CN113437735B - Optical fiber differential protection capacitance current compensation method suitable for superconducting cable - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000013307 optical fiber Substances 0.000 title claims abstract description 24
- 238000004891 communication Methods 0.000 claims abstract description 11
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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
- H02H7/28—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 for meshed systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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Abstract
The optical fiber differential protection capacitance current compensation method suitable for the superconducting cable is characterized by comprising the following steps of: step 1, establishing a differential protection network model of a superconducting cable communication system, and acquiring a differential connection mode of the model in a working or fault state; step 2, calculating a capacitance current compensation value according to the differential connection mode; and 3, judging faults in the network model based on practical differential criteria of the Berlong model, and starting corresponding differential protection. The method can construct a differential protection network model of the meshed superconducting cable communication system and judge network faults by utilizing a practical differential criterion.
Description
Technical Field
The invention relates to the field of superconducting cables, in particular to an optical fiber differential protection capacitance current compensation method suitable for a superconducting cable.
Background
The application of superconducting technology in power systems is various, and is one of the main directions of superconducting application research in recent years. Compared with the power cable, the superconducting cable has great advantages such as: the power transmission capability is strong, the cost is saved, the occupied space is small, the line impedance is extremely low, the power transmission loss is small, and the anti-magnetic interference capability is strong; the power transmission device allows long-distance power transmission by adopting relatively low voltage, and can also transmit underground power so as to avoid noise, electromagnetic pollution and potential safety hazard caused by ultra-high voltage high-altitude power transmission and protect ecological environment.
Currently, a berlong model is generally adopted in capacitive current compensation technology related to differential protection of high-temperature superconducting cables. However, although this model enables the differential protection criteria to be immune to capacitive currents, the sensitivity of the criteria is susceptible to single-phase-to-ground short-circuits non-faulted-phase imbalance differential flows within the zone. When the maximum unbalanced differential flow of the non-fault phase is large, the fault sensitivity in the zone is greatly reduced, and under the condition, the existing criterion has the problem of seriously affecting the differential protection performance.
Therefore, a new method for compensating the differential protection capacitor current of the optical fiber suitable for the superconducting cable is needed.
Disclosure of Invention
In order to solve the defects existing in the prior art, the invention aims to provide the optical fiber differential protection capacitor current compensation method suitable for the superconducting cable, and the sensitivity of the differential criterion is improved by constructing a differential protection network model of a superconducting cable communication system and judging network faults by using a practical differential criterion.
The invention adopts the following technical scheme.
The optical fiber differential protection capacitance current compensation method suitable for the superconducting cable comprises the following steps:
step 1, establishing a differential protection network model of a superconducting cable communication system, and obtaining a differential connection mode of the model in a working or fault state; step 2, calculating a capacitance current compensation value according to the differential connection mode; and 3, judging faults in the network model based on practical differential criteria of the Berlong model, and starting corresponding differential protection.
Preferably, the number, the position, and the compensation capability of the arc suppression coils installed in the network model are determined based on the calculated capacitance current compensation value, and the differential protection network model of the superconducting cable communication system is updated.
Preferably, in the differential connection mode, the master device and the slave device are confirmed according to the value of the longitudinal code and the channel interruption state in the differential protection device.
Preferably, for the differential connection line, if a shunt reactor is provided in the middle of the line, the shunt reactor is equivalent to one side of the line and the capacitance current compensation value of the current line is calculated.
Preferably, the current i of the shunt reactor is solved by using a transient processing method Lm And then, the parallel reactor current is equivalent to the near side for compensation, and the capacitance current of two sides to be compensated is calculated.
Preferably, the practical differential criterion of the berlong model isWherein (1)>The fundamental wave amplitude value of differential current at two sides in the differential connection line is obtained; n is three phases of a, b and c, < >>The current values calculated by the Berhelone algorithm are respectively the current sampling values of the j side and the k side, < ->The j-side and k-side current samples, respectively.
Preferably, when the differential connection line is short-circuited to ground in an internal single phase, a fixed threshold and a weight of the maximum differential current in the non-faulty phase are used as the braking amount.
Preferably, the method for braking by using the practical differential criterion is as follows:
if the corresponding phase of the differential connection circuit is in fault, judging that the corresponding phase of the differential connection circuit is in fault; wherein I is 0 To fix threshold, K fd Is the braking coefficient.
Preferably, the fixed threshold is set according to the maximum possible unbalanced differential current when the differential connection is in normal operation, or when it fails outside its zone.
Preferably, the maximum possible unbalanced differential current is determined based on the external fault and the unbalanced differential current at the time of fault removal, at the time of no-load closing.
