CN102135561B - Measuring device and method for zero-sequence current of non-effectively neutral grounded system - Google Patents
Measuring device and method for zero-sequence current of non-effectively neutral grounded system Download PDFInfo
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- CN102135561B CN102135561B CN2011100431723A CN201110043172A CN102135561B CN 102135561 B CN102135561 B CN 102135561B CN 2011100431723 A CN2011100431723 A CN 2011100431723A CN 201110043172 A CN201110043172 A CN 201110043172A CN 102135561 B CN102135561 B CN 102135561B
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Abstract
The invention relates to a measuring device and method for the zero-sequence current of a non-effectively neutral grounded system. In the invention, a measuring device and measuring method for a single-phase ground fault wire selection device of the non-effectively neutral grounded system is improved, and the sensibility and the accuracy for measuring the zero-sequence current are enhanced. The output of a zero-sequence current transformer is connected in series with a resistor R2 which is connected in parallel with a primary coil of a small-sized voltage transformer; the output of a secondary coil of the small-sized voltage transformer is connected in series with a resistor R3; one end of the resistor R3 is grounded, and the other end of the resistor R3 is connected with one input end of a computing circuit; the output of the computing circuit is connected with a proportional amplifier II and a proportional amplifier III; the proportional amplifier II and the proportional amplifier III are connected with a microcomputer system after being respectively connected with an A/D (Analog/Digital) conversion circuit; the microcomputer system is connected with a D/A (Digital/Analog) conversion circuit; the output of the D/A conversion circuit is connected with a proportional amplifier I; and the output of the proportional amplifier I is connected with the other input end of the computing circuit.
Description
Technical field
The present invention relates to field of relay protection in power, particularly a kind of system with non-effectively earthed neutral zero sequence current measurement device and method.
Background technology
During the electric system single phase ground fault of power transformer isolated neutral, there is no short-circuit loop, can not produce short-circuit current, relay protection of power system can trip, and electric system allows to continue operation a period of time.But single-phase earthing also is harmful to electric system.Therefore, during this system single phase ground fault, relay protection must be sent alerting signal, by operator, makes respective handling, finally faulty line is carried out interruption maintenance.For faulty line is carried out interruption maintenance, relay protection should be sent alerting signal and be pointed out faulty line.Relay protection judges whether single phase ground fault is easy to realize.But the capacity current during the isolated neutral system single phase ground fault is less, judges which bar line failure just very difficult.So far the performance factor of one-phase grounding wire-selective device is very low both at home and abroad.
Way commonly used is that when singlephase earth fault occurs, the fault amount of utilizing electric system self to produce detects.Group's amplitude ratio of each circuit zero sequence current amplitude size is relatively arranged than principle; Relatively each other faciation comparison principle of circuit zero sequence current and phase difference is arranged; Group's width faciation comparison principle that both combinations are also arranged.Capacity current during due to the electric system generation singlephase earth fault of isolated neutral changes with the variation of system architecture and the method for operation, sometimes very large, sometimes very little, add current transformer TA error, the impact of the factors such as the measuring error of one-phase grounding wire-selective device, in a lot of situations, be difficult to judge faulty line.
For solving the low problem of performance factor of one-phase grounding wire-selective device, application for a patent for invention number is a kind of method that 931113091 patent of invention has proposed additional AC signal.Application for a patent for invention number is that 2004100240158 patent of invention has proposed a kind of small grounding current system fault line selection method for single-phase-to-ground fault.These methods need the external signal power supply, use inconvenience, and device performance does not still meet the demands.
When singlephase earth fault occurred, the principle that the fault amount of utilizing electric system self to produce detects was reliable, and subject matter is that measured zero-sequence current is very little, and the measurement device error is large, causes the performance factor of one-phase grounding wire-selective device very low.
Summary of the invention
Purpose of the present invention is exactly in order to address the above problem, a kind of system with non-effectively earthed neutral zero sequence current measurement device and method is provided, it, by improving measurement links and the measuring method of system with non-effectively earthed neutral single-phase earth fault line selection device, improves sensitivity and the precision of measuring zero-sequence current.
