Description:FIELD
The present disclosure generally relates to electrical power distribution and protection. More particularly, the present disclosure pertains to a low tension (LT) panel protection system for overcurrent and earth fault protection.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Electrical power distribution systems are commonly used in industrial, commercial, and utility environments to supply low voltage power to various loads through Low Tension (LT) panels. These panels include protective devices such as air circuit breakers (ACBs) to isolate circuits during overcurrent or earth fault conditions and maintain operational safety.
In known systems, LT panel protection is typically achieved using OEM-specific electronic releases integrated within the ACBs. These self-powered protection releases derive operating energy from internal current transformers embedded in the breakers and include overcurrent and earth fault protection features. While these systems offer a compact design, they suffer from several drawbacks. The protection logic is manufacturer-dependent, making it difficult to standardize across different panels or breakers. Moreover, these integrated releases do not support fault data logging, lack flexibility in configuration, and require special OEM kits or procedures for testing. Replacement or upgrade often involves changing the entire ACB, increasing maintenance costs and downtime.
Furthermore, the inability to perform trial tripping by current injection easily results in longer commissioning and troubleshooting times. These limitations hinder scalability, interoperability, and cost-effectiveness in modern electrical installations that demand modular, testable, and data-capable protection systems.
Therefore, there is a need for a system and a method that address the above limitations by proposing a modular LT panel protection architecture that offers improved flexibility, easier maintenance, and enhanced fault management capabilities.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a system and a method that provide a low tension (LT) panel protection architecture capable of overcoming the limitations of conventional OEM-specific, self-powered LT releases.
Another object of the present disclosure is to provide a system and a method that implement a modular and standardized protection approach using conventional current transformers (CTs) and an auxiliary-powered numerical relay.
A yet another object of the present disclosure is to provide a system and a method that enable overcurrent and earth fault protection through a numerical relay applying ANSI protection functions 50, 51, 50N, and 51N.
A further object of the present disclosure is to provide a system and a method that support fault recording, simplified testing, and trial tripping without requiring full panel shutdown or OEM-specific tools.
A still further object of the present disclosure is to provide a system and a method that reduce maintenance effort and enhance component interchangeability by decoupling the protection logic from the breaker make and model.
An object of the present disclosure is to provide a system and a method that utilize existing 230V AC shunt trip coils in air circuit breakers to execute protective tripping, thereby reducing cost and improving retrofit compatibility.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a low tension (LT) panel protection system, the system comprising:
a) at least one current transformer (CT) mounted on a low-voltage (LV) side of a transformer or on a lower tension (LT) panel, the CT configured to measure electrical current in at least three-phase conductors and a neutral conductor, and to generate analog current signals representative of the measured currents;
b) a numerical relay, operatively coupled to the CTs and powered by an auxiliary 230V AC supply, the numerical relay comprising:
• at least four current input elements configured to receive the analog current signals from the CTs;
• a digital signal processing unit configured to perform real-time calculation of individual phase currents and the resultant earth fault current by summing vectorially the inputs from said phase and neutral currents (la + lb + lc + ln); and
• a protection logic module configured to continuously monitor the calculated currents and apply overcurrent (ANSI 50, 51) and earth fault protection functions (ANSI 50N, 51N) based on user-defined threshold values and time-current characteristics;
c) an air circuit breaker (ACB), connected downstream of transformer and comprising a 230V AC shunt trip coil, the ACB operatively coupled to the numerical relay, wherein the trip coil is actuated in response to a trip signal output from the numerical relay;
d) wherein said numerical relay, upon detecting an overcurrent or earth fault condition, generates a trip signal and transmits it to the ACB, causing the shunt trip coil to actuate and thereby disconnect the LT panel from the electrical load.
In an embodiment, each CT is selected based on predefined parameters comprising current transformation ratio, rated burden, and protection class, such that signal integrity and compatibility with the input ratings of the numerical relay are maintained.
