CN112448372B - 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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- CN112448372B CN112448372B CN202011195966.7A CN202011195966A CN112448372B CN 112448372 B CN112448372 B CN 112448372B CN 202011195966 A CN202011195966 A CN 202011195966A CN 112448372 B CN112448372 B CN 112448372B
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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]
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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 metal loop longitudinal differential protection device is arranged in each of a first converter station, a second converter station and a third converter station, a metal loop fault line selection device is also arranged in each of the third converter stations, and a bus area is also arranged in each of the third converter stations and is provided with a quick isolating switch; the method comprises the following steps: the metal loop longitudinal differential protection device of the converter station triggers corresponding protection actions according to the current of the opposite pole direct current line of the station and the current of the opposite pole direct current line of the station; the metal loop fault line selection device judges the type of the metal loop 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 refers to a direct current transmission system of three or more converter stations, and is characterized in that multiple power supplies or multiple drop points are powered, and when multiple power supply areas are arranged on one transmission corridor to supply power to multiple load centers, the parallel multi-terminal direct current transmission system is more economical and flexible than the direct current transmission system at two ends.
The metal loop operation mode of the direct current transmission system refers to a monopole operation mode that one pole exits operation and the other pole uses the transmission line 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 loop. Compared with the conventional two-end direct current transmission system, the topological structure of the metal loop running mode of the parallel multi-end direct current transmission system is more complex, the metal loop line is divided into different line sections by the converter station, and the conventional protection and fault clearing method for the fault configuration of the metal loop by direct current is not fully 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 transmission system, which optimizes the configuration scheme of the original metal loop longitudinal differential protection and is suitable for the parallel multi-terminal direct current transmission system.
In order to achieve the above 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 comprises the following steps of
At least comprises:
the first convertor station is positioned in the first area and is 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 convertor station;
a second converter station in the second area for converting the direct current input by the direct current transmission line connected with the second converter station into alternating current
A step of supplying a converted ac power to an ac power grid of the second region;
the third converter station is positioned in a third area, is connected with the first converter station and the second converter station in parallel through a direct current transmission line, is used for switching to a rectification operation mode when receiving a rectification operation instruction, converts alternating current of a three-phase alternating current power grid in the third area into direct current after the third area is put into operation, and transmits the converted direct current through the direct current transmission line connected with the third area; switching to an inversion operation mode when receiving an inversion operation instruction, converting direct current input by a direct current transmission line connected with the inverter into alternating current after the inverter operation instruction 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 respectively provided with a metal loop longitudinal differential protection device, the third converter station is also provided with a metal loop fault line selection device, and the third converter station is also provided with a bus bar area and a quick isolating switch;
the method comprises the following steps:
the metal loop longitudinal differential protection device of the converter station triggers corresponding protection actions according to the current of the opposite pole direct current line of the station and the current of the opposite pole direct current line of the station;
the metal loop fault line selection device judges the type of the metal loop fault according to the protection action and adopts a corresponding fault clearing strategy.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the following steps:
when the third converter station operates, the protection of the metal loop line 1 is opened, and the criterion is that:
|IdL_op_SA–IdL1_op|>Δ；
when the third converter station exits, the protection of the whole length of the metal loop line is opened, and the criterion is that:
|IdL_op_SA–IdL_op_SC|>Δ
the metal loop line 1 is a metal loop between the first converter station and the third converter station, and the metal loop line 1 and the full-length protection criterion of the line cannot be opened at the same time, and the criterion meets the post-protection action.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the following steps:
when the first converter station and the third converter station are operated simultaneously, the protection of the metal loop line 1 is opened, and the criterion is that:
|IdL_op_SA–IdL1_op|>Δ
when the third converter station and the second converter station are operated simultaneously, the protection of the metal loop line 2 is opened, and the criterion is that:
|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, and protection criteria of the metal loop line 1 and the metal loop line 2 may be simultaneously opened, and any criterion satisfies a post-protection action.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the following steps:
when the third converter station operates, the protection of the metal loop line 2 is opened, and the criterion is:
|IdL_op_SC–IdL3_op|>Δ；
when the third converter station exits, the protection of the whole length of the metal loop line is opened, and the criterion is that:
|IdL_op_SA–IdL_op_SC|>Δ
the metal loop 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.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the steps that the protection action result of each converter station is divided into two sections, and the action delay and action strategies of each section are respectively as follows:
the action delay of the first section is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is satisfied for the second time within 10 seconds;
the action delay of the second section is 1000ms, and the action strategy is as follows: line fault blocking.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the following steps:
according to the longitudinal differential protection action result of the metal loop of the third converter station, identifying the fault position of the metal loop line fault:
when the protection action of the metal loop line 1 is exported, judging that the metal loop line 1 fails;
when the protection action of the metal return line 2 is exported, the metal return line 2 is judged to be faulty.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the following steps:
1) After receiving the line fault locking action signal, judging whether the system runs at two ends, if so, turning to the step 8); if the operation is not the two-end operation, the step 2 is switched to
2) Judging whether the metal loop line 1 is faulty or not, if yes, turning to the step 3); if not, turning to step 5);
3) Judging whether the first converter station is the only type converter station or not, and if so, converting to the step 8); if not, turning to step 4);
4) And locking the first converter station, simultaneously executing phase shifting restart once, pulling a bipolar quick disconnecting switch HSS1 of the third converter station after the current is reduced, isolating a fault line from the first converter station, and finally automatically restarting the third converter station and the second converter station to realize continuous operation of the system.