For achieving the above object, the present invention adopts following technical scheme:
A kind of system with non-effectively earthed neutral zero sequence current measurement device, it comprises:
Small-size voltage transformer TV, its first siding ring input voltage amount, secondary side resistance in series R3, resistance R 3 one end ground connection, an input end of other end concatenation operation circuit; The output terminal of computing circuit is connected with at least one proportional amplifier, and proportional amplifier is connected with corresponding A/D analog to digital conversion circuit, and the A/D analog to digital conversion circuit is connected with microsystem;
Microsystem, its output terminal are by at least one D/A D/A converting circuit, and the D/A D/A converting circuit is connected with corresponding ratio amplifying circuit, and this ratio amplification circuit output end connects another input end of computing circuit.
The voltage of the first siding ring input of described small-size voltage transformer TV is the voltage at resistance R 2 two ends, resistance R 2 is connected on the secondary side of primary system zero sequence current mutual inductor, resistance R 2 voltage dependent resistor (VDR) R1 in parallel, capacitor C 1, resistance R 2 are obtained and the proportional voltage of primary system zero-sequence current.
Described resistance R 3 shunt capacitance C2.
The output terminal of described computing circuit is connected with ratio amplifying circuit II, ratio amplifying circuit III respectively, and ratio amplifying circuit II, ratio amplifying circuit III are connected with A/D analog to digital conversion circuit II with corresponding A/D analog to digital conversion circuit I respectively.
Described D/A D/A converting circuit is connected with ratio amplifying circuit I, and ratio amplifying circuit I output is connected with another input end of computing circuit.
A kind of method of work that adopts system with non-effectively earthed neutral zero sequence current measurement device, its process is:
When electric system normally moves, system with non-effectively earthed neutral zero sequence current measurement device starts to put into operation, the voltage at resistance R 2 two ends that is connected on the output of zero sequence current mutual inductor is connected to the small-size voltage transformer TV first siding ring of device, the both end voltage U1 that is connected on the resistance R 3 of small-size voltage transformer TV second siding ring inputs one of them input terminal of computing circuit, the output voltage of computing circuit obtains the U1 digital signal through proportional amplifier II and A/D analog to digital conversion circuit I, and the input microsystem;
Microsystem is processed the video digital signal Un of rear formation U1 to the U1 digital signal, microsystem is exported to the D/A D/A converting circuit to Un, the simulating signal that the output of D/A D/A converting circuit is corresponding with digital signal Un, this simulating signal is through another input terminal of proportional amplifier I input computing circuit, computing circuit carries out computing to the signal of two input ends, and it is zero that operation result makes computing circuit output voltage U 3;
If U3 does not reduce to zero, microsystem is proceeded to process to the U1 digital signal, forms the new video digital signal Un of U1, and microsystem is exported to the D/A D/A converting circuit to new Un; So repeatedly, until U3 reaches minimum value; The one section periodic digital signal of Un when microsystem reaches minimum value to U3 deposits microsystem long storer storage time in as memory signal Um;
Microsystem is no longer got U1 voltage waveform digital signal from A/D analog to digital conversion circuit I after obtaining memory signal Um; But memory signal Um is exported to the D/A D/A converting circuit periodically; And from A/D analog to digital conversion circuit II, get U1 voltage waveform digital signal;
Electric system generation singlephase earth fault, the U1 voltage waveform digital signal that microsystem is obtained from A/D analog to digital conversion circuit II be measurement device to transmission line of electricity the capacitive zero-sequence current.
The invention has the beneficial effects as follows: the capacitive zero-sequence current must arrive amplification in the first link of metering circuit; Various Static disturbance signals are just eliminated foremost at device body; Device body can amplify useful zero sequence current signal as far as possible, and fault line selection device is greatly improved to measurement sensitivity and the precision of zero-sequence current, guarantees that fault line selection device makes selecting properly.
