CN112448372A - Method for realizing metal longitudinal differential protection of parallel multi-terminal direct-current transmission system - Google Patents
Method for realizing metal longitudinal differential protection of parallel multi-terminal direct-current transmission system Download PDFInfo
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- CN112448372A CN112448372A CN202011195966.7A CN202011195966A CN112448372A CN 112448372 A CN112448372 A CN 112448372A CN 202011195966 A CN202011195966 A CN 202011195966A CN 112448372 A CN112448372 A CN 112448372A
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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
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/262—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 involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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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
- 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 discloses a method for realizing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system, which relates to the technical field of direct-current transmission systems, wherein a first converter station, a second converter station and a third converter station are all provided with metal return longitudinal differential protection devices, the third converter station is also provided with a metal return fault line selection device, and the third converter station also has a bus bar area and is provided with a quick isolating switch; the method comprises the following steps: the metal return wire longitudinal difference protection device of the converter station triggers corresponding protection actions according to the current of the opposite-pole direct current line of the current station and the current of the opposite-pole direct current line of the opposite station; and the metal return line fault line selection device judges the type of the metal return line fault according to the protection action and adopts a corresponding fault clearing strategy.
Description
Technical Field
The invention relates to the technical field of direct current transmission systems, in particular to a method for realizing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system.
Background
The parallel multi-terminal direct-current transmission system is a direct-current transmission system of three or more converter stations, and is remarkably characterized by multi-power supply or multi-drop power receiving, and is more economical and flexible than a two-terminal direct-current transmission system when a plurality of power supply areas supply power to a plurality of load centers on one power transmission corridor.
The metal return operation mode of the direct current transmission system is a single-pole operation mode in which one pole is taken out of operation and the transmission line of the other pole is taken as a current return path between neutral points of the converter stations, and a line connecting the neutral points of the converter stations is called a metal return. Compared with a conventional two-end direct-current transmission system, a topological structure of a metal return line operation mode of the parallel multi-end direct-current transmission system is more complex, a metal return line is divided into different line sections by a converter station, and a conventional direct-current protection and fault clearing method for metal return line fault configuration is not completely applicable any more.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method for realizing the metal longitudinal differential protection of a parallel multi-terminal direct-current power transmission system, which optimizes the configuration scheme of the original metal return longitudinal differential protection and is suitable for the parallel multi-terminal direct-current power transmission system.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method for realizing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system is provided, the parallel multi-terminal direct current transmission system is provided with
At least comprises the following steps:
the first converter station is positioned in a first area and used for converting alternating current of a three-phase alternating current power grid in the first area into direct current and transmitting the converted direct current out through a direct current transmission line connected with the first converter station;
a second converter station located in the second area and used for converting the direct current input by the direct current transmission line connected with the second converter station into alternating current
Galvanically and inputting the converted alternating current into an alternating current grid of the second area;
the third converter station is positioned in a third area and connected with the first converter station and the second converter station in parallel through a direct current transmission line, and is used for switching to a rectification operation mode when receiving a rectification operation instruction, converting alternating current of a three-phase alternating current power grid in the third area into direct current after the third converter station is put into operation, and transmitting the converted direct current out through the direct current transmission line connected with the third converter station; switching to an inversion operation mode when an inversion operation instruction is received, converting direct current input by a direct current transmission line connected with the inverter into alternating current after the inverter is put into operation, and inputting the converted alternating current into an alternating current power grid of the third area;
the first converter station, the second converter station and the third converter station are all provided with a metal return longitudinal differential protection device, the third converter station is also provided with a metal return fault line selection device, and the third converter station also has a bus bar area and is provided with a quick isolating switch;
the method comprises the following steps:
the metal return wire longitudinal difference protection device of the converter station triggers corresponding protection actions according to the current of the opposite-pole direct current line of the current station and the current of the opposite-pole direct current line of the opposite station;
and the metal return line fault line selection device judges the type of the metal return line fault according to the protection action and adopts a corresponding fault clearing strategy.
