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THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - AN IMPROVED PREEMPTIVE RATE OF RISE OF
CURRENT BASED ACTUATING DEVICE FOR CIRCUIT BREAKER TRIPPING
2. Appljcant(s)
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS: L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
The present invention relates to a device to detect over current/fault current and tripping of circuit breakers. More particularly, the invention relates to an improved rate-of-rise current (di(t)/dt) based actuating device to sense the high fault current flowing in a conductor and promptly tripping the circuit breakers when rate of rise of fault current exceeds a predefined value.
BACKGROUND OF THE INVENTION
Electrical systems in residential, commercial and industrial applications are usually routed through protection devices for receiving electrical power from a utility source and/or captive generation. These protection devices are typically circuit interrupters such as circuit breakers and fuses which are designed to interrupt the electrical current if predefined fault conditions are detected on the protected lines. The over current conditions are deemed to have occurred when the current exceeds of the pre-set multiple of nominal current of the conductor/equipment.
A typical power circuit breaker employed in system protection schemes enabling clear discrimination with downstream protection devices is required to withstand the maximum through fault current. Whilst it should respond instantaneously if the fault current is higher than the pre-set current value designated for withstand. Withstanding such high electrodynamics forces requires a significant amount of compensation. Compensation of these forces can be done either through special current path configurations or from an advantageous combination of both such configurations and mechanical arrangements, as have been illustrated in various prior arts. These types of compensation require an external actuation or impetus for operation/de-latching. These actuation means are achieved through either microprocessor /microcontroller based schemes or solenoid drive based schemes in

prior arts. However both are primarily dependent on instantaneous current value hence may be classified as corrective measures rather than predictive schemes.
US 4,679,019 discloses an electronically driven trip actuator for multipole industrial rated molded case circuit breakers is installed within a common housing with the circuit breaker operating mechanism. The trip actuator consists of a mechanical actuator cooperatively connected with a magnetic latch. The magentic latch arrangement holds the trip actuator against an actuating spring bias. Upon receiving an appropriate signal response, the magnetic latch releases, allowing the mechanical actuator to move into contact with the circuit breaker latch under the influence of the actuator spring. The arrangement of the mechanical actuator and actuator spring provides a low latching force to the magnetic latch, while providing a large trip force to the circuit breaker latch.
US 4,894,631 discloses an integrated protection unit is a circuit breaker which includes basic overcurrent protection facility along with selective electrical accessories. A molded plastic accessory access cover secured to the integrated protection unit cover protects the accessory components contained within the integrated protection unit cover from the environment. A combined overcurrent trip actuator and multiple accessory unit can be field-installed within the integrated protection unit. The combined actuator-accessory unit includes electronic control circuitry for the accessories along with mechanical trip and reset interface components.
US 6,972,936 discloses fault abatement circuit breaker for providing protection of critical loads. The circuit breaker provides both arc fault protection and fault lockout protection in one integrated circuit breaker. The fault lockout protection reduces the risk of short circuit damage by predicting and preventing the event. The arc fault protection trips the circuit breaker when arcing is sensed. The integrated circuit thus provides for a minimum of short circuit damage, thereby maximizing process and/or equipment up time.

US 6,211,757 discloses a trip actuator (66) includes a trip spring (106) to bias the trip arm (104) in a clockwise direction about trip arm pivot (120). In the latched and ready to operate state, the clockwise moment about the axis of the latch pivot (132) created by force "F" opposes the counterclockwise moment created about the axis of the latch pivot (132) created by the horizontal component "fx" of force "f", to hold the latch (110) in the upright position against the force of the trip arm (104). When a trip (triggering) signal is provided to the flux shifter (102), the flux shifter (102) releases the plunger (130). With the force "F" removed, the trip arm (104) will drive the latch pin (134), causing the latch (110) to rotate counterclockwise about the latch pivot (132), As the latch (110) and trip arm (104) rotate, the latch pin (134) slides off the latch surface (126), fully releasing the trip arm (104) and allowing the trip paddle (96) to move the secondary latch tab (50).
US 6,777,635 discloses a limiting circuit breaker comprises two separable contacts 68, 70 and a mechanism 12 with energy storage 36 operated by an opening catch 30. The mechanism 12 drives a movable cage 58 between a closed position and an open position to perform opening of the contacts. One of the contacts is movable with respect to the cage 58 in the closed position and can thus take a separated position. A Thomson effect electromechanical actuator 100 is provided to drive the movable contact 68 to the separated position. A latch 80 enables the movable contact to be held in the separated position. In the event of a fault requiring a very high-speed response, separation of the contacts is obtained by means of the Thomson effect actuator and is then confirmed by opening of the mechanism. In other cases, only the mechanism operates to perform opening.
US 5,841,616 discloses a module for use with the circuit breaker, the module being arranged to be mounted on an end of the circuit breaker and to monitor and/or control the circuit breaker and/or an electrical circuit control thereby in use. The module can be active or passive, and, where circuit breakers are ganged in side-by-side relationship, the module can be equal in width to the width of the gang breaker

