CN103779833B - DC leakage current detection and protection circuit and detection and guard method - Google Patents
DC leakage current detection and protection circuit and detection and guard method Download PDFInfo
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- CN103779833B CN103779833B CN201410059669.8A CN201410059669A CN103779833B CN 103779833 B CN103779833 B CN 103779833B CN 201410059669 A CN201410059669 A CN 201410059669A CN 103779833 B CN103779833 B CN 103779833B
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Abstract
The invention discloses a kind of DC leakage current detection and protection circuit and detection and guard method; use the testing circuit for the output electric current with input current difference detecting DC source; difference signal amplifies and comparison circuit; relay interlocking and IGCT (controllable silicon) control protection electric circuit, DC leakage protection test circuit.The present invention uses the method measuring sampling resistor pressure drop difference to detect leakage current, it is ensured that the capacity of resisting disturbance of circuit.Voltage drop difference is amplified by the subtractor circuit consisted of operational amplifier, and utilizes the comparison circuit that precision voltage regulator TL431 constitutes, and exports earth leakage protective control signal.When leakage current exceedes maximum permissible value, cut off the power supply of load by relay and IGCT.DC leakage current detection functionality is integrated by the present invention with break protecting, has the advantages such as degree of accuracy is high, reliability is high, capacity of resisting disturbance is strong, install simply, debugging is convenient.
Description
Technical field
The present invention relates to a kind of DC leakage current detection and protection circuit and detection and guard method.
Background technology
Currently, DC source is widely used.Can there is leakage at DC circuit with protection circuit in DC leakage detection
During electrical phenomena, it is ensured that equipment and the safety of personnel.Direct current cabinet is the abbreviation of DC operation power supply system.Simply
Saying, direct current cabinet is just to provide the equipment of stable dc power supply.Electric operation power in power plant and transformer station is existing
Modern employing is all DC source, and it is to control load and the offer such as living load and direct current emergency lighting load
Power supply, is present age electric power system control, the basis of protection.DC leakage is that power system direct current operative power source is normal
One of fault seen, is likely to result in advertiser, controls loop and the misoperation of relay protection, or make
Circuit breaker trip.Therefore, it is necessary to direct current operative power source is carried out continuous print monitoring, when electric leakage occurs in its certain point
During fault, sending alarm signal immediately, staff searches and gets rid of leak current fault, thus stops because of direct current system
System leaks electricity and causes electric power system fault.
In straight-flow system leak current fault detection field, mainly there are 3 class devices.One class device is based on to bus
The method injecting low frequency small-signal, and utilize current transformer and external capacitor directly to vibrate to produce sinusoidal wave skill
Art detects, such as " transformer station direct current system microcomputer insulation monitoring and warning device Branch-circuit check module " (patent application
Number: CN 201320214241).Another kind of device is to realize DC leakage current detection by magnetic modulator technology, as
" DC leakage indicator " (number of patent application: CN 03227311).Also having a class device is to use Hall electricity
Flow sensor carries out DC leakage current detection, such as " direct current leakage protective circuit " (number of patent application: CN
201220334154).In actual application, these method Shortcomings, subject matter goes out at sensor
Receive the impact of distribution capacity, remanent magnetism change impact, wire relative to position impact, environment electromagnetics interference
And the ripple interference etc. in measured DC, thus affect the precision and stability of detection, to field adjustable band
Carry out inconvenience greatly.
Therefore, it is necessary to design a kind of DC leakage current detection and protection circuit and detection and guard method.
Summary of the invention
The technical problem to be solved is to provide a kind of DC leakage current detection and protection circuit and detection
With guard method, the detection of this DC leakage current can realize leakage-current alarm with protection circuit and detection with guard method,
Reliability is high, and capacity of resisting disturbance is strong.
