CN114417241B - Monopole grounding short circuit calculation method and system of offshore wind power flexible-direct system - Google Patents
Monopole grounding short circuit calculation method and system of offshore wind power flexible-direct system Download PDFInfo
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Abstract
The invention provides a monopole grounding short circuit calculation method and a monopole grounding short circuit calculation system for an offshore wind power flexible direct-current system, which are used for acquiring direct-current voltage and direct-current before failure, failure position and short circuit transition resistance of a flexible direct-current power transmission system; dividing faults in and out of the zone according to the fault positions, and establishing T-shaped equivalent models of direct current circuits on two sides of the fault point and a discharge loop equation from the capacitance of the direct current circuits to the fault point; according to a loop equation and rated direct current voltage, solving the short circuit current of the line capacitor; and calculating the shunt coefficients of loops at two sides of the fault point, and solving the short-circuit current at the protection installation position of the direct current line. The invention considers the specificity brought by larger distributed capacitance of the submarine cable, is more suitable for practical engineering, has higher accuracy of short circuit calculation, and can better provide support for short circuit calculation and relay protection research of the offshore wind power flexible direct system.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a method and a system for calculating a monopole grounding short circuit of an offshore wind power flexible direct current system.
Background
In recent years, offshore wind power has been an important direction for the development of renewable energy sources because of its advantages such as high energy efficiency and suitability for concentrated development. By the end of 2019, the newly increased installed capacity of the Chinese offshore wind power is the first two years in the world, 2.4GW of the created records is reached, and the accumulated installed capacity is 6.8GW. Along with the expansion and increase of the installed capacity and offshore distance of offshore wind power, the flexible direct current transmission technology has the advantages of low remote transmission loss, no commutation failure, independent control of active power and reactive power and the like, and is widely applied to the offshore wind power field.
The short circuit calculation of the offshore wind power flexible direct system is an important basis for fault analysis and relay protection research. In this regard, the related short circuit calculation methods currently include: the short-circuit current calculation method for the pseudo bipolar soft direct system comprises the following steps: and solving the state equation by modifying the state variable and coefficient matrix in the state equation before the fault and solving the state equation by using a differential equation numerical solution method, thereby solving the fault current. However, the conventional land flexible direct current transmission system using the overhead line as the transmission line is mainly focused, and the specificity caused by the larger distributed capacitance of the submarine direct current cable is not fully considered, so that a line capacitance discharging loop is often ignored. The fault current calculation method aiming at the bipolar short circuit of the flexible-direct system comprises the following steps: the north-opening flexible direct current power grid is taken as a research object, and the fault characteristics and the coupling mechanism of the bipolar short circuit of the power transmission line are analyzed; analyzing the relation between the fault current and the voltages at two sides of the two ports; and obtaining a practical calculation method of the fault line current. But it does not address the problem of single pole ground faults with higher failure rate in a soft-straight system. The unipolar fault short-circuit current calculation method for the flexible-direct system comprises the following steps: aiming at the problem of rapid and selective isolation of direct current line faults in the application of a direct current breaker, a symmetrical monopole multi-terminal flexible direct current line fault clearing strategy is researched. But it only considers the discharge loop of a single-sided multilevel converter when analyzing the unipolar ground fault characteristics. This is common in bipolar short fault analysis because the circuits on both sides of the fault point are decoupled during bipolar short circuit. However, for a single pole ground fault, the dc systems on both sides of the fault point remain in electrical communication, and therefore need to be uniformly taken into account in fault analysis. In summary, the current monopole short circuit calculation method for the offshore wind power flexible direct system is not perfect, and most of the monopole short circuit calculation methods do not consider calculation differences caused by larger distributed capacitance of the submarine cable. Aiming at the problem, the invention provides a monopole grounding short circuit calculation method of an offshore wind power flexible-direct system, which is used for providing support for short circuit calculation and relay protection research of the offshore wind power flexible-direct system.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide the monopole grounding short circuit calculation method and the monopole grounding short circuit calculation system of the offshore wind power flexible-direct system, which take the specificity brought by larger distributed capacitance of the submarine cable into consideration, are more attached to actual engineering, have higher accuracy of short circuit calculation, and can provide support for short circuit calculation and relay protection research of the offshore wind power flexible-direct system.