5) Judging whether the fault is the fault of the metal loop line 2, if so, turning to the step 6); if not, turning to step 8);
6) Judging whether the second converter station is the only type converter station or not, and if so, converting to the step 8); if not the only type converter station, turning to step 7);
7) And locking the second converter station, simultaneously executing phase shifting restart once, pulling a bipolar quick disconnecting switch HSS3 of the third converter station after the current is reduced, isolating a fault line from the second converter station, and finally automatically restarting the first converter station and the third converter station to realize continuous operation of the system.
8) And locking all converter stations of the station, and stopping the system.
According to the implementation method of the parallel multi-terminal direct current transmission system metal longitudinal differential protection, when the differential current is calculated by the metal loop longitudinal differential protection of each converter station, the current of the current station needs to be subjected to delay treatment, and the delay time is the inter-station communication transmission time.
The implementation method of the metal longitudinal differential protection of the parallel multi-terminal direct current transmission system further comprises the step that 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.
Compared with the prior art, the invention has the beneficial effects that: 1. different fault clearing strategies are configured according to different system operation modes and fault positions, so that all current transmission power levels are maintained when the metal loop is blocked due to faults; 2. the metal loop 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; 3. the fault line selection function of the metal loop line is configured, the fault position can be determined after the fault, and the fault clearing strategy is convenient to select.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following description will briefly explain the drawings needed in the embodiments, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a three-terminal dc power transmission system in which station B operates in a rectifying mode.
Fig. 2 is a schematic diagram of a three-terminal dc power transmission system in which station B operates in an inverter mode.
Fig. 3 is a schematic diagram of a fault clearing strategy when a metal loop of the three-terminal direct current transmission system is blocked.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.
Examples:
it should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations 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 or inherent to such process, method, article, or apparatus.
In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise. Furthermore, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
It should be understood that, in this embodiment, the first converter station, the third converter station, and the second converter station are denoted by the station a, the station B, and the station C, respectively; furthermore, some technical terms in the present invention are described: phase shift restarting once: the rectifier increases the triggering 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 transmission system, a fault pole is retreated to a locking state, and a converter is still connected with a direct current field; line fault blocking: the invention aims at a locking mode of line fault configuration of a parallel multi-terminal direct current transmission system, and a locked converter station is required to be selected according to the system operation mode and the fault position; unique type of converter station: a unique rectifying station or a unique inverting station in the system.
In order to better understand the invention, the prior art scheme is simply introduced, the metal loop longitudinal differential protection is the main protection for detecting the fault of the metal loop line, and the metal loop longitudinal differential protection function of the conventional direct current transmission system is configured as follows:
|IdL_op-IdL_op_os|>Max(IdL_op、IdL_op_os)×0.2，
i section: delaying for 600ms, restarting the phase shift once, and locking if the phase shift is performed for the second time within 10 s;
II section: delay 1000ms, and directly lock.
Where IdL _op is the local counter-electrode direct current and IdL _op_os is the counter-electrode direct current.
The metal loop longitudinal differential protection is only effective in the rectifying station in the metal loop mode of operation.
Under the metal loop running mode, the conventional two-end direct current transmission system only has one metal loop transmission line, and when the metal loop has a ground fault and cannot eliminate the fault once in phase shifting restarting, a locking instruction is protected, and the system is directly stopped.
