CN113572189A - Bipolar flexible direct current system for offshore wind power and transformer fault switching method thereof - Google Patents
Bipolar flexible direct current system for offshore wind power and transformer fault switching method thereof Download PDFInfo
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- CN113572189A CN113572189A CN202110841829.4A CN202110841829A CN113572189A CN 113572189 A CN113572189 A CN 113572189A CN 202110841829 A CN202110841829 A CN 202110841829A CN 113572189 A CN113572189 A CN 113572189A
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- 230000005540 biological transmission Effects 0.000 description 7
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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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- 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
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0073—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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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 bipolar flexible direct current system for offshore wind power and a transformer fault switching method thereof, wherein a first transformer of a positive pole converter and a second transformer of a negative pole converter of the bipolar flexible direct current system share a hot standby third transformer, and valve side switches of the first transformer and the second transformer of the bipolar flexible direct current system are connected with a valve side switch of the third transformer through a change-over switch; the redundant design of the bipolar flexible direct current system for the offshore wind power can be met, only three groups of transformers are configured, the number of the transformers is reduced, and the running loss of the transformers is reduced. The fault switching method provided by the invention comprises the following steps: the heat standby requirement of the double-pole flexible direct current system transformer for the offshore wind power can be met by adopting the double-pole asymmetric initial operation state and the double-pole asymmetric operation mode, and when any transformer fails, the fault switching can be rapidly realized, so that the double-pole flexible direct current system can recover the full-power operation.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission of a power system, in particular to a bipolar flexible direct current system for offshore wind power and a transformer fault switching method thereof.
Background
The existing projects for transmitting the flexible direct current power for the offshore wind power are both flexible direct current power transmission projects with two ends adopting symmetrical monopole structures, and the power transmission capacity is limited. With the further development of deep and distant sea wind power resources, the wind power transmission capacity demand is increased, the flexible direct current system with the symmetrical monopole structure cannot meet the power transmission requirement, and a bipolar flexible direct current system for offshore wind power needs to be adopted.
Because the offshore environment is relatively inconvenient to overhaul and maintain, in order to improve the operation reliability and the availability of offshore wind power direct current output projects, in the prior art, the single-pole systems of the offshore converter stations all require two sets of converter transformers to be in parallel connection redundancy design and mutually serve as heat standby, and the other set of transformers can operate at full direct current power by utilizing overload capacity under the condition of failure of one set of transformers. For a bipolar flexible direct current system for offshore wind power, according to the conventional redundancy design principle, two groups of transformers which are mutually standby are required to be configured on each pole, and four groups of transformers are required to be configured on the bipolar; in addition, since the standby transformer cannot be directly connected to the system in a long-term cold standby state, two sets of transformers corresponding to the positive pole need to be connected in parallel to operate in the prior art, and two sets of transformers corresponding to the negative pole need to be configured to operate in parallel.
In the prior art, a bipolar flexible direct current system for offshore wind power needs a large number of transformers, and has high total capacity and large operation loss.
Disclosure of Invention
The embodiment of the invention provides a bipolar flexible direct current system for offshore wind power and a transformer fault switching method thereof, which can reduce the number of transformers and reduce the running loss of the transformers on the premise of meeting the redundancy design of the system.
An embodiment of the present invention provides a bipolar flexible dc system for offshore wind power, including: the system comprises an alternating current bus, a positive pole converter, a negative pole converter, a first transformer, a second transformer and a third transformer;
a first end of the first transformer is connected with the alternating current bus through a first grid side switch, and a second end of the first transformer is connected with the positive converter through a first valve side switch;
a first end of the second transformer is connected with the alternating current bus through a second grid side switch, and a second end of the second transformer is connected with the negative pole converter through a second valve side switch;
the first end of the third transformer is connected with the alternating current bus through a third grid side switch, the second end of the third transformer is connected with the first end of the third valve side switch, the second end of the third valve side switch is respectively connected with the first end of the first third change-over switch and the first end of the second third change-over switch, the second end of the first third change-over switch is connected with the positive pole converter, and the second end of the second third change-over switch is connected with the negative pole converter.
