CN110829396B - Hybrid direct-current transmission fault processing system and method based on current limiter and circuit breaker - Google Patents
Hybrid direct-current transmission fault processing system and method based on current limiter and circuit breaker Download PDFInfo
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- CN110829396B CN110829396B CN201911125575.5A CN201911125575A CN110829396B CN 110829396 B CN110829396 B CN 110829396B CN 201911125575 A CN201911125575 A CN 201911125575A CN 110829396 B CN110829396 B CN 110829396B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
- H02H9/023—Current limitation using superconducting elements
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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
- H02H7/268—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 dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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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- 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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention relates to a power system and an automation technology, in particular to a hybrid direct-current transmission fault processing system and a hybrid direct-current transmission fault processing method based on a current limiter and a circuit breaker. The method of the system has effectiveness and applicability when processing direct current faults, particularly for a voltage source converter type converter station, the method can effectively restrain direct current fault current rise, reduce transient voltage duration time and obviously reduce dissipation energy of a hybrid circuit breaker, and the method can be used as an effective backup means for a power grid phase change type converter station to ensure timely fault isolation. The robustness of the whole hybrid direct-current power transmission system is effectively improved.
Description
Technical Field
The invention belongs to the technical field of power systems and automation, and particularly relates to a hybrid direct-current transmission fault processing system and method based on a current limiter and a circuit breaker.
Background
The conventional High Voltage Direct Current (HVDC) transmission technology includes a Line Commutated Converter (LCC) High Voltage Direct Current transmission technology and a Voltage Source Converter (VSC) High Voltage Direct Current transmission technology. In recent years, the hybrid direct-current transmission technology is a novel implementation scheme for achieving the purpose of long-distance large-capacity transmission, and is receiving more and more attention from domestic and foreign scholars. The hybrid direct-current transmission technology integrates the advantages of the LCC-HVDC and the VSC-HVDC, and the LCC converter station is used as a rectifier station, so that the cost can be effectively reduced; the VSC converter station is used as an inverter station, so that the operation flexibility can be enhanced. In addition, the hybrid direct current transmission technology has the following advantages: (1) the risk of commutation failure is eliminated; (2) the supporting capability of a weak power grid or even a passive power grid is enhanced; (3) the flexible control of active power and reactive power is realized.
For some problems of the hybrid direct-current power transmission technology in engineering application, researches of domestic and foreign scholars mainly focus on aspects of how to enhance the robustness of a system under an alternating-current fault, how to establish a small-signal model of the system and the like, and researches on how to enhance the robustness of the system under the direct-current fault are few. In a hybrid direct-current transmission system, a direct-current short-circuit fault, particularly a bipolar grounding fault, occurs in a transmission line, which is a very serious fault, and if the short-circuit current cannot be limited in time, the short-circuit current may cause irreversible damage to equipment, even cause breakdown of the whole system. For the direct-current short-circuit current of an LCC converter station in a hybrid direct-current transmission system, a better direct-current short-circuit current suppression effect can be achieved by adjusting a trigger angle and adding a current limiting scheme; for the direct current short-circuit current of the VSC converter station, even if the power electronic switch is locked immediately after the fault occurs, the rising speed of the direct current fault current is very fast due to the discharge of the direct current capacitor. Therefore, it is necessary to introduce a method capable of rapidly isolating a dc fault in a hybrid dc power transmission system.
In a high-voltage direct-Current transmission system, a resistive Superconducting Current Limiter (SFCL) is often used to limit the magnitude of short-circuit Current, and the SFCL mainly utilizes the quench principle of a Superconducting material to realize Current limiting, and the Current limiting principle can be intuitively described as follows: under the normal operation state, the equivalent resistance of the superconducting current limiter is 0 due to the superconducting characteristic, the current flowing through the superconducting current limiter is the normal working current of the system, the access of the current limiter does not influence the system, when a direct current fault occurs, the fault current rapidly rises due to the short circuit of a line to cause superconducting quench, and the resistance value of the current limiter is greatly increased due to the superconducting quench, so that the fault current limiting is realized.
