CN102520309A - Method for judging open circuit of secondary loop of current transformer - Google Patents
Method for judging open circuit of secondary loop of current transformer Download PDFInfo
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- CN102520309A CN102520309A CN2011104030680A CN201110403068A CN102520309A CN 102520309 A CN102520309 A CN 102520309A CN 2011104030680 A CN2011104030680 A CN 2011104030680A CN 201110403068 A CN201110403068 A CN 201110403068A CN 102520309 A CN102520309 A CN 102520309A
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Abstract
The invention relates to a method for judging the open circuit of a secondary loop of a current transformer. The method is characterized by comprising the following steps of: acquiring signals through a micro-processor; making an open circuit judgment of the secondary loop under two conditions including a formula, namely the absolute value of Ib-Ic is more than K*MAX(Ib, Ic)+I, and a condition on whether only one homonymous phase current mutation amount is reduced; if the two conditions are satisfied, judging that the secondary loop is open-circuit; and if both the two conditions are not satisfied, repetitively sampling and judging according to user set frequencies. In the event of judging that the secondary loop is open-circuit, the method is also capable of automatically operating a pre-set protection program. The invention provides the method for judging the open circuit of the secondary loop of the current transformer without a protection dead zone.
Description
Technical field
The invention belongs to the electric power online monitoring technical field, specifically be meant a kind of method of judging the secondary loop of mutual inductor open circuit.
Background technology
Current transformer (abbreviating CT in the power industry usually as) is according to electromagnetic induction principle, is made up of the iron core and the winding of closure.Its umber of turn seldom go here and there in the circuit of the electric current that needs are measured, so it often has whole electric currents of circuit to flow through; The Secondary Winding turn ratio is more, is serially connected in measurement instrument and protects in the loop, and current transformer in use; A windings in series is in test line, and the Secondary Winding number of turn is many, the use of connecting with current coils such as measurement instrument and relays; The impedance of current coil such as measurement instrument and relay is very little, thus when normally moving CT near short-circuit condition.The size of CT secondary current determines by primary current, and magnetic potential that secondary current produces is the magnetic potential that is used for the balance primary current.If second open circuit, its impedance is infinitely great, and secondary current equals zero, and its magnetic potential also equals zero, magnetic potential that just can not the generation of balance primary current, and primary current will all act on excitatoryly so, make iron core seriously saturated.Magnetic saturation will make iron loss increase, and CT heating, the insulation of CT coil also can be burnt out because of overheated.Also can on iron core, produce remanent magnetism, increase transformer error.The most serious is because magnetic saturation, and the sine wave of alternating flux becomes trapezoidal wave, in magnetic flux vertiginous moment; To induce very high voltage on the secondary coil; Its peak value can reach several kilovolts, and so high voltage acts on secondary coil and the secondary circuit, and the person and equipment are all existed serious threat; When situation is serious, can burns CT even blast.So CT does not allow the secondary side open running.To above reason, all be provided with open-circuit protecting device on the CT secondary circuit mostly.
Existing CT open-circuit protector for secondary loop all adopts overvoltage protection mostly, is divided into following 2 big types according to design.
1, electronic circuit formula CT open-circuit protector for secondary loop, its inside comprise parts such as tension measuring circuit, pressure limiting circuit, amplifying circuit, logic judging circuit, executive circuit, display circuit, automatic electrify restoration circuit, manual reset circuit.When the secondary side voltage peak of CT≤360V, flow into the every road leakage current≤20 μ A of CT open-circuit protecting device.It is far smaller than secondary side full scale electric current 5A.Thereby in normal operation, do not influence the work of measurement, protective relaying device.When current transformer open circuit, secondary voltage peak value >=360V, the exit relay contact is the corresponding Secondary Winding short circuit of CT, thereby eliminates superpotential, installs on the panel corresponding light emitting diode simultaneously and lights, and informs the open circuit information of operations staff CT.The maintainer can check corresponding secondary circuit under situation about not having a power failure, after secondary circuit is intact, press SR, and light emitting diode extinguishes; If be in off-state on the secondary circuit, press SR, light emitting diode is still lighted, and continues the corresponding secondary circuit of inspection, till intact.
