CN112271709B - Time domain distance protection method suitable for wind power plant output line - Google Patents
Time domain distance protection method suitable for wind power plant output line Download PDFInfo
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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
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0092—Details of emergency protective circuit arrangements concerning the data processing means, e.g. expert systems, neural networks
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Abstract
The invention discloses a time domain distance protection method for a wind power plant transmission line, which specifically comprises the following steps: collecting instantaneous values of phase voltage, phase current and zero sequence current, and forming a signal sequence respectively; constructing the signal sequence into a Hankel matrix, carrying out singular value decomposition on the Hankel matrix, and extracting component signals corresponding to the signal sequence; calculating a differential equation of a corresponding protection installation position after the line fails, and obtaining the differential equation with the positive sequence resistance and the inductance of the line from a fault point to the protection installation position as unknown quantities by using a differential method; substituting elements in the component signals of the electric quantities into an equation and solving to obtain resistance parameter estimated values and inductance parameter estimated values, and calculating accurate resistance parameters and inductance parameters according to sampling data. The method can quickly and accurately identify the fault of the output line of the wind power plant under various fault types, and is particularly suitable for the wind power grid-connected system with the double-fed wind driven generator.
Description
Technical Field
The invention relates to a relay protection method for a power system, in particular to a time domain distance protection method suitable for a transmission line of a wind power plant.
Background
At present, a traditional protection scheme is still adopted for a transmission line of a wind power plant, the protection configuration of the transmission line of 110kV and above for transmitting electric energy of the wind power plant in a long distance mode is generally configured according to a conventional system, the distance protection based on a Fourier algorithm is generally used as main protection or backup protection of the transmission line, and the special fault property of a grid-connected system of the wind power plant is ignored.
At present, a doubly-fed wind generator (DFIG) is widely applied to a wind power grid-connected system, however, the fault characteristics of the DFIG are complex and different from those of a synchronous generator, and great challenges are brought to the applicability of traditional relay protection. When the voltage drop is deep, the short-circuit current provided by the DFIG will be dominated by the transient dc component and the transient ac component of the rotational speed frequency. The change range of the rotating speed of the DFIG is generally 0.7-1.3 pu, so that at the initial stage of fault occurrence, the main frequency component of the current provided by the DFIG is 35-65 Hz alternating current component determined by the rotating speed of the fan, and the alternating current component is difficult to filter by a low-pass filter, so that a fundamental frequency phasor amplitude and a fundamental frequency phasor phase cannot be accurately extracted by a power frequency Fourier algorithm, the action performance of a distance protection section without delay action cannot be ensured, and the performance degradation can occur when the distance protection based on the DFIG algorithm is applied to the side of a wind field of a transmission line.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects of the prior art, the invention provides a time domain distance protection method suitable for a wind power plant sending-out line, which can overcome the influence of special fault characteristics of a wind power plant and ensure the operation safety of a system for a wind power grid-connected system with a double-fed wind driven generator.
The technical scheme is as follows: the time domain distance protection method suitable for the wind power plant sending line comprises the following steps:
s1, acquiring signal arrays of zero-sequence current, three-phase current and three-phase earth voltage instantaneous values on a protected line on the wind farm side in 1 period after the fault, and constructing a Hankel matrix;
s2, performing singular value decomposition on the Hankel matrix constructed in the step S1, and connecting the first row vector of the component matrix corresponding to the first singular value of the matrix after the singular value decomposition with the transposition of the last column vector to obtain a component signal sequence of the original signal sequence;
s3, establishing a differential equation of a corresponding protection installation position after the line has a fault, observing the differential equation, and calculating the square sum of each error;
s4, solving the resistance parameter estimation value and the inductance parameter estimation value when the sum of squares of all errors has the minimum value, and obtaining calculation formulas of the resistance parameter estimation value and the inductance parameter estimation value;
and S5, sampling the resistance and inductance values, and calculating the positive sequence resistance and inductance from the fault point to the protection installation line according to the sampling values.
Step S3 includes the following steps:
and calculating a differential equation of the corresponding protection installation position after the line has the fault, wherein the differential equation is shown as the following formula.