In a high-voltage direct-current transmission system, in order to ensure safe and reliable operation of the system, a direct-current breaker is arranged to rapidly remove faults, and isolation of fault parts is indispensable. In the development process of the DC Circuit Breaker, there are mechanical DC Circuit breakers, solid-state DC Circuit breakers, Hybrid DC Circuit Breakers (HDCB) and other types of Circuit breakers. The mechanical direct current circuit breaker has strong load carrying capacity, stable operation, small on-state loss and large on-off capacity, but the time for cutting off fault current is long, and equipment is easy to be burnt by electric arc during cutting off; the solid-state direct-current circuit breaker is high in cut-off speed, but a large number of power electronic switches need to be connected in series, the requirements on voltage-sharing and current-sharing technologies are high, and the use of the large number of power electronic switches increases the on-state loss of the direct-current circuit breaker under the normal conduction condition; the HDCB combines the mechanical switch and the solid-state switch, retains the advantages of small on-state loss, strong loading capacity and high response speed of the solid-state switch of the mechanical switch, and realizes quick and safe cut-off of direct current.
Disclosure of Invention
The invention aims to provide a mixed direct-current transmission fault processing system and method based on a resistance type superconducting current limiter-mixed direct-current breaker, when a direct-current fault occurs, the action time of a resistance type SFCL and an HDCB is coordinated to isolate the direct-current fault, so that the rise of direct-current fault current can be inhibited, the transient voltage duration time is shortened, the dissipation energy of the direct-current breaker is reduced, a converter station in the system is ensured not to be damaged by the fault current when the fault occurs, and the robustness under the direct-current fault of the mixed direct-current transmission system is improved.
In order to achieve the purpose, the invention adopts the technical scheme that: a hybrid direct-current transmission fault processing system based on a current limiter and a circuit breaker comprises a first resistance type superconducting current limiter device and a second resistance type superconducting current limiter device which are respectively connected with an inlet and an outlet of a transmission line, and the first resistance type superconducting current limiter device and the second resistance type superconducting current limiter device are respectively connected in series with a first hybrid direct-current circuit breaker device and a second hybrid direct-current circuit breaker device.
In the hybrid direct-current transmission fault processing system based on the current limiter and the circuit breaker, the transmission line inlet comprises a first alternating-current power grid, a rectification side transformer connected with the first alternating-current power grid, and an LCC converter station connected with the rectification side transformer; the outlet of the power transmission line comprises a second alternating current power grid, an inversion side transformer connected with the second alternating current power grid and a VSC converter station connected with the inversion side transformer; the LCC converter station is connected with a first resistive superconducting current limiter device, and the VSC converter station is connected with a second resistive superconducting current limiter device.
In the above-mentioned hybrid direct-current transmission fault processing system based on the current limiter and the circuit breaker, the LCC converter station and the VSC converter station respectively employ controllers for determining direct current and direct voltage.
In the above-mentioned hybrid direct-current transmission fault processing system based on the current limiter and the circuit breaker, both the first and second resistive superconducting current limiter devices adopt simplified models, and the resistance change rule thereof is described as formula (1):
wherein t is time, tquenchThe quench initiation time; rSCIs a superconducting resistor; t isSCThe time constant of the resistive superconducting current limiter is reflected by the transition from the superconducting state to the normal state.
In the hybrid direct-current transmission fault processing system based on the current limiter and the circuit breaker, the first hybrid direct-current circuit breaker equipment and the second hybrid direct-current circuit breaker equipment respectively comprise a current-carrying transfer branch circuit, a main circuit breaker and a disconnecting switch; the current-carrying transfer branch circuit comprises a quick mechanical switch and a load change-over switch which are connected in series and are used for current circulation when in normal operation; the main circuit breaker comprises a solid-state switch branch and an energy absorption branch; the solid-state switch branch comprises a cascaded solid-state switch group, and the energy absorption branch comprises nonlinear bleeder resistors connected in parallel; when a fault occurs, the main circuit breaker completes the phase change, the cutoff and the energy release of fault current, so that the turn-off of the hybrid direct current circuit breaker is realized; the isolating switch isolates the line after the fault current is cut off.
