FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"System for Short Circuit I2T on Protection for Electrical Circuit Breakers and
Method Therefor"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. O. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

System for Short Circuit I2T on Protection for Electrical Circuit Breakers and
Method Therefor
Field of the invention
The present invention relates to circuit breakers, and more particularly, to a system and method for short circuit I2T ON protection for electrical circuit breakers using energy based accumulation.
Background of the invention
Short circuit protection is one of the basic protections provided in electronic trip unit . One of the techniques of the short circuit protection uses loading of a timer according to a fault current flowing through the conductors, wherein after the trip time elapses, the controller issues a trip. As this method requires timer to keep track of the time elapsed, this increases the burden on the microcontroller. Eliminating the need of a timer makes a peripheral free for other usage.
US Patent Application No. 2011/0026181 discloses a protective switching device for monitoring the electrical current flow to an electrical user, including a switching functionality, an excess current triggering functionality and a short circuit triggering functionality. In at least one embodiment, the protective switching device includes a first microcontroller with a first input signal filter, wherein the first microcontroller is configured for monitoring the excess current triggering functionality and wherein a second microcontroller is provided with a second input signal filter that is configured for monitoring the short circuit triggering functionality, wherein the two input signal filters are designed differently, and wherein the switching functionality is provided in one of the two microcontrollers. A method is further disclosed for monitoring the electrical current flow to an electrical user by way of a protective switching device.
However, the '181 patent application uses two measuring devices for example, two microcontrollers to determine whether a short circuit Protection has occurred. This increases cost of the device.

Accordingly, there exist a need to provide device and a method a for short circuit I2T ON protection for electrical circuit breakers which uses a single microcontroller and overcomes drawbacks of the prior art
Objects of the invention
An object of the present invention is to eliminate the problem of current ramp up or ramp down.
Another object of the present invention is to eliminate need of any timer required to keep track of the time elapsed.
Summary of the invention
Accordingly, in one aspect, the present invention provides a system for short circuit protection for electrical circuit breakers. The system comprises a microcontroller, a signal conditioning system capable of providing DC shifted output signal to the microcontroller, a trip circuitry for enabling a tripping mechanism of the electrical circuit breaker on receiving input from the microcontroller and a power supply source for powering the signal conditioning circuitry, the microcontroller and the trip circuitry. Wherein, the microcontroller processes the signal form the signal conditioning system, detects whether short circuit fault is present and gives a command to the trip circuitry to start the trip mechanism.
In another aspect the present invention provides a method for short circuit I2T on protection for electrical circuit breakers. The method comprises detecting maximum fault current in a phase out of four phases, finding a value of a ratio of fault current (IFault) to overload pick-up (Ir) for the four phases. If the maximum fault current is greater than a short circuit pick-up the accumulation process starts. If the value of the ratio of fault current (IFault) to overload pick-up (Ir) is greater than predefined threshold Thl, the ratio of fault current (IFault) to overload pick-up (Ir) is forced to Thl. If the value of the ratio of fault current (IFault) to overload pick-up (Ir) is not

greater than the predefined threshold Thl, the actual value of the ratio is used. Energy is calculated after regular intervals using the value of the ratio of fault current (IFauIt) to overload pick-up (Ir); accumulating the calculated energy with previous slot energies and generating a trip command if the energy of any phase of the four phases is greater than predefined threshold energy, wherein if the energy of any phase of the four phases is not greater than predefined threshold energy, the accumulation of energy continues, and making the energy to 0, if the maximum current is not greater than short circuit pick-up.
Brief description of the drawings
Figure 1 shows a block diagram of the system for short circuit I2T on protection for electrical circuit breakers, in accordance with the present invention; and
Figure 2 shows a flow chart for short circuit 12T on protection, in accordance with the present invention.
Detailed description of the invention
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides a system for short circuit I2T on protection for electrical circuit breakers and method therefor. The system and method eliminates the problem of current ramp up or ramp down. Further, the system eliminates need of any timer required to keep track of the time elapsed for short circuit I2T on protection.
Referring now to figure 1, there is shown a system (100) for short circuit I2T on protection for electrical circuit breaker, in accordance with one aspect of the present invention. The system (100) includes a microcontroller (10), a signal conditioning system (20), a trip circuitry (30) and a power supply source (40).