unit to which the module is mounted. The invention also resides in the combination of a module and a circuit breaker.
US 20080272659 discloses an electromagnetic force driving actuator and a circuit breaker using the same is disclosed. The actuator comprises a casing that forms two paths having a certain length in longitudinal direction, and forms a middle wall by the two paths; a main magnetic field generation element that is allocated on the both face wall of the two paths of the casing; and a moving element that, as the middle wall is located in the center, a coil, which is bound in the orthogonal direction to longitudinal direction of the paths, is in a body that its left and right sides passes through the paths and its front and back side are exposed to outside, when forward direction or reverse direction current is provided in the coil, moves forward and backward along the longitudinal direction of the paths.
US 6,285,270 discloses an electromagnetic actuator for a circuit breaker having a pair of relatively moveable contacts is disclosed. The actuator includes primary actuator coupled to at least one of the contacts by a link mechanism operable to provide closing and holding forces to the contacts of the circuit breaker and a secondary, faster acting actuator which, on tripping thereof, provides sufficient force to at least initiate opening of the contacts by the configuration of the link mechanism. The secondary actuator includes a stored energy latch which has a permanent magnet flux circuit for providing a holding force and a coil connected to receive a trigger signal to overcome the permanent magnet flux to trip the latch.
The disadvantage of the above mentioned prior art is that prior art electromechanical systems being instantaneous current based and are slow acting are not capable of providing preemptive, reliable and selective protection to the power system. The prior art systems involved in significant delay in tripping the circuits which has proved detrimental to the efficacy of the fault clearing schemes. Moreover the schemes provided were complex where the actuation means are achieved through either microprocessor /microcontroller based schemes or solenoid drive based schemes.

Thus there is a need to provide an improved rate of rise current based actuating device that will provide pre-emptive action for circuit breaker tripping, thus will have low cutoff and low let through energy. Further to provide an improved actuating device that will maintain linearity even at high fault currents and immunity to external magnetic fields.
OBJECTS OF THE INVENTION
The basic object of the present invention is to overcome the disadvantages of the prior art.
Another object of the present invention is to provide an improved rate of rise current based actuating device that will provide pre-emptive action for circuit breaker tripping.
Yet another object of the present invention is to provide an improved actuating device that will provide reliable and selective protection to the power system.
Yet another object of the present invention is to provide an improved actuating device based on di/dt principle that sense, analyze and release purpose built actuator for circuit breaker tripping.
Yet another object of the present invention is to provide an improved actuating device designed to remain idle, irrespective of the output voltage from air core coil, up to the designated pre-set value.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an improved preemptive rate of rise of current based actuating device for tripping circuit breakers/operating mechanisms when rate of rise of fault current exceeds a predefined value, said device comprising:

(i) plurality of primary conductors;
(ii) plurality of sensing means magnetically coupled with said primary conductors adapted to sense/measure high rate of rise of fault current as its input signal and develop a bidirectional signal/voltage as its output;
(iii) atleast one single phase converter means operatively coupled with said sensing means adapted to convert said output voltage of said sensing means to unidirectional signal/voltage ; and
(iv) atleast one actuator means operatively coupled with said converter means adapted for tripping of said operating mechanism/circuit breaker through mechanical integrator.
DETAILED DESCRIPTION OF THE INVENTION
The present invention describes about an improved device based on di/dt principle that sense, analyze and release purpose built magnetic actuator for circuit tripping.
The device consists of 4 main sub-devices namely di/dt sensor, Converter, Electromechanical Actuator and Mechanical Integrator. High fault current is associated with high di/dt, which is sensed by a non-magnetic core coil, preferable a rogowski coil or the like. A Rogowski Coil output is a scaled time derivative, di(t)/dt of the primary current. The output voltage of the coil is converted into a unidirectional wave form through a converter circuit and output of such a circuit is utilized to operate a voltage operated Electro-mechanical Actuator. This mechanical displacement of the actuator is used for tripping, of the protection device through a mechanical integrator. Electromechanical Actuator is designed to remain idle, irrespective of the output voltage from air core coil, up to the designated pre-set value.