Compared with the prior art, the optical fiber differential protection capacitance current compensation method suitable for the superconducting cable has the advantages that a differential protection model of the superconducting cable communication system can be built, and faults can be judged by utilizing a practical differential criterion.
The beneficial effects of the invention also include:
1. for a differential protection circuit with a shunt reactor in the middle of the circuit, the shunt reactor can be equivalent to one side or two sides of the circuit, and the calculation is simplified;
2. by using the new differential current criterion, the defect that the sensitivity of the Berlong differential criterion is influenced by single-phase grounding short-circuit non-fault phase unbalanced differential current in the region in the prior art is overcome, the characteristic that the Berlong criterion is not influenced by capacitance current in the prior art is maintained, and the sensitivity of fault judgment is greatly improved.
Drawings
FIG. 1 is a schematic flow chart of a method for compensating the current of an optical fiber differential protection capacitor suitable for a superconducting cable;
FIG. 2 is a schematic diagram of an equivalent circuit with resistors on both sides of a line in a method for compensating a differential protection capacitor current of an optical fiber suitable for a superconducting cable according to the present invention;
FIG. 3 is a schematic diagram of an equivalent circuit with a resistor in the middle of the line in a method for compensating the differential protection capacitance current of an optical fiber for a superconducting cable according to the present invention;
FIG. 4 is a schematic diagram of calculated voltage values and actual voltage values at the point where the high reactance is installed in the optical fiber differential protection capacitor current compensation method applicable to the superconducting cable according to the present invention;
FIG. 5 is a schematic diagram of calculated current values and actual current values at a high reactance point in an optical fiber differential protection capacitor current compensation method suitable for a superconducting cable according to the present invention;
FIG. 6 shows a method for compensating the current of the differential protection capacitor of an optical fiber for a superconducting cable according to the present invention NF Schematic diagram of the relationship to the location of the fault.
Detailed Description
The present application is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present invention and are not intended to limit the scope of protection of the present application.
Fig. 1 is a schematic flow chart of a method for compensating the differential protection capacitor current of an optical fiber suitable for a superconducting cable in the present invention. As shown in fig. 1, a method for compensating the differential protection capacitance current of an optical fiber suitable for a superconducting cable comprises the following steps: step 1, establishing a differential protection model of a superconducting cable communication system, and obtaining a differential connection mode of the model in a working or fault state.
It will be appreciated that the differential protection model of the present invention may be obtained by modeling the network model of the superconducting cable communication system in actual operation. Various differential protection network models commonly used in the art can be employed.
Preferably, in the differential connection mode, the master device and the slave device are confirmed according to the values of the longitudinal codes and the channel interruption states in the differential protection devices.
It can be appreciated that the present invention may employ an adaptive master-slave switching technique to automatically adjust the master-slave state of the device according to the conditions of the differential communication channels. According to the principle, each side protection device can be allocated a different identification code (0-65535), namely a longitudinal code. When the devices at all ends communicate, the side with the largest identification code can be selected as the master machine according to the size of the identification code, the other sides are the slaves, and all the slaves follow the master machine to adjust sampling interruption. When a certain optical fiber is interrupted, the device can automatically switch between the master and the slave.
And 2, calculating a capacitance current compensation value according to the differential connection mode.
The distributed capacitance current of the ultra-high voltage long wire is always a main factor influencing the current differential protection performance, the thickness of the insulating layer of the high-temperature superconducting cable is basically consistent with that of the conventional cable, and the equivalent radius of the conductive cable core is increased due to the fact that a cooling channel is arranged in the superconducting cable, so that the capacitance of the high-temperature superconducting cable is larger than that of the conventional cable.
For a superconducting line, the capacitance of the superconducting cable is larger per kilometer than that of a conventional cable, and the calculated capacitance current can be smaller due to low voltage level and short line, so that the steady-state capacitance current of the line is increased along with the increase of the length of the superconducting cable and the increase of the voltage level. Because of the existence of the distributed capacitance of the line, when the line is short-circuited outside the area, the short-circuited outside the area is cut off, the line is empty and charged, and the like, the capacitance current of the line has high-frequency component capacitance current which is more than 50Hz besides the power frequency component capacitance current. The magnitude of the high-frequency current is related to the voltage initial phase angle during short circuit, if short circuit occurs at the moment of maximum electromotive force, the stored energy is maximum due to the highest voltage on the capacitor, and the high-frequency transient component current after fault is also maximum, which may reach several times of steady-state current. The decay time of this high frequency transient is related to the line R/L/C parameter and eventually decays to zero. Therefore, the capacitive current after the occurrence of the line out-of-zone short circuit, out-of-zone short circuit cutting and line empty charge may affect the action behavior of the differential relay, so that it is necessary to study the capacitive current compensation problem of the superconducting line.