Preferably, the arrangement of the first, second and third net side switches comprises a series arrangement of circuit breakers and disconnectors; the structure of the third valve side switch includes a series structure of a circuit breaker and a disconnecting switch or a circuit breaker only structure.
Preferably, the configuration of the first and second third transfer switches includes a series configuration of a circuit breaker and a disconnector or a disconnector only configuration.
Preferably, the connection form of the alternating current bus comprises a double-bus form, a double-bus section form or a half breaker form.
Preferably, the alternating current bus is used for connecting a plurality of wind power inlet groups;
the high-voltage side of the positive converter is used for connecting a positive direct-current line;
the high-voltage side of the negative pole converter is used for connecting a negative pole direct current circuit;
the low-voltage side of the positive pole converter is connected with the low-voltage side of the negative pole converter, and the low-voltage side of the positive pole converter is also used for being connected with a metal neutral line.
The embodiment of the invention also provides a transformer fault switching method of the bipolar flexible direct current system for the offshore wind power, and the method adopting the bipolar flexible direct current system for the offshore wind power provided by any one of the embodiments comprises the following steps:
closing a first network side switch, a first valve side switch, a second network side switch, a second valve side switch, a third network side switch, a third valve side switch and a first third change-over switch, switching a first transformer into a positive pole to normally operate, switching a second transformer into a negative pole to normally operate, and switching a third transformer into a hot standby state to normally operate in parallel with the first transformer;
when the second transformer has a fault, disconnecting the second grid side switch, the second valve side switch, the third valve side switch and the first third change-over switch, switching out the second transformer, and enabling the third transformer to have no load; and after the third transformer is in no-load preset time, the second third change-over switch and the third valve side switch are closed, and the third transformer is put into negative operation.
Preferably, the method further comprises:
and when the first transformer fails, the first grid side switch and the first valve side switch are disconnected, and the first transformer is switched off.
Preferably, the method further comprises:
and when the third transformer fails, the third grid side switch and the third valve side switch are disconnected, and the third transformer is switched off.
The embodiment of the invention also provides a transformer fault switching method of the bipolar flexible direct current system for the offshore wind power, and the method adopting the bipolar flexible direct current system for the offshore wind power provided by any one of the embodiments comprises the following steps:
closing the first network side switch, the first valve side switch, the second network side switch and the second valve side switch, and enabling the first transformer and the second transformer to normally operate;
closing a third network side switch, and enabling a third transformer to run in an electrified no-load mode;
when the first transformer fails, the first grid side switch and the first valve side switch are disconnected, and the first transformer is switched off; and closing the first third change-over switch and the third valve side switch, and putting the third transformer into positive operation.
Preferably, the method further comprises:
when the second transformer fails, the second grid side switch and the second valve side switch are disconnected, and the second transformer is switched off; and closing the second third change-over switch and the third valve side switch, and putting the third transformer into negative operation.
The invention provides a bipolar flexible direct current system for offshore wind power and a transformer fault switching method thereof.A first transformer of a positive pole converter and a second transformer of a negative pole converter of the bipolar flexible direct current system share a hot standby third transformer, valve side switches of the first transformer and the second transformer of the bipolar flexible direct current system are connected with a valve side switch of a third transformer through a change-over switch, and the third transformer is switched to the converter of any pole fault transformer of the bipolar flexible direct current system through the valve side switch and the change-over switch; the method can realize that only three groups of transformers are configured on the bipolar flexible direct current system for the offshore wind power, and can reduce the number of the transformers and the operation loss of the transformers on the premise of meeting the redundancy design of the system. The fault switching method provided by the invention comprises the following steps: the bipolar asymmetric initial operation state and the bipolar asymmetric operation mode are adopted, the hot standby requirement of the bipolar flexible direct current system transformer can be met, and when any transformer fails, equipment switching can be rapidly realized, so that the bipolar flexible direct current system recovers full-power operation.
Drawings
Fig. 1 is a schematic structural diagram of a bipolar flexible direct current system for offshore wind power provided by an embodiment of the invention;
fig. 2 is a schematic structural diagram of a bipolar flexible direct current system for offshore wind power according to another embodiment of the present invention;
fig. 3 is a schematic flow chart of a transformer fault switching method of a bipolar flexible direct current system for offshore wind power according to an embodiment of the present invention;
fig. 4 is a schematic flow chart of a transformer fault switching method of a bipolar flexible direct current system for offshore wind power according to another embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the 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 invention, 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 invention.