The parallel multi-terminal direct current transmission system is provided with at least two or more metal loop transmission lines in a metal loop operation mode, when a certain metal loop transmission line fails and needs to be locked, on the premise of ensuring reliable fault isolation, the protection needs to ensure that each converter station can continue to operate to the greatest extent, so that the loss of the transmission power of the system is reduced. Therefore, the existing metal loop longitudinal differential protection cannot meet the requirements of the parallel multi-terminal direct current transmission system, and research on a metal loop longitudinal differential protection configuration scheme and a fault clearing strategy suitable for the parallel multi-terminal direct current 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 loop, so that the method is suitable for a parallel multi-terminal direct current transmission system; the metal loop fault position identification function is added, so that the rapid identification and recognition of the metal loop fault position of the multi-terminal direct current transmission system are realized; different fault clearing strategies are adopted aiming at metal loop faults at different positions, so that the faults are cleared rapidly 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 rectifying mode. Fig. 2 is a schematic diagram of a three-terminal dc power transmission system in which station B operates in an inverter mode. Fig. 3 is a schematic diagram of a fault clearing strategy when a metal loop of the three-terminal direct current transmission system is blocked.
A method for realizing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system comprises three or more converter stations, wherein each converter station is provided with metal loop longitudinal differential protection, metal loop fault line selection logic is increased, and different fault clearing strategies are adopted for metal loop faults at different positions so as to reduce power loss during line fault locking.
In a parallel multi-terminal dc power transmission system, the intermediate converter station may operate in either a rectifying mode or an inverting mode, with a bus bar area and with a fast disconnector (HSS) as shown in fig. 1 and 2. The configuration schemes of the metal loop longitudinal differential protection of the intermediate converter stations are the same, so that the configuration scheme of the metal loop longitudinal differential protection of the parallel three-terminal direct current transmission system and the fault clearing strategy are used for description.
As an alternative embodiment, in some embodiments, the station a is configured with a metal loop longitudinal differential protection, where the protection range is the metal loop line 1 or the full length of the metal loop line.
When the station B operates, the protection of the metal loop line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ；
when the station B exits, the protection of the whole length of the metal loop line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the line 1 and the full-length protection criterion of the line cannot be opened at the same time, and the criterion meets the post-protection action.
As an alternative embodiment, in some embodiments, a metal loop longitudinal differential protection is configured at station B, with the protection range being metal loop line 1 and metal loop line 2.
When the station A and the station B operate simultaneously, the protection of the metal loop line 1 is opened, and the criterion is as follows:
|IdL_op_SA–IdL1_op|>Δ
when the station B and the station C operate simultaneously, the protection of the metal loop line 2 is opened, and the criterion is that:
|IdL_op_SC–IdL3_op|>Δ
the protection criteria of the line 1 and the line 2 may be simultaneously opened, and any criterion satisfies the post-protection action.
As an alternative embodiment, in some embodiments, the station C is configured with a metal loop longitudinal differential protection, where the protection range is the metal loop line 2 or the full length of the metal loop line.
When the station B operates, the protection of the metal loop line 2 is opened, and the criterion is:
|IdL_op_SC–IdL3_op|>Δ；
when the station B exits, the protection of the whole length of the metal loop line is opened, and the criterion is as follows:
|IdL_op_SA–IdL_op_SC|>Δ
the line 2 and the full-length protection criterion of the line are not opened at the same time, and the criterion meets the post-protection action.
As an alternative implementation manner, in some embodiments, each converter station collects the current on the metal loop line of other converter stations through inter-station communication, and a certain time is required for inter-station communication data transmission, so that when the differential current is calculated by each converter station metal loop longitudinal differential protection, the current of the current station needs to be delayed, and the delay time is the inter-station communication transmission time.
As an alternative implementation manner, in some embodiments, the protection action result of each station is divided into two sections, and the action delay and action policy of each section are respectively:
the action delay of the first section is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is satisfied for the second time within 10 seconds;
the action delay of the second section is 1000ms, and the action strategy is as follows: line fault blocking.
As an alternative implementation, in some embodiments, metal loop fault line selection logic is added. The protection action result can be used for judging whether the protected line has a ground fault or not, and the protection range of the longitudinal differential protection of the metal loop of the station A and the station C can be changed along with the operation working condition of the system, so that the fault line selection function is only configured in the intermediate station.
According to the station B metal loop longitudinal differential protection action result, the fault position identification of the metal loop line fault can be realized:
when the protection action of the metal loop line 1 is exported, judging that the metal loop line 1 fails;
when the protection action of the metal return line 2 is exported, the metal return line 2 is judged to be faulty.