The invention adopts the following technical scheme.
The invention provides a monopole grounding short circuit calculation method of an offshore wind power flexible-direct system, which is characterized by comprising the following steps of:
Step 1, obtaining direct current voltage and direct current before failure, failure position and short circuit transition resistance of a flexible direct current transmission system, dividing the internal and external failures of a direct current region according to the failure position, and executing step 2 if the internal failures of the direct current region occur; if the direct current region faults occur, executing the step 5;
Step 2, respectively establishing a T-shaped equivalent model aiming at direct current lines at two sides of a fault point of a fault pole in a direct current region, and establishing a T-shaped equivalent model aiming at a direct current line of a non-fault pole in the direct current region; calculating equivalent inductance from the capacitance of the non-fault line to the fault point;
step 3, according to the fault equivalent model in the step 2, a discharge loop equation from the non-fault pole direct current line capacitor to a fault point is established, and a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitor is obtained;
step 4, establishing a definite solution condition equation according to the result of the step 3, solving the short-circuit current of the non-fault line capacitance, and executing the step 8;
Step 5, respectively establishing a T-shaped equivalent model aiming at direct current lines of a fault pole and a non-fault pole outside the direct current region;
Step 6, according to the fault equivalent model in step 5, a discharge loop equation from the fault pole and non-fault pole direct current line capacitors to fault points is established, and a second-order constant coefficient differential equation of short-circuit currents of the fault pole and non-fault pole direct current line capacitors is obtained;
Step 7, establishing a definite solution condition equation according to the result of the step 6, solving the short-circuit current of the fault pole and the non-fault pole capacitance, and executing the step 8;
And 8, calculating the short-circuit current of the direct-current line protection installation position according to the line capacitance short-circuit current and the direct-current before fault obtained in the step 4 or the step 6.
Preferably, in step 1, if the fault location is on the line side of the smoothing reactor, a fault in the dc region is considered to occur, and step 2 is executed; and if the fault position is at the converter side of the smoothing reactor, considering that a direct-current out-of-zone fault occurs, and executing the step 5.
Preferably, the equivalent inductance of the non-faulty line capacitance to the fault point in step 2 is expressed by the following formula,
Wherein:
L 1 and L 2 are the equivalent inductances of the two loops from the non-fault pole capacitance to the fault point respectively,
L arm represents the single-phase leg reactance of the converter,
L dc represents the dc ripple reactance,
L l represents the total inductance of a single dc line,
Lambda represents the fault position and the value range is 0-100%.
Preferably, the discharge loop equation from the non-fault pole dc line capacitance to the fault point in step 3 is expressed as follows,
Wherein:
R f is a short-circuit transition resistance,
I cn is the short-circuit current of the non-faulty line capacitance, the reference positive direction is the earth flow direction to the line,
U dc is the pre-fault dc voltage of the flexible dc power transmission system,
T is time;
c ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line;
U cn is the voltage of the non-fault line capacitor, and the reference positive direction is the line pointing to the ground;
the second order ordinary coefficient differential equation of the non-faulty line capacitance is expressed as:
Wherein:
R f is a short-circuit transition resistance,
I cn is the short-circuit current of the non-faulty line capacitance, the reference positive direction is the earth flow direction to the line,
T is the time period of time, and the time period of the time period is,
C ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line.