Description of drawings
Fig. 1 represents a kind of system with non-effectively earthed neutral zero sequence current measurement device logic diagram;
Wherein, 1. microsystem, 2. ratio amplifying circuit I, 3. ratio amplifying circuit II, 4. ratio amplifying circuit III, 5. D/A D/A converting circuit, 6. A/D analog to digital conversion circuit I, 7. A/D analog to digital conversion circuit II, 8. computing circuit.
Embodiment
The present invention will be further described below in conjunction with accompanying drawing.
A kind of system with non-effectively earthed neutral zero sequence current measurement device as shown in Figure 1.Resistance R 2 of output terminal series connection of zero sequence current mutual inductor, to obtain voltage proportional to zero-sequence current.The zero sequence current mutual inductor of fault line selection device in the past output be the zero-sequence current that has reduced according to the zero sequence current mutual inductor no-load voltage ratio, in primary system, the capacitive zero-sequence current is original just very little, through current transformer ratio, it is less that Current Transformer Secondary is surveyed zero-sequence current.Then Current Transformer Secondary side zero-sequence current gives another shape small size current mutual inductor of fault line selection device, and zero-sequence current is through another shape small size current mutual inductor no-load voltage ratio of fault line selection device, and shape small size current mutual inductor secondary side zero-sequence current reduces again.Resistance of shape small size current mutual inductor secondary side series connection, to obtain voltage proportional to zero-sequence current, this residual voltage is less.Very little zero-sequence current in conversion, is easy to be disturbed by the shape small size current mutual inductor exciting current of the exciting current of zero sequence current mutual inductor and fault line selection device, and zero-sequence current information is even buried by the exciting current of two current transformers.
The present invention is in resistance R 2 of output series connection of the zero sequence current mutual inductor of primary system, and very little zero-sequence current can obtain larger residual voltage value, and the capacitive zero-sequence current must arrive amplification in the first link of metering circuit.The larger residual voltage value in resistance R 2 two ends is not easy disturbed in transmitting procedure, can do not buried by the shape small size current mutual inductor exciting current of the exciting current of zero sequence current mutual inductor and fault line selection device, therefore, device is greatly improved to measurement sensitivity and the precision of zero-sequence current.
No matter the transmission line of electricity of power transformer isolated neutral is normal operation, phase fault still occurs, all there is no zero-sequence current.Zero sequence current mutual inductor secondary side open circuit not there will be high voltage, particularly primary side three-phase conducting wire to pass the cable zero sequence current mutual inductor of annular core, and the secondary side open circuit not there will be high voltage.If the zero sequence current mutual inductor (as shown in Figure 1) of threephase current transformer TAa, TAb, the addition of TAc secondary side, due to the imbalance of threephase current transformer error and environment, will have uneven zero-sequence current; Zero sequence current mutual inductor secondary side open circuit will produce very large superpotential.In order to reduce the impact of uneven zero-sequence current, resistance R 2 of zero sequence current mutual inductor output series connection; And when uneven zero-sequence current was large, resistance R 2 got the small value; Uneven zero-sequence current hour, resistance R 2 is got large value; Neither produce superpotential, can obtain again larger residual voltage value.In order to prevent that high frequency interference from producing superpotential at resistance R 2 two ends, resistance R 2 voltage dependent resistor (VDR) R1 in parallel, voltage are during less than setting, and voltage dependent resistor (VDR) R1 is very large; Voltage is during greater than setting, and voltage dependent resistor (VDR) R1 is very little, and superpotential is by voltage dependent resistor (VDR) R1 discharge, Protection secondary circuit equipment.Resistance R 2 capacitor C 1 in parallel, small-size voltage transformer TV secondary coil capacitor C 2 in parallel, capacitor C 1, C2 are anti-interference capacitor; Reduce the impact of transient state impulse disturbances on the measurement device circuit.
