CN113765059A - Differential protection method suitable for main transformer of photovoltaic power station - Google Patents
Differential protection method suitable for main transformer of photovoltaic power station Download PDFInfo
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- CN113765059A CN113765059A CN202111003366.0A CN202111003366A CN113765059A CN 113765059 A CN113765059 A CN 113765059A CN 202111003366 A CN202111003366 A CN 202111003366A CN 113765059 A CN113765059 A CN 113765059A
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- main transformer
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- 230000004224 protection Effects 0.000 title claims abstract description 49
- 238000000034 method Methods 0.000 title claims abstract description 22
- 230000008859 change Effects 0.000 claims abstract description 17
- 230000035772 mutation Effects 0.000 claims abstract description 4
- 230000000903 blocking effect Effects 0.000 claims description 5
- 230000010354 integration Effects 0.000 claims description 3
- 230000009471 action Effects 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 3
- 230000005284 excitation Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000002889 sympathetic effect Effects 0.000 description 1
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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
- H02H7/04—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 for transformers
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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
- H02H7/04—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 for transformers
- H02H7/045—Differential protection of transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
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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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Supply And Distribution Of Alternating Current (AREA)
Abstract
The invention discloses a differential protection method suitable for a main transformer of a photovoltaic power station, which comprises the following steps: collecting three-phase currents on two sides of a main transformer differential protection of a photovoltaic power station when the main transformer differential protection is locked through a current transformer, and obtaining three-phase differential currents through phasor summation; comparing the difference value between the second harmonic phase and the double phase of the fundamental wave, and determining the change time of the difference value as the mutation time of the differential current; and calculating a second harmonic ratio of the three-phase differential current at the moment of sudden change of the differential current, comparing whether the second harmonic ratio is higher than a fault fixed value, if so, protecting the opening and cutting off the fault until the second harmonic ratio is lower than the fixed value of the inrush current, and protecting the closing and the locking. The differential protection of the main transformer of the photovoltaic power station can still reliably distinguish the internal fault state and open in time when the differential protection is locked and suffers from internal faults due to two types of inrush currents, and the action refusing of protection caused by high-content second harmonic waves due to short-circuit current provided by a photovoltaic power supply is prevented.
Description
Technical Field
The invention belongs to the technical field of transformers, and relates to a differential protection method suitable for a main transformer of a photovoltaic power station.
Background
The differential protection is one of main protections configured for the main transformer of the photovoltaic power station, has the advantages of reliably distinguishing internal and external faults of a protection area, instantaneously removing the internal faults and avoiding the interferences such as excitation surge current and the like, and plays an extremely important role in the safe operation of the photovoltaic power station. In most cases, in order to meet the requirements of power grid dispatching and auxiliary power and natural energy fluctuation characteristics, main transformers in a photovoltaic power station are mostly switched between a working state and a shutdown state, terminal voltage of one main transformer is suddenly changed due to no-load switching-on of the main transformer, iron core magnetic flux saturation is caused, and excitation inrush current is generated. In addition, when the main transformer has an in-zone fault, the short-circuit current provided by the photovoltaic power supply may contain a large second harmonic content due to the existence of power electronic devices such as inverters in the photovoltaic power generation units. Therefore, when the main transformer differential protection of the photovoltaic power station is locked due to two types of inrush currents and suffers from internal faults, due to high-content second harmonics caused by short-circuit current provided by the photovoltaic power supply, the protection is mistaken to continue to be locked in an inrush current state during the internal faults, and therefore the protection cannot be opened in time to remove the internal faults and generate rejection.
Disclosure of Invention
The invention aims to provide a differential protection method suitable for a main transformer of a photovoltaic power station, and solves the problem that in the prior art, when differential protection locked by inrush current has an internal fault, the protection cannot be opened in time to remove the internal fault due to high-content second harmonic waves caused by short-circuit current provided by a photovoltaic power supply, so that action rejection is generated.
