CN106405191B - Zero sequence current sampling circuit for accurate judgment of alternating current grounding and judgment method thereof - Google Patents
Zero sequence current sampling circuit for accurate judgment of alternating current grounding and judgment method thereof Download PDFInfo
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- CN106405191B CN106405191B CN201610501337.XA CN201610501337A CN106405191B CN 106405191 B CN106405191 B CN 106405191B CN 201610501337 A CN201610501337 A CN 201610501337A CN 106405191 B CN106405191 B CN 106405191B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
Abstract
The invention discloses a zero-sequence current sampling circuit for accurate judgment of alternating-current grounding, which comprises an A-phase sampling circuit, a B-phase sampling circuit, a C-phase sampling circuit, a zero-sequence current amplitude A/D conversion module, a zero-sequence resistance phase preprocessing module and an intelligent microprocessor, wherein the A-phase sampling circuit, the B-phase sampling circuit and the C-phase sampling circuit respectively sample three-phase power supply currents and transmit three-phase current signals to the zero-sequence current amplitude A/D conversion module and the zero-sequence resistance phase preprocessing module after overlapping the three-phase current signals, and the zero-sequence current amplitude and the zero-sequence resistance phase preprocessing module carry out correct grounding fault judgment, alarm or output protection signals. The invention has simple structure, reliable operation and high cost performance, and effectively ensures the safe and economic operation of the power grid.
Description
Technical Field
The invention relates to a zero sequence current sampling circuit and a grounding judgment method, in particular to a zero sequence current sampling circuit for accurate judgment of alternating current grounding and a judgment method thereof.
Background
The ground fault of the power grid is a common fault, and if the ground fault happens, the ground fault is eliminated in time, otherwise, the safe operation of the power grid is affected. At present, each connection gateway of the power grid is generally provided with a ground fault protection device, an alarm signal is sent out when the ground fault protection device detects the ground fault, and a tripping signal for disconnecting the ground fault line is sent out after the set time is exceeded, so that the expansion of accidents is avoided.
Because of the diversity of the power grid structure and the grounding mode, the existing power grid grounding protection device products have the problem of inaccurate grounding judgment, and the ground fault is frequently misreported and missed, so that the safety and economic operation of the power grid are endangered.
The main reason for inaccurate ground fault judgment of the existing power grid ground protection device products is that the sampling of zero sequence current generated by a ground fault is inaccurate, because the sampling of zero sequence current generated by the ground fault involves measures such as high-voltage electrical isolation and the like and smaller ground fault current is mixed in a load heavy current, signals which are linearly proportional to the actual ground fault current in amplitude and phase and can be read by an intelligent micro-processing circuit are difficult to obtain.
Disclosure of Invention
The invention aims to provide a zero sequence current sampling circuit for accurate judgment of alternating current grounding and a judgment method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
a zero sequence current sampling circuit for accurate judgment of AC grounding is characterized in that: the zero-sequence current amplitude A/D conversion module and the zero-sequence resistance phase preprocessing module are used for judging correct ground faults, alarming or outputting protection signals.