A hybrid direct-current transmission fault processing method based on a current limiter and a circuit breaker comprises the following steps:
step 1, under the condition that no fault occurs in a power transmission line, direct current flows through a resistance type superconducting current limiter device in a normal working state, and a current path is formed through a current-carrying transfer branch of a hybrid direct current breaker device;
step 2.1, after the direct current fault occurs, the fault current starts to rise sharply, and when the limit of the critical current is exceeded, the resistance type superconducting current limiter acts, so that the rising speed of the fault current is reduced;
2.2, the fault current continues to rise, after the resistance type superconducting current limiter device acts, the hybrid direct current breaker device starts to act after a section of controllable delay, at the moment, the load transfer switch is opened, the current-carrying transfer branch is disconnected, the solid-state switch group cascaded by the main breaker is closed to form a current path, and the current is phase-converted from the current-carrying transfer branch to the solid-state switch branch of the main breaker;
step 2.3, after the current commutation is finished, a fast mechanical switch of the hybrid direct current breaker equipment is opened to isolate a load transfer switch, so that power electronic devices in the load transfer switch are protected from being damaged, and meanwhile, a solid-state switch group of the main breaker cascade is disconnected again;
and 2.4, transferring the fault current to a nonlinear bleeder resistor of the energy-absorbing branch, absorbing residual energy by the nonlinear bleeder resistor, reducing the fault current to zero, and opening the isolating switch to finish fault line isolation.
The invention has the beneficial effects that: when the hybrid direct-current transmission direct-current fault is processed, the rising of direct-current short-circuit current can be effectively restrained for the VSC converter station, the duration time of transient voltage is shortened, and the dissipation energy of the hybrid direct-current circuit breaker is remarkably reduced. The LCC converter station can be used as an effective backup means to ensure timely fault isolation. In the whole view, the robustness under the direct-current fault of the hybrid direct-current power transmission system can be improved.
Drawings
Fig. 1 is a schematic diagram of a ± 320kV hybrid hvdc transmission system equipped with a resistive superconducting current limiter-hybrid dc breaker in an example application of the present invention;
FIG. 2 is a diagram of control strategies for an LCC converter station and a VSC converter station in an example application of the present invention;
FIG. 3 is an equivalent model of a resistive superconducting current limiter in an exemplary application of the present invention;
FIG. 4 is a graph showing the quench characteristics of a resistive superconducting current limiter in an exemplary application of the present invention;
FIG. 5 is a topological circuit of a hybrid DC circuit breaker in an exemplary application of the present invention;
fig. 6 is a diagram illustrating the open current characteristic of a hybrid dc circuit breaker in an exemplary application of the present invention;
fig. 7 is a typical architecture of a hybrid dc circuit breaker in an example application of the invention;
FIG. 8 is a flow chart of fault isolation for a resistive superconducting current limiter and a hybrid DC circuit breaker in the event of a DC fault in an exemplary application of the present invention;
FIG. 9(a) is a graph of R in an example application of the present inventionSC-VSCFault current characteristics of the LCC converter station when changed;
FIG. 9(b) is a graph of R in an example application of the present inventionSC-VSCFault current characteristics of the VSC converter station when changed;
FIG. 10(a) is a graph of R in an example application of the present inventionSC-VSCResponding to the transient voltage characteristic of the hybrid direct-current circuit breaker at the LCC converter station side during changing;
FIG. 10(b) is a graph of R in an example application of the present inventionSC-VSCResponding to the transient voltage characteristic of a hybrid direct current breaker at the VSC converter station side during change;
FIG. 11(a) is a graph of T in an example application of the present inventiondFault current characteristics of the LCC converter station when changed;
FIG. 11(b) is a graph of T in an example application of the present inventiondFault current characteristics of the VSC converter station when changed;
FIG. 12(a) is a graph of T in an example application of the present inventiondTransient voltage characteristics of a hybrid direct current breaker at the LCC converter station side are changed;
FIG. 12(b) is a graph of T in an example application of the present inventiondTransient voltage characteristics of the VSC converter station side hybrid direct current breaker are changed.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The embodiment provides a high-voltage direct-current transmission fault processing method based on a resistance type superconducting current limiter and a hybrid direct-current breaker aiming at the technical characteristics of a hybrid high-voltage direct-current transmission system, and the direct-current fault problem in the high-voltage direct-current transmission system is effectively processed through the cooperation of the resistance type superconducting current limiter and the hybrid direct-current breaker. The embodiment is realized by the following technical scheme:
a mixed direct-current transmission fault processing system based on a current limiter and a circuit breaker comprises a set of resistance type superconducting current limiter equipment respectively installed at an inlet and an outlet of a transmission line, and a set of mixed direct-current circuit breaker equipment respectively installed in series.