The invention adopts the technical scheme that the differential protection method suitable for the main transformer of the photovoltaic power station comprises the following steps:
step 1, collecting two-side three-phase currents when the main transformer differential protection of the photovoltaic power station is locked through a current transformer
Obtaining three-phase differential current through phasor summation;
step 2, comparing the difference value delta theta of the second harmonic phase and the double phase of the fundamental wave in the three-phase differential current, and determining the change time of the delta theta value as the mutation time of the differential current;
step 3, calculating the second harmonic ratio K of the three-phase differential current at the moment of sudden change of the differential currentdComparison KdWhether or not it is higher than a constant value Kdset,faultIf K isdHigher than a constant value Kdset,faultThen the fault is removed until KdConstant value K below inrush currentdset,inrushAnd the protection exits the locking.
The invention is also characterized in that:
the differential current abrupt change timing is a timing at which the value of Δ θ fluctuates around 0 ° or 180 °.
Constant value Kdset,faultTake the maximum value during the duration of the inrush current.
K of inrush currentdset,inrushTaking the fixed value of 0.15-0.2 of the conventional inrush current blocking.
The change time of the delta theta value is obtained by adopting a curve fitting method in a numerical integration discipline.
The invention has the beneficial effects that:
the differential protection method applicable to the main transformer of the photovoltaic power station can ensure that the differential protection of the main transformer of the photovoltaic power station can still reliably and correctly distinguish the internal fault state and open in time when the inrush current blocking state exists; based on the fact that the second harmonic ratio of differential current is higher than the maximum value of the second harmonic ratio when the differential protection of a main transformer of a photovoltaic power station has internal faults, the second harmonic ratio fixed value at the moment of the internal faults is established, so that the differential protection is opened in time to remove the faults, the differential protection rejection caused by high-content second harmonic waves when the photovoltaic system has the internal faults is prevented, and the differential protection working mode with excellent distinguishing performance is established.
Drawings
FIG. 1 is a flow chart of a differential protection method for a main transformer of a photovoltaic power station according to the present invention;
FIG. 2 is a schematic diagram of differential protection simulation of the differential protection method for the main transformer of the photovoltaic power station according to the present invention;
FIG. 3 is a waveform diagram of three-phase differential current and second harmonic ratio in the presence of inrush current and faults in a differential protection method for a main transformer of a photovoltaic power station according to the present invention;
fig. 4 is a diagram of a change law of a differential current phase difference in a differential protection method applicable to a main transformer of a photovoltaic power station.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
A differential protection method suitable for a main transformer of a photovoltaic power station, as shown in fig. 1, includes the following steps:
step 1, collecting two-side three-phase currents when the main transformer differential protection of the photovoltaic power station is locked through a current transformer
Obtaining three-phase differential current through phasor summation;
step 2, comparing the difference value delta theta of the second harmonic phase and the double phase of the fundamental wave in the three-phase differential current, and determining the time when the delta theta fluctuates at 0 degrees or 180 degrees as the sudden change time of the differential current;
the principle of judging the sudden change time of the differential current is as follows: the change of a delta theta value in the differential current in the inrush current locking process is obtained by adopting a curve fitting method in a numerical integration discipline according to the existing fault current recording data: since the decay rate of the free component of the sympathetic inrush current is slow, the value of delta theta is basically kept at 0 degrees or 180 degrees, while the decay rate of the free component of the short-circuit current at the time of the fault is fast, and the value of delta theta fluctuates around 0 degrees or 180 degrees. Therefore, the occurrence timing of the fault current in the differential current can be discriminated from the value of Δ θ.
Step 3, calculating the second harmonic ratio K of the sudden change moment according to the three-phase differential currentdComparison KdWhether or not it is higher than a constant value Kdset,faultIf K isdHigher than a constant value Kdset,faultThen the fault is removed until KdConstant value K below inrush currentdset,inrushProtection quit locking; wherein, the constant value Kdset,faultTaking the maximum value in the continuous process of the inrush current and the constant value K of the inrush currentdset,inrushTaking the fixed value of 0.15-0.2 of the conventional inrush current blocking.
Through the mode, the differential protection method applicable to the main transformer of the photovoltaic power station can ensure that when the differential protection of the main transformer of the photovoltaic power station is in the inrush blocking state, the internal fault state can still be reliably and correctly distinguished and opened in time under the condition of high-content second harmonic waves brought by a photovoltaic system when the internal fault occurs; based on the fact that the second harmonic ratio of differential current is higher than the maximum value of the second harmonic ratio when the differential protection of a main transformer of a photovoltaic power station has internal faults, the second harmonic ratio fixed value at the moment of the internal faults is established, so that the differential protection is opened in time to remove the faults, the differential protection rejection caused by the problem of high content of second harmonic waves brought by the internal faults of a photovoltaic system is prevented, and the differential protection working mode with excellent distinguishing performance is established.
