DESC:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to a protection relay and switchgears, and more particularly to an electronic circuit in the protection relay for detecting phase loss 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, overvoltage, overload, phase loss, temperature rise and other such detrimental effects which cause damage or failure of the electrical power system.

[003] Various electrical devices are operated on a three phase electrical system. Therefore it is essential to protect such device against overload using an overload relay protection device that monitors continuous current flowing in the three phase system as an electrical network becomes imbalanced due to an overload or an under load condition in at least one of the phases. The phase imbalance condition can have the same effect on electrical devices as the overload or phase loss condition. For example, whenever a power source supply is connected to a device, ensure the power source supply is 415VAC line to line voltage. If power source supply phase voltage is not 415VAC and measured voltage is less than the 200VAC of all phases then we provide the fault of “GRID OFF” and if measured voltage of the single phase is below the 300VAC, the electrical load devices such as Induction motor, protection relay, switch gear etc will not start operating. Then a particular phase loss/single phasing in a respective phase of predefined R-Y-B pattern is indicated. The loss of any one of the three phases of the electrical system can cause improper operation or significant damage to the electrical device. Therefore it is desirable that the overload relay is capable of detecting a phase loss condition in an electrical network.

[004] Currently, phase loss/single phasing protection is provided through software program. Sometimes such software program detects phase loss fault and provides the protection, however it may cause malfunctioning of other component and sometimes may also create severe damagesto a protection relay product because of calculation of software program and defined time by CPU programmer. For example, it is well known that, software is always written based on the schedulers or sequence execution of program. For example standard fault protection is given in 20ms routines of software program. When we “Power ON” thesystem. It takes some time of hardware component internal time and also time for CPU initialization and then it comes to the software program routines to execute particular software fault in our case Phase Loss fault. All over summation of software fault is exceeds the almost 100ms. In between particular time, it may be create severe damage to protection relay product and also connected equipment like MOTOR, Feeder, and Transformer etc.It is not always creates the severe damage but always reduce the life of the Product and connected equipment.

[005] The prior-art patent document US 4823226 discloses a method for phase loss detection. The patent document US 4823226relates to a phase loss and phase failure relay detection and control circuit for a three-phase electrical system for providing instantaneous detection of the loss of a phase and providing protection after a predetermined time interval to three-phase motors connected to the circuit. The circuit detects the loss of a phase by sensing and rectifying the instantaneous voltage and comparing the instantaneous voltage with a scaled proportional voltage. However such devices sensing current flowing in the protected circuit may be limited in its accuracy and ability to detect phase imbalance due to harmonically distorted current wave shapes. These harmonically distorted wave shapes appear to the overload relay as a phase loss condition and thereby may cause a nuisance tripping.

[006] The prior-art patent document US 4724503 disclosed a method of phase loss and phase imbalance protection to be incorporated into a reduced voltage starter. The device disclosed in US 4724503 senses the voltage waveform and compares the zero crossing point of each phase to determine phase loss and phase imbalance. The device is a high end device which is significantly more complex and thereby requires many more electrical components which increase the manufacturing cost.

[007] The prior-art patent US 7355866 B2 discloses a method for detecting the phase-loss state of the three phase power supply, and the phase-loss state of the power source is determined through detecting the variations of a ripple voltage on the DC bus by means of software calculations instead of the hardware detection circuit. However such method disclosed in US 7355866 may cause malfunctioning of other component in the circuit and sometimes it may also create severe damage to the protection relays due toperiodic iteration of such software programs.

[008] Further, the existing hitherto techniques for detection of phase loss faults in a electrical power system using software model, are complex, much costlier, and require extra man power for their operation and maintenance.

[009] Thus, in view of the above mentioned drawbacks, there exists a need for providing an phase loss detection circuit in a protection relay that eliminates the requirements of software models to drive the operation of a detecting faults due to phase loss in a three phase electrical network and that is simple to construct, inexpensive, and thereby obtain more accurate results making the protection relay devices robust.

SUMMARY OF THE INVENTION

[0010] 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.

