FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003 COMPLETE SPECIFICATION
(See Section 10 and rule 13)


TITLE OF THE INVENTION:
TRIP DEVICE FOR AIR CIRCUIT BREAKER
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra . INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to the circuit breakers and particularly to a trip device used in the air circuit breakers. The present invention more particularly relates to a current transformer for the trip device used in the air circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] Generally a trip device in the air circuit breaker is used to trip the current flow in an electrical power circuit which is to be protected during overload or short circuit conditions. The typical trip device includes a plurality of current transformers which is associated to a conductor of the electrical power circuit. The current transformer commonly includes a secondary winding and a core surrounding the conductor of the electrical power circuit. The conductor of the electrical power circuit carries an alternating current through it. The current transformer surrounding the conductor of the electrical power circuit induces a current in the secondary winding, which is proportional to the alternating current flowing through the conductor of the electrical power circuit due to electromagnetic induction.
[0003] The trip device includes electronic tripping circuitry which is connected to the secondary winding of the current transformer. The current transformer in the trip device supplies the electrical power that is necessary for the operation of the electronic tripping
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circuitry. The current transformer are supposed to provide a low intensity secondary current which is proportional to very high primary current, to the electronic tripping circuitry.
[0004] The current transformers have the potential to cause damages to the electronic tripping circuitry by providing excess power during over load and short circuit conditions. Hence there is a need to provide the trip devices with the current transformers which are suitable to dissipate the excess energy transformed into heat in the transformer itself. Also there is a need to develop a current transformer which reduces the secondary current induced at high current level in the primary conductor to limit the excess power supplied to the electronic tripping circuitry.
[0005] Further there is a need to provide an electrically saturated current transformer to eliminate the problems such as bigger size and overheating across the whole range of the trip devices. There is yet another need to provide a saturated current transformer having a non-linear response, which limits the excess power supplied to the processing unit of the trip device and dissipates the excess power in the current transformer itself.
[0006] There is a requirement to design a low cost electrically saturated current transformer which ensures the satisfactory operation of the trip device fitted in the air circuit breaker, between 0.2 to 10 times rated primary current in the primary conductor. Also there is a need of a compact trip device accommodating multiple ratings of primary current.
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[0007] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECTS OF THE INVENTION
[0008] The primary object of the present invention is to develop a trip device with an electrically saturated current transformer for air circuit breakers.
[0009] Another object of the present invention is to develop a trip device provided with an electrically saturated current transformer which is saturated based on the principle of impedance addition to limit the current supplied to the processor units, even when a high current is passed through the primary of the transformer.
[0010] Yet another object of the present invention is to develop a trip device provided with an electrically saturated current transformer to dissipate the excess power in the current transformer itself and to limit the excess power supplied to electronic circuitry of the processor unit.
[0011] Yet another object of the present invention is to develop a trip device with electrically saturated current transformers to provide satisfactory operation, even when a current of 0.2 to 10 times the rated current is passed through the primary.
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[0012] Yet another object of the present invention is to develop a trip device with an electrically saturated current transformer to eliminate the problems such as bigger size and overheating across the whole range of the breaker ratings.
[0013] Yet another object of the present invention is to develop a trip device with an electrically saturated current transformer having a non-linear response, to limit the excess power supplied to the processing unit of the trip device and to dissipate the excess power in the current transformer itself.
[0014] Yet another object of the present invention is to develop a trip device with a low cost, electrically saturated current transformer to ensure the satisfactory operation of the trip device between 0.2 to 10 times the rated primary current in the primary conductor.
[0015] Yet another object of the present invention is to develop a compact trip device with an electrically saturated current transformer to accommodate multiple ratings of the primary current.
[0016] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
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D) SUMMARY OF THE INVENTION
[0017] The various embodiments of the present invention provide a trip device comprising electrically saturated current transformer for air circuit breakers. According to one embodiment of the present invention, a trip device for an air circuit breaker has a current sensor and a processor unit connected to the current sensor. At least one transformer is connected to the processor unit. A metering and protection circuit is connected to the current sensor. The transformer is added with reverse turns in at least one limb in the core to saturate the current passed through the transformer to limit the current supplied to the processor unit, when a high current is passed through the primary conductor. The transformer is added with reverse turns in atleast one limb to add the impedance to the transformer so that the effective number of turns is less than the total number of turns to ensure the early power on the processor unit and to limit the current passed to the processor unit through the secondary winding, when a high current is passed through the primary of the transformer. The transformer is a current transformer with a rectangular core or a circular core. The current sensor is an air core sensor. The reverse turn is formed at anywhere in the windings provided at the transformer.
