DESC:TECHNICAL FIELD

The present invention generally relates to circuit breakers protection and metering, and more particularly to a micro-controller based method for earth fault detection using current unbalance.

BACKGROUND AND THE PRIOR ART

A Ground Fault is an unwanted connection between the system conductors and ground. Undetected ground fault can shut down power and damage equipment, which disrupts the flow of production leading to hours or even days of lost productivity. Ground faults can lead to safety hazards such as equipment malfunctions, fire and electric shock. The conventional circuit breakers have transformer based earth fault detection. The “insulation fault current” is measured in the neutral - earth link of the LV transformer. With introduction of electronic trip units in circuit breakers, Micro-controller based approach is used for earth fault detection. The work presented here uses four phase input current to detect the earth fault.

Traditionally, the earth fault detection was done through core balance current transformer where all the line and neutral currents would flow and current equivalent to unbalance would be produced at secondary which would be used for threshold comparison and tripping.

Alternate method was to have individual samples of line and neutral currents and then taking vector addition would result signal equivalent to core balance current transformer method. In some industries neutral is not routed through the breaker and so is not sensed. Absence of neutral current sensing in the breaker leads to tripping in earth fault. Nuisance trips will often require that an operator manually reset a breaker often which is undesirable.

To overcome the disadvantages, there exists a need to provide an improved method for avoiding tripping in circuit breaker.

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/ drawbacks of the known art.

Another object of the present invention is to provide a method of earth fault detection in circuit breakers using current unbalance.

Yet another object of the present invention is to provide a novel method to avoid tripping in circuit breaker.

Yet another object of the present invention is to provide a method for earth fault detection using current unbalance.

Yet another object of the present invention is to provide a micro-controller based method for earth fault detection using current unbalance.

Yet another object of the present invention to provide a method for individual current sampling and earth fault signal generation, using vector addition technique.

Yet another object of the present invention is to provide a method for configurable pickup and delay settings.

Still another object of the present invention is to provide a method for configuration through DIP or rotary switches, display or communication mechanism.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVNENTION

This summary is provided to introduce concepts related to method for earth fault detection using current unbalance. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

Accordingly, in one implementation, a method for fault detection based on a signal received, to be used in circuit breakers, thereby avoids tripping of the electronic tripping unit of the circuit breaker is disclosed. The method comprises of:
· Calculating the earth current in a microcontroller of the electronic tripping unit by using the signal received. Detecting whether the said earth current is greater than the predefined threshold
· If said earth current is greater than predefined threshold then using the microcontroller, checking the presence of neutral current thereby
· calculating an earth current, using a microcontroller of the electronic tripping unit, based the signal received, thereby detecting the earth current calculated is greater than a first predefined threshold value, and if the earth current detected is greater than the first predefined threshold value, using the microcontroller, checking a presence of a neutral current, thereby
· if present, checking if a value of the neutral current is greater than a second predefined threshold value and if greater than the second predefined threshold value issuing a trip command by the electronic tripping unit, and
· if the value of the neutral current is less than a second predefined threshold value, finding a value of a current unbalanced, thereby checking if the value of the current unbalanced is greater than a third predefined threshold value issuing a trip command to the electronic tripping unit.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Figure 1 illustrates a method using neutral presence and current unbalance to avoid tripping if current unbalance is above a predefined threshold, according to an embodiment of this invention;

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.

Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

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 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 are 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 dictates 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.

In the embodiments provided in the present application, it should be understood that the disclosed method, device, and data frame may be implemented in other manners. For example, the described device embodiments are merely exemplary. For example, the unit division is merely logical function division and can be other division in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features are negligible or not performed.
When the functions are implemented in the form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present invention essentially, or the part contributing to the prior art, or part of the technical solutions may be implemented in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for instructing a computer device (which may be a personal computer, a server, a network device, or the like) to perform all or a part of the steps of the method described in the embodiment of the present invention. The storage medium includes: any medium that can store program codes, such as a USB flash disk, a removable hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk, or an optical disk.

Accordingly, present invention provides a novel method to avoid tripping in circuit breaker.

While aspects of method for earth fault detection using current unbalance may be implemented in any number of different computing systems, environments, and/or configurations, the embodiments are described in the context of the following exemplary system.

The present method uses neutral presence and current unbalance to avoid tripping if current unbalance is above a predefined threshold as shown in figure 1.

Earth current is calculated using vector sum as by using the formula give below:

Wherein,
Ig indicates an Earth current
IR indicates R phase current
IY indicates Y phase current
IB indicates B phase current
IN indicates Neutral current

Referring now to figure 1 illustrates a method using neutral presence and current unbalance to avoid tripping if current unbalance is above a predefined threshold, according to an embodiment of this invention;

In one implementation, the method uses four phase input current to detect the earth fault. The method may use digital filter to extract the fundamental component of the signal received by the micro-controller.

In one implementation, the method uses neutral presence and current unbalance to avoid tripping if current unbalance is above a predefined threshold.

In one implementation, if Earth current is above a predefined threshold then neutral current presence is checked. If neutral current is above a threshold called zero thresholds then neutral is connected and system issues the action.

Neutral current below a (zero) threshold indicates neutral disconnect. If neutral current is below the (zero) threshold, then calculate current unbalance. Unbalance above a certain limit indicates earth fault presence and take action. If no current imbalance is observed then earth current formation is due to neutral absence and take action accordingly.