[0011] An object of the present invention is to provide a simple and compactphase loss 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.

[0012] Another object of the present invention is to provide an alternative solution which is non-existent today to obviate the problems of the phase loss/single phasing protection through software programs.

[0013] Yet another object of the present invention is to improve the design and make robust protection relays product, by providing a hardware protection of the phase loss/single phasing.

[0014] Accordingly, in one implementation, a protection relay device to generate an Phase loss / Single Phasing fault, to be used in three-phase electric power systems is disclosed. The protection relay device comprises at least one zero crossing detector circuit, at least one signal amplification circuit, at least one comparator circuit, and at least one fault detection circuit. The zero crossing detector circuit is adapted to detect a zero crossing of a three phase input signal. The signal amplification circuit is adapted to amply the three phase input signal detected to generate an amplified signal. The comparator circuit isadapted to receive at least one reference signal, and the amplified signal and compare the amplified signal with the reference signal to generate a phase loss output. The fault detection circuit adapted to receive the phase loss output and generate the over voltage fault signal based on a pre-set condition based on the comparison.

[0015] In one implementation, the present invention provides a phase loss detection circuit in a protection relay for protecting an electrical power system against phase loss faults. The phase loss circuit essentially detects faults due to phase loss in atleast one of the phases of a three phase electrical power system using electrical components and thereby eliminating the need of software models to drive the operation of detecting faults due to phase loss in an electrical power system.

[0016] In one implementation,the present invention provides a protection relay with a phase loss detection circuit, comprising means for detecting zero crossing reference voltages of three phases, means for amplifying the three phase voltages, means for comparing the amplified output signal with a reference voltage (Vref) to determine a processed value, means for responding to the processed value by disconnecting a power system from the load in the event that the processed value is not within preset limits.

[0017] In one implementation, the present invention provides a phase loss detection circuit which comprises a zero crossing detector circuit for detecting zero crossing reference voltages of three phases, a signal amplification circuit for amplifying the zero crossing reference voltages, a comparator for comparing the output of the signal amplification circuit to a reference voltage (Vref) and an indicator for indicating a phase loss conditions in an electrical power system.

[0018] In one implementation of the present invention the processed value from a comparator in a phase loss 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.

[0019] In one implementation of the present invention, the processor in a protection relay indicates an event of phase loss fault on a display without waiting for execution of software instructions to detect a fault.

[0020] In one implementation, the phase loss detection circuit disclosed in the present invention provides protection against phase loss faults in a three phase electrical power system using internal simplified structures.

[0021] 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:

[0022] Figure 1 illustratesablock diagram representation of the phase loss detection circuit used in a protection relay, in accordance with an embodiment of the present subject matter.

[0023] Figure 2 illustrates a circuitry arrangement of electrical components for detecting phase loss fault in an electrical circuit, in accordance with an embodiment of the present subject matter.

[0024] Figure 3 illustrates input waveforms and output waveforms during a phase loss fault, in accordance with an embodiment of the present subject matter.

[0025] 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

[0026] 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.

[0027] 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.

[0028] 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.

[0029] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Figure 1 illustrates a block diagram representation of the phase loss detection circuit. A person skilled in the art will appreciate that for understanding purpose, the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0034] Figure 2 illustrates a circuitry arrangement for detection of phase loss in a circuit. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0035] Referring now to figure 1, in one implementation, the phase loss detection circuit comprises Zero crossing detector circuit for three phase detection of voltages, a signal amplification circuit for amplifying the voltages detected, a comparator circuit for comparing the output of the signal amplification circuit to a reference voltage (Vref) and an indicator indicating a phase loss event in an electrical power system.

