A blocking circuit for photovoltaic grid-connected power supply systems

Abstract

This utility model relates to the field of substation electrical control technology, specifically a blocking circuit for a photovoltaic grid-connected substation power supply system. It includes closing blocking circuits for the substation power supply system sectionalizing switches 4DL and 5DL, and a tripping circuit for the photovoltaic branch switch Q2. Substation power supply transformers No. 1, No. 2, and No. 3 are connected to the 400V I-section busbar, II-section busbar, and III-section busbar respectively via the first incoming line switch 1DL, the second incoming line switch 2DL, and the third incoming line switch 3DL. Sectioning switches 4DL and 5DL establish connections between the busbars. The photovoltaic branch switch Q2 participates in the closing circuit blocking of sectionalizing switches 4DL and 5DL. The incoming line switch 3DL, sectionalizing switches 4DL and 5DL, as well as the sectionalizing automatic transfer switch, act in reverse on the tripping circuit of the photovoltaic branch switch Q2. This achieves the requirement of "self-generation and self-consumption, surplus power to the grid, and prohibition of supplying production loads" for the photovoltaic system.

Description

Technical Field

[0001] This utility model relates to the field of electrical control technology for substations, specifically a locking circuit for photovoltaic grid-connected substation power systems. Background Technology

[0002] Installing photovoltaic glass in substations to generate new energy is of strategic necessity. It not only responds to the national "dual carbon" policy requirements and reduces the carbon emission intensity of the power grid, but also efficiently activates the idle space resources on the roof and facade of substations. Through self-consumption and grid connection of surplus electricity, the cost of purchasing electricity can be significantly reduced. At the same time, typical photovoltaic system projects have an investment payback period of 5-7 years and an environmental benefit of reducing carbon emissions by 800 tons per megawatt per year. This makes the model a key path for building a new power system and promoting the green upgrading of substations, with significant economic benefits and demonstration value.

[0003] The connection of a photovoltaic (PV) system to the power grid should be determined based on its own power generation capacity, the local power supply network, and a comprehensive consideration of the transmission and distribution capacity, power quality, and other technical requirements of the grid at the voltage level to be connected. According to the "Technical Regulations for Grid Connection of Photovoltaic Power Stations by the State Grid Corporation of China," considering factors such as system power flow balance and system acceptance capacity, and after technical and economic analysis, PV systems within substations are typically connected to the station's power system at a voltage level of 400V.

[0004] Substation power supply system loads are classified into three levels—Class I, Class II, and Class III—based on power supply reliability requirements. Class I and Class II loads are more critical, while Class III loads are those for which prolonged power outages will not directly affect operation and production. Given the intermittent and fluctuating output power of photovoltaic (PV) power generation systems, their power supply reliability is insufficient to meet the power quality requirements of Class I and Class II loads. Based on operational experience and multi-level technical reviews and assessments, it is recommended that PV power generation systems, in principle, only connect to Class III load buses, prioritizing residential loads. Electrical isolation design should ensure complete decoupling between the PV system and production load circuits. This approach ensures the reliability of power supply to critical equipment within the substation while maximizing the on-site consumption of PV power.

[0005] Currently, the main wiring configurations of grid-connected photovoltaic (PV) power systems vary, primarily in the location of the PV access point. PV power generation systems are generally equipped with anti-reverse current devices, strictly limiting the PV system's power feed to the grid. In some cases, the PV access point is mixed with production and residential power supply on the same busbar, making the power supply target unclear. Other PV power generation systems rely on anti-islanding protection for complete grid disconnection, or on anti-reverse current devices to disconnect some PV modules from the grid, without establishing interlocking relationships with the power station's switches or participating in the operation logic of the power station's automatic transfer switch.

[0006] The disadvantages of the above technology are as follows:

[0007] 1) Poor economic efficiency

[0008] Current photovoltaic systems used in substations are designed based on the principle of self-consumption with surplus power not being fed into the grid. They are equipped with anti-reverse current devices and smart energy management tools. When the photovoltaic system generates more power than the load of the bus, it automatically disconnects from the substation power system or disconnects some photovoltaic modules from the grid. This makes it impossible to feed surplus power into the grid, thus failing to fully realize the economic benefits of installing photovoltaic modules and resulting in a long investment payback period.

