CN114977122A - Fault current limiting device and method for high-voltage direct current converter station - Google Patents
Fault current limiting device and method for high-voltage direct current converter station Download PDFInfo
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- CN114977122A CN114977122A CN202210355440.3A CN202210355440A CN114977122A CN 114977122 A CN114977122 A CN 114977122A CN 202210355440 A CN202210355440 A CN 202210355440A CN 114977122 A CN114977122 A CN 114977122A
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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
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
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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 relates to a fault current limiting device and method for a high-voltage direct current converter station, which comprises the following steps: when the direct current system operates in a unipolar or asymmetric steady state, steady-state direct current flows through a neutral line, and the direct current passes through a fault current limiting device preset in a neutral line area of the flexible direct current system; when a flexible direct current system has a fault, a neutral loop region flows through a fault current, when the fault current suddenly changes, a large reverse voltage drop is generated at two ends of a fault current limiting device, the fault current amplitude is restrained by the fault current limiting device, the attenuation of a fault current direct-current component is accelerated, and the problem that an alternating-current switch cannot be normally switched off due to the fact that the fault current at the converter transformer valve side has no zero point is solved by reducing the peak value of the fault current. The invention can be widely applied to the technical field of high-voltage direct current.
Description
Technical Field
The invention relates to the technical field of high-voltage direct current, in particular to a fault current limiting device and method for a high-voltage direct current converter station.
Background
The premise that the flexible direct current transmission can effectively play a role in transmitting new energy is to ensure the safety, reliability and continuous operation of the project. Compared with the traditional alternating current transmission, the flexible direct current engineering mainly composed of power electronic devices is a low-inertia system, and due to the fact that the IGBT device in the converter is weak in overcurrent tolerance, fault current can reach the upper tolerance limit of the IGBT device within a few milliseconds after a direct current fault occurs, the power electronic devices in the converter can be damaged, and the flexible direct current engineering is poor in the capability of tolerating serious short circuit faults. Therefore, the protection system of the flexible and straight engineering needs to have extremely high response speed and needs to be cooperated with a breaker with high breaking speed and strong capacity. In addition, the arrangement of a fault current device for a high voltage direct current converter station is also an effective means for solving the above-mentioned engineering problems.
The flexible direct current converter station wiring mainly has two forms of symmetrical monopole wiring and symmetrical dipole wiring. The symmetrical single-pole connection is a main loop mode which is widely applied to flexible direct current transmission at the present stage, and is shown in figure 1. In this connection, the entire converter station contains only 1 converter unit. In order to provide a ground potential reference for a direct current system, a converter station generally adopts a mode that a neutral point of a winding on a valve side of a transformer is grounded through a large resistor or a mode that a valve side of the transformer is grounded through a large reactor. A schematic wiring diagram of the symmetrical bipolar wiring scheme is shown in fig. 2. The converter station under this mode of connection comprises two poles, and the region of connecting positive negative pole is the neutral line region, and the gentle straight system passes through neutral line region ground connection, and the earth potential is usually provided by the earthing pole. The valve side winding of the flexible direct current transformer generally adopts Y or delta connection, and plays a role in isolating a zero sequence current path. A conventional symmetrical bipolar wiring scheme is shown in detail in fig. 3. The neutral area of the connection is typically grounded through the metal return or ground of the bipolar neutral area via a metal return switch and a neutral current limiting reactance (if any). After the soft straight system has a valve-side single-phase ground fault, the fault loop is as shown in fig. 4, for example, the soft straight bridge arm submodule forms a discharge loop through the grounding electrode lead and the fault grounding point, and a large fault current is generated in the fault transient process, which threatens the safe and stable operation of the direct current equipment. Under the wiring mode of the flexible-straight system, because the impedance on the grounding electrode and the lead wire thereof is too small, the problems that the transient current of a fault loop exceeds the standard and the alternating current switch cannot be normally opened due to too slow attenuation of the fault current are easily caused. Typical fault currents on the valve side of the fault lower straightening system are shown in fig. 5a, 5 b. When no inhibiting measure is taken, the fault current of the flexible direct current system under the fault is large, the current waveform has the characteristics of obvious direct current bias and unobvious zero crossing point, and the conventional on-off of the circuit breaker is not facilitated. In addition, the circuit impedance of the fault current of the phase-splitting part after the circuit breaker is opened is small, the attenuation of the fault current is slow, and higher design requirements are provided for internal equipment of a direct current system.
