DESC:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to a protection relay, and more particularly to an electronic circuit in the protection relay for detecting overcurrent faults and thereby protecting an electrical power system.

BACKGROUND

[002] Electrical power systems are used for transmission and distribution of power to electrical loads. In order to protect the major components of the electrical power system, protection relays are used which provides protection against overcurrent, overcurrent, overload, phase loss, temperature rise and other such detrimental effects which cause damage or failure of the electrical power system.For example, motor protection relays (MPR) used only for motor protection and to protect motor and thereby increasing life of such motor devices. Just as the MPRs provide protection related to motor, transformer protection relay provides transformer related protection.

[003] Overcurrent detection circuit provides protection against excessive currents or currents beyond the acceptable current ratings, which are resulting from short circuits, ground faults and overload conditions in an electrical power system. A protection relay monitors current in the electrical power system and compares it against a selected pickup point. The protection relay senses an overcurrent condition and trips a circuit breaker connected between the electrical power system and the electrical load when the monitored current is above the selected preset value. In such events timing is initiated in accordance with a selected time-current characteristic curve and after the timing is completed the circuit breaker trips thereby cutting off the power supply.Currently, the protections are provided through software program. When CPU energizes and operates the program and then calculates the current and detects faults. Then it gives the faults of protections taking defined time by CPU programmer. In that particular time power source supply is reached at device or machine. It may decrease the life of the devices or machine. Sometimes, it may also create the severe damages to the devices or machines.

[004] Microprocessor based overcurrent relay is well known in the art. The microprocessor uses a memory to store a preset value and time-current characteristics curves. Such microprocessor relay uses software programs or algorithms for detecting faults. The microprocessor converts the monitored current to a digital value and compares the digital value against a selected preset value. When the digital value exceeds the selected preset value, a connected circuit breaker is tripped. However, since such microprocessor based relay gives fault indication after a processor takes a definite time therefore there are events wherein in that particular time, power source supply may reach an electrical load or device, causing severe damages to the electrical load or device.

[005] The prior art document EP 0231793 B1 discloses load current feedback to the excitation circuit by means of at least one additional winding of the load circuit around part of the excitation flow circuit. This does not protect the relay against excess current, but is to ensure safe response of the relay when the excitation winding and load current circuit are fed from the same voltage source and a high switching-on current of the load circuit results in breakdown of the voltage on the excitation winding.

[006] The prior art document US 20130250464 A, wherein a method and circuit for de0tecting and providing protection against an overcurrent condition is disclosed. The overcurrent detection circuit uses an opto-isolator component to generate an overcurrent condition signal to drive a protection relay in case of an overcurrent fault. However opto-isolators have limitations and cannot be used in all electrical systems. Also, high humidity may negatively affect opto-isolators as it causes electricity to arc and subsequently causing internal arc fault in the circuit.

[007] The existing hithertotechniques for detection of overcurrent faults in a device using software model,are complex, much costlier, and require extra man power for their operation and maintenance.

[008] Thus, in view of the above mentioned drawbacks, there exists a need for providingan overcurrentdetection circuit that eliminates the requirements of software models to drive the operation of a detecting faults due to overcurrent in an electrical power system and that is simple to construct, inexpensive, and thereby obtain more accurate results making the protection relay devices robust.

SUMMARY OF THE INVENTION

[009] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0010] An object of the present invention is to provide a simple and compactovercurrent detection circuit in protection relay devices in order to improve the design of the existing protection relay and thereby make the protection relay device more robust.

[0011] Another object of the present invention is to provide an alternative solution which is non-existent today to obviate the problems of the microprocessor based protection relays.

[0012] Another object of the present invention is to improve the design and make robust protection relays product, by providing the hardware protection and detection of the over current.

[0013] Accordingly, in one implementation, a protection relay device to generate an over current fault are disclosed. Theprotection relay device comprises at least one current sensing circuit adapted receive an input signal and measures a current passing through the protection relay device;at least one processor configured to receive the input signal, amplify the signal received, and transmit the signal amplified to at least one analog to digital converter (ADC) to sense the voltage amplified and generate a count, the count provides an actual voltage by deducting offset from the voltage amplified and by adding gain, The protection relay device characterized in that comprises:a comparator circuit adapted to receive the signal amplified and at least one reference signal;compare the voltage values of the signal amplified and the reference signal received to detect the overcurrent fault based on a result of comparison; and thereby generate, if the result of comparison is greater than a pre-set value, an interrupt to trip at least one hardware coupled to the protection relay device.

[0014] In one implementation, the present invention provides an overcurrent detection circuit in a protection relay for protecting an electrical power system. The overcurrent circuit essentially detects faults due to overcurrent in the electrical power system using electrical components and thereby eliminating the need of software models to drive the operation of detection faults due to overcurrent in an electrical power system.

