CN201637809U - DC (direct current) earth fault detection circuit - Google Patents
DC (direct current) earth fault detection circuit Download PDFInfo
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- CN201637809U CN201637809U CN2010200228392U CN201020022839U CN201637809U CN 201637809 U CN201637809 U CN 201637809U CN 2010200228392 U CN2010200228392 U CN 2010200228392U CN 201020022839 U CN201020022839 U CN 201020022839U CN 201637809 U CN201637809 U CN 201637809U
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Abstract
The utility model discloses a detection circuit of a DC earth resistor. One end of a positive bus current-limiting resistor is connected with the positive pole of a DC system; the other end of the positive bus current-limiting resistor is connected with one output end of a first light-operated electronic switch; the other output end of the first light-operated electronic switch is connected with one output end of a second light-operated electronic switch and one end of a sampling resistor together to form a voltage sampling point; the other end of a sampling resistor is earthed; the other output end of the second light-operated electronic switch is connected with one end of a negative bus current-limiting resistor; and the other end of the negative bus current-limiting resistor is connected with the negative pole of the DC system. The voltage sampling point is connected with a precise rectification circuit and the positive and negative value judgement circuits of the voltages (U) of both ends of the sampling resistor to send a sampling result and a judgement result to a CPU (Central Processing Unit). The utility model overcomes the interference of nonlinear factors, improves the resistor detection precision and the consistency of an instrument, simplifies the production and debugging process and reduces the production cost of the instrument.
Description
Technical field
The utility model be a kind of high precision that is used to realize electric system direct current operative power source positive and negative busbar and branch road cable resistance to earth at line detection circuit, belong to the technical field of Power System Faults Detection.
Background technology
DC earthing is one of electric system direct current operative power source common faults.When straight-flow system generation one point earth fault (directly ground connection or insulation against ground resistance reduce); generally can not produce the harmfulness consequence immediately; but if 2 ground connection are simultaneously taken place; then may cause the misoperation of telltale, control loop and protective relaying device; cause circuit breaker trip; or directly cause the direct current operative power source short circuit, thereby cause serious power system accident.Therefore, do not allow straight-flow system long-time running under the situation of ground connection on one point.Must carry out continuous on-line to direct current operative power source and monitor that when earth fault appears in its a certain point, send alerting signal immediately, the prompting staff searches and gets rid of earth fault, thereby stops to cause electric power system fault because of dc system grounding.
At present, the DC ground fault detection method that has practical value and obtain applying has following severally, and they all exist weak point separately, simply introduce below.
Inject the low-frequency ac signal detection method, be exactly between positive and negative bus of direct current and ground, apply the low-frequency ac voltage signal respectively,, can calculate straight-flow system positive and negative electrode resistance value over the ground according to the amplitude of low-frequency ac voltage and the amplitude and the phase place of detected low-frequency ac electric current.According to the path of low-frequency ac electric current, can judge the branch road or the earth point at earth fault place.The advantage of this method is that the branch road detecting sensor is cheap, and shortcoming is: need ac signal circuit, system is comparatively complicated; Testing result is influenced by system's distributed capacitance, when distributed capacitance numerical value is big, almost can't detect; To the AC signal less than 20V that system applies, an interference volume for big amplitude has harmful effect to straight-flow system.According to whether applying signal frequency converting, inject the low-frequency ac signal detection method and can be divided into constant frequency method and frequency variation method.Frequency variation method can alleviate the influence of distributed capacitance to a certain extent, detects effect and is better than the constant frequency method.
When straight-flow system generation earth fault, can produce leakage current at the branch road of ground connection, the base area can calculate straight-flow system resistance to earth value to the leakage current value of magnitude of voltage He each branch road of direct current positive and negative busbar, according to the position that leakage current occurs, judge the place of failure point of DC grounding.The DC ground fault detection method that Here it is detects based on leakage current.The advantage of this method is to inject any signal to straight-flow system, and system is had no adverse effects; Testing result is not influenced by system's distributed capacitance; System is simple.Weak point is, accuracy of detection is not high, detection sensitivity and being limited in scope.
Adopt two light-operated switches, the positive and negative Ground leakage current that is respectively straight-flow system provides path, adopt light-coupled isolation to measure both positive and negative polarity to vagabond current, detect d-c bus voltage value, calculate straight-flow system resistance to earth numerical value according to Circuit Theorem, according to each branch road leakage current, can judge earth point place branch road, the DC detection method that Here it is switches based on switch.This method is except having all advantages based on creepage detection method, also has the accuracy of detection height, sensing range is big, remarkable advantages such as detection sensitivity height, cooperate the little split-core type current table of direct current, occasion in that execution conditions allow can find earth fault exactly, is the detection method of present performance the best.Its weak point is to have adopted the non-linear detection element, and the non-linear detection element is greatly dispersed, in order accurately to detect the numerical value of stake resistance, need measure the characteristic of nonlinear element one by one and carry out curve fitting, so production run is very loaded down with trivial details, element displacement property is poor on the detecting instrument, be unfavorable for safeguarding, produce difficulty in batches, and nonlinear element also limited the further raising of accuracy of detection.