The embodiment of the invention provides a bipolar flexible direct current system for offshore wind power, which is shown in fig. 1 and is a schematic structural diagram of the bipolar flexible direct current system for offshore wind power provided by the embodiment of the invention, and the system comprises: the system comprises an alternating current bus, a positive pole converter, a negative pole converter, a first transformer, a second transformer and a third transformer;
a first end of the first transformer is connected with the alternating current bus through a first grid side switch, and a second end of the first transformer is connected with the positive converter through a first valve side switch;
a first end of the second transformer is connected with the alternating current bus through a second grid side switch, and a second end of the second transformer is connected with the negative pole converter through a second valve side switch;
the first end of the third transformer is connected with the alternating current bus through a third grid side switch, the second end of the third transformer is connected with the first end of the third valve side switch, the second end of the third valve side switch is respectively connected with the first end of the first third change-over switch and the first end of the second third change-over switch, the second end of the first third change-over switch is connected with the positive pole converter, and the second end of the second third change-over switch is connected with the negative pole converter.
In this embodiment, the system includes: the transformer comprises an alternating current bus, a positive pole converter, a negative pole converter, a first transformer T1, a second transformer T2 and a third transformer T3;
a first end of a first transformer T1 is connected with an alternating current bus through a first grid side switch K1.1, and a second end of a first transformer T1 is connected with a positive converter through a first valve side switch K1.2;
a first end of a second transformer T2 is connected with the alternating current bus through a second grid side switch K2.1, and a second end of a second transformer T2 is connected with the negative pole converter through a second valve side switch K2.2;
a first end of a third transformer T3 is connected to the ac bus through a third grid-side switch K3.1, a second end of the third transformer T3 is connected to a first end of a third valve-side switch K3.2, a second end of the third valve-side switch K3.2 is connected to a first end of a first third switch K13 and a first end of a second third switch K23, a second end of the first third switch K13 is connected to the positive inverter, and a second end of the second third switch K23 is connected to the negative inverter.
It should be noted that, when the bipolar flexible direct current system for offshore wind power uses parallel connection of multiple sets of transformers per pole, or uses a connection mode that multiple sets of transformers per pole share one set of hot standby transformer, the valve side switches of the working transformers per multiple sets of bipolar flexible direct current system for offshore wind power are connected with the valve side switch of the hot standby transformer through an isolation switch after valve side confluence, and the hot standby transformer can be switched to the current converter of any fault transformer of the bipolar flexible direct current system for offshore wind power through the isolation switch. According to the bipolar flexible direct current system for the offshore wind power, the first transformer of the positive pole converter and the second transformer of the negative pole converter of the bipolar flexible direct current system for the offshore wind power share the same hot standby third transformer, the valve side switches of the first transformer and the second transformer of the bipolar flexible direct current system are connected with the valve side switch of the third transformer through the change-over switch, and the third transformer can be switched to the converter of any pole fault transformer of the bipolar flexible direct current system through the valve side switch and the change-over switch; the system can rapidly recover full-power operation under the condition that any one group of transformers has a fault under the condition that only 3 groups of transformers are configured in a bipolar flexible direct-current system.
In yet another embodiment provided by the present invention, the arrangement of the first, second and third grid side switches comprises a series arrangement of circuit breakers and disconnectors; the structure of the third valve side switch includes a series structure of a circuit breaker and a disconnecting switch or a circuit breaker only structure.
In this embodiment, K1.1 is a switching device between the ac bus and the first transformer T1, and K1.2 is a switching device between the first transformer T1 and the ac side of the positive inverter; k2.1 is a switchgear between the ac bus and the second transformer T2, K2.2 is a switchgear between the second transformer T2 and the ac side of the negative inverter;
the configuration of the switching devices of K1.1, K1.2, K2.1, K2.2 and K3.1 may be a series configuration of a circuit breaker and a disconnector. The structure of the switchgear of K3.2 may be a series structure of a circuit breaker and a disconnector or a circuit breaker only structure.