The device comprises plurality of primary conductors, plurality of sensing means which are magnetically coupled with the primary conductors for sensing/measuring high rate of rise of fault current as its input signal and develop a bidirectional signal/voltage as its output. The device comprises one or more single phase converter operatively coupled with the sensing means adapted to convert output voltage of the sensing means to unidirectional signal/voltage. One or more actuators are operatively coupled with the converter means for tripping of the operating mechanism/circuit breaker through mechanical integrator.
The actuator comprises a permanent magnet enclosed within a shield, an armature, a flux diverter, a plunger operatively magnetized to synchronize with the magnet to develop unidirectional magnetic main flux Øm and formulate magnetic force Fm. Plurality of coil is placed substantially in between said flux diverter to develop reversal flux Ør. The plunger is spring biased and provides a spring force Fs.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the generalized block diagram of an instrumentation system embodying principles of the present invention
Figure 2 illustrates wave form of the performance characteristics of the present invention
Figure 3 illustrates wave form of the performance characteristics during the fault clearing by downstream devices of the present invention.
Figure 4 illustrates schematic diagram iliustrating details of Fig. 1
Figure 5 illustrates schematic diagram illustrating details of Fig. 1
Figure 6 illustrates a schematic diagram showing further detail of a portion (Electromechanical actuator) of the device FIG. 2

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 is the generalized block diagram of an instrumentation system embodying
principles of the present invention
M - Operating Mechanism A - Electro-mechanical Actuator C - Converter Circuit S - Source
The Basic block diagram of Device 1. The sources S are Air-core Coils that sense the change in current of the primary conductors and Converter circuit C converts them into a unidirectional signal. This unidirectional voltage signals are subsequently used for tripping of Electro-mechanical actuators(s) A. The output of this Electro-mechanical actuator(s) A can be utilized for tripping of the operating mechanism M through Mechanical integrator.
Fig.2 is the illustrated wave form of the performance characteristics of the present invention
Input Current - The current that flows in the primary circuit during fault.
Sensor output voltage - The emf induced proportional to the variation in time of the current, in the air core coil magnetically coupled with the primary conductor. Sensor output voltage being offset by 90 degrees with the primary fault current will attain the peak at the instant of fault occurred. These sensors are fast responsive being reactance is very low. Accuracy of these types of coil may be affected by the winding tolerance, turns density and cross sectional area. In addition Rogowski coils exhibit some sensitivity to the position of the conductor.
Converter output voltage - The unidirectional voltage rectified by converter circuit using fast acting diodes preferably Schottky diodes or the like.

Fig.3 is the illustrated wave form of the performance characteristics during the fault clearing by downstream devices of the present invention.
Input Current - The dotted line shows the prospective fault current that would have passed through in the absence of current limiting device. The solid line shows the limited fault current that is passed through, during fault clearing by the downstream current limiting device.
Sensor output voltage - The dotted line shows the induced voltage in the sensor that would have occurred in the absence of downstream current limiting device where the solid line shows the actual output voltage corresponding to the limited primary fault current.
Converter output voltage - The dotted line shows the expected output voltage from the converter circuit where the solid line shows the actual unidirectional voltage wave corresponds to the sensor output voltage. This output voltage is used to operate electro-mechanical actuator.
Fig. 4 is a schematic diagram illustrating details of Fig. 1
1 - Smart Device
2 - Primary Conductor
3 - Sensing Device (Air Core Coil)
4 - Electro-mechanical Actuator
C1 - Converter circuit for R-phase
C2 - Converter circuit for Y-phase
C3 - Converter circuit for B-phase
The Basic structure of the 'Smart device' 1. An Air-core coil 2 consists in a toroidal solenoid that encircles a primary conductor 3 which current is to be measured. The said Air-core coil is magnetically coupled to the primary conductor 3, so that an emf proportional to the variation in time of the current is induced. This Induced voltage in coils is utilized to energize the coil of an Electro-mechanical actuator 4 built with high

magnetic efficiency. These single phase converter circuits C1, C2, and C3 are provided to convert the o/p signal of the individual sensing coils to unidirectional signal before utilizing to actuate the electro-mechanical devices 4. Sensing device being an Air-core Coil 2, does not saturate at a very high current hence o/p is linear at even high fault current. Coil being wound on a low permeability material is immune to external electromagnetic fields.
Fig. 5 is a schematic diagram illustrating details of Fig. 1
1 - Smart Device
2 - Primary Conductor
3 - Sensing Device (Air Core Coil)
4 - Electro-mechanical Actuator C4 - 3-phase Converter circuit
The Basic structure of the 'Smart device' 1. Scope of the design may extended by reducing the number of Electro-mechanical actuators as low as to 1 for a 3 a 3-phase 3-wire or 3-phase 4-wire system by using a 3-phase converter circuit C4.
Fig. 6 is a schematic diagram showing further detail of a portion (Electro-mechanical actuator) of the device FIG. 2
5 - Armature 9 - Plunger
6-Shielding 10-Coil
7 - Permanent Magnet 11 - Striking Disc
8 - Flux Diverter 12 - spring
Fm - Magnetic Force Fs - Spring Force
Øm - Main flux Ør - Reversal flux

