A high-capacity three-winding photovoltaic containerized transformer system and its control method

Abstract

This invention relates to a large-capacity three-winding photovoltaic containerized transformer system and its control method, comprising: a container cabin module, internally divided into a high-voltage compartment unit, a transformer compartment unit, and a low-voltage compartment unit; a three-winding transformer module, disposed within the transformer compartment unit, comprising an iron core, a high-voltage winding wound on the iron core, and two electrically independent low-voltage windings symmetrically arranged vertically along the iron core axis; a high-voltage switch module, disposed within the high-voltage compartment unit, electrically connected to the high-voltage side of the three-winding transformer module; and a low-voltage distribution module, disposed within the low-voltage compartment unit, comprising two low-voltage incoming line cabinets, each electrically connected to one of the two low-voltage windings of the three-winding transformer module. The advantages of this invention are: reduced losses; the ability to perform single-sided maintenance without interrupting operation; and the use of a segmented layered insulation structure for the transformer main circuit, improving short-circuit withstand capability and operational reliability.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power equipment technology, specifically to a large-capacity three-winding photovoltaic containerized transformer system and its control method. Background Technology

[0002] A photovoltaic containerized transformer system is a modular power conversion device that highly integrates core equipment such as photovoltaic inverters, step-up transformers, high and low voltage distribution units, and intelligent monitoring systems within a standard shipping container. As centralized photovoltaic power plants develop towards larger capacity and higher voltage levels, 34.5kV grid-connected photovoltaic systems are increasingly widely used.

[0003] In existing technologies, conventional solutions use double-split transformers paired with low-voltage parallel cabinets, which have the problems of multiple transformer links and large footprint. At the same time, the high magnetic coupling of the double low-voltage windings makes it easy to generate circulating currents. When the output of the two circuits is unbalanced, local overheating is likely to occur. Moreover, maintenance of a single circuit requires a complete shutdown of the entire station, resulting in low power station availability. Furthermore, the main air circuit insulation structure of 35kV oil-immersed transformers mostly adopts conventional layered insulation, which is insufficient for short circuit resistance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application proposes a large-capacity three-winding photovoltaic containerized transformer system and its control method, which can achieve 34.5kV grid connection, reduce losses, and features electrically independent and magnetically decoupled dual low-voltage circuits, enabling single-sided maintenance without interrupting operation. The transformer's main circuit adopts a segmented layered insulation structure, combined with U-shaped and L-shaped soft corner rings, as well as a double-sided support bar heat dissipation structure and winding margin, improving short-circuit withstand capability and enhancing the long-term operational reliability of the transformer.

[0005] The following is the technical solution of the present invention: a large-capacity three-winding photovoltaic containerized transformer system, comprising: The container cabin module is internally divided into a high-voltage compartment unit, a transformer compartment unit, and a low-voltage compartment unit; The three-winding transformer module is located in the transformer room unit. The three-winding transformer module includes an iron core, a high-voltage winding wound on the iron core, and two low-voltage windings that are symmetrically arranged vertically along the iron core axis and electrically independent. The high-voltage switch module is located in the high-voltage compartment unit and is electrically connected to the high-voltage side of the three-winding transformer module. The low-voltage power distribution module is located in the low-voltage room unit and includes two low-voltage incoming cabinets, which are electrically connected to the two low-voltage windings of the three-winding transformer module respectively. The intelligent measurement, control and protection module is connected to the three-winding transformer module, the high-voltage switch module and the low-voltage power distribution module respectively, and is used for electrical quantity acquisition, status monitoring and hierarchical protection control; The heat dissipation and protection module is used to provide heat dissipation and protection for the various units within the container cabin module.

[0006] As a preferred embodiment of the present invention, the container cabin module's cabin frame is formed by welding steel profiles, and the high-voltage chamber unit and the transformer chamber unit, as well as the transformer chamber unit and the low-voltage chamber unit, are separated by welding cold-rolled steel plates, with fireproof and heat-insulating cotton provided on the separating steel plates.

[0007] As a preferred embodiment of the present invention, in the three-winding transformer module, the high-voltage winding is arranged outside the two low-voltage windings, and in the main air-channel insulation structure between the high-voltage winding and the low-voltage winding, a support bar, a cardboard layer, a soft corner ring assembly, a cardboard layer and a support bar are arranged sequentially from the low-voltage winding side to the high-voltage winding side. The soft corner ring assembly includes a U-shaped soft corner ring and an L-shaped soft corner ring.