In the formula, u and i are respectively the instantaneous values of voltage and current measured at the protection installation, R, L are respectively the positive sequence resistance and inductance of the line from the fault point to the protection installation, and the following differential equation set is established by taking two points:
subscripts 1,2 in the formula represent failure points 1 and 2, respectively; for simplicity of expression, use D 1 Substitute forD 2 Substitute forThe system of differential equations described above is solved by:
taking two different sampling moments t k 、t k+1 The corresponding sampling values of the measured voltage and the current are u respectively k 、u k+1 、i k 、i k+1 For simplifying the expression of the formula, let y k =(u k +u k+1 )/2,x k =(i k +i k+1 )/2,D k =(i k+1 -i k )/T s The following difference equation is established:
y k =Rx k +LD k (4)
for the ground fault, taking the phase a ground fault as an example, the voltage substituted in the differential equation is the phase a relative ground voltage, and the current is the phase a current with zero sequence current compensation, and there are:
in the above formula, u ak 、u ak+1 And i ak 、i ak+1 、i 0k 、i 0k+1 Are respectively component signalsAndmiddle t k 、t k+1 Elements corresponding to the moments; k is R And K L Respectively is a zero-sequence resistance compensation coefficient and a zero-sequence reactance compensation coefficient, and has
For the phase-to-phase fault, taking an AB two-phase fault as an example, if the voltage substituted in the differential equation is an AB phase-to-phase voltage and the current is an AB phase-to-phase current, then:
in the above formula u bk 、u bk+1 And i bk 、i bk+1 Are respectively provided withAndmiddle correspondence t k 、t k+1 An element of a time of day.
(5) N observations were made for equation (3), with the sum of the squares of the errors:
further, step S4 includes the steps of:
the partial derivatives of R and L are separately calculated and made equal to zero, then:
solving the simultaneous equations (12) and (13) to obtain the estimated value of the resistance parameterAnd an inductance parameter estimateThe calculation formula of (c):
step S4 includes the following steps: dividing the sampling points into i groups according to the number of the sampling points of each cycle, obtaining resistance and inductance values of i at different moments, respectively recording as R (i) and L (i), wherein the 1 st group is the current moment, the i th group is the historical moment, and after obtaining data of a complete adoption period, obtaining R and L finally entering distance protection calculation by adopting the following algorithm:
has the advantages that: compared with the prior art, the invention has the following remarkable advantages: a Hankel matrix is constructed for the signal sequence generated by the collected electrical quantities and singular value decomposition is carried out to obtain component signals of all electrical quantities, so that errors and noise interference are reduced; the method is not influenced by frequency domain information, the influence of attenuated rotating speed frequency components of short-circuit current on the wind field side when a circuit sent by the doubly-fed wind power plant fails is overcome in principle, the fault distance can be accurately calculated, the performance is superior to distance protection based on a Fourier algorithm, more and more data are used for calculating the fault distance along with the time, and the accuracy of a calculation result is guaranteed.
Drawings
FIG. 1 is a power grid equivalent model of a doubly-fed wind farm according to an embodiment of the invention.
Detailed Description
The technical scheme of the invention is further explained by combining the drawings and the embodiment.
Step 1: by means of measuring elements, collecting the protected lineZero sequence current, three phase current and three phase earth voltage, and sampling frequency T s And collecting instantaneous values of current and voltage within 1 period after the fault to obtain N sampling points, and generating a signal array by the sampling points.
Step 2: constructing a Hankel matrix from the generated signal sequence, and performing singular value decomposition on the constructed Hankel matrix to obtain a component signal of the signal sequence, wherein the specific steps are as follows:
setting signal sequences generated by the collected ABC three-phase currents as I a 、I b And I c The signal sequence generated by the three-phase voltage sampling points is U a 、U b And U c The collected zero sequence current instantaneous value generates a signal array I 0 。
Array I of signals a 、I b 、I c 、I 0 、U a 、U b And U c Respectively constructing a Hankel matrix, and performing singular value decomposition on the generated Hankel matrix to obtain I a 、I b 、I c 、I 0 、U a 、U b And U c Respective first component signal sequenceAnd
with I a For example, let the generated Hankel matrix be A H Then to A H Singular value decomposition is carried out to obtain:
A H =UΛV T
where the matrix U ═ U 1 ,u 2 ,…,u m ]And V ═ V 1 ,v 2 ,...,v n ]All belong to orthogonal matrices.