[0009] 2) Poor reliability

[0010] The photovoltaic power generation system and the substation power supply system remain relatively independent, with no interlocking logic between them. This lack of coordination during fault switching poses a certain operational risk. Furthermore, some substations have both residential and industrial loads connected to the same busbar; the integration of the photovoltaic power generation system will, to some extent, reduce the reliability of power supply to the industrial loads.

[0011] Therefore, how to achieve the requirement of "self-generation and self-consumption, surplus power to the grid, and prohibition of supply to production load" between photovoltaic systems and station power systems is a technical problem that needs to be solved. Utility Model Content

[0012] The problem to be solved is to establish an interlocking control between the photovoltaic system and the power supply system to achieve the requirement of "self-generation and self-consumption, surplus power to the grid, and prohibition of supply to production loads" for the photovoltaic system.

[0013] To achieve the above objectives, this utility model provides the following technical solution: a blocking circuit for a photovoltaic grid-connected substation power supply system, including closing blocking circuits for substation power supply system sectionalizing switches 4DL and 5DL, and tripping circuits for photovoltaic branch circuit switches Q2; three incoming power supplies include substation transformer No. 1, substation transformer No. 2, and substation transformer No. 3; substation transformer No. 1, substation transformer No. 2, and substation transformer No. 3 are respectively connected to the first incoming switch 1DL, the second incoming switch 2DL, and the third incoming switch 5DL. The three-way incoming line switch 3DL is connected to the 400V section I bus, section II bus, and section III bus; the sectionalizing switch 4DL is connected between section I bus and section II bus, and the sectionalizing switch 5DL is connected between section II bus and section III bus; the photovoltaic branch switch Q2 participates in the closing circuit interlocking of sectionalizing switches 4DL and 5DL, and the incoming line switch 3DL, sectionalizing switch 4DL, sectionalizing switch 5DL, and the sectionalizing backup automatic transfer switch act in reverse on the tripping circuit of the photovoltaic branch switch Q2.

[0014] Preferably, in the closing interlocking circuits of sectionalizing switches 4DL and 5DL:

[0015] The closing conditions for section switch 4DL are: switch Q2 is in the open state and incoming switch 1DL is in the open state, or incoming switch 2DL and incoming switch 3DL are in the open state, or section switch 5DL and incoming switch 3DL are in the open state.

[0016] The closing conditions for sectionalizing switch 5DL are: switch Q2 is in the open state and incoming switch 2DL is in the open state, or incoming switch 1DL and incoming switch 3DL are in the open state, or sectionalizing switch 4DL and incoming switch 3DL are in the open state.

[0017] Preferably, the tripping circuit of the photovoltaic branch switch Q2 is equipped with a shunt tripping device MX, which is triggered to trip when any of the following conditions are met:

[0018] The No. 3 substation has been taken out of service, and the incoming line switch 3DL is in the open state.

[0019] Section switch 4DL or section switch 5DL closed;

[0020] When the sectional automatic transfer switch 1DL or the incoming switch 2DL trips simultaneously at the outlet of the busbar.

[0021] Preferably, a normally open auxiliary contact of switch Q2 is connected in series in the tripping circuit to automatically disconnect the tripping circuit after the switch is opened.

[0022] Preferably, the photovoltaic system only connects to the III busbar to send the surplus power to the No. 3 substation transformer, and it is prohibited to supply power to the production loads of the I and II busbars.

[0023] Compared with existing technologies, this utility model provides a blocking circuit for photovoltaic grid-connected substation power supply systems, which has the following beneficial effects: This utility model proposes an optimized blocking circuit scheme for photovoltaic grid-connected substation power supply systems. By establishing a bidirectional blocking interlocking mechanism between the photovoltaic system switch and the traditional substation power supply system switch, and coordinating it with the timing of segmented automatic transfer switching, it can ensure the reliable isolation of photovoltaic power sources during the backup process and avoid backup failure due to improper timing coordination. This scheme simultaneously solves the dual requirements of safe and reliable operation of photovoltaic grid connection and substation power supply systems, providing a systematic solution for this typical configuration of photovoltaic grid-connected substation power supply systems, and realizing the requirements of "self-generation and self-consumption, surplus power to the grid, and prohibition of supply to production loads" for photovoltaic systems. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the photovoltaic grid-connected power supply system of this utility model;

