CN111030051A - Differential protection system and method - Google Patents
Differential protection system and method Download PDFInfo
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- CN111030051A CN111030051A CN201911172261.0A CN201911172261A CN111030051A CN 111030051 A CN111030051 A CN 111030051A CN 201911172261 A CN201911172261 A CN 201911172261A CN 111030051 A CN111030051 A CN 111030051A
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- mutual inductor
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- differential
- differential protection
- electromagnetic
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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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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/20—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/175—Indicating the instants of passage of current or voltage through a given value, e.g. passage through zero
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Protection Of Transformers (AREA)
Abstract
The invention discloses a differential protection system and a differential protection method, which comprise an electromagnetic mutual inductor, an electronic mutual inductor and a differential protection device, wherein one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the input end of a protected device, and the other one is used for collecting the current of the output end of the protected device; the differential protection device can calculate the differential current of the protected equipment according to the current values collected by the electromagnetic mutual inductor and the electronic mutual inductor, and control the differential protection action according to the differential current and the saturation state of the electromagnetic mutual inductor; the invention provides a differential protection system and a method thereof: a criterion for identifying the saturation of the electromagnetic mutual inductor is added, and the condition of differential protection misoperation caused by the condition of external fault is effectively locked.
Description
Technical Field
The invention relates to a differential protection system and a differential protection method, and belongs to the technical field of relay protection.
Background
When differential protection both sides are electromagnetism and electronic transformer respectively, if regional trouble takes place, thereby both sides mutual-inductor can have the saturation of different degrees to lead to differential protection to be started by the mistake, influences in-service use, also can influence the life of each part:
establishing a simulation model, wherein the system voltage level is 500kV, the frequency is 50Hz, the line length is 100km, and a Bergeron model is adopted; as shown in fig. 1; the simulation results are shown in fig. 2 and 3:
the simulation result can be obtained. When one end of the differential relay is electromagnetic and the other end of the differential relay is photoelectric, the electromagnetic CT is saturated and the photoelectric CT is not saturated, so that a large unbalanced current flows through the differential relay, and the differential protection malfunctions.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a differential protection system and a differential protection method: a criterion for identifying the saturation of the electromagnetic mutual inductor is added, and the condition of differential protection misoperation caused by the condition of external fault is effectively locked.
A differential protection system comprises an electromagnetic mutual inductor, an electronic mutual inductor and a differential protection device, wherein one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the input end of a protected device, and the other one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the output end of the protected device;
the differential protection device can calculate the differential current of the protected equipment according to the current values collected by the electromagnetic mutual inductor and the electronic mutual inductor, and control the differential protection action according to the differential current and the saturation state of the electromagnetic mutual inductor.
A differential protection method of the differential protection system, the method comprising the steps of:
when the differential protection device judges that the differential current is greater than the set starting current, the saturation state of the electromagnetic transformer is further identified: if the electromagnetic mutual inductor is saturated, locking to protect differential protection; otherwise, the differential protection is opened.
Further, the method for judging the saturation of the electromagnetic mutual inductor comprises the following steps:
determining a virtual zero crossing point according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformer;
calculating the maximum value of the differential current at the virtual zero crossing point moment, and carrying out error correction on the maximum value, and recording as id；
Calculating the current error i of the sampling point except the virtual zero crossing point moment according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformerdn；
Statistics idn≤idAnd if the number K is larger than or equal to M, judging that the electromagnetic transformer is saturated, wherein M is 0.25N-2, and N is the number of sampling points per period.
Further, the method for calculating the maximum value of the differential current at the virtual zero-crossing time comprises the following steps:
determining two corresponding moments n when the absolute value of the secondary current value of the electromagnetic mutual inductor is the minimum valuet1、nt2Is a virtual zero crossing;
calculating the maximum value of the differential current at the virtual zero-crossing time by adopting a formula (1):
id′＝max(|iM01-iE01|,|iM02-iE02|) (1)
in the formula: i.e. iM01、iM02Are each nt1、nt2The secondary current value of the electromagnetic mutual inductor at the moment; i.e. iE01、iE02Are each nt1、nt2And the secondary current value of the electronic transformer at the moment.
Further, the maximum value is error-corrected using equation (2):
id＝K′i′d(2)
in the formula: k' is an introduced error constant coefficient, and the value range is 1.3-2.5; i.e. id' is the maximum value of the differential current at the moment of the virtual zero crossing point; i.e. idThe current value is obtained by error correction of the maximum value of the differential current at the virtual zero-crossing point time.
