• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.2
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• pp.59-64
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• 2001

The distribution of current in the conductors influenced by the armature geometry and velocity is an important parameter for determining performance of an electromagnetic launcher(EML). the electric current in the early launching stage tends to flow on the outer surfaces of the conductors, resulting in very high local electric current density. However, the tendency for current to concentrate on the surface is driven by the velocity skin effect later in launching stage. The high current density produces high local heating and, consequently, increases armature wear which causes several defects on EML system. This paper investigates the effects of rail/armature geometry on current density distribution, launcher inductance gradient (L'), and contact force. Three geometrical parameters are used here to characterize the railgun system. These are the ratio of contact length to root length, relative position of contact leading edge to root trailing edge, and the ratio of rail overhang to the rail height. The distribution of current density, L', contact force between various configurations of the armature and the rail are analyzed and compared by using the EMAP3D program.

• 전기의세계
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• v.21 no.4
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• pp.15-21
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• 1972

For the conventional DC machine, the armature MMF is negligible compared with field MMF except when the machine is under heavy load or transient conditions. During the motor starting or reversal, the transient armature current and corresponding MMF effect the flux density of each pole in the machine magnetic circuit. However, the circuit flux density is restored to normal values by the field winding MMF after the transient armature current dies in an electromagnetic DC motor. Permanent magnet servomotor have no field windings about the circuit poles to restore circuit flux density through the demagnetized part of each pole after the transient armature MMF dies, and portions of the magnetic circuit stay permanently demagnetized. Thus the problem of stabilizing a magnet pole piece under the influence of the transient armature current need attentions. This work present the recoil operation of the servomotor with PM poles in conjunctions with the influence of the armature reaction effect. The development of an analytical and quantatative study is presented for predicting the regime of the recoil operation under this condition.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.21-26
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• 2001

Superconducting synchronous generators and motors are designed based on 2 dimensional electro-magnetic approach. In the case of generator, if the machine output rating and terminal voltage are decided the armature rating current will be decided automatically according to its power factor. However, in the case of motor, if the output rating is given with [hp] or [kw] units, the armature terminal voltage and current are not decided directly because the machines armature input power and mechanical output are different by way of losses. So in order to calculate the armature current more accurately. the machine losses must be included in the design procedure. In this paper the machine loss of superconducting motor are analyzed and used for decision of the armature input power and current. Moreover, the differences of voltage equations between superconducting synchronous generator and motor are considered.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1674-1681
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• 2015

This paper presented an improved analytical method for calculating armature-reaction field in the surface-mounted permanent magnet machines accounting for opening slots. The analytical model is divided into two types of subdomains. The current of the armature is centralized in the center of the slots. The field solution of each subdomain is obtained by applying the interface and boundary conditions of the model. Two 30-pole/36-slot prototype machines with different slot-opening width are used for validation. The FE (finite element) results confirm the validity of the analytical results with the proposed model. The investigation shows that the wider the slot-opening width is, the smaller the peak value of radial and circumferential components of flux density, and the analytical armature-reaction field produced by centralized current in the slots is similar with the armature-reaction field produced by distributed current in the slots in the FE.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1639-1647
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• 2016

This paper deals with eddy current loss analysis of Slotless Double sided Cored type permanent magnet linear generator by using analytical method, space harmonic method. In order to calculate eddy current, this paper derives analytical solution by the Maxwell equation, magnetic vector potential, Faraday's law and a two-dimensional(2-D) cartesian coordinate system. First, we derived the armature reaction field distribution produced by armature wingding current. Second, by using derived armature reaction field solution, the analytical solution for eddy current density distribution are also obtained. Finally, the analytical solution for eddy current loss induced in permanent magnets(PMs) are derived by using equivalent, electrical resistance calculated from PMs volume and eddy current density distribution solution. The analytical result from space harmonic method are validated extensively by comparing with finite element method(FEM).

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.1
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• pp.101-109
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• 1993

Dynamic characteristics of an electro-magnetic clutch transmission system were investigated by using Bondgraph modeling method. Simulation results showed that when the rotor engaged with the armature, the response time of the current, the driver torque, the rotational speed and the relative sliding time between the driver and the driven side decreased, as the gap size between the rotor and the armature decreased and the number of coil turns increased. Also, when the rotor disengaged with the armature, the delay time increased with the decreased gap size and the increased number of coil turns. It was found that the experimental results of the current, the driver torque, the rotational speeds were in good accordance with the theoretical results. The results of this study can be used as basic design materials of the electro-magnetic clutch.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.12
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• pp.848-855
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• 1987

The currents in the rails of an electromagnetic railgun are concentrated in a near surface region. In order to understand this phenomenon, this paper deals with computation of the current distribution related to skin effect in a railgun. An analytical solution is obtained for a twodimensional model. It is found that current concentration at the interface between the rails and the armature is affected by the velocity, length and conductivity of the armature, that skin effect in the rails is affected by the relative velocity between the rails and the armature rather than other factors, and that skin depth in the rails is inversely proportional nearly to the square root of the velocity.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.10
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• pp.694-701
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• 1988

Distributed-type railguns are designed to maintain the armature current and the length between the armature and the current-feed region nearly constant with time. This paper deals with factors affecting current distribution, effective resistance and effective skin depth in the rail of a distributed-type railgun. Analytical solutions for the current distributions and resistance in the rail are presented for a simple two-dimensional model under steady-state contions. For diffusion limited current, it is found that effective rail resistance is proportional to the square root of the relative velocity, the permeability of the rail and the length between the armature and that effective skin depth of the rail is proportional to the square root of the length and inversely proportional to the square root of the permeability, the conductivity and the velocity.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.5-9
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• 1990

A permanent magnet synchronous motor(PMSM) differs from an ordinary synchronous motor in that the former has no field winding and the field flux can not be controlled by field current. A field-weakening control of PMSM utilizing the demagnetization due to d-axis armature reaction is equivalent to reducing the field current. In this paper, the armature resistance is considered for the optimum field-weakening control.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.73-75
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• 1993

In this paper, the transient shielding characteristics of slitted electrothermal shield of superconducting alternator is studied. The field current and the armature currents variations during three phase short circuit fault are calculated and compared to those of the conventional one. And the response of the armature current due to step-up of the excitation voltage showes the feasibility of the quick response excitation system available for improving the transient stability.