Accordingly, in one implementation, a method for fault detection based on a signal received, to be used in circuit breakers, thereby avoids tripping of the electronic tripping unit of the circuit breaker is disclosed. The method comprises of:
· Calculating the earth current in a microcontroller of the electronic tripping unit by using the signal received. Detecting whether the said earth current is greater than the predefined threshold
· If said earth current is greater than predefined threshold then using the microcontroller, checking the presence of neutral current thereby
· calculating an earth current, using a microcontroller of the electronic tripping unit, based the signal received, thereby detecting the earth current calculated is greater than a first predefined threshold value, and if the earth current detected is greater than the first predefined threshold value, using the microcontroller, checking a presence of a neutral current, thereby
· if present, checking if a value of the neutral current is greater than a second predefined threshold value and if greater than the second predefined threshold value issuing a trip command to the electronic tripping unit, and
· if the value of the neutral current is less than a second predefined threshold value, finding a value of a current unbalanced, thereby checking if the value of the current unbalanced is greater than a third predefined threshold value issuing a trip command to the electronic tripping unit.

In one implementation, the earth current is calculated based on fundamental components values selected from a group comprising phase currents and neutral current.

In one implementation, the first threshold value is selected from a range set by the user through User Interface such as DIP or rotary switches, display or communication through HMI. It may be understood that the range may be differ as per the applicability of the present invention.

In one implementation, the second threshold value is selected from a range 0% to 5 % of the system rated representing the noise threshold.

In one implementation, wherein the third threshold value is selected from a range set by the user through User Interface such as DIP or rotary switches, display or communication through HMI

In one implementation, said signal received is an earth fault signal.

In one implementation, said fundamental components values are extracted using a digital filter.

In one implementation, said sum is obtained using a vector summation of said fundamental components values.

In one implementation, said tripping is a delayed tripping obtained by using a timer.

A person of ordinary skill in the art may understand that, all or a part of the steps of the foregoing method embodiments may be implemented by a program instructing relevant hardware. The aforementioned program may be stored in a computer readable storage medium. When the program runs, the steps of the forgoing method embodiments are performed. The storage medium includes any medium capable of storing program code, such as a ROM, a RAM, a magnetic disk, or an optical disc.

The methodology and techniques described with respect to the exemplary embodiments can be performed using a machine, circuit breaker, switchgears, transformers and the like devices, within which a set of instructions, when executed, may cause the machine to perform any one or more of the methodologies discussed above. In some embodiments, the machine operates as a standalone device. In some embodiments, the machine may be connected (e.g., using a network) to other machines. In a networked deployment, the machine may operate in the capacity of a server or a client user machine in a server-client user network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may comprise a server computer, a client user computer, a personal computer (PC), a tablet PC, a laptop computer, a desktop computer, a control system, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.

NOVEL FEATURES:
1) Micro-controller based earth fault detection
2) Individual current sampling and earth fault signal generation using vector addition.
3) Configurable pickup and delay setting
4) Configuration through DIP or rotary switches, display or communication

Although the method for earth fault detection using current unbalance have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features are disclosed as examples of implementations for method for earth fault detection using current unbalance.

In interpreting the appended claims, it should be understood that:

a) the word “comprising” does not exclude the presence of other elements or acts than those listed in a given claim;
b) the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements;
c) any reference signs in the claims do not limit their scope;
d) several “means” may be represented by the same item or hardware or software implemented structure or function;
e) any of the disclosed elements may be comprised of hardware portions (e.g., including discrete and integrated electronic circuitry), software portions (e.g., computer programming), and any combination thereof;
f) hardware portions may be comprised of one or both of analog and digital portions;
g) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise; and
h) no specific sequence of acts or steps is intended to be required unless specifically indicated.
,CLAIMS:1. A method for fault detection based on a signal received, to be used in circuit breakers, thereby avoids tripping of the electronic tripping unit of the circuit breaker, the method comprising:
calculating an earth current, using a microcontroller of the electronic tripping unit, based the signal received, thereby detecting the earth current calculated is greater than a first predefined threshold value, and if the earth current detected is greater than the first predefined threshold value, using the microcontroller, checking a presence of a neutral current, thereby
if present, checking if a value of the neutral current is greater than a second predefined threshold value and if greater than the second predefined threshold value issuing a trip command to the electronic tripping unit, and
if the value of the neutral current is less than a second predefined threshold value, finding a value of a current unbalanced, thereby checking if the value of the current unbalanced is greater than a third predefined threshold value issuing a trip command to the electronic tripping unit.

2. The method as claimed in claim 1, wherein the earth current is calculated based on fundamental components values selected from a group comprising phase currents and neutral current.

3. The method as claimed in any of the preceding claims, wherein the first threshold value and second threshold value is selected from a pre-defined range set by one or more user through an user interface selected from at least one of DIP or rotary switches, display or communication through HMI

4. The method as claimed in any of the preceding claims, wherein the second threshold value is selected from a range of 0% to 5% of the system rated representing the noise threshold.

5. The method as claimed in any of the preceding claims, wherein said signal received is an earth fault signal.

6. The method as claimed in any of the preceding claims, wherein said fundamental components values are extracted using a digital filter.

7. The method as claimed in any of the preceding claims, wherein said sum is obtained using a vector summation of said fundamental components values.
8. The method as claimed in any of the preceding claims, wherein said tripping is a delayed tripping obtained by using a timer.