FORM 2
THE PATENTS ACT, 1970 (39 Of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
"Electronic trip unit for direct current circuit breakers"
2.APPLICANT(S)
(a) NAME: Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c) ADDRESS: L&T House, Ballard Estate, Mumbai-400 001, India
3. PREAMBLE TO THE DESCRITION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Title
Electronic Trip Unit for Direct Current Circuit Breakers
Field of the invention
The present disclosure relates to electronic circuit breaker, more particularly to an ■electronic trip unit applied either to a moulded case circuit breaker or an air circuit breaker, which provides protection against direct current overload or short circuit condition, by interrupting the direct current from input power supply to load.
Background of the invention
Electromechanical direct current circuit breakers are available in the prior art. These circuit breakers comprise bi-metallic strip, magnetic coil and permanent magnet as essential parts for providing protection by interrupting the direct current in case of abnormal condition like over-current or short circuit and saving electrical circuitry from damage. The drawback of these direct current circuit breakers is that they do not provide precise protection.
Further, the conventional breaker comprises bi-metallic strip due to which conventional breakers have problem of in-consistent tripping, non-repeatability, dependency upon ambient temperature and requirement of calibration.
Also, electromechanical direct current circuit breakers of prior art provide only basic protection, over-current and short circuit protection; no other features such as and including energy metering, display, communication, remote monitoring, diagnostic functions are available in electromechanical direct current circuit breakers of prior art.
Objects of the invention
Accordingly, an object of the present invention is to overcome the aforementioned limitations and drawbacks of prior art.
Summary of the invention
In accordance with the above objects, there is provided a direct current-operated electronic trip unit for a moulded case circuit breaker or an air circuit breaker, for providing protection to electrical circuitry and equipment from damage due to faults occurring in direct current system such as direct current overload and short circuit condition, comprising:
a primary sensor unit for providing a voltage signal proportional to the direct current following through main lines;

a secondary sensor comprising a current transformer and a Rogowski coil;
a tripper comprising:
a voltage circuitry through which the tripper is powered by main lines, the voltage circuitry comprising a voltage regulation unit and a voltage measurement unit;
an isolation and amplification circuitry for receiving the voltage signal provided by the primary sensor unit and isolating and amplifying the voltage signal;
a voltage signal conditioning unit for conditioning the voltage signal;
an override protection circuitry receiving input from the secondary sensor, for powering up the tripper in an event of transient short circuit or instantaneous fault condition and also for providing an output signal in an event of transient short circuit or instantaneous fault condition;
a microcontroller having an analogue-to-digital convertor (ADC), the ADC receiving voltage signal from the voltage circuitry through the voltage regulation unit and the voltage measurement unit for further analysis such as and including undervoltage protection, overvoltage protection, phase reverse protection and power measurement; the microcontroller receiving input also from the voltage signal conditioning unit and the override protection circuitry and also having a software program for generating tripping pulse as required according to selected rating; and
a tripping circuitry receiving trip signal from the microcontroller and bumping off any nuisance tripping received; and
a trip coil for receiving input from the tripping circuitry and tripping the circuit breaker.
Brief Description of Drawings
Figurel shows Block Diagram of direct current operated electronic trip device in accordance with the present invention.
Figure 2 shows Block Diagram of override protection circuitry in accordance with the present invention.

List of Components

Component No. Name of the Component
la Primary sensing unit
lb Secondary sensing unit
2a Current transformer
2b Rogowski coil
3 Tripper
4 Voltage circuitry
5a Voltage regulation unit
5b Voltage measurement unit
6 Isolation and amplification circuitry
7 Voltage signal conditioning unit
8 Override protection circuitry
9 Microcontroller
10 Trip Coil
11 Pick-up Power supply unit
12 Current signal conditioning circuitry
13 Tripping circuitry
Detailed Description
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 following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and the claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a", "an" and "the" include plural referents unless the context clearly indicates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Accordingly, a direct current-operated electronic trip unit is presented for direct current circuit breakers, which provides protection for electrical circuitry and equipment from damage due to faults occurring in direct current system such as direct current overload and short circuit condition
The trip unit provides overload and short circuit/instantaneous direct current protection by electronic means which are precise and temperature-independent. Selection switches are provided for multiple settings of overload and short circuit/instantaneous direct current. Time delay of overload and short circuit direct current protection is also selectable. Selection switches are provided also for deciding whether under voltage, over voltage and phase reverse features are required or not.
The trip unit of the present invention is also compatible with energy metering solutions, communication, display, remote monitoring, automation and diagnostic functions.

