CN114217171B - Single-phase grounding fault detection method for converter valve side of flexible direct current transmission system - Google Patents
Single-phase grounding fault detection method for converter valve side of flexible direct current transmission system Download PDFInfo
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- CN114217171B CN114217171B CN202111533753.5A CN202111533753A CN114217171B CN 114217171 B CN114217171 B CN 114217171B CN 202111533753 A CN202111533753 A CN 202111533753A CN 114217171 B CN114217171 B CN 114217171B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/088—Aspects of digital computing
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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
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
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- Testing Of Short-Circuits, Discontinuities, Leakage, Or Incorrect Line Connections (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
The invention discloses a single-phase grounding fault detection method for a converter valve side of a flexible direct current transmission system. The single-phase earth fault detection method comprises the following steps: identifying the breaking state of a circuit breaker in the flexible direct current transmission system; selecting different single-phase ground fault detection strategies according to the breaking state of the circuit breaker; the single-phase earth fault detection strategy comprises a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy. The scheme effectively improves the sensitivity of distinguishing the grounding faults of the converter valve through different single-phase grounding fault detection strategies.
Description
Technical Field
The embodiment of the invention relates to the technology of power systems, in particular to a single-phase grounding fault detection method for a converter valve side of a flexible direct current transmission system.
Background
The flexible direct current transmission system based on the modularized multi-level symmetrical monopole structure generally adopts a high-resistance grounding mode to provide a zero potential point, and when the system has a single-phase grounding fault at the converter transformer valve side, a current differential protection method adopted by a traditional fault detection method can not effectively identify fault characteristics due to small grounding current caused by the high-resistance grounding system structure; in other cases, after a single-phase grounding fault occurs during charging of the flexible direct-current power transmission system with the symmetrical monopole structure with the starting resistor, the starting resistor loop is connected in series with the grounding fault loop, so that fault current is smaller, and the differential current is hardly changed by adopting a current differential protection method, so that fault characteristics cannot be effectively identified.
Disclosure of Invention
The invention provides a single-phase grounding fault detection method for a converter valve side of a flexible direct current transmission system, which is used for realizing the selection of different grounding fault detection strategies according to the presence or absence of a starting resistor in the identified flexible direct current transmission system, thereby effectively improving the sensitivity of distinguishing the single-phase grounding fault of the converter valve side.
The embodiment of the invention provides a single-phase grounding fault detection method for a converter valve side of a flexible direct current transmission system, which comprises the following steps:
identifying the breaking state of a circuit breaker in the flexible direct current transmission system;
selecting different single-phase ground fault detection strategies according to the breaking state of the circuit breaker;
the single-phase earth fault detection strategy comprises a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy.
Optionally, selecting different ground fault detection strategies according to the breaking state of the circuit breaker includes:
selecting a neutral overvoltage fault detection strategy when the circuit breaker is identified to be in a separated state;
and selecting a neutral point overcurrent fault detection strategy when the circuit breaker is identified to be in a closed state.
Optionally, the neutral point overvoltage fault detection strategy includes:
collecting fundamental wave voltages of each phase at the converter valve side;
superposing fundamental wave voltages of all phases of the converter valve side to obtain zero sequence voltage;
judging whether the zero sequence voltage is larger than a first preset voltage value or not;
and when the zero sequence voltage is larger than the first preset voltage value, judging that a single-phase grounding fault occurs.
Optionally, when the zero sequence voltage is greater than the first preset voltage value, after determining the ground fault, the method further includes:
and starting the neutral point overvoltage protection action after the first preset time.
An optional amount, the neutral point overcurrent fault detection strategy includes:
collecting neutral point current at the side of a converter valve;
judging whether the neutral point current at the converter valve side is larger than a first preset current value or not;
and if the neutral point current at the converter valve side is larger than the first preset current value, judging that a single-phase grounding fault occurs.
Optionally, if the current of the neutral point on the converter valve side is greater than the first preset current value, after the ground fault is determined to occur, the method further includes:
and after the second preset time, starting the neutral point overcurrent protection action.
Optionally, the second preset time is smaller than the first preset time.
Optionally, the initiating neutral overvoltage protection action includes:
and controlling a transistor in the converter valve to be disconnected.
Optionally, the starting the neutral point overcurrent protection action includes:
and controlling a transistor in the converter valve to be disconnected.