Further, the phase A sampling circuit structure is that a current transformer La1 is arranged on a three-phase power supply phase A line to sample current, one end of the current transformer La1 is connected with one end of a converting resistor Ra1 and one end of a voltage dividing regulating potentiometer Ra2, the other end of the current transformer La1 is connected with the other end of the converting resistor Ra1 and the other end of a voltage dividing resistor Ra3, the other ends of the voltage dividing regulating potentiometer Ra2 and the voltage dividing resistor Ra3 are connected with one end of a current limiting protection resistor Ra4, the other end of the current limiting protection resistor Ra4 is connected with a base electrode of a signal following PNP type triode Da1 and one end of a phase feedback regulating inductance La2, the other end of the phase feedback regulating inductance La2 is connected with one end of a phase feedback limiting resistor Ra5, the other end of the phase feedback limiting resistor Ra5 is connected with a collector electrode of the signal following PNP type triode Da1 and one end of a phase feedback proportional resistor Ra6, an emitter of the signal following PNP type triode Da1 is connected with one end of a signal limiting resistor Ra7 and one end of a signal following shunt resistor Ra8, the other end of the signal following shunt resistor Ra8 is grounded, the positive electrode of an overvoltage protection device Da2 is connected with the other end of the current transformer La1, and the overvoltage protection device Da2 is connected with the negative electrode of the signal following triode Da 1;
the B-phase sampling circuit structure is that a current transformer Lb1 is arranged on a three-phase power supply B-phase line to sample current, one end of the current transformer Lb1 is connected with one end of a converting resistor Rb1 and one end of a voltage dividing regulating potentiometer Rb2, the other end of the current transformer Lb1 is connected with the other end of the converting resistor Rb1 and the other end of a voltage dividing resistor Rb3, the other ends of the voltage dividing regulating potentiometer Rb2 and the voltage dividing resistor Rb3 are connected with one end of a current limiting protection resistor Rb4, the other end of the current limiting protection resistor Rb4 is connected with the base electrode of a signal following PNP type triode Db1 and one end of a phase feedback regulating inductance Lb2, the other end of the phase feedback regulating inductance Lb2 is connected with one end of a phase feedback limiting resistor Rb5, the other end of the phase feedback limiting resistor Rb5 is connected with the collector electrode of the signal following PNP type triode Db1 and one end of a phase feedback proportional resistor Rb6, the emitter of the signal following PNP type triode Db1 is connected with one end of a signal limiting resistor Rb7 and one end of a signal following shunt resistor Rb8, the other end of the signal following shunt resistor Rb8 is grounded, the positive electrode of an overvoltage protection device Db2 is connected with the other end of the current transformer Lb1, and the overvoltage protection device Db2 is connected with the negative electrode of the signal following triode Db 1;
the C-phase sampling circuit structure is characterized in that a current transformer Lc1 is arranged on a three-phase power supply C line for current sampling, one end of the current transformer Lc1 is connected with one end of a converting resistor Rc1 and one end of a voltage dividing regulating potentiometer Rc2, the other end of the current transformer Lc1 is connected with the other end of the converting resistor Rc1 and the other end of a voltage dividing resistor Rc3, the other ends of the voltage dividing regulating potentiometer Rc2 and the voltage dividing resistor Rc3 are connected with one end of a current limiting protection resistor Rc4, the other end of the current limiting protection resistor Rc4 is connected with the base of a signal following PNP type triode Dc1, one end of a phase feedback regulating inductor Lc2 is connected with one end of a phase feedback limiting resistor Rc5, the other end of the phase feedback limiting resistor Rc5 is connected with the collector of the signal following PNP type triode Dc1 and one end of a phase feedback proportional resistor Rc6, the emitter of the signal following PNP type triode Dc1 is connected with one end of a signal limiting resistor Rc7 and a signal following shunt resistor Rc8, the other end of the signal following shunt resistor Rc8 is grounded, the positive electrode of an overvoltage protection device Dc2 is connected with the other end of the current transformer Lc1, and the overvoltage protection device Dc2 is connected with the negative electrode of the signal following PNP type triode Dc 1.
Further, one end of the voltage bias resistor R9 is connected with the working direct current power supply VDD, the other end of the voltage bias resistor R9 is connected with the other end of the current transformer La1, the other end of the current transformer Lc1 and one end of the voltage bias resistor R10, the other end of the voltage bias resistor R10 is grounded, the positive electrode of the overvoltage protection device Da2 is connected with the negative electrode of the overvoltage protection device D3, the positive electrodes of the overvoltage protection device D3 and the overvoltage protection device Db2 are grounded, and the positive electrode of the overvoltage protection device Dc2 is connected with the other end of the current transformer Lc 1.
Further, the other ends of the phase feedback proportional resistor Ra6, the phase feedback proportional resistor Rb6 and the phase feedback proportional resistor Rc6 are connected with a working DC power supply VDD, the negative electrode of an overvoltage protection device D4 and the collector of a zero-sequence current extraction PNP triode D5, the positive electrode of the overvoltage protection device D4 is grounded, the other ends of the signal limiting resistor Ra7, the signal limiting resistor Rb7 and the signal limiting resistor Rc7 are connected with the base electrode of the zero-sequence current extraction PNP triode D5, the emitter electrode of the zero-sequence current extraction PNP triode D5 is connected with one end of a zero-sequence current load resistor R11, the input end of a zero-sequence current amplitude A/D conversion module and the input end of a zero-sequence resistor phase preprocessing module, and the output ends of the zero-sequence current amplitude A/D conversion module and the zero-sequence resistor phase preprocessing module are connected with an intelligent microprocessor.