[0025] Figure 2 This is a schematic diagram of the segment switches and the switch closing interlocking circuit of this utility model;

[0026] Figure 3 This is a schematic diagram of the photovoltaic system switch tripping circuit of this utility model. Detailed Implementation

[0027] The technical solutions of the present utility model will now be described with reference to the accompanying drawings in the embodiments of the present utility model:

[0028] Based on the problems raised in the background art, this utility model proposes a locking circuit for a photovoltaic grid-connected station power system. This system, premised on meeting the principle of "self-generation and self-consumption, surplus power to the grid, and prohibition of supplying production loads" for photovoltaic systems, introduces an interlocking mechanism between the photovoltaic system and the station power system, and optimizes the coordination relationship between the segmented automatic transfer switch operation logic and the photovoltaic branch switch tripping circuit, thus fully ensuring the safe and reliable operation of the photovoltaic grid-connected station power system.

[0029] The main wiring diagram of the power supply system for grid-connected photovoltaic substations is as follows: Figure 1 As shown. The power supply system of this station includes three incoming power sources: substation transformer No. 1, substation transformer No. 2, and substation transformer No. 3. Substation transformers No. 1 and No. 2 are respectively drawn from the low-voltage side of two main transformers within the substation, while substation transformer No. 3 is drawn from an external power source. The interlocking circuit of the photovoltaic grid-connected substation power supply system includes the closing interlocking circuit of the substation power supply system sectionalizing switch 4DL and sectionalizing switch 5DL, as well as the tripping circuit of the photovoltaic branch switch Q2. Substation transformers No. 1-3 are all operating transformers. On the low-voltage side, each of the incoming line switches 1DL, 2DL, and 3DL connects to a section of 400V busbar (section I, section II, and section III busbar). Section sectionalizing switch 4DL is connected between section I and section II busbars, and section sectionalizing switch 5DL is connected between section II and section III busbars. The photovoltaic branch switch Q2 participates in the closing circuit interlocking of the sectionalizing switches 4DL and 5DL. The incoming switch 3DL, sectionalizing switches 4DL, 5DL and the sectionalizing backup automatic transfer switch act in reverse on the tripping circuit of the photovoltaic branch switch Q2.

[0030] In the closing interlocking circuits of sectionalizing switches 4DL and 5DL: the closing conditions for sectionalizing switch 4DL are: switch Q2 is in the open state, and incoming line switch 1DL is in the open state, or incoming line switch 2DL and incoming line switch 3DL are in the open state, or sectionalizing switch 5DL and incoming line switch 3DL are in the open state; the closing conditions for sectionalizing switch 5DL are: switch Q2 is in the open state, and incoming line switch 2DL is in the open state, or incoming line switch 1DL and incoming line switch 3DL are in the open state, or sectionalizing switch 4DL and incoming line switch 3DL are in the open state.

[0031] Under normal operating conditions, incoming line switch 1DL, incoming line switch 2DL and incoming line switch 3DL are closed, and sectionalizing switch 4DL and sectionalizing switch 5DL are open. Any two of the substation service transformers at station 1, station 2 and station 3 are prohibited from operating in parallel.

[0032] The HVAC, lighting, and other living loads in the main control and communication building are handled by Figure 1The photovoltaic (PV) substation shown in the diagram has two incoming lines: one connects to the low-voltage side section III busbar of substation No. 3 via switches Q1 and Q0, and the other connects to the PV system via switch Q2. The PV system only connects to the section III busbar to supply surplus power to substation No. 3, and is prohibited from supplying power to the production loads on sections I and II busbars. The production loads within the substation are supplied by substation No. 1 and substation No. 2, respectively. When either substation No. 1 or substation No. 2 is out of service, the corresponding section switch 4DL or section switch 5DL is switched on by the sectional backup automatic switching system, enabling substation No. 3 to supply power to the production loads within the substation via section switch 4DL or section switch 5DL.

[0033] Considering the safety of the working power supply, the general principle for photovoltaic system access station power system is as follows: the photovoltaic power generation system only supplies power to the residential loads connected to the photovoltaic sub-screens, adopts the principle of "self-generation and self-consumption, surplus power to the grid", and prohibits supplying power to the production loads of the station power system's Section I busbar and Section II busbar.