When electric system normally moved, system with non-effectively earthed neutral zero sequence current measurement device started to put into operation, and at this moment transmitting loop does not have zero-sequence current, and resistance R 2 two ends are uneven residual voltage.The voltage at resistance R 2 two ends is connected to the small-size voltage transformer TV primary winding of device through cable, small-size voltage transformer TV secondary coil resistance in series R3, the both end voltage U1 input ratio of resistance R 3 adds (subtracting) computing circuit 8, the output voltage U 3 that ratio adds (subtracting) computing circuit 8 obtains the U1 digital signal through proportional amplifier II3 and A/D analog to digital conversion circuit I6, and input microsystem 1; Microsystem 1 is controlled the voltage signal of A/D analog to digital conversion circuit I6 Comparative Examples amplifier II3 output and is sampled and analog to digital conversion, and the U1 simulating signal becomes after digital quantity the storer that deposits microsystem 1 in.
1 pair of U1 digital signal of microsystem is processed, form the video digital signal Un of U1, then the Un digital signal is exported to D/A D/A converting circuit 5, D/A D/A converting circuit 5 is converted to simulating signal to the Un digital signal, this analog output signal is through proportional amplifier I2 output U2 voltage signal (for example: the U2 waveform voltage signal is opposite with the U1 voltage waveform), and input adds (subtracting) computing circuit 8, (for example: addition), making U3 is zero through adding 8 computings of (subtracting) computing circuit for U2 voltage and U1 voltage.As seen, the target that 1 pair of U1 digital signal of microsystem is processed the video digital signal Un that forms U1 is that to make U3 be zero, or as far as possible little.1 pair of U1 digital signal of microsystem is processed the fairly simple disposal route of the video digital signal Un that forms U1, is to the U1 negate; Be the negate of U1 positive voltage ripple, as Un negative voltage ripple; The negate of U1 negative voltage ripple, as Un positive voltage ripple.Another easily disposal route be, 1 of microsystem is processed the power frequency sinusoidal signal in the U1 digital signal, the target that forms the video digital signal Un of U1 is that to make the power frequency sinusoidal signal in U3 be zero, or as far as possible little.Non-power frequency sinusoidal signal in the U1 digital signal, processed by other analog filters or digital filter.Microsystem 1 makes U3 less, and needed disposal route is more complicated.So the performance index of device need be weighed processing with the processing complexity.
If U3 does not reduce to zero, 1 pair of U1 digital signal of microsystem is proceeded to process, and forms the new video digital signal Un of U1, and microsystem 1 is exported to D/A D/A converting circuit 5 to new Un; So repeatedly, until U3 reaches minimum value; The one section periodic digital signal of Un when microsystem 1 reaches minimum value to U3 deposits microsystem long storer storage time in as memory voltage signal Um;
Electric system generation singlephase earth fault, the U1 voltage waveform signal that obtains from the A/D analog to digital conversion circuit II7 that is connected with proportional amplifier III4 be measurement device to transmission line of electricity capacitive zero-sequence current waveform; Microsystem 1 is obtained the zero-sequence current of all transmission lines of electricity that are connected with bus, judges accordingly faulty line.
When electric system normally moved, the U1 voltage waveform signal that the A/D analog to digital conversion circuit II7 that connects from proportional amplifier III4 obtains was very little, is the Static disturbance signal.During electric system generation singlephase earth fault, transmission line of electricity has zero-sequence current; The A/D analog to digital conversion circuit II7 that connects from proportional amplifier III4 can obtain zero-sequence current information.If it is less to obtain zero-sequence current information from A/D analog to digital conversion circuit II7, the enlargement factor that can strengthen proportional amplifier III4 improves measurement sensitivity and the precision of device.Because the Static disturbance signal is reduced, the enlargement factor of proportional amplifier III4 can be larger.Thereby improve measurement sensitivity and the precision of device to zero-sequence current.
The Static disturbance signal may change along with the change of power system operation mode, memory voltage signal Um in microsystem 1 can upgrade automatically according to the Fixed Time Interval of design, the zero-sequence current situation of change adaptive updates that measures before also can occurring according to the electric system single-line to ground fault.Before occurring, the electric system single-line to ground fault make the Static disturbance signal minimum to the interference of device; So that after the electric system single-line to ground fault occurs, device can obtain large as far as possible zero sequence current measurement sensitivity and precision.
