|Title of Invention||
AN ELECTROMAGNETIC CURRENT LIMITER DEVICE
|Abstract||The present invention provides a one-pot process for the preparation of alkali metal salts of Feropenem. The present inventors has developed advantageous processes for preparation of alkali metal salts of feropenem and hydrates thereof in a one pot process avoiding the tedious work-up procedure and isolation of the intermediates at each stage.|
|Full Text||FORM -2
THE PATENTS ACT, 1970
(39 of 1970)
THE PATENTS RULES, 2003
(See section 10 and rule 13)
DEO PRAFULLA RAJABHAU
an Indian National
of X-17 MIDC Bhosari, Pune 411 026, Maharashtra, India
THE FOLLOWING SPEC IFICATION DESCRIBES THE INVENTION.
The present invention relates to the field of current limiters.
In particular, this invention relates to current limiters in alternating current circuits adapted for use during starting, stalling of AC motors or occurrence of overloads or faults in the electrical power system.
BACKGROUND OF THE INVENTION
Current limiting in Power systems and various components thereof is desirable to prevent overheating, voltage drops and system interruptions. Over-current conditions are created due to starting of large motors and short circuits.
Various current limiting devices are in use including thyristor devices, superconducting current limiters and fixed impedance inductors. Conventional Inductors with ferromagnetic or nonmagnetic cores are cost efficient, sturdy simple and reliable but are fixed impedance devices for a particular frequency and if kept continuously in circuit lead to running voltage drops under normal operations. The higher the value of the inductor impedance the better is the over-current control. But the normal running voltage drop increases proportionally. Switched inductors are not preferred due the switching time of switching devices. Large fixed impedance inductors will also lead to, fault hanging, wherein for high impedance faults the current is too low for protective relays to operate quickly and reliably.
Conventional fixed impedance inductors are built with windings wound on either a magnetic core or nonmagnetic core or a combination of the two. The
permeability of the core is substantially constant for the magnetization from low to saturation flux densities. This leads to a constant inductance value. When a magnetic field is applied a flux is forced through the soft ferromagnetic material. The flux is proportional to the magnetic field intensity. The ratio of flux density to the magnetic field intensity remains substantially constant. This ratio is called the permeability of the magnetic material (mu). Upon magnetization the unaligned domains rotate toward alignment in the direction of magnetization and the size of aligned domains increases.
The value of mu for isotropic materials is nearly constant from low flux density to peak flux density. Inductors built employing constant permeability magnetic materials will have nearly constant inductance and inductive reactance for low and high currents at same frequency.
There is thus a need for a current limiting proportional inductance device, which can be continuously in circuit, with very low impedance and voltage drop for normal currents, but responds to the over-currents instantaneously, by building up high impedance without switching devices, so that the current limiting action is proportional to the over-current.
It is an object of the present invention to provide for an inductive current limiting device that satisfies this need.
This invention discloses a current proportional incremental permeability electromagnetic current limiter (IPCL) utilizing the incremental permeability
of radially pre-aligned magnetic domains in two soft ferromagnetic material cores (SFMC) enclosing a current carrying winding of conducting material.
In accordance with one embodiment of the present invention there is provided a current proportional incremental permeability electromagnetic current limiter comprising: soft ferromagnetic incremental permeability cores enclosing a winding of electrically conducting material with insulated turns; and two terminals configured for attaching the device in series with an alternating current carrying conductor.
According to another aspect of this invention there is provide a current proportional incremental permeability electromagnetic current limiter device for current limiting in an alternating current circuit, comprising: a winding of conducting material enclosed by two incremental permeability soft ferromagnetic cores such that the device offers an inductance and inductive reactance incremental with the alternating current passing through the device so as to allow, alternating currents up to rated value to pass with negligible voltage drop, but to limit the higher alternating currents passing through the device upon starting, stalling of an AC motor or occurrence of a fault or overload condition in the circuit by providing a alternating current proportional impedance between the alternating current source and the alternating current load.
Typically, the increase in the winding current increases the permeability and flux per unit current in the radially pre-aligned magnetic domain soft ferromagnetic core, thereby increasing the inductance and inductive reactance of the winding till the soft ferromagnetic core saturates.
Typically, the property of incremental permeability in the soft ferromagnetic core is achieved by pre-alignment of the magnetic domains in the soft ferromagnetic core material in a direction perpendicular to the direction of flux produced in the core due to the current in the winding.
These and other features , aspects and advantages of the present invention will be described in the following detailed description when read with reference to the accompanying drawings where like characters represent like parts throughout the drawings.
FIG. 1 is the cross sectional view of the soft magnetic core with randomly
aligned magnetic domains with reference to the background art;
FIG. 2 is the cross sectional view of the soft magnetic core after cold
working to achieve radially aligned magnetic domains in accordance with
the preferred embodiment;
FIG.3 illustrates the incremental permeability curve of the core in
accordance with the preferred embodiment;
FIG 4 illustrates the perspective view of the current proportional incremental
permeability electromagnetic current limiter arrangement in accordance with
the preferred embodiment;
FIG. 5 illustrates the connection of the present invention as a soft starter
and current limiter for AC motors;
FIG. 7 illustrates the connection of the present invention as a current limiter
at the bus tie line.
Fig 1 of the accompanying drawings illustrates schematically a cross section of isotropic soft magnetic material core (SFMC) 12, wherein the magnetic domains 13 are randomly aligned so that the net alignment is nearly zero in the un-magnetized condition.