In another embodiment, the numerical relay comprises an integrated fault recording module configured to capture and store timestamped data including the type, magnitude, and duration of the fault, wherein said data is accessible for post-event diagnostic analysis.
In yet another embodiment, the system further comprises an interface module operatively connected to the numerical relay, the interface module is configured to accept secondary current injection signals for the simulation of fault conditions without requiring disconnection of power to the LT panel, thereby validating the performance of the protection functions.
In a further embodiment, the shunt trip coil is configured to support a manual test mode by allowing a temporary short-circuit across the relay’s trip output contact, thereby verifying tripping integrity without requiring actual fault current.
In a still further embodiment, the numerical relay comprises standardized and detachable terminal blocks for plug-and-play installation, enables the replacement of relays without alteration to wiring topology or mechanical interfaces or the ACB.
The present disclosure further envisages a method for detecting and isolating faults in a low tension (LT) panel protection system, the method comprising the steps of:
• installing current transformers (CTs) on a low-voltage side of a transformer or LT panel, and sensing current values in each of the phase lines and the neutral line;
• transmitting the sensed analog current signals to a numerical relay powered by an auxiliary 230V AC supply;
• converting the analog current signals into digital form and calculating an earth fault current by vectorially summing the phase and neutral currents within the numerical relay;
• detecting overcurrent or earth fault conditions based on predefined threshold settings for ANSI functions 50, 51, 50N, and 51N;
• generating a trip signal when any of said fault conditions are detected;
• transmitting the trip signal to a 230V AC shunt trip coil of an air circuit breaker (ACB); and
• actuating the trip coil to mechanically open the ACB and disconnect power from the downstream LT panel.
In an embodiment, the method further comprising injecting a test current into the secondary terminals based on relay setting of the CTs through an interface to simulate fault conditions and validate relay operation without interrupting the live operation of the LT panel.
In another embodiment, the method further comprising the step of manually initiating a test trip by shorting the trip contact of the numerical relay, thereby verifying the integrity of the tripping mechanism and confirming operational readiness of the shunt trip coil.
In yet another embodiment, the method further comprising recording timestamped fault data including fault magnitude, duration, and type into a non-volatile memory of the numerical relay, the data being retrievable for diagnostic and forensic analysis.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A system and a method for detecting and isolating faults in a low tension (LT) panel protection system of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a block diagram of a system for detecting and isolating faults in a low tension (LT) panel protection system in accordance with an embodiment of the present disclosure; and
Figure 2 illustrates a block diagram of method steps for detecting and isolating faults in a low tension (LT) panel protection system in accordance with an embodiment of the present disclosure.
LIST OF REFERENCE NUMERALS USED IN THE DESCRIPTION AND DRAWING:
100 System
CT Current Transformer
C10, C30, C50 Three-Phase Conductors
C70 Neutral Conductor
ACB Air Circuit Breaker
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known assembly structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms “comprises”, “comprising”, “including” and “having” are open-ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
When an element is referred to as being “mounted on”, “engaged to”, “connected to” or “coupled to” another element, it may be directly on, engaged, connected, or coupled to the other element. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed elements.
The conventional LT breaker protection relies on non-interchangeable, OEM-specific releases most of which do not support fault data recording. These releases differ across OEMs and lack compatibility, leading to challenges during failures and limited technical support. Proposals to replace faulty releases or breakers are often costly, impractical, and unsustainable. Testing such releases is cumbersome, as it requires specialized kits and often results in prolonged investigations and system shutdowns. The absence of fault data recording, combined with the difficulty of testing, contributes to extended diagnostic times when misoperations occur. Overall, the conventional approach lacks efficiency, poses significant challenges in maintenance and troubleshooting, and is more expensive to sustain due to dependence on OEMs and their monopoly over replacement parts.