Moreover, the resistive superconducting current limiter device adopts a simplified model, and the resistance change rule of the resistive superconducting current limiter device is described as formula (1):
wherein t is time, tquenchThe quench initiation time; rSCIs a superconducting resistor; t isSCThe time constant of the resistive superconducting current limiter is reflected by the transition from the superconducting state to the normal state.
Furthermore, the hybrid DC circuit Breaker device is manufactured based on the principle that an Insulated Gate Bipolar Transistor (IGBT) valve set series connection technology is combined with a fast mechanical Switch, and includes a current-carrying transfer branch formed by an ultra fast Switch (UFD) and a Load Communication Switch (LCS) for current flowing during normal operation, a Main circuit Breaker (Main DC Breaker, MDB) formed by cascading a plurality of solid state Switch sets and nonlinear bleed resistors in parallel, the Main circuit Breaker serving as a solid state Switch branch and an energy-absorbing branch, and completing phase change, current breaking and energy release of fault current when a fault occurs, thereby achieving turn-off of the hybrid DC circuit Breaker. And an isolating switch is also adopted to isolate the line after the fault current is cut off.
The method for processing the fault by using the hybrid direct-current transmission fault processing system based on the current limiter and the circuit breaker comprises the step of designing controllable delay to coordinate the action time intervals of the superconducting current limiter equipment and the hybrid direct-current circuit breaker equipment when the direct-current fault occurs so as to realize the cooperation between the superconducting current limiter equipment and the hybrid direct-current circuit breaker equipment and effectively process the line fault in the hybrid direct-current transmission system. Two working cases are described:
1) under the condition of no fault, the direct current flows through the resistance type superconducting current limiter equipment in the normal working state, and when passing through the hybrid direct current breaker equipment, a current-carrying transfer branch circuit formed by a closed isolating switch, a closed rapid mechanical switch and a load change-over switch forms a current path.
2) Under the condition that a direct current fault occurs in a transmission line, the method coordinates a resistance type superconducting current limiter device and a hybrid direct current breaker device to complete fault isolation of a hybrid direct current transmission system, and the isolation process can be explained as follows:
i) after the direct current fault occurs, the fault current starts to rise sharply, and when the fault current exceeds the limit of critical current, the resistance type superconducting current limiter acts, so that the rising speed of the fault current is reduced;
ii) the fault current continues to rise, after the resistance type superconducting current limiter device acts, the hybrid direct current breaker device starts to act after a controllable delay, at the moment, the load transfer switch is opened, the current-carrying transfer branch is disconnected, the solid-state switch group of the main breaker cascade is closed to form a current path, and the current is phase-converted from the current-carrying transfer branch to the solid-state switch branch of the main breaker;
iii) after the current commutation is completed, the fast mechanical switch of the hybrid direct current breaker equipment is opened to isolate the load transfer switch, so as to protect the power electronic devices in the load transfer switch from being damaged, and the solid-state switch group of the main breaker is disconnected again;
iv) the fault current is transferred to the nonlinear bleeder resistor of the energy-absorbing branch circuit, the nonlinear bleeder resistor absorbs the residual energy, the fault current drops to zero, and at the moment, the isolating switch is opened to finish the fault line isolation.
In particular, as shown in fig. 1, a hybrid hvdc transmission system is provided with a resistive superconducting current limiter device and a hybrid dc breaker device. The hybrid high-voltage direct-current transmission system comprises a first alternating-current power grid 1, a rectifier side transformer, an LCC converter station, a transmission line, a VSC converter station, an inverter side transformer and a second alternating-current power grid 2. The entrance and the exit of the transmission line are respectively provided with a first resistance type superconducting current limiter device and a first mixed direct current breaker device, and a second resistance type superconducting current limiter device and a second mixed direct current breaker device;
in the hybrid high-voltage direct-current transmission system, controllers for respectively determining direct current and direct voltage are respectively adopted in the LCC converter station and the VSC converter station, and fig. 2 shows control curves of the LCC converter station and the VSC converter station.