When a magnetic field of intensity H is applied a flux Phi is forced through the soft ferromagnetic material. The flux is proportional to the magnetic field intensity. The ratio of flux density B to the magnetic field intensity H remains substantially constant. This ratio is called the permeability of the magnetic material (mu). Upon magnetization the unaligned domains rotate toward alignment in the direction of magnetization and the size of aligned domains increases.
As stated earlier the value of mu for isotropic materials is nearly constant from low flux density to peak flux density. Inductors built employing constant permeability magnetic materials will have nearly constant inductance and inductive reactance for low and high currents at same frequency.
In the preferred embodiment, methods are disclosed for the construction of a current proportional incremental permeability inductive current limiter (IPCL).
FIG. 2 illustrates a typical cross section of a cold worked incremental permeability soft magnetic core (IPSFC) 12, with radially aligned magnetic
domains 8, in accordance with the present invention. Cold working processes such as pressing, bending & punching induce radial stresses in the core material such as silicon steel and magnetic steel which results into pre-alignment of magnetic domains in the radially outward direction.
FIG.3 illustrates the incremental relationship between the permeability mu of the IPSFC with respect to the magnetic field strength H in the present invention when H is in a direction perpendicular to the domain pre-alignment. For the radially pre-aligned domain condition as illustrated in FIG 2 the circumferential direction is perpendicular to all the magnetic domain directions. The permeability is low for low H and increases with higher H. As the magnetic domains are radially pre-aligned they do not move or grow with small value of circumferential H. For higher H values magnetic domain rotation and growth is achieved resulting into higher mu.
Fig 4 is a perspective view of one embodiment of the present invention wherein the Current proportional incremental permeability inductive current limiter (IPCL) 1 comprises; a coil 4, of electrically conducting material 5, incremental permeability soft ferromagnetic cores (IPSFC) 2,3 with central holes 9, with radially outward pre-aligned domains 8 , enclosing the two coil sides 10,11, set of two terminals 6,7 for connecting the IPCL in series with an AC current I carrying conductor from the supply to the load.
When a current I passes through the coil 4, a magnetic field intensity H is produced as per the relationship
H = N*I (1)
where, N is the number of turns of the coil 4.
The direction of the magnetic field H is circumferential which forces a flux per unit current (Phi/I) through the IPSFC 2,3 as per the relationship
(Phi/1) =(N*mu*h)/ (Pi*D*T) (2)
D is the effective mean diameter of the IPSFC, mu is the permeability of the IPSFC, H is the length of the core and T is dimension from inner hole periphery to the outer diameter of the core. The terms N, D, H and T are constants for a particular dimension of winding and soft ferromagnetic core. Thus (Phi/I) is directly proportional to mu for a particular winding and core.
For values of current less than or equal to rated current the magnetic field intensity is low and is not enough to align the magnetic domains in the IPSFC to the direction of magnetization resulting into low mu and low (Phi/I). For high values of current such as starting of AC motors or overloads or faults in the power system the magnetic field intensity is high and sufficient to progressively align the magnetic domains with the direction of magnetization resulting into a higher mu and hence higher (Phi/I).
The inductance of the current carrying winding is
L = N* (Phi/I) (3)
For values of current less than or equal to rated current (Phi/I) is low and hence inductance (L) is low. For high value of current (I), (Phi/I) is high, and consequently the winding inductance (L) is high.
The impedance (Z) offered by the IPCL device for alternating currents is governed by the equation
Z = R+jX (4)
where, R is the resistance of the winding and is negligible and X is the inductive reactance given by
where f is the frequency of supply and L is the inductance of the winding.
The Current proportional incremental permeability electromagnetic current limiter device (IPCL) thus has a low inductive reactance(X) for low alternating currents and high inductive reactance(X) for high alternating currents. The IPCL device hence acts as a current limiter for alternating current circuits.
The important consideration for design the choice of inner hole diameter and number of turns so that the magnetic field intensity H for normal currents is low giving low permeability. Second important consideration for design is to choose the mean diameter D and radial thickness T such that the IPSFC does not saturate at the maximum current value.
This in accordance with a preferential embodiment of this invention there is disclosed a current proportional incremental permeability electromagnetic current limiter device
( 1 ) comprising : incremental permeability soft ferromagnetic cores (2,3 ) enclosing a winding(4) of conducting material(5) with connection terminals(6,7) wherein an alternating current in the winding(4) produces a flux per unit current in the soft ferromagnetic cores(2,3) proportional to the alternating current ; any one of the connection terminal(6) or( 7) connected to an alternating current source and second terminal (7)or (6) connected to
an alternating current load wherein the device operates so as to produce a low inductance and inductive reactance at lower alternating currents and high inductance and inductive reactance at higher alternating currents to limit the current passing though the device upon occurrence of a fault or overload or AC motor starting or stalling.
While considerable emphasis has been placed herein on the specific structure of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.
|Indian Patent Application Number||305/MUM/2008|
|PG Journal Number||04/2014|
|Date of Filing||12-Feb-2008|
|Name of Patentee||DEO PRAFULLA RAJABHAU|
|Applicant Address||FLAT NO.6, S.N.1/8 JEEVAN SANGEET APARTMENT, ERANDWANE, PUNE-411004|
|PCT International Classification Number||H02H9/02|
|PCT International Application Number||N/A|
|PCT International Filing date|