The present disclosure relates to Low Tension Panel (LTP) protection and proposes a transition from the conventional self-powered, release-based protection philosophy to an auxiliary-powered protection architecture. In the proposed approach, conventional current transformers (CTs) and an auxiliary-powered numerical relay are installed within the LT panel. The existing Air Circuit Breaker (ACB), equipped with a 230V AC shunt trip coil, is utilized to execute tripping operations during fault conditions. Fault currents are sensed by the CTs, which are selected based on acceptable current ratio, burden, and protection class, and are installed either on the transformer's low-voltage side or within the LT panel.
The numerical relay, featuring four current input elements, is capable of recording fault events and is configured to provide protection functions for overcurrent (ANSI 50 and 51) and earth fault (ANSI 50N and 51N) conditions based on measured current values. Earth fault current is determined by summing the individual phase currents Ia, Ib, Ic, and the neutral current In, where In represents the residual or balancing current under unbalanced load conditions. This architecture effectively integrates conventional CTs with advanced numerical relay logic while reusing existing 230V shunt trip coils in the LT breaker, ensuring cost-effective, standardized, and easily maintainable panel protection.
The present disclosure will now be described with reference to Figure 1. The present disclosure envisages a low tension (LT) panel protection system (100).
The system (100) comprises at least one current transformer (CT) mounted on a low-voltage (LV) side of a transformer or on a lower tension (LT) panel. The CT is configured to measure electrical current in at least three-phase conductors (C10, C30, C50) and a neutral conductor (C70). The CT is further configured to generate analog current signals representative of the measured currents.
In an embodiment, each CT is selected based on predefined parameters comprising current transformation ratio, rated burden, and protection class, such that signal integrity and compatibility with the input ratings of the numerical relay are maintained.
The system (100) comprises a numerical relay, operatively coupled to the CTs and powered by an auxiliary 230V AC supply. The numerical relay comprises at least four current input elements configured to receive the analog current signals from the CTs. Further, the numerical relay comprises a digital signal processing unit configured to perform real-time calculation of individual phase currents and the resultant earth fault current by summing vectorially the inputs from said phase and neutral currents (la + lb + lc + ln).
The numerical relay additionally comprises a protection logic module configured to continuously monitor the calculated currents and apply overcurrent (ANSI 50, 51) and earth fault protection functions (ANSI 50N, 51N) based on user-defined threshold values and time-current characteristics.
In an embodiment, the numerical relay comprises an integrated fault recording module configured to capture and store timestamped data including the type, magnitude, and duration of the fault, wherein said data is accessible for post-event diagnostic analysis.
The system (100) further comprises an air circuit breaker (ACB), connected downstream of the LT panel, comprising a 230V AC shunt trip coil, the ACB is operatively coupled to the numerical relay, wherein the trip coil is actuated in response to a trip signal output from the numerical relay.
In an embodiment, the shunt trip coil is configured to support a manual test mode by allowing a temporary short-circuit across the relay’s trip output contact, thereby verifying tripping integrity without requiring actual fault current.
In another embodiment, the numerical relay comprises standardized and detachable terminal blocks for plug-and-play installation, enables the replacement of relays without alteration to wiring topology or mechanical interfaces or the ACB.
The numerical relay, upon detecting an overcurrent or earth fault condition, generates a trip signal and transmits it to the ACB, causing the shunt trip coil to actuate and thereby disconnect the LT panel from the electrical load.
In an embodiment, the system (100) further comprises an interface module operatively connected to the numerical relay, the interface module configured to accept secondary current injection signals for simulation of fault conditions without requiring disconnection of power to the LT panel, thereby validating the performance of the protection functions.
Figure 2 will now be described which illustrates a flowchart of a method (200) for detecting and isolating faults in a low tension (LT) panel protection system (100). The method comprising the steps of:
• installing current transformers (CTs) on a low-voltage side of a transformer or LT panel, and sensing current values in each of the phase lines and the neutral line (202);
• transmitting the sensed analog current signals to a numerical relay powered by an auxiliary 230V AC supply (204);
• converting the analog current signals into digital form and calculating an earth fault current by vectorially summing the phase and neutral currents within the numerical relay (206);
• detecting overcurrent or earth fault conditions based on predefined threshold settings for ANSI functions 50, 51, 50N, and 51N (208);
• generating a trip signal when any of said fault conditions are detected (210);
• transmitting the trip signal to a 230V AC shunt trip coil of an air circuit breaker (ACB) (212); and
• actuating the trip coil to mechanically open the ACB and disconnect power from the downstream LT panel (214).