The technical solution of invention is as follows:
A kind of DC leakage current detection and protection circuit, including measuring resistance, amplifying circuit, comparison circuit and control
Circuit processed；
Described measurement resistance includes that the first measurement resistance R1 and second measures resistance R3；The one main electricity of termination of R1
The anode in source, the other end of R1 is designated as M end and the first end with load [when now there is electric leakage, is only connected
Report to the police, load not power-off]；One end ground connection of R3, the other end of R3 is designated as N end the second end phase with load
Even；
Amplify and comparison circuit compares after the voltage amplification on R1 and R3, and by control signal outfan
CTL exports control signal；
Control circuit include IGCT U3 and U4, PNP triode Q1, start key K1, stop key K2 and
4 relay: RL1～RL4；
The e pole of Q1 connects accessory power supply positive pole, and the b pole of Q1 connects described control signal outfan through resistance R16
CTL；The c pole of Q1 is through the coil ground connection of RL4；The common of RL4 connects accessory power supply positive pole；RL4's is normal
Opening contact unsettled, the normally-closed contact of RL4 connects the positive pole of IGCT U4 through the coil of RL3；The minus earth of U4；
Accessory power supply positive pole is activated key K1 and resistance R17 successively and connects the triggering end of IGCT U4；
The common of RL3 connects accessory power supply positive pole, and the normally-closed contact of RL3 is successively through light emitting diode D2 and electricity
Resistance R19 ground connection；The normally opened contact of RL3 connects the normally-closed contact of RL2 through the coil of RL1；The common of RL1
Connect M end；
One termination accessory power supply positive pole of the coil of RL2, the other end is through stop key K2 ground connection；The normally opened of RL2 touches
Point is unsettled；The common of RL2 connects the positive pole of IGCT U3, the minus earth of U3, and start key K1 is through resistance
R17 and R18 is respectively connected to triggering end and the triggering end of U3 of U4.
Another way, M end is connected with the first end of load by the normally opened contact of relay R L1, i.e. RL1
Normally-closed contact unsettled, the normally opened contact of RL1 is connected with the first end of described load.[when now there is electric leakage,
Not only report to the police, load also power-off]
Described amplifying circuit include four high guaily unit integrated circuit U1[ used 3 operational amplifier A therein,
B、C】；Comparison circuit uses precision voltage regulator TL431 to constitute.
The positive power source terminal of operational amplifier is connected on accessory power supply, the negative power end ground connection of operational amplifier；
The the first dividing potential drop branch road being made up of resistance R4 and R6 is connected across between main power source and ground, operational amplifier
The in-phase input end of U1A connects the dividing point of the first dividing potential drop branch road；The inverting input of U1A meets M through resistance R8
End；Between inverting input and the outfan of U1A, bridging has resistance R10；The outfan of U1A is through resistance R12
Connect the in-phase input end of U1C；
The the second dividing potential drop branch road being made up of resistance R9 and R11 is connected across between N end and ground, operational amplifier U1B
In-phase input end connect the dividing point of the second dividing potential drop branch road；The inverting input of U1B is through resistance R5 ground connection；U1B
Inverting input and outfan between bridging have resistance R7；The outfan of U1B connects the anti-of U1C through resistance R13
Phase input；
The in-phase input end of operational amplifier U1C is through R15 ground connection；The inverting input of operational amplifier U1C with
Adjustable resistance RV2 it is connected between outfan；
1 foot [i.e. with reference to pole, R end] of precision voltage regulator TL431 connects the outfan of U1C；2 foot ground connection are [i.e.
Positive pole, A end], 3 feet [i.e. negative pole, K end] are described control signal outfan CTL；3 feet are through R14
Connect accessory power supply.
Described DC leakage current detection also includes with protection circuit testing circuit；Test circuit includes being serially connected in M
Feeler switch K3, variable resistance RV1 and ammeter between end and ground.
A kind of DC leakage current detection and guard method, it is characterised in that use aforesaid to possess warning merit
The DC leakage current detection of energy and protection circuit；
The size of current that main power source exports and returns is detected respectively by resistance R1 and R3；By amplifying and ratio
Relatively circuit compares after the voltage amplification on R1 and R3, and is controlled by control signal outfan CTL output
Signal；
When electric leakage reaches setting value, then real by the Control light emitting diode D2 luminescence in control circuit
The most do not cut off the leakage-current alarm of load supplying.
