Air-gap Type Research Articles

Flexible Inductive Transducer with Magnetic Resistance Influenced by Variable Overlap Area

Inductive transducers for measuring displacement are divided into two groups according to their measurement range. A variable air-gap type transducer is widely used for a measurement small range. A conventional variable air-gap type transducer has high sensitivity but lacks a linear measurement range. The air gap is also increased to maintain linearity as the measurement range increases, which induces a loss of sensitivity. The proposed variable overlap-area type transducer retains the original sensitivity and its linearity does not deteriorate in spite of variations of the measurement range. The proposed transducer is a flexible system that can increase its measurement range as well as maintain high sensitivity and linearity. The experimental results obtained using the prototype indicate that the sensitivity is higher than 2200 mV·V-1 mm-1 and the linearity error is below ±0.075% in the range of ±200 µm.

Study on characteristics of high temperature superconducting magnetic thrust bearing for 25 kW h flywheel

An axial air gap type thrust bearing of the outer diameter of 620 mm for 25 kW h flywheel which combined with the permanent magnet of Nd–Fe–B and 10 pieces of high temperature YBaCuO superconductors of the diameter of 150 mm directly cooled by the refrigerator was fabricated, and its performance tests were conducted. Load capacity which could support a planned rotor weight of 8.2 kN was confirmed, and also the stiffness of the radial direction and the axial direction were measured in case of several initial cooling conditions. Spring and damping coefficients in zero field cooling were also measured in the tapping test, and it was found that axial spring coefficients were about 10 times as large as radial spring coefficients, though damping coefficients were almost the same.

A 30 kVA superconducting generator development and basic tests

A 30 kVA superconducting generator has been designed, developed and successfully tested by the Korea Electrotechnology Research Institute (KERI). The design is based on a 2-dimensional electromagnetic field analysis of cylindrical coordinates. The field winding of rotor has been wound with superconducting wire of NbTi alloy and tested after assembly with other rotor components. The stator has air-gap type armature windings, which produce higher terminal voltage, and a more sinusoidal voltage waveform than conventional iron cored machines. Steady-state open and short-circuit tests and lamp load tests have also been conducted. The results of these tests are given in this paper and compared with design quantities. Moreover, the cooling scheme and characteristics of the test system are included.

Impact of Sand/Dust Pollution on the Engineering Design Criteria of High Voltage Air Insulated Networks

Outdoor air insulated, high voltage transmission and distribution networks are frequently exposed to atmospheric pollution in the form of sand and dust storms which can affect the breakdown and prebreakdown characteristics and insulation performance of air gaps. This paper summarizes the findingks of an extensive study carried out to determine the effect of sand/dust contamination on the high voltage impulse breakdown characteristics of different types of air gaps. Analysis of the results of this study highlight the influence of airborne and surface adhering sand/dust contamination on the engineering design criteria to specify clearances of overhead lines and station equipment, design and performance of protective rod gaps and the accuracy of high voltage measurements using sphere gaps.

Volt-time characteristics of short air gaps under nonstandard lightning voltage waves

[6 SM 421-8 PWRD, T-PWRD January 1997]. The goal of the present study was to perform a series of statistically designed tests on several types of short air gaps under lightning voltages of nonstandard waveshapes. The objective was to compare the critical breakdown voltage levels, V50, and the volt-time characteristics of these short air gaps under lightning voltages of various waveshapes. The results of the critical breakdown voltages were presented previously. The results of the volt-time characteristics are presented in this paper.

Development and performance testing of a 200 kVA damperless superconducting generator

A 200 kVA, 3000 RPM superconducting generator has been developed and tested. The rotor has been wound with superconducting wire of Nb-Ti alloy. A closed-circuit liquid helium system has been designed and installed for cooling the superconducting windings. The stator carries the air-gap type armature windings and a laminated-iron flux-shield. A new concept in the design of superconducting generators with high short-circuit ratio (more than 5) has been introduced. This eliminates the requirement of an electromagnetic damper and quick response excitation system. The generator has been comprehensively tested in the superconducting state. Open-circuit and sustained short-circuit tests, three-phase sudden short-circuit tests, synchronization with the grid and parallel operation with power systems have been conducted. The synchronous machine was operated up to its rated kVA in the four quadrants-as a generator and as a condenser with leading and lagging power factors. A few special tests on superconducting generators, which were not reported earlier, such as direct-online starting of a 20 hp squirrel-cage induction motor and negative phase sequence tests have also been performed successfully. Test results and conclusions are given.

Defects in Synthetic Quartz and the Q-Values of the -18.5° X-Cut Bar

-18.5° X-cut bar crystal blanks, 25.0×1.50×1.25 mm in size, were cut from different synthetic mother quartz. Defects in the bars were observed by light scattering tomography and X-ray traverse topography, Q-values were measured in the second overtone mode of 200 kHz in the air gap type holder and the maximum Q of 5.4×106 was obtained. Infrared absorption of the mother quartz, observed defects and the measured Q-values were discussed.

The clival-perpendicular or modified Water's view in compound tomography.

The air gap type of CT scanner with tilting gantry allows the use of head positions other than the standard semi-axial. The modified Water's or clival-perpendicular position is especially useful in the diagnosis of posterior fossa disease. The position offers a view that is approximately coronal to the clivus and tentorium. The clival-perpendicular view easily separates the supra- and infratentorial compartments. It also helps to differentiate extra- and intra-axial lesions and to locate the fourth ventricle, and it gives far better vertical orientation of posterior fossa pathology.

Design of air-gapped magnetic-core inductors for superimposed direct and alternating currents

Using data readily available from manufacturers on standard magnetic-material properties and standard core sizes for air gap type cores, an algorithm designed for a computer solution is developed which optimally determines the air gap length and locates the quiescent point on the normal magnetization curve so as to yield an inductor design with the minimum number of turns for a given ac voltage and frequency and with a given dc bias current superimposed in the same winding. Magnetic-material data used in the design are the normal magnetization curve and a family of incremental permeability curves. A second procedure, which requires a simpler set of calculations, starts from an assigned quiescent point on the normal magnetization curve and first screens candidate core sizes for suitability, then determines the required turns and air gap length.

Theory of the Bridge-Rectified Synchronous Generator with a Large Number of Stator Phases - Part II

The usefulness of the previously derived equations for commutation phenomenons and other related characteristics is demonstrated by means of a numerical example of the Salient Pole and Constant Airgap type machine. These two limiting cases bracket the characteristics of an actual Salient Pole type machine including the pole edge fringing flux. The results are discussed and commented upon in detail.

The Optimum Design of the Toroidal Resonator

The optimum design of a class of toroidal resonators which are capacitively loaded and therefore short in wavelengths is considered. The possibility of including magnetic cores with various types of air gaps is included and it is shown that below a certain critical size, which is a function of the magnetic merit factor, the net Q may be improved with the optimum material and the optimum air gap. Even without magnetic cores these resonators obtain a higher Q per unit volume than any other known electrical resonator.

A differential reluctance measuring system and its application to model and ship testing

A measuring system is described which has been developed at the David Taylor Model Basin for use in model and full-scale ship testing. The system utilizes transducers of the differential air-gap type, special designs of which permit measurement of torque or thrust in rotating shafts without the use of slip rings. The system includes instrumentation for direct recording and for visual or automatic digital readout. Accuracies of ±½% or better are obtainable.

Chapter VIII: Principles of Mounting Quartz Plates

IT IS the object of this chapter to show some of the fundamental considerations involved that govern the design of mountings or holders of quartz crystals. This discussion is restricted to the three common types, namely, rod or clamp type, wire type and airgap type. The development of these three types of mountings for applications in telephone transmission and radio systems has led to many and varied forms. Commercial designs of units for telephone uses employing these principles are described in detail in a later chapter.