In yet another embodiment provided by the present invention, the configuration of the first and second three switches includes a series configuration of a circuit breaker and a disconnector or a disconnector only configuration.
In the specific implementation of the present embodiment, K3.1 is a switching device between the ac bus and the third transformer T3, and K3.2 and K13, K3.2 and K23 are switching devices between the third transformer T3 and the ac sides of the positive and negative inverters, respectively;
the configuration of the K13 and K23 switchgear may be one of a series configuration of circuit breakers and disconnectors or a configuration of disconnectors only.
The functions of the switching devices of K1.1, K1.2, K2.1, K2.2 and K3.1 and the functions of the switching devices of K3.2 are different from those of the switching devices of K13 and K23, so that the structures of the switching devices are not completely the same when the switching devices are implemented, and the adaptive switching structures are selected to ensure the safety of the system.
It should be noted that, in specific implementation, a valve-side switch of the third transformer of the present invention may be omitted, the third transformer is connected to the positive converter through a first third switch, and the third transformer is connected to the negative converter through a second third switch;
referring to fig. 2 in detail, the schematic structural diagram of a bipolar flexible dc system for offshore wind power according to another embodiment of the present invention is shown, where the system includes: the transformer comprises an alternating current bus, a positive pole converter, a negative pole converter, a first transformer T1, a second transformer T2 and a third transformer T3;
a first end of a first transformer T1 is connected with an alternating current bus through a first grid side switch K1.1, and a second end of a first transformer T1 is connected with a positive converter through a first valve side switch K1.2;
a first end of a second transformer T2 is connected with the alternating current bus through a second grid side switch K2.1, and a second end of a second transformer T2 is connected with the negative pole converter through a second valve side switch K2.2;
the first end of the third transformer T3 is connected to the ac bus via a third grid-side switch K3.1, the third transformer T3 is connected to the positive inverter via a first third switch K13, and the third transformer T3 is connected to the negative inverter via a second third switch K23.
At this time, the K13 and K23 switchgear may have a structure of a series circuit breaker and a disconnector, and the switching process is more convenient by omitting the third valve side switch.
In still another embodiment provided by the present invention, the connection form of the ac bus includes a double bus form, a double bus section form, or a half breaker form.
When the embodiment is implemented specifically, the connection form of the alternating current bus comprises a double-bus form, a double-bus segmentation form or a half circuit breaker form, and the bipolar flexible direct current system for the offshore wind power is suitable for alternating current buses with different connection forms and has strong applicability.
In another embodiment provided by the present invention, the ac bus is used for connecting a plurality of wind power input line groups;
the high-voltage side of the positive converter is used for connecting a positive direct-current line;
the high-voltage side of the negative pole converter is used for connecting a negative pole direct current circuit;
the low-voltage side of the positive pole converter is connected with the low-voltage side of the negative pole converter, and the low-voltage side of the positive pole converter is also used for being connected with a metal neutral line.
In the specific implementation of this embodiment, referring to fig. 1, the ac bus is used to connect a plurality of wind power inlet groups; and different wind power inlet wire sets are connected with different fans WT and used for supplying power to the current converter through the alternating current bus and the transformer.
The high-voltage side of the positive converter is used for connecting a positive direct-current line; the high-voltage side of the negative pole converter is used for connecting a negative pole direct current circuit; the low-voltage side of the positive pole converter is connected with the low-voltage side of the negative pole converter, and the low-voltage side of the positive pole converter is also used for being connected with a metal neutral line. And the receiving end is supplied with power through the positive direct current circuit, the negative direct current circuit and the metal neutral line.
The embodiment of the invention provides a bipolar flexible direct current system for offshore wind power, which comprises an alternating current bus, a positive pole converter, a negative pole converter and three transformers; the first transformer of the positive pole converter and the second transformer of the negative pole converter of the bipolar flexible direct current system share a hot standby third transformer, valve side switches of the first transformer and the second transformer of the bipolar flexible direct current system are connected with a valve side switch of the third transformer through a change-over switch, and the third transformer can be switched to the converter of any pole fault transformer of the bipolar flexible direct current system through the valve side switch and the change-over switch; the method can realize that only three groups of transformers are configured on the bipolar flexible direct current system for the offshore wind power, and can reduce the number of the transformers and the operation loss of the transformers on the premise of meeting the redundancy design of the system.