2, lightning arrester formula CT open-circuit protector for secondary loop, Zinc-Oxide Arrester utilize the good non-linear volt-ampere characteristic of zinc paste, when normal working voltage, flow through the electric current minimum (microampere or milliampere level) of lightning arrester; When the superpotential effect, resistance sharply descends, the superpotential energy of releasing, thus reach the effect of overvoltage protection when the CT secondary circuit is opened a way.
Yet; Electronic circuit formula CT open-circuit protector for secondary loop and two kinds of CT second open circuit protectors of lightning arrester formula CT open-circuit protector for secondary loop are all existing the protection dead band aspect design and the installation, this main relevant with the CT secondary connection position of CT open-circuit protector for secondary loop (the CT secondary connection of CT secondary circuit open circuit unit protection is from switch cubicle terminal row lead-in wire generally speaking).If CT secondary circuit open circuit occurs in the B place shown in the accompanying drawing 1 (being between CT secondary connection and protection, observing and controlling, the WT-MSR of switch cubicle terminal row CT open-circuit protector for secondary loop); At this moment above-mentioned two kinds of CT second open circuit protectors can both regular event with the CT short circuit, prevent that high pressure from jeopardizing the safety of the person, equipment.If but CT secondary circuit open circuit occurs in the residing Secondary Winding of protective device, sees from accompanying drawing 1, protective device is owing to gather less than electric current; The ruuning situation that can not correctly reflect primary side if CT secondary circuit open circuit occurs in the protection group, takes place under the phase fault situation simultaneously; Because the CT secondary current is bigger, if wiring place crimping is bad, resistance is bigger; With heating burnout here, the CT secondary is opened a way; CT second open circuit protector action output node is with CT secondary circuit short circuit.Because B does not have electric current (6kV, 10kV adopt A, C two phase CT to install mostly) mutually, A mutually or C mutually since the CT second open circuit by short circuit, the protective device collection can not correctly be tripped less than this fault phase secondary current.In addition, from the angle of safe operation, should stop transport and handle the CT second open circuit.According to the rules, when handling the CT second open circuit, the staff must stand on the insulating mat; Carry out insulation measures; Prevent the injury of high pressure to the person, but because site disposal is difficult to hold the effective and safe operating distance (CT second open circuit place owing to burn, two ends be difficult to receive together again) of human body to switch cubicle; Contact CT second open circuit produces high-pressure section easily, and the accident of human electric shock is taken place.
CT secondary circuit open circuit takes place if CT secondary circuit open circuit occurs in the A place shown in the accompanying drawing 1 (like a certain place between CT secondary root binding post or CT secondary root and switch cubicle terminal row); The A place still has high voltage to CT secondary circuit root binding post place; And A place (the CT secondary breaks off the other end) is to CT second open circuit protector connecting terminal block place no-voltage; At this moment CT second open circuit device does not just have protective effect, even break off moment generation high pressure, makes CT protective device action output one node short circuit; Can not eliminate the high voltage that CT secondary root open circuit produces, influence the CT safe operation.
In sum, the opened a way restriction of determination methods of the CT open-circuit protector for secondary loop under the prior art all exists the protection dead band, has certain potential safety hazard.
Summary of the invention
The technical matters that the present invention will solve is that a kind of method of not protecting the judgement secondary loop of mutual inductor open circuit in dead band is provided.
For solving the problems of the technologies described above, technical scheme provided by the invention is: a kind of method of judging the secondary loop of mutual inductor open circuit, and it may further comprise the steps:
(1) on same current transformer, sets up a protective current mutual inductor sample group and a measurement current transformer set of samples;
(2) microprocessor reads current signal value by the frequency that the user is provided with to protective current mutual inductor sample group and a measurement current transformer set of samples;
(3) microprocessor is by formula: | and Ib-Ic|＞K * MAX (Ib, Ic)+I judges, if the formula establishment then moves subsequent step; If formula is false, the frequency that then is provided with by the user is sampled to the variable that relates in the above-mentioned formula again, and whether judgment formula is set up, and (in the formula, Ib is a protective current mutual inductor sample group sampling effective value; Ic is for measuring current transformer set of samples sampling effective value; K is accuracy of protective current mutual inductor sample group sampled data and the coefficient of difference of measuring the accuracy of current transformer set of samples sampled data, and this coefficient is between 0.7～0.8; (Ib Ic) is meant maximal value between Ib and the Ic to MAX; I is a fixed value, the action threshold of protective current mutual inductor sample group);
(4) judge whether difference of phase currents of the same name has only one to reduce, if then be judged to be the secondary loop of mutual inductor open circuit, and operation corresponding protection program; If not then returning step (2).