[0018] According to one embodiment, a trip device used in the air circuit breakers comprises a plurality of current transformer, a current sensor such as an air core sensor, a processing unit including electronic tripping circuitry and metering and protection circuits. The current transformer is used to power-on the processing unit from which a trip command is to be sent to the air circuit breaker during over load and short circuit
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conditions. The current sensor is connected to the metering and protection circuits of the trip device.
[0019] The current transformer comprises a core such as a rectangular core, circular core ,etc, surrounding a primary conductor of a power circuit and a secondary winding having reverse turn winding wound on a part of the core. The primary conductor of the power circuit carries a primary current from the main power to the load devices in the power circuit. The current transformer is associated to the primary conductor in which the primary current flows. The secondary winding of the current transformer includes output wires which are connected to the processing unit of the trip device. The output wires of the secondary winding supplies current to the processing unit for the operation of the trip unit.
[0020] The rectangular core of the current transformer includes two limbs in which either of the limbs or both the limbs are added with the reverse turn winding. The reverse turn windings provided on both the limbs are either equal or unequal. The saturation of the current transformer is obtained by providing the core of the current transformer with the reverse turn windings. Hence the effective number of turns on the limb of the core is less than the total number of turns on the limb to ensure the power-on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
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[0021] The reverse turn winding on each limb increase the impedance of the current transformer at saturation. Due to increasing of impedance, the secondary winding of the transformer induces only essential amount of current even when the primary current carried through the primary conductor of the power circuit is high. The current transformer dissipates the excess power in the current transformer itself and prevents from the situation of the excess power supplied to the electronic circuitry of the processing unit, since the current transformer has a non-linear response. The percentage of the saturation in the current transformer is dependent on the position and number of turns of the reverse windings on each limb of the current transformer.
[0022] According to one embodiment of the present invention, the core of the current transformer is made up of iron material such as Cold Rolled Grain Oriented steel (CRGO). A graph curve is drawn for the CRGO steel using magnetic flux density (B) at Y-axis and magnetic field strength (H) at X-axis. At lower zone of the B-H curve of the CRGO steel, the resistance of the reverse turn winding is low as the permeability of the core is high (i.e. L»R). Hence the impedance of the current transformer remains the same when normal primary current flows in the primary conductor and the secondary winding induces the essential amount of current to provide the processing unit of the trip device.
[0023] At upper zone of the B-H curve, the resistance of the reverse turn winding is high where the permeability of the core decreases (i.e. L«R). Hence the impedance of the current transformer increases when higher primary current flows in the primary conductor, due to the increase in the resistance of the reverse turn winding. Because of the high
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impedance of the current transformer during the higher primary current at the primary conductor, the excess power is dissipated in the current transformer itself and the essential current is only induced in the secondary winding. Also the secondary windings are arranged in opposite directions, the inductive effect of the winding gets cancelled at all operating points.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0025] FIG. 1 illustrates a schematic representation of a current transformer in a trip device for an air circuit breaker according to one embodiment of the present invention.
[0026] FIG. 2 illustrates a schematic representation of a current transformer in a trip device for air circuit breaker according to one embodiment of the present invention.
[0027] FIG. 3 illustrates a schematic representation of a current transformer with reverse turn windings at both the limbs in a trip device for air circuit breaker according to one embodiment of the present invention.
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[0028] FIG. 4 illustrates a schematic representation of a current transformer with reverse turn windings at one limb in a trip device for air circuit breaker according to one embodiment of the present invention.
[0029] FIG. 5 illustrates a diagrammatic representation of a current transformer with reverse turn windings at one limb for air circuit breaker according to one embodiment of the present invention.
[0030] FIG. 6 illustrates a graph representing a curve drawn between magnetic flux density (B) and magnetic field strength (H) for Cold Rolled Grain Oriented (CRGO) steel, used in the core of the current transformer in a trip device for air circuit breaker according to one embodiment of the present invention.
[0031] FIG. 7 illustrates a schematic representation of a winding arrangement with unequal turns on the limbs of the current transformer in a trip device for an air circuit breaker according to one embodiment of the present invention.