A kind of DC leakage current detection and guard method, use the aforesaid DC leakage not only reported to the police but also cut off the electricity supply
Stream detection and protection circuit；
The size of current that main power source exports and returns is detected respectively by resistance R1 and R2；By amplifying and ratio
Relatively circuit compares after the voltage amplification on R1 and R2, and is controlled by control signal outfan CTL output
Signal；
When electric leakage reaches setting value, then real by the Control light emitting diode D2 luminescence in control circuit
Existing leakage-current alarm, cuts off the power supply of load simultaneously.
Amplify and comparison circuit is based on operational amplifier LM324 and the integrated chip of precision voltage regulator TL431；Bag
Include direct current main power source output electric current pressure drop amplifying circuit on resistance R1 and direct current main power source input current at electricity
Pressure drop amplifying circuit on resistance R3, and the subtractor circuit being made up of LM324, for being amplified to pressure drop difference
The requirement set, and change the value of adjustable resistance RV2, the permissible value (circuit of maximum leakage current can be set
Acquiescence maximum leakage current is 30mA).
1st pin of the integrated chip of precision voltage regulator TL431 connects the outfan of amplifier, and its 3rd pin exports
Leakage current control signal.
The control circuit that described relay is constituted with IGCT (controllable silicon) etc., according to amplifying and comparison circuit
The leakage current control signal of output, when leakage current is less than setting value, the magnitude of voltage of control signal is higher, PNP
Audion Q1 ends.When by touching start key, by relay R L3, RL2, RL1, IGCT U4, U3 quilt
Triggering and conducting, relay R L3, RL1 switch motion, load R20 obtains electric.
When leakage current is more than setting value, the magnitude of voltage of control signal is relatively low, and PNP triode Q1 turns on, and continues
Electrical equipment RL4 switch motion [when leakage current is more than setting value, the 3 foot output low levels of TL431 so that Q1
Conducting] so that the switch motion of relay R L3, last relay R L1 switch motion, cut off load R20
Power supply, reach the purpose of protection, and light emitting diode D2 be bright reports to the police.
According to actual needs load can also be received M end, so when leakage current exceedes setting value, this circuit
Only report to the police with light emitting diode D2, without cutting off the power supply of load.
The work process of described DC leakage current protection test circuit is: when by when touching feeler switch, produce simulation
Leakage current；And by adjustable resistance RV1 and the RV2 joint debugging in difference signal amplifying circuit, can accurately set
Put maximum allowable leakage current.
Beneficial effect:
DC leakage current detection and protection circuit and detection and the guard method of the present invention, is used for detecting direct current
The output electric current of power supply and the testing circuit of input current difference, difference signal amplifies and comparison circuit, relay
Interlocking and IGCT (controllable silicon) control protection electric circuit, DC leakage protection test circuit.The present invention uses survey
Leakage current is detected by the method for amount sampling resistor pressure drop difference, it is ensured that the capacity of resisting disturbance of circuit.Pass through
Voltage drop difference is amplified by the subtractor circuit that operational amplifier is constituted, and utilizes precision voltage regulator TL431
The comparison circuit constituted, exports earth leakage protective control signal.When leakage current exceedes maximum permissible value, by continuing
Electrical equipment cuts off the power supply of load with IGCT.
The present invention detects DC leakage current, and profit by the current differential in extracting directly direct current main power source bus
Jointly provide warning and DC leakage open circuit protection (also can not change straight-flow system with relay interlocking and IGCT
Operating condition, only reports to the police), it is achieved DC leakage current detection and the integrated circuit of protection.
The core component of the circuit of the present invention is operational amplifier, precision voltage regulator, relay and IGCT；No
Relating to CPU, thus be also not related to program, i.e. use the circuit of devices at full hardware, this is also that its reliability is high
One of reason.
The present invention by the outfan of direct current main power source and input concatenation current sample small resistor, compare this two
The pressure drop difference of individual resistance, during without leaky, pressure drop difference is zero；When there being leaky, pressure drop difference is through computing
After amplifier amplifies, then compared output control signal by precision voltage regulator TL431, make IGCT and relay shape
State changes, it is achieved reports to the police and protects.Sampling resistor can affect the power of load, but as long as adjusting circuit
Amplification, micro-slightly pressure drop of sampling small resistor does not then interfere with the normal work of load.Said process is not subject to
The impact of environment electromagnetics interference, does not the most increase extra low frequency signal, does not has particular/special requirement to lead location yet,
And relay and IGCT use interlocking connection mode, are not also afraid of the impact of DC ripple, it is achieved thereby that inspection
Survey the advantages such as degree of accuracy is high, reliability is high, capacity of resisting disturbance is strong, installation is simple, debugging is convenient.