The resistive superconducting current limiter adopts a second generation Yttrium Barium Copper Oxide (YBCO) material. Fig. 3 is an equivalent model of the resistive superconducting current limiter, fig. 4 is a quench characteristic curve of the resistive superconducting current limiter, and a variation law of the resistance value of the resistive superconducting current limiter is described as formula (1). Different from an accurate resistive superconducting current limiter model based on a power law equation, the simplified equivalent resistive superconducting fault current limiter model can effectively reflect the transient characteristics of the resistive superconducting fault current limiter through two operation sections by reasonably setting transition parameters.
The topology of the hybrid dc circuit breaker apparatus shown in fig. 5 shows the open current characteristic as shown in fig. 6. A typical hybrid dc circuit breaker apparatus is composed of three parts, as shown in fig. 7, one part is a current-carrying transfer branch (formed by connecting a mechanical switch and a solid-state switch in series), one part is a solid-state switch branch (formed by connecting a solid-state switch group in series), and one part is an energy absorption branch (formed by a nonlinear bleeder resistor). In normal operation, the current of the hybrid direct current breaker device flows through the current-carrying transfer branch. After the fault, the fault current is transferred to the solid-state switch branch circuit from the current-carrying transfer branch circuit; and finally, residual energy is absorbed by the energy-absorbing branch circuit, and the mixed direct-current circuit breaker equipment finishes the turn-off process.
In the mixed direct current breaker equipment, a current-carrying transfer branch of the breaker is formed by a quick mechanical switch and a load transfer switch of which the component is a solid-state switch, a main breaker of the mixed direct current breaker equipment comprises a cascaded solid-state switch group and a nonlinear bleeder resistor connected in parallel, the main breaker is used as a solid-state switch branch and an energy absorption branch to participate in the breaking process of the breaker when a fault occurs, and in addition, a disconnecting switch is adopted to separate the fault line after the fault current is cut off. The working principle of the hybrid dc breaker apparatus can be described as: under the normal operation condition, when current flows through the hybrid direct current breaker equipment, the current-carrying transfer branch circuit formed by the closed rapid mechanical switch and the load transfer switch circulates through the closed isolating switch, after a fault occurs, the load transfer switch is opened, the fault current is transferred to the solid-state switch branch circuit from the current-carrying transfer branch circuit, the solid-state switch branch circuit is disconnected after a period of time, the fault current is transferred to the energy-absorbing branch circuit formed by the nonlinear bleeder resistor, the residual energy is absorbed by the energy-absorbing branch circuit, the isolating switch is opened to isolate the fault circuit, and the hybrid direct current breaker completes the turn-off process.
In the implementation object, the LCC converter station adopts constant direct current control, and the fault analysis electrical equation is as follows:
wherein R iseq、LeqIs equivalent direct current resistance and inductance, subscript LCC denotes LCC converter station, IfIs a direct fault current, ULCCmIs the root mean square voltage of the first AC network 1, alpha is the firing angle, T and XTIs the turn ratio and reactance of the transformer at the side of the LCC converter station, UgIs the residual voltage at the fault location, which is related to the fault resistance as shown in equation (3):
Ug＝Rg(If-LCC+If-VSC) (3)
wherein If-VSCIs the direct current fault current of the VSC converter station, and is derived from the formula (4):
wherein C iseqIs equal toEffective capacitance, UdcIs a dc voltage and the subscript VSC indicates the VSC converter station. It follows from this that for LCC converter stations, the firing angle controller may influence the power supply If-LCCAnd the trigger angle is controlled to achieve a better current limiting effect than the current limiting effect obtained by adjusting the resistance of the LCC converter station side resistance type superconducting current limiter; and for the VSC converter station, the resistance type superconducting current limiter can play a better current limiting effect when a fault occurs compared with the condition that the control angle of the converter station is changed.
In the present embodiment, the combination of the resistive superconducting current limiter and the hybrid dc breaker is used as a main method for fault current processing, and a dc fault processing method as shown in fig. 8 is configured. Under the normal working condition of the resistance type superconducting current limiter-hybrid direct current breaker system, direct current flows through the normal resistance type superconducting current limiter and flows through a current-carrying transfer branch formed by a closed isolating switch, a closed rapid mechanical switch and a load change-over switch when flowing through the hybrid direct current breaker.