Preferably, the solution condition equation in step 4 is:
Wherein:
t 0 represents a fault time;
the short-circuit current of the non-fault line capacitor is as follows:
Wherein:
Preferably, the discharge loop equation from the fault pole and non-fault pole dc line capacitances to the fault point in step 6 is expressed as follows,
Wherein:
i cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
L dc represents the dc ripple reactance,
T is the time period of time, and the time period of the time period is,
R l represents the total resistance of a single dc line,
L l represents the total inductance of a single dc line,
R f represents the short-circuit transition resistance,
U dc denotes the pre-fault dc voltage of the flexible dc power transmission system,
C ln represents the capacitance to ground of the T-shaped equivalent model of the non-faulty pole line.
The second order ordinary coefficient differential equation of the short circuit current of the fault pole and non-fault line capacitance is expressed as follows,
In the method, in the process of the invention,
L dc represents the dc ripple reactance,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
I cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
R l represents the total resistance of a single dc line,
R f represents the short-circuit transition resistance,
T is the time period of time, and the time period of the time period is,
L l represents the total inductance of a single dc line.
Preferably, the definite solution condition equation in step 7 is expressed by the following formula,
Wherein:
t 0 represents a fault time;
the short circuit currents of the failed pole and non-failed line capacitances are represented by the following formula,
In the method, in the process of the invention,
Preferably, in case of a fault in the DC domain, the short-circuit current at the DC line protection installation in step 8 is represented by the following formula,
Wherein:
i P1p denotes the short-circuit current at the fault pole protection installation at a distance from the fault point lambda, the reference positive direction being the converter flow direction line,
I P1n denotes the short-circuit current at the non-faulty pole protection installation, at a distance from the fault point lambda, the reference positive direction being the converter flow direction line,
I P2p denotes the short-circuit current at the fault pole protection installation at a distance from the fault point (1-lambda), the reference positive direction being the converter flow direction line,
I P2n denotes the short-circuit current at the non-faulty pole protection installation at a distance from the fault point (1-lambda), the reference positive direction being the converter flow direction line,
I dc is the pre-fault dc current.
Preferably, in case of a dc out-of-zone fault, the short circuit current at the dc line protection installation in step 8 is represented by the following formula,
Wherein:
i P3p denotes the short-circuit current at the fault pole protection installation, far from the fault point, the reference positive direction being the converter flow direction line,
I P3n denotes the short-circuit current at the non-faulty pole protection installation, remote from the fault point, the reference positive direction being the converter flow direction line,
I P4p denotes the short-circuit current at the fault pole protection installation near the fault point, the reference positive direction is the converter flow direction line,
I P4n denotes the short-circuit current at the non-faulty pole protection installation near the fault point, the reference positive direction being the converter flow direction line.
The second aspect of the invention provides a monopole ground short circuit computing system of an offshore wind power flexible-direct system, comprising: the system comprises a fault judging module, a direct current zone internal fault equivalent model establishing module, a direct current zone internal differential equation establishing module, a direct current zone internal defining condition equation establishing module, a direct current zone external fault equivalent model establishing module, a direct current zone external differential equation establishing module, a direct current zone external defining condition equation establishing module and a short circuit current calculating module, and is characterized in that:
The fault judging module is used for acquiring direct current voltage and direct current before fault, fault position and short circuit transition resistance of the flexible direct current transmission system and dividing faults in the direct current region and faults out of the direct current region according to the fault position;
The direct current region internal fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current lines on two sides of a fault point of a fault pole in the direct current region respectively and building a T-shaped equivalent model aiming at a non-fault pole direct current line in the direct current region; calculating equivalent inductance from the capacitance of the non-fault line to the fault point;
the direct current region internal differential equation establishing module is used for establishing a discharge loop equation from the non-fault pole direct current line capacitor to a fault point and solving a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitor;
The direct-current region internal defining condition equation establishing module is used for establishing a defining condition equation and solving the short-circuit current of the non-fault circuit capacitor;
The direct current off-zone fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current off-zone fault poles and non-fault pole direct current lines respectively;
The direct current region external differential equation establishing module is used for establishing a discharge loop equation from the direct current line capacitance of the fault electrode and the non-fault electrode to the fault point, and solving a second-order constant coefficient differential equation of the short-circuit current of the fault electrode and the non-fault line capacitance;
The direct current region external solution condition equation building module is used for solving the short-circuit current of the fault pole and the non-fault pole circuit capacitor;
The short-circuit current calculation module is used for calculating the short-circuit current of the direct-current line protection installation position.
