CN115603287A - Distributed photovoltaic maximum access capacity realization method considering current quick-break protection - Google Patents
Distributed photovoltaic maximum access capacity realization method considering current quick-break protection Download PDFInfo
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- CN115603287A CN115603287A CN202110719714.8A CN202110719714A CN115603287A CN 115603287 A CN115603287 A CN 115603287A CN 202110719714 A CN202110719714 A CN 202110719714A CN 115603287 A CN115603287 A CN 115603287A
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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
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention relates to a distributed photovoltaic maximum access capacity realization method considering current quick-break protection, which obtains the maximum value of current increase percentage by a preset mode when calculating the maximum photovoltaic capacity which can be accessed by a switch station on the premise of not false-operating the current quick-break protection, further calculates to obtain a reliability coefficient and a maximum current amplitude, and calculates to obtain the maximum photovoltaic accessible capacity after converting the maximum photovoltaic capacity into the distributed photovoltaic capacity.
Description
Technical Field
The invention relates to a technology in the field of power control, in particular to a distributed photovoltaic maximum access capacity realization method considering normal work of current quick-break protection.
Background
After large-scale distributed photovoltaic is connected to a power distribution network, due to the intermittent nature of photovoltaic power generation and the nonlinear relation between output current and grid-connected point voltage, fault current characteristics are changed, distributed photovoltaic can generate an increase assisting effect on downstream current quick-break protection of a grid-connected switching station, so that the protection range of the current quick-break protection is enlarged, false operation of the current quick-break protection can be caused, and the power failure area is enlarged. In addition, the distributed photovoltaic is an inverter power supply, the control is very flexible, and during a line fault, the distributed photovoltaic may be in different power factors, which may cause the phase of the output current of the distributed photovoltaic to change, and also may cause the strength of the boosting effect to change, thus aggravating the fluctuation of the current protection range after the distributed photovoltaic is connected to the power distribution network.
Disclosure of Invention
The invention provides a distributed photovoltaic maximum access capacity implementation method considering current quick-break protection, aiming at the defect that the prior art does not consider the boosting effect strength change caused by different phases of distributed photovoltaic short-circuit current, and based on the influence of the boosting effect of distributed photovoltaic on the current quick-break protection of a power distribution network, the influence of different power factors of the distributed photovoltaic on the current quick-break protection range during a fault is considered, and no matter how the power factor is during the fault of the distributed photovoltaic, when a lower-level line fails, the current quick-break protection cannot be mistaken, so that the condition that the current quick-break protection is mistaken due to excessive access of the distributed photovoltaic can be avoided, and a theoretical basis can be provided for the evaluation of the power distribution network on the distributed photovoltaic absorption.
The invention is realized by the following technical scheme:
the invention relates to a distributed photovoltaic maximum access capacity realization method considering current quick-break protection.
The method specifically comprises the following steps:
The percentage of current increase is: when the downstream line of the switching station connected with the distributed photovoltaic system fails, the distributed photovoltaic system has an increase assisting effect on the downstream line protection, and the current increase amount
Wherein: e is the potential of the equivalent voltage source of the network, Z S Is the system equivalent impedance, Z 1 Line impedance from the switching station to the fault point, R g Is a transition resistance of I PV The short-circuit current provided for distributed photovoltaic, | · | is the modulus of phasor; percent increase in current
The maximum value of the current increase percentage is as follows: when the distributed photovoltaic operates at different power factors, I PV The phase of (A) is in a range of [0, 360 DEG ] under distributed photovoltaic different power factors]The range of percent increase in current is:
before calculating current quick-break protection against malfunctionAnd when the maximum photovoltaic capacity which can be accessed by the switch station is improved, the maximum value of the percentage increase of the current is obtained, so that the current quick-break protection is ensured not to be operated mistakenly.