Examples
As shown in fig. 2, in the present embodiment, a photovoltaic power station simulation model with a capacity of 50MW is provided, a transformer T1 is set to be switched on in an unloaded state, and a fault occurs at f1 in a protection area of an operating transformer T2.
Step 1, collecting two-side three-phase currents when the main transformer differential protection of the photovoltaic power station is locked through a current transformer
Three-phase differential currents are obtained through phasor summation, and are shown in FIG. 3;
step 2, comparing the difference value delta theta of the second harmonic phase and the double phase of the fundamental wave in the three-phase differential current, obtaining the change characteristic of the delta theta through cosine curve fitting, and determining the time when the delta theta fluctuates at 0 degrees or 180 degrees as the mutation time of the differential current, wherein the change characteristic is shown in fig. 4;
step 3, calculating the second harmonic ratio K of the three-phase differential current at the sudden change momentdComparison KdWhether or not it is higher than a constant value Kdset,faultIf K isdHigher than a constant value Kdset,faultThen the fault is removed until KdK below inrush currentdset,inrushProtection quit locking; wherein, three-phase K after various internal faults are simulatedd,faultHigher than the maximum value K during the duration of the inrush currentd,inrushTo set, see Table 1, for a constant value of Kdset,inrushTaking conventional 0.15-0.2.
TABLE 1 second harmonic ratio at different internal faults
Claims (5)
1. A differential protection method suitable for a main transformer of a photovoltaic power station is characterized by comprising the following steps:
step 1, collecting three-phase currents on two sides of main transformer differential protection of photovoltaic power station when locking through current transformer
Obtaining three-phase differential current through phasor summation;
step 2, comparing the difference value delta theta of the second harmonic phase and the double phase of the fundamental wave in the three-phase differential current, and determining the change time of the delta theta value as the mutation time of the differential current;
step 3, calculating a second harmonic ratio K of the three-phase differential current at the moment of sudden change of the differential currentdComparison KdWhether or not it is higher than a constant value Kdset,faultIf K isdHigher than a constant value Kdset,faultThen the fault is removed until KdConstant value K below inrush currentdset,inrushAnd the protection exits the locking.
2. The differential protection method for the main transformer of the photovoltaic power station as claimed in claim 1, wherein the time of the differential current abrupt change is a time when the value of Δ θ fluctuates around 0 ° or 180 °.
3. The differential protection method for main transformer of photovoltaic power station as claimed in claim 1, characterized in that said constant value K isdset,faultTake the maximum value during the duration of the inrush current.
4. The differential protection method applicable to the main transformer of the photovoltaic power station as claimed in claim 1, wherein the K of the inrush current isdset,inrushTaking the fixed value of 0.15-0.2 of the conventional inrush current blocking.
5. The differential protection method for the main transformer of the photovoltaic power station as claimed in claim 1, wherein the variation time of the Δ θ value is obtained by a curve fitting method in numerical integration discipline.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202111003366.0A CN113765059A (en) | 2021-08-30 | 2021-08-30 | Differential protection method suitable for main transformer of photovoltaic power station |
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| CN202111003366.0A CN113765059A (en) | 2021-08-30 | 2021-08-30 | Differential protection method suitable for main transformer of photovoltaic power station |
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| CN113765059A true CN113765059A (en) | 2021-12-07 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116706835A (en) * | 2022-12-29 | 2023-09-05 | 国家电网有限公司 | Method, device, medium and equipment for identifying inrush current of transformer |
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2021
- 2021-08-30 CN CN202111003366.0A patent/CN113765059A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116706835A (en) * | 2022-12-29 | 2023-09-05 | 国家电网有限公司 | Method, device, medium and equipment for identifying inrush current of transformer |
| CN116706835B (en) * | 2022-12-29 | 2024-02-23 | 国家电网有限公司 | Method, device, medium and equipment for identifying inrush current of transformer |
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