Compared with the prior art, the technical scheme of the invention is different from the prior art, which mainly focuses on the conventional land flexible direct current transmission system taking overhead lines as transmission lines, does not fully consider the specificity brought by larger distributed capacitance of the submarine direct current cable, fully considers the discharging loop of the submarine cable capacitance in the calculation of the single-pole short-circuit current in and out of the area, and establishes a more perfect fault analysis model. The technical scheme of the invention is more suitable for actual engineering, the accuracy of short circuit calculation is higher, and the support can be better provided for the short circuit calculation and relay protection research of the offshore wind power flexible direct system.
Drawings
Fig. 1 is a flowchart of a method for calculating a monopole ground short according to the present invention.
Detailed Description
The application is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present application, and are not intended to limit the scope of the present application.
As shown in fig. 1, the invention provides a monopole ground short circuit calculation method of an offshore wind power flexible-direct system, which comprises the following steps:
Step 1, obtaining direct current voltage and direct current before failure, failure position and short circuit transition resistance of a flexible direct current transmission system, and dividing direct current region internal and external failures according to the failure position:
if the fault position is at the line side of the smoothing reactor, the fault in the direct current area is considered to occur, and the step 2 is entered;
If the fault position is at the converter side of the smoothing reactor, the direct-current out-of-zone fault is considered to occur, and the step 5 is entered.
Step 2, respectively establishing a T-shaped equivalent model aiming at direct current lines at two sides of a fault point of a fault pole in a direct current region, and establishing a T-shaped equivalent model aiming at a direct current line of a non-fault pole in the direct current region; and calculating the equivalent inductance from the non-fault line capacitance to the fault point.
In a preferred but non-limiting embodiment of the present invention, the equivalent inductance of the non-faulty line capacitance to the point of failure is:
Wherein:
L 1 and L 2 are equivalent inductances of two loops from the non-fault pole capacitance to the fault point respectively;
L arm is the reactance of a single-phase bridge arm of the converter;
l dc is direct current smoothing reactance;
l l is the total inductance of a single direct current line;
Lambda represents the fault position and the value range is 0-100%.
Step 3, according to the fault equivalent model in the step 2, a discharge loop equation from the non-fault pole direct current line capacitor to a fault point is established, and a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitor is obtained;
The discharge loop equation from the non-fault pole direct current line capacitor to the fault point is as follows:
Wherein:
R f is a short-circuit transition resistance;
i cn is the short-circuit current of the non-fault line capacitor, and the reference positive direction is the ground flow direction line;
U dc is the pre-fault direct current voltage of the flexible direct current transmission system;
t is time;
c ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line;
u cn is the voltage of the non-faulty line capacitance, and the reference positive direction is the line pointing to ground.
The second-order constant coefficient differential equation of the non-fault line capacitance is as follows:
R f is a short-circuit transition resistance,
I cn is the short-circuit current of the non-faulty line capacitance, the reference positive direction is the earth flow direction to the line,
T is the time period of time, and the time period of the time period is,
C ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line.
Step 4, establishing a definite solution condition equation, and solving the short-circuit current of the non-fault circuit capacitor; step 8 is entered;
the definite solution condition equation is:
Wherein:
t 0 is the fault time.
The short-circuit current of the non-fault line capacitor is as follows:
Wherein:
and 5, respectively establishing a T-shaped equivalent model aiming at the direct current lines of the fault pole and the non-fault pole outside the direct current region.