The alternating current grounding accurate judgment method is characterized by comprising the following steps of:
accurate sampling of A phase current: the A-phase current is converted into voltage signals at two ends of the conversion resistor Ra1 through the conversion resistor Ra1 after being electrically isolated by the current transformer La1, a signal with an accurate proportion in amplitude is output at the joint of the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 through the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 and voltage division adjustment, the signal is sent to a base electrode of the signal follower PNP triode Da1 through the current limiting protection resistor Ra4, and an A-phase current sampling signal with an accurate proportion in amplitude and an accurate consistent in phase is output at the joint of an emitter of the signal follower PNP triode Da1 and the signal follower shunt resistor Ra8 through the phase feedback adjustment inductor La2, the phase feedback limiting resistor Ra5 and the phase feedback proportional resistor Ra 6;
b phase current accurate sampling: the B-phase current is converted into voltage signals at two ends of the conversion resistor Rb1 through the conversion resistor Rb1 after being electrically isolated by the current transformer Lb1, signals with accurate proportion to the B-phase current in amplitude are output at the connection position of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3 through voltage division and voltage division adjustment of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3, the signals are sent to the base electrode of the signal following PNP triode Db1 through the current limiting protection resistor Rb4, and B-phase current sampling signals with accurate proportion to the B-phase current in amplitude and accurate consistent in phase are output at the connection position of the emitter of the signal following PNP triode Db1 and the signal following shunt resistor Rb8 through phase feedback adjustment inductor Lb2, phase feedback limiting resistor Rb5 and phase feedback proportion resistor Rb 6;
c phase current accurate sampling: the C-phase current is converted into voltage signals at two ends of the conversion resistor Rc1 through the conversion resistor Rc1 after being electrically isolated by the current transformer Lc1, signals with accurate proportion in amplitude with the C-phase current are output at the joint of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3 through voltage division adjustment of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3, the signals are sent to the base electrode of the signal following PNP triode Dc1 through the current limiting protection resistor Rc4, and C-phase current sampling signals with accurate proportion in amplitude and accurate consistent in phase with the C-phase current are output at the joint of the emitter of the signal following PNP triode Dc1 and the signal following shunt resistor Rc8 through phase feedback adjustment inductor Lc2, phase feedback limiting resistor Rc5 and phase feedback proportion resistor Rc 6;
accurate sampling of zero sequence current: A. b, C three-phase current is collected to the base of a PNP type triode D5 for extracting zero-sequence current through a signal limiting resistor Ra7, a signal limiting resistor Rb7 and a signal limiting resistor Rc7 respectively, zero-sequence current signals are output at the joint of the emitter of the PNP type triode D5 for extracting zero-sequence current and a zero-sequence current load resistor R11, the amplitude of the zero-sequence current signals is digitized through a zero-sequence current amplitude A/D conversion module, the phase of the zero-sequence current signals is digitized through a zero-sequence resistance phase preprocessing module and then is sent to an intelligent microprocessor, and the intelligent microprocessor carries out correct ground fault judgment, alarm or output protection signals according to the amplitude and the phase of accurate zero-sequence current.
Further, the voltage bias resistor R9 and the voltage bias resistor R10 provide bias voltage, ensure normal sampling of A-phase alternating current, and the overvoltage protection device Da 2/the overvoltage protection device Db 2/the overvoltage protection device Dc2 and the overvoltage protection device D3 limit overvoltage of the front part of the overvoltage protection device to avoid damage to the circuits of the rear part of the overvoltage protection device.
Further, the overvoltage protection device D4 limits damaging overvoltages introduced by the power supply.
Compared with the prior art, the invention has the following advantages and effects: the device has the advantages of simple structure, reliable operation and high cost performance, and can accurately judge the alternating current grounding condition of the power grid grounding protection device product through zero sequence current sampling, so that the grounding protection device product can accurately send an alarm signal to a grounding fault or accurately send a tripping signal for disconnecting a grounding fault line, and the safe and economic operation of the power grid is ensured.
Drawings
Fig. 1 is a circuit diagram of a zero sequence current sampling circuit for accurate determination of ac ground.