Technical effects
The invention integrally solves the defect that the prior art does not consider the enhancement effect strength change caused by different phases of the distributed photovoltaic short-circuit current, considers different power factors during the fault period of the distributed photovoltaic when deducing the maximum photovoltaic capacity which can be accessed by the switch station under the premise of no misoperation of the current quick-break protection, selects the condition of maximizing the enhancement effect, and deduces the maximum photovoltaic capacity which can be accessed by the switch station under the premise of no misoperation of the current quick-break protection under the condition. Compared with the prior art, the method provided by the invention considers different power factors of distributed photovoltaic in the fault period, selects the condition with the maximum boosting effect, and deduces the maximum photovoltaic capacity which can be accessed by the switch station on the premise of preventing false operation of the current quick-break protection under the condition. The problem of the maximum photovoltaic access capacity error that the default distributed photovoltaic output power factor is 1 during the default fault period of the prior art finally leads to the circuit current quick-break protection maloperation is solved.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of a 10kV power distribution network of an embodiment;
fig. 3 is a schematic diagram of current flowing through the second protection circuit 2 when the distributed photovoltaic is not connected and a three-phase short circuit occurs at the end of the circuit in the embodiment;
in the figure: (a) is instantaneous value; (b) is the amplitude;
fig. 4 is a schematic diagram of a current flowing through the second protection circuit 2 under different power factors of distributed photovoltaic when the photovoltaic capacity does not exceed the maximum access capacity in the embodiment;
in the figure: (a) a power factor of 1; (b) a power factor of 0.8; (c) a power factor of 0.5; (d) a power factor of 0;
fig. 5 is a schematic diagram of currents flowing through the second protection circuit 2 under different power factors of distributed photovoltaic when the photovoltaic capacity exceeds the maximum access capacity in the embodiment;
in the figure: (a) a power factor of 1; (b) a power factor of 0.8; (c) a power factor of 0.5; and (d) the power factor is 0.
Detailed Description
As shown in fig. 1, the present embodiment relates to a method for implementing a maximum access capacity of a distributed photovoltaic system in consideration of normal operation of current quick-break protection, and is directed to a 10kV radial circuit including a distributed photovoltaic power distribution network structure, including:
As shown in fig. 2, in this embodiment, a 10kV distribution network in the shanghai region is used as verification, and the topology structure includes: the high-voltage side of the head-end transformer is connected with a high-voltage grade power supply, the low-voltage grade supplies power to a lower-level 10kV line, the 10kV power distribution network is overall radial, switch stations are arranged on every two sections of lines, and loads and distributed photovoltaic are connected into the switch stations.
The line is configured with three-stage current protection, distributed photovoltaics are connected to the grid by a switching station 90408, in this embodiment, according to line, transformer and voltage class parameter values in fig. 2, the maximum photovoltaic access capacity of the switching station calculated by the above method is 5.52MW, and the following is a specific state simulation of the current quick-break protection operation characteristics of the second protection line 2 under different distributed photovoltaic access capacities:
when the switchyard 90408 is not connected to the distributed photovoltaic and when the end of the second protection line 2 (f in fig. 2) 1 Where) is a power factor of; generation of metallic three phasesThe current flowing during the short circuit is shown in fig. 3. As can be seen from the figure, the amplitude of the current flowing through the second protection circuit 2 is 2.34kA, so the current quick-break protection setting value of the second protection circuit 2 is 2.34 × 1.1=2.57ka.
(1) When the access distributed photovoltaic capacity of the switchyard 90408 is 4MW, the access distributed photovoltaic capacity of the switchyard 90408 does not exceed the maximum photovoltaic accessible capacity of the switchyard 90408 by 5.52MW, the active and reactive proportion of the power supplied by the distributed photovoltaic during the fault is different, that is, the power factor is different, and the current flows through the second protection line 2 as shown in fig. 4. As can be seen from the figure, when the distributed photovoltaic power accessed by the switchyard 90408 does not exceed the maximum photovoltaic accessible capacity of the switchyard 90408, no matter what power factor the distributed photovoltaic power is under, the current flowing through the second protection line 2 is always smaller than the setting value of the current quick-break protection, so that the second protection line 2 does not have the situation of malfunction when the head end of the lower-stage line is short-circuited.