[0008] As a preferred embodiment of the present invention, the high-voltage switch module includes a vacuum circuit breaker, a disconnecting switch, a grounding switch, and a five-proof interlocking mechanism, which forms a mechanical interlock between the vacuum circuit breaker, the disconnecting switch, the grounding switch, and the high-voltage compartment door.

[0009] As a preferred embodiment of the present invention, the low-voltage power distribution module further includes a busbar transition cabinet, and two low-voltage incoming cabinets and the busbar transition cabinet are arranged in a triangular pattern within the low-voltage compartment unit. Each low-voltage incoming switchgear is internally divided into an upper-level busbar incoming unit and a lower-level photovoltaic branch access unit. The upper-level busbar incoming unit is equipped with an incoming circuit breaker and connected to the corresponding low-voltage winding, while the lower-level photovoltaic branch access unit is equipped with multiple photovoltaic branch molded case switches.

[0010] As a preferred embodiment of the present invention, the intelligent measurement and control and protection module includes independent measurement and control protection units corresponding to the high-voltage side, the first low-voltage circuit, and the second low-voltage circuit, as well as a communication management unit and a transformer temperature control unit connected to each measurement and control protection unit.

[0011] As a preferred embodiment of the present invention, the intelligent measurement, control and protection module is configured to perform three levels of protection: The first level is overload and short-circuit protection for the molded case switch of the photovoltaic branch in the low-voltage power distribution module; The second level is the graded protection of the low-voltage incoming line cabinet circuit breaker and the overcurrent protection of the high-voltage switch module circuit breaker. The third level is the gas and temperature protection of the three-winding transformer module, as well as the instantaneous overcurrent and zero-sequence protection on the high-voltage side.

[0012] As a preferred embodiment of the present invention, the heat dissipation and protection module includes: The transformer room's natural heat dissipation unit is achieved through the mesh door structure set in the transformer room unit and the corrugated oil tank of the three-winding transformer module; The high and low pressure chamber forced ventilation and heat dissipation unit includes an axial flow fan and air inlet louvers installed in the high pressure chamber unit and the low pressure chamber unit; The condensation control unit includes a condensation controller and a heater located in the high-pressure chamber unit and the low-pressure chamber unit.

[0013] A control method for a large-capacity three-winding photovoltaic containerized substation system includes the following steps: S1. Initialize the system and configure parameters; S2. By collecting the output current and power of the two low-voltage circuits, adjust the output of the corresponding photovoltaic sub-array inverters so that the difference in output power between the two low-voltage circuits does not exceed the preset percentage of the rated capacity of a single circuit, and the output current tends to be consistent. S3. Collect system electrical quantities and equipment status data, and issue early warnings for data approaching protection thresholds; S4. When a fault occurs, the protection action is executed according to the preset three-level protection logic.

[0014] In a preferred embodiment of the present invention, in S4, when one of the low-voltage circuits fails and is disconnected, the other low-voltage circuit is controlled to continue operating under rated load, and the operating parameters are adjusted.