Detailed Description
The present invention will be described in further detail by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and not limited to the following examples.
As shown in the figure, the zero-sequence current sampling circuit for accurate judgment of alternating-current grounding comprises an A-phase sampling circuit, a B-phase sampling circuit, a C-phase sampling circuit, a zero-sequence current amplitude A/D conversion module 1, a zero-sequence resistance phase preprocessing module 2, an intelligent microprocessor 3, wherein the A-phase sampling circuit, the B-phase sampling circuit and the C-phase sampling circuit respectively sample three-phase power supply currents and transmit three-phase current signals to the zero-sequence current amplitude A/D conversion module 1 and the zero-sequence resistance phase preprocessing module 2 after overlapping the three-phase current signals, so that the amplitude and the phase of the zero-sequence current are subjected to correct grounding fault judgment, alarm or protection signals are output.
The A-phase sampling circuit structure is that a current transformer La1 is arranged on an A-phase line of a three-phase power supply to sample current, one end of the current transformer La1 is connected with one end of a conversion resistor Ra1 and one end of a voltage dividing regulating potentiometer Ra2, the other end of the current transformer La1 is connected with the other end of the conversion resistor Ra1 and the other end of a voltage dividing resistor Ra3, the other ends of the voltage dividing regulating potentiometer Ra2 and the voltage dividing resistor Ra3 are connected with one end of a current limiting protection resistor Ra4, the other end of the current limiting protection resistor Ra4 is connected with a base electrode of a signal following PNP type triode Da1 and one end of a phase feedback regulating inductor La2, the other end of the phase feedback regulating inductor La2 is connected with one end of a phase feedback limiting resistor Ra5, the other end of the phase feedback limiting resistor Ra5 is connected with a collector electrode of the signal following PNP type triode Da1 and one end of a phase feedback proportional resistor Ra6, an emitter of the signal following PNP type triode Da1 is connected with one end of a signal limiting resistor Ra7 and a signal following shunt resistor Ra8, the other end of the signal following shunt resistor Ra8 is grounded, an anode of an overvoltage protection device Da2 is connected with the other end of the current transformer La1, and the overvoltage protection device Da2 is connected with the base electrode of the signal following PNP type triode Da 1;
the B-phase sampling circuit structure is that a current transformer Lb1 is arranged on a B-phase line of a three-phase power supply to sample current, one end of the current transformer Lb1 is connected with one end of a converting resistor Rb1 and one end of a voltage dividing regulating potentiometer Rb2, the other end of the current transformer Lb1 is connected with the other end of the converting resistor Rb1 and the other end of a voltage dividing resistor Rb3, the other ends of the voltage dividing regulating potentiometer Rb2 and the voltage dividing resistor Rb3 are connected with one end of a current limiting protection resistor Rb4, the other end of the current limiting protection resistor Rb4 is connected with the base electrode of a signal following PNP type triode Db1 and one end of a phase feedback regulating inductor Lb2, the other end of the phase feedback regulating inductor Lb2 is connected with one end of a phase feedback limiting resistor Rb5, the other end of the phase feedback limiting resistor Rb5 is connected with the collector electrode of the signal following PNP type triode Db1 and one end of a phase feedback proportional resistor Rb6, the emitter of the signal following PNP type triode Db1 is connected with one end of a signal limiting resistor Rb7 and one end of a signal following shunt resistor Rb8, the other end of the signal following shunt resistor Rb8 is grounded, the positive electrode of an overvoltage protection device Db2 is connected with the other end of the current transformer Lb1, and the overvoltage protection device Db2 is connected with the negative electrode of the signal following triode Db 1;
the C-phase sampling circuit structure is that a current transformer Lc1 is arranged on a three-phase power supply C line to sample current, one end of the current transformer Lc1 is connected with one end of a converting resistor Rc1 and one end of a voltage dividing regulating potentiometer Rc2, the other end of the current transformer Lc1 is connected with the other end of the converting resistor Rc1 and the other end of a voltage dividing resistor Rc3, the other ends of the voltage dividing regulating potentiometer Rc2 and the voltage dividing resistor Rc3 are connected with one end of a current limiting protection resistor Rc4, the other end of the current limiting protection resistor Rc4 is connected with the base of a signal following PNP type triode Dc1, one end of a phase feedback regulating inductor Lc2 is connected with one end of a phase feedback limiting resistor Rc5, the other end of the phase feedback limiting resistor Rc5 is connected with the collector of the signal following PNP type triode Dc1, one end of a phase feedback proportional resistor Rc6, the emitter of the signal following PNP type triode Dc1 is connected with one end of a signal limiting resistor Rc7 and a signal following shunt resistor Rc8, the other end of the signal following shunt resistor Rc8 is grounded, the positive electrode of an overvoltage protection device Dc2 is connected with the other end of the current transformer Lc1, and the overvoltage protection device Dc2 is connected with the negative electrode of the PNP type triode Dc 1.
