CN112838609A - MMC converter station ground fault analysis method based on two-port network - Google Patents
MMC converter station ground fault analysis method based on two-port network Download PDFInfo
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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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- 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
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention relates to a MMC converter station ground fault analysis method based on a two-port network, and belongs to the technical field of relay protection of a power system. A converter transformer is equivalent to a two-port network from an MMC direct-current side outlet in an MMC converter station, the two-port network direct-current side outlet is provided with two terminals, and when the two-port network direct-current side outlet works normally, direct current flows out from one terminal and flows in from the other terminal. When a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the network is zero. When a ground fault occurs in the network, the sum of the current vectors of the two terminals at the direct current side is not zero any more due to the new ground point. The method judges whether the two-port network has ground fault or not by calculating whether the sum of the current vectors of the two is zero or not, and can provide support for a large database of the smart grid in the future.
Description
Technical Field
The invention relates to a MMC converter station ground fault analysis method based on a two-port network, and belongs to the technical field of relay protection of a power system.
Background
The rapid development of the high-voltage direct-current transmission technology plays an important role in optimizing and configuring resources in a large range in China. The high-voltage direct-current transmission system has the advantages of long-distance and large-capacity transmission, and is widely applied in the world due to the advantages of realization of networking of a plurality of large-scale regional power grids, convenience and rapidness in transmission control, limitation of short-circuit current and economy of the system and the like. With the development of manufacturing and control technology of high-power fully-controlled power electronic devices, flexible direct-current transmission technology based on MMC (modular multilevel converter) comes from the beginning, and the flexible direct-current transmission technology has the advantages of small floor area, low harmonic level, suitability for forming a multi-terminal direct-current system, no reactive compensation problem, no commutation failure problem, independent control of active power and reactive power, high reliability and the like. However, the flexible dc power transmission system based on MMC cannot simply rely on converter control to complete the clearing of the dc side fault, and presents inherent vulnerability in the dc side fault. The MMC direct-current transmission system has multiple grounding modes, namely a valve side star reactor grounding mode through a large resistor, a transformer valve side neutral point grounding mode through a large resistor, a direct-current bus grounding mode through a clamping resistor and a direct-current neutral bus grounding mode. The first three grounding modes are common in an MMC pseudo bipolar direct-current power transmission system, and the direct-current neutral bus grounding mode is more common in a true bipolar direct-current power transmission system. At present, the topological structure of MMC and the fault of a direct current transmission line are researched more, and the ground fault in a current conversion station is researched less.
Disclosure of Invention
The invention aims to solve the technical problem of providing a two-port-network-based ground fault analysis method for an MMC converter station, wherein one converter station of an MMC true bipolar direct-current transmission system is divided into two-port networks (a network I and a network II), so that the specific two-port network can be effectively identified to have a ground fault inside. And support is provided for a large database of a future smart grid.
The technical scheme of the invention is as follows: a converter transformer is equivalently formed into a two-port network from a direct current side outlet of an MMC in the MMC converter station, the direct current side outlet of the two-port network is provided with two terminals, and when the MMC converter station operates normally, direct current flows out from one terminal and flows in from the other terminal. When a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the network is zero, and when a ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side is no longer zero due to the occurrence of a new ground point. The grounding mode of the MMC converter station related by the invention is a direct current bus grounding mode through a clamping resistor and a direct current neutral bus grounding mode.
The method comprises the following specific steps:
step 1: in the MMC converter station, a converter transformer is equivalent to an MMC direct-current side outlet to form a two-port network, the direct-current side outlet of the network is provided with two terminals, and one terminal has current idThe direction is out of the network and the other terminal is current id’The direction is into the network.
Step 2: when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the two-port network is zero, and according to the current direction specified by Step1, when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum is expressed as:
icd＝|id-id'|≤ε (1)
in the formula icdThe current difference value of the two-port network is epsilon, the epsilon is a value larger than zero, and the setting value of the current difference value needs to consider unbalanced current caused by transmission error of a mutual inductor and stray capacitance in a current converter during normal operation.
Step 3: when a ground fault occurs in the network, the sum of the current vectors at the two terminals on the direct current side is no longer zero due to the new ground point, and is expressed as follows according to the current direction specified by Step 1:
icd＝|id-id'|＞ε (2)
step 4: if equation (2) is satisfied, it indicates that a two-port network internal ground fault has occurred.
For a true bipolar MMC direct-current transmission system, each converter station can be divided into two-port networks (a network I and a network II), and the network with the specific grounding fault can be screened according to the steps.
The invention has the beneficial effects that: the method provided by the invention utilizes the port characteristics of the two-port network to analyze the grounding fault of the converter station of the MMC direct-current transmission system, has certain practical engineering significance, and can provide support for a large database of a future intelligent power grid.
Drawings
FIG. 1 is a two-port network equivalent of the present invention;
FIG. 2 is a diagram of a direct current bus of the MMC direct current transmission system of the present invention connected to a map via a clamping resistor;
FIG. 3 is a DC neutral bus connection map of the MMC DC transmission system of the present invention;
FIG. 4 is a two-port network equivalent diagram of one converter station of the MMC true bipolar DC power transmission system of the present invention;
fig. 5 is a comparison diagram of the current of the outlet terminal of the direct current side when the network two of the MMC true bipolar direct current transmission system of the present invention fails.