[0034] Under normal operating conditions, when the power generation of the photovoltaic system is greater than the energy consumption of the main control communication building's living load, the excess power is connected to the III section busbar through switches Q1 and Q0, and then supplied to the power grid through the No. 3 substation transformer; when the power generation of the photovoltaic system is less than the energy consumption of the main control communication building's living load, the photovoltaic system's power generation and the No. 3 substation transformer simultaneously supply power to the load on the photovoltaic sub-screen.

[0035] When the photovoltaic system experiences a power generation failure, switch Q2 is tripped, and power is supplied directly to the control and communication building's living load on the photovoltaic sub-screen via switch Q0 and switch Q1 from station No. 3.

[0036] When the No. 3 station transformer fails and goes out of service, the anti-islanding protection will automatically disconnect the photovoltaic system from the grid. At this time, the No. 1 or No. 2 station transformer can supply power to the load on the photovoltaic panel by manually closing the 4DL or 5DL sectionalizing switch.

[0037] When the No. 1 or No. 2 substation service transformer fails and goes out of service, the sectionalized automatic transfer switch will trip the 1DL switch of the substation service transformer at the same time as the sectionalized automatic transfer switch disconnects the bus outlet, and trips the switch Q2, so that the photovoltaic system is disconnected from the grid. After a certain delay, the sectionalized switch 4DL or sectionalized switch 5DL will be closed, and the No. 3 substation service transformer will supply power to the production load of the I section bus and the II section bus.

[0038] Based on the general principles of photovoltaic grid connection mentioned above, the closing interlocking circuits of sectionalizing switches 4DL and 5DL are optimized, such as... Figure 2 As shown. The closing interlocking circuits of incoming line switches 1DL, 2DL, and 3DL are consistent with existing technical solutions, and will not be described again in this utility model. The closing interlocking circuits of sectionalizing switches 4DL and 5DL are designed as follows: Figure 2As shown, before closing sectionalizing switch 4DL or sectionalizing switch 5DL, it must be ensured that switch Q2 of the photovoltaic branch is in the open position to prevent photovoltaic system power from entering the I or II busbar. For closing sectionalizing switch 4DL, closing sectionalizing switch 4DL is permitted when incoming switch 1DL is in the open position; when incoming switch 1DL is in the closed position, incoming switch 3DL must be in the open position, and at least one of incoming switch 2DL and sectionalizing switch 5DL must be in the open position to prevent parallel operation of the station service transformer. The interlocking circuit for closing sectionalizing switch 5DL maintains a symmetrical design with sectionalizing switch 4DL, following the same anti-misoperation principle. Closing sectionalizing switch 5DL is permitted when incoming switch 2DL is in the open position; when incoming switch 2DL is in the closed position, incoming switch 3DL must be in the open position, and at least one of incoming switch 1DL and sectionalizing switch 4DL must be in the open position to prevent parallel operation of the station service transformer. This ensures the safe and reliable operation of the system under various fault conditions. Incoming line switch 1DL, incoming line switch 2DL, incoming line switch 3DL, sectionalizing switch 4DL, sectionalizing switch 5DL, and switch Q2 are all connected in series in the closing interlocking circuit of sectionalizing switch 4DL and sectionalizing switch 5DL in the form of normally closed auxiliary contacts.

[0039] It should be noted that the automatic switching logic of the station power system is unidirectional, supporting only automatic switching operations from the No. 3 station power transformer to either the I or II busbar. Reverse operations must be performed manually.

[0040] The tripping circuit of photovoltaic branch switch Q2 is configured with a shunt trip device MX and a fuse FU. Auxiliary contacts of incoming line switch 3DL, sectionalizing switch 4DL, and sectionalizing switch 5DL, as well as a sectionalizing backup automatic transfer switch output, are connected in parallel between fuse FU and shunt trip device MX. The tripping operation principle of shunt trip device MX is as follows: Figure 3 As shown. Specifically: 1) Substation No. 3 is taken out of operation, and incoming line switch 3DL is in the open state; 2) Section switch 4DL or section switch 5DL is closed; 3) When the section backup automatic transfer trips incoming line switch 1DL or incoming line switch 2DL, and simultaneously disconnects the busbar operation output; The tripping action of the shunt trip device MX is triggered when any of the above conditions 1), 2), and 3) are met. To prevent damage to the trip coil from prolonged energization, a normally open auxiliary contact of switch Q2 is connected in series in the trip circuit to automatically disconnect the trip circuit after the switch is opened. Furthermore, to ensure that the section backup transfer can reliably complete the closing operation of the section switches, the shunt tripping action time of the photovoltaic branch switch Q2 should be avoided when setting the closing and closing time parameters of the section switches.