The power supply source (40) powers the microcontroller (10), the signal conditioning circuitry (20) and the trip circuitry (30).
The signal conditioning system (20) is capable of providing DC shifted output signal to the microcontroller (20). The microcontroller (10) processes the signal form the signal conditioning system (20), detects whether short circuit fault is present and if yes, gives a command to the trip circuitry (30) to start the trip mechanism. Specifically, the trip circuitry (30) enables the tripping mechanism of the electrical circuit breaker on receiving input from the microcontroller.
Referring now to figure 2, there is shown a method (200) for short circuit I2T on protection for electrical circuit breakers. Algorithm for method (200) is provided in the trip unit of the electrical circuit breaker.
At first step, the method includes detecting maximum fault current in a phase out of four phases supplying power to the electrical circuit breaker.
At second step, the method includes finding a value of a ratio of fault current (IFault) to overload pick-up (Ir) for the four phases if the maximum fault current is greater than a short circuit pick-up. If the maximum fault current is not greater than short circuit pickup, the energy is made to 0.
At third step, the method includes forcing the value of the ratio of fault current (IFault) to overload pick-up (Ir) to a threshold value if the value of the ratio of fault current (IFault) to overload pick-up (Ir) is greater than predefined threshold Thl. Specifically, the threshold Thl is the value of IFault/ Ir after which trip time is constant.
At fourth step, the method includes using the actual value of the ratio of fault current (IFault) to overload pick-up (Ir) if the ratio value of the ratio of fault current (IFault) to overload pick-up (Ir) is not greater than the predefined threshold Thl.

At fifth step, the method includes calculating energy after regular intervals using the value of the ratio of fault current (IFault) to overload pick-up (Ir) and accumulating the calculated energy with previous slot energies.
At sixth step, the method includes generating a trip command if the energy of any phase of the four phases is greater than predefined threshold energy. If the energy of any phase of the four phases is not greater than predefined threshold energy, the accumulation of energy continues.
Advantages of the invention
1. In the system (100), the trip timing is modified according to current ramp up.
2. In the system (100), the trip timing modified according to current Ramp down.
3. In the system (100), no timer required for time elapsed maintenance.
4. In the system (100), only one microcontroller required for detecting short circuit
fault.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim
1. A system for short circuit protection for electrical circuit breakers, the
system comprising:
a microcontroller;
a signal conditioning system capable of providing DC shifted output signal to the microcontroller;
a trip circuitry for enabling a tripping mechanism of the electrical circuit breaker on receiving input from the microcontroller; and
a power supply source for powering the signal conditioning circuitry, the microcontroller and the trip circuitry,
wherein, the microcontroller processes the signal form the signal conditioning system, detects whether short circuit fault is present and gives a command to the trip circuitry to start the trip mechanism.
2. A method for short circuit I2T on protection for electrical circuit
breakers, the method comprising:
detecting maximum fault current in a phase out of four phases;
finding a value of a ratio of fault current (IFauIt) to overload pick-up (Ir) for the four phases if the maximum fault current is greater than a short circuit pick-up;
forcing the value of the ratio of fault current (IFauIt) to overload pick-up (lr) to a threshold value if the value of the ratio of fault current (IFauIt) to overload pick-up (Ir) is greater than predefined threshold Thl,
using the actual value of the ratio of fault current (IFauIt) to overload pick-up (Ir) if the ratio value of the ratio of fault current (IFauIt) to overload pick-up (Ir) is not greater than the predefined threshold Thl;
calculating energy after regular intervals using the value of the ratio of fault current (IFauIt) to overload pick-up (Ir);
accumulating the calculated energy with previous slot energies;
generating a trip command if the energy of any phase of the four phases is greater than predefined threshold energy, wherein if the energy of any phase of the four

phases is not greater than predefined threshold energy, the accumulation of energy continues; and
making the energy to 0, if the maximum current is not greater than short circuit pick-up.
3. The method as claimed in claim 2, wherein the threshold Thl is the value of IFault/ Ir after which trip time is constant.