Accompanying drawing explanation
Fig. 1 is the circuit theory diagrams [band power-off protection function] of DC leakage current detection and protection circuit；
Detailed description of the invention
Below with reference to the drawings and specific embodiments, the present invention is described in further details:
Embodiment 1: mode of cutting off the electricity supply
Use the mode of connection of Fig. 1, will load and be connected to relay R L1, by relay R L1 as load
On and off switch.
A kind of DC leakage current detection and protection circuit, including measuring resistance, amplifying circuit, comparison circuit, control
Circuit processed；
Described measurement resistance includes that the first measurement resistance R1 and second measures resistance R3；The one main electricity of termination of R1
The anode in source, the other end of R1 is designated as the M end the first end phase by the normally opened contact of relay R L1 with load
Even, i.e. the normally-closed contact of RL1 is unsettled, and the normally opened contact of RL1 is connected with the first end of described load.The one of R3
End ground connection, the other end of R3 is designated as N end and is connected with the second end of load；
Amplify and comparison circuit compares after the voltage amplification on R1 and R2, and by control signal outfan
CTL exports control signal；
Control circuit include IGCT U3 and U4, PNP triode Q1, start key K1, stop key K2 and
4 relay: RL1～RL4；
The e pole of Q1 connects accessory power supply positive pole, and the b pole of Q1 connects described control signal outfan through resistance R16
CTL；The c pole of Q1 is through the coil ground connection of RL4；The common of RL4 connects accessory power supply positive pole；RL4's is normal
Opening contact unsettled, the normally-closed contact of RL4 connects the positive pole of IGCT U4 through the coil of RL3；The minus earth of U4；
Accessory power supply positive pole is activated key K1 and resistance R17 successively and connects the triggering end of IGCT U4；
The common of RL3 connects accessory power supply positive pole, and the normally-closed contact of RL3 is successively through light emitting diode D2 and electricity
Resistance R19 ground connection；The normally opened contact of RL3 connects the normally-closed contact of RL2 through the coil of RL1；The common of RL1
Connect M end；
One termination accessory power supply positive pole of the coil of RL2, the other end is through stop key K2 ground connection；The normally opened of RL2 touches
Point is unsettled；The common of RL2 connects the positive pole of IGCT U3, the minus earth of U3, and start key K1 is through resistance
R17 and R18 is respectively connected to triggering end and the triggering end of U3 of U4.
Described amplifying circuit include four high guaily unit integrated circuit U1[ used 3 operational amplifier A therein,
B、C】；Comparison circuit uses precision voltage regulator TL431 to constitute.
The positive power source terminal of operational amplifier is connected on accessory power supply, the negative power end ground connection of operational amplifier；
The the first dividing potential drop branch road being made up of resistance R4 and R6 is connected across between main power source and ground, operational amplifier
The in-phase input end of U1A connects the dividing point of the first dividing potential drop branch road；The inverting input of U1A meets M through resistance R8
End；Between inverting input and the outfan of U1A, bridging has resistance R10；The outfan of U1A is through resistance R12
Connect the in-phase input end of U1C；
The the second dividing potential drop branch road being made up of resistance R9 and R11 is connected across between N end and ground, operational amplifier U1B
In-phase input end connect the dividing point of the second dividing potential drop branch road；The inverting input of U1B is through resistance R5 ground connection；U1B
Inverting input and outfan between bridging have resistance R7；The outfan of U1B connects the anti-of U1C through resistance R13
Phase input；
The in-phase input end of operational amplifier U1C is through R15 ground connection；The inverting input of operational amplifier U1C with
Adjustable resistance RV2 it is connected between outfan；
1 foot [i.e. with reference to pole, R end] of precision voltage regulator TL431 connects the outfan of U1C；2 foot ground connection are [i.e.
Positive pole, A end], 3 feet [i.e. negative pole, K end] are described control signal outfan CTL；3 feet are through R14
Connect accessory power supply.