As an optional implementation manner, in some embodiments, after receiving the line fault blocking action signal, different fault clearing strategies are adopted for metal loop faults at different positions so as to reduce power loss during line fault blocking, and specific strategies are as follows:
1) After receiving the line fault locking action signal, judging whether the system runs at two ends, if so, turning to the step 8); if the operation is not the two-end operation, the step 2 is switched to
2) Judging whether the metal loop line 1 is faulty or not, if yes, turning to the step 3); if not, turning to step 5);
3) Judging whether the station A is a unique type converter station or not, and if so, converting to the step 8); if not, turning to step 4);
4) And (3) locking the station A, simultaneously executing phase shifting restarting once, pulling out a bipolar fast disconnecting switch HSS1 of the station B after the current is reduced, isolating a fault line from the station A, and finally automatically restarting the station B and the station C to realize continuous operation of the system.
5) Judging whether the fault is the fault of the metal loop line 2, if so, turning to the step 6); if not, turning to step 8);
6) Judging whether the station C is a unique type converter station or not, and if so, converting to the step 8); if not the only type converter station, turning to step 7);
7) And (3) locking the station C, simultaneously performing phase shifting restarting once, pulling out a bipolar fast disconnecting switch HSS3 of the station B after the current is reduced, isolating a fault line from the station C, and finally automatically restarting the station A and the station B to realize 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 metal loop protection configuration scheme and the fault clearing method may be implemented by an embedded industrial control platform or a PC device, where the two devices are devices commonly used in the dc power transmission field.
Compared with the closest prior art, the invention has the technical advantages that:
the metal loop longitudinal differential protection of the conventional two-end direct current transmission system is only configured in the rectifying station, a unique metal loop line is protected, two stations are directly locked when the metal loop faults are locked, and the system is stopped.
The topological structure of the metal loop running mode of the parallel multi-terminal direct current transmission system is more complex, and the conventional metal loop fault clearing method is not fully applicable any more. According to the invention, the metal loop 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; the fault line selection function of the line metal loop line is configured, and the fault position can be determined after the fault; different fault clearing strategies are configured according to different system operation modes and fault positions, all the current power level is maintained when the metal loop is blocked due to faults, and the blocking of the current power level is prevented.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means 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 present invention. In this specification, schematic representations of the above terms are not necessarily directed 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, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the essence of the present invention are intended to be included within the scope of the present invention.
Claims (9)
1. A method for realizing metal longitudinal differential protection of a parallel multi-terminal direct current transmission system comprises the following steps:
the first convertor station is positioned in the first area and is 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 convertor station;
the second converter station is positioned in the second area and is used for converting direct current input by a 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, is connected with the first converter station and the second converter station in parallel through a direct current transmission line, is used for switching to a rectification operation mode when receiving a rectification operation instruction, converts alternating current of a three-phase alternating current power grid in the third area into direct current after the third area is put into operation, and transmits the converted direct current through the direct current transmission line connected with the third area; switching to an inversion operation mode when receiving an inversion operation instruction, converting direct current input by a direct current transmission line connected with the inverter into alternating current after the inverter operation instruction is put into operation, and inputting the converted alternating current into an alternating current power grid of the third area;
the device is characterized in that the first converter station, the second converter station and the third converter station are respectively provided with a metal loop longitudinal differential protection device, the third converter station is also provided with a metal loop fault line selection device, and the third converter station is also provided with a bus bar area and a quick isolating switch;
the method comprises the following steps:
the metal loop longitudinal differential protection device of the converter station triggers corresponding protection actions according to the current of the opposite pole direct current line of the station and the current of the opposite pole direct current line of the station;
the metal loop fault line selection device judges the type of the metal loop fault according to the protection action and adopts a corresponding fault clearing strategy.
2. The method for implementing metal longitudinal differential protection of parallel multi-terminal direct current transmission system according to claim 1, wherein the metal loop longitudinal differential protection device of the first converter station adopts the following criteria:
when the third converter station operates, the protection of the metal loop line 1 is opened, and the criterion is that:
| IdL_op_SA – IdL1_op | >Δ；
when the third converter station exits, the protection of the whole length of the metal loop line is opened, and the criterion is that:
| IdL_op_SA – IdL_op_SC |>Δ
the IdL _op_SA is the antipodal direct current line current of the first converter station, idL1_op is the antipodal direct current line current of the metal loop line 1, delta is a protection action fixed value, and IdL _op_SC is the antipodal direct current line current of the third converter station; the metal loop line 1 is a metal loop between the first converter station and the third converter station, and the metal loop line 1 and the full-length protection criterion of the line cannot be opened at the same time, and the criterion meets the post-protection action.