The utility model content
The utility model proposes a kind of new DC ground fault testing circuit, can overcome the deficiency that prior art exists, have accuracy of detection height, instrument high conformity, cost low, to advantages such as system have no adverse effects.
The testing circuit of a kind of DC ground resistance of the utility model, this circuit comprise positive bus-bar current-limiting resistance R1, negative busbar current-limiting resistance R2, sampling resistor R3 and the first light-controlled electronic switch S 1, the second light-controlled electronic switch S 2; The positive pole of the termination straight-flow system of positive bus-bar current-limiting resistance R1 (+KM), the other end of positive bus-bar current-limiting resistance R1 links to each other with an output terminal of the first light-controlled electronic switch S 1, another output terminal of the first light-controlled electronic switch S 1 terminates at one of an output terminal of the second light-controlled electronic switch S 2, sampling resistor R3, be the voltage sampling point, another termination the earth of sampling resistor R3, another output terminal of the second light-controlled electronic switch S 2 links to each other with the end of negative busbar current-limiting resistance R2, and the negative pole of another termination straight-flow system of negative busbar current-limiting resistance R2 (KM).
Adopt four resistance (R8, R9, R10, R11), two diodes (D1, D2) and two operational amplifiers (U1A, U1B) to form typical precise rectification circuit, adopt operational amplifier U2A to form the positive and negative value decision circuitry of resistance R 3 both end voltage U; Precise rectification circuit is connected the voltage sample point with the positive and negative value decision circuitry of resistance R 3 both end voltage U, give CPU the absolute value of resistance R 3 both end voltage U by precise rectification circuit analog input channel ACH1, give CPU the positive and negative judged result that the positive and negative value decision circuitry of resistance R 3 both end voltage U obtains by decision circuitry analog input channel ACH2.
Principle of work of the present utility model and thinking:
As shown in Figure 1, straight-flow system positive and negative electrode insulation against ground resistance is Rp, Rn, and its position has uncertainty, + KM is the positive bus-bar of direct current operative power source,-KM is the negative busbar of direct current operative power source, supposes DC bus-bar voltage, promptly+KM and-voltage between the KM is E.R1, R2 are respectively the positive and negative bus current-limiting resistance that is connected with positive and negative bus, suppose that its resistance is R (known).S1, S2 are two light-controlled electronic switches.R3 is a sampling resistor.R4, R5, R6, R7 are current-limiting resistance, for triode Q1, Q2 provide suitable bias current.The selection principle of R1, R2 and R3 numerical value, the one, the numerical value that guarantee sampling resistor R3 both end voltage remains between-5 to+5V, the 2nd, the numerical value of R1, R2 will big as far as possible and R3 both end voltage U stake resistance Rp, Rn are being paid close attention to most susceptibility in the scope high as far as possible between compromise consider.By changing the state of light-controlled electronic switch, can produce 4 kinds of circuit states, by detecting the voltage at each state down-sampling resistance R 3 two ends,, set up and find the solution a series of system of equations according to Circuit Theorem, just can obtain waiting to ask the numerical value of parameter.This is a kind of new detection method of quantity of electricity, can be generalized to other application scenario.In order to try to achieve the numerical value of Rp, Rn, must measure DC bus-bar voltage.Because two amounts to be asked are arranged, so two system of equations of needs that is to say, two efficient circuit state: S1 of needs open, S2 turn-offs, and establishing the voltage that records on the R3 is U1, according to connection in series-parallel voltage distribution relation, can obtain formula (1); S1 turn-offs, S2 is open-minded, and establishing and recording the last voltage of R3 is U2, according to connection in series-parallel voltage distribution relation, can obtain formula (2):
This system of equations of simultaneous solution can obtain the numerical value of both positive and negative polarity resistance to earth Rp, Rn at an easy rate.