(2) When the access distributed photovoltaic capacity of the switchyard 90408 is 6MW, the access distributed photovoltaic capacity of the switchyard 90408 exceeds the maximum photovoltaic accessible capacity of the switchyard 90408 by 5.52MW, the active and reactive proportion of the power supplied by the distributed photovoltaic system during the fault is different, that is, the power factor is different, and the current flows through the second protection line 2 as shown in fig. 5. As can be seen from the figure, when the distributed photovoltaic connected to the switchyard 90408 exceeds the maximum photovoltaic connectable capacity of the switchyard 90408, and when the distributed photovoltaic power factor is 0, the current flowing through the second protection line 2 is greater than the setting value of the current quick-break protection, and at this time, the second protection line 2 has a risk of malfunction when the head end of the lower-level line is short-circuited.
Compared with the prior art, the method realizes the limit value distributed photovoltaic access capacity according to the distributed photovoltaic maximum access capacity considering the normal work of the current quick-break protection, can effectively avoid the condition of current quick-break protection misoperation, and improves the fault identification and isolation capability of the power distribution network.
The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (4)
1. A distributed photovoltaic maximum access capacity realization method considering current quick-break protection is characterized in that when the maximum photovoltaic capacity which can be accessed by a switch station is calculated on the premise that the current quick-break protection is not operated mistakenly in a setting mode in advance, the maximum value of the current increase percentage is obtained, then a reliability coefficient and a maximum current amplitude value are calculated, and the maximum photovoltaic accessible capacity is obtained after the maximum photovoltaic accessible capacity is converted into the distributed photovoltaic capacity.
2. The method for realizing the distributed photovoltaic maximum access capacity considering the current quick-break protection as claimed in claim 1, is characterized by comprising the following steps:
step 1, when a downstream line of a switching station connected with distributed photovoltaic is in fault, obtaining a maximum value delta I of a current increase percentage when the maximum photovoltaic capacity which can be accessed by the switching station is calculated on the premise that current quick-break protection is not operated mistakenly in a preset mode;
step 2, passing through delta I% +1<K rel I Obtaining a reliability factor K rel Ⅰ Calculating the maximum current amplitude
Convert it into distributed photovoltaic capacity
Calculating to obtain the maximum photovoltaic accessible capacity, wherein: i is act Ⅰ For a line current quick-break protection setting value, K rel Ⅰ As a reliability factor, I k To protect the current amplitude, P, flowing when a three-phase short circuit occurs at the end of the line PV For distributed photovoltaic maximum access capacity, U N And k is the rated voltage of the power grid, and k is the over-current multiple of the distributed photovoltaic.
3. The test of claim 2The method for realizing the maximum access capacity of the distributed photovoltaic system considering the current quick-break protection is characterized in that the current increase percentage refers to: when the downstream line of the switching station connected with the distributed photovoltaic system fails, the distributed photovoltaic system has an increase assisting effect on the downstream line protection, and the current increase amount
Wherein: e is the potential of the equivalent voltage source of the network, Z S Is the system equivalent impedance, Z 1 Line impedance, R, for a switching station to a fault point g To transition resistance, I PV The short-circuit current provided for distributed photovoltaic, | · | is a phasor modulus; percent increase in Current
4. The method for realizing the distributed photovoltaic maximum access capacity considering the current quick-break protection as claimed in claim 2, wherein the maximum value of the current increase percentage is as follows: when the distributed photovoltaic operates at different power factors, I PV The phase of (A) is in a range of [0, 360 DEG ] under distributed photovoltaic different power factors]The range of percent current increase is:
when the maximum photovoltaic capacity which can be accessed by a switch station is calculated on the premise that the current quick-break protection is not operated mistakenly, the maximum value of the current increase percentage is obtained, so that the current quick-break protection is ensured not to be operated mistakenly.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117638868A (en) * | 2023-10-23 | 2024-03-01 | 天津大学 | Distribution network direction current protection applicable boundary assessment method under distributed photovoltaic access |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117638868A (en) * | 2023-10-23 | 2024-03-01 | 天津大学 | Distribution network direction current protection applicable boundary assessment method under distributed photovoltaic access |
| CN117638868B (en) * | 2023-10-23 | 2024-06-04 | 天津大学 | Distribution network direction current protection applicable boundary assessment method under distributed photovoltaic access |
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