Described DC leakage current detection also includes with protection circuit testing circuit；Test circuit includes being serially connected in M
Feeler switch K3, variable resistance RV1 and ammeter between end and ground.
The innovation of the present invention is: leakage current test, is to be realized by pressure drop difference, is protected by amplifying circuit
Demonstrate,prove minimum to load effect and accuracy of detection be high, utilize relay and IGCT interlocking, it is ensured that high reliability and
Strong anti-interference ability.Illustrate with open circuit protection with load detection of electrical leakage below:
Main power source is exactly the DC source of supply load, and accessory power supply is just supplied with the work electricity of circuit of the present invention
Source.Accessory power supply can obtain after main power source suitably processes, it is also possible to other 5V DC source replaces.?
After access system of the present invention, before not starting, load R20 and main power source are in the relation of cut-out, sampling resistor
R1, R3 are substantially all no current, and the output voltage of difference signal amplifying circuit 3 is less than precision voltage regulator TL431
Reference voltage 2.5V, then the comparison circuit that TL431 is constituted from the 3rd pin output close to the electricity of accessory power supply
Pressure value, PNP triode Q1 is ended；Additionally light emitting diode D2 is bright.
When by when touching start key K1, controllable silicon U4, U3 obtain triggering signal, and U4 first turns on, relay
Device RL3 switch motion, U3 must conduct, the switch motion of relay R L1, and load R20 obtains main power source
Power supply, R1 has the electric current flowing into load R20, and R3 has the electric current flowing out load R20, time normal, this
Two electric currents should be equal；Additionally light emitting diode D2 extinguishes.
When by tactile stop key K2, RL2 action, IGCT U3 dead electricity turns off, the switch motion of relay R L1,
Load R20 and main power source are in the relation of cut-out；Additionally light emitting diode D2 is bright.Utilize the latching characteristics of IGCT,
Unclamp K1 or K2, do not affect the state that circuit is original.Utilize the annexation that relay interlocks, circuit can be made
After state changes, when there being various interference to occur, do not have the situation of perseveration, it is ensured that circuit reliability
High.Circuit state must be artificial by tactile start key or stop key, could change.
When load R20 obtain electric after, if there is leaky, then the electric current that the electric current on R3 is less than on R1,
Their pressure drop is amplified about 10 times (100K Ω/10K Ω) respectively by operational amplifier LM324U1A and U1B.
If maximum allowable leakage current is set to 30mA, when leakage current is 30mA, then relevant with leakage current pressure drop energy
Being amplified to 30mV, the subtractor circuit constituted through operational amplifier LM324U1C takes out and amplifies about 82 times again
After (820K Ω/10K Ω), this signal is about 2.5V (30mV × 82), makes the 3rd pin output of TL431
The voltage of about 1V, so that the conducting of PNP triode Q1, the switch motion of relay R L4, relay R L3
Switch motion, the switch motion of relay R L1, load R20 disconnects with main power source；Additionally light emitting diode D2
Bright carry out leakage-current alarm.Can also according to actual needs load R20 be received between feeler switch and R3, so
When leakage current exceedes setting value, this circuit is only reported to the police with light emitting diode D2, without cutting off load
Power supply.
Utilize DC leakage protection test circuit, by adjustable resistance RV1 and difference signal amplifying circuit
RV2 joint debugging, can accurately arrange maximum allowable leakage current.In order to verify that the present invention the most normally works, permissible
Can, at set intervals, by touching feeler switch K3, observe light emitting diode D2 and light warning, can load by
Cut off the electricity supply.
Embodiment 2: mode of not cutting off the electricity supply.
Load is connected between sampling resistor R3 and feeler switch K3, so when electric leakage occurs, is not turned off bearing
The power supply carried, only light emitting diode D2 lights and reports to the police.Other parts of circuit are with embodiment 1.