[0032] FIG. 8 illustrates a schematic representation of a winding arrangement with equal turns on the limbs of the current transformer in a trip device for air circuit breaker according to one embodiment of the present invention.
[0033] FIG. 9 illustrates a graph representing current response curves of a linear conventional current transformer and a non-linear current transformer for the same number
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of turns in a trip device for air circuit breaker, according to one embodiment of the present invention.
[0034] Although the specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
E) DETAILED DESCRIPTION OF THE INVENTION
[0035] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0036] The various embodiments of the present invention provide a trip device comprising electrically saturated current transformer for air circuit breakers. According to one embodiment of the present invention, a trip device for an air circuit breaker has a current sensor and a processor unit connected to the current sensor. At least one transformer is connected to the processor unit. A metering and protection circuit is connected to the current sensor. The transformer is added with reverse turns in at least one limb in the core
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to saturate the current passed through the transformer to limit the current supplied to the processor unit, when a high current is passed through the primary turns of the transformer. The transformer is added with reverse turns in atleast one limb to add the impedance to the transformer so that the effective number of turns is less than the total number of turns to ensure the early power on the processor unit and to limit the current passed to the processor unit through the secondary winding, when a high current is passed through the primary of the transformer. The transformer is a current transformer with a rectangular core or circular core. The current sensor is an air core sensor. The reverse winding is formed at any position in the turns wound on the core.
[0037] According to one embodiment, a trip device used in the air circuit breakers comprises atleast one current transformer, a current sensor such as an air core sensor, a processing unit including electronic tripping circuitry and the metering and protection circuits. The current transformer is used to power-on the processing unit from which a trip command is to be sent to the air circuit breaker during over load and short circuit conditions. The current sensor is connected to the metering and protection circuits of the trip device.
[0038] The current transformer comprises a core, such as a rectangular circular core , square core etc., surrounding a primary conductor of a power circuit and a secondary winding having reverse turn winding wound on a part of the core. The primary conductor of the power circuit carries a primary current from the main power to the load devices in the power circuit. The current transformer is associated to the primary conductor in which the
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primary current flows. The secondary winding of the current transformer includes output wires which are connected to the processing unit of the trip device. The output wires of the secondary winding supplies current to the processing unit for the operation of the trip device.
[0039] The rectangular core of the current transformer includes two limbs in which either of the limbs or both the limbs are added with the reverse turn winding. The reverse turn windings provided on both the limbs are either equal or unequal. The saturation of the current transformer is obtained by providing the core of the current transformer with the reverse turn windings. Hence the effective number of turns on the limb of the core is less than the total number of turns on the limb to ensure the power-on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
[0040] The reverse turn winding on each limb increase the impedance of the current transformer at saturation. Due to increasing of impedance, the secondary winding of the transformer induces only essential amount of current even when the primary current carried through the primary conductor of the power circuit is high. The current transformer dissipates the excess power in the current transformer itself and prevents from the situation of the excess power supplied to the electronic circuitry of the processing unit, since the current transformer has a non-linear response. The percentage of the saturation in the current transformer is dependent on the position and number of turns of the reverse windings on each limb of the current transformer.
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[0041] According to one embodiment of the present invention, the core of the current transformer is made up of iron material such as Cold Rolled Grain Oriented steel (CRGO). A graph curve is drawn for the CRGO steel using magnetic flux density (B) at Y-axis and magnetic field strength (H) at X-axis, At lower zone of the B-H curve of the CRGO steel, the resistance of the reverse turn winding is low as the permeability of the core is high (i.e. L»R). Hence the impedance of the current transformer remains the same when normal primary current flows in the primary conductor and the secondary winding induces the essential amount of current to provide the processing unit of the trip device.
[0042] At upper zone of the B-H curve, the resistance of the reverse turn winding is high where the permeability of the core decreases (i.e. L«R). Hence the impedance of the current transformer increases when higher primary current flows in the primary conductor, due to the increase in the resistance of the reverse turn winding. Because of the high impedance of the current transformer during the higher primary current at the primary conductor, the excess power is dissipated in the current transformer itself and the essential current is only induced in the secondary winding. Also the secondary windings are arranged in opposite directions, the inductive effect of the winding gets cancelled at all operating points.
