CN101776723B - Method for detecting earth fault of direct current system by utilizing frequency deviation method - Google Patents
Method for detecting earth fault of direct current system by utilizing frequency deviation method Download PDFInfo
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- CN101776723B CN101776723B CN 200910200837 CN200910200837A CN101776723B CN 101776723 B CN101776723 B CN 101776723B CN 200910200837 CN200910200837 CN 200910200837 CN 200910200837 A CN200910200837 A CN 200910200837A CN 101776723 B CN101776723 B CN 101776723B
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Abstract
The invention discloses a method for detecting earth fault of a direct current system by utilizing a frequency deviation method, belonging to electrical measurement field. The method is as follows: a sensor is arranged in a direct current output circuit to measure differential current flowing through the circuit of the sensor, the secondary of the sensor is utilized as the inductance coil of an active oscillator, a pulse counter is utilized for colleting the oscillation frequency of the active oscillator, and the oscillation frequency and the reference frequency of the active oscillator are compared by a microprocessor; if the frequency of the active oscillator is larger than a set value, a trigger signal is output and an alarming device is started to output an alarm signal; and field staff can rapidly find the position of an earth-return circuit according to the indication of an alarm lamp. The method not only overcomes the harm caused by that earth fault is searched by interrupting each circuit one by one when a balanced bridge method is utilized, but also has no need of injecting alternative current signals, is not related to the distributed capacitance of a direct current system and has no electric relation with a system to be tested, thus being capable of realizing distributed installation and real-time on-line monitoring. The method can be widely applied to the monitoring field of the direct current system.
Description
Technical field
The invention belongs to the electrical measurement field, relate in particular to a kind of detection method that is used for transformation and distribution system DC power-supply system electric fault.
Background technology
The straight-flow system of generating plant, transformer station is a very important working power in the electric system, and it provides power supply for secondary devices such as electric, thermal technology, aut.eq., electric protection, emergency lighting, communications; The operate as normal of these secondary devices is very important for the safe operation that ensures generating plant, transformer station, and direct supply stable operation and its loop intact under nominal parameter is the necessary condition that guarantees transformer station's normal running and protective device correct operation; Therefore require straight-flow system and network thereof to have the reliability of height.
Above-mentioned straight-flow system all adopts the method for operation of " insulation against ground ".
When " ground connection " fault takes place a bit in straight-flow system, operation to whole straight-flow system can't cause any harm, but must in time handle, otherwise when " ground connection " fault of another point takes place whole straight-flow system again, might make protective relaying device or relay protection relay that " misoperation " or " tripping work " takes place; Perhaps, might cause the direct supply short circuit, cause fuse blows, or fast independent power source switch disconnection, make equipment lose operating power, cause electric system catastrophic failure and even accident.Therefore, do not allow straight-flow system long-play under " ground connection " situation on one point, must strengthen on-line monitoring, search rapidly and get rid of earth fault, stop the electric power system fault that causes because of dc system grounding.
In the actual motion practice, also find, " ground connection " fault takes place in straight-flow system, also can cause the equipment that adopts straight-flow system power supply/control to produce " malfunction " or " tripping ", so that device damage, cause large-area power-cuts, finally might cause power supply system to be disintegrated, produce extremely serious consequence.
Therefore " ground connection " problem of straight-flow system can not only go to look at problem from the angle of a transformer station, a generating plant, and should go to consider how to search and take precautions against from whole electrical network.
The method that existing straight-flow system insulation detects and the problem of existence:
1, utilize principle of balance bridge to detect:
For transformer station and generating plant, after operation for many years, cable insulation generally descends, the damages of getting rusty such as various terminal boxs and mechanism case, and sealing property descends, and meets rain, snow, greasy weather gas, and " ground connection " fault easily takes place; And mostly be nonmetal character ground connection (resistance height over the ground), the less formation symmetry of the difference of multipoint earthing, both positive and negative polarity insulation resistance " ground connection " fault.And the bridge balance principle is all adopted in the warning of the device of present various dc system groundings, can't effectively monitor above-mentioned high resistant symmetry ground connection.