Step 6, according to the fault equivalent model in step 5, a discharge loop equation from the fault pole and non-fault pole direct current line capacitors to fault points is established, and a second-order constant coefficient differential equation of short-circuit currents of the fault pole and non-fault pole direct current line capacitors is obtained;
and discharging loop equations from the fault pole and non-fault pole direct current line capacitors to fault points:
Wherein:
i cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
L dc represents the dc ripple reactance,
T is the time period of time, and the time period of the time period is,
R l represents the total resistance of a single dc line,
L l represents the total inductance of a single dc line,
R f represents the short-circuit transition resistance,
U dc denotes the pre-fault dc voltage of the flexible dc power transmission system,
C ln represents the capacitance to ground of the T-shaped equivalent model of the non-faulty pole line.
The second-order constant coefficient differential equation of the short-circuit current of the fault pole and the non-fault pole circuit capacitor is as follows:
l dc represents the dc ripple reactance,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
I cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
R l represents the total resistance of a single dc line,
R f represents the short-circuit transition resistance,
T is the time period of time, and the time period of the time period is,
L l represents the total inductance of a single dc line.
Step 7, establishing a definite solution condition equation, and solving the short-circuit current of the fault pole and the non-fault pole line capacitor;
The solution condition equation is:
The short circuit current of the line capacitance of the fault electrode and the non-fault electrode is as follows:
In the method, in the process of the invention,
And 8, calculating the short-circuit current at the protection installation position of the direct-current line according to the line capacitance short-circuit current and the direct-current before the fault.
If the fault is in the direct current area, the short circuit current at the direct current line protection installation part is as follows:
Wherein:
i P1p and i P1n are short-circuit currents at the fault pole and non-fault pole protection installation positions which are separated from a fault point lambda respectively, and the reference positive direction is the current direction line of the converter;
i P2p and i P2n are short-circuit currents at the fault pole and non-fault pole protection installation positions at a distance from a fault point (1-lambda), and the reference positive direction is the current-converter flow direction line;
I dc is the pre-fault dc current.
If the direct current is out-of-zone fault, the short circuit current at the direct current line protection installation part is as follows:
Wherein:
i P3p and i P3n are short-circuit currents at fault pole and non-fault pole protection installation positions far away from a fault point respectively, and the reference positive direction is the current direction line of the converter;
i P4p and i P4n are short-circuit currents at fault pole and non-fault pole protection installation positions near a fault point respectively, and the reference positive direction is the current of the converter flow direction line.
The embodiment 2 of the invention provides a monopole ground short circuit calculation method for a marine wind power flexible straight system, which comprises the following steps: the system comprises a fault judging module, a direct current zone internal fault equivalent model establishing module, a direct current zone internal differential equation establishing module, a direct current zone internal defining condition equation establishing module, a direct current zone external fault equivalent model establishing module, a direct current zone external differential equation establishing module, a direct current zone external defining condition equation establishing module and a short circuit current calculating module, wherein:
The fault judging module is used for acquiring direct current voltage and direct current before fault, fault position and short circuit transition resistance of the flexible direct current transmission system and dividing faults in the direct current region and faults out of the direct current region according to the fault position;
The direct current region internal fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current lines on two sides of a fault point of a fault pole in the direct current region respectively and building a T-shaped equivalent model aiming at a non-fault pole direct current line in the direct current region; calculating equivalent inductance from the capacitance of the non-fault line to the fault point;
the direct current region internal differential equation establishing module is used for establishing a discharge loop equation from the non-fault pole direct current line capacitance to a fault point, and solving a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitance;
the direct-current region internal definition condition equation establishing module is used for establishing a definition solution condition equation and solving the short-circuit current of the non-fault circuit capacitor;
The direct current off-zone fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current off-zone fault poles and non-fault pole direct current lines respectively;
The direct current out-of-area differential equation building module is used for building a discharge loop equation from the direct current line capacitance of the fault pole and the non-fault pole to the fault point, and solving a second-order constant coefficient differential equation of the short-circuit current of the fault pole and the non-fault line capacitance;
The direct current region external definite solution condition equation building module is used for solving the short-circuit current of the fault pole and the non-fault pole circuit capacitor;
The short circuit current calculation module is used for calculating the short circuit current of the direct current line protection installation position.