In order to realize the separation of the original signal and extract the detail component of the signal, the matrix A is H Expressed in the following form:
wherein u is i (i-1, 2, …, q) and v i (i ═ 1,2, …, q) the ith column vector, U, of matrices U and V, respectively i ∈R m ×1 ,v i ∈R n×1 ,q=min(m,n);A H Component matrix ofA i ∈R m×n . Matrix A H The component matrix corresponding to the first singular value is A 1 A is 1 First horizontal vector H i,1 And the last column vector L i,n The transposes of the original signal sequence are connected to obtain the component signals of the original signal sequenceSimilarly, the component signal sequence of other electrical quantity signal sequences can be obtainedAnd
and calculating a differential equation of the corresponding protection installation position after the line has the fault, wherein the differential equation is shown as the following formula.
Where u and i are instantaneous values of the voltage and current measured at the protection installation, respectively, and R, L are positive sequence resistance and inductance of the line from the fault point to the protection installation, respectively. Taking two points, the following system of differential equations can be established
For simple writing, use D 1 Instead of the formerD 2 Instead of the formerSolving the system of differential equations as
And 4, step 4: taking two different sampling times t k 、t k+1 The corresponding sampling values of the measured voltage and the current are u respectively k 、u k+1 、i k 、i k+1 . For simple writing, set y k =(u k +u k+1 )/2,x k =(i k +i k+1 )/2,D k =(i k+1 -i k )/T s Then, the following difference equation can be established:
y k =Rx k +LD k
for the ground fault, taking the phase a ground fault as an example, the voltage substituted in the differential equation is the phase a ground voltage, and the current is the phase a current with zero sequence current compensation, and there are:
in the above formula, u ak 、u ak+1 And i ak 、i ak+1 、i 0k 、i 0k+1 Are respectively a series of numbersAndmiddle t k 、t k+1 Elements corresponding to the moments; k R And K L Are respectively zero sequence resistance compensation coefficient and zero sequence reactance compensation coefficient, and have
For the phase-to-phase fault, taking an AB two-phase fault as an example, the voltage substituted in the differential equation is an AB phase-to-phase voltage, and the current is an AB phase-to-phase current, then:
in the above formula u bk 、u bk+1 And i bk 、i bk+1 Are respectively provided withAnd withMiddle correspondence t k 、t k+1 The elements of the time of day.
And 5: n observations were made for equation (5), with the sum of the squares of the errors:
the principle of the least squares method is to find R and L when J is taken as the minimum, so that the partial derivatives of R and L are found and made equal to zero, respectively, then:
the two formulas are combined to solve to obtain the resistance parameter estimation valueAnd an inductance parameter estimateThe calculation formula of (2):
and substituting the specific numerical values to obtain the resistance parameter estimation value and the inductance parameter estimation value.
Dividing the sampling points into i groups according to the number of the sampling points of each cycle, obtaining resistance and inductance values at different moments i, respectively recording the resistance and inductance values as R (i) and L (i), wherein the 1 st group is the current moment, the i th group is the historical moment, and after obtaining data of a complete adoption period, obtaining R and L which finally enter distance protection calculation by adopting the following algorithm:
taking 24 sampling points of a weekly wave of a domestic mainstream manufacturer as an example, taking every three sampling points as a group of data windows, obtaining resistance and inductance values at different moments m, respectively recording as R (m) and L (m), wherein the 24 points can be divided into 8 groups, the 1 st group is the current moment, the 8 th group is the historical moment, and after obtaining 24 points of data of a complete adopted period, calculating R and L finally entering distance protection calculation according to the following formula.
