CN108695823B - Differential protection locking method for trailing current of series transformer - Google Patents
Differential protection locking method for trailing current of series transformer Download PDFInfo
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- CN108695823B CN108695823B CN201810665937.9A CN201810665937A CN108695823B CN 108695823 B CN108695823 B CN 108695823B CN 201810665937 A CN201810665937 A CN 201810665937A CN 108695823 B CN108695823 B CN 108695823B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
- H02H7/045—Differential protection of transformers
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- Protection Of Transformers (AREA)
Abstract
The invention provides a differential protection locking method for a trailing current of a series transformer. The trailing current is judged according to the trend of the current sampling value in the phase current, differential protection is performed according to phase locking, the judging accuracy of the trailing current is effectively improved, the protection is not rejected when a fault occurs, the protection is not mistakenly operated when the trailing current occurs in the CT, the accident expansion is prevented, and better guarantee is provided for the safe and stable operation of a power grid.
Description
Technical Field
The invention belongs to the field of relay protection of a power system, and particularly relates to a differential protection locking method for trailing current of a series transformer.
Background
The application occasion and the wiring form of the series transformer are greatly different from those of the common transformer.
The series transformer adopts a bypass switch-on mode to isolate the transformer. When the series transformer normally operates, the bypass switch is in an open circuit state, and at the moment, the current flowing through the grid side winding of the series transformer is the line tide. When the bypass switch is switched on, the two ends of the series transformer winding are completely short-circuited.
Because the transformer belongs to an inductive component, when the series transformer winding is short-circuited, the current in the series transformer winding cannot change suddenly, and an attenuated direct-current component is formed. Meanwhile, the secondary side of the electromagnetic current transformer still has attenuated current, namely the trailing phenomenon of the current transformer. After the two parts of trailing current are transmitted by the protection device CT, the phenomenon of trailing current zero crossing point can occur. Because the attenuation time constants of all sides of the series transformer are different, when the zero crossing point phenomenon occurs and the two sides are asynchronous, the differential flow can be calculated by the differential protection of the series transformer. At this time, the braking current is not large, so that the differential protection easily meets the action characteristic curve, and further, the misoperation risk exists.
At present, the common judgment of the trailing current mainly aims at the failure protection. In the patent CN105929217A, a method for judging the trailing of the failure protection current based on the latching of the dc component utilizes the proportion of the dc component in the phase current to judge the trailing current of the failure, and this method needs to separate the dc component and the ac component in the phase current, and has complex calculation and a long calculation time window. Patent CN 201410281034.2-a method for preventing trailing current of current transformer from influencing breaker failure protection "proposes: 1. judging the time of three continuous zero crossings of the phase current to judge the trailing current; 2. when the time delay of the failure protection action time constant value is satisfied, whether the current is reduced or not is judged to judge the trailing current, and the failure protection action time constant value is generally 50 ms. The two methods both require longer calculation time and have slower discrimination speed.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the differential protection locking method for the trailing current of the series transformer is provided, and the problem that the trailing current possibly causes differential protection misoperation when the bypass of the series transformer is switched on is solved.
In order to achieve the purpose, the invention adopts the technical scheme that:
a differential protection locking method for tail current of series transformer includes the following steps,
step 1, defining the maximum branch number of differential protection as n, and taking the absolute value of the sampling instantaneous value of the current sampling point of the ith branch current as ip (i);
step 2, comparing ip (i) with the absolute value Ik (i) of the sampling instantaneous value of the sampling point at the current of the ith branch; if ip (i) < Ik (i), recording the current trend of the current sampling point of the i-th side current as monotone decreasing;
step 3, judging whether the ith branch current is always in a monotone decreasing state in a period with continuous duration being Tset, if so, judging that the ith side current is in a trailing state, and locking corresponding differential protection;
wherein, Tset is a trailing discrimination delay fixed value, and i is 1,2,3 … n.
The same branch current is respectively judged according to phases, if any phase meets the trailing characteristic, only the differential protection of the phase is locked, and other phase differential protection is not locked. The branch currents in the difference loop are independently distinguished and are not related to each other.
The invention has the following effects: the method and the device utilize the instantaneous current change trend of the phase current to judge whether the absolute value of the phase current is in a monotonous decreasing state within a period of time, can simply and reliably identify whether the series transformer is in a current trailing state after the bypass is closed, and further prevent the differential protection of the series transformer from being mistakenly operated due to trailing current after the bypass is closed. The method has short calculation time and high discrimination speed.