Further, the current error i of the sampling point except for the virtual zero-crossing point moment is calculated by adopting the formula (3)dn：
idn＝iMn-iEn(3)
In the formula: i.e. iMnThe secondary current value of the electromagnetic mutual inductor at the nth sampling point is obtained; i.e. iEnThe secondary current value of the electronic transformer at the nth sampling point is obtained; n is 0,1, …, N, the nth sampling point corresponds to a non-virtual zero-crossing point in time, and N is the number of sampling points per period.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the technical scheme, on the basis of the existing differential protection, the identification of the saturation state of the electromagnetic mutual inductor is added, and the misoperation condition caused by different degrees of saturation of the mutual inductor is eliminated;
2. the technical scheme has the advantages of simple and reliable principle and concise flow, and improves the working efficiency and the working reliability.
Drawings
FIG. 1 is a schematic diagram of a simulation model of the background art;
FIG. 2 is a simulation result of an electronic transformer and an electromagnetic transformer in a simulation model in the background art;
FIG. 3 is a simulation result of relay action signals in a simulation model in the background art;
fig. 4 is a block diagram of a differential protection system according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. 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.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.
A differential protection system comprises an electromagnetic mutual inductor, an electronic mutual inductor and a differential protection device, wherein one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the input end of a protected device, and the other one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the output end of the protected device;
the differential protection device can calculate the differential current of the protected equipment according to the current values collected by the electromagnetic mutual inductor and the electronic mutual inductor, and control the differential protection action according to the differential current and the saturation state of the electromagnetic mutual inductor;
in the differential protection of the electromagnetic mutual inductor and the electronic mutual inductor, because the electromagnetic mutual inductor is saturated and the electronic mutual inductor is not saturated, when an external fault occurs, a large differential current can be caused to cause the differential protection misoperation, and the identification of the saturation state of the electromagnetic mutual inductor is added in the technical scheme to eliminate the misoperation.
A differential protection method of the differential protection system, the method comprising the steps of:
when the differential protection device judges that the differential current is greater than the set starting current, the saturation state of the electromagnetic transformer is further identified: if the electromagnetic mutual inductor is saturated, locking to protect differential protection; otherwise, the differential protection is opened.
Further, the method for judging the saturation of the electromagnetic mutual inductor comprises the following steps:
determining a virtual zero crossing point according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformer;
calculating the maximum value of the differential current at the virtual zero crossing point moment, and carrying out error correction on the maximum value, and recording as id；
Calculating the current error i of the sampling point except the virtual zero crossing point moment according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformerdn；
Statistics idn≤idIf the number K is larger than or equal to M, judging that the electromagnetic transformer is saturated, wherein M is 0.25N-2; n is the number of samples per cycle, typically 24. It should be noted that: in very special cases, such as experimental ones, N will also be 36, 48 points, so M will not be a fractional possibility. Here, the result of the calculation of (0.25N-2) may be rounded to ensure that M is an integer.
Further, the method for calculating the maximum value of the differential current at the virtual zero-crossing time comprises the following steps:
determining two corresponding moments n when the absolute value of the secondary current value of the electromagnetic mutual inductor is the minimum valuet1、nt2Is a virtual zero crossing;
calculating the maximum value of the differential current at the virtual zero-crossing time by adopting a formula (1):
id′＝max(|iM01-iE01|,|iM02-iE02|) (1)
in the formula: i.e. iM01、iM02Are each nt1、nt2The secondary current value of the electromagnetic mutual inductor at the moment; i.e. iE01、iE02Are each nt1、nt2And the secondary current value of the electronic transformer at the moment.
In one embodiment, the maximum is error corrected using equation (2):
id＝K′i′d(2)
in the formula: k' is an introduced error constant coefficient, the value range is 1.3-2.5, and 1.5 can be selected according to actual experience in the embodiment; i.e. id' is the maximum value of the differential current at the moment of the virtual zero crossing point; i.e. idThe current value is obtained by error correction of the maximum value of the differential current at the virtual zero-crossing point time.
In one embodiment, equation (3) is used to calculate the current error i at the sampling point except for the virtual zero crossing pointdn：
idn＝iMn-iEn(3)
In the formula: i.e. iMnFor the n-th miningSampling point electromagnetic transformer secondary current value; i.e. iEnThe secondary current value of the electronic transformer at the nth sampling point is obtained; n is 0,1, …, N, the nth sampling point corresponds to a non-virtual zero-crossing point in time, and N is the number of sampling points per period.