In order to solve the problems, the conventional scheme is to add a resistor in the neutral line area of the flexible direct current system of the symmetrical bipolar wiring, limit the fault current amplitude during the fault of the symmetrical bipolar flexible direct current system through the damping effect of the resistor, improve the fault current waveform and accelerate the attenuation speed of the fault current after the circuit breaker is tripped. The problem with this solution is that when the system is turned into unipolar operation, a steady-state current will flow through the neutral conductor, which will cause extra losses in the resistor and will require a high heat dissipation from the resistor.
The improved scheme is that the resistor is connected with a bypass switch in parallel for cooperative use, when the system is switched to a single-pole mode, the bypass switch is closed, and the resistor is bypassed from a current loop, so that extra loss is not generated, and the problem of steady-state heat dissipation of the resistor is reduced. However, the solution still has the problems of no fault current suppression measures when the system is operated in a single pole, and system reliability reduction after the switching device is added.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a fault current limiting device and method for a high voltage dc converter station, which solve the problems of excessive transient current and abnormal tripping of an ac switch in a system fault state caused by small impedance of a ground electrode and a lead thereof in a symmetric bipolar multilevel flexible dc (MMC) system, and improve the problems of poor adaptability and low reliability of a conventional neutral line region series resistor or resistor-bypass switch scheme to a dc system operation mode.
In order to achieve the purpose, the invention adopts the following technical scheme: a fault current limiting method for a high-voltage direct current converter station comprises the following steps: when the direct current system operates in a unipolar or asymmetric steady state, steady-state direct current flows through a neutral line, and the direct current passes through a fault current limiting device preset in a neutral line area of the flexible direct current system; when a flexible direct system breaks down, a neutral loop region flows through fault current, when the current changes suddenly, large reverse voltage drop is generated at two ends of a fault current limiting device, the fault current limiting device inhibits the amplitude of the fault current and accelerates the attenuation of the direct current component of the fault current, and the problem that an alternating current switch cannot be normally switched off due to the fact that the fault current on a converter transformer valve side does not have an over zero point is solved by reducing the peak value of the fault current.
Further, the fault current limiting device is connected in series with the neutral line region of the flexible-straight system.
Further, the fault current limiting device comprises a resistor and an inductor; the resistor and the inductor are connected in parallel.
Further, when the direct current system operates in a unipolar or asymmetric steady state, steady-state direct current flows through the neutral line, and all the direct current passes through an inductive loop of the fault current limiting device.
Further, when the current suddenly changes according to the calculation formula of the voltage U at the two ends of the inductor, a large reverse voltage drop will be generated at the two ends of the fault current limiting device, the equivalent impedance of the inductor will become large, and the fault current will start to flow through a resistance loop in the fault current limiting device, so as to suppress the amplitude of the fault current and accelerate the attenuation of the dc component of the fault current.
A fault current limiting device for a high-voltage direct-current converter station is used for achieving the fault current limiting method for the high-voltage direct-current converter station and is formed by connecting a resistor and an inductor in parallel.
Further, the fault current limiting device is connected in series in the neutral line region of the soft and straight system.