Because of being subjected to the restriction of bridge balance principle, this type of device can only be judged the insulation status of total system, can not directly determine concrete " ground connection " point, must utilize " open line method " one by one each road DC load to be carried out " outage " more respectively and check, could determine to take place the point/loop of " ground connection " fault.So-called " retracting the road " cuts off the direct supply (power off time should less than three seconds) in this loop exactly, and general the lighting loop inspection rises earlier from signal circuit, and again to operation circuit, protection loop or the like is checked.Because electrical secondary system becomes increasingly complex; most factory station is because the variety of problems of leaving in construction or the enlarging; make the differentiation of signal circuit and control loop and protection loop neither one strictness; and more also form some improper closed loops; use this kind method in this case, must increase and retract the difficulty that earth fault is searched on the road.Because circuit connection exists uncertain, often makes in the process of " retracting the road ", and artificial " tripping operation " accident usually takes place, and adds the extensive application of Microcomputer Protection, Microcomputer Protection is not because the operation characteristic of computing machine allows random outage yet.
So the disadvantage of the method is exactly to cut off the operation or the signal power source in the loop that supplies, cause the loop that cuts off the power supply can not divide the major loop switch/closing operation at short notice, in case when main current supply circuit just in time breaks down, the normal operation of entail dangers to system.
2, exchange pouring-in detection method:
The existing domestic microcomputer type branch road line selection apparatus that injects ac signaling to system that is extensive use of, what mainly adopt is " low frequency " probe method and " frequency conversion " probe method dual mode.Promptly between direct current fault bus and ground, inject the AC signal of a low frequency or frequency conversion, detect, find " ground connection " branch road and tangible difference occurs and determine " ground connection " point according to low-frequency current before and after " ground connection " point with pincerlike current probe pointwise.
Along with installing and using of a large amount of anti-interference capacitors of Microcomputer Protection, the employing of the straight-flow system open loop radiation type electric supply method of operation increases the capacitive earth current of straight-flow system.When capacitance current during to the setting valve of insulation resistance leakage current, will cause mistaking signal greater than pick-up unit, influence the correct judgement of device.Simultaneously owing to will inject AC signal to tested straight-flow system, very little although its amplitude is compared with DC bus-bar voltage, concerning the very high electric system of security requirement, the AC signal of injection also can be brought unsafe factor to system.
3, Hall magnetic-type balancing method:
The ultimate principle of Hall magnetic-type equilibrium principle as shown in Figure 1.Observe the arbitrary branch road of straight-flow system, from the electric current I of power positive end outflow
L+, after the whole loads of the branch road of flowing through, the branch current that returns power supply negative terminal is I
L –, when this branch road does not have ground current, I
L+=I
L –, the size of current of passing sensor equates the sensor no-output.
And when earth fault takes place, suppose to be connected on branch road on the positive electrode bus through resistance R ground connection, ground current is I
R, I then
L+=I
L –+ I
R, the size of current of the sensor of flowing through does not wait, this difference of a reaction of sensor output I
RThe signal of size and Orientation is judged the size of stake resistance and the polarity of ground connection branch road in view of the above.
Though this kind method has overcome the influence of system's distributed capacitance, still there is weak point in it, and subject matter goes out on active sensor; Adopt the magnetic balance principle, make active sensor, when primary side has electric current to change or rush of current is arranged, remanent magnetism easily takes place change, especially when sensing is passive, be subjected to rush of current after, the remanent magnetism variation is bigger.This remanent magnetism variation can seriously cause the direct current offset of electric current, voltage amplifier and A/D converter, cause the line selection apparatus of making in order to last method constantly to drift about zero point, need the zero point and the sensor characteristic of timely regulating device, the precision that could guarantee line selection apparatus reaches stable, not only bring great inconvenience and trouble, and cause the inaccurate of line selection apparatus to the scene.
As fully visible, there is a certain distance in the know-why that present all kinds of insulation detection device adopted with the actual conditions at scene, can not accomplish in time, judge accurately for DC earthing searching, causes apparatus function to be difficult to satisfy fully on-the-spot actual needs.
Summary of the invention
Technical matters to be solved by this invention provides a kind of method that adopts frequency deviation method to detect DC system earth fault, the oscillation frequency of the caused active oscillating device of spill current that produces when it passes through to measure straight-flow system " ground connection " changes, and monitors the generation of straight-flow system " ground connection " fault; It had both overcome the harm of when utilizing balanced bridge method each loop being cut off the power supply one by one and being brought when searching, need not in system, to inject AC signal again, and it is irrelevant with the distributed capacitance of straight-flow system, with system under test (SUT) without any electrical link, distributed installation can be realized, and real time on-line monitoring can be realized.