Drawings
Fig. 1 is a flowchart illustrating the determination of the tail current of the series transformer.
Detailed Description
The invention is further described below with reference to fig. 1. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
Fig. 1 is a flowchart illustrating the determination of the tail current of the series transformer. The invention relates to a differential protection locking method for a trailing current of a series transformer, which comprises the following steps,
step 1, defining the maximum branch number of differential protection as n, and taking the absolute value of the sampling instantaneous value of the current sampling point of the ith branch current as ip (i);
step 2, comparing ip (i) with the absolute value Ik (i) of the sampling instantaneous value of the sampling point at the current of the ith branch; if ip (i) < Ik (i), recording the current trend of the current sampling point of the i-th side current as monotone decreasing;
step 3, judging whether the ith branch current is always in a monotone decreasing state in a period with continuous duration being Tset, if so, judging that the ith side current is in a trailing state, and locking corresponding differential protection;
wherein, Tset is a trailing discrimination delay fixed value, and i is 1,2,3 … n.
In principle, the value of Tset needs to be more than 5 ms. The reason is that for a standard 50HZ sine waveform, after the sine value is taken as the absolute value, the monotonous descending interval of the instantaneous value is 5 ms; therefore, a value of Tset greater than 5ms can distinguish between a normal sinusoidal current and a trailing current. Compared with a trailing current discrimination method in the prior art, the method is short in calculation time and high in discrimination speed.
The current at the same side is respectively judged according to phases, if any phase meets the trailing characteristic, only the differential protection of the phase is locked, and other phase differential protection is not locked; the currents at each side in the difference loop are independently judged and are not related to each other.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.
Claims (3)
1. A differential protection locking method for a trailing current of a series transformer is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
step 1, defining the maximum branch number of differential protection as n, and taking the absolute value of the sampling instantaneous value of the current sampling point of the ith branch current as ip (i);
step 2, comparing ip (i) with the absolute value Ik (i) of the sampling instantaneous value of the sampling point at the current of the ith branch; if ip (i) < Ik (i), recording the current trend of the current sampling point of the i-th side current as monotone decreasing;
step 3, judging whether the ith branch current is always in a monotone decreasing state in a period with continuous duration being Tset, if so, judging that the ith side current is in a trailing state, and locking corresponding differential protection;
wherein, Tset is a trailing discrimination delay fixed value, and i is 1,2,3 … n.
2. The differential protection blocking method for the tail current of the series transformer according to claim 1, characterized in that: and the current on the same side is respectively judged according to the phase, and if any phase meets the trailing characteristic, the differential protection of the phase is locked.
3. A differential protection blocking method for tail current of series transformer according to claim 1 or 2, characterized by: the currents on each side in the differential circuit are independently distinguished and are not related to each other.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201810665937.9A CN108695823B (en) | 2018-06-26 | 2018-06-26 | Differential protection locking method for trailing current of series transformer |
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| CN201810665937.9A CN108695823B (en) | 2018-06-26 | 2018-06-26 | Differential protection locking method for trailing current of series transformer |
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| CN108695823B true CN108695823B (en) | 2020-07-28 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111614061B (en) * | 2020-05-27 | 2022-06-28 | 国网江苏省电力有限公司 | Locking method for differential protection of series transformer |
| CN111797699A (en) * | 2020-06-10 | 2020-10-20 | 积成软件有限公司 | Method for identifying fault-removal CT trailing waveform |
| CN113363953A (en) * | 2021-06-17 | 2021-09-07 | 北京四方继保工程技术有限公司 | Method for inhibiting malfunction of fault-removing differential protection by means of hysteresis characteristics |
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| FR2954613B1 (en) * | 2009-12-17 | 2013-06-07 | Schneider Electric Ind Sas | DEVICE AND METHOD FOR DIFFERENTIAL PROTECTION AND ELECTRICAL APPARATUS COMPRISING SUCH A DEVICE |
| CN104134972B (en) * | 2014-06-20 | 2016-09-07 | 南京国电南自软件工程有限公司 | A kind of method preventing current transformer tail currents from breaker fail protection being affected |
| CN106569163A (en) * | 2015-10-08 | 2017-04-19 | 南京南瑞继保电气有限公司 | Method for detecting trailing amount of transformer |
| CN105914714B (en) * | 2016-05-16 | 2018-06-29 | 国电南瑞科技股份有限公司 | The method for preventing breaker fail protection malfunction based on current waveform identification |
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