The method for implementing metal longitudinal differential protection of the parallel multi-terminal dc transmission system further includes that the metal return longitudinal differential protection device of the first converter station adopts the following criteria:
when the third converter station operates, the protection of the metallic return line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ；
when the third converter station exits, the protection of the full length of the metal return line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the metal return line 1 is a metal return line between the first converter station and the third converter station, the metal return line 1 and the full-length protection criterion of the line cannot be opened simultaneously, and the criterion meets the post-protection action.
The method for implementing metal longitudinal differential protection of the parallel multi-terminal dc transmission system further includes that the metal return longitudinal differential protection device of the third converter station adopts the following criteria:
when the first converter station and the third converter station operate simultaneously, the protection of the metallic return line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ
when the third converter station and the second converter station operate simultaneously, the protection of the metallic return line 2 is open, and the criterion is as follows:
|IdL_op_SC–IdL3_op|>Δ
the metal loop line 1 is a metal loop between the first converter station and the third converter station, the metal loop line 2 is a metal loop between the second converter station and the third converter station, the protection criteria of the metal loop line 1 and the protection criteria of the metal loop line 2 may be simultaneously opened, and any criterion satisfies the post-protection action.
The method for implementing metal longitudinal differential protection of the parallel multi-terminal dc transmission system further includes that the metal return longitudinal differential protection device of the second converter station adopts the following criteria:
when the third converter station operates, the protection of the metallic return line 2 is opened, and the criterion is as follows:
|IdL_op_SC–IdL3_op|>Δ；
when the third converter station exits, the protection of the full length of the metal return line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the metal return line 2 and the full-length protection criterion of the line cannot be opened at the same time, and the criterion meets the post-protection action.
In the method for implementing metal longitudinal differential protection of the parallel multi-terminal direct current transmission system, further, the protection action result of each converter station is divided into two sections, and the action delay and the action strategy of each section are respectively as follows:
the first stage action delay is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is met for the second time within 10 s;
the second stage action delay is 1000ms, and the action strategy is as follows: and (4) line fault locking.
The method for implementing metal longitudinal differential protection of the parallel multi-terminal direct-current transmission system further includes that the metal return line fault line selection device adopts the following logic:
and identifying the fault position of the metal return line fault according to the longitudinal differential protection action result of the metal return line of the third converter station:
when the protection action of the metal return line 1 exits, judging that the metal return line 1 has a fault;
when the protection action of the metallic return line 2 exits, the metallic return line 2 is judged to be in fault.
The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system further includes:
1) after receiving a line fault locking action signal, judging whether the system operates at two ends, and if the system operates at two ends, turning to the step 8); if the operation is not two-end operation, turning to step 2)
2) Judging whether the fault of the metal return line 1 exists or not, and turning to the step 3) if the fault of the metal return line 1 exists; if not, turning to step 5);
3) judging whether the first converter station is the only type converter station, if so, turning to the step 8); if not, turning to the step 4);
4) and locking the first converter station, simultaneously executing phase shift restarting once, pulling open a bipolar quick isolating switch HSS1 of the third converter station after the current is reduced, isolating the fault line from the first converter station, and finally automatically restarting the third converter station and the second converter station to realize the continuous operation of the system.
5) Judging whether the fault of the metal return line 2 exists or not, and turning to the step 6) if the fault of the metal return line 2 exists; if not, go to step 8);
6) judging whether the second converter station is the only type converter station, if so, turning to the step 8); if the station is not the only type of converter station, switching to step 7);
7) and locking the second converter station, simultaneously executing phase shift restarting once, pulling open a bipolar quick isolating switch HSS3 of the third converter station after the current is reduced, isolating the fault line from the second converter station, and finally automatically restarting the first converter station and the third converter station to realize the continuous operation of the system.
8) And locking all converter stations of the station, and stopping the system.
According to the method for realizing the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system, further, when the metal return longitudinal differential protection of each converter station calculates the differential current, the current of the station needs to be subjected to delay processing, and the delay time is the communication transmission time between stations.