Compared with the prior art, the invention has the beneficial effects that the specificity caused by larger distribution capacitance of the submarine direct current cable is fully considered, the discharge loop of the submarine cable capacitance is fully considered in the calculation of the monopolar short-circuit current in and out of the area, and a more perfect fault analysis model is established. The technical scheme of the invention is more suitable for actual engineering, the accuracy of short circuit calculation is higher, and the support can be better provided for the short circuit calculation and relay protection research of the offshore wind power flexible direct system.
While the applicant has described and illustrated the embodiments of the present invention in detail with reference to the drawings, it should be understood by those skilled in the art that the above embodiments are only preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not to limit the scope of the present invention, but any improvements or modifications based on the spirit of the present invention should fall within the scope of the present invention.
Claims (9)
1. A monopole grounding short circuit calculation method of an offshore wind power flexible-direct system is characterized by comprising the following steps of:
Step 1, obtaining direct current voltage and direct current before failure, a failure position and a short circuit transition resistance of a flexible direct current transmission system, dividing the internal and external failures of a direct current region according to the failure position, and if the failure position is at the line side of a smoothing reactor, considering that the internal failures of the direct current region occur, and executing step 2; if the fault position is at the converter side of the smoothing reactor, the direct-current out-of-zone fault is considered to occur, and the step 5 is executed;
Step 2, respectively establishing a T-shaped equivalent model aiming at direct current lines at two sides of a fault point of a fault pole in a direct current region, and establishing a T-shaped equivalent model aiming at a direct current line of a non-fault pole in the direct current region; calculating equivalent inductance from the capacitance of the non-fault line to the fault point;
step 3, according to the fault equivalent model in the step 2, a discharge loop equation from the non-fault pole direct current line capacitor to a fault point is established, and a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitor is obtained;
step 4, establishing a definite solution condition equation according to the result of the step 3, solving the short-circuit current of the non-fault line capacitance, and executing the step 8;
Step 5, respectively establishing a T-shaped equivalent model aiming at direct current lines of a fault pole and a non-fault pole outside the direct current region;
Step 6, according to the fault equivalent model obtained in the step 5, a discharge loop equation from the fault pole and non-fault pole direct current line capacitors to fault points is established, and a second-order constant coefficient differential equation of the short-circuit currents of the fault pole and non-fault pole direct current line capacitors is obtained;
Step 7, establishing a definite solution condition equation according to the result of the step 6, solving the short-circuit current of the fault pole and the non-fault pole capacitance, and executing the step 8;
and 8, calculating the short-circuit current of the direct-current line protection installation position according to the line capacitance short-circuit current and the direct-current before fault obtained in the step 4 or the step 7.
2. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 1, wherein the method comprises the following steps of:
The equivalent inductance of the non-faulty line capacitance to the fault point in step 2 is expressed by the following formula,
Wherein:
L 1 and L 2 are the equivalent inductances of the two loops from the non-fault pole capacitance to the fault point respectively,
L arm represents the single-phase leg reactance of the converter,
L dc represents the dc ripple reactance,
L l represents the total inductance of a single dc line,
Lambda represents the fault position and the value range is 0-100%.
3. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 2, wherein the method comprises the following steps of:
the discharge loop equation from the non-fault pole dc line capacitance to the fault point in step 3 is expressed as follows,
Wherein:
R f is a short-circuit transition resistance,
I cn is the short-circuit current of the non-faulty line capacitance, the reference positive direction is the earth flow direction to the line,
U dc is the pre-fault dc voltage of the flexible dc power transmission system,
T is time;
c ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line;
U cn is the voltage of the non-fault line capacitor, and the reference positive direction is the line pointing to the ground;
the second order ordinary coefficient differential equation of the non-faulty line capacitance is expressed as:
Wherein:
R f is a short-circuit transition resistance,
I cn is the short-circuit current of the non-faulty line capacitance, the reference positive direction is the earth flow direction to the line,
T is the time period of time, and the time period of the time period is,
C ln is the capacitance to ground of the T-shaped equivalent model of the non-fault pole line.