One end of a voltage bias resistor R9 is connected with a working direct current power supply VDD, the other end of the voltage bias resistor R9 is connected with the other end of a current transformer La1, the other end of the current transformer Lc1 and one end of a voltage bias resistor R10, the other end of the voltage bias resistor R10 is grounded, the positive electrode of an overvoltage protection device Da2 is connected with the negative electrode of an overvoltage protection device D3, the positive electrodes of the overvoltage protection device D3 and an overvoltage protection device Db2 are grounded, and the positive electrode of the overvoltage protection device Dc2 is connected with the other end of the current transformer Lc 1. The other ends of the phase feedback proportional resistor Ra6, the phase feedback proportional resistor Rb6 and the phase feedback proportional resistor Rc6 are connected with a working DC power supply VDD, the negative electrode of an overvoltage protection device D4 and the collector of a zero sequence current extraction PNP type triode D5, the positive electrode of the overvoltage protection device D4 is grounded, the other ends of the signal limiting resistor Ra7, the signal limiting resistor Rb7 and the signal limiting resistor Rc7 are connected with the base electrode of the zero sequence current extraction PNP type triode D5, the emitter electrode of the zero sequence current extraction PNP type triode D5 is connected with one end of a zero sequence current load resistor R11, the input end of a zero sequence current amplitude A/D conversion module and the input end of a zero sequence resistor phase preprocessing module, and the output ends of the zero sequence current amplitude A/D conversion module and the zero sequence resistor phase preprocessing module are connected with an intelligent microprocessor.
An accurate judgment method for AC grounding comprises the following steps:
accurate sampling of A phase current: the A-phase current is converted into voltage signals at two ends of the conversion resistor Ra1 through the conversion resistor Ra1 after being electrically isolated by the current transformer La1, a signal with an accurate proportion in amplitude is output at the joint of the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 through the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 and voltage division adjustment, the signal is sent to a base electrode of the signal follower PNP triode Da1 through the current limiting protection resistor Ra4, and an A-phase current sampling signal with an accurate proportion in amplitude and an accurate consistent in phase is output at the joint of an emitter of the signal follower PNP triode Da1 and the signal follower shunt resistor Ra8 through the phase feedback adjustment inductor La2, the phase feedback limiting resistor Ra5 and the phase feedback proportional resistor Ra 6; the voltage bias resistor R9 and the voltage bias resistor R10 provide bias voltage, ensure normal sampling of A-phase alternating current, and the overvoltage protection device Da2 and the overvoltage protection device D3 limit overvoltage of the front part of the overvoltage protection device to avoid circuit damage of the rear part of the overvoltage protection device
B phase current accurate sampling: the B-phase current is converted into voltage signals at two ends of the conversion resistor Rb1 through the conversion resistor Rb1 after being electrically isolated by the current transformer Lb1, signals with accurate proportion to the B-phase current in amplitude are output at the connection position of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3 through voltage division and voltage division adjustment of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3, the signals are sent to the base electrode of the signal following PNP triode Db1 through the current limiting protection resistor Rb4, and B-phase current sampling signals with accurate proportion to the B-phase current in amplitude and accurate consistent in phase are output at the connection position of the emitter of the signal following PNP triode Db1 and the signal following shunt resistor Rb8 through phase feedback adjustment inductor Lb2, phase feedback limiting resistor Rb5 and phase feedback proportion resistor Rb 6; the voltage bias resistor R9 and the voltage bias resistor R10 provide bias voltage, ensure normal sampling of A-phase alternating current, and the overvoltage protection device Db2 and the overvoltage protection device D3 limit overvoltage of the front part of the overvoltage protection device to avoid circuit damage of the rear part of the overvoltage protection device