[0043] Thus the saturated iron current transformer induces only essential less secondary current when higher primary current flows through the primary conductor and limits the
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excess power supplied to the processing unit which sends the trip signal to the circuit breaker during over load and short circuit conditions.
[0044] FIG. 1 illustrates a diagrammatic representation of a current transformer associated to an air core sensor according to one embodiment of the present invention. With respect to FIG. 1, a primary conductor 102 of a power circuit which is to be protected is passed through a current transformer 104 and the centre of a current sensor 106 such as an air core sensor. The primary conductor 102 carries a primary current from the main power to the load devices in the power circuit. The current transformer 104 and the current sensor 106 surround the primary conductor 102 carrying the primary current.
[0045] The current transformer 104 comprises a core like a rectangular core surrounding the primary conductor 102 of the power circuit and a secondary winding having reverse turn winding wound on a part of the core. The secondary winding of the current transformer 104 includes output wires 108 which are connected to the processing unit of the trip device. The output wires 108 of the secondary winding are used to supply the induced current to the processing unit for the operation of the trip device.
[0046] When the primary current flows through the primary conductor 102, the current transformer 104 induces a current according to the primary current, into the secondary winding due to the electromagnetic induction. The induced current is supplied to the processing unit of the trip device for its operation through the output wires 108 of the secondary winding of the current transformer 104. Further the current sensor 106 includes
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output wires 110 which are connected to the metering and protection circuits of the trip device. The output wires 110 of the current sensor 106 supplies a signal that is representative of the primary current flowing in the primary conductor 102, to the metering and protection circuits of the trip device. The current transformer 104 and the current sensor 106 may be preferably fixed to one another.
[0047] FIG. 2 illustrates a diagrammatic representation of a current transformer associated to an air core sensor according to one embodiment of the present invention. With respect to FIG. 2, a primary conductor 202 of a power circuit which is to be protected is passed through a current transformer 204 and the centre of a current sensor 206 such as an air core sensor. The primary conductor 202 carries a primary current from the main power to the load devices in the power circuit. The current transformer 204 and the current sensor 206 surround the primary conductor 202 carrying the primary current.
[0048] The current transformer 204 comprises a core surrounding the primary conductor 202 of the power circuit and a secondary winding having reverse turn winding wound on a part of the core. The core of the current transformer may be a circular core. The secondary winding of the current transformer 204 includes output wires 208 which are connected to the processing unit of the trip device.
[0049] When the primary current flows through the primary conductor 202, the current transformer 204 induces a current according to the primary current, into the secondary winding due to the electromagnetic induction. The induced current is supplied to the processing unit of the trip device for its operation through the output wires 208 of the
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secondary winding of the current transformer 204. Further the current sensor 206 includes output wires 210 which are connected to the metering and protection circuits of the trip device. The output wires 210 of the current sensor 206 supplies a signal that is representative of the primary current flowing in the primary conductor 202, to the metering and protection circuits of the trip device. The current transformer 204 and the current sensor 206 may be preferably fixed to one another.
[0050] FIG. 3 illustrates a diagrammatic representation of a current transformer with reverse turn windings according to one embodiment of the present invention. With respect to FIG. 3, the current transformer 300 comprises a rectangular core 302 having limbs 3041 and 3042. Both the limbs 3041 and 3042 include the secondary winding having reverse turn winding according to the requirement. One part of the limbs 3041 and 3042 includes secondary winding rounded in one direction (i.e. from left to right direction) and other part of same limbs 3041 and 3042 includes the reverse turn winding in opposite direction (i.e. from right to left direction). The reverse turn windings have equal and/or unequal windings on the limbs 3041 and 3042. The saturation of the current transformer 300 is obtained by the rectangular core 302 with the secondary winding having the reverse turn windings. The primary conductor of the power circuit is passed through the centre of the rectangular core 302 of the current transformer 300. Hence the effective number of turns of the secondary winding on the limbs 3041 and 3042 of the rectangular core 302 is less than the total number of turns of the secondary winding on the limbs 3041 and 3042 to ensure the power-
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on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