[0015] In one implementation, the protection relay with an overcurrent detection circuit comprises means for detecting a current analog signal representative of the operating condition, to measurecurrent flowing in conductor or load, the Current Sensor or CT. The Design of current sensor itself has the burden resistor and directly gives the 0 to 4V, or some ICS ACS754-KCB-150B and ACS754-LCB-050 gives the output voltage 0 to 1.5V according to current ratio decided by the designer to design the Current Sensing Circuit. In CT the burden resistor is provided to measure the voltage. Means as per the ohms law, V = IR, we have I(Current) and If we add the Burden R Resistor, then we get the Voltage. Voltage output signal is amplified by non-inverting amplifier. The Amplified output signal is given in the Summing amplifier where DC offset is added for the ADC to make 0 to 3V, and signal is given to the Processor or DSPmeans for converting the current analog signal , means for deriving a maximum and minimum digital value or count representing the series of digital processor will calculate the current by Adding the gain and Deducting the offset from ADC Count and then compare with user defined current limit for over current and then gives the over current fault.

[0016] In another implementation of the present invention, the CT or current sensor measure the current and give the voltage signal as explained above, Voltage signal is given to the non-inverting OPAMP. Amplified voltage signal is given to the rectifier with OPAMP where Rectifier convert sine wave voltage signal to full wave rectified signal and we get the full wave rectified waveform as shown in Figure 2 (V10). Other DC Reference (V12) is compared with V10 and if the current value is exceeds the decided reference value. Then comparator output will go low and Indicator will show the Over current fault. And also there is reset mechanism for over current to trip the protection relays.

[0017] In one implementation of the present invention the processed value from the overcurrent detection circuit is transmitted to a trip zone interrupt of a processor in a protection relay to respond to a fault instantaneously and subsequently terminate the flow of a power supply to the connected load or device.

[0018] In one implementation, the overcurrent circuit disclosed in the present invention provides protection against overcurrent faultsin an electrical power system using internal simplified structures.

[0019] Conventionally, the over current protection and detection are provided through software program in protection relays products. In addition to software program, the present invention enables to add the hardware protection and detection of the over current. The current relays productenables to measure the current through (CT) and then gives it to the CPU. To give the measured current to ADC, the present invention uses the basic fundamental circuit of the operational amplifier to make 0 to 3V AC. And ADC will sense the voltage and gives the count and from count we get the actual current by deducting offset and adding gain in count. This actual current is used to detect the over current fault.In addition to this, basic fundamental circuit may remain same, and the present invention enables to add the comparator to make the hardware protection of over current. In one example, to make the hardware protection, the present inventions have simulated the design for over current.

[0020] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0021] Figure 1 illustratesa block diagram representation of an overcurrent detection circuit in a protection relay, in accordance with an embodiment of the present subject matter.

[0022] Figure 2 illustrates simulation result of the hardware over current, in accordance with an embodiment of the present subject matter.

[0023] 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

[0024] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0025] 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 of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0026] 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.

[0027] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0028] 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.

[0029] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0030] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0031] Figure 1 illustrates a block diagram of overcurrent detection circuit. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0032] Referring now to figure 1, in one implementation, the overcurrent detection circuit comprises a currentsensor or current transformer to measure an operating analog signal, a signal amplification circuit for amplifying the operating analog signal, an analog to digital (ADC) convertor for converting the operatinganalog voltage signal to digital samples and an processor detect and calculate san event wherein the input current signal is beyond a threshold limit.

[0033] Referring now to figure 1, in one implementation, the ADC scanner senses an input current and determines a count or digital current depending on a preset maximum and a minimum current and based on the count or digital current determined, the ADC scanner determines an event if the input current exceeds the preset maximum current.

[0034] Referring now to figure 1, in one implementation, an event determined by an processor/micro controller, wherein the input current exceeds a preset maximum current, an additional circuit comprising full wave rectifier converting the input AC voltage signal to DC voltage value and a comparator that compares the converted DC voltagevalue with a preset DC reference voltage value and thereby the comparator indicating an overcurrent fault.

[0035] Referring now to figure 1, in one implementation, a comparator indicates a high/low output to a trip zone interrupt of a processor to response to overcurrent faults and subsequently terminating the power supply. Addition to the trip one interrupt, there is reset mechanism for the Trip of the protection relays.

[0036] In one implementation, the sensing currentranges from 0 to 3 AC. In one example, the minimum current is taken as 0 V and the maximum current is taken as 2.85 V AC. In one example, the ADC used is a 12 bit ADC that determines 4096 count in case of 2.85V AC and 0 count in case of 0V AC. In the event wherein a current increases beyond 2.85VAC (maximum current),connected circuit with the comparator output will go low and thereby giving an over current fault. The comparator high/low output is given to the Trip zone interrupt of a processor in a protection relay to immediately response of protection. The protection relays causes an electrical switching device to trip instantaneously.