C phase current accurate sampling: the C-phase current is converted into voltage signals at two ends of the conversion resistor Rc1 through the conversion resistor Rc1 after being electrically isolated by the current transformer Lc1, signals with accurate proportion in amplitude with the C-phase current are output at the joint of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3 through voltage division adjustment of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3, the signals are sent to the base electrode of the signal following PNP triode Dc1 through the current limiting protection resistor Rc4, and C-phase current sampling signals with accurate proportion in amplitude and accurate consistent in phase with the C-phase current are output at the joint of the emitter of the signal following PNP triode Dc1 and the signal following shunt resistor Rc8 through phase feedback adjustment inductor Lc2, phase feedback limiting resistor Rc5 and phase feedback proportion resistor Rc 6; the voltage bias resistor R9 and the voltage bias resistor R10 provide bias voltage, ensure normal sampling of A-phase alternating current, and the overvoltage protection device Dc2 and the overvoltage protection device D3 limit overvoltage of the front part of the overvoltage protection device to avoid circuit damage of the rear part of the overvoltage protection device
Accurate sampling of zero sequence current: A. b, C three-phase current is collected to the base of a PNP type triode D5 for extracting zero-sequence current through a signal limiting resistor Ra7, a signal limiting resistor Rb7 and a signal limiting resistor Rc7 respectively, zero-sequence current signals are output at the joint of the emitter of the PNP type triode D5 for extracting zero-sequence current and a zero-sequence current load resistor R11, the amplitude of the zero-sequence current signals is digitized through a zero-sequence current amplitude A/D conversion module, the phase of the zero-sequence current signals is digitized through a zero-sequence resistance phase preprocessing module and then is sent to an intelligent microprocessor, and the intelligent microprocessor carries out correct ground fault judgment, alarm or output protection signals according to the amplitude and the phase of accurate zero-sequence current.
Wherein the overvoltage protection device D4 limits damaging overvoltages introduced by the power supply.
The foregoing description of the invention is merely exemplary of the invention. Various modifications or additions to the described embodiments may be made by those skilled in the art to which the invention pertains or in a similar manner, without departing from the spirit of the invention or beyond the scope of the invention as defined in the appended claims.
Claims (6)
1. A zero sequence current sampling circuit for accurate judgment of AC grounding is characterized in that: the system comprises an A-phase sampling circuit, a B-phase sampling circuit, a C-phase sampling circuit, a zero-sequence current amplitude A/D conversion module, a zero-sequence resistance phase preprocessing module and an intelligent microprocessor, wherein the A-phase sampling circuit, the B-phase sampling circuit and the C-phase sampling circuit respectively sample three-phase power supply current and transmit three-phase current signals to the zero-sequence current amplitude A/D conversion module and the zero-sequence resistance phase preprocessing module after overlapping, so that the amplitude and the phase of the zero-sequence current are subjected to correct ground fault judgment, alarm or protection signal output;
the A-phase sampling circuit structure is characterized in that a current transformer La1 is arranged on an A-phase line of a three-phase power supply to sample current, one end of the current transformer La1 is connected with one end of a converting resistor Ra1 and one end of a voltage dividing regulating potentiometer Ra2, the other end of the current transformer La1 is connected with the other end of the converting resistor Ra1 and the other end of a voltage dividing resistor Ra3, the other ends of the voltage dividing regulating potentiometer Ra2 and the voltage dividing resistor Ra3 are connected with one end of a current limiting protection resistor Ra4, the other end of the current limiting protection resistor Ra4 is connected with a base electrode of a signal following PNP type triode Da1 and one end of a phase feedback regulating inductance La2, the other end of the phase feedback regulating inductance La2 is connected with one end of a phase feedback limiting resistor Ra5, the other end of the phase feedback limiting resistor Ra5 is connected with a collector electrode of the signal following PNP type triode Da1 and one end of a phase feedback proportional resistor Ra6, an emitter of the signal following PNP type triode Da1 is connected with one end of a signal following shunt resistor Ra7 and the other end of the signal following shunt resistor Ra8, the positive electrode of the overvoltage protection device Da2 is connected with the other end of the current transformer La1, and the overvoltage protection device Da2 is connected with the negative electrode of the signal following PNP type triode Da 1;