Technical scheme of the present invention is: a kind of method that adopts frequency deviation method to detect DC system earth fault is provided, is included in the flow through loop spill current of sensor of sensor measurement is set on the direct current output circuit, it is characterized in that:
A, an active LC oscillator is set, the secondary telefault of described sensor as active LC oscillator;
When B, straight-flow system are normally moved,, and send into microcontroller circuit, be initialized as reference frequency f by the natural mode shape f of an impulse meter collection active LC oscillator this moment
0
C, microcontroller circuit record and Memory Reference frequency f
0
D, impulse meter continue to gather the oscillation frequency f of active LC oscillator
1, and send into microcontroller circuit;
E, microcontroller circuit are to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze; Described comparison/analysis comprises the value of calculating df/dt respectively and calculates oscillation frequency f
1With reference frequency f
0Poor;
F, if the calculated value of df/dt greater than the first setting value D
1, carry out the H step, otherwise, the E step returned;
G, if the oscillation frequency f of active LC oscillator
1With reference frequency f
0Difference greater than the second setting value D
2, and the duration is greater than the 3rd setting value D
3The time, carry out the H step, otherwise, the E step returned;
H, microcontroller circuit output trigger pip are to trigger;
I, trigger output signal start warning device, output alarm signal;
J, field personnel find the position of ground loop according to the indication of stand by lamp/hummer.
Further, described microcontroller circuit all by the natural mode shape f of impulse meter collection active LC oscillator this moment, is initialized as reference frequency f behind each power-off restarting
0
Concrete, the described first setting value D
1For
The described second setting value D
2Be f
1-f
0200Hz; Described the 3rd setting value D
3Be T〉100ms.
When described straight-flow system is normally moved, the loop of the described sensor of flowing through difference Dian Liu ⊿ I=I
L+-I
L-=0, this moment, the natural mode shape f of active LC oscillator was initialized as reference frequency f by microcontroller circuit
0, and be stored in the register of microcontroller circuit, wherein, the electric current that flows out from power positive end is I
L+, after the whole loads of the branch road of flowing through, the branch current that returns power supply negative terminal is I
L-
As the loop of the described sensor of flowing through difference Dian Liu ⊿ I=I
L+-I
L-=I
R≠ 0 o'clock, if
Perhaps △ f=f
1-f
0When the also lasting 100ms of 200Hz was above, then described microcontroller circuit judged that earth fault appears in the DC loop at this sensor place, described microcontroller circuit output trigger pip, cause the flip-flop circuit upset, output alarm signal, wherein, the electric current that flows out from power positive end is I
L+, after the whole loads of the branch road of flowing through, the branch current that returns power supply negative terminal is I
L-, when earth fault takes place, suppose to be connected on branch road on the positive electrode bus through resistance R ground connection, ground current is I
R
Correspondence is provided with a sensor respectively on a plurality of power supply output loops of described straight-flow system, the corresponding active LC oscillator of each sensor, each sensor secondary respectively as the telefault of corresponding active LC oscillator; Corresponding to each active LC oscillator, correspondence is provided with impulse meter, microcontroller circuit, trigger and a warning device respectively.
Further, described impulse meter calculates the measurement result of active LC oscillator oscillation frequency in the following manner:
Measured result=survey frequency * scale+offset frequency is set
Wherein, scale is Hz or 10KHz, and bigoted frequency setting is 10KHz.
Described impulse meter is gathered the oscillation frequency f of active LC oscillator
1, microcontroller circuit is to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze and microcontroller circuit output trigger pip is carried out in real time to trigger.
Compared with the prior art, advantage of the present invention is:
1. the oscillation frequency of the caused active oscillating device of spill current that produces during by measurement straight-flow system " ground connection " changes, monitor the generation of straight-flow system " ground connection " fault, directly send alerting signal, avoided drawing back one by one the harm that is brought when the loop outage is checked;
2. this method need not to inject AC signal in system, the influence that operation is produced to straight-flow system in the time of can avoiding ac-current inject method to detect;
3. because sensor surveys is DC earthing electric current difference I
RSize, therefore irrelevant with the distributed capacitance of straight-flow system;
4. the frequency of being surveyed derives from the secondary coil of sensor, with system under test (SUT) without any electrical link, can better guarantee the normal operation of original system;
If with whole monitoring device integrated/miniaturization, be separately positioned on the terminal row place that each output loop of straight-flow system is connected with load, promptly can realize distributed installation, each output loop that detects straight-flow system of adding system more, and can realize real time on-line monitoring very easily.
