FIELD OF THE INVENTION

The present Invention relates to the fields of an electrical circuit breaker. The present invention specifically relates to a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior.

BACKGROUND OF THE INVENTION

Circuit breakers are widely used to protect electrical loads such as electrical circuits or electrical equipments. The breakers are designed to protect the loads from damage caused by an overload or a short circuit by interrupting the power supply to the loads if the current level flowing through the circuit breaker exceeds preset thresholds or limits. In case of excessive current loads, the circuit breaker automatically breaking the electrical circuit to disconnect a portion of the network connected to the loads. The circuit breakers are designed in such a way to determine the current level in relation to the rated current. The current level above the rated current level constitutes an overload condition, which eventually results in tripping of the breaker to interrupt the power supply to the loads.

Nowadays, a variety of electric circuit breakers is on the market for a variety of different rated currents, adapted to the variety of needs which arise from the existing variety of types of consumers, load levels and network load constraints. However, one or more of these parameters of an electrical installation may change sometimes for various reasons. In a power distribution network, a need may arise to update the tripping current level or the degree of protection for the circuit protected by the circuit breaker. To achieve this with conventional circuit breakers, it is necessary to replace the existing electric circuit breaker having a first rated current by another electric circuit breaker having another rated current adapted to the new situation. This is laborious, time consuming and particularly disadvantageous in large electricity distribution networks. Further, change of the tripping current level during the ongoing operation of the circuit breaker is impossible.

Conventionally, various mechanisms are utilized for controlling the closing and opening circuits in the circuit breaker during fault conditions. These mechanisms utilize the current transformer for measuring the phase currents, along with other electrical components, to make up the breaker system. The current transformers used in existing circuit breaker devices are designed to supply power to the circuit and to sense the phase current ranges. If secondary faults and severe overloads are occurred in the circuit, the conventional circuit breaker fails to terminate the supply power to the circuit, which leads to damage of the transformers and hence affects the overall operation and lifetime of the breaker.

With respect to the conventional approaches, it does not protect the transformer in case of secondary faults and severe overloads, which results in inappropriate operation and damage to the transformer. Moreover, it is necessary to install a variety of different circuit breakers with a variety of given rated currents and to replacement of the damaged transformer, which leads to inflexibilities with adverse impacts on the costs for maintenance and administration. Therefore, it is desirable to provide a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior, which is capable of overcoming the aforementioned drawbacks.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior, which effectively protects the transformer against damage due to secondary faults and severe overloads in a highly cost effective manner.

Another object of the present invention is to provide a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior, which facilitates safer operation, more reliable service and visual warning of the existence of uneconomical loading conditions with less installation cost.

According to one aspect, the present invention, which achieves the objectives, relates to a programmable breaker comprising current transformers (CT) connected to power supply cables of a circuit for measuring current values in the circuit. A resistance temperature detector unit is associated with the transformers for measuring temperature of the transformers, where the temperature comprises oil temperature and winding temperature. A control unit is interfaced with the transformers and the resistance temperature detector unit for acquiring and digitizing the measured current values in the circuit and the measured temperature of the transformers. A latch relay means is interconnected with the control unit and is placed in between the transformers and loads for opening and closing the circuit depending on a load condition and control signals from the control unit. The control unit determines and analyzes the measured current values and the measured temperature with respect to a rated current value and a desired temperature and outputs the appropriate control signals to switch on/off the latch relay means in accordance with analysis of the measured current values and the measured temperature. Such arrangement of the programmable breaker protects the transformer against damage due to secondary faults and severe overloads and also provides safer operation, more reliable service and visual warning of the existence of uneconomical loading conditions with less installation cost.

In addition, the control unit further comprises signal conditioners that are interconnected with the transformers for conditioning and digitizing the measured current values. A programmable microcontroller is associated with the signal conditioners to acquire and analyze the measured current values and the temperature of the transformers in comparison with the rated current value and the desired temperature. Driver units are in communication with the microcontroller and the latch relay means for driving the appropriate control signals to the latch relay means. The microcontroller is connected with an external memory for storing a password security, a fault message, the measured current values, the measured temperature, the rated current value and the desired temperature. The microcontroller is communicated with a display unit for displaying the measured current values, the measured temperature and the fault message. The microcontroller is configured with a reset button for resetting operation of the programmable breaker after resolving any faults.