3. The method for implementing metal longitudinal differential protection of parallel multi-terminal direct current transmission system according to claim 1, wherein the metal loop longitudinal differential protection device of the third converter station adopts the following criteria:
when the first converter station and the third converter station are operated simultaneously, the protection of the metal loop line 1 is opened, and the criterion is that:
| IdL_op_SA – IdL1_op | >Δ
when the third converter station and the second converter station are operated simultaneously, the protection of the metal loop line 2 is opened, and the criterion is that:
| IdL_op_SC – IdL3_op | >Δ
wherein IdL _op_SA is the antipodal direct current line current of the first converter station, idL1_op is the antipodal direct current line current of the metal loop line 1, delta is a protection action fixed value, idL _op_SC is the antipodal direct current line current of the third converter station, idL3_op is the antipodal direct current line current of the metal loop line 3; 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, and protection criteria of the metal loop line 1 and the metal loop line 2 may be simultaneously opened, and any criterion satisfies the post-protection action.
4. The method for implementing metal longitudinal differential protection of parallel multi-terminal direct current transmission system according to claim 1, wherein the metal loop longitudinal differential protection device of the second converter station adopts the following criteria:
when the third converter station operates, the protection of the metal loop line 2 is opened, and the criterion is:
| IdL_op_SC – IdL3_op | >Δ；
when the third converter station exits, the protection of the whole length of the metal loop line is opened, and the criterion is that:
| IdL_op_SA – IdL_op_SC |>Δ
wherein IdL _op_sc is the antipodal dc link current of the third converter station; idL3_op is the opposite direct current of the metal loop line 3; delta is a protection action fixed value; idL _op_SA is the epipolar direct current of the first converter station; the metal loop line 2 and the full-length protection criterion of the line are not opened at the same time, and the criterion meets the post-protection action.
5. The method for realizing metal longitudinal differential protection of the parallel multi-terminal direct current transmission system according to claim 1, wherein the protection action result of each converter station is divided into two sections, and the action delay and action strategies of each section are respectively as follows:
the action delay of the first section is 600ms, and the action strategy is as follows: restarting the phase shift once, and locking the line fault if the phase shift is satisfied for the second time within 10 seconds;
the action delay of the second section is 1000ms, and the action strategy is as follows: line fault blocking.
6. The method for implementing metal longitudinal differential protection of parallel multi-terminal direct current transmission system according to claim 1, wherein the metal loop fault line selection device adopts the following logic:
according to the longitudinal differential protection action result of the metal loop of the third converter station, identifying the fault position of the metal loop line fault:
when the protection action of the metal loop line 1 is exported, judging that the metal loop line 1 fails;
when the protection action of the metal return line 2 is exported, the metal return line 2 is judged to be faulty.
7. The method for implementing metal longitudinal differential protection of a parallel multi-terminal dc power transmission system according to claim 1, wherein the fault clearing strategy comprises:
1) After receiving the line fault locking action signal, judging whether the system runs at two ends, if so, turning to the step 8); if the two ends are not operated, turning to the step 2);
2) Judging whether the metal loop line 1 is faulty or not, if yes, turning to the step 3); if not, turning to step 5);
3) Judging whether the first converter station is the only type converter station or not, and if so, converting to the step 8); if not, turning to step 4);
4) The first converter station is locked, phase shifting restarting is carried out once at the same time, a bipolar quick disconnecting switch HSS1 of the third converter station is pulled open after current is reduced, a fault line and the first converter station are isolated, and finally the third converter station and the second converter station are automatically restarted, so that the continuous operation of the system is realized;
5) Judging whether the fault is the fault of the metal loop line 2, if so, turning to the step 6); if not, turning to step 8);
6) Judging whether the second converter station is the only type converter station or not, and if so, converting to the step 8); if not the only type converter station, turning to step 7);
7) Blocking the second converter station, simultaneously executing phase shifting restart once, pulling a bipolar rapid disconnecting switch HSS3 of the third converter station after current is reduced, isolating a fault line and the second converter station, and finally automatically restarting the first converter station and the third converter station to realize continuous operation of the system;
8) And locking all converter stations at the operation station, and stopping the system.
8. The method for implementing metal longitudinal differential protection of parallel multi-terminal dc power transmission system according to any one of claims 1 to 7, wherein when calculating differential current, the current of the current station needs to be delayed, and the delay time is inter-station communication transmission time.
9. The method for implementing metal longitudinal differential protection of parallel multi-terminal dc power 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 may be embedded industrial control platforms or PC devices.
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