[0051] FIG. 4 illustrates a diagrammatic representation of a current transformer with reverse turn windings according to one embodiment of the present invention. With respect to FIG. 4, the current transformer 400 comprises a thin rectangular core 402 having a limb 404, The limb 404 includes the secondary winding having reverse turn winding. One part of the limb 404 includes secondary winding rounded in one direction (i.e. from left to right direction) and other part of same limb 404 includes the reverse turn winding in opposite direction (i.e. from right to left direction). The reverse turn windings have equal and/or unequal windings on the limb 404. The saturation of the current transformer 400 is obtained by the rectangular core 402 with the secondary winding having the reverse turn windings. The primary conductor of the power circuit is passed through the centre of the rectangular core 402 of the current transformer 400. Hence the effective number of turns of the secondary winding on the limb 404 of the rectangular core 402 is less than the total number of turns of the secondary winding on the limb 404 to ensure the power-on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
[0052] FIG. 5 illustrates a diagrammatic representation of a current transformer with reverse turn windings according to one embodiment of the present invention. With respect to FIG. 5, the current transformer 500 comprises a core 502 having a limb 504 which has a semi-circular shape. The limb 504 includes the secondary winding having reverse turn
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winding. One part of the limb 504 includes secondary winding rounded in one direction (i.e. from left to right direction) and other part of same limb 504 includes the reverse turn winding in opposite direction (i.e. from right to left direction). The reverse turn windings have equal and/or unequal windings on the limb 504. The saturation of the current transformer 500 is obtained by the rectangular core 502 with the secondary winding having the reverse turn windings. The primary conductor of the power circuit is passed through the centre of the rectangular core 502 of the current transformer 500. Hence the effective number of turns of the secondary winding on the limb 504 of the rectangular core 502 is less than the total number of turns of the secondary winding on the limb 504 to ensure the power-on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
[0053] FIG. 6 illustrates a graph representing a curve drawn between magnetic flux density (B) and magnetic field strength (H) for Cold Rolled Grain Oriented steel (CRGO) iron, according to one embodiment of the present invention. With respect to FIG. 6, a magnetic hysteresis curve is drawn for the iron material such as Cold Rolled Grain Oriented steel (CRGO) in which the core of the current transformer is made up. The magnetic flux density (B) of the CRGO steel is taken at Y-axis and magnetic field strength (H) of the CRGO steel is taken at X-axis. At lower zone of the B-H curve of the CRGO steel, the resistance of the reverse turn winding is low as the permeability of the core is high (i.e. L»R). Hence the impedance of the current transformer remains the same when normal
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primary current flows in the primary conductor and the secondary winding induces the essential amount of current to provide the processing unit of the trip device.
[0054] At upper zone of the B-H curve, the resistance of the reverse turn winding is high where the permeability of the core decreases (i.e. L«R). Hence the impedance of the current transformer increases when higher primary current flows in the primary conductor, due to the increase in the resistance of the reverse turn winding. Because of the high impedance of the current transformer during the higher primary current at the primary conductor, the excess power is dissipated in the current transformer itself and the essential current is only induced in the secondary winding of the current transformer.
[0055] FIG. 7 illustrates a diagrammatic representation of the secondary winding arrangement on the limbs of the current transformer according to one embodiment of the present invention. With respect to FIG. 7, one limb of the core in the current transformer carry the secondary winding wound in one direction (i.e. from left to right direction) and the other limb of the core carry the secondary winding wound in the opposite direction (i.e. from right to left direction). Thus unequal turn distribution of the secondary winding is formed on the limbs of the core in the current transformer. The secondary winding arrangement increases the impedance of the current transformer at saturation. Since the secondary winding arrangements are in the opposite direction to each other, the inductive effect of the secondary winding arrangements gets cancelled at all operating points.
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[0056] FIG. 8 illustrates a diagrammatic representation of the secondary winding arrangement on the limbs of the current transformer according to one embodiment of the present invention. With respect to FIG. 8, one part of each limb of the core of the current transformer includes secondary winding wound in one direction (i.e. from left to right direction) and other part of same limb includes the reverse turn winding wound in the opposite direction (i.e. from right to left direction). The reverse turn windings have equal and/or unequal windings wound on each limb of the core. The saturation of the current transformer is obtained by providing the core of the current transformer with the reverse turn windings. Hence the effective number of turns of the secondary winding on the limb of the core is less than the total number of turns of the secondary winding on the limb to ensure the power-on process of the processing unit and to limit the power provided to the processing unit at higher primary current flowing through the primary conductor.