Moreover, the latch relay means is arranged with a set of terminals for connecting the transformers to the loads and a set of conducting wires connected to the control unit for receiving the control signals. The current values comprise R-phase current value, Y-phase current value and B-phase current value. If the measured temperature is more than 90°C of the desired temperature irrespective of the current values, the control unit switches off the latch relay means to open the circuit and switches on the latch relay means to close the circuit after 10% reduction of the measured temperature. Similarly, if the measured current values are more than 200% of the rated current value at any measured temperature, the control unit switches off the latch relay means to open the circuit and switches on the latch relay means to close the circuit after expiration of a desired time period. If the measured current values still remain more than 200% of the rated current value, the control unit switches off the latch relay means to open the circuit and/or terminates operation of the programmable breaker until activation of the reset button.

Furthermore, if the measured current values are more than 150% of the rated current value at the measured temperature of 60°C, the control unit switches off the latch relay means to open the circuit and switches on the latch relay means to close the circuit after 5% reduction of the measured temperature. If the measured current values are more than 130% of the rated current value at the measured temperature of 70°C, the control unit switches off the latch relay means to open the circuit and switches on the latch relay means to close the circuit after 5% reduction of the measured temperature. If the measured current values are more than 120% of the rated current value at the measured temperature of SO^C, the control unit switches off the latch relay means to open the circuit and switches on the latch relay means to close the circuit after 5% reduction of the measured temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be discussed in greater detail with reference to the accompanying Figures.

FIG. 1 illustrates a block diagram of a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior, in accordance with an exemplary embodiment of the present invention;

FIG. 2 illustrates a schematic view depicting connection of a control unit, current transformers (CT), a resistance temperature detector (RTD) and a latch relay, in accordance with an exemplary embodiment of the present invention;

FIG. 3 illustrates s schematic view of the current transformers (CT), in accordance with an exemplary embodiment of the present invention; and

FIG. 4 illustrates a schematic view of the latch relay, in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a block diagram of a programmable breaker for opening and closing a circuit depending on load condition and transformer behavior is illustrated, in accordance with an exemplary embodiment of the present invention. The programmable breaker is a conditioned based transformer circuit breaker to open and close an electrical circuit depending on load conditions and transformer parameters. The transformer parameters include, but are not limited to temperature and current. The programmable breaker can be designed to easily integrate with transformers such as current transformer 2, of different ratings up to 100 KVA. The programmable breaker is mainly configured with a control unit 1, a set of current transformers (CT) 2, a resistance temperature detector (RTD) 3 and a latch relay 4. The control unit 1 is arranged with a microcontroller 11, a set of analog to digital signal conditioners 12, a set of driver units 13 and a set of output units 14.

The micro controller 11 can be programmable at any time and configured with Atmen 89S52, which is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable flash memory. The micro controller 11 is manufactured using Atmen’s high-density nonvolatile memory technology and is compatible with the Industry-standard 80C51 instruction set and pinot. The on-chip flash allows the program memory to be reprogrammed in-system or by a nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable flash on a monolithic chip, the microcontroller 11 provides a highly-flexible and cost-effective solution to many embedded control applications.

Such microcontroller 11 also provides 8K bytes of flash, 256 bytes of RAM, 32 I/O lines, watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the microcontroller 11 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The idle mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.

The current transformers 2 are connected to cables of a circuit for measuring phase current values of the circuit. The R-phase, Y-Phase and B- Phase current transformers 2 respectively measure R-phase current value, Y- phase current value and B-phase current value. The analog to digital signal conditioners 12 of the control unit 1 are interconnected with the current transformers 2 for conditioning and digitizing the phase current values measured by each current transformer 2. The microcontroller 11 is associated with the signal conditioners 12 to receive and process the phase current values and temperature of the current transformers 2 measured by the RTD thermocouple 3. The temperature of the transformers 2 includes, but is not limited to oil temperature and winding temperature.

Further, the microcontroller 11 analyzes the phase current values and the measured temperature in comparison with a rated current value and a preset temperature, respectively. The microcontroller 11 is in communication with the driver units 13 and the output units 14 for actuating the appropriate driver units 13 to drive appropriate output signals of the output units 14. Each output unit 14 generates the output or control signal that contains pulsating or control voltage for switching on/off of the latch relay 4, which is connected to loads 100 in the circuit. The output signals include, but are not limited to output signal-1, output signal-2, output signal-3 and output signal-4, which are activated in accordance with analysis of the phase current values and the measured temperature.