But because about the about 250V of DC bus-bar voltage, the high precision linear measurement need be used expensive Hall element, so, can consider measurement to DC bus-bar voltage, also adopt the method for measuring indirectly, that is to say that the number by increasing effective on off state and the number of system of equations are asked for the numerical value of DC bus-bar voltage.It is all open-minded to control S1, S2, obtains the 3rd efficient circuit state, and establishing the voltage that records on the resistance R 3 is U3, according to kirchhoff's principle, adopts the voltage node method, lists the nodal voltage equation group, after simultaneous is eliminated other intermediate variable, can obtain formula (3).That is to say that it is as follows to try to achieve system of equations:
Find the solution this system of equations, can obtain required Rp and Rn.The DC ground resistance that requires according to the numerical value of Rp and Rn and the electric system alarming value of adjusting can determine whether system DC ground fault takes place.
The utility model owing to equation coefficient in formula (1), (2), (3) is constant, has overcome the interference of non-linear factor, has improved the resistance detection precision of instrument and the consistance of instrument, has simplified production and debug process, has reduced the production cost of instrument.
Description of drawings
Fig. 1 is the circuit theory diagrams of utility model
Embodiment
Followingly the utility model is described in further detail with reference to drawings and Examples.
Shown in Fig. 1 was, the testing circuit of the utility model DC ground resistance, this circuit comprised positive bus-bar current-limiting resistance R1, negative busbar current-limiting resistance R2, sampling resistor R3 and the first light-controlled electronic switch S 1, the second light-controlled electronic switch S 2; The positive pole of the termination straight-flow system of positive bus-bar current-limiting resistance R1 (+KM), the other end of positive bus-bar current-limiting resistance R1 links to each other with an output terminal of the first light-controlled electronic switch S 1, another output terminal of the first light-controlled electronic switch S 1 terminates at one of an output terminal of the second light-controlled electronic switch S 2, sampling resistor R3, be the voltage sampling point, another termination the earth of sampling resistor R3, another output terminal of the second light-controlled electronic switch S 2 links to each other with the end of negative busbar current-limiting resistance R2, and the negative pole of another termination straight-flow system of negative busbar current-limiting resistance R2 (KM).Adopt four resistance (R8, R9, R10, R11), two diodes (D1, D2) and two operational amplifiers (U1A, U1B) to form typical precise rectification circuit, give CPU the absolute value of resistance R 3 both end voltage U by precise rectification circuit analog input channel ACH1, operational amplifier U2A forms the positive and negative value decision circuitry of resistance R 3 both end voltage U, and gives CPU with the result by decision circuitry analog input channel ACH2.
Wherein: the electronic switch (also claiming photoswitch) that S1, S2 adopt photoelectricity to isolate, P1, P2 are the control signal from CPU or other control circuit; Resistance R 3 both end voltage U import the analog quantity input and the digital quantity input port of microcomputer through absolute value circuit and symbol decision circuit; Control P1 is that high level, P2 are low level, and then S1 conducting, S2 turn-off; Control control P2 is that high level, P1 are low level, and then S2 conducting, S1 turn-off; Control P1, P2 are high level, the then equal conducting of S1, S2.Produce three kinds of efficient circuit states thus.Resistance R 8, R9, R10, R11, diode D1, D2 and operational amplifier U1A, U1B form precise rectification circuit, give CPU the absolute value of resistance R 3 both end voltage U by precise rectification circuit analog input channel ACH1, operational amplifier U2A forms the positive and negative value decision circuitry of resistance R 3 both end voltage U, and gives CPU with positive and negative judged result by decision circuitry analog input channel ACH2.CPU can calculate the numerical value of Rp, Rn according to the absolute value of U1, U2, U3 and positive and negative according to formula (1)～formula (3), thereby realizes the detection to DC ground resistance Rp, Rn.The DC ground resistance that requires according to the numerical value of Rp and Rn and the electric system alarming value of adjusting can determine whether system DC ground fault takes place.
Therefore, this circuit can be finished the detection of DC ground resistance by following step:
A, directly measure DC bus-bar voltage E;
B, get the first light-controlled electronic switch S, 1 closure, the second light-controlled electronic switch S 2 disconnects, and asks for the equation of DC bus-bar voltage E, sampled voltage U (establish this moment numerical value be U1) and each current-limiting resistance R1, R2 (resistance is R) and sampling resistor R3; R
pU
2=ER
3-(U
1+ U
2) (R+R
3)
C, get S2 closure, S1 and disconnect, can ask for the equation of DC bus-bar voltage E, sampled voltage U (establish this moment numerical value be U2) and each current-limiting resistance R1, R2 (resistance is R) and sampling resistor R3;
R
nU
1＝ER
3-(U
1+U
2)(R+R
3)
D, separate thus the system of equations that two equations are formed, can obtain the numerical value of positive and negative electrode resistance to earth to be asked (Rp, Rn).
