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)
TITLE OF THE INVENTION
Load current sensing power distribution transformer
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Bes£mt Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Yargole Arun Dattatraya of Crompton Greaves Ltd , New Product Technology Cell, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India, an Indian National
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed :

FIELD OF THE INVENTION
This invention relates to a load current sensing power distribution transformer.
This invention also relates to a method for measuring the load current being drawn from a power distribution transformer,
BACKGROUND OF THE INVENTION
Power distribution transformers are generally oil filled type or dry type. A power distribution transformer comprises atleast one primary or low voltage winding and atleast one secondary or high voltage winding wound on a magnetic material core. In the case of an oil filled transformer the core coil assembly is immersed in transformer oil contained in a tank. In the case of a dry transformer, the core coil assembly is impregnated or encapsulated with a resin. Overloading of a power distribution transformer due to overdrawing of current, authorised or otherwise, is one of the main reasons for premature transformer failure. It can also lead to explosions and accidents. Current and volt meters are generally used to measure the current flowing through the transformer and to measure the voltage across the transformer respectively. These meters are located outside the transformer and current being drawn from the transformer is calculated based on the readings of the current and volt meters. Since the current and volt meters are located outside the transformer, they can be easily tampered with.
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OBJECTS OF THE INVENTION
An object of the invention is to provide a load current sensing power distribution transformer which cannot be tampered with and which senses the current being drawn from the transformer accurately.
Another object of the invention is to provide a load current sensing power distribution transformer which is simple in construction and is cost effective.
Another object of the invention is to provide a load current sensing power distribution transformer which is reliable and which prevents premature failure of the transformer and also accidents.
Another object of the invention is to provide a method for measuring the load current being drawn from a power distribution transformer which method is simple, easy and convenient to carry out and is reliable and accurate and is tamper proof.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a load current sensing power distribution transformer comprising a sensor comprising a sensor coil wound on a magnetic material core and mounted on the transformer core or mounted in the proximity of the transformer windings electrostatically shielded from the transformer windings.
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According to the invention there is also provided a method for measuring the current being drawn from a power distribution transformer, the method comprising sensing the voltage or current induced by the leakage flux from the transformer core within the transformer and processing the voltage or current signal.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Figs 1, 2 and 3 are top view, elevation and side view of a single phase power distribution transformer according to an embodiment of the invention;
Fig 4 is a view of the sensor of the transformer of Figs 1, 2 and 3;
Fig 5 is a load current vs induced voltage graph across the sensor of a typical power distribution transformer of the invention; and
Fig 6 is a load current vs ampere turns graph of the sensor of a typical power distribution transformer of the invention.
The transformer 1 as illustrated in Figs 1 to 4 of the accompanying drawings comprises a primary winding 2 and a secondary winding 3 wound on a former 4 and inserted over a magnetic material core 5. 6 is a sensor coil wound on a magnetic material core 7 and mounted on the transformer core 5 and electrostatically shielded from the windings by non-magnetic metallic support such as aluminium support 8. Instead of mounting the sensor on the transformer core it can also be mounted or
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located in the proximity of the transformer windings electrostatically shielded from the windings. During operation of the transformer, there will be always a magnetic flux flowing through the transformer core 5 and there will be always a leakage flux flowing out of the core 5. This leakage flux is proportional to the current being drawn from the transformer and it induces a voltage across the sensor coil. The induced voltage across the sensor coil or the current being drawn from the sensor coil due to the induced voltage is a measure of the current being drawn from the transformer. The voltage or current signal from the sensor coil is processed to measure the current being drawn from the transformer.
.A sensor coi) comprising 60 turns was wound on a magnetic materia} core and mounted on the core of a 25 KVA power distribution transformer. The sensor coil was electrostatically shielded from the transformer windings by an aluminium sheet support. Voltage across the primary and secondary of the transformer were 6.35 V and 250 V, respectively. Voltage across the sensor coil at different percentages of load currents were measured and were as shown in Fig 5 of the accompanying drawings. Load current x ampere turns (AT) at various percentages of load current were measured and were as shown in Fig 6 of the accompanying drawings. Figs 5 and 6 clearly show that both voltage and current across the sensor coil and through the sensor coil respectively increased linearly with the increase in the percentages of load current.
As is evident from the above experimental data, the transformer of the invention comprising the sensor is a reliable and accurate in sensing and indicating the load current being drawn from the transformer. The invention helps to monitor the current
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being drawn from the transformer. Consequently appropriate and timely action can be taken to maintain the health of the transformer and to prevent premature failure of the transformer and accidents. As the leakage flux is proportional to the current being drawn from the transformer, the induced voltage and current in the sensor coil also indicate accurately the current being drawn from the transformer. Therefore, the method of the invention is also reliable. Besides the method is simple and easy to carry out. As the sensing is done within the transformer, tampering is not possible and the invention is tamper proof. The cost of the sensor is negligible. Therefore, the transformer of the invention is cost effective. Besides it is also simple in construction.
The transformer can comprise more than one phase. There can be more than one primary and secondary windings. Such variations of the invention are obvious to those skilled in the art and are to be construed and understood to be within the scope of the invention.
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We claim :
1) A load current sensing power distribution transformer comprising a sensor comprising a sensor coil wound on a magnetic material core and mounted on the transformer core or mounted in the proximity of the transformer windings electrostatically shielded from the transformer windings.
2) A method for measuring the current being drawn from a power distribution transformer, the method comprising sensing the voltage or current induced by the leakage flux from the transformer core within the transformer and processing the voltage or current signal.
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