In addition, an external memory 7 is in communication with the microcontroller 11 for storing information like password security, previous phase current values and temperature, preset temperature, rated current value, etc. A display unit 6, preferably LCD, is connected with the microcontroller 11 for displaying the phase current values, the transformer temperature and fault messages such as short-circuit fault, overloading fault, etc. A light emitting diode (LED) is configured for displaying an operational status of the programmable breaker. An automatic or manual reset button 5 is connected with the microcontroller 11 for resetting operation of the programmable breaker after resolving the short circuit faults.

Referring to FIG. 2, a schematic view depicting connection of the control unit 1, the current transformers (CT) 2, the resistance temperature detector (RTD) 3 and the latch relay 4 is illustrated, in accordance with an exemplary embodiment of the present invention. The current transformers 2 are connected to the respective phase cables of the circuit at its primary side to measure the three-phase current values of the circuit. Each current transformer 2 is provided with wire leads 2a for transferring the phase current values measured in the circuit, as shown in FIG. 3, which illustrates a schematic view of the current transformers 2, in accordance with an exemplary embodiment of the present invention. In addition, each current transformer 2 has a cable in 2b and a cable out 2c through which primary current and secondary current flows. The transformers 2 supply electrical power to the loads 100 through its secondary side via the latch relay 4. As shown in FIG.2, the latch relay 4 is arranged with a set of terminal connectors 4a for connecting the secondary side of the transformers 2 to the loads 100, and a set of conducting wires 4b, preferably three, connected to the control unit 1 for opening and closing of the latch relay 4.

The control unit 1 is connected with the wire leads 2a of each transformer 2 to receive and digitizes the measured phase current values of the circuit. The control unit 1 also receives oil and winding temperature of the transformer with the help of RTD 3. The control unit 1 compares the measured phase current values and the temperature with respect to the rated current value and the preset temperature. The control unit 1 actuates the driver units 13 to switches on the appropriate output or control signals based on the comparison result. If the measured temperature is more than 90°C of the preset temperature irrespective of the phase current values, then the control unit switches on the output signal-1 and again switches on the output signal-4 after 10% reduction of oil temperature, i.e. 81 "C.

If the measured phase current value is more than 200% of the rated current value at any measured temperature, then the control unit 1 switches on the output signal-2 within a second. After expiration of a desired time (for example, 5 minutes), the control unit 1 switches on the output signal-4. The control unit 1 switches on the output signal-2, if the measured phase current value still remains more than 200% of the rated current value. This cycle is repeated up to 2 times in two minutes of intervals. Even though, the measured phase current value still remains more than 200% of the rated current value, then the control unit 1 stops the operation of the programmable breaker until the reset button is activated.
Similarly, if the measured phase current value is more than 150% of the rated current value at oil temperature of 60°C, the control unit 1 switches on the output signal-3 within a second and again switches on the output signal-4 after 5% reduction of oil temperature. If the measured phase current value is more than 130% of the rated current value at oil temperature of 70°C, the control unit 1 switches on the output signal-3 within a second and again switches on the output signal-4 after 5% reduction of oil temperature. If the measured phase current value is more than 120% of the rated current value at oil temperature of 80°C, the control unit 1 switches on the output signal-3 within a second and again switches on the output signal-4 after 5% reduction of oil temperature.
The control unit 1 is provided with the output signals and a common signal that acts as ground. The three conducting wires 4b of the latch relay 4 are electrically connected to the output signals and the common signal of the control unit 1. Each output signals from the control unit 1 generate a pulsating voltage (12v) to either switch on or off the latch relay 4. The latch relay 4 is an electromechanical device that operates a switch to open or close based on the pulsating voltage received from the output signals, particularly opening and closing of relay contacts 4c in one-second voltage pulse width. In the three conducting wires 4b of the latch relay 4, first wire is used for opening the relay contacts 4c, second wire is used for closing the relay contacts 4c and third wire is connected to ground, as shown in FIG. 4, which illustrates a schematic view of the latch relay, in accordance with an exemplary embodiment of the present invention.
Accordingly, as shown in FIG. 2, the output signals 1 to 3 are shorted and connected to the first wire of the relay 4 for opening the relay contacts 4c whereas the output signal-4 is connected to the second wire of the relay 4 for closing the relay contacts 4c. The third wire is connected to the common signal of the control unit 1. Therefore, if the control unit 1 switches on the output signal-1 or output signal-2 or output signal-3, the relay contacts 4c are opened to prevent supply of the electric power to the loads 100. Similarly, if the control unit 1 switches on the output signal-4, the relay contacts 4c are closed to supply the electric power to the loads 100. Such arrangement of the programmable breaker protects the transformer 2 against damage due to secondary faults and severe overloads. It also provides safer operation, more reliable service and visual warning of the existence of uneconomical loading conditions with less installation cost. Hence, the overall lifespan of the programmable breaker can be enhanced. Alternatively, the control unit 1 can be connected to a power transformer to supply the electric power to the loads 100 only when the relay contacts 4c are opened, which enables continuous supply of power to the loads 100.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only. It is evident to those skilled in the art that although the invention herein is described in terms of specific embodiments thereof, there exist numerous alternatives, modifications and variations of the invention. It is intended that all such modifications and alterations be included insofar as they come within the spirit and scope of the invention as claimed or the equivalents thereof. Hence all variations, modifications and alternatives that falls within the broad scope of the appended claims comes under the gamut of the invention.