After a transmission line has a fault, the fault current starts to rise sharply, when the fault current exceeds the critical current limit, the resistance type superconducting current limiter device acts, meanwhile, the trigger angle controller of the LCC converter station is activated, the maximum trigger angle control is adopted, the trigger angle is controlled to be 155 degrees, the short-circuit current of the LCC converter station is effectively restrained, and the LCC converter station is guaranteed not to be damaged by the fault current during the fault occurrence period. And then, after a period of controllable time delay, the hybrid direct-current circuit breaker equipment starts to act, the load transfer switch of the current-carrying transfer branch is opened, meanwhile, the solid-state switch group cascaded by the main circuit breaker is closed to form a current path, and the current is phase-converted from the current-carrying transfer branch to the solid-state switch branch of the main circuit breaker. When the current is completely transferred to the solid-state switch branch of the main circuit breaker, the current commutation is completed, the quick mechanical switch is switched off to isolate the load transfer switch at the moment, the power electronic device is protected from being damaged, meanwhile, the solid-state switch group cascaded by the main circuit breaker is switched on again, so that the current is transferred to the nonlinear discharge resistor of the energy-absorbing branch, the nonlinear discharge resistor absorbs the residual energy, the fault current is reduced to zero, and the isolation switch is switched on to complete the fault line isolation. Main circuit breaker as an important part of the overall fault isolationA loop defining a time interval between actuation of the resistive superconducting current limiter and reopening of the cascaded solid-state switch bank of the main circuit breaker, as a delay Td。
The hybrid direct-current transmission fault processing method based on the current limiter and the circuit breaker in the embodiment has the following expected effects: 1) limiting the rise of the direct current short-circuit current; 2) shortening the duration of the transient voltage; 3) The dissipation energy of the hybrid direct current breaker is reduced. The method has a remarkable effect of improving the robustness under the direct current fault.
To verify the specific performance of the present embodiment related to the isolation method, a detailed electromagnetic transient simulation model was established with reference to fig. 1. The main parameters of the hybrid direct current transmission system are shown in the attached table 1.
Table 1 attached main parameters of a hybrid dc transmission system in an embodiment of the invention
Example one: the starting time of the fault is t0The fault location is set at the dc transmission line midpoint for 3s, the fault resistance (also called transition resistance) is set to 1 Ω, and the fault duration is 250 ms. Resistance R of inversion side resistance type superconducting current limiterSC-VSCThe resistances R of the rectifying side resistive superconducting current limiter are set to 0 Ω (no SFCL), 20 Ω, 30 Ω, 40 Ω, and 50 ΩSC-LCCRemaining at 50 Ω. The fault current responses at the LCC converter station and the VSC converter station are shown in fig. 9(a) and 9(b), and the transient voltage responses at the LCC converter station and the VSC converter station side hybrid dc breakers are shown in fig. 10(a) and 10 (b). The VSC converter station side response data is shown in attached table 2.
Attached table 2 shows VSC converter station side fault response data when change inversion side SFCL resistance size
Example two: the starting time of the fault is t03s, the fault position is arranged at the midpoint of the direct current transmission line,the fault resistance (also called transition resistance) is set to 1 Ω and the fault duration is 250 ms. Resistance R of inversion side resistance type superconducting current limiterSC-VSCResistance R of 30 omega rectification side resistance type superconductive current limiterSC-LCCSet to 50 Ω, delay time T of main breakerdSet to 3ms, 4ms, 5ms, 6ms, 7 ms. The fault current responses at the LCC converter station and the VSC converter station are obtained as shown in fig. 11(a) and 11(b), and the transient voltage responses at the LCC converter station and the VSC converter station side hybrid dc breakers are obtained as shown in fig. 12(a) and 12 (b). The response data of the VSC converter station side is shown in attached table 3.
Supplementary table 3 VSC converter station side fault response data when main circuit breaker delay time is changed
By integrating the simulation results of the first example and the second example, the effectiveness and the applicability of the hybrid direct-current transmission fault processing method based on the current limiter and the circuit breaker in processing the direct-current fault are verified, particularly for a VSC converter station in a hybrid direct-current transmission system, the hybrid direct-current transmission fault processing method can effectively inhibit the rise of direct-current fault current, reduce the duration time of transient voltage and obviously reduce the dissipation energy of the hybrid direct-current circuit breaker, for an LCC converter station in the hybrid direct-current transmission system, the current limiter is introduced to bring a certain current limiting effect, and the current limiting rate is improved along with the increase of the resistance of the current limiter, so that the hybrid direct-current transmission fault processing method has important significance for relieving the on-off pressure of the direct-current circuit breaker. If the fixed trigger angle control fails, the current limiting effect of the rectifier side current limiter is more prominent, so that the current limiter can be used as a competitive backup protection method after the fixed trigger angle control fails, and timely fault isolation is ensured. The robustness of the whole direct current transmission system is effectively improved.