The embodiment of the present invention further provides a transformer fault switching method for a bipolar flexible direct current system for offshore wind power, where the bipolar flexible direct current system for offshore wind power provided in any one of the above embodiments is adopted, refer to fig. 3, which is a schematic flow diagram of the transformer fault switching method for the bipolar flexible direct current system for offshore wind power provided in the embodiment of the present invention, and the method includes steps S301 to S302:
s301, a first network side switch, a first valve side switch, a second network side switch, a second valve side switch, a third network side switch, a third valve side switch and a first third change-over switch are closed, a first transformer is put into a positive pole to normally operate, a second transformer is put into a negative pole to normally operate, and the third transformer is in a hot standby state and is in parallel operation with the first transformer;
s302, when the second transformer has a fault, the second grid side switch, the second valve side switch, the third valve side switch and the first third change-over switch are switched off, the second transformer is switched off, and the third transformer is enabled to be unloaded; and after the third transformer is in no-load preset time, the second third change-over switch and the third valve side switch are closed, and the third transformer is put into negative operation.
In the specific implementation of the embodiment, a bipolar asymmetric operation mode is adopted, K1.1, K1.2, K2.1, K2.2, K3.1, K3.2 and K13 are closed, the first transformer T1 is put into the positive electrode operation, and the second transformer T2 is put into the negative electrode normal operation; the third transformer T3 is in a hot standby state and operates in parallel with the first transformer T1; at the moment, the standby transformer and the positive transformer run in parallel;
when the second transformer T2 has a fault, K2.1, K2.2, K3.2 and K31 are disconnected, the second transformer is cut out, and the third transformer 3 is disconnected from the positive pole converter; because the positive and negative offsets with opposite polarities exist on the direct current voltages of the two pole valve sides to the ground, the valve side of the third transformer needs no-load preset time, which can be 2 minutes in particular, and then is connected to the negative converter in consideration of the influence of the direct current polarity reversal voltage on the insulation of the transformer; specifically, after the third transformer T3 is unloaded for a preset time, K23 and K3.2 are closed, and the third transformer is put into negative operation.
It should be noted that, in this embodiment, a specific switching manner of the transformer is described by taking the parallel operation of the standby transformer and the positive transformer as an example, and the same standby transformer may also be operated in parallel with the negative transformer, and the specific switching manner is the same as that of this embodiment, and is not described in detail here.
In another embodiment provided by the present invention, the method further includes step S303:
and S303, when the first transformer has a fault, disconnecting the first grid side switch and the first valve side switch, and switching out the first transformer.
In the specific implementation of the present embodiment, when the first transformer T1 fails, K1.1 and K1.2 need to be disconnected to switch out the first transformer T1;
in another embodiment provided by the present invention, the method further includes step S304:
s304, when the third transformer fails, the third grid side switch, the third valve side switch and the first switch are disconnected, and the third transformer is switched off. In the specific implementation of the embodiment, when the third transformer T3 fails, K3.1, K3.2 and K23 need to be disconnected to switch out the third transformer T3;
the embodiment of the invention provides a transformer fault switching method of a bipolar flexible direct current system for offshore wind power, which adopts a bipolar asymmetric initial operation state, namely a standby transformer and a transformer of one of two poles operate in parallel, and a group of transformers of the other pole operate to form a bipolar asymmetric operation mode of changing two groups of one pole and one group of one pole; when a transformer of one group of transformer operation poles has a fault, a valve side switch of a standby transformer connected to the other pole for operation needs to be disconnected, and the fault pole is connected again after the standby transformer is in idle for a period of time; the heat standby requirement of the bipolar flexible direct current system transformer can be met through a bipolar asymmetric operation mode, and fault switching can be rapidly realized when any transformer fails, so that the bipolar flexible direct current system recovers full-power operation.