In the method for implementing the metal longitudinal differential protection of the parallel multi-terminal direct-current transmission system, further, the metal return longitudinal differential protection device and the metal return fault line selection device may adopt an embedded industrial control platform or a PC device.
Compared with the prior art, the invention has the beneficial effects that: 1. different fault clearing strategies are configured according to different operation modes and fault positions of the system, all the current converter stations are prevented from being locked when the metal return line is locked due to faults, and the current transmission power level is maintained; 2. the method comprises the following steps that metal return wire longitudinal differential protection is configured on each converter station, and the protection range is determined, so that the protection can be suitable for a multi-terminal direct current transmission system; 3. the fault line selection function of the metal return line is configured, so that the fault position can be determined after the fault, and the fault clearing strategy can be conveniently selected.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic diagram of a three-terminal dc power transmission system in which station B operates in a rectification mode.
Fig. 2 is a schematic diagram of a three-terminal dc transmission system in which station B operates in an inverter mode.
Fig. 3 is a schematic diagram of a fault clearing strategy when a three-terminal dc power transmission system metallic return line is locked due to a fault.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Example (b):
it should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise. Furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, as they may be fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
It is to be understood that the present embodiment refers to station a, station B and station C as the first converter station, the third converter station and the second converter station, respectively; in addition, some technical terms in the present invention are introduced: restarting the phase shift once: the rectifier increases the trigger angle to a set angle at a certain speed, so that the rectifier is converted into an inversion state to operate; locking: in a conventional direct-current power transmission system, a fault pole is retreated to a locked state, and a current converter is still connected with a direct-current field; line fault locking: aiming at a locking mode of line fault configuration of a parallel multi-terminal direct current transmission system, a locked converter station needs to be selected according to a system operation mode and a fault position; the only type of converter station: a single rectifying station or a single inverting station in the system.
To better understand the present invention, a simple introduction is made to the prior art scheme, the metallic return longitudinal differential protection is the main protection for detecting the metallic return line fault, and the metallic return longitudinal differential protection function configuration of the conventional dc power transmission system is as follows:
|IdL_op-IdL_op_os|>Max(IdL_op、IdL_op_os)×0.2，
stage I: delaying for 600ms, restarting the phase shift once, and locking if the phase shift is started for the second time within 10 s;
and II, section: delaying for 1000ms, and directly locking.
Wherein IdL _ op is the current of the opposite-pole DC line of the current station, and IdL _ op _ os is the current of the opposite-pole DC line of the current station.
The metal return longitudinal differential protection is only effective in the rectifier station in the metal return operation mode.
In a conventional two-end direct current transmission system, only one metal return transmission line is arranged in a metal return operation mode, and when the metal return fails to be grounded and cannot be eliminated after phase-shifting restart once, a locking instruction is sent in a protection mode, and the system is directly stopped.
The parallel multi-terminal direct current transmission system is provided with at least two or more than two metal loop transmission lines in a metal loop operation mode, and when a certain metal loop transmission line has a fault and needs to be locked, on the premise of ensuring reliable fault isolation, protection needs to be carried out to ensure that each converter station can continue to operate to the maximum extent, so that the loss of system transmission power is reduced. Therefore, the existing metal return longitudinal differential protection can not meet the requirements of the parallel multi-terminal direct-current power transmission system, and the research on a metal return longitudinal differential protection configuration scheme and a fault clearing strategy which are suitable for the parallel multi-terminal direct-current power transmission system plays an important role in improving the reliability of the system.
The invention optimizes the configuration scheme of the longitudinal differential protection of the original metal return wire, so that the method is suitable for a parallel multi-terminal direct current power transmission system; the metal return line fault position identification function is added, so that the rapid judgment and identification of the metal return line fault position of the multi-terminal direct-current power transmission system are realized; different fault clearing strategies are adopted aiming at the metal return line faults at different positions, so that the faults are cleared quickly and the transmission power of the system is maintained.