Description of drawings
Fig. 1 is the detection schematic diagram of existing Hall magnetic-type equilibrium principle;
Fig. 2 is a detection method synoptic diagram of the present invention.
Embodiment
The present invention will be further described below in conjunction with accompanying drawing.
Among Fig. 1, the positive and negative bus (power end) of straight-flow system is U
+, U
-, the two ends of a certain road load L respectively successively with U
+And U
–The corresponding connection, the electric current at the load L two ends of then flowing through is used I respectively
L+And I
L –Represent, load L two ends and power supply just/link circuit of negative terminal on, suit is provided with a sensor (actual is a current transformer) CT, the primary coil of this CT by load L two ends and power supply just/link circuit of negative terminal serves as, the output terminal of its secondary coil is connected with the microcomputer decision circuitry with signal Processing (generally including filtering, shaping, amplification and/or threshold circuit).
Observe the arbitrary branch road of straight-flow system, from power positive end U
+The electric current I that flows out
L+, after the whole loads of this branch road of flowing through, the branch current that returns power supply negative terminal U-is I
L –, when this branch road does not have ground current, I
L+=I
L –, the size of current of passing sensor CT equates the sensor no-output.
And when earth fault takes place, suppose to be connected on branch road on the positive electrode bus through resistance R ground connection, ground current is I
R, I then
L+=I
L –+ I
R, the size of current of the sensor of flowing through is no longer equal, this difference of a reaction of sensor output I
RThe signal of size and Orientation is judged the size of stake resistance and the polarity of ground connection branch road in view of the above.
Among Fig. 2, basic detection method of the present invention is:
1, the flow through loop spill current of sensor of sensor measurement is set on direct current output circuit;
2, an active LC oscillator is set, the secondary telefault of described sensor as active LC oscillator;
When 3, straight-flow system is normally moved,, and send into microcontroller circuit, be initialized as reference frequency f by the natural mode shape f of an impulse meter collection active LC oscillator this moment
0
4, microcontroller circuit record and Memory Reference frequency f
0
5, impulse meter continues to gather the oscillation frequency f of active LC oscillator
1, and send into microcontroller circuit;
6, microcontroller circuit is to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze; Described comparison/analysis comprises the value of calculating df/dt respectively and calculates oscillation frequency f
1With reference frequency f
0Poor;
7, if df/dt〉1kHz/s, carried out for the 9th step, otherwise, returned for the 6th step;
8, if the oscillation frequency f of active LC oscillator
1With reference frequency f
0Difference greater than 200Hz, and duration during greater than 100ms, carried out for the 9th step, otherwise, returned for the 6th step;
9, microcontroller circuit output trigger pip is to trigger;
10, trigger upset, the output alarm enabling signal starts warning device, output alarm signal.
This method is by measuring the oscillation frequency of active LC oscillator, realize the Design of DC System Grounding Fault Detection function, flow through system's spill current of sensor of its sensor measurement of mainly making by the magnetic sensor, the secondary telefault of sensor as active LC oscillator, because the electromagnetic balance principle as can be known, when the electric current of the sensor of flowing through changed, the magnetomotive force of magnet ring must change, further cause the variation of secondary coil inductance value L, by the frequency of oscillator
As can be known, when the L value changed, its frequency f certainly will change, and when the variation of frequency reaches threshold value, promptly sent alarm signal.
In other words, when straight-flow system is normally moved, the Cha Liu ⊿ I=I of the direct current detection terminal of flowing through
L+-I
L-=0, this moment, the natural frequency of active LC oscillator was initialized to reference frequency f
0, this numerical value can be stored in the register of microcontroller circuit.
Because the different issuable f of DC load
0Different, thus impulse meter and microcontroller circuit can the reference frequency behind each power-off restarting be detected, thereby guarantee the correctness and the real-time of the reference frequency of the active LC oscillator in this loop.