The trip unit of the invention gets powered from main terminals of the circuit breaker via a voltage circuitry module. The voltage circuitry gets input from main line terminals and powers a microcontroller after step down, filtration and regulation of voltage.
A primary sensor unit provided in the electronic trip unit, which is compact enough to be installed inside the circuit breaker and comprising a shunt in a preferred embodiment, is used for voltage signal measurement equivalent and proportional to the direct current flowing through the main lines in the electrical closed loop circuit. The primary sensor unit may alternatively comprise a Hall-effect sensor. The primary sensor unit has dimensions in the range of 15 cubic millimetres to 70 cubic millimetres depending upon the frame size of the circuit breaker, and is thus capable of being installed inside the circuit breaker. Further, the primary sensor unit has resistance in a range of 5 micro-ohms to 300 micro-ohms so as to permit power dissipation compatibly with plastic support of the circuit breaker, both at rated current state as well as short circuit current condition.
Further, a secondary sensor is provided, comprising a current transformer and a Rogowski coil.
The primary sensor unit and the secondary sensor unit are connected to a tripper.
The tripper comprises a voltage circuitry through which the tripper is powered by main lines, the voltage circuitry comprising a voltage regulation unit and a voltage measurement unit; an isolation and amplification circuitry for receiving the voltage signal provided by the primary sensor unit and isolating and amplifying the voltage signal; a voltage signal conditioning unit for conditioning the voltage signal; an override protection circuitry receiving input from the secondary sensor, for powering up the tripper in an event of transient short circuit or instantaneous fault condition and also for providing an output signal in an event of transient short circuit or instantaneous fault condition; a microcontroller having an analogue-to-digital convertor (ADC), the ADC receiving voltage signal from the voltage circuitry through the voltage regulation unit and the voltage measurement unit for further analysis such as and including undervoltage protection, overvoltage protection, phase reverse protection and power measurement; the microcontroller receiving input also from the voltage signal conditioning unit and the override protection circuitry and also having a software program for generating tripping pulse as required according to selected rating; and a tripping circuitry receiving trip signal from the microcontroller and bumping off any nuisance tripping received. The tripping circuitry comprises IGBT or any switching device suitable for direct current application.
The tripper is connected to a trip coil for receiving input from the tripping circuitry and tripping the circuit breaker.

The override protection circuitry comprises a pick-up power supply circuitry and a current signal conditioning circuitry, wherein the pick-up power supply circuitry gets input from the current transformer energized by a DC current gradient during a short-circuit and powers up the trip unit during short circuit condition; and the current signal conditioning circuitry gets input from the Rogowski coil; which provides an output proportional to the derivative of the main line current, and processes it through an integrator/filter to generate same primary signal, which is fed to the microcontroller for further processing. The override protection circuitry thus receives output from the secondary sensor unit and trips the circuit breaker only in override situation.
The output of the shunt is fed to the analogue-to-digital convertor (ADC) of the microcontroller via a specific isolation and amplification driver IC for further measurements, since the voltage signal viz. the output of the shunt is a small value signal in the range of few mV and therefore cannot be directly processed for analysis. The specific isolates the electronic trip unit from the main live terminals. Furthermore the microcontroller contains a software program which has appropriate code to generate tripping pulse as required according to selected rating. The microcontroller senses the ADC input signal and makes decision accordingly. When the ADC input signal exceeds a predefined threshold limit the microcontroller generates an output signal either after a certain time interval or immediately (as per the setting of selection switches and the microcontroller programming) to trip the circuit breaker, and opens the current closed loop. The selection switches are provided for multiple settings of overload and short circuit/instantaneous direct current, for deciding whether under voltage, over voltage and phase reverse features are required or not, and for selecting time delay of overload and short circuit direct current protection.
The output of the microcontroller is fed to the tripping circuit. The tripping circuit bumps off any nuisance tripping.
The output of the tripping circuitry is then fed to the tripping coil that trips the circuit breaker mechanism.
Being an intelligent combination of electronic circuitry and microcontroller, electronic trip unit of the present invention provides reliable and precise protection. The trip unit is independent of ambient temperature and also there is no requirement of calibration. The programmability of the trip unit renders it extremely versatile.
Furthermore, by using microcontroller it is possible to provide various functions like communication, remote monitoring, display, energy metering.
Also, it is possible to achieve any time-current characteristic by introducing minimal modifications in the microcontroller programming.

