A METHOD AND DEVICE FOR MAGNETIC SHIELDING IN AN ELECTRICAL EQUIPMENT
Area of Invention:
[1] The invention generally relates to the field of electrical engineering and more particularly to a method and device for magnetic shielding in an electrical equipment.
Object of the Invention:
[2] It is an object of the invention to provide a method and a device for enabling magnetic shielding in an electrical equipment. It is also an object of the invention to advantageously reduce the electromagnetic interference present in an electrical equipment.
Prior Art:
[3] Switch-Mode Power Supplies (SMPSs) provide high power conversion efficiency along with their ability to regulated power to the electrical gadgets they are used. This has made SMPS very desirable in most of applications from a cell-phone charger to aviation and Space Electronic circuit.
[4] An SMPS comprises of
A control circuit;
Power switches (like transistor, MOSFET or IGBT);
Magnetics , including voltage step-up/step-down transformers, inductors.
[5] These inductors and transformers are fabricated using a variety of ferrite cores. The cores can vary in size, shape material content and density. They are selected in an application according to the requirements of power to be handled and frequency of operation.
[6] Among the different shapes, E-E, E-l and pot-cores are mostly used for the reason that winding can be done on a separate bobbin/ former and then the core can be slid into.
When the core is slid, there remains a very thin air gap between two surfaces. In case of filter inductors, air gap is inserted to avoid saturation of the core. This air gap allows a small amount of magnetic field to escape which becomes strong source of Electro Magnetic Induction (EMI).
[7] The conventional set up with E-E ferrite cores used for construction of transformers and filter inductors commonly used in SMPS is shown in Figurel. It also depicts the flux escaping from the gaps at interface of core elements. This occurs due to the presence of air in the gaps. The magnetic permeability of air is very less compared to ferrite material. Hence, the air is unable to link all the magnetic field lines (flux) from one core element to another, thereby causing an escape of flux into surroundings.
[8] Such a loss of flux is undesirable as it results in induction of electric currents due to EMI. The EMI effects are detrimental to the performance of the device such as SMPS. Hence such an effect should be mitigated to enhance the performance of SMPSs. Further, there is a need for a method and device that can effectively mitigate the EMI induced effects and act as a magnetic shield.
Brief Description of the Drawings:
Figure 1. shows a block diagram of a E-E type of cores commonly employed in the construction of transformers and filter inductors. The figure also highlights the flux leakage at the gaps of the core.
[10] Figure 2. shows a block diagram of a E-E type of core with magnetic shielding provided, according to an embodiment of the invention.
Summary of the Invention:
[11] The invention provides a method and a device for magnetic shielding in electrical
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equipment. More particularly, the invention provides a method and a device for advantageously reducing the undesirable effects of the induced EMI formed due to the flux leakage from the gap existing in the transformer and/or filter inductor core.
Detailed Description of the Invention:
[12] The invention described herein provide a method and device for magnetic shielding in an electrical equipment. There is a need for filling the gap that exists between the cores such as E-E type of cores commonly utilized in transformers and/or filter inductors in order to effectively reduce the EMI induced effects. The gap needs to be filled with a material that is magnetically conducting and electrically non conducting. The electrically non conducting property advantageously helps in reducing eddy currents. Further the said material employed having magnetically conducting and electrically non conducting property advantageously reduces the undesirable EMI effects by providing a magnetic shield.
[13] Further, the said material thus employed having Magnetically conducting and Electrically non-conducting property makes the magnetic field lines (flux) to be contained in the gap itself and avoid leaking outside. Such a prevention of leakage of magnetic fields from the cores of the transformers and/or filter inductors results in the said material performing the function of a magnetic shield. The utilization of the said material to be employed as a magnetic shield is illustrated by figure 2.
[14] In one embodiment of the Invention, ferrite powder is utilized as a magnetically conducting and electrically non-conducting material. The said ferrite powder should be electrically non-conducting to avoid eddy current losses. In an example of the invention the said ferrite powder is advantageously mixed with a bonding material such as a gel or fluid to hold the powder in place. Further the bonding material utilized should have viscosity
properties so as to be held in a very small gap. Also the mechanical properties of fluid
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should be persistent when subjected to heat developed in the device. The said ferrite powder and the said bonding material having the said properties such as thermal stability and high viscosity are mixed synergistically to achieve a stable sol-gel phase. In the said sol-gel phase, the said ferrite powder will have magnetically conducting and electrically non conducting properties. The sol-gel form of the ferrite powder thus obtained by the process as described herein is then filled into the gap existing in the cores of the transformers and/or filter inductors. The filling of the gap by the said sol-gel form of ferrite powder will allow maximum of the flux in the region of gap itself, minimizing the leakage to near zero.
[15] In addition to mechanical properties of this filling material, the magnetic properties also should be controllable. When inductors are designed to handle a DC component in the current through them, a reluctance is introduced in the magnetic path to avoid saturation of the core. A filling comprising merely of ferrite powder can result in alterations to the magnetic properties of the core. However, the said sol-gel form of the said ferrite powder filled in the said gap existing in the core of the inductors does not alter the magnetic properties of the device. The sol-gel form of the said ferrite powder enables controlling of the magnetic properties of the filling material. Further introduction of the said sol-gel form of the ferrite powder will mitigate the radiated EMI at the source itself and provides near 100% elimination of EMI from magnetic devices in SMPS, thereby effectively providing a magnetic shielding to the equipment.
[16] The invention described in detail herein and as illustrated by the examples provides a method and a device for magnetic shielding in an electrical equipment.
[17] The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person
skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
Claims:
We Claim:
1. A method for magnetic shielding in an electrical equipment wherein the said magnetic shielding is achieved by filling the gap existing in the cores of the transformers and/or filter inductors.
2. A method of Claim 1, wherein the said filling of the gap is achieved by a magnetically conducting and electrically non-conducting material advantageously inserted into the said gap.
3. A method of Claim 1, wherein the said material is a sol-gel form of ferrite powder.
4. A method of Claim 1, wherein the said sol-gel form of ferrite powder is obtained by synergistic mixture of ferrite powder and a bonding material such as a gel or fluid.
5. A method of Claim 1, wherein the said bonding material utilized for synergistic mixture of the said ferrite powder has properties such as high viscosity and high temperature tolerance.
6. A method of Claim 1, wherein the said high viscosity of the said bonding material enables to bind the said ferrite powder in the said gap and further wherein the said high temperature tolerance of the said bonding material advantageously prevents the melting of the said sol gel form of the said ferrite powder.
7. A method of Claim 1, wherein the said sol gel form of the said ferrite powder filled introduced in the said gap of the said cores effectively reduces the undesirable EMI induced effects.
8. A device for magnetic shielding in an electrical equipment wherein the said device
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comprises of
the said sol-gel form of the said ferrite powder introduced in the said gap of the said cores of transformers and/or filter inductors; and
the said transformers and/or filter inductors, wherein the said gaps in the said cores of the said transformers and/or filter inductors are advantageously filled with the said sol-gel form of the said ferrite powder.
9. A device of Claim 1, wherein the said sol-gel form of the said ferrite powder introduced in the said gaps of the said cores of said transformers and/or filter inductors advantageously provides a magnetic shielding by effectively mitigating the undesirable EMI induced effects.