After adopting above method; The present invention has following advantage: 1, pass through microprocessor; Two groups of sampled signals are compared; Than before the independent protective device controller of employing can judge the open-circuit position more accurately, simultaneously, effectively avoided the protection dead band of current transformer because two groups of signals are sampled simultaneously.2, added the sampling of the sudden change amount of phase current of the same name, effectively avoided the erroneous judgement that causes because of current transformer primary circuit open circuit.
As improvement; MAX in step (3) (Ib, during Ic) greater than the rated current of 1.2 times of secondary circuits, microprocessor is skipped subsequent step and is directly sent alerting signal; And the preset defence program of operation; This improvement is directly reported to the police when microprocessor detects the abnormal current above rated current, and the preset defence program of operation, effectively raises the protection efficient to current transformer.
As further improvement, also be provided with secondary loop of mutual inductor broken string tripping operation control word on the said microprocessor, when little processing is judged to be the secondary loop of mutual inductor open circuit, can send trip signal immediately; This improves item and can directly trip through microprocessor control through secondary circuit broken string tripping operation control word, need not by third-party controller the protection efficient of raising and the reliability of whole device.
Description of drawings
Fig. 1 is the scheme of installation of second open circuit protector of current mutual inductor in the prior art.
Fig. 2 is the process flow diagram of the method for the judgement secondary loop of mutual inductor open circuit that the present invention relates to.
As shown in the figure: 1, phase line, 2, the primary circuit, 3, secondary circuit, 4, protection/observing and controlling/WT-MSR, 5, the CT open-circuit protector for secondary loop.
Embodiment
Below in conjunction with accompanying drawing the present invention is done further detailed description.
In conjunction with accompanying drawing 2, a kind of method of judging the secondary loop of mutual inductor open circuit that the present invention relates to, it comprises the steps:
(1) on same current transformer, sets up a protective current mutual inductor sample group and a measurement current transformer set of samples;
(2) microprocessor reads current signal value by the frequency that the user is provided with to protective current mutual inductor sample group and a measurement current transformer set of samples;
(3) microprocessor is by formula: | and Ib-Ic|＞K * MAX (Ib, Ic)+I judges, if the formula establishment then moves subsequent step; If formula is false, the frequency that then is provided with by the user is sampled to the variable that relates in the above-mentioned formula again, and whether judgment formula is set up, and (in the formula, Ib is a protective current mutual inductor sample group sampling effective value; Ic is for measuring current transformer set of samples sampling effective value; K is accuracy of protective current mutual inductor sample group sampled data and the coefficient of difference of measuring the accuracy of current transformer set of samples sampled data, and this coefficient is between 0.7～0.8; (Ib Ic) is meant maximal value between Ib and the Ic to MAX; I is a fixed value, the action threshold of protective current mutual inductor sample group); During practical implementation, the K value can be made as 0.75, and I is the action threshold of protective current mutual inductor sample group, need set according to the load current value of protective current mutual inductor during practical implementation, if not high 2 times of can be set to rated current of protection accuracy requirement.
(4) judge whether difference of phase currents of the same name has only one to reduce, if then be judged to be the secondary loop of mutual inductor open circuit, and operation corresponding protection program; If not then returning step (2).
During practical implementation, the MAX in step (3) (Ib, during Ic) greater than the rated current of 1.2 times of secondary circuits, skip subsequent step and directly send alerting signal, and the preset defence program of operation by microprocessor.
Also be provided with secondary loop of mutual inductor broken string tripping operation control word on the said microprocessor, when little processing is judged to be the secondary loop of mutual inductor open circuit, can send trip signal immediately.