[0036] Referring now to figure 2, in one implementation, Zero crossing reference of three phases, R-Y-B voltage(VA, VB, VC) is detected using a zero crossing detector circuit which later is given as an input to an operational amplifier. The output of operational amplifier(U1A,U1B,U1C) is input to a transistor (Q1 1R1001) and further the output signal of the transistor is input to input terminals (5 & 6) of a comparator (U2B) circuit. Zero crossing reference is detected from R,Y,B respectively. Output of the OPAMPS (U1A,U1B,U1C) are high at summed point A, when the 3 Phase is present according to the 360°(phase difference between the phase of R,Y and B is 120°.when phase angle is 360° then time is 20ms and when phase angle is 120° then almost time will be 6.6ms between two phase and we sum three phase we get almost 20ms time and angle 360°), When 3 phase is healthy, the time will be 20ms. According to that capacitor will charge and signal will go beyond the transistor. When any phase is lost we get the total time almost 13ms. Capacitor will discharge for that time and transistor will operate and signal is given to the comparator circuit. Comparator circuit gets the reference voltage(Vref) and Transistor output.Comparator(U2B) compare the signal with reference voltage decided by designer and according to comparison, it get the High/Low signal. In this case high andan indicator indicates a phase loss fault in a circuit. In one example, the indicator is a light emitting diode.

[0037] In one implementation, the output signal from the comparator is given toa trip zone interrupt of a processor in a protection relay. In one example, the trip zone interrupt of the processor is general purposes input-output (GPIO) pins of the processor thatactivates relay drivers in the event of phase loss fault.

[0038] Referring now to figure 3, the input and output waveforms of the phase loss detection circuit is provided. In one example, the output simulation is based on 380 Volts AC, 50 Hz frequency.

[0039] In one implementation, the zero crossing of the R-Y-B Phase for software calculation and protection are considered. By using this circuit the present invention enables to add more hardware protection of R-B-Y phase loss/single phasing.Block diagram of the Phase loss/single phasing is shown in figure 1. The zero crossing of the 3 phase and amplify the output is taken into consideration. Amplified output is given to the comparator. Comparator will give the phase loss fault and also we can provide the comparator output to the trip zone interrupt of the processor.

[0040] Zero crossing reference of three phases may be given to operational amplifier and output signal of the op-amp is given to transistor. Based on transistor output signal is given to the comparator and if comparator output is high then it will glow the LED and same time the signal may be given to GPIO of the processor. Also processor may show the phase loss fault on the display. It will detect any one or more phases are not coming then gives the fault and necessary protection to the relays without waiting of software execution of fault. The output of this simulation is shown in the wave forms in figure 3. Output waveforms of the simulation based on 380VAC, 50Hz frequency.

[0041] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1. The present invention provides a hardware phase loss protection in protection relays.
2. The present invention provides a phase loss detection circuit for switchgear devices which do not contain a processor, and thereby giving the hardware protection to such devices against faults due to phase loss in a three phase electrical power system.
3. The present invention provides a phase loss 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 phase loss fault, to be used in three-phase electric power systems, the protection relay device comprising:
at least one zero crossing detector circuit adapted to detect a zero crossing of a three phase input signal;
at least one signal amplification circuit adapted to amply the three phase input signal detected to generate an amplified signal;
at least one comparator circuit adapted to receive at least one reference signal, and the amplified signal and compare the amplified signal with the reference signal to generate a phase loss output; and
at least one fault detection circuit adapted to receive the phase loss output and generate the phase loss fault signal based on a pre-set condition based on the comparison.

2. The protection relay device as claimed in claim 1, further comprises a processor configured to receive the phase loss fault and issues an interrupt to trip electric power system.

3. The protection relay device as claimed in claim 1, wherein the signal amplification circuit comprises an operational amplifier adapted to receive the zero crossing reference of three phases and thereby amply the three phase input signal to generate the amplified signal.

4. The protection relay device as claimed in claim 1 and 3, comprises a transistor adapted to receive the amplified signal and generate an output signal fed to the comparator circuit.

5. The protection relay device as claimed in any of the preceding claims, comprises an indicator means configured to glow if the output signal fed to the comparator circuit is high as compared to the reference signal.

6. The protection relay device as claimed in claim 5, any of the preceding claims, comprises a display means to display a the phase loss fault if the output signal fed to the comparator circuit is high as compared to the reference signal.

7. The protection relay device as claimed in claim 2, wherein the processor comprises a general-purpose input/output (GPIO).