Claims (2)
1. A time domain distance protection method suitable for a wind power plant transmission line is characterized by comprising the following steps:
s1, collecting signal arrays of current and voltage instantaneous values within 1 period after the fault, and constructing a Hankel matrix;
s2, performing singular value decomposition on the Hankel matrix constructed in the step S1, and connecting the first row vector of the component matrix corresponding to the first singular value of the matrix after the singular value decomposition with the transposition of the last column vector to obtain a component signal sequence of the original signal sequence;
s3, establishing a differential equation of the corresponding protection installation position after the line fails, observing the differential equation, and calculating the square sum of all errors;
the step S3 includes the steps of:
and calculating a differential equation of a corresponding protection installation position after the line has the fault, wherein the differential equation is shown as the following formula:
in the formula, u and i are respectively the instantaneous values of voltage and current measured at the protection installation, R, L are respectively the positive sequence resistance and inductance of the line from the fault point to the protection installation, and the following differential equation set is established by taking two points:
in the formula, subscripts 1 and 2 represent fault points 1 and 2 respectively; for simplicity of expression, use D 1 Instead of the formerD 2 Instead of the formerSolving the above system of differential equations has
Taking two different sampling moments t k 、t k+1 The corresponding sampling values of the measured voltage and the current are u respectively k 、u k+1 、i k 、i k+1 For simple writing, set y k =(u k +u k+1 )/2,x k =(i k +i k+1 )/2,D k =(i k+1 -i k )/T s The following difference equation is established:
y k =Rx k +LD k (4)
for the ground fault, taking the phase a ground fault as an example, the voltage substituted in the differential equation is the phase a ground voltage, and the current is the phase a current with zero sequence current compensation, and there are:
in the above formula, u ak 、u ak+1 And i ak 、i ak+1 、i 0k 、i 0k+1 Array of component signals, each being a voltage relative to groundSequence of component signals of A-phase currentWith zero sequence currentMiddle t k 、t k+1 Elements corresponding to the moments; k is R And K L Respectively is a zero-sequence resistance compensation coefficient and a zero-sequence reactance compensation coefficient, and has
For the phase-to-phase fault, taking an AB two-phase fault as an example, the voltage substituted in the differential equation is an AB phase-to-phase voltage, and the current is an AB phase-to-phase current, then:
in the above formula u bk 、u bk+1 And i bk 、i bk+1 Are respectively provided withAndmiddle correspondence t k 、t k+1 An element of a time of day;
n observations were made for equation (3), with the sum of the squares of the errors:
s4, solving the resistance parameter estimation value and the inductance parameter estimation value when the sum of squares of all errors has the minimum value, and obtaining calculation formulas of the resistance parameter estimation value and the inductance parameter estimation value;
the step S4 includes the steps of:
the polarization of R and L are separately calculated and made equal to zero to obtain the following equation:
solving the simultaneous equations (12) and (13) to obtain the estimated value of the resistance parameterAnd an inductance parameter estimateThe calculation formula of (c) is as follows:
the step S4 includes the steps of: dividing the sampling points into i groups according to the number of the sampling points of each cycle, obtaining resistance and inductance values of i at different moments, respectively recording as R (i) and L (i), wherein the 1 st group is the current moment, the i th group is the historical moment, and after obtaining data of a complete adoption period, obtaining R and L finally entering distance protection calculation by adopting the following algorithm:
and S5, sampling the resistance and the inductance value, and calculating the positive sequence resistance and the inductance from the fault point to the protection installation line according to the sampling value.
2. Time domain distance protection method applicable to wind farm outgoing lines according to claim 1, characterized in that said signal sequence comprises zero sequence currents, three phase currents and three phase ground voltages on the wind farm side protected line.
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CN108023338B (en) * | 2017-11-28 | 2019-02-26 | 国网浙江省电力公司台州供电公司 | The judgment method of differential protection for multiterminal T connection electric transmission line |
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CN104242267A (en) * | 2014-09-11 | 2014-12-24 | 国家电网公司 | Distance protection method for wind power generation transmission line |
WO2018129842A1 (en) * | 2017-01-10 | 2018-07-19 | 华北电力大学 | Pilot protection method for transmission line of new energy station based on current waveform similarity |
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