FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
THE PATENTS RULES, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION
A system for monitoring atleast two transformers for hot spot formations therein
2. APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli,
Mumbai 400 030, Maharashtra, India, an Indian Company
3. INVENTOR
(a) Name : Pardesi Suraj
(b) Nationality : Crompton Greaves Limited, Electronic Development Centre, CG Global R&D Centre, Kanjurmarg (E), Mumbai 400042, Maharashtra, India
(c) Address : an Indian National
4. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed.

BACKGROUND OK THE INVENTION
Transformers have been an integral part of the power transmission and distribution system. Since the performance of almost all power equipments depend on the temperature they operate in, it is of a prime importance to monitor equipments such as transformers continuously for the temperature. In traditional methods used for temperature measurements thermocouples, thermistors or resistance thermometers generate electrical signals which are then converted into temperature readings.
However in applications such as the transformers it is desirable to measure temperature using non-electrical techniques to invade a transformer. These techniques are mainly desirable because of presence of high electric or magnetic fields. One method for measurement of the temperatures inside the transformers includes using fiber-bragg-grating principle.
Generally for temperature measurement techniques that use non-electrical invasion is one suggested in US 7127132B1 which discloses A fiber optic sensor system includes a plurality of sensor segments, each sensor segment further comprising a plurality n of sensor gratings for making measurements. Each sensor grating of the sensor segment operates within a unique wavelength channel, such that a plurality m of sensor segments have m sensors in each wavelength channel, and n wavelength channels, for the sensors. A broadband optical source is gated for a duration of time which enables individual all-of the sensors on a sensor segment to reflect optical signal corresponding to their center wavelength. In this manner, n wavelength channels of measurement can be time-multiplexed to measure sensors.

However, the above method may be restricted to be used on one equipment at a time. Since the fiber-bragg-grating principle makes use of costly equipments to analyze the signals use of such analysis equipment for each electrical equipment may not be economical.
There is therefore required a system which provides an economic and scalable system to detect hot-spots in transformers.
SUMMARY
A system for monitoring atleast two transformers for hot spot formations therein is described. In one embodiment of the present invention the system allows monitoring of two or more transformers using a single laser source and a single interrogator unit. The system utilizes fiber-bragg-grating sensors placed in fibers fitted onto each transformer for sensing the temperature using fiber-bragg-grating principle.
The system as described here for hot-spot measurement thus provides an economic method to enable use of single interrogator to analyze reflected signals corresponding to multiple electrical equipments such as transformers. Also fiber optic cable being all dielectric is very suitable for the application in transformers. The fiber-bragg-grating sensors can be incorporated into the windings during manufacture with ease. Also the system allows quasi distributed temperature measurements to be made with resolution of 0.1 °C and long term stability of better than 1°C. Using the above system, a network monitoring several transformers, some of which are even kilometers away can be implemented with least cost.

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. Although 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 a system for monitoring atleast two transformers for hot spot formations as per one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A system for monitoring atleast two transformers for hot spot formations therein is described. In one embodiment of the present invention the system allows monitoring of two or more transformers using a single laser source and a single interrogator unit, The system utilizes fiber-bragg-grating sensors placed in fibers fitted onto each transformer for sensing the temperature using fiber-bragg-grating principle.
The shift of wavelength is measured at an interrogator unit which conforms to more than one transformer.
In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without these details. One

skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into various assembly line stages. It is understood that one skilled in art may modify or change the data used in the examples described in the specification.
Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
A system for monitoring atleast two transformers for hot spot formations therein is described with reference to figure 1. In this exemplary embodiment two transformers 151 and 153 are being monitored continuously.
As per one embodiment of the present invention the system comprises of atleast two separate optical fibers 161, 163 containing fiber-bragg-grating sensors 161a, 163 a, located in each transformer. The placement of the fibre-bragg-grating sensors may depend on the conditions under which transformer operates and the accuracy of the temperature profile containing hot-spot details of the transformer required by the user. For example, the location of the fiber-bragg-grating sensors being close to each other would produce more detailed temperature profile of the transformer as compared to the condition where the fiber-bragg-grating sensors being kept at more distance from each other. The user may refer to an engineer who designs and monitors the system.

Each of the fiber-bragg-grating sensors is designed to reflect a particular wavelength which is distinct from the wavelength reflected by other fiber-bragg-grating sensor. A laser source 111 configured to produce an incident signal is needed in the system. The incident signal produced by the laser source is given to a circulator 121. The circulator is configured to receive the incident signal from said laser source and transmit the incident signals to each transformer intermittently. The circulator may intermittently switch between each transformer providing incident signal to one at a time. The circulator thereby isolates the signals received from each of the transformers.
The fiber-bragg-grating sensors located in optic fiber reflect the wavelength that they are designed for. As the temperature of the spot where the sensor is placed increases there is observed a shift in wavelength of the reflected signal there from.
The circulator receives corresponding reflected signals from each of the transformers and forwards the said reflected signal to an interrogator 123 which is further configured to compute respective temperature profile for hot-spot formations in each transformer using the reflected signals.
In one embodiment of the present invention an interface 125 may be used to receive the temperature profile of the transformers and present same to user in a graphical form. Any other ways of representing the analysis may be programmed therein. Also, the interface may be configured to accumulate the temperature profile of the transformers over a period of time to enable the user to analyze the shift in temperature of the individual spots.

The system as described here for hot-spot measurement thus provides an economic method to enable use of single interrogator to analyze reflected signals corresponding to multiple electrical equipments such as transformers. Also fiber optic cable being all dielectric is very suitable for the application in transformers, The fiber-bragg-grating sensors can be incorporated into the windings during manufacture with ease. Also the system allows quasi distributed temperature measurements to be made with resolution of 0.1 "C and long term stability of better than 1°C.
Using the above system, a network monitoring several transformers, some of which are even kilometers away can be implemented with least cost.
The foregoing description of the invention has been described for purposes of clarity and understanding. Although embodiments of the present invention have been described relative to a few standards, and associated attributes therein, one skilled in the art will recognize that the present invention is also very much applicable to other such methods and systems. It is not intended to limit the invention to the precise form disclosed. Various modifications may be possible within the scope and equivalence of the appended claims.

We Claim:
1. A system for monitoring atleast two transformers for hot spot formations
therein the system comprising:
atleast two separate optical fibers containing fiber-bragg-grating sensors, located in each transformer;
a laser source configured to produce an incident signal;
a circulator configured to receive the incident signal from said laser source and transmit the incident signals to each transformer intermittently, and receive corresponding reflected signals from each transformer thereby isolating the signals received from each of the transformers;
an interrogator configured to receive corresponding reflected signals of each transformer from said circulator and compute respective temperature profile for hot-spot formations in each transformer.
2. The system as in claim 1, wherein the temperature profile includes hot-spot measurement of each transformer.
3. The system as in claim 1, further comprising an interface to receive temperature profile of each transformer and present the findings to a user graphically.
4. The system as in claim 3, wherein the interface is also configured to store the
temperature profile of each transformer for analysis thereof over a period of time.

5. The system as in claim 1, wherein the circulator is configured to intermittently receive the incident signal from said laser source and transmit the incident signals to each transformer, and receie corresponding reflected signals from each of the transformer based on time division multiplexing of signals.