[0037] In one implementation, in addition to basic fundamental circuit the present invention enables to add the comparator to make the hardware protection of over current. To make the hardware protection, we have simulated the design for over current. IN one example, during simulation, the reference as before current sensing circuit means should not be change in the design of the present invention.In design, the sensing voltage 0 to 3 AC is considered. With this sensing voltage make circuit may detect over current of respective phase. In parallel circuit, if 0V means minimum count and 2.85V AC means maximum count of ADC. Means suppose 12 bit ADC it takes 4096 count when 2.85V AC and 0 count when 0V AC. If the voltage increase 2.85VAC then there is parallel circuit of hardware protection will come in picture and comparator output will go low and gives the over current fault. The present inventionenables the trip the protection relays without waiting the software fault. In one implementation, the present invention gives the comparator high/low output to the Trip zone interrupt of the processor to immediately response of protection and trip. The present invention enables to provide the parallel circuit to all phase and take output of three comparator for single protection and trip the hardware as well as provide the hardware interrupt to the trip zone of the CPU.

[0038] In one implementation, as shown in the Figure 1, the present invention starts from the block of full wave rectifier and a DC Reference to comparator. An output of the comparator decides the over current. The software protection for the over current may be present.It senses the current and takes time to execute the software fault. In this particular time, the load or device connected to the protection device may damage or create a severe damage. To overcome the limitation, a hardware protection is given which immediately give the overcurrent fault by taking component internal time. However, this fast comparison may include software fault. The ADC scanning is well known in the art and conventional technique uses the same topology, however, giving the hardware protection through the same topology adding the hardware part is one of the essential aspects of the present invention.

[0039] Referring now to figure 2, simulation resultant waveform showing the digital output waveform of the event when the detected analog input voltage is above the maximum preset voltage. In one example when sensing circuit output of ADC is above the 2.85V AC. Comparator output will be change as shown in waveform (d). It goes low and gives an indication to the protection for over current fault. As soon as the over current fault occurs, the protection relay cuts off the power supply by causing the circuit breaker to trip.

[0040] In one implementation, as shown in figure 2, to measure current flowing in conductor or load, the Current Sensor or CT are used. The Design of current sensor itself has the Burden Resistor and directly gives the 0 to 4V, or some ICS ACS754-KCB-150B and ACS754-LCB-050 gives the Output voltage 0 to 1.5V according to current ratio decided by the Designer to design the Current Sensing Circuit. In CT the burden resistor is added to measure the voltage. Means as per the ohms law, V = IR, have I (Current) and if the Burden R Resistor is added, then the Voltage is obtained. Voltage output signal is amplified by non-inverting amplifier. The amplified output signal is given in the summing amplifier where DC offset is added for the ADC to make 0 to 3V, and signal is given to the Processor or DSP for current measurement. Also, Amplified voltage signal is given to the rectifier with op amp where the rectifier converts sine wave voltage signal to full wave rectified signal and get the full wave rectified waveform as shown in figure 2 (V10). Other DC Reference (V12) is compared with V10 and if the current value is exceeds the decided reference value. Then comparator output will go low and Indicator will show the over current fault, and also there is reset mechanism for over current to trip the protection relays.

[0041] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1. The present invention provides a hardware overcurrent protection for protection relays.
2. The present invention provides anovercurrent detection circuit for switchgear devices which do not contain a processor, and thereby giving the hardware protection to such devices against faults due to overcurrent in an electrical power system.
3. The present invention provides an overcurrent circuit that provides protection to the components in a device against severe damage due to instantaneous cutting off power supply.
4. The present invention provides a protection relay that is more robust.
,CLAIMS:1. A protection relay device to generate an overcurrent fault, comprising:
at least one current sensing circuit adapted receive an input signal and measuresa current passing through the protection relay device;
at least one processor configured to receive the input signal, amplify the signal received, and transmit the signal amplified to at least one analog to digital converter (ADC) to sense the voltage amplified and generate a count, the count provides an actual currentby deducting offset from the voltage amplified and by adding gain; wherein
the protection relay device characterized in that comprises:
a comparator circuit adapted to:
receive the signal amplified and at least one reference signal;
compare the voltage values of the signal amplified and the reference signal received to detect the overcurrent fault based on a result of comparison; and thereby
generate, if the result of comparison is greater than a pre-set value, an interrupt to trip at least one hardware coupled to the protection relay device.

2. The protection relay device as claimed in claim 1, wherein the comparator circuit is adapted to receive the amplified signal if the voltage measured in the current passing through is greater than a pre-set voltage, preferably over the 2.85VAC for trip circuit.

3. The protection relay device as claimed in claim 1, wherein when the result of comparison is greater than the pre-set value, the comparator circuit generate a low as output and thereby detects the over current fault.

4. The protection relay device as claimed in claim 1, the reference signal is feed to the comparator circuit at the time of manufacturing or is pre-stored in the comparator circuit and is re-configurable.

5. The protection relay device as claimed in claim 1, comprises a mechanism, preferably a software technique, configured to provide the over current fault based on the actual currentof the count, and thereby tripping the protection relay device.

6. The protection relay device as claimed in claim 1, wherein the current sensing circuit comprises a current sensor or a Current transformer, and further comprises a Burden Resistor.