In another embodiment of the present invention, a transformer fault switching method for a bipolar flexible dc system for offshore wind power is provided, where the bipolar flexible dc system for offshore wind power described in any one of the above embodiments is adopted, and fig. 4 is a schematic flow chart of the transformer fault switching method for the bipolar flexible dc system for offshore wind power provided in another embodiment of the present invention; the method comprises steps S401 to S403:
s401, a first grid side switch, a first valve side switch, a second grid side switch and a second valve side switch are closed, and a first transformer and a second transformer run normally;
s402, a third network side switch is closed, and a third transformer runs in a live and no-load mode;
s403, when the first transformer fails, disconnecting the first grid side switch and the first valve side switch, and switching out the first transformer; and closing the first third change-over switch and the third valve side switch, and putting the third transformer into positive operation.
In the specific implementation of the embodiment, a standby transformer with no load is adopted, K1.1, K1.2, K2.1 and K2.2 are closed, the first transformer T1 is put into the positive pole operation, and the second transformer T2 is put into the negative pole operation;
k3.1 is closed, and the third transformer T3 is in a hot standby live no-load state;
when the first transformer T1 fails, K1.1, K1.2 are opened, the first transformer T1 is switched off, K13 and K3.2 are closed, and the third transformer is put into positive operation.
In another embodiment provided by the present invention, the method further includes step S404:
s404, when the second transformer has a fault, disconnecting the second grid side switch and the second valve side switch, and switching out the second transformer; and closing the second third change-over switch and the third valve side switch, and putting the third transformer into negative operation.
In the specific implementation of the embodiment, when the second transformer T2 fails, K2.1 and K2.2 are opened, the second transformer T2 is cut off, K23 and K3.2 are closed, and the third transformer is put into negative operation.
The method is characterized in that a standby transformer live and no-load operation mode is adopted, namely, a group of transformers on each pole operate in a working state, the standby transformer runs in a live and no-load mode, and no pole is connected to a valve side; when a certain set of working transformers is not available, a spare transformer can be immediately put into the pole. The hot standby requirement of the bipolar flexible direct current system transformer can be met by the running mode of the standby transformer with electricity and no load, and when any transformer fails, equipment switching can be quickly realized, so that the bipolar flexible direct current system recovers full-power running.
The invention provides a bipolar flexible direct current system for offshore wind power and a transformer fault switching method thereof, wherein a first transformer of a positive pole converter and a second transformer of a negative pole converter of the bipolar flexible direct current system share a hot standby third transformer, valve side switches of the first transformer and the second transformer of the bipolar flexible direct current system are connected with a valve side switch of the third transformer through a change-over switch, and are switched to the converter of any pole fault transformer of the bipolar flexible direct current system through the valve side switch and the change-over switch; the method can be realized on a bipolar flexible direct current system, only three groups of transformers are configured, and the number of the transformers can be reduced and the running loss of the transformers can be reduced on the premise of meeting the redundancy design of the system.
It should be noted that the bipolar flexible direct-current system adopted in the embodiment of the present invention is generally applied to an offshore wind power direct-current power transmission system, but the bipolar flexible direct-current system provided by the present invention may also be applied to other direct-current power transmission systems, and the circuit structure of the bipolar flexible direct-current system is the same as the principle of the present invention, and the switching method of the transformer is the same as the principle of the present invention, and is within the protection scope of the present invention.
The fault switching method provided by the invention comprises the following steps:
when one of the two groups of transformers run in parallel, the fault transformer can be directly cut off, a network side switch and a valve side switch of the fault transformer are switched off, and each pole keeps one group of transformers to run; when a transformer of one group of transformer operation poles has a fault, a valve side switch of a standby transformer connected to the other pole for operation needs to be disconnected, and the fault pole is connected again after the standby transformer is in idle for a period of time;
the method is characterized in that a standby transformer live and no-load operation mode is adopted, namely, a group of transformers in each pole operate in a working state, the standby transformer network side runs in a live and no-load mode, and the valve side is not connected with any pole; when a certain set of working transformers is not available, a spare transformer can be immediately put into the pole. The hot standby requirement of the bipolar flexible direct current system transformer can be met by the running mode of the standby transformer with electricity and no load, and when any transformer fails, the fault switching can be rapidly realized, so that the bipolar flexible direct current system can recover the full-power running.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (10)
1. A bipolar flexible DC system for offshore wind power, the system comprising: the system comprises an alternating current bus, a positive pole converter, a negative pole converter, a first transformer, a second transformer and a third transformer;
a first end of the first transformer is connected with the alternating current bus through a first grid side switch, and a second end of the first transformer is connected with the positive converter through a first valve side switch;
a first end of the second transformer is connected with the alternating current bus through a second grid side switch, and a second end of the second transformer is connected with the negative pole converter through a second valve side switch;
the first end of the third transformer is connected with the alternating current bus through a third grid side switch, the second end of the third transformer is connected with the first end of the third valve side switch, the second end of the third valve side switch is respectively connected with the first end of the first third change-over switch and the first end of the second third change-over switch, the second end of the first third change-over switch is connected with the positive pole converter, and the second end of the second third change-over switch is connected with the negative pole converter.