According to the saturation curve of the electromagnetic mutual inductor in the background technology, the electromagnetic mutual inductor can be found out that no saturation occurs at the moment of starting a fault and a partial linear transmission region exists in each period;
then calculating the current differential by using the sampling point;
when the fault occurs in the area, the differential current is equal to 0 only at the moment of the current zero crossing point, and the rest points have large differential current; when the electromagnetic mutual inductor is in an external fault and is saturated, the differential current is equal to 0 in both the current zero crossing point and the linear transmission area;
so, among the sampling points based on the entire period, the point of the minimum value is set as a virtual zero-crossing point;
applying differential current at two sides of a virtual zero crossing point moment, and introducing an error coefficient concept, namely a threshold value causing the differential current;
calculating the current differential value at other moments, if the current differential value is smaller than a threshold value, the differential current is considered to be absent, and if the current differential value is larger than the threshold value, the differential current is considered to be present;
if the differential protection is misoperation caused by an external fault, namely, in each period, a plurality of points with 0 differential protection exist, and if the internal fault exists, except for a zero crossing point, each point has larger differential current;
based on the theoretical basis, the following criteria are added in the traditional protection, and the differential protection misoperation of the external fault can be effectively avoided.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (6)
1. The differential protection system is characterized by comprising an electromagnetic mutual inductor, an electronic mutual inductor and a differential protection device, wherein one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the input end of a protected device, and the other one of the electromagnetic mutual inductor and the electronic mutual inductor is used for collecting the current of the output end of the protected device;
the differential protection device can calculate the differential current of the protected equipment according to the current values collected by the electromagnetic mutual inductor and the electronic mutual inductor, and control the differential protection action according to the differential current and the saturation state of the electromagnetic mutual inductor.
2. A differential protection method of a differential protection system according to claim 1, characterized in that the method comprises the steps of:
when the differential protection device judges that the differential current is greater than the set starting current, the saturation state of the electromagnetic transformer is further identified: if the electromagnetic mutual inductor is saturated, locking to protect differential protection; otherwise, the differential protection is opened.
3. The differential protection method according to claim 2, wherein the method for determining the saturation of the electromagnetic transformer comprises the following steps:
determining a virtual zero crossing point according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformer;
calculating the maximum value of the differential current at the virtual zero crossing point moment, and carrying out error correction on the maximum value, and recording as id；
Calculating the current error i of the sampling point except the virtual zero crossing point moment according to the secondary current value of the electromagnetic transformer and the secondary current value of the electronic transformerdn；
Statistics idn≤idAnd if the number K is larger than or equal to M, judging that the electromagnetic transformer is saturated, wherein M is 0.25N-2, and N is the number of sampling points per period.
4. The differential protection method according to claim 3, wherein the method of calculating the maximum value of the differential current at the virtual zero-crossing point comprises the steps of:
determining two corresponding moments n when the absolute value of the secondary current value of the electromagnetic mutual inductor is the minimum valuet1、nt2Is a virtual zero crossing;
calculating the maximum value of the differential current at the virtual zero-crossing time by adopting a formula (1):
id′＝max(|iM01-iE01|,|iM02-iE02|) (1)
in the formula: i.e. iM01、iM02Are each nt1、nt2The secondary current value of the electromagnetic mutual inductor at the moment; i.e. iE01、iE02Are each nt1、nt2And the secondary current value of the electronic transformer at the moment.
5. The differential protection method according to claim 3, characterized in that the maximum value is error-corrected using equation (2):
id＝K′i′d(2)
in the formula: k' is an introduced error constant coefficient, and the value range is 1.3-2.5; i.e. id' is the maximum value of the differential current at the moment of the virtual zero crossing point; i.e. idThe current value is obtained by error correction of the maximum value of the differential current at the virtual zero-crossing point time.
6. Differential protection method according to claim 3, characterized in that the current error i at the sampling point is calculated with the formula (3) except for the virtual zero crossing point instantdn：
idn＝iMn-iEn(3)
In the formula: i.e. iMnThe secondary current value of the electromagnetic mutual inductor at the nth sampling point is obtained; i.e. iEnThe secondary current value of the electronic transformer at the nth sampling point is obtained; n is 0,1, …, N, the nth sampling point corresponds to a non-virtual zero-crossing point in time, and N is the number of sampling points per period.
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