Due to the adoption of the technical scheme, the invention has the following advantages:
the fault current limiting device effectively solves the problem that the alternating current breaker cannot be normally tripped due to slow fault current attenuation of the traditional symmetrical bipolar flexible direct current system. Compared with a neutral line series resistor scheme and an improved scheme of a parallel bypass switch thereof, the method has the advantages of no limitation on the operation mode of a direct current system, adoption of all static elements, simple and reliable structure, easiness in implementation, low steady-state loss and the like, and well meets the isolated current limitation of a multilevel flexible direct current (MMC) system of a symmetrical bipolar ground return line topology.
Drawings
FIG. 1 is a diagram of a prior art symmetrical single pole wiring scheme;
FIG. 2 is a diagram of a prior art symmetrical bipolar wiring scheme;
FIG. 3 is a detailed structure diagram of a symmetrical bipolar wiring scheme in the prior art;
FIG. 4 is a diagram of a fault current path when the converter transformer side is grounded in the prior art;
FIG. 5a is a schematic diagram of a typical fault current when no inhibiting action is taken in the prior art;
FIG. 5b is a schematic view of a typical fault current for a circuit breaker opening a rear section when no inhibiting action is taken in the prior art;
FIG. 6 is a schematic diagram of a fault current limiting device in an embodiment of the present invention connected in a limp-straight system;
fig. 7 is a schematic structural diagram of a fault current limiting device in an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The invention provides a fault current limiting device and method for a high-voltage direct current converter station, which are suitable for the technical field of multilevel flexible direct current (MMC) systems adopting symmetrical bipolar ground return topology. The invention provides a fault current limiting device for a high-voltage direct-current converter station, which is formed by connecting an inductor and a resistor in parallel for a direct-current system. The fault current limiting device is connected in series with a neutral line region of a symmetrical bipolar flexible-straight system to play a role in restraining fault current and accelerating the attenuation of the fault current. The fault current limiter disclosed by the invention adopts static elements, is simple and reliable in structure, easy to realize and low in steady-state loss, and well meets the current limiting requirement of a multilevel flexible direct current (MMC) system of a symmetrical bipolar ground loop topology.
In one embodiment of the invention, a fault current limiting method for a high-voltage direct current converter station is provided. In this embodiment, the method is applied to a direct current project adopting a symmetrical bipolar connection mode, and as shown in fig. 6 and 7, the method specifically includes the following steps in steady-state operation and fault:
1) when the direct current system operates in a unipolar or asymmetric steady state, steady-state direct current flows through a neutral line, and the direct current passes through a fault current limiting device preset in a neutral line area of the flexible direct current system;
2) when the flexible direct current system breaks down, a fault current flows through a neutral loop region, when the current changes suddenly, a large reverse voltage drop is generated at two ends of a fault current limiting device, the fault current limiting device inhibits the amplitude of the fault current and accelerates the attenuation of the direct current component of the fault current, and the problem that an alternating current switch cannot be normally switched on and off due to the fact that the fault current on the converter transformer valve side does not have an over zero point is solved by reducing the peak value of the fault current.
In this case, the fault current flowing through the neutral circuit region is large, that is, the difference between the pre-fault neutral current and the post-fault neutral current is large. When a fault occurs, the grounding area and a fault point form a fault loop, so that a larger fault current different from a steady-state current appears in the neutral line area, and the fault current is related to the moment of the fault and the state of a system during the fault.
In the above embodiments, the fault current limiting device is connected in series in the neutral region of the compliance system. The fault current limiting device comprises a resistor and an inductor; the resistor and the inductor are connected in parallel.
In the above embodiment, when the dc system operates in a unipolar or asymmetric steady state, the steady-state dc current will flow through the neutral line and all the dc current will pass through the inductor loop of the fault current limiting device, and since the resistance of the inductor coil is small, almost no loss will be generated. Therefore, the fault current limiting device can be ensured to be free from the need of bypassing the resistor when the switch equipment runs in a steady state of the system, the loss of a power transmission system is reduced, and meanwhile, the extra heat dissipation is not required to be considered.