WE CLAIM:

1. A programmable breaker, comprising:

a plurality of current transformers connected to power supply cables of a circuit for measuring one or more current values in the circuit;

a resistance temperature detector unit associated with said transformers for measuring temperature of said transformers, the temperature comprises oil temperature and winding temperature;

a control unit interfaced with said transformers and said resistance temperature detector unit for acquiring and digitizing the measured current values in the circuit and the measured temperature of said transformers; and

a latch relay means interconnected with said control unit and placed in between said transformers and loads for opening and closing the circuit depending on a load condition and one or more control signals from said control unit, wherein said control unit determines and analyzes the measured current values and the measured temperature with respect to a rated current value and a desired temperature and outputs the appropriate control signals to switch on/off said latch relay means in accordance with analysis of the measured current values and the measured temperature.

2. The breaker as claimed in claim 1, wherein said control unit further comprising:

one or more signal conditioners interconnected with said transformers for conditioning and digitizing the measured current values;

a programmable microcontroller associated with said signal conditioners to acquire and analyze the measured current values and the temperature of said transformers in comparison with the rated current value and the desired temperature; and

one or more driver units in communication with said microcontroller and said latch relay means for driving the appropriate control signals to said latch relay means.

3. The breaker as claimed in claim 2, wherein said programmable microcontroller is connected with an external memory for storing a password security, a fault message, the measured current values, the measured temperature, the rated current value and the desired temperature.

4. The breaker as claimed in claim 2, wherein said programmable microcontroller is communicated with a display unit for displaying the measured current values, the measured temperature and the fault message.

5. The breaker as claimed in claim 2, wherein said programmable microcontroller Is configured with a reset button for resetting operation of said programmable breaker after resolving any faults.

6. The breaker as claimed in claim 1, wherein said latch relay means is arranged with one or more terminals for connecting said transformers to the loads and one or more conducting wires connected to said control unit for receiving the control signals.

7. The breaker as claimed in claim 1, wherein the current values comprise R- phase current value, Y-phase current value and B-phase current value.

8. The breaker as claimed in claim 1, wherein if the measured temperature is more than 90°C of the desired temperature irrespective of the current values, said control unit switches off said latch relay means to open the circuit and switches on said latch relay means to close the circuit after 10% reduction of the measured temperature.

9. The breaker as claimed in claim 1, wherein if the measured current values are more than 200% of the rated current value at any measured temperature, said control unit switches off said latch relay means to open the circuit and switches on said latch relay means to close the circuit after expiration of a desired time period.

10. The breaker as claimed in claim 9, wherein if the measured current values still remain more than 200% of the rated current value, said control unit switches off said latch relay means to open the circuit and/or terminates operation of said programmable breaker until activation of said reset button.

11. The breaker as claimed in claim 1, wherein if the measured current values are more than 150% of the rated current value at the measured temperature of 60°C, said control unit switches off said latch relay means to open the circuit and switches on said latch relay means to close the circuit after 5% reduction of the measured temperature.

12. The breaker as claimed in claim 1, wherein if the measured current values are more than 130% of the rated current value at the measured temperature of 70°C, said control unit switches off said latch relay means to open the circuit and switches on said latch relay means to close the circuit after 5% reduction of the measured temperature.

13. The breaker as claimed in claim 1, wherein if the measured current values are more than 120% of the rated current value at the measured temperature of 80°C, said control unit switches off said latch relay means to open the circuit and switches on said latch relay means to close the circuit after 5% reduction of the measured temperature.