[0057] The reverse turn winding on each limb increase the impedance of the current transformer at saturation. Due to increasing of impedance, the secondary winding of the transformer induces only essential amount of current even when the primary current carried through the primary conductor of the power circuit is high. The current transformer dissipates the excess power in the current transformer itself and prevents from the situation of the excess power supplied to the electronic circuitry of the processing unit, since the current transformer has a non-linear response. The percentage of the saturation in the current transformer is dependent on the position and number of turns of the reverse windings on each limb of the current transformer.
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[0058] FIG. 9 illustrates a graph representing current response curves of a linear conventional current transformer and a non-linear current transformer for the same number of turns, according to one embodiment of the present invention. With respect to FIG. 9, the current response curves are drawn between the induced secondary current (Is) and the primary current (Ip) of a linear conventional current transformer as well as a non-linear current transformer described in the present invention for the same number of winding turns. The induced secondary current (Is) is taken at Y-axis and the primary current (Ip) is taken at X-axis in the current response curve. A first current response curve 902 represents the current response of the conventional current transformer of known type which is not having a reverse turn winding. The aspect of the current response curve 902 of the conventional current transformer is a linear curve. The secondary current (Is) of the conventional current transformer in the current response curve 902 is appreciably proportional to the primary current (Ip) of the conventional current transformer. A second current response curve 904 represents the current response of the current transformer according to an embodiment of the present invention comprising the secondary winding arrangement having reverse turn winding.
[0059] As long as the primary current (lp) is in lower value, the secondary currents (Is) of the conventional current transformer and the current transformer of the present invention corresponding to the current response curves 902 and 904 have the similar values. When the primary current (Ip) increases, the current response curve 904 of the current transformer comprising the secondary winding arrangement having reverse turn winding, becomes
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weaker than the current response curve 902 of the conventional current transformer without a reverse turn winding. For example, the current transformer of the present invention comprising a reverse turn winding supplies a secondary current of about 0.5A for a primary current of 1500A, whereas the conventional current transformer without a reverse turn winding supplies a secondary current of about 2A according to the current response curves 902 and 904.
G) ADVANTAGES OF THE INVENTION
[0060] The various embodiments of the present invention provide a trip device comprising electrically saturated current transformers having a reverse turn winding arrangement for air circuit breakers. The saturated current transformer in the trip device eliminates efficiently the problems such as bigger size and overheating across the whole range of a typical trip device. The saturated current transformer has a non-linear response, which limits the excess power supplied to the processing unit of the trip device and thus dissipates the excess power in the current transformer itself.
[0061] The electrically saturated current transformers ensures the satisfactory operation of the trip device fitted in the air circuit breaker, between 0.2 to 10 times rated primary current in the primary conductor. The saturated iron current transformer reduces the secondary current at higher primary currents and limits the power supplied to the processing units that sends trip signal to the air circuit breaker. The trip device is a compact trip device accommodates multiple ratings of primary current and provides a low cost design.
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[0062] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0063] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.
Dated this the 16tn day of September, 2009

Itesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA

To,
The Controller of Patents,
The Patent office,
At Mumbai

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CLAIMS
What is claimed is:
1. A trip device for air circuit breaker comprising: A current sensor; A processor unit:
At least one transformer connected to the processor unit; and A metering and protection circuit connected to the current sensor; Wherein the transformer is added with reverse turns in at least one limb at the core to saturate the current passed through the transformer to limit the current supplied to the processor unit, when a high current is passed through the primary turns of the transformer.
2. The trip device according to claim 1, wherein the transformer is added with reverse turns in atleast one limb to add the impedance to the transformer so that the effective number of turns is less than the total number of turns to ensure the early power on the processor unit and to limit the current passed to the processor unit through the secondary winding, when a high current is passed through the primary of the transformer.
3. The trip device according to claim 1, wherein the transformer is a current transformer.
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4. The trip device according to claim 1, wherein the transformer is a current transformer with a rectangular core.
5. The trip device according to claim 1, wherein the transformer is a current transformer with a circular core.
6. The trip device according to claim 1, wherein the transformer is a current transformer with a square core.
7. The trip device according to claim 1, wherein the current sensor is an air core sensor.
8. The trip device according to claim 1, wherein the reverse winding turns are formed at any position in the turns wound on the core.
Date: September 16,2009
Place: Bangalore. Patent Agent