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
Example 1: as shown in fig. 1, an MMC direct current transmission system as shown in fig. 2 was established as a simulation model. The valve side windings of the connecting transformer are connected in a triangular mode, the alternating current sides of the connecting transformer are connected in a star mode, and the direct current bus is grounded through a clamping resistor. The direct current voltage is +/-320 kV, and a single-phase earth fault occurs on the side of the rectifier valve. In this case,. epsilon. is 0.1 kA.
Step 1: in the MMC converter station, a converter transformer is equivalent to an MMC direct-current side outlet to form a two-port network, the direct-current side outlet of the network is provided with two terminals, and one terminal has current idDirection flowing from the network, another terminal current id’The direction is into the network.
Step 2: when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the two-port network is zero. According to the current direction specified by Step1, when a fault occurs outside the network or a non-ground fault occurs inside the network, the formula is as follows:
icd＝|id-id'|≤ε (1)
icdthe two-port network current difference value is epsilon, which is a value larger than zero, and the setting value needs to consider unbalanced current caused by transformer transmission error and stray capacitance in a current converter during normal operation.
Step 3: when a ground fault occurs in the network, the sum of the current vectors of the two terminals at the direct current side is not zero any more due to the new ground point. According to the current direction specified by Step1, the formula is as follows:
icd＝|id-id'|＞ε (2)
step 4: as shown in FIG. 5, a current difference i is calculatedcdIf equation (2) is satisfied at 1.19kA, it indicates that a two-port network internal ground fault has occurred.
Example 2: an MMC true bipolar direct current power transmission system shown in a grounding mode in the attached figure 3 is established as a simulation model. An equivalent model of a two-port network in a converter station is shown in fig. 4. The direct current voltage is +/-320 kV, and a two-phase short circuit and grounding fault is set on the second rectifier valve side of the network. In this case,. epsilon. is 0.1 kA.
Step 1: in the MMC converter station, a converter transformer is equivalent to an MMC direct-current side outlet to form a two-port network, the direct-current side outlet of the network is provided with two terminals, and one terminal has current idDirection flowing from the network, another terminal current id’The direction is into the network.
Step 2: when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the two-port network is zero. According to the current direction specified by Step1, when a fault occurs outside the network or a non-ground fault occurs inside the network, the formula is as follows:
icd＝|id-id'|≤ε (1)
icdthe current difference of the two-port network is a value with epsilon larger than zero, and the setting value needs to consider the transmission error of a mutual inductor and stray electricity in a current converter during normal operationAnd the resulting unbalanced current.
Step 3: when a ground fault occurs in the network, the sum of the current vectors of the two terminals at the direct current side is not zero any more due to the new ground point. According to the current direction specified by Step1, the formula is as follows:
icd＝|id-id'|＞ε (2)
step 4: if the formula (2) is satisfied, it indicates that a two-port network internal ground fault occurs.
Network-computing current difference icd1＝7.4×10-5kA, does not satisfy formula (2); calculating a current difference value i by using a network IIcd225.95kA, equation (2) is satisfied. It indicates that the two-port network internal ground fault occurs in the network two.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit and scope of the present invention.
Claims (2)
1. A ground fault analysis method for an MMC converter station based on a two-port network is characterized by comprising the following steps: the method comprises the steps that a converter transformer is equivalent to a two-port network from an outlet of a direct current side of an MMC in the MMC converter station, the outlet of the direct current side of the two-port network is provided with two terminals, when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of current vectors of the two terminals on the direct current side of the network is zero, and when a ground fault occurs inside the network, the sum of current vectors of the two terminals on the direct current side is not zero any more.
2. The MMC converter station ground fault analysis method based on two-port network of claim 1, characterized by comprising the specific steps of:
step 1: in the MMC converter station, a converter transformer is equivalent to an MMC direct-current side outlet to form a two-port network, the direct-current side outlet of the network is provided with two terminals, and one terminal has current idThe direction is out of the network and the other terminal is current id’Is directed into the netComplexing;
step 2: when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side of the two-port network is zero, and according to the current direction specified by Step1, when a fault occurs outside the network or a non-ground fault occurs inside the network, the sum is expressed as:
icd＝|id-id'|≤ε (1)
in the formula icdIs a two-port network current difference value, epsilon is a value greater than zero;
step 3: when a ground fault occurs inside the network, the sum of the current vectors of the two terminals on the direct current side is not zero, and is expressed as follows according to the current direction specified by Step 1:
icd＝|id-id'|＞ε (2)
step 4: if equation (2) is satisfied, it indicates that a two-port network internal ground fault has occurred.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2934620A1 (en) * | 2022-10-31 | 2023-02-23 | Univ Madrid Politecnica | System and method for locating ground faults in a direct current and alternating current electrical installation with a multilevel modular converter (Machine-translation by Google Translate, not legally binding) |
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- 2021-01-17 CN CN202110059025.9A patent/CN112838609A/en active Pending
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES2934620A1 (en) * | 2022-10-31 | 2023-02-23 | Univ Madrid Politecnica | System and method for locating ground faults in a direct current and alternating current electrical installation with a multilevel modular converter (Machine-translation by Google Translate, not legally binding) |
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