It should be understood that parts of the specification not set forth in detail are well within the prior art.
Although specific embodiments of the present invention have been described above with reference to the accompanying drawings, it will be appreciated by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is only limited by the appended claims.
Claims (1)
1. A processing method of a hybrid direct current transmission fault processing system based on a current limiter and a circuit breaker comprises the steps that an inlet and an outlet of a transmission line are respectively connected with a first resistance type superconducting current limiter device and a second resistance type superconducting current limiter device and then are respectively connected with a first hybrid direct current circuit breaker device and a second hybrid direct current circuit breaker device in series;
the inlet of the power transmission line comprises a first alternating current power grid, a rectification side transformer connected with the first alternating current power grid and an LCC converter station connected with the rectification side transformer; the outlet of the power transmission line comprises a second alternating current power grid, an inversion side transformer connected with the second alternating current power grid and a VSC converter station connected with the inversion side transformer; the LCC converter station is connected with first resistive superconducting current limiter equipment, and the VSC converter station is connected with second resistive superconducting current limiter equipment;
the first and second hybrid direct current breaker devices comprise isolating switches, current-carrying transfer branches and main breakers, wherein the isolating switches are closed during normal operation, and the lines are isolated after fault current is cut off; the current-carrying transfer branch circuit comprises a quick mechanical switch and a load change-over switch which are connected in series and are used for current circulation when in normal operation; the main circuit breaker comprises a solid-state switch branch and an energy-absorbing branch, the solid-state switch branch comprises a cascaded solid-state switch group, the energy-absorbing branch comprises nonlinear bleeder resistors connected in parallel, and the main circuit breaker completes phase change, current breaking and energy release of fault current when a fault occurs, so that the turn-off of the hybrid direct-current circuit breaker is realized;
the processing method is characterized by comprising the following steps:
step 1, under the normal working condition, direct current flows through a resistance type superconducting current limiter under the normal working condition, and flows through a current-carrying transfer branch formed by a closed isolating switch, a closed rapid mechanical switch and a load transfer switch when flowing through a hybrid direct current breaker;
step 2, after the power transmission line fails, activating an LCC converter station trigger angle controller on the LCC converter station side, and adopting maximum trigger angle control, wherein the trigger angle is controlled to be 155 degrees, the short-circuit current of the LCC converter station is restrained, and the LCC converter station is ensured not to be damaged by the fault current during the failure; if the fixed trigger angle control fails, the fault current rapidly rises, and the resistance type superconducting current limiter equipment and the hybrid direct current breaker equipment on the LCC converter station side are started as a backup protection means;
step 3, after the transmission line breaks down, the fault current starts to rise sharply at the VSC converter station side, when the fault current exceeds the critical current limit, the resistance type superconducting current limiter device acts, meanwhile, after a controllable time delay, the hybrid direct-current breaker device acts, the load change-over switch of the current-carrying transfer branch circuit is opened, meanwhile, the solid-state switch group of the main breaker cascade connection is closed to form a current path, and the current is changed from the current-carrying transfer branch circuit to the solid-state switch branch circuit of the main breaker;
step 4, when the current on the VSC converter station side is completely transferred to the solid-state switch branch of the main circuit breaker, finishing current commutation; the quick mechanical switch is switched off to isolate the load transfer switch and protect the power electronic devices thereof from being damaged; and meanwhile, the solid-state switch group cascaded by the main circuit breaker is opened again, so that the current is transferred to the nonlinear bleeder resistor of the energy-absorbing branch circuit, the nonlinear bleeder resistor absorbs the residual energy, the fault current is reduced to zero, and the isolating switch is opened to finish fault line isolation.
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| CN111832196A (en) * | 2020-09-14 | 2020-10-27 | 杭州电力设备制造有限公司 | Modeling method for direct-current fault analysis model of power grid commutation converter |
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