Optionally, before starting the neutral point overvoltage protection action, the method further comprises:
judging whether the converter valve is in a locking stage or not;
and when the converter valve is in the locking stage, starting a neutral point overvoltage protection action.
According to the embodiment of the invention, the breaking state of the circuit breaker in the flexible direct current transmission system is identified; then selecting different single-phase ground fault detection strategies according to the breaking state of the circuit breaker; the single-phase earth fault detection strategy comprises a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy. The scheme effectively improves the sensitivity of distinguishing the grounding faults of the converter valve through different single-phase grounding fault detection strategies, and solves the problem that the fault characteristics cannot be effectively identified by adopting a current differential detection method in the prior art.
Drawings
Fig. 1 is a flowchart of a single-phase grounding fault detection method of a converter valve side of a flexible direct current transmission system provided by an embodiment of the invention;
fig. 2 is a schematic structural diagram of a flexible dc power transmission system according to an embodiment of the present invention;
fig. 3 is a flowchart of another method for detecting a single-phase grounding fault on a converter valve side of a flexible direct current transmission system according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.
Fig. 1 is a flowchart of a single-phase grounding fault detection method on a converter valve side of a flexible direct current transmission system, as shown in fig. 1, according to an embodiment of the present invention, the single-phase grounding fault detection method on the converter valve side of the flexible direct current transmission system includes the following steps:
s110, identifying the breaking state of a breaker in the flexible direct current transmission system.
Fig. 2 is a schematic structural diagram of a flexible dc power transmission system according to an embodiment of the present invention, and as shown in fig. 2, the flexible dc power transmission system includes a transformer 10, a starting resistor R, a circuit breaker QF, and a converter valve 20; the breaker QF is arranged on the three-phase alternating current bus in series; the breaker QF is electrically connected with the starting resistor R in parallel, and the transformer 10 is arranged between the three-phase alternating current bus and the grounding point; the converter valve 20 is electrically connected in series with the breaker QF; the flexible direct current transmission system also comprises a grounding resistor Rr; the grounding resistor Rr is in a high resistance state; when the breaker QF is disconnected, the starting resistor R is connected to the three-phase alternating current bus; when the breaker QF is closed, the starting resistor R is bypassed and the starting resistor R is not connected to the three-phase ac bus. The scheme judges whether the starting resistor R is connected to the three-phase alternating current bus or not by identifying the breaking state of the circuit breaker.
S120, selecting different single-phase grounding fault detection strategies according to the breaking state of the circuit breaker.
The single-phase earth fault detection strategy comprises a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy. Selecting a neutral overvoltage fault detection strategy when the breaker is identified to be in a separated state; when the circuit breaker is identified as being in a closed state, a neutral point overcurrent fault detection strategy is selected.
It should be noted that, as shown in fig. 2, fig. 2 only illustrates a single-phase power transmission condition in the flexible dc power transmission system, if a single-phase ground fault occurs on the side of the converter valve 20 (such as the ground fault occurs at the point F in fig. 2), the single-phase ground point current changes from zero to non-zero, that is, the current passing through the transformer 10 is not zero; while the ground point currents of the other phases do not change, it is understood that when no ground fault occurs, the sum of the ground point currents of the phases is zero, so that the sum of the calculated ground point currents is changed from zero to non-zero, that is, the neutral point current is not zero.
If a single-phase ground fault occurs on the converter valve 20 side (e.g., a ground fault occurs at point F in fig. 2), the single-phase fundamental voltage is changed from a certain value to zero, i.e., the voltage value passing through Q is zero; it is understood that the sum of the fundamental voltages of the phases is zero when the ground fault does not occur, and therefore the sum of the fundamental voltages of the phases is changed from zero to non-zero, that is, the neutral point voltage is not zero.