The Basic structure of the Electro-mechanical Actuator 4:
A direct current linear drive actuator includes a Permanent Magnet 7 magnetized in synchronize with the armature 5, flux diverter 8 & plunger 9. The unidirectional magnetic main fluxes 0m take the low reluctance path to complete the magnetic path through armature 5 and plunger 9. The spring biased plunger 9 hold to a neutral/balanced position between the spring force Fs and the magnetic force Fm. Magnetic force Fm is the force generated due to flux lines passed through plunger. Energization of the coil 10 by the output voltage from converter circuit E (Shown in Fig.1) provides a Reversal flux 0r in anti parallel direction to the main flux through plunger 9, armature 5 and diverter 8. Thus reduces the main flux 0m strength in the plunger 9 that reduces the magnetic pull strength, making the basing spring force dominating in popping out the plunger 9 linearly. The time for full through of the plunger 9 and the striking disc 11 will be decided by the inertia of the moving bodies and the spring load characteristics. If the output voltage of the converter circuit C is less than the operating voltage of the Electro-mechanical actuator 4 then the reversal flux 0r generated will not be sufficient to de-strengthen the main flux 0m.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

We Claim
1. An improved preemptive rate of rise of current based actuating device for
tripping circuit breakers/operating mechanisms when rate of rise of fault
current exceeds a predefined value, said device comprising:
(i) plurality of primary conductors;
(ii) plurality of sensing means magnetically coupled with said primary conductors adapted to sense/measure high rate of rise of fault current as its input signal and develop a bidirectional signal/voltage as its output;
(iii) atleast one single phase converter means operatively coupled with said sensing means adapted to convert said output voltage of said sensing means to unidirectional signal/voltage ; and
(iv) atleast one actuator means operatively coupled with said converter means adapted for tripping of said operating mechanism/circuit breaker through mechanical integrator.
2. Device as claimed in claim 1 wherein said actuator means comprising :
(a) a permanent magnet enclosed within a shield;
(b) an armature, a flux diverter, a plunger operatively magnetized to synchronize with said magnet adapted to develop unidirectional magnetic main flux Øm and formulate magnetic force Fm;
(c) plurality of coil placed substantially in between said flux diverter adapted to develop reversal flux Ør and
(d) a spring biased with said plunger adapted to provide a spring force Fs.

3. Device as claimed in claim 1 wherein said sensing means comprises air core coil adapted to convert said fault current to sensor output voltage.
4. Device as claimed in claim 3 wherein said sensor output voltage is offset by 90° with said fault current adapted to attain the peak at the instant of fault occurrence.
5. Device as claimed in claim 3 wherein said air core coil is further adapted to produce an emf (voltage) proportional to variation in time of said fault current induced.
6. Device as claimed in claim 1 wherein saicj converter means comprises Schottky diodes or the like .
7. Device as claimed in claims 1 and 2 wherein said actuator means further comprises a striking disc operatively connected/associated with said plunger adapted for tripping of said operating mechanism/circuit breaker.
8. Device as claimed in claim 2 wherein said coil of actuator is energized by said unidirectional output voltage of said converter to provide said reversal flux fax in anti parallel direction of said magnetic main flux Øm through said plunger, said armature and said diverter.
9. Device as claimed in claim 2 wherein said spring biased plunger is held in a neutral /balanced position between said spring force Fs and said magnetic force Fm.
10. Device as claimed in claim 8 wherein said reversal flux Ør is adapted to reduce said magnetic force Fm than said spring force Fs when said flux 0r is higher than said main magnetic flux Øm.
11. Device as claimed in claim 2 wherein said spring force Fs is higher than said magnetic force Fm adapted to push said plunger in outward direction impinging said striking disc

12. An improved preemptive rate of rise of current based actuating device for tripping circuit breakers/operating mechanisms when rate of rise of fault current exceeds a predefined value as substantially described hereinbefore with reference to accompanying drawings.