The concrete structure explanation of circuit:
A kind of DC leakage current detection and protection circuit, including measuring resistance, amplification and comparison circuit, control electricity
Road；
Described measurement resistance includes that the first measurement resistance R1 and second measures resistance R3；The one main electricity of termination of R1
The anode in source, the other end of R1 be designated as M end directly with load the first end be connected [now exist leak electricity time,
Only report to the police, load not power-off]；One end ground connection of R3, the other end of R3 is designated as the second end phase of N end and load
Even；
Amplify and comparison circuit compares after the voltage amplification on R1 and R2, and by control signal outfan
CTL exports control signal；
Control circuit include IGCT U3 and U4, PNP triode Q1, start key K1, stop key K2 and
4 relay: RL1～RL4；
The e pole of Q1 connects accessory power supply positive pole, and the b pole of Q1 connects described control signal outfan through resistance R16
CTL；The c pole of Q1 is through the coil ground connection of RL4；The common of RL4 connects accessory power supply positive pole；RL4's is normal
Opening contact unsettled, the normally-closed contact of RL4 connects the positive pole of IGCT U4 through the coil of RL3；The minus earth of U4；
Accessory power supply positive pole is activated key K1 and resistance R17 successively and connects the triggering end of IGCT U4；
The common of RL3 connects accessory power supply positive pole, and the normally-closed contact of RL3 is successively through light emitting diode D2 and electricity
Resistance R19 ground connection；The normally opened contact of RL3 connects the normally-closed contact of RL2 through the coil of RL1；The common of RL1
Connect M end；
One termination accessory power supply positive pole of the coil of RL2, the other end is through stop key K2 ground connection；The normally opened of RL2 touches
Point is unsettled；The common of RL2 connects the positive pole of IGCT U3, the minus earth of U3, and start key K1 is through resistance
R17 and R18 is respectively connected to triggering end and the triggering end of U3 of U4.
Described amplifying circuit include four high guaily unit integrated circuit U1[ used 3 operational amplifier A therein,
B、C】；Comparison circuit uses precision voltage regulator TL431 to constitute.
The positive power source terminal of operational amplifier is connected on accessory power supply, the negative power end ground connection of operational amplifier；
The the first dividing potential drop branch road being made up of resistance R4 and R6 is connected across between main power source and ground, operational amplifier
The in-phase input end of U1A connects the dividing point of the first dividing potential drop branch road；The inverting input of U1A meets M through resistance R8
End；Between inverting input and the outfan of U1A, bridging has resistance R10；The outfan of U1A is through resistance R12
Connect the in-phase input end of U1C；
The the second dividing potential drop branch road being made up of resistance R9 and R11 is connected across between N end and ground, operational amplifier U1B
In-phase input end connect the dividing point of the second dividing potential drop branch road；The inverting input of U1B is through resistance R5 ground connection；U1B
Inverting input and outfan between bridging have resistance R7；The outfan of U1B connects the anti-of U1C through resistance R13
Phase input；
The in-phase input end of operational amplifier U1C is through R15 ground connection；The inverting input of operational amplifier U1C with
Adjustable resistance RV2 it is connected between outfan；
1 foot [i.e. with reference to pole, R end] of precision voltage regulator TL431 connects the outfan of U1C；2 foot ground connection are [i.e.
Positive pole, A end], 3 feet [i.e. negative pole, K end] are described control signal outfan CTL；3 feet are through R14
Connect accessory power supply.
Described DC leakage current detection also includes with protection circuit testing circuit；Test circuit includes being serially connected in M
Feeler switch K3, variable resistance RV1 and ammeter between end and ground.This
The parameter of component is to be+5V at main power source, and accessory power supply is to set in the case of+5V, change
Main power source and the size of accessory power supply, then need suitably to adjust the parameter of relevant components and parts in circuit.