In an embodiment, the method further comprises injecting a current based on relay setting into the secondary terminals of the CTs through interface terminal blocks to simulate fault conditions, without taking entire LT switchgear shutdown, by restoring supply through LT tie and bus, and keeping breaker open for testing.
In another embodiment, the method further comprising the step of manually initiating a test trip by shorting the trip contact of the numerical relay, thereby verifying the integrity of the tripping mechanism and confirming operational readiness of the shunt trip coil.
In yet another embodiment, the method further comprising recording timestamped fault data including fault magnitude, duration, and type into a non-volatile memory of the numerical relay, the data being retrievable for diagnostic and occurence investigation analysis.
The LTP (Low Tension Panel) Protection Alternate Approach introduces a shift from conventional, OEM-specific, self-powered release mechanisms to a more flexible and standardized auxiliary-powered protection architecture. The proposed system involves the installation of conventional current transformers (CTs) and a numerical relay within the LT panel. Additionally, existing Air Circuit Breakers (ACBs) equipped with 230V AC shunt trip coils are utilized for executing breaker tripping operations during fault conditions. In this scheme, fault currents are sensed using conventional CTs of appropriate current ratio, burden, and protection class from recommended makes. These CTs are installed either on the low-voltage (LV) side of the transformer or directly on the LT panel busbars. The CTs are connected to a numerical relay with four current input elements, which is capable of recording fault events and executing protection functions for overcurrent (ANSI 50, 51) and earth fault (ANSI 50N, 51N) conditions. The earth fault current is computed by vectorially summing the phase and neutral currents (Ia + Ib + Ic + In), where 'In' represents the balancing current in the case of an unbalanced load. The numerical relay, powered by an auxiliary 230V AC supply, processes the CT inputs in real time and triggers the shunt trip coil in the ACB upon detection of a fault. This integration of traditional CTs, advanced numerical relay logic, and existing breaker trip coils ensures efficient and standardized protection for the LT panel, while significantly reducing OEM dependency.
In conventional systems, switching from one release to another—or even upgrading to a newer version from the same OEM—is often not feasible due to embedded, breaker-specific CTs and releases. These integrated systems lack backward or cross-OEM compatibility. The proposed scheme decouples the three building blocks of the protection system: CTs, relay, and trip coil. With conventional, standardized secondary CTs and auxiliary-powered trip coils, switching from one OEM relay to another, or between release versions, becomes seamless and cost-effective. Current protection setups use OEM-specific release mechanisms, resulting in inconsistencies and high inventory requirements. Under the new scheme, the entire protection system is standardized: CTs with 5A secondary output, a numerical relay powered by 230V AC, and ACBs with 230V AC shunt trip coils. This standardization streamlines design, testing, maintenance, and inventory management across multiple installations.
In the conventional setup, protection testing is only possible using proprietary OEM kits or high current injection setups. The new scheme supports easy testing with standard secondary injection kits. Current practice requires full panel shutdown, lengthy downtime, and allows only partial function checks (usually earth fault only). The new approach allows testing with the breaker kept open, by injecting current at CT secondary terminals—no full panel shutdown is required. Trial tripping under current practices requires real fault currents or simulated conditions. The new setup allows trial tripping simply by shorting the trip contact, facilitating easy health checks of the trip coil and mechanism. This minimizes long-term risk of mechanical seizure due to inactivity.
The numerical relay includes fault recording capabilities with date and time stamping. This feature supports faster and more effective post-event diagnostics, reducing investigation time and improving fault response planning. The proposed LTP protection scheme strategically addresses a longstanding industry need for cost-effective, modular, and OEM-independent breaker protection. By separating the CTs, relay, and trip mechanism, and leveraging conventional components and auxiliary power, the system delivers operational flexibility, reliability, ease of testing, and enhanced fault analysis—while eliminating the constraints of OEM-specific solutions.