Need to prove, the present invention in the specific implementation, the microprocessor of employing is a single-chip microcomputer, the 51 type standard single-chip microcomputers that can directly select for use.One sudden change amount in the difference of phase currents of the phase that described difference of phase currents of the same name is sampled and Ib, two sample rate currents of Ic just can conclude it is the secondary circuit open circuit of current transformer when both have only one to reduce.Because CT uses is the P level in protection, and measuring be 0.5 grade or even 0.2 grade (measure, metering some places possibly be connected in series public one group of CT Secondary Winding).In that relatively more serious short trouble situation once takes place is primary current when big (phase fault), and protection CT does not have saturated, and has been far longer than its rated current owing to measure CT; Saturated; Both are under the situation that does not have open circuit, and the electric current difference is very big, might judge the CT second open circuit by accident.But electric current is (occur the CT second open circuit during fault again, ultimate current also reduces) that reduces during owing to the CT second open circuit, and electric current increases during phase fault, and sudden change amount just increases, subtracts difference, can distinguish primary fault or CT second open circuit.Comprehensive above the analysis drawn the basis for estimation of CT second open circuit.| Ib-Ic|＞K * MAX (Ib, Ic)+I and difference of phase currents of the same name have only 1 to reduce two conditions; When this criterion is normally moved at CT; Can normally judge the CT second open circuit; Even when a phase fault, because the protection secondary current is bigger, current terminal is arranged the tight and heating burnout of screw in flakes and is caused the open circuit of CT; Also can accurately judge, mainly be to utilize difference of phase currents of the same name only when CT opens a way, just to reduce this principle.
The present invention is not limited to above a kind of embodiment, and the conspicuous variation under conceiving based on the present invention is all within protection domain of the present invention.
Claims (3)
1. method of judging secondary loop of mutual inductor open circuit, it is characterized in that: it may further comprise the steps:
(1) on same current transformer, sets up a protective current mutual inductor sample group and a measurement current transformer set of samples;
(2) microprocessor reads current signal value by the frequency that the user is provided with to protective current mutual inductor sample group and a measurement current transformer set of samples;
(3) microprocessor is by formula: | and Ib-Ic|＞K * MAX (Ib, Ic)+I judges, if the formula establishment then moves subsequent step; If formula is false, the frequency that then is provided with by the user is sampled to the variable that relates in the above-mentioned formula again, and whether judgment formula is set up, and (in the formula, Ib is a protective current mutual inductor sample group sampling effective value; Ic is for measuring current transformer set of samples sampling effective value; K is accuracy of protective current mutual inductor sample group sampled data and the coefficient of difference of measuring the accuracy of current transformer set of samples sampled data, and this coefficient is between 0.7～0.8; (Ib Ic) is meant maximal value between Ib and the Ic to MAX; I is a fixed value, the action threshold of protective current mutual inductor sample group);
(4) judge whether difference of phase currents of the same name has only one to reduce, if then be judged to be the secondary loop of mutual inductor open circuit, and operation corresponding protection program; If not then returning step (2).
2. a kind of method of judging the secondary loop of mutual inductor open circuit according to claim 1; It is characterized in that: the MAX (Ib in step (3); During Ic) greater than the rated current of 1.2 times of secondary circuits; Microprocessor is skipped subsequent step and is directly sent alerting signal, and the preset defence program of operation.
3. a kind of method of judging the secondary loop of mutual inductor open circuit according to claim 1; It is characterized in that: also be provided with secondary loop of mutual inductor broken string tripping operation control word on the said microprocessor; When little processing is judged to be the secondary loop of mutual inductor open circuit, can send trip signal immediately.