Referring to fig. 1-3, fig. 1 is a schematic diagram of a three-terminal dc power transmission system in which station B operates in a rectification mode. Fig. 2 is a schematic diagram of a three-terminal dc transmission system in which station B operates in an inverter mode. Fig. 3 is a schematic diagram of a fault clearing strategy when a three-terminal dc power transmission system metallic return line is locked due to a fault.
A method for realizing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system is characterized in that the parallel multi-terminal direct-current transmission system comprises three or more converter stations, metal return longitudinal differential protection is configured at each converter station, metal return fault line selection logic is added, and different fault clearing strategies are adopted aiming at metal return faults at different positions so as to reduce power loss when a line fault is locked.
In a parallel multi-terminal dc transmission system, the intermediate converter station can operate in both a rectification mode and an inversion mode, with a busbar zone and a fast disconnector (HSS) provided, as shown in fig. 1 and 2. The configuration schemes of the vertical differential protection of the metal return wires of the intermediate converter stations are the same, so the configuration scheme and the fault clearing strategy of the vertical differential protection of the metal return wires of the parallel three-terminal direct-current transmission system are explained.
As an alternative, in some embodiments, the metallic return longitudinal differential protection is configured at station a, and the protection range is metallic return line 1 or the full length of the metallic return line.
When the station B operates, the protection of the metal return line 1 is opened, and the criteria are as follows:
|IdL_op_SA–IdL1_op|>Δ；
when the station B exits, the protection of the full length of the metal return line is opened, and the criteria are as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the line 1 and the line full-length protection criterion cannot be opened simultaneously, and the criterion meets the post-protection action.
As an alternative, in some embodiments, the station B is configured with longitudinal metallic return protection, which is in the range of metallic return line 1 and metallic return line 2.
When the station A and the station B operate simultaneously, the protection of the metal return line 1 is opened, and the criteria are as follows:
|IdL_op_SA–IdL1_op|>Δ
when the station B and the station C operate simultaneously, the protection of the metal return line 2 is opened, and the criteria are as follows:
|IdL_op_SC–IdL3_op|>Δ
the line 1 and line 2 protection criteria may be open at the same time, either criterion satisfying the post-protection action.
As an alternative, in some embodiments, the metallic return longitudinal protection is configured at station C, and the protection range is metallic return line 2 or the full length of the metallic return line.
When the station B operates, the protection of the metal return line 2 is opened, and the criteria are as follows:
|IdL_op_SC–IdL3_op|>Δ；
when the station B exits, the protection of the full length of the metal return line is opened, and the criteria are as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the line 2 and the line full-length protection criterion cannot be opened simultaneously, and the criterion meets the post-protection action.
As an optional implementation manner, in some embodiments, each converter station acquires current on a metallic return line of another converter station through inter-station communication, and data transmission through inter-station communication needs a certain time, so that when longitudinal difference protection of the metallic return line of each converter station calculates a difference stream, current of the station needs to be delayed, and the delay time is inter-station communication transmission time.
As an optional implementation manner, in some embodiments, the protection action result of each station is divided into two segments, and the action delay and the action policy of each segment are respectively:
the first stage action delay is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is met for the second time within 10 s;
the second stage action delay is 1000ms, and the action strategy is as follows: and (4) line fault locking.
As an alternative implementation, in some embodiments, metal loop fault line selection logic is added. Whether the protected line has a ground fault or not can be judged through the protection action result, and the fault line selection function is only configured at the intermediate station because the protection ranges of the metal return line longitudinal differential protection of the station A and the station C can be changed along with the operation condition of the system.
According to the longitudinal differential protection action result of the metal return wire of the station B, the fault position identification of the line fault of the metal return wire can be realized:
when the protection action of the metal return line 1 exits, judging that the metal return line 1 has a fault;
when the protection action of the metallic return line 2 exits, the metallic return line 2 is judged to be in fault.