4. A method for calculating a monopole ground short circuit of an offshore wind power flexible direct system as defined in claim 3, wherein the method comprises the following steps:
the solution condition equation in the step 4 is:
Wherein:
t 0 represents a fault time;
the short-circuit current of the non-fault line capacitor is as follows:
Wherein:
5. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 1, wherein the method comprises the following steps of:
The discharge loop equation from the fault pole and non-fault pole dc line capacitances to the fault point in step 6 is expressed as follows,
Wherein:
i cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
L dc represents the dc ripple reactance,
T is the time period of time, and the time period of the time period is,
R l represents the total resistance of a single dc line,
L l represents the total inductance of a single dc line,
R f represents the short-circuit transition resistance,
U dc denotes the pre-fault dc voltage of the flexible dc power transmission system,
C ln represents the capacitance to ground of the T-shaped equivalent model of the non-fault pole line;
the second order ordinary coefficient differential equation of the short circuit current of the fault pole and non-fault line capacitance is expressed as follows,
In the method, in the process of the invention,
L dc represents the dc ripple reactance,
I cn denotes a short-circuit current of a non-faulty pole line capacitance, the reference positive direction is the earth flow direction to the line,
I cp denotes the short-circuit current of the line capacitance of the faulty pole, the reference positive direction being the earth flow direction to the line,
R l represents the total resistance of a single dc line,
R f represents the short-circuit transition resistance,
T is the time period of time, and the time period of the time period is,
L l represents the total inductance of a single dc line.
6. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 5, wherein the method comprises the following steps of:
the definite solution conditional equation in step 7 is expressed by the following formula,
Wherein:
t 0 represents a fault time;
the short circuit currents of the failed pole and non-failed line capacitances are represented by the following formula,
In the method, in the process of the invention,
7. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 4, wherein the method comprises the following steps of:
the short-circuit current at the dc line protection installation in step 8 is expressed by the following formula,
Wherein:
i P1p denotes the short-circuit current at the fault pole protection installation at a distance from the fault point lambda, the reference positive direction being the converter flow direction line,
I P1n denotes the short-circuit current at the non-faulty pole protection installation, at a distance from the fault point lambda, the reference positive direction being the converter flow direction line,
I P2p denotes the short-circuit current at the fault pole protection installation at a distance from the fault point (1-lambda), the reference positive direction being the converter flow direction line,
I P2n denotes the short-circuit current at the non-faulty pole protection installation at a distance from the fault point (1-lambda), the reference positive direction being the converter flow direction line,
I dc is the pre-fault dc current.
8. The method for calculating the monopole ground short circuit of the offshore wind power flexible direct system according to claim 6, wherein the method comprises the following steps of:
the short-circuit current at the dc line protection installation in step 8 is expressed by the following formula,
Wherein:
i P3p denotes the short-circuit current at the fault pole protection installation, far from the fault point, the reference positive direction being the converter flow direction line,
I P3n denotes the short-circuit current at the non-faulty pole protection installation, remote from the fault point, the reference positive direction being the converter flow direction line,
I P4p denotes the short-circuit current at the fault pole protection installation near the fault point, the reference positive direction is the converter flow direction line,
I P4n denotes the short-circuit current at the non-faulty pole protection installation near the fault point, the reference positive direction being the converter flow direction line.