We claim:
1. A direct current-operated electronic trip unit for a moulded case circuit breaker or an air circuit breaker, for providing protection to electrical circuitry and equipment from damage due to faults occurring in direct current system such as direct current overload and short circuit condition, comprising:
a primary sensor unit for providing a voltage signal proportional to the direct current following through main lines;
a secondary sensor comprising a current transformer and a Rogowski coil;
a tripper comprising:
a voltage circuitry through which the tripper is powered by main lines, the voltage circuitry comprising a voltage regulation unit and a voltage measurement unit;
an isolation and amplification circuitry for receiving the voltage signal provided by the primary sensor unit and isolating and amplifying the voltage signal;
a voltage signal conditioning unit for conditioning the voltage signal;
an override protection circuitry receiving input from the secondary sensor, for powering up the tripper in an event of transient short circuit or instantaneous fault condition and also for providing an output signal in an event of transient short circuit or instantaneous fault condition;
a microcontroller powered by the voltage circuitry after receiving input from main line terminals and stepping down, filtering and regulating the same, the microcontroller having an analogue-to-digital convertor (ADC), the ADC receiving voltage signal from the voltage circuitry through the voltage regulation unit and the voltage measurement unit for further analysis such as and including undervoltage protection, overvoltage protection, phase reverse protection and power measurement; the microcontroller receiving input also from the voltage signal conditioning unit and the override protection circuitry and also having a software program for generating tripping pulse as required according to selected rating; and

a tripping circuitry receiving trip signal from the microcontroller and bumping off any nuisance tripping received; and
a trip coil for receiving input from the tripping circuitry and tripping the circuit breaker.
2. The electronic trip unit of Claim 1 wherein further comprising plurality of selection switches for multiple settings of overload and short circuit/instantaneous direct current, for deciding whether under voltage, over voltage and phase reverse features are required or not, and for selecting time delay of overload and short circuit direct current protection.
3. The electronic trip unit of Claim 2 wherein when the ADC input signal exceeds a predefined threshold limit the microcontroller generates an output signal either after a certain time interval or immediately, as per setting of the selection switches and the microcontroller programming, to trip the circuit breaker.
4. The electronic trip unit of Claim 1 wherein the override protection circuitry trips the circuit breaker only in override situation, and further comprises a pick-up power supply circuitry and a current signal conditioning circuitry, wherein the pickup power supply circuitry gets input from the current transformer energized by a DC current gradient during a short-circuit and powers up the trip unit during short circuit condition; and the current signal conditioning circuitry gets input from the Rogowski coil; which provides an output proportional to the derivative of the main line current, and processes it through an integrator/filter to generate same primary signal, which is fed to the microcontroller for further processing.
5. The electronic trip unit of Claim 1 wherein the primary sensor unit comprises a shunt or a Hall effect sensor having dimensions in the range of 15 cubic millimetres to 70 cubic millimetres depending upon the frame size of the circuit breaker, and is thus capable of being installed inside the circuit breaker.
6. The electronic trip unit of Claim 1 wherein the primary sensor unit has resistance in a range of 5 micro-ohms to 300 micro-ohms so as to permit power dissipation compatibly with plastic support of the circuit breaker, both at rated current state as well as short circuit current condition.
7. The electronic trip unit of Claim 1 wherein the tripping circuitry comprises IGBT or any switching device suitable for direct current application.

8. The electronic trip unit of Claim 1 which can be rendered compatible with additional functions and/or solutions for energy metering, communication, display, remote monitoring, automation, diagnosis, achieving any time-current characteristics, and the like, by connecting thereto respective hardware equipment and providing operating code in the software program of the microcontroller.
9. The electronic trip unit of Claim 1 the functioning whereof is rendered independent of ambient temperature by virtue of absence of any bi-metal element.