2. The bipolar flexible direct current system for offshore wind power of claim 1, wherein the configuration of the first grid side switch, the first valve side switch, the second grid side switch, the second valve side switch and the third grid side switch comprises a series configuration of a circuit breaker and a disconnector;
the structure of the third valve side switch includes a series structure of a circuit breaker and a disconnecting switch or a circuit breaker only structure.
3. Bipolar flexible direct current system for offshore wind power according to claim 1, characterized in that the configuration of the first and second three switches comprises a series configuration of circuit breaker and disconnector or a disconnector only configuration.
4. Bipolar flexible direct current system for offshore wind power according to claim 1, characterized in that the wiring form of the alternating current busbars comprises a double busbar form, a double busbar section form or a half breaker form.
5. The bipolar flexible direct current system for offshore wind power according to claim 1, wherein the alternating current bus is used for connecting a plurality of wind power inlet groups;
the high-voltage side of the positive converter is used for connecting a positive direct-current line;
the high-voltage side of the negative pole converter is used for connecting a negative pole direct current circuit;
the low-voltage side of the positive pole converter is connected with the low-voltage side of the negative pole converter, and the low-voltage side of the positive pole converter is also used for being connected with a metal neutral line.
6. A transformer fault switching method of a bipolar flexible direct current system for offshore wind power is characterized in that the bipolar flexible direct current system for offshore wind power as claimed in any one of claims 1-5 is adopted, and the method comprises the following steps:
closing a first network side switch, a first valve side switch, a second network side switch, a second valve side switch, a third network side switch, a third valve side switch and a first third change-over switch, switching a first transformer into a positive pole to normally operate, switching a second transformer into a negative pole to normally operate, and switching a third transformer into a hot standby state to normally operate in parallel with the first transformer;
when the second transformer has a fault, disconnecting the second grid side switch, the second valve side switch, the third valve side switch and the first third change-over switch, switching out the second transformer, and enabling the third transformer to have no load; and after the third transformer is in no-load preset time, the second third change-over switch and the third valve side switch are closed, and the third transformer is put into negative operation.
7. The method of transformer failover for an offshore wind power bipolar flexible direct current system of claim 6, further comprising:
and when the first transformer fails, the first grid side switch and the first valve side switch are disconnected, and the first transformer is switched off.
8. The method of transformer failover for an offshore wind power bipolar flexible direct current system of claim 6, further comprising:
and when the third transformer fails, the third grid side switch and the third valve side switch are disconnected, and the third transformer is switched off.
9. A transformer fault switching method of a bipolar flexible direct current system for offshore wind power is characterized in that the bipolar flexible direct current system for offshore wind power as claimed in any one of claims 1-5 is adopted, and the method comprises the following steps:
closing the first network side switch, the first valve side switch, the second network side switch and the second valve side switch, and enabling the first transformer and the second transformer to normally operate;
closing a third network side switch, and enabling a third transformer to run in an electrified no-load mode;
when the first transformer fails, the first grid side switch and the first valve side switch are disconnected, and the first transformer is switched off; and closing the first third change-over switch and the third valve side switch, and putting the third transformer into positive operation.
10. The method of transformer failover for an offshore wind power bipolar flexible direct current system of claim 9, further comprising:
when the second transformer fails, the second grid side switch and the second valve side switch are disconnected, and the second transformer is switched off; and closing the second third change-over switch and the third valve side switch, and putting the third transformer into negative operation.
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