the B-phase sampling circuit structure is that a current transformer Lb1 is arranged on a three-phase power supply B-phase line to sample current, one end of the current transformer Lb1 is connected with one end of a converting resistor Rb1 and one end of a voltage dividing regulating potentiometer Rb2, the other end of the current transformer Lb1 is connected with the other end of the converting resistor Rb1 and the other end of a voltage dividing resistor Rb3, the other ends of the voltage dividing regulating potentiometer Rb2 and the voltage dividing resistor Rb3 are connected with one end of a current limiting protection resistor Rb4, the other end of the current limiting protection resistor Rb4 is connected with the base electrode of a signal following PNP type triode Db1 and one end of a phase feedback regulating inductance Lb2, the other end of the phase feedback regulating inductance Lb2 is connected with one end of a phase feedback limiting resistor Rb5, the other end of the phase feedback limiting resistor Rb5 is connected with the collector electrode of the signal following PNP type triode Db1 and one end of a phase feedback proportional resistor Rb6, the emitter of the signal following PNP type triode Db1 is connected with one end of a signal limiting resistor Rb7 and one end of a signal following shunt resistor Rb8, the other end of the signal following shunt resistor Rb8 is grounded, the positive electrode of an overvoltage protection device Db2 is connected with the other end of the current transformer Lb1, and the overvoltage protection device Db2 is connected with the negative electrode of the signal following triode Db 1;
the C-phase sampling circuit structure is characterized in that a current transformer Lc1 is arranged on a three-phase power supply C line for current sampling, one end of the current transformer Lc1 is connected with one end of a converting resistor Rc1 and one end of a voltage dividing regulating potentiometer Rc2, the other end of the current transformer Lc1 is connected with the other end of the converting resistor Rc1 and the other end of a voltage dividing resistor Rc3, the other ends of the voltage dividing regulating potentiometer Rc2 and the voltage dividing resistor Rc3 are connected with one end of a current limiting protection resistor Rc4, the other end of the current limiting protection resistor Rc4 is connected with the base of a signal following PNP type triode Dc1, one end of a phase feedback regulating inductor Lc2 is connected with one end of a phase feedback limiting resistor Rc5, the other end of the phase feedback limiting resistor Rc5 is connected with the collector of the signal following PNP type triode Dc1 and one end of a phase feedback proportional resistor Rc6, the emitter of the signal following PNP type triode Dc1 is connected with one end of a signal limiting resistor Rc7 and a signal following shunt resistor Rc8, the other end of the signal following shunt resistor Rc8 is grounded, the positive electrode of an overvoltage protection device Dc2 is connected with the other end of the current transformer Lc1, and the overvoltage protection device Dc2 is connected with the negative electrode of the signal following PNP type triode Dc 1.
2. The zero sequence current sampling circuit for accurate ac grounding determination according to claim 1, wherein: one end of a voltage bias resistor R9 is connected with a working direct current power supply VDD, the other end of the voltage bias resistor R9 is connected with the other end of a current transformer La1, the other end of the current transformer Lc1 and one end of a voltage bias resistor R10, the other end of the voltage bias resistor R10 is grounded, the positive electrode of an overvoltage protection device Da2 is connected with the negative electrode of an overvoltage protection device D3, the positive electrodes of the overvoltage protection device D3 and an overvoltage protection device Db2 are grounded, and the positive electrode of the overvoltage protection device Dc2 is connected with the other end of the current transformer Lc 1.
3. A zero sequence current sampling circuit for accurate determination of ac ground according to claim 1 or 2, characterized in that: the other ends of the phase feedback proportional resistor Ra6, the phase feedback proportional resistor Rb6 and the phase feedback proportional resistor Rc6 are connected with a working DC power supply VDD, the negative electrode of an overvoltage protection device D4 and the collector of a zero sequence current extraction PNP type triode D5, the positive electrode of the overvoltage protection device D4 is grounded, the other ends of the signal limiting resistor Ra7, the signal limiting resistor Rb7 and the signal limiting resistor Rc7 are connected with the base electrode of the zero sequence current extraction PNP type triode D5, the emitter electrode of the zero sequence current extraction PNP type triode D5 is connected with one end of a zero sequence current load resistor R11, the input end of a zero sequence current amplitude A/D conversion module and the input end of a zero sequence resistor phase preprocessing module, and the output ends of the zero sequence current amplitude A/D conversion module and the zero sequence resistor phase preprocessing module are connected with an intelligent microprocessor.
