FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
AN IMPROVED CURRENT TRANSFORMER;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF INVENTION
The present invention relates to current transformers. BACKGROUND OF INVENTION
Current sensors like Rogowski coils and Hall effect transducers have gained large dominance as a current measurement technique owing to low cost, high reliability, high accuracy and wide measuring range. The conventional technique of current measurement includes use of iron core current transformed which can be rather bulky and saturate quite early due to use of laminated iron cores. air core rogowski coils offer.multiple advantages over the existing techniques.
However, such coils are incapable of delivering adequate power output for signal processing, annunciation or operating tripping devices. Also, other electronic sensors like hall effect sensors require auxiliary power. TO overcome this disadvantage, Power Current transformers are used in conjunction with such sensors.
A novel current transformer is therefore required for an improved VA characteristics and the same is disclosed as follows.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide improved designs in current transformers used in measurement and powering purposes-
Another object of the present invention is to offer relatively flat VA output characteristics so as to satisfy the purpose of supplying power for metering, signal processing, annunciation and operating actuating devices in limited space constraint.
Yet another object of the present invention is to draw power from current flow in an electrical conductor by using an iron core current transformer and to limit the power output by either restricting the flux through the iron core or bypassing it away from the secondary coil.
In accordance with this, there is provided an improved and compact current transformer. The improved current transformer comprises a primary coil, a secondary coil, a main core on which a laminated ferromagnetic flux bypass path is adhered, and a bypass arrangement.
The bypass arrangement may have a bypass limb held in place through plastic spacers. The bypass arrangement may be placed between primary coil and secondary coil. When

current passes through the primary coil, the output from the secondary coil can be clamped by ensuring that the main core saturates at a very low operating currents and then the flux is partially diverted to the bypass arrangement.
In various embodiments herein the power delivered by the secondary coil depends on the net iron weight of the core. Also the output power is clamped effectively after a particular magnitude of current.
In one embodiment herein, the bypass arrangement is incorporated within the current transformer.
In one embodiment herein the bypass arrangement is external to the current transformer.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Afthough the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Fig. 1 shows the improved current transformer with the bypass arrangement incorporated within the current transformer according to an embodiment of the present invention.
Fig. 2 shows the improved current transformer with the bypass arrangement external to the current transformer according to an embodiment of the present invention.
Fig. 3 shows the different shape or profile of the bypass arrangement according to an embodiment of the present invention.
Fig. 4 shows the bypass limb extruding out of the plane of main iron core path according to an embodiment of the present invention.
Fig. 5 is the graph of improved current transformer versus the conventional current transformer.
DESCRIPTION OF THE INVENTION
The present invention provides improved designs in current transformers used in measurement and powering purposes and thus offering relatively flat VA output characteristics so as to satisfy the purpose of supplying power for metering, signal processing, annunciation and operating actuating devices in limited space constraint.
In one embodiment herein, an improved current transformer comprising a bypass arrangement including a bypass limb held in place through plastic spacers. The bypass

arrangement may be placed between primary coil and secondary coil such that when current passes through the primary coil, the output from the secondary coil can be clamped by ensuring that the main core saturates at very low operating currents and then the flux is partially diverted to the bypass arrangement.
Fig. 1 shows the improved current transformer with the bypass arrangement 101 incorporated within the current transformer according to an embodiment of the present invention. The improved current transformer comprises a primary coil 103, a secondary coil 102, a main core 104 on which a laminated ferromagnetic flux bypass path 101 is adhered, and a bypass arrangement.
The bypass arrangement 101 comprises a bypass limb held in place through plastic spacers, and a bypass structure placed between primary coil 103 and secondary coil 102. When current passes through the primary coil 103, the magnetic field flux generated by the coil 103 due to current flow links with the laminated iron core 104 and thereby an EMF is induced in the secondary coil 102 owing due Faraday's induction principle. The power delivered by the secondary coil 102 depends on the net iron weight of the core 104.
As a limited output is only needed in general cases, the output can be clamped by ensuring that the main iron core 104 saturates at a very low operating currents and then the flux is partially diverted to the bypass arrangement 101. This not only ensures that output power is clamped effectively after a particular magnitude of current but also the ratings of electronic components which are required for rectification and efficient utilization of derived power get reduced. Thus the presents invention provides a very compact technique for drawing operational power in conjunction with a Rogowski coil or any other current sensor known in the prior art.
Fig. 2 shows the improved current transformer with the bypass arrangement 101 external to the current transformer according to an embodiment of the present invention. The figure illustrates an alternate arrangement 101 having spacers 201 along the similar principles as mentioned in Rg1. The only difference being that the bypass arrangement 101 and spacers 201 are completely external to the current transformer. Any of the embodiments as shown in Fig. 1 and Fig. 2 may be employed depending on the space available in a given electrical unit or system. The second arrangement is slightly more advantageous as it would need lesser magnetizing power due to small iron core path in the similar space configurations. However, from this arrangement, the output may not get absolutely clamped as some part of the flux from the primary coil can get directly linked to the secondary coil.
Further, this arrangement also needs an external clamping assembly to hold the outer bypass limb in place.

In both the arrangements as discussed in Fig. 1 and Fig. 2, the spacers decide the air gap in the bypass route and are thereby instrumental in deciding percentage of flux that gets diverted after primary core saturation.
Fig. 3 shows the different shape or profile of the bypass arrangement according to an embodiment of the present invention. The bypass path is an external component which may be easily assembled in an existing current transformer configuration. Also, the bypass arrangement delivers the flexibility of using other lower permeability materials as any specific design may demand. The structure also offers the advantage of choosing any shape or cross-section as demanded by space constraints (rectangular, circular or any other arbitrary shape).
Fig. 4 shows the bypass limb extruding out of the plane of main iron core path according to an embodiment of the present invention. In certain designs, the improved current transformers may also be modified to have the bypass limb extruding out of the plane of main iron core path so as to enhance the flux bypass feature.
Fig. 5 is the graph of improved current transformer versus the conventional current transformer.
Thus the present invention provides an improved current transformer that is compact in size, reliable and gives consistent power output applicable for AC systems. Also, complete electrical isolation of the sensor from the live conductor can be ensured.
Further there are no temperature rise issues and the manufacturability and assembly of the improved current transformer is also very simple and easy.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

We Claim
1. An improved current transformer comprising:
a primary coil;
a secondary coil;
a main core on which a laminated ferromagnetic flux bypass path is adhered;
a bypass arrangement placed between primary coil and secondary coil, the bypass arrangement having a bypass limb held in place through plastic spacers;
wherein when current passes through the primary coil, the output from the secondary coil can be clamped by ensuring that the main core saturates at a very low operating currents and then the flux is partially diverted to the bypass arrangement.
2. An improved current transformer as in claim 1, wherein when current passes through the primary coil, the magnetic field flux generated by the coil due to current ffow, links with the laminated iron core and thereby inducing an EMF in the secondary coil.
3. An improved current transformer as in claim 1, wherein the power delivered by the secondary coil depends on the net iron weight of the core.
4. An improved current transformer as in claim 1, wherein the output power is clamped effectively after a particular magnitude of current.
5. An improved current transformer as in claim 1, wherein the ratings of electronic components required for rectification and efficient utilization of derived power get reduced.
6. An improved current transformer as in claim 1, wherein the bypass arrangement is of different shape and profile.
7. An improved current transformer as in claim 1, wherein the bypass arrangement is incorporated within the current transformer.

8. An improved current transformer as in claim 1, wherein the bypass arrangement is external to the current transformer.