Specifically, simulation can be performed based on superconducting cable parameters, so that the steady-state differential flow of the line and the transient differential flow characteristics of the line during off-zone faults and no-load closing are researched.
Fig. 2 is a schematic diagram of an equivalent circuit of resistors on both sides of a line in a method for compensating a differential protection capacitor current of an optical fiber suitable for a superconducting cable according to the present invention. As shown in fig. 2, in the prior art, a compensation method when the two sides of the line are provided with high reactance is provided according to the characteristic that parallel reactors are possibly arranged at the two sides and the middle of the ultra-high voltage transmission long line, but a corresponding correction scheme of various compensation methods when the middle of the line is provided with high reactance is not provided. Therefore, the present invention is optimized for this content.
Fig. 3 is a schematic diagram of an equivalent circuit of a resistor in the middle of a line in a method for compensating a differential protection capacitor current of an optical fiber for a superconducting cable according to the present invention. As shown in fig. 3, in the differential connection line, if a shunt reactor is provided in the middle of the line, the shunt reactor is preferably equivalent to one side of the line, and the capacitance current compensation value of the current line is calculated.
Specifically, similar to the steady-state compensation method in the prior art, the parallel reactor installed in the middle of the line can be equivalently moved to one side or two sides of the line, and the situation that the parallel reactor is arranged on the two sides of the line is obtained. Meanwhile, the voltage at the installation position of the shunt reactor can be firstly calculated, and then the current of the shunt reactor can be calculated.
For a line j-k with a shunt reactor in the middle, the shunt reactor at the m point in the middle of the line can be equivalent to two ends of the line, for example, the j point or the k point. Therefore, the instantaneous value of each sequence voltage at the m point can be calculated according to each sequence network diagram and sequence parameters. Firstly, the calculation formula of the instantaneous value of each sequence voltage at the m point is as follows:
wherein L is j1 And L j0 Positive sequence and zero sequence inductances of the lines j-k respectively, R j1 And R is j0 Positive and zero sequence resistances of lines j-k, respectively, u m1 、u m2 、u m0 Respectively m-point positive sequence, negative sequence and zero sequence voltage instantaneous values, u j1 、u j2 、u j0 Respectively j-point positive sequence, negative sequence and zero sequence voltage instantaneous values, i j1 、i j2 、i j0 The instantaneous values of the positive sequence, the negative sequence and the zero sequence currents of the j points are respectively.
The calculation formula of each phase voltage of the m points is as follows:
wherein,respectively the m-point A-phase voltage, the B-phase voltage and the C-phase voltage instantaneous values,respectively j point A phase voltage, B phase voltage, C phase voltage instantaneous value, +.>Respectively j point A phase current, B phase current, C phase current instantaneous value, k L0 I is the zero sequence compensation coefficient of the line 0 (t) is zero sequence current sampling value, alpha=e j120 。
Preferably, the current i of the shunt reactor is solved by using a transient processing method Lm And then, the parallel reactor current is equivalent to the near side for compensation, and the capacitance current of which the two sides need to be compensated can be calculated.
The capacitance currents to be compensated at the two sides are respectively as follows:
wherein,the j point is respectively the instantaneous values of the capacitance currents of the phase A, the phase B and the phase C after being compensated by the shunt reactor, < >>The instantaneous values of the A-phase current, the B-phase current and the C-phase capacitance current before the compensation of the j point through the shunt reactor are respectively +.>The instantaneous values of the current flowing through the A phase, the B phase and the C phase of the shunt reactor are respectively +.>The k point is respectively the instantaneous values of the capacitance currents of the phase A, the phase B and the phase C after being compensated by the shunt reactor, < >> The instantaneous values of the capacitor current of A, B, C phases before the k points are compensated by the shunt reactor respectively.
FIG. 4 is a schematic diagram of calculated voltage values and actual voltage values at the point where the high reactance is installed in the optical fiber differential protection capacitor current compensation method applicable to the superconducting cable according to the present invention; fig. 5 is a schematic diagram of calculated current values and actual current values at a position where a high reactance is installed in the optical fiber differential protection capacitor current compensation method applicable to a superconducting cable according to the present invention. As shown in fig. 4 and 5, by the above method, the voltage and current values at the place where the high reactance is installed in the line can be calculated. It can be seen that there is a certain error between the calculated value and the actual value, which is caused by neglecting the transient component of the voltage and neglecting the distributed capacitance of the line when the voltage is calculated.