Because the breaker QF is disconnected and the starting resistor R is connected to the three-phase alternating current bus, the flexible direct current transmission system comprises the grounding resistor Rr and the starting resistor R, and the single-phase grounding point current is not obvious in change, the neutral point current is not obvious in change, so that the scheme adopts a neutral point overvoltage fault detection strategy, namely, the ground fault is judged by detecting the overvoltage condition of the neutral point voltage obtained by adding the fundamental wave voltages of all phases when the breaker QF is disconnected. When the breaker QF is closed, the starting resistor R is not connected to the three-phase alternating current bus, the flexible direct current transmission system only comprises the grounding resistor Rr, the single-phase grounding point current has obvious change, and the neutral point current has obvious change, so that the grounding fault can be judged by detecting the neutral point current. Therefore, the scheme effectively improves the sensitivity of distinguishing the single-phase grounding faults at the converter valve side through different single-phase grounding fault detection strategies, and solves the problem that the fault characteristic cannot be effectively identified by adopting a current differential detection method in the prior art.
Optionally, based on the foregoing embodiment, fig. 3 is a flowchart of another method for detecting a single-phase ground fault on a converter valve side of a flexible direct current power transmission system according to an embodiment of the present invention, where, as shown in fig. 3, the single-phase ground fault detection method includes:
s210, identifying the breaking state of a breaker in the flexible direct current transmission system.
And S220, selecting a neutral point overvoltage fault detection strategy when the breaker is identified to be in a separated state.
Specifically, the neutral overvoltage fault detection strategy includes: collecting fundamental wave voltages of each phase at the converter valve side; illustratively, referring to fig. 2, a U-phase Q-point fundamental voltage Ua on the converter valve 20 side is acquired; collecting V-phase Q-point fundamental wave voltage Ub on the side of the converter valve 20 and collecting W-phase Q-point fundamental wave voltage Uc on the side of the converter valve 20; then, the fundamental voltages of all phases on the converter valve side are overlapped to obtain zero sequence voltage U, wherein U=Ua+Ub+Uc; judging whether the zero sequence voltage U is larger than a first preset voltage value or not; and when the zero sequence voltage is larger than a first preset voltage value, judging that a single-phase grounding fault occurs.
And S230, starting the neutral point overvoltage protection action after the first preset time.
When a single-phase earth fault is detected, after a first preset time, the first preset time is 10s, starting a neutral point overvoltage protection action to prevent false triggering action; the method is characterized in that the starting of the neutral point overvoltage protection action comprises the step of controlling the disconnection of a transistor in the converter valve, so that after a single-phase grounding fault occurs, the external output direct current is timely cut off, and the electricity reliability is ensured.
It should be noted that, before starting the neutral point overvoltage protection action, the method further includes: judging whether the converter valve is in a locking stage or not; when the converter valve is in the locking stage, the neutral point overvoltage protection action is started. The converter valve 20 is divided into two working phases, wherein the first phase is a charging locking phase; the second stage is a rectifying stage; in a charging locking stage, a starting resistor is generally connected into a direct current transmission system to charge a capacitor in a converter valve; in the rectifying stage, a starting resistor is not connected into the direct current transmission system, and the purpose of rectification is realized by controlling the on-off of a transistor; the starting resistor is connected in the charging stage of the converter valve, and the sensitivity of collecting neutral point voltage in the charging stage of the converter valve to determine single-phase grounding faults is high, so that whether the converter valve is in the locking stage can be determined before starting the overvoltage protection action of the neutral point; when the converter valve is in a locking stage, the neutral point overvoltage protection action is started, and the reliability of the protection action is ensured.
And S240, selecting a neutral point overcurrent fault detection strategy when the breaker is identified to be in a closed state.
Specifically, the neutral point overcurrent fault detection strategy includes: collecting neutral point current at the side of a converter valve; illustratively, referring to fig. 2, a ground point current Ia is collected through the U-phase transformer on the converter valve 20 side; collecting grounding point current Ib passing through the V-phase transformer at the side of the converter valve 20 and grounding point current Ic passing through the W-phase transformer at the side of the converter valve 20; then, superposing the current of each phase place of the converter valve side to obtain a neutral point current I of the converter valve side, wherein I=ia+Ib+ic; judging whether the neutral point current I at the converter valve side is larger than a first preset current value or not; and if the neutral point current I at the converter valve side is larger than a first preset current value, judging that the ground fault occurs.
S250, starting the neutral point overcurrent protection action after a second preset time.