When institute's detection line takes place by ground connection, certainly will cause that flowing through detection terminal produces spill current ， ⊿ I=I
L+-I
L-=I
R, work as I
RWhen reaching threshold value, just the natural frequency to oscillator causes enough big variation.
By the detection of impulse meter, can detect the capable natural frequency f of the active LC oscillator of normal fortune
0Failure-frequency f during with ground connection
RTwo different frequencies, and be sent to microprocessor.
Microprocessor is analyzed two frequencies, by
The time, perhaps △ f〉100Hz and continue 100ms when above, promptly export trigger pip and arrive trigger.
When trigger obtains trigger pip, can trigger startup warning output.
More specifically, adopt this method, can be on a plurality of output loops of straight-flow system respectively correspondence a sensor is set, the corresponding active LC oscillator of each sensor, each sensor secondary respectively as the telefault of corresponding active LC oscillator; Corresponding to each active LC oscillator, correspondence is provided with impulse meter, microcontroller circuit, trigger and a warning device respectively.
Further, described impulse meter calculates the measurement result of active LC oscillator oscillation frequency in the following manner:
Measured result=survey frequency * scale+offset frequency is set
Wherein, scale is Hz or 10KHz, and bigoted frequency setting is 10KHz.
Above-mentioned impulse meter is gathered the oscillation frequency f of active LC oscillator
1, microcontroller circuit is to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze and microcontroller circuit output trigger pip is carried out in real time to trigger.
Adopt integrated technology and surface mount elements, foregoing circuit can be integrated in the less housing fully, make and the similar integrated form connection terminal of connecting terminal block size, upper and lower end at this integrated form connection terminal, be connected with the output loop of straight-flow system, the input circuit of load respectively, can constitute the connecting terminal block that has the intelligent integrated of normal operation/earth fault indication and have monitoring function.
The monitoring terminal that utilizes aforesaid way to make can distributed earth be installed on each terminal loop of straight-flow system, and the field personnel only need check the indication of the stand by lamp of each terminal, can find the position of ground loop rapidly.
More specifically, in technique scheme, impulse meter can adopt general frequency counter to get final product.
Frequency is the number of times that the signal generating period changes in the unit interval.If we can count signal waveform, and count results is shown, just can read the frequency of measured signal in the given time.
Frequency counter at first obtains relatively stable and correct time, simultaneously measured signal is converted to the pulse signal that amplitude and waveform all can be discerned by digital circuit, calculate the pulse number of this section in the time interval by counter then, with gained data recording and output.
Measured result=survey frequency * scale+offset control
Wherein, scale is Hz or 10KHz, and bigoted frequency setting is 10KHz.
Trigger can adopt integrated JK flip-flop, for the door input pattern, receiving input signal at trigger is 1 o'clock entirely, trigger is output as high level, makes stand by lamp bright.
Owing to sensor (in fact being exactly a micro-transformer of current), active LC pierce circuit, impulse meter circuit, measure the frequency of measurand and microcontroller circuit and flip-flop circuit by step-by-step counting and be prior art, its concrete principle of work, element select and connected mode is no longer narrated at this.
Those of ordinary skill in the art after having grasped the thinking and method that the present invention deals with problems, can reproduce technical scheme of the present invention, technique effect and goal of the invention without performing creative labour fully.
Because the oscillation frequency of the caused active oscillating device of spill current that produces when the present invention passes through to measure straight-flow system " ground connection " changes, monitor the generation of straight-flow system " ground connection " fault, directly send alerting signal, need not in system, to inject AC signal, the harm that is brought when the loop outage is checked, the influence that operation is produced to straight-flow system in the time of also can avoiding ac-current inject method to detect have been avoided drawing back one by one; In addition, because the sensor survey is the size of DC earthing electric current difference IR, therefore the distributed capacitance with straight-flow system has nothing to do; Add that the frequency of being surveyed derives from the secondary coil of sensor, with system under test (SUT) without any electrical link, can better guarantee the normal operation of original system, in addition, whole proposal can realize distributed installation, each output loop that detects straight-flow system of adding system more, and can realize real time on-line monitoring very easily.
The present invention can be widely used in the straight-flow system monitoring/protection field of electric system/transformation and distribution system.