9. A single pole ground short circuit calculation system of an offshore wind turbine flexible system operating a single pole ground short circuit calculation method of an offshore wind turbine flexible system according to any one of claims 1 to 8, comprising: the system comprises a fault judging module, a direct current zone internal fault equivalent model establishing module, a direct current zone internal differential equation establishing module, a direct current zone internal defining condition equation establishing module, a direct current zone external fault equivalent model establishing module, a direct current zone external differential equation establishing module, a direct current zone external defining condition equation establishing module and a short circuit current calculating module, and is characterized in that:
The fault judging module is used for acquiring direct current voltage and direct current before fault, fault position and short circuit transition resistance of the flexible direct current transmission system and dividing faults in the direct current region and faults out of the direct current region according to the fault position;
The direct current region internal fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current lines on two sides of a fault point of a fault pole in the direct current region respectively and building a T-shaped equivalent model aiming at a non-fault pole direct current line in the direct current region; calculating equivalent inductance from the capacitance of the non-fault line to the fault point;
the direct current region internal differential equation establishing module is used for establishing a discharge loop equation from the non-fault pole direct current line capacitance to a fault point, and solving a second-order constant coefficient differential equation of the short-circuit current of the non-fault pole direct current line capacitance;
the direct-current region internal definition condition equation establishing module is used for establishing a definition solution condition equation and solving the short-circuit current of the non-fault circuit capacitor;
The direct current off-zone fault equivalent model building module is used for building a T-shaped equivalent model aiming at direct current off-zone fault poles and non-fault pole direct current lines respectively;
The direct current out-of-area differential equation building module is used for building a discharge loop equation from the direct current line capacitance of the fault pole and the non-fault pole to the fault point, and solving a second-order constant coefficient differential equation of the short-circuit current of the fault pole and the non-fault line capacitance;
The direct current region external definite solution condition equation building module is used for solving the short-circuit current of the fault pole and the non-fault pole circuit capacitor;
The short circuit current calculation module is used for calculating the short circuit current of the direct current line protection installation position.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105896488A (en) * | 2016-04-29 | 2016-08-24 | 浙江大学 | Short circuit fault processing method for flexible DC power grid based on combined-type high-voltage DC circuit breaker |
| CN108933445A (en) * | 2018-06-28 | 2018-12-04 | 东北电力大学 | DC grid short-circuit current calculation method based on the loop method of analysis |
| CN109633361A (en) * | 2019-01-14 | 2019-04-16 | 上海交通大学 | Middle straightening stream generator outlet short trouble steady-state current detection method |
| CN111799766A (en) * | 2020-07-22 | 2020-10-20 | 广东电网有限责任公司电力科学研究院 | Offshore wind power flexible direct grid-connected overcurrent protection method, system and equipment |
| WO2021129822A1 (en) * | 2019-12-26 | 2021-07-01 | 南京南瑞继保电气有限公司 | Control method and control apparatus for direct-current side grounding fault of high-voltage direct-current power transmission system |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2599199B1 (en) * | 2010-07-30 | 2018-02-28 | General Electric Technology GmbH | Hvdc converter comprising fullbridge cells for handling a dc side short circuit |
-
2021
- 2021-12-15 CN CN202111534357.4A patent/CN114417241B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105896488A (en) * | 2016-04-29 | 2016-08-24 | 浙江大学 | Short circuit fault processing method for flexible DC power grid based on combined-type high-voltage DC circuit breaker |
| CN108933445A (en) * | 2018-06-28 | 2018-12-04 | 东北电力大学 | DC grid short-circuit current calculation method based on the loop method of analysis |
| CN109633361A (en) * | 2019-01-14 | 2019-04-16 | 上海交通大学 | Middle straightening stream generator outlet short trouble steady-state current detection method |
| WO2021129822A1 (en) * | 2019-12-26 | 2021-07-01 | 南京南瑞继保电气有限公司 | Control method and control apparatus for direct-current side grounding fault of high-voltage direct-current power transmission system |
| CN111799766A (en) * | 2020-07-22 | 2020-10-20 | 广东电网有限责任公司电力科学研究院 | Offshore wind power flexible direct grid-connected overcurrent protection method, system and equipment |
Non-Patent Citations (1)
| Title |
|---|
| 海上风电接入柔直系统交流侧故障特征及对保护的影响分析;郑黎明;《电力系统保护与控制》;20211031;第49卷(第20期);第1-13页 * |
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