When the time-domain capacitance-current compensation method is adopted, the instantaneous value of the capacitance current required to be compensated on each of the two sides of the line is firstly obtained according to the specific condition of the linei bk (t); and calculating the instantaneous values of the compensated differential current and the braking current as follows:
wherein,for the line differential current after compensation of each phase, < >>The compensated line brake current for each phase, < >>Original sampling currents of each phase on two sides of j and k respectively, < + >>The capacitance currents are compensated for each phase at both sides of j and k respectively.
Finally, the amplitude values of the differential current and the braking current after compensation are obtained through a filtering algorithm
And 3, judging faults in the network model based on practical differential criteria of the Berlong model, and starting corresponding differential protection.
The Berlong equivalent circuit is a relatively accurate power transmission line model, converts the wave process of distributed parameters into a centralized parameter circuit only comprising resistors and current sources, and reflects the relationship between voltage and current at two ends when no faults exist in the power transmission line. The circuit differential protection based on the Berlong model overcomes the influence of capacitance current in principle.
The maximum advantage of the Berlong differential criterion is that the criterion is not influenced by capacitance current, but the sensitivity is influenced by single-phase grounding short-circuit non-fault phase unbalanced differential current in the zone, when the non-fault phase maximum unbalanced differential current is larger, the fault sensitivity in the zone is greatly reduced, and the performance of differential protection is seriously influenced.
In order to overcome the defect that the sensitivity of the Berlong differential criterion is influenced by single-phase grounding short-circuit non-fault phase unbalanced differential current in a zone and simultaneously keep the characteristic that the original criterion is not influenced by capacitance current, the invention provides a differential protection practical criterion based on a Berlong model on the basis of original judgment.
Preferably, the practical differential criterion of the berlong model is
Wherein n is three phases of a, b and c,the fundamental wave amplitude value of differential current at two sides in the differential connection line is obtained; />The current values of the current sampling values of the j side and the k side are calculated by the Berlong algorithm respectively; />The j-side and k-side current samples, respectively.
Preferably, when the differential connection line is short-circuited to ground in an internal single phase, a fixed threshold and a weight of the maximum differential current in the non-faulty phase are used as the braking amount.
Preferably, the method for braking by using the practical differential criterion is as follows:
if the corresponding phase of the differential connection circuit is in fault, judging that the corresponding phase of the differential connection circuit is in fault;
wherein I is 0 To fix threshold, K fd Is the braking coefficient.
Specifically, when the internal single-phase short circuit grounding occurs in the line, differential currents of the fault phase and the non-fault phase are respectively:
wherein, among them,differential current for fault phase +.>Differential current for non-faulty phase,/->For fault current +.>Time from point j to point F for zero-mode component of fault current, +.>Time for line mode component of fault current to pass from point j to point F of fault, +.>Time from k point to fault F point for zero-mode component of fault current, +.>The time from point k to point F is taken for the line mode component of the fault current.
Taking a Berlong equivalent calculation circuit as an example, there areIndicating that the fault phase differential current of the new criterion is twice that of the original criterion. FIG. 6 shows k in a method for compensating a differential protection capacitor current of an optical fiber suitable for a superconducting cable according to the present invention NF Schematic diagram of the relationship to the location of the fault. As shown in fig. 6, k F The value change of (2) is very small and basically is [0.07435,0.07545 ]]Internal variation, where the maximum occurs at the midpoint of the line, where k NF ＝0.07545。
In order to ensure that the non-fault phase does not malfunction when single-phase fault occurs in the area, the criterion adopts a fixed threshold and other two-phase differential currentsThe braking quantity is formed by the weight of the non-fault phase, and the threshold of the non-fault phase is automatically improved by utilizing the fault phase differential current, so that the unbalanced differential current of the non-fault phase can be flexibly avoided; meanwhile, the differential current of the non-fault phase is smaller, so that the action threshold of the fault phase is lower, and the sensitivity is high. K (K) fd To ensure that the braking amount must avoid the maximum unbalance differential current possible, the ratio K of the differential current of the non-fault phase to the differential current of the fault phase must be found f The maximum point is obviouslyTaking K by taking a certain margin into consideration fd When the line is less than 500km, it can be smaller.
In the invention, compared with the original judgment, the practical criterion is the ratio K of the maximum differential current of the non-fault phase to the current difference of the fault phase f The sensitivity is doubled by decreasing 0.0758 to 0.0377. Although the Berhelson model is not suitable for the situation of the fault in the area, the transient capacitance current during the fault in the area cannot be calculated through the Berhelson model, but the differential practical criterion based on the Berhelson model is increased compared with the original judgment action quantity during the fault in the area, and has high sensitivity.