Claims (8)
1. method that adopts frequency deviation method to detect DC system earth fault is included in the flow through loop spill current of sensor of sensor measurement is set on the direct current output circuit, it is characterized in that:
A, an active LC oscillator is set, the secondary telefault of described sensor as active LC oscillator;
When B, straight-flow system are normally moved,, and send into microcontroller circuit, be initialized as reference frequency f by the natural mode shape f of an impulse meter collection active LC oscillator this moment
0
C, microcontroller circuit record and Memory Reference frequency f
0
D, impulse meter continue to gather the oscillation frequency f of active LC oscillator
1, and send into microcontroller circuit;
E, microcontroller circuit are to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze; Described comparison/analysis comprises the value of calculating df/dt respectively and calculates oscillation frequency f
1With reference frequency f
0Poor;
F, if the calculated value of df/dt greater than the first setting value D
1, carry out the H step, otherwise, the E step returned;
G, if the oscillation frequency f of active LC oscillator
1With reference frequency f
0Difference greater than the second setting value D
2, and the duration is greater than the 3rd setting value D
3The time, carry out the H step, otherwise, the E step returned;
H, microcontroller circuit output trigger pip are to trigger;
I, trigger output signal start warning device, output alarm signal;
J, field personnel find the position of ground loop according to the indication of stand by lamp/hummer.
2. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that described microcontroller circuit is behind each power-off restarting, all, be initialized as reference frequency f by the natural mode shape f of impulse meter collection active LC oscillator this moment
0
3. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that the described first setting value D
1For
The described second setting value D
2Be f
1-f
0200Hz; Described the 3rd setting value D
3Be T〉100ms.
4. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that when described straight-flow system is normally moved, the loop of the described sensor of flowing through difference Dian Liu ⊿ I=I
L+-I
L-=0, this moment, the natural mode shape f of active LC oscillator was initialized as reference frequency f by microcontroller circuit
0, and be stored in the register of microcontroller circuit, wherein, the electric current that flows out from power positive end is I
L+, after the whole loads of the branch road of flowing through, the branch current that returns power supply negative terminal is I
L-
5. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that as the loop of the described sensor of flowing through difference Dian Liu ⊿ I=I
L+-I
L-=I
R≠ 0 o'clock, if
Perhaps △ f=f
1-f
0When the also lasting 100ms of 200Hz was above, then described microcontroller circuit judged that earth fault appears in the DC loop at this sensor place, described microcontroller circuit output trigger pip, cause the flip-flop circuit upset, output alarm signal, wherein, the electric current that flows out from power positive end is I
L+, after the whole loads of the branch road of flowing through, the branch current that returns power supply negative terminal is I
L-, when earth fault takes place, suppose to be connected on branch road on the positive electrode bus through resistance R ground connection, ground current is I
R
6. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that on a plurality of power supply output loops of described straight-flow system correspondence is provided with a sensor respectively, the corresponding active LC oscillator of each sensor, each sensor secondary respectively as the telefault of corresponding active LC oscillator; Corresponding to each active LC oscillator, correspondence is provided with impulse meter, microcontroller circuit, trigger and a warning device respectively.
7. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that described impulse meter calculates the measurement result of active LC oscillator oscillation frequency in the following manner:
Measured result=survey frequency * scale+offset frequency is set
Wherein, scale is Hz or 10KHz, and bigoted frequency setting is 10KHz.
8. detect the method for DC system earth fault according to the described employing frequency deviation method of claim 1, it is characterized in that described impulse meter gathers the oscillation frequency f of active LC oscillator
1, microcontroller circuit is to the oscillation frequency f of active LC oscillator
1With reference frequency f
0Compare/analyze and microcontroller circuit output trigger pip is carried out in real time to trigger.
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| CN 200910200837 CN101776723B (en) | 2009-12-25 | 2009-12-25 | Method for detecting earth fault of direct current system by utilizing frequency deviation method |
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|---|---|---|---|
| CN 200910200837 CN101776723B (en) | 2009-12-25 | 2009-12-25 | Method for detecting earth fault of direct current system by utilizing frequency deviation method |
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|---|---|---|---|---|
| EP2628015B1 (en) * | 2010-10-14 | 2014-06-25 | ABB Research Ltd. | Fault direction parameter indicator device using only current and related methods |
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