As an optional implementation manner, in some embodiments, after receiving the line fault lockout action signal, different fault clearing strategies are adopted for the metal return line faults at different positions to reduce power loss when the line fault is locked out, and the specific strategies are as follows:
1) after receiving a line fault locking action signal, judging whether the system operates at two ends, and if the system operates at two ends, turning to the step 8); if the operation is not two-end operation, turning to step 2)
2) Judging whether the fault of the metal return line 1 exists or not, and turning to the step 3) if the fault of the metal return line 1 exists; if not, turning to step 5);
3) judging whether the station A is the only type converter station or not, and if so, turning to the step 8); if not, turning to the step 4);
4) and locking the station A, simultaneously executing phase shift restarting once, pulling out a bipolar quick isolating switch HSS1 of the station B after the current is reduced, isolating the fault line from the station A, and finally automatically restarting the station B and the station C to realize the continuous operation of the system.
5) Judging whether the fault of the metal return line 2 exists or not, and turning to the step 6) if the fault of the metal return line 2 exists; if not, go to step 8);
6) judging whether the station C is the only type converter station, if so, turning to the step 8); if the station is not the only type of converter station, switching to step 7);
7) and locking the station C, simultaneously executing phase shift restarting once, pulling out a bipolar quick isolating switch HSS3 of the station B after the current is reduced, isolating the fault line from the station C, and finally automatically restarting the station A and the station B to realize the continuous operation of the system.
8) And locking all converter stations of the station, and stopping the system.
As an alternative implementation, in some embodiments, the metallic return protection configuration scheme and the fault clearing method may be implemented by an embedded industrial control platform or a PC device, which are devices commonly used in the field of dc power transmission.
Compared with the closest prior art, the invention has the technical advantages that:
the metal return wire longitudinal differential protection of the conventional two-end direct current transmission system is only configured at a rectifying station, a unique metal return wire line is protected, two stations are directly locked when the metal return wire is locked due to faults, and the system is shut down.
The topological structure of the operation mode of the metal return wire of the parallel multi-terminal direct-current transmission system is more complex, and the conventional metal return wire fault clearing method is not completely applicable any more. According to the invention, the metal return wire longitudinal differential protection is respectively configured at each converter station, and the protection range is determined, so that the protection can be suitable for a multi-terminal direct current transmission system; a line metal return line fault line selection function is configured, and a fault position can be determined after a fault; different fault clearing strategies are configured according to different operation modes and fault positions of the system, all the current converter stations are prevented from being locked when the metal return line is locked due to faults, and the current transmitted power level is maintained.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.
Claims (9)
1. A method for realizing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system is provided, wherein the parallel multi-terminal direct current transmission system at least comprises:
the first converter station is positioned in a first area and used for converting alternating current of a three-phase alternating current power grid in the first area into direct current and transmitting the converted direct current out through a direct current transmission line connected with the first converter station;
the second converter station is positioned in a second area and used for converting direct current input by the direct current transmission line connected with the second converter station into alternating current and inputting the converted alternating current into an alternating current power grid of the second area;
the third converter station is positioned in a third area and connected with the first converter station and the second converter station in parallel through a direct current transmission line, and is used for switching to a rectification operation mode when receiving a rectification operation instruction, converting alternating current of a three-phase alternating current power grid in the third area into direct current after the third converter station is put into operation, and transmitting the converted direct current out through the direct current transmission line connected with the third converter station; switching to an inversion operation mode when an inversion operation instruction is received, converting direct current input by a direct current transmission line connected with the inverter into alternating current after the inverter is put into operation, and inputting the converted alternating current into an alternating current power grid of the third area;
the method is characterized in that the first converter station, the second converter station and the third converter station are all provided with a metal return longitudinal differential protection device, the third converter station is also provided with a metal return fault line selection device, and the third converter station also has a bus bar area and is provided with a quick isolating switch;
the method comprises the following steps:
the metal return wire longitudinal difference protection device of the converter station triggers corresponding protection actions according to the current of the opposite-pole direct current line of the current station and the current of the opposite-pole direct current line of the opposite station;
and the metal return line fault line selection device judges the type of the metal return line fault according to the protection action and adopts a corresponding fault clearing strategy.
2. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system according to claim 1, wherein the metal return longitudinal differential protection device of the first converter station adopts the following criteria:
when the third converter station operates, the protection of the metallic return line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ；
when the third converter station exits, the protection of the full length of the metal return line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the metal return line 1 is a metal return line between the first converter station and the third converter station, the metal return line 1 and the full-length protection criterion of the line cannot be opened simultaneously, and the criterion meets the post-protection action.
3. The method according to claim 1, wherein the metal longitudinal differential protection device of the third converter station adopts the following criteria:
when the first converter station and the third converter station operate simultaneously, the protection of the metallic return line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ
when the third converter station and the second converter station operate simultaneously, the protection of the metallic return line 2 is open, and the criterion is as follows:
|IdL_op_SC–IdL3_op|>Δ
the metal loop line 1 is a metal loop between the first converter station and the third converter station, the metal loop line 2 is a metal loop between the second converter station and the third converter station, the protection criteria of the metal loop line 1 and the protection criteria of the metal loop line 2 may be simultaneously opened, and any criterion satisfies the post-protection action.
4. The method according to claim 1, wherein the metal longitudinal differential protection device of the second converter station adopts the following criteria:
when the third converter station operates, the protection of the metallic return line 2 is opened, and the criterion is as follows:
|IdL_op_SC–IdL3_op|>Δ；
when the third converter station exits, the protection of the full length of the metal return line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the metal return line 2 and the full-length protection criterion of the line cannot be opened at the same time, and the criterion meets the post-protection action.
5. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system according to claim 1, wherein the protection action result of each converter station is divided into two segments, and the action delay and the action strategy of each segment are respectively as follows:
the first stage action delay is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is met for the second time within 10 s;
the second stage action delay is 1000ms, and the action strategy is as follows: and (4) line fault locking.
6. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system according to claim 1, wherein the metal return fault line selection device adopts the following logic:
and identifying the fault position of the metal return line fault according to the longitudinal differential protection action result of the metal return line of the third converter station:
when the protection action of the metal return line 1 exits, judging that the metal return line 1 has a fault;
when the protection action of the metallic return line 2 exits, the metallic return line 2 is judged to be in fault.
7. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct-current transmission system according to claim 1, wherein the fault clearing strategy comprises:
1) after receiving a line fault locking action signal, judging whether the system operates at two ends, and if the system operates at two ends, turning to the step 8); if the operation is not two-end operation, turning to step 2)
2) Judging whether the fault of the metal return line 1 exists or not, and turning to the step 3) if the fault of the metal return line 1 exists; if not, turning to step 5);
3) judging whether the first converter station is the only type converter station, if so, turning to the step 8); if not, turning to the step 4);
4) and locking the first converter station, simultaneously executing phase shift restarting once, pulling open a bipolar quick isolating switch HSS1 of the third converter station after the current is reduced, isolating the fault line from the first converter station, and finally automatically restarting the third converter station and the second converter station to realize the continuous operation of the system.
5) Judging whether the fault of the metal return line 2 exists or not, and turning to the step 6) if the fault of the metal return line 2 exists; if not, go to step 8);
6) judging whether the second converter station is the only type converter station, if so, turning to the step 8); if the station is not the only type of converter station, switching to step 7);
7) and locking the second converter station, simultaneously executing phase shift restarting once, pulling open a bipolar quick isolating switch HSS3 of the third converter station after the current is reduced, isolating the fault line from the second converter station, and finally automatically restarting the first converter station and the third converter station to realize the continuous operation of the system.
8) And locking all converter stations of the station, and stopping the system.
8. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system according to any one of claims 1 to 7, wherein when the metal longitudinal differential protection of each converter station metal loop is used for calculating a differential current, the current of the station needs to be delayed, and the delay time is the communication transmission time between stations.
9. The method for implementing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system according to any one of claims 1 to 7, wherein the metal loop longitudinal differential protection device and the metal loop fault line selection device can adopt an embedded industrial control platform or a PC device.
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