A kind of system with non-effectively earthed neutral zero sequence current measurement device logic diagram that Fig. 1 represents, only measure a power transmission line zero-sequence electric current; One cover system with non-effectively earthed neutral fault line selection device need to be measured many power transmission line zero-sequence electric currents, so, need to the measurement mechanism that many covers Fig. 1 represents be made up, can realize the failure line selection task.
System with non-effectively earthed neutral zero sequence current measurement device and method of the present invention can manufacture and design with prior art, can realize fully.Broad prospect of application is arranged.
Claims (1)
1. method of work that adopts system with non-effectively earthed neutral zero sequence current measurement device, described system with non-effectively earthed neutral zero sequence current measurement device comprises with lower component, small-size voltage transformer TV, its first siding ring input voltage amount, secondary side resistance in series R3, resistance R 3 one end ground connection, an input end of other end concatenation operation circuit; The output terminal of computing circuit is connected with at least one ratio amplifying circuit, and the ratio amplifying circuit is connected with corresponding A/D analog to digital conversion circuit, and the A/D analog to digital conversion circuit is connected with microsystem; Microsystem, its output terminal are by at least one D/A D/A converting circuit, and the D/A D/A converting circuit is connected with corresponding ratio amplifying circuit, and this ratio amplification circuit output end connects another input end of computing circuit; Computing circuit is inputted the simulating signal that the power transmission line zero-sequence electric current is inputted through the D/A D/A converting circuit through simulating signal and the microsystem of small-size voltage transformer TV input simultaneously, it is characterized in that, its process is:
When electric system normally moves, system with non-effectively earthed neutral zero sequence current measurement device starts to put into operation, the voltage at resistance R 2 two ends that is connected on the output of zero sequence current mutual inductor is connected to the small-size voltage transformer TV first siding ring of device, the both end voltage U1 that is connected on the resistance R 3 of small-size voltage transformer TV second siding ring inputs one of them input terminal of computing circuit, the output voltage of computing circuit obtains the U1 digital signal through ratio amplifying circuit II and A/D analog to digital conversion circuit I, and the input microsystem;
Microsystem is processed the video digital signal Un of rear formation U1 to the U1 digital signal, microsystem is exported to the D/A D/A converting circuit to Un, the simulating signal that the output of D/A D/A converting circuit is corresponding with digital signal Un, this simulating signal is through another input terminal of ratio amplifying circuit I input computing circuit, computing circuit carries out computing to the signal of two input ends, and it is zero that operation result makes computing circuit output voltage U 3;
If U3 does not reduce to zero, microsystem is proceeded to process to the U1 digital signal, forms the new video digital signal Un of U1, and microsystem is exported to the D/A D/A converting circuit to new Un; So repeatedly, until U3 reaches minimum value; The one section periodic digital signal of Un when microsystem reaches minimum value to U3 deposits microsystem long storer storage time in as memory signal Um;
Microsystem is no longer got U1 voltage waveform digital signal from A/D analog to digital conversion circuit I after obtaining memory signal Um; But memory signal Um is exported to the D/A D/A converting circuit periodically; And from A/D analog to digital conversion circuit II, get U1 voltage waveform digital signal;
Electric system generation singlephase earth fault, the U1 voltage waveform digital signal that microsystem is obtained from A/D analog to digital conversion circuit II be measurement device to transmission line of electricity the capacitive zero-sequence current.
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| CN104111370A (en) * | 2014-06-30 | 2014-10-22 | 陕西和硕电气有限公司 | Method for measuring zero-sequence current in three-phase ungrounded system |
| CN106093709B (en) * | 2016-08-15 | 2019-04-09 | 国网山东省电力公司潍坊供电公司 | A kind of Single-phase Earth-fault Selection in Distribution Systems and localization method differential based on broad sense |
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| CN101839958A (en) * | 2010-04-28 | 2010-09-22 | 华北电力大学 | Electrified locating device for single-phase earth fault of electric distribution network |
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| US4857855A (en) * | 1988-11-03 | 1989-08-15 | Toyo Communication Equipment Co., Ltd. | Method for compensating for phase of insulation resistance measuring circuit |
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