This circuit can also be finished the detection of DC ground resistance by following step:
A, get S1 closure, S2 and disconnect, can ask for the equation of DC bus-bar voltage E, sampled voltage U (establish this moment numerical value be U1) and each current-limiting resistance R1, R2 (resistance is R) and sampling resistor R3;
R
pU
2＝ER
3-(U
1+U
2)(R+R
3)
B, get S2 closure, S1 and disconnect, can ask for the equation of DC bus-bar voltage E, sampled voltage U (establish this moment numerical value be U2) and each current-limiting resistance R1, R2 (resistance is R) and sampling resistor R3;
R
nU
1＝ER
3-(U
1+U
2)(R+R
3)
C, to get S1 and S2 all closed, can ask for the equation of DC bus-bar voltage E, sampled voltage U (establish this moment numerical value be U3) and each current-limiting resistance R1, R2 (resistance is R) and sampling resistor R3;
D, separate thus the system of equations that three equations are formed, can obtain the numerical value of positive and negative electrode resistance to earth to be asked (Rp, Rn).
Claims (2)
1. the testing circuit of a DC ground resistance comprises positive bus-bar current-limiting resistance (R1), negative busbar current-limiting resistance (R2), sampling resistor (R3) and the first light-controlled electronic switch (S 1), the second light-controlled electronic switch (S2); It is characterized in that: the positive pole of a termination straight-flow system of positive bus-bar current-limiting resistance (R1) (+KM), the other end of positive bus-bar current-limiting resistance (R1) links to each other with an output terminal of the first light-controlled electronic switch (S1), an output terminal of another output terminal of the first light-controlled electronic switch (S1) and the second light-controlled electronic switch (S2), one of sampling resistor (R3) terminates at together, be the voltage sampling point, another termination the earth of sampling resistor (R3), another output terminal of the second light-controlled electronic switch (S2) links to each other with an end of negative busbar current-limiting resistance (R2), and the negative pole of another termination straight-flow system of negative busbar current-limiting resistance (R2) (KM).
2. according to the testing circuit of the described a kind of DC ground resistance of claim 1, it is characterized in that: adopt four resistance (R8, R9, R10, R11), two diodes (D1, D2) and two operational amplifiers (U1A, U1B) to form precise rectification circuit, adopt operational amplifier (U2A) to form the positive and negative value decision circuitry of sampling resistor (R3) both end voltage (U); The positive and negative value decision circuitry of precise rectification circuit and sampling resistor (R3) both end voltage (U) is connected on the voltage sample point.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2010200228392U CN201637809U (en) | 2010-01-08 | 2010-01-08 | DC (direct current) earth fault detection circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2010200228392U CN201637809U (en) | 2010-01-08 | 2010-01-08 | DC (direct current) earth fault detection circuit |
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| CN201637809U true CN201637809U (en) | 2010-11-17 |
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| CN2010200228392U Expired - Fee Related CN201637809U (en) | 2010-01-08 | 2010-01-08 | DC (direct current) earth fault detection circuit |
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| CN (1) | CN201637809U (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102749523A (en) * | 2012-07-16 | 2012-10-24 | 山东奥太电气有限公司 | Direct-current ground resistance detection circuit applied to photovoltaic inverter system |
| CN102841259A (en) * | 2012-09-24 | 2012-12-26 | 冶金自动化研究设计院 | Device and method for detecting insulation resistance of direct current system |
| CN103176036A (en) * | 2011-12-20 | 2013-06-26 | 首瑞（北京）投资管理集团有限公司 | Device and method for monitoring alternating current entering direct current system |
-
2010
- 2010-01-08 CN CN2010200228392U patent/CN201637809U/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103176036A (en) * | 2011-12-20 | 2013-06-26 | 首瑞（北京）投资管理集团有限公司 | Device and method for monitoring alternating current entering direct current system |
| CN103176036B (en) * | 2011-12-20 | 2016-03-23 | 首瑞（北京）投资管理集团有限公司 | Monitoring alternating current seals in the device and method of straight-flow system |
| CN102749523A (en) * | 2012-07-16 | 2012-10-24 | 山东奥太电气有限公司 | Direct-current ground resistance detection circuit applied to photovoltaic inverter system |
| CN102841259A (en) * | 2012-09-24 | 2012-12-26 | 冶金自动化研究设计院 | Device and method for detecting insulation resistance of direct current system |
| CN102841259B (en) * | 2012-09-24 | 2015-06-03 | 冶金自动化研究设计院 | Device and method for detecting insulation resistance of direct current system |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20101117 Termination date: 20130108 |
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| CF01 | Termination of patent right due to non-payment of annual fee |