Wherein the second preset time is on the order of milliseconds, the second preset time being less than the first preset time, and exemplary, the second preset time being 10ms; when a single-phase earth fault is detected, after a second preset time, starting a neutral point overcurrent protection action, preventing false triggering action and ensuring the accuracy of the protection action; here, the step of starting the neutral point overcurrent protection action may include controlling the transistor in the converter valve to be turned off, so that when the ground fault occurs, the external output direct current is timely turned off, and the reliability of electricity consumption is ensured.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (9)
1. The single-phase grounding fault detection method for the converter valve side of the flexible direct current transmission system is characterized by comprising the following steps of:
identifying the breaking state of a circuit breaker in the flexible direct current transmission system;
selecting different single-phase ground fault detection strategies according to the breaking state of the circuit breaker;
the single-phase earth fault detection strategy comprises a neutral point overvoltage fault detection strategy and a neutral point overcurrent fault detection strategy;
the neutral point overcurrent fault detection strategy comprises the following steps: collecting neutral point current at the side of a converter valve; judging whether the neutral point current at the converter valve side is larger than a first preset current value or not; and if the neutral point current at the converter valve side is larger than the first preset current value, judging that a single-phase grounding fault occurs.
2. The ground fault detection method of claim 1, wherein selecting different single-phase ground fault detection strategies according to the breaking state of the circuit breaker comprises:
selecting the neutral overvoltage fault detection strategy when the breaker is identified to be in a separated state;
and selecting the neutral point overcurrent fault detection strategy when the circuit breaker is identified to be in a closed state.
3. The ground fault detection method of claim 2, wherein the neutral overvoltage fault detection strategy comprises:
collecting fundamental wave voltages of each phase at the converter valve side;
superposing fundamental wave voltages of all phases of the converter valve side to obtain zero sequence voltage;
judging whether the zero sequence voltage is larger than a first preset voltage value or not;
and when the zero sequence voltage is larger than the first preset voltage value, judging that a single-phase grounding fault occurs.
4. A method of ground fault detection according to claim 3, wherein when the zero sequence voltage is greater than the first predetermined voltage value, then after determining a single phase ground fault, further comprising:
and starting the neutral point overvoltage protection action after the first preset time.
5. The ground fault detection method according to claim 1, wherein if the converter valve side neutral point current is greater than the first preset current value, after determining that a single-phase ground fault has occurred, further comprising:
and after the second preset time, starting the neutral point overcurrent protection action.
6. The ground fault detection method of claim 5, wherein the second preset time is less than the first preset time.
7. The ground fault detection method of claim 4, wherein the initiating neutral overvoltage protection action comprises:
and controlling a transistor in the converter valve to be disconnected.
8. The ground fault detection method of claim 5, wherein the initiating neutral point over-current protection action comprises:
and controlling a transistor in the converter valve to be disconnected.
9. The ground fault detection method of claim 4, further comprising, prior to initiating the neutral overvoltage protection action:
judging whether the converter valve is in a locking stage or not;
and when the converter valve is in the locking stage, starting a neutral point overvoltage protection action.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106026048A (en) * | 2016-07-15 | 2016-10-12 | 浙江大学 | DC grid fault handling strategy based on in-situ detection and in -situ protection |
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| CN107346003B (en) * | 2016-05-05 | 2020-09-08 | 南京南瑞继保电气有限公司 | Voltage source converter fault detection and positioning method and system |
| CN107490749B (en) * | 2017-09-14 | 2019-08-02 | 南方电网科学研究院有限责任公司 | The fault detection method and device of extra-high voltage flexible HVDC transmission system starting-up later time |
| CN107966633B (en) * | 2017-11-15 | 2021-05-18 | 国网宁夏电力公司电力科学研究院 | Method and system for rapidly judging single-phase earth fault line of power distribution network of power supply system |
| CN109119975B (en) * | 2018-08-22 | 2020-04-28 | 许继集团有限公司 | Direct current system and failure protection method of circuit breaker in starting process of direct current system |
| CN110361623B (en) * | 2019-07-16 | 2021-07-23 | 北京四方继保自动化股份有限公司 | Small resistor switching method for single-point ground fault positioning of multi-terminal direct-current system |
| CN112886556B (en) * | 2021-03-04 | 2022-12-16 | 中国南方电网有限责任公司 | Single-phase earth fault control protection method for flexible direct current transmission alternating current connection line area |
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| CN106026048A (en) * | 2016-07-15 | 2016-10-12 | 浙江大学 | DC grid fault handling strategy based on in-situ detection and in -situ protection |
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