Claims (6)
1. a DC leakage current detection and protection circuit, it is characterised in that include measuring resistance, amplifying circuit, ratio
Relatively circuit and control circuit；
Described measurement resistance includes that the first measurement resistance R1 and second measures resistance R3；The one termination main power source of R1 is just
End, the other end of R1 is designated as M end and the first end with load is connected；One end ground connection of R3, the other end of R3 is designated as N
End the second end with load are connected；
After voltage difference on R1 and R3 is amplified by amplifying circuit, export by control signal outfan CTL through comparison circuit
Control signal；
Control circuit includes that IGCT U3 and U4, PNP triode Q1, start key K1, stop key K2 and 4 continue
Electrical equipment: RL1～RL4；
The e pole of Q1 connects accessory power supply positive pole, and the b pole of Q1 meets described control signal outfan CTL through resistance R16；
The c pole of Q1 is through the coil ground connection of RL4；The common of RL4 connects accessory power supply positive pole；The normally opened contact of RL4 is unsettled,
The normally-closed contact of RL4 connects the positive pole of IGCT U4 through the coil of RL3；The minus earth of U4；Accessory power supply positive pole is successively
It is activated key K1 and resistance R17 and connects the triggering end of IGCT U4；
The common of RL3 connects accessory power supply positive pole, and the normally-closed contact of RL3 is successively through light emitting diode D2 and resistance R19
Ground connection；The normally opened contact of RL3 connects the normally-closed contact of RL2 through the coil of RL1；The common of RL1 connects M end；
One termination accessory power supply positive pole of the coil of RL2, the other end is through stop key K2 ground connection；The normally opened contact of RL2 is unsettled；
The common of RL2 connects the positive pole of IGCT U3, the minus earth of U3, and start key K1 is through resistance R17 and R18 respectively
Be connected to U4 triggers end and the triggering end of U3.
DC leakage current the most according to claim 1 detection and protection circuit, it is characterised in that M end passes through relay
The normally opened contact of device RL1 is connected with the first end of load, i.e. the normally-closed contact of RL1 is unsettled, the normally opened contact of RL1 and institute
The first end stating load is connected.
DC leakage current the most according to claim 1 and 2 detection and protection circuit, it is characterised in that described puts
Big circuit includes 3 operational amplifiers: U1A, U1B and U1C；Comparison circuit uses source of stable pressure TL431；
The positive power source terminal of operational amplifier is all connected on accessory power supply, the equal ground connection of negative power end of operational amplifier；
The the first dividing potential drop branch road being made up of resistance R4 and R6 is connected across between main power source and ground, and operational amplifier U1A's is same
The dividing point of the first dividing potential drop branch road of input termination mutually；The inverting input of U1A connects M end through resistance R8；U1A's is anti-phase defeated
Enter bridging between end and outfan and have resistance R10；The outfan of U1A connects the in-phase input end of U1C through resistance R12；
The the second dividing potential drop branch road being made up of resistance R9 and R11 is connected across between N end and ground, and operational amplifier U1B's is same
The dividing point of the second dividing potential drop branch road of input termination mutually；The inverting input of U1B is through resistance R5 ground connection；The anti-phase input of U1B
Between end and outfan, bridging has resistance R7；The outfan of U1B connects the inverting input of U1C through resistance R13；
The in-phase input end of operational amplifier U1C is through R15 ground connection；The inverting input of operational amplifier U1C and outfan
Between be connected to adjustable resistance RV2；
1 foot of source of stable pressure TL431 connects the outfan of U1C；2 foot ground connection, 3 feet are described control signal outfan
CTL；3 feet connect accessory power supply through R14.
DC leakage current the most according to claim 1 and 2 detection and protection circuit, it is characterised in that also include surveying
Examination circuit；Test circuit includes feeler switch K3, variable resistance RV1 and the ammeter being serially connected between M end and ground.
5. a DC leakage current detection and guard method, it is characterised in that use the direct current leakage described in claim 1
Current detecting and protection circuit；
The size of current that main power source exports and returns is detected respectively by resistance R1 and R3；By amplifying circuit and compare
Circuit compares after the voltage amplification on R1 and R3, and is exported control signal by control signal outfan CTL；
When electric leakage reaches setting value, then realize not cutting by the Control light emitting diode D2 luminescence in control circuit
The leakage-current alarm of disconnected load supplying.
6. a DC leakage current detection and guard method, it is characterised in that use the direct current leakage described in claim 2
Current detecting and protection circuit；
The size of current that main power source exports and returns is detected respectively by resistance R1 and R3；By amplifying circuit and compare
Circuit compares after the voltage amplification on R1 and R3, and is exported control signal by control signal outfan CTL；
When electric leakage reaches setting value, then realize electric leakage by the Control light emitting diode D2 luminescence in control circuit
Report to the police, cut off the power supply of load simultaneously.
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