[0041] This utility model discloses a photovoltaic grid-connected substation power system that connects to the substation power system under the principle of "self-generation and self-consumption, surplus power to the grid, and prohibition of supplying production loads." The external power source serves not only as a hot backup power source for the substation's production loads but also as the grid connection point for the photovoltaic power generation system. The optimized blocking circuit scheme for the substation power system after photovoltaic grid connection comprehensively considers the timing coordination of segmented automatic transfer switches. The tripping circuit of the photovoltaic branch switch Q2, in coordination with the action timing of the segmented automatic transfer switches in the substation power system, can fully guarantee the safe and reliable operation of the photovoltaic grid-connected substation power system, providing multiple safeguards for its safe and reliable operation. It realizes the overall principle of "self-generation and self-consumption, surplus power to the grid, and prohibition of supplying production loads" for the photovoltaic system; it not only solves the power supply reliability problems that may arise after photovoltaic grid connection but also avoids the risks of power paralleling and mis-supply through the reverse action of the segmented automatic transfer switches on the tripping circuit of the photovoltaic branch switch Q2. It features a clear structure, rigorous logic, and simple implementation, and is suitable for the renovation and new construction projects of substation power systems with various photovoltaic connections.

[0042] The above embodiments are merely some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

Claims

1. A latching circuit for a photovoltaic grid-tied station service system, characterized by: The system includes the closing interlocking circuits of the sectionalizing switches 4DL and 5DL for the station power system, and the tripping circuit of the photovoltaic branch switch Q2. Three incoming power supplies are provided: station transformer No. 1, station transformer No. 2, and station transformer No.

3. Station transformers No. 1, 2, and 3 are connected to the 400V I-section busbar, II-section busbar, and III-section busbar respectively via the first incoming switch 1DL, the second incoming switch 2DL, and the third incoming switch 3DL. Sectioning switch 4DL is connected between the I-section busbar and the II-section busbar, and sectioning switch 5DL is connected between the II-section busbar and the III-section busbar. Photovoltaic branch switch Q2 participates in the closing circuit interlocking of sectionalizing switches 4DL and 5DL. Incoming switches 3DL, sectionalizing switches 4DL and 5DL, as well as the sectionalizing backup automatic transfer switch, act in reverse on the tripping circuit of photovoltaic branch switch Q2.

2. The interlocking circuit for a photovoltaic grid-connected substation power supply system as described in claim 1, characterized in that: In the closing interlocking circuits of sectionalizing switches 4DL and 5DL: The closing conditions for section switch 4DL are: switch Q2 is in the open state and incoming switch 1DL is in the open state, or incoming switch 2DL and incoming switch 3DL are in the open state, or section switch 5DL and incoming switch 3DL are in the open state. The closing conditions for sectionalizing switch 5DL are: switch Q2 is in the open state and incoming switch 2DL is in the open state, or incoming switch 1DL and incoming switch 3DL are in the open state, or sectionalizing switch 4DL and incoming switch 3DL are in the open state.

3. The interlocking circuit for a photovoltaic grid-connected substation power supply system as described in claim 1, characterized in that: The tripping circuit of the photovoltaic branch switch Q2 is equipped with a shunt tripping device MX, which will trigger the tripping action of the shunt tripping device MX if any of the following conditions are met: The No. 3 substation has been taken out of service, and the incoming line switch 3DL is in the open state. Section switch 4DL or section switch 5DL closed; When the sectional automatic transfer switch 1DL or the incoming switch 2DL trips simultaneously at the outlet of the busbar.

4. The interlocking circuit for a photovoltaic grid-connected substation power supply system as described in claim 3, characterized in that: A normally open auxiliary contact of switch Q2 is connected in series in the trip circuit to automatically disconnect the trip circuit after the switch is opened.

5. A blocking circuit for a photovoltaic grid-connected substation power supply system as described in claim 1, characterized in that: The photovoltaic system will only connect to the III busbar to send the surplus power to the No. 3 substation transformer, and it is prohibited to supply power to the production loads of the I and II busbars.

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