In the above embodiment, when the flexible direct current system has a fault, for example, a single-phase ground fault on the valve side of the converter transformer occurs, according to a calculation formula of the voltage U across the inductor, when the current suddenly changes, a large reverse voltage drop will be generated across the fault current limiting device, and the equivalent impedance of the inductor will become large.
Where L is an inductance value and i is a fault current instantaneous value.
At this time, the fault current starts to flow through a resistance loop in the fault current limiting device, and then the functions of restraining the amplitude of the fault current and accelerating the attenuation of the direct-current component of the fault current are achieved.
In an embodiment of the present invention, a fault current limiting device for a high voltage direct current converter station is provided, which is used for implementing the fault current limiting method for the high voltage direct current converter station in the above embodiments. As shown in fig. 7, the device includes a resistor and an inductor; the resistor and the inductor are connected in parallel to form a fault current limiting device.
Wherein, the resistor and the inductor are used for the high-voltage direct-current system.
In the above embodiment, the fault current limiting device formed by connecting the resistor and the inductor in parallel is connected in series in the neutral line region of the symmetrical bipolar flexible direct current system. In practical application, the fault current limiting device is suitable for all flexible and straight operation modes, and the structure does not need to be changed according to the operation modes of a flexible and straight system.
In conclusion, the fault current limiting device for the high-voltage direct-current converter station can normally pass current when a direct-current system operates in a steady state, and can play a role in limiting current and improving fault current waveforms after the flexible direct-current system breaks down.
The apparatus provided in this embodiment is used for executing the above method embodiments, and for specific flows and details, reference is made to the above embodiments, which are not described herein again.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A fault current limiting method for a high-voltage direct current converter station is characterized by comprising the following steps:
when the direct current system operates in a unipolar or asymmetric steady state, steady-state direct current flows through a neutral line, and the direct current passes through a fault current limiting device preset in a neutral line area of the flexible direct current system;
when a flexible direct system breaks down, a neutral loop region flows through fault current, when the current changes suddenly, large reverse voltage drop is generated at two ends of a fault current limiting device, the fault current limiting device inhibits the amplitude of the fault current and accelerates the attenuation of the direct current component of the fault current, and the problem that an alternating current switch cannot be normally switched off due to the fact that the fault current on a converter transformer valve side does not have an over zero point is solved by reducing the peak value of the fault current.
2. The method of current limiting for a hvdc converter station according to claim 1, wherein said fault current limiting device is connected in series in the neutral region of the vdc system.
3. The method of current limiting for a hvdc converter station of claim 2, wherein said fault current limiting device comprises a resistor and an inductor; the resistor and the inductor are connected in parallel.
4. A method for limiting a fault in a hvdc converter station according to claim 3 wherein during monopolar or asymmetric steady state operation of said dc system, all steady state dc current will flow on the neutral conductor through the inductor loop of the fault current limiting device.
5. The method according to claim 3, wherein when the current suddenly changes according to the calculation formula of the voltage U across the inductor, a large reverse voltage drop will be generated across the fault current limiting device, the equivalent impedance of the inductor will become large, and the fault current will start to flow through a resistance loop in the fault current limiting device, so as to suppress the amplitude of the fault current and accelerate the attenuation of the DC component of the fault current.
6. A fault current limiting device for a HVDC converter station, characterized in that the device is used for implementing a fault current limiting method for a HVDC converter station according to any of claims 1 to 5, and the device is formed by connecting a resistor and an inductor in parallel.
7. The fault current limiting device for a hvdc converter station according to claim 6, wherein said fault current limiting device is connected in series in the neutral region of the compliance system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210355440.3A CN114977122A (en) | 2022-04-06 | 2022-04-06 | Fault current limiting device and method for high-voltage direct current converter station |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210355440.3A CN114977122A (en) | 2022-04-06 | 2022-04-06 | Fault current limiting device and method for high-voltage direct current converter station |
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| CN202210355440.3A Pending CN114977122A (en) | 2022-04-06 | 2022-04-06 | Fault current limiting device and method for high-voltage direct current converter station |
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