4. The alternating current grounding accurate judgment method is characterized by comprising the following steps of:
accurate sampling of A phase current: the A-phase current is converted into voltage signals at two ends of the conversion resistor Ra1 through the conversion resistor Ra1 after being electrically isolated by the current transformer La1, a signal with an accurate proportion in amplitude is output at the joint of the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 through the voltage division adjustment potentiometer Ra2 and the voltage division resistor Ra3 and voltage division adjustment, the signal is sent to a base electrode of the signal follower PNP triode Da1 through the current limiting protection resistor Ra4, and an A-phase current sampling signal with an accurate proportion in amplitude and an accurate consistent in phase is output at the joint of an emitter of the signal follower PNP triode Da1 and the signal follower shunt resistor Ra8 through the phase feedback adjustment inductor La2, the phase feedback limiting resistor Ra5 and the phase feedback proportional resistor Ra 6;
b phase current accurate sampling: the B-phase current is converted into voltage signals at two ends of the conversion resistor Rb1 through the conversion resistor Rb1 after being electrically isolated by the current transformer Lb1, signals with accurate proportion to the B-phase current in amplitude are output at the connection position of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3 through voltage division and voltage division adjustment of the voltage division adjustment potentiometer Rb2 and the voltage division resistor Rb3, the signals are sent to the base electrode of the signal following PNP triode Db1 through the current limiting protection resistor Rb4, and B-phase current sampling signals with accurate proportion to the B-phase current in amplitude and accurate consistent in phase are output at the connection position of the emitter of the signal following PNP triode Db1 and the signal following shunt resistor Rb8 through phase feedback adjustment inductor Lb2, phase feedback limiting resistor Rb5 and phase feedback proportion resistor Rb 6;
c phase current accurate sampling: the C-phase current is converted into voltage signals at two ends of the conversion resistor Rc1 through the conversion resistor Rc1 after being electrically isolated by the current transformer Lc1, signals with accurate proportion in amplitude with the C-phase current are output at the joint of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3 through voltage division adjustment of the voltage division adjustment potentiometer Rc2 and the voltage division resistor Rc3, the signals are sent to the base electrode of the signal following PNP triode Dc1 through the current limiting protection resistor Rc4, and C-phase current sampling signals with accurate proportion in amplitude and accurate consistent in phase with the C-phase current are output at the joint of the emitter of the signal following PNP triode Dc1 and the signal following shunt resistor Rc8 through phase feedback adjustment inductor Lc2, phase feedback limiting resistor Rc5 and phase feedback proportion resistor Rc 6;
accurate sampling of zero sequence current: A. b, C three-phase current is collected to the base of a PNP type triode D5 for extracting zero-sequence current through a signal limiting resistor Ra7, a signal limiting resistor Rb7 and a signal limiting resistor Rc7 respectively, zero-sequence current signals are output at the joint of the emitter of the PNP type triode D5 for extracting zero-sequence current and a zero-sequence current load resistor R11, the amplitude of the zero-sequence current signals is digitized through a zero-sequence current amplitude A/D conversion module, the phase of the zero-sequence current signals is digitized through a zero-sequence resistance phase preprocessing module and then is sent to an intelligent microprocessor, and the intelligent microprocessor carries out correct ground fault judgment, alarm or output protection signals according to the amplitude and the phase of accurate zero-sequence current.
5. The method for accurately judging ac grounding according to claim 4, wherein: the voltage bias resistor R9 and the voltage bias resistor R10 provide bias voltage, ensure normal sampling of A-phase alternating current, and the overvoltage protection device Da 2/the overvoltage protection device Db 2/the overvoltage protection device Dc2 and the overvoltage protection device D3 limit overvoltage of the front part of the overvoltage protection device to avoid damage to the circuits of the rear part of the overvoltage protection device.
6. The method for accurately judging ac grounding according to claim 4, wherein: the overvoltage protection device D4 limits damaging overvoltages introduced by the power supply.
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