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| Application Number | Priority Date | Filing Date | Title |
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| CN2011104030680A CN102520309A (en) | 2011-12-07 | 2011-12-07 | Method for judging open circuit of secondary loop of current transformer |
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| CN2011104030680A CN102520309A (en) | 2011-12-07 | 2011-12-07 | Method for judging open circuit of secondary loop of current transformer |
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN102830264A (en) * | 2012-09-04 | 2012-12-19 | 南京南瑞集团公司 | Sampling value switching method applicable to safe stable control device under intelligent substation environment |
| CN103278724A (en) * | 2013-04-22 | 2013-09-04 | 国家电网公司 | Specific current module used for monitoring defect of secondary loop of current transformer in electric power system |
| CN104332951A (en) * | 2014-11-11 | 2015-02-04 | 国家电网公司 | Protection system for secondary-side open circuit of current transformer |
| CN104882866A (en) * | 2015-05-27 | 2015-09-02 | 北京四方继保自动化股份有限公司 | Method for protection device to use pulse quantity to distinguish CT secondary side line breaking |
| CN104898006A (en) * | 2014-03-04 | 2015-09-09 | 国家电网公司 | Current transformer secondary side open circuit anticipation device |
| CN105098711A (en) * | 2014-11-24 | 2015-11-25 | 芜湖蓝宙电子科技有限公司 | Intelligent selection current transformer winding secondary-side open-circuit protector circuit |
| CN105093058A (en) * | 2015-06-03 | 2015-11-25 | 国家电网公司 | Method for determining whether secondary circuit of current transformer is left open-circuited and corresponding determining apparatus |
| CN106371049A (en) * | 2016-08-31 | 2017-02-01 | 贵州电网有限责任公司贵阳供电局 | Current transformer secondary open circuit identification method |
| CN110908285A (en) * | 2019-12-10 | 2020-03-24 | 国网山西省电力公司长治供电公司 | Adaptive control system of composite transformation ratio current transformer |
| CN112731206A (en) * | 2020-12-07 | 2021-04-30 | 南京国电南自电网自动化有限公司 | Analog input type merging unit protection current transformer disconnection detection method |
| CN115166603A (en) * | 2022-06-24 | 2022-10-11 | 北京天能继保电力科技有限公司 | Virtual connection judgment method and device for secondary circuit wiring terminal of power grid voltage transformer |
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Cited By (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102830264B (en) * | 2012-09-04 | 2015-05-13 | 国电南瑞科技股份有限公司 | Sampling value switching method applicable to safe stable control device under intelligent substation environment |
| CN102830264A (en) * | 2012-09-04 | 2012-12-19 | 南京南瑞集团公司 | Sampling value switching method applicable to safe stable control device under intelligent substation environment |
| CN103278724B (en) * | 2013-04-22 | 2015-12-16 | 国家电网公司 | For monitoring the ratio flow module of defect of secondary loop of current transformer in electric system |
| CN103278724A (en) * | 2013-04-22 | 2013-09-04 | 国家电网公司 | Specific current module used for monitoring defect of secondary loop of current transformer in electric power system |
| CN104898006A (en) * | 2014-03-04 | 2015-09-09 | 国家电网公司 | Current transformer secondary side open circuit anticipation device |
| CN104332951A (en) * | 2014-11-11 | 2015-02-04 | 国家电网公司 | Protection system for secondary-side open circuit of current transformer |
| CN104332951B (en) * | 2014-11-11 | 2018-04-03 | 国家电网公司 | Current Transformer Secondary side open-circuit-protection system |
| CN105098711A (en) * | 2014-11-24 | 2015-11-25 | 芜湖蓝宙电子科技有限公司 | Intelligent selection current transformer winding secondary-side open-circuit protector circuit |
| CN104882866A (en) * | 2015-05-27 | 2015-09-02 | 北京四方继保自动化股份有限公司 | Method for protection device to use pulse quantity to distinguish CT secondary side line breaking |
| CN105093058A (en) * | 2015-06-03 | 2015-11-25 | 国家电网公司 | Method for determining whether secondary circuit of current transformer is left open-circuited and corresponding determining apparatus |
| CN106371049A (en) * | 2016-08-31 | 2017-02-01 | 贵州电网有限责任公司贵阳供电局 | Current transformer secondary open circuit identification method |
| CN106371049B (en) * | 2016-08-31 | 2023-09-26 | 贵州电网有限责任公司贵阳供电局 | Current transformer secondary open circuit identification method |
| CN110908285A (en) * | 2019-12-10 | 2020-03-24 | 国网山西省电力公司长治供电公司 | Adaptive control system of composite transformation ratio current transformer |
| CN112731206A (en) * | 2020-12-07 | 2021-04-30 | 南京国电南自电网自动化有限公司 | Analog input type merging unit protection current transformer disconnection detection method |
| CN112731206B (en) * | 2020-12-07 | 2023-08-15 | 南京国电南自电网自动化有限公司 | Analog input type merging unit protection current transformer broken line detection method |
| CN115166603A (en) * | 2022-06-24 | 2022-10-11 | 北京天能继保电力科技有限公司 | Virtual connection judgment method and device for secondary circuit wiring terminal of power grid voltage transformer |
| CN115166603B (en) * | 2022-06-24 | 2023-02-28 | 北京天能继保电力科技有限公司 | Virtual connection judgment method and device for secondary circuit wiring terminal of power grid voltage transformer |
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Application publication date: 20120627 |