In a representative industrial installation—such as a medium-sized manufacturing plant—the low tension (LT) panel protection system (100) disclosed in the present disclosure is implemented downstream of a step-down power transformer. The installation begins with the placement of current transformers (CTs) on the low-voltage side of the transformer or directly onto the LT panel busbars. These CTs are installed to monitor the electrical currents flowing through three-phase conductors (C10, C30, C50) and the neutral conductor (C70). Each CT is carefully chosen based on defined parameters, including its current transformation ratio, burden rating, and protection class, to ensure compatibility with the input requirements of the numerical relay and to maintain signal integrity across the system.
The analog output signals from the CTs, which are proportional to the real-time current in the monitored lines, are transmitted to the numerical relay—an essential component of the protection system (100). The numerical relay is powered by an auxiliary 230V AC supply and is equipped with at least four current input elements dedicated to receiving signals from the CTs. Inside the relay, a digital signal processing unit performs continuous real-time analysis, including vector summation of phase currents (Ia from C10, Ib from C30, Ic from C50) and neutral current (In from C70), to compute the resultant earth fault current. This computation enables the detection of unbalanced loading or genuine earth fault conditions.
The protection logic module within the relay applies ANSI standard protection functions, specifically 50/51 for overcurrent protection and 50N/51N for earth fault protection. These are evaluated against user-configured threshold values and time-current curves tailored for the specific load and safety requirements of the plant. For instance, if a sudden overcurrent occurs due to a motor short circuit, or if an insulation failure causes a sudden current increase, the relay identifies the deviation, verifies it against its protection settings, and generates a corresponding trip signal.
This trip signal is transmitted to the 230V AC shunt trip coil of the air circuit breaker (ACB), which is positioned downstream within the LT panel. Upon receipt of the signal, the shunt trip coil activates, mechanically opening the ACB, and thereby instantaneously disconnecting the downstream electrical loads to isolate the fault. This disconnection protects critical equipment and prevents potential cascading failures or fire hazards.
To ensure high reliability and maintainability, the numerical relay also includes an integrated fault recording module. This module logs critical event data—such as fault type, current magnitude, and duration—along with timestamps into non-volatile memory. This logged data is crucial for diagnostic and forensic analysis post-event and significantly reduces downtime during fault investigation.
Additionally, the protection system (100) supports both manual and automated testing capabilities. An interface module allows engineers to inject secondary currents into the relay via the CT terminals without requiring entire LT bus shutdown, by providing power through LT tie and bus while keeping breaker open for testing. This capability simulates fault conditions and validates protection function performance. Furthermore, the relay allows a simple manual test by shorting its trip output contact to verify ACB trip coil integrity and breaker mechanism health. These features enhance system safety, support predictive maintenance, and reduce operational risk.
The inclusion of standardized, detachable terminal blocks in the relay ensures quick replacement or upgrade without the need for reconfiguration of wiring or mechanical interfaces, making the system truly modular and OEM-independent. This modular design aligns with modern electrical infrastructure goals—scalability, flexibility, and reduced total cost of ownership.
The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment but are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a system and method for detecting and isolating faults in a low tension (lt) panel protection system, that:
• provides a low tension (LT) panel protection architecture capable of overcoming the limitations of conventional OEM-specific;
• provides auxiliary powered numerical relays;
• implement a modular and standardized protection approach;
• uses conventional current transformers (CTs) and an auxiliary-powered numerical relay;
• enables overcurrent and earth fault protection through a numerical relay applying ANSI protection functions 50, 51, 50N, and 51N;
• supports fault recording, simplified testing, and trial tripping;
• does not require full panel shutdown or OEM-specific tools; and
• reduces maintenance effort and enhance component interchangeability by decoupling the protection logic from the breaker make and model.
Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles, or the like that has been included in this disclosure is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions, or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the dislcosure specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
, Claims:WE CLAIM:
1. A low tension (LT) panel protection system, the system comprising:
a) at least one current transformer (CT) mounted on a low-voltage (LV) side of a transformer or on a lower tension (LT) panel, the CT configured to measure electrical current in at least three-phase conductors and a neutral conductor, and to generate analog current signals representative of the measured currents;
b) a numerical relay, operatively coupled to the CTs and powered by an auxiliary 230V AC supply, the numerical relay comprising:
• at least four current input elements configured to receive the analog current signals from the CTs;
• a digital signal processing unit configured to perform real-time calculation of individual phase currents and the resultant earth fault current by summing vectorially the inputs from said phase and neutral currents (la + lb + lc + ln); and
• a protection logic module configured to continuously monitor the calculated currents and apply overcurrent (ANSI 50, 51) and earth fault protection functions (ANSI 50N, 51N) based on user-defined threshold values and time-current characteristics;
c) an air circuit breaker (ACB), connected downstream of the LT panel, comprising a 230V AC shunt trip coil, the ACB operatively coupled to the numerical relay, wherein the trip coil is actuated in response to a trip signal output from the numerical relay;
d) wherein said numerical relay, upon detecting an overcurrent or earth fault condition, generates a trip signal and transmits it to the ACB, causing the shunt trip coil to actuate and thereby disconnect the LT panel from the electrical load.
2. The system as claimed in claim 1, wherein each CT is selected based on predefined parameters comprising current transformation ratio, rated burden, and protection class, such that signal integrity and compatibility with the input ratings of the numerical relay are maintained.
3. The system as claimed in claim 1, wherein said numerical relay comprises an integrated fault recording module configured to capture and store timestamped data including the type, magnitude, and duration of the fault, wherein said data is accessible for post-event diagnostic analysis.
4. The system as claimed in claim 1, further comprises an interface module operatively connected to the numerical relay, the interface module configured to accept secondary current injection signals for simulation of fault conditions without requiring entire shutdown of the LT panel, thereby validating the performance of the protection functions.
5. The system as claimed in claim 1, wherein the shunt trip coil is configured to support a manual test mode by allowing a temporary short-circuit across the relay’s trip output contact, thereby verifying tripping integrity without requiring actual fault current.
6. The system as claimed in claim 1, wherein the numerical relay comprises standardized and detachable terminal blocks for plug-and-play installation, enables the replacement of relays without alteration to wiring topology or mechanical interfaces or the ACB.
7. A method for detecting and isolating faults in a low tension (LT) panel protection system, the method comprising the steps of:
• installing current transformers (CTs) on a low-voltage side of a transformer or LT panel, and sensing current values in each of the phase lines and the neutral line;
• transmitting the sensed analog current signals to a numerical relay powered by an auxiliary 230V AC supply;
• converting the analog current signals into digital form and calculating an earth fault current by vectorially summing the phase and neutral currents within the numerical relay;
• detecting overcurrent or earth fault conditions based on predefined threshold settings for ANSI functions 50, 51, 50N, and 51N;
• generating a trip signal when any of said fault conditions are detected;
• transmitting the trip signal to a 230V AC shunt trip coil of an air circuit breaker (ACB); and
• actuating the trip coil to mechanically open the ACB and disconnect power from the downstream LT panel.
8. The method as claimed in claim 7, further comprising injecting a test current into the secondary terminals of the CTs through the interface to simulate fault conditions and validate relay operation without requiring entire shutdown the LT bus.
9. The method as claimed in claim 8, further comprising the step of manually initiating a test trip by shorting the trip contact of the numerical relay, thereby verifying the integrity of the tripping mechanism and confirming operational readiness of the shunt trip coil.
10. The method as claimed in claim 7, further comprising recording timestamped fault data including fault magnitude, duration, and type into a non-volatile memory of the numerical relay, the data being retrievable for diagnostic and occurence analysis.

Dated this 29th day of July 2025

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R. K. DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI