Magnetic Shunt Research Articles

WELDING TRANSFORMER CONTROL BY THE ELECTRONIC CONTROL OF LEAKAGE FLUX

ABSTRACT In this paper, the triac is used to control the welding transformer leakage reactances and thus the welding currents. This new method keeps the input and output currents and voltages in sinusoidal wave forms. The triac is connected across the terminals of a coil wound on a fixed limb magnetic shunt. A simple triggering circuit is used to control the current of the triac and thus the current of magnetic shunt coil. This leads to variation of welding transformer leakage flux, leakage reactances and thus a variation of welding current. The distortion due to the triac is only affecting the leakage flux of the welding transformer. The leakage flux is very small (compared with main flux) and most of it passes in the transformer window. Then, no harmonic pollution in the bus–bar or in the welding transformer. Thus, high operating efficiency is obtained. This new method can be used with single or three phase are welding transformer. In this work, a three phase multi–operator welding transformer is experimentally checked with the new system. The recorded wave forms support the system advantages. Performance characteristics are experimentally measured and give adequate results.

Magnetoresistive read transducer having hard magnetic shunt bias

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Line trapped charge discharging characteristic of gas insulated magnetic voltage transformer

Line charge, which is trapped after opening the line circuit breaker of a long overhead transmission line or power cable, is discharged through magnetic voltage transformers (VTs) or shunt reactors, if either is connected to the power line or cable. Although this duty is very important for a VT, there is no description or specification on the relevant international standards. The authors analyze the discharging conditions and their effects on the gas insulated magnetic VT design and propose a specification based on full-scale discharging tests at a laboratory using gas insulated magnetic VTs with various voltage ratings. >

IEE Power Division: Chairman's address. Power transformers—the second century

The first transformer was built in 1885. Progress for the first century was linear, based more on experience than on science. Improvements included material developments to reduce no-load loss generated in the core and load loss generated in the windings and structural parts. High capitalisation rates used to evaluate cost of ownership have driven materials suppliers to produce very low loss core steels and has encouraged the development of amorphous steel. Measures taken to control load loss have included the fitting of magnetic shunts to provide an alternative path for leakage flux. High reliability in service is a major requirement for power transformer design. New failure mechanisms have been identified that include part-winding resonance, fast-front transients, geomagnetic disturbances and static electrification. These new phenomena must be understood and design philosophies developed to encompass the potential problems. Progress in the second century is science based with the application of rigorous design control procedures to ensure that every innovative change is correctly reviewed to establish the pedigree of the change and foresee all possible ramifications of the change on the transformer in test or in service

Compensation Method for Phase Distortion of Output Voltage in the Three-phase Triport UPS System

A new three-phase constant-voltage transformer is described. In this circuit, load unbalance and input voltage asymmetry can in principle be removed by ring-connected compensation windings. When the, triac of an Automatic Voltage Regulator (AVR) is controlled to give a constant output voltage, phase differences between the output voltages are kept at 120°. This principle can also be applied to conventional three-phase constant-voltage transformers with magnetic shunts and to three-phase Triport UPS systems.

Compound, series, axial flux induction machines: single phase analogy

The characteristics of the single phase analogy of a pair of axial flux, polyphase induction motors having their respective stator windings and also their magnetic circuits in series, with provision for 'out of balance' flux, arising due to differences in the two rotor speeds, to pass through a saturating magnetic shunt are investigated. Theoretical and experimental results show that when such a pair of machines, fed from a single, variable frequency supply, is used to drive two wheels of one electronic vehicle, torque/speed characteristics that more closely match those of the ideal mechanical differential are obtained than when two independent induction machines are fed either in series or in parallel from a single supply.

Dynamic telephone receiver with magnetic shunt

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三相トライポートＵＰＳシステムにおける出力電圧位相歪の補償法

A new three-phase constant voltage transformer is presented. In this circuit, unbalance of loads and asymmetry of input voltages can be removed in principle by ring connected compensation windings. When the triac of Automatic Voltage Regulator (AVR) is controlled to give a constant output voltage, phase differences between output voltages are kept at 120 degrees. This principle can also be applied to the conventional three-phase constant voltage transformer with magnetic shunts or the three-phase Triport UPS system.

Dandy-Walker Cyst Upward Herniation: The Role of Magnetic Resonance Imaging and Double Shunts

Upward transtentorial herniation of a Dandy-Walker cyst is a potentially fatal complication, particularly after solitary shunting of the lateral ventricle for associated hydrocephalus. Two patients with upward transtentorial herniation of their Dandy-Walker cysts are presented to illustrate the diagnostic value of magnetic resonance (MR) imaging with the demonstration of unique 'keyhole' and 'snail' signs on the axial and sagittal MR images, respectively. In both patients, double and simultaneous shunting en-Y of a lateral ventricle and the posterior fossa cyst resulted in the resolution of the herniation syndrome.

Leakage flux in the steel tank of a 2.5-kVA single phase transformer

The effects of aluminum magnetic shielding and mild steel magnetic shunts on the leakage flux in the steel tank of a single-phase 50-Hz 2.5-kVA transformer and consequently on the tank temperature have been investigated.

Very high speed 450 pages-per-minute experimental magnetic printer

Starting from the MP magnetographic technology an experimental research program has been conducted to assess the potential of the technology for extension to much higher speeds. The magnetic shunt of the MP drum media was found to be the most limiting factor to significant speed increase. Characterization of various experimental media, in terms of write time constant, permitted to come up with a new 'fast' drum structure. As a result, a full function, 8 1/2 inch-wide, experimental magnetic printer was built and tested up to speeds of 450 pages per minute.

Leakage flux in a single phase transformer

The effects of aluminium magnetic shielding and mild steel magnetic shunts on the leakage flux in the steel tank of a single-phase 50 Hz low power transformer have been investigated.

Design of a passive magnetic shunt for the extraction of electron beams from a photon tagging spectrometer

A method is described in which a passive magnetic shunt is used to provide clean extraction of primary electron beams from a photon tagging spectrometer. For a wide range of magnetic fields and incident electron energies, the point at which the primary beam leaves the system can be very well localized. The design, fabrication and testing of the magnetic shunt are described.

Stray Losses in the Step of a Transformer Yoke with a Horizonatal Magnetic Shunt

Stray Losses in the Step of a Transformer Yoke with a Horizonatal Magnetic Shunt

Stray Losses in the Step of a Transformer Yoke with a Horizontal Magnetic Shunt

The distribution of stray losses in the step of a laminated transformer yoke with a horizontal magnetic shunt is solved using a network approach. Total losses, maximum loss density, and leakage flux return along the yoke all vary with gap spacings between shunt and yoke. Design trade-offs among these variables are possible through choice of gap spacings.

Active power loss in thick plate generated by one side inductor heater

A method of calculation of electromagnetic field and eddy-current losses produced in semi-infinite magnetic solid by a.c. flowing through parallel conductors in presence of a magnetic shunt in cylinder form is presented in the paper. The integral equation approach is applied, which permits to obtain an approximate solution of the problem considered. The distribution of the active power density on the surface of the conducting solid is considered.

Interaction of fluid dynamics phenomena and generator efficiency in two-phase liquid-metal gas magnetohydrodynamic power generators

The two-phase-flow (liquid-metal and gas) magnetohydrodynamic (LMMHD) generator and its associated thermodynamic cycle offer a promising alternative to conventional means of electrical power generation. Several advantages can be gained from its application. The LMMHD cycle can be applied to a very wide range of operating temperatures (heat sources) either alone or as a topping or bottoming part of a binary cycle. The potential is high for extreme design simplicity and reliability, because the need for high-speed rotating machinery, as used in turbine power plants, is eliminated. The electrical conductivities, proportional to the power densities, are higher by three or four orders of magnitude than in plasma MHD generators; thus, generator efficiency is potentially higher. Also, because of the intimate contact between liquid-metal and gas in the generator, the expansion process is nearly isothermal (an ‘infinite reheat’ turbine). Therefore, with proper heat regeneration, the cycle is a quasi-Ericsson cycle. The choice of working fluids may be either an ideal gas (e.g. helium, argon) or a condensible fluid (e.g. steam, CO 2). This paper relates the potential loss mechanisms in the LMMHD generator to various fluid dynamic phenomena that are discussed. Among these are effects resulting from velocity slip, vorticity generation and suppression by the magnetic field, wall friction, and shunt currents in liquid boundary layers. Experimental data relating to the internal flow phenomena and to overall generator performance are shown. The relative importance of these effects is discussed in relation to experimental evidence and known theory. It is concluded that the slip loss, resulting from a churn-turbulent flow pattern, is the major source of loss. A proposed means of creating a stable, homogeneous foam flow with virtually no slip, using the surface active properties of liquid metals, is discussed. Means are also suggested for reduction of wall shunt and frictional losses. The effects of end losses in two-phase flows are also described.

3-dimensional computation of the effect of the horizontal magnetic shunt on transformer leakage fields

By using a magnetic scalar potential function, leakage fields in a power transformer are calculated in three dimensions. The effects of the horizontal magnetic shunt are investigated with particular attention to the position of the shunt with respect to yoke. The calculations show how the leakage fields change with respect to the length of a small gap between shunt and yoke.

Influence of core gap in design of current-limiting transformers

Core gaps are used in the magnetic shunt paths of current-limiting transformers to limit secondary current under short-circuit conditions. It is shown here that for short-circuit current limited to twice normal a current limiting transformer has only 55% of the rating of a noncurrent-limiting transformer of the same physical size. Part of the reduction in rating stems from the space required for magnetic shunts, part from the greater space needed for winding insulation, and part from the increased loss due to the gaps. Reliability of a previously tested gap-loss equation is established, and design examples are given for both stamped laminations and strip-wound cores.

Magnetic Shunt for Three Phase Reactors

For three phase shunt reactors to function effectively in EHV power systems the behavior of the circuit reluctance must be known under all operating conditions. Difficulties have occurred in effectively designing electromagnetic circuits with multiple air gaps in shunt reactors. This paper describes design techniques for magnetic shunts which can be applied to three phase shunt reactors resulting in size and weight reduction. Performance characteristics of shunt reactors under imbalanced system conditions are presented and magnetic shunt performance for a 345 kV, 100 MVAR three phase shunt reactor is given.