Preferably, the fixed threshold is set according to the maximum possible unbalanced differential current when the differential connection is in normal operation, or when it fails outside its zone. The maximum possible unbalanced differential current is determined based on the external fault and the unbalanced differential current at the time of fault removal and no-load closing.
In particular when there is no fault inside the lineThree-phase motion quantityZero, but considering the effects of various errors and simplified losses, not absolutely zero, I 0 Is selected to be greater than the maximum possible unbalanced differential current setting during no-load closing when external faults are removed。
Compared with the prior art, the optical fiber differential protection capacitance current compensation method suitable for the superconducting cable has the advantages that a differential protection network model of a reticular superconducting cable communication system can be constructed, and network faults can be judged by utilizing a practical differential criterion.
The beneficial effects of the invention also include:
1. based on the design of redundant channels in network connection, the automatic switching function of a master-slave machine, the differential direct-jump function and the switching of N-end-to-N-M-end differential operation modes after individual channel faults can be realized;
2. for a differential protection circuit with a shunt reactor in the middle of the circuit, the shunt reactor can be equivalent to one side or two sides of the circuit, and the calculation is simplified;
3. by using the new differential flow criterion, the defect that the sensitivity of the Berlong differential criterion is influenced by single-phase grounding short-circuit non-fault phase unbalanced differential current in the region in the prior art is overcome, the characteristic that the Berlong criterion is not influenced by capacitance current in the prior art is maintained, and the sensitivity of fault judgment is greatly improved.
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 (8)
1. The optical fiber differential protection capacitance current compensation method suitable for the superconducting cable is characterized by comprising the following steps of:
step 1, establishing a differential protection network model of a superconducting cable communication system, and acquiring a differential connection mode of the model in a working or fault state;
the number and the positions of the arc suppression coils in the network model and the compensation capacity of the arc suppression coils are determined based on the calculated capacitance current compensation value, and the differential protection network model is updated;
step 2, calculating a capacitance current compensation value according to the differential connection mode;
if a shunt reactor is arranged in the middle of the differential connection circuit, the shunt reactor is equivalent to one side of the circuit and the capacitance current compensation value of the current circuit is calculated;
step 3, judging faults in the network model based on practical differential criteria of the Berlong model, and starting corresponding differential protection;
the practical differential criterion comprises differential current and braking current, and the differential current and the braking current are determined according to the capacitance current compensation value.
2. A method of compensating for differential protection capacitor currents in a superconducting cable as claimed in claim 1, wherein:
in the differential connection mode, the master and slave devices are confirmed according to the value of the longitudinal code and the channel interruption state in the differential protection device.
3. A method of compensating for differential protection capacitor currents in a superconducting cable as claimed in claim 1, wherein:
solving current i of shunt reactor by transient treatment method Lm And then, the parallel reactor current is equivalent to the near side for compensation, and the capacitance current of two sides to be compensated is calculated.
4. A method of compensating for differential protection capacitor currents in a superconducting cable as claimed in claim 1, wherein:
the practical differential criterion of the Berlong model is
Wherein,the fundamental wave amplitude value of the differential current at two sides in the differential connection line is given; n is three phases of a, b and c,
the current values calculated by the berlong algorithm are respectively the current sampling values of the j side and the k side,
the j-side and k-side current samples, respectively.
5. The method for compensating for differential protection capacitor current of a superconducting cable according to claim 4, wherein:
when the differential connection circuit is grounded by an internal single-phase short circuit, the weight of the fixed threshold and the maximum differential current in the non-fault phase is adopted as the braking quantity.
6. The method for compensating for differential protection capacitor current of a superconducting cable according to claim 5, wherein:
the method for braking by using the practical differential criterion comprises the following steps:
judging whether or not there isIf yes, judging that the corresponding phase of the differential connection circuit fails;
wherein I is 0 To fix threshold, K fd Is the braking coefficient.
7. The method for compensating for differential protection capacitor current of a superconducting cable according to claim 6, wherein:
the fixed threshold is set according to the maximum possible unbalanced differential current when the differential connection is in a normal operation state or fails outside its zone.
8. The method for compensating for differential protection capacitor current of a superconducting cable according to claim 7, wherein:
the maximum possible unbalanced differential current is determined based on the external fault and the unbalanced differential current at the time of fault removal and no-load closing.
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| 郑玉平.基于贝瑞隆模型的线路差动保护实用判据.《电力系统自动化》.2004,第50-55页. * |
| 陈生贵.《电力系统继电保护》.重庆大学出版社,2003,第272页. * |
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