constituent dipoles of the log periodic dipole antenna. Typical theoretical results are given for different values of axial feed displacement.

On the mechanism of catalysis by vitamin B12.

The requirements for alkylation and binding of nitrogenous ligands to cobalamins and cobinamides suggest that the central cobalt atom can exist either approximately in the plane of the corrin or axially displaced above this plane. Distortion of the normal octahedral complex by axial displacement results when the dimethylbenzimidazole moiety of the coenzyme is prevented from coordinating with the cobalt. A general hypothesis of B(12) coenzyme catalysis that involves the potential of Co(III)-R([unk]) and Co(I)-R([unk]) transitions is proposed on the basis of these considerations.