[0015] The beneficial effects of this invention are: 1. In this invention, 34.5kV grid connection can be achieved, reducing losses. At the same time, the dual low-voltage circuits are electrically independent and magnetically decoupled, enabling single-sided maintenance without interrupting operation. The transformer main circuit adopts a segmented layered insulation structure, combined with U-shaped and L-shaped soft corner rings, as well as a double-sided support bar heat dissipation structure and winding margin, which improves short-circuit withstand capability and enhances the long-term operational reliability of the transformer. 2. In this invention, a three-unit low-voltage cabinet structure with a triangular arrangement is adopted, which improves the space utilization rate. At the same time, the cabinet is divided into a double-layer structure. The two incoming cabinets can accommodate up to 32 320A molded case switches. With the 6 expansion switches reserved in the transition cabinet, the total number of connected branches can reach 38, which greatly improves the system scalability. In addition, it can be operated inside the cabinet, avoiding the impact of outdoor weather on equipment and operation, and improving operational safety. 3. In this invention, only hoisting, cable connection and grid connection commissioning are required on site, which shortens the installation cycle. It is equipped with five-proof interlocking and remote operation and maintenance interface, and can be connected to the photovoltaic power station SCADA or cloud platform to achieve unattended operation and improve applicability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the container transformer system of the present invention; Figure 2 This is a cross-sectional schematic diagram of the main air channel insulation structure of the transformer of the present invention; Figure 3A schematic diagram of the triangular arrangement of the low-voltage power distribution module of the present invention; Figure 4 These are the steps of the container transformer substation operation control method of the present invention; 1. Container cabin module; 101. Cabin frame; 102. Cabin partition structure; 103. High-voltage compartment unit; 104. Transformer compartment unit; 105. Low-voltage compartment unit; 2. Three-winding transformer module; 201. Core assembly; 202. Low-voltage winding assembly; 203. High-voltage winding assembly; 204. Main air passage insulation structure; 2041. First support bar; 2042. First cardboard layer; 2043. U-shaped soft corner ring; 2044. L-shaped soft corner ring; 2045. Second cardboard layer; 2046. Second support bar; 205. Fuel tank assembly; 206. Temperature control assembly; 3. High-voltage switch module; 301. Vacuum circuit breaker; 302. Disconnecting switch; 303. Grounding switch; 304. 305. Surge arrester; 306. Voltage transformer; 307. Current transformer; 308. Five-proof interlocking mechanism; 309. High-voltage cabinet; 4. Low-voltage distribution module; 401. Low-voltage incoming line cabinet; 402. Busbar transition cabinet; 5. Intelligent measurement and control and protection module; 501. High-voltage side measurement and control protection unit; 502. Dual low-voltage side independent measurement and control protection unit; 503. Transformer temperature control unit; 504. Communication management unit; 505. Human-machine interaction unit; 506. Remote operation and maintenance interface; 6. Heat dissipation and protection module; 601. Transformer room natural heat dissipation unit; 602. High and low voltage room forced ventilation heat dissipation unit; 603. Condensation control unit; 604. Grounding protection unit; 605. Fire protection unit. Detailed Implementation

[0017] To make the technical problems solved by the present invention, the technical solutions adopted, and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0018] like Figures 1 to 3 As shown, a high-capacity three-winding photovoltaic containerized transformer system includes: The container cabin module 1 is internally divided into a high-voltage chamber unit 103, a transformer chamber unit 104, and a low-voltage chamber unit 105. The three-winding transformer module 2 is located in the transformer room unit 104. The three-winding transformer module 2 includes an iron core, a high-voltage winding wound on the iron core, and two low-voltage windings that are symmetrically arranged vertically along the iron core axis and electrically independent. The high-voltage switch module 3 is located in the high-voltage chamber unit 103 and is electrically connected to the high-voltage side of the three-winding transformer module 2; The low-voltage power distribution module 4 is located in the low-voltage room unit 105 and includes two low-voltage incoming cabinets 401. The two low-voltage incoming cabinets 401 are electrically connected to the two low-voltage windings of the three-winding transformer module 2 respectively. The intelligent measurement, control and protection module 5 is connected to the three-winding transformer module 2, the high-voltage switch module 3 and the low-voltage power distribution module 4 respectively, and is used for electrical quantity acquisition, status monitoring and hierarchical protection control. The heat dissipation and protection module 6 is used to provide heat dissipation and protection for the various units within the container cabin module 1.

[0019] In this embodiment, the container cabin module 1 is used to integrate and install various functional modules, and to provide physical isolation and protection. The container cabin module 1 includes a cabin frame 101, a cabin partition structure 102, a high-voltage chamber unit 103, a transformer chamber unit 104, and a low-voltage chamber unit 105.

[0020] The cabin frame 101 is made of Q235B cold-rolled steel welded together, and 8 standard corner pieces are welded to the 8 top and bottom corners of the cabin respectively.

[0021] The compartment partition structure 102 is located between the high-voltage chamber unit 103 and the transformer chamber unit 104, and between the transformer chamber unit 104 and the low-voltage chamber unit 105. It is made of cold-rolled steel plate with a thickness of 2.5mm and welded to the compartment frame 101. The partition steel plate is covered with Class A fireproof and heat-insulating cotton with a thickness of 5mm or more on the side of the partition steel plate facing the transformer chamber.

[0022] The high-voltage chamber unit 103 is a sealed cabin structure. A single-opening maintenance door is set on the front of the cabin, with an observation window and a door lock. The door lock is interlocked with the high-voltage switch module 3 for five-proof protection. A cable inlet hole is set at the bottom of the cabin, and the inlet hole is equipped with a waterproof gland. A high-voltage equipment installation beam is set inside the cabin. The beam is made of 80*60*4mm square tube welded to the cabin frame 101, with pre-fabricated installation holes to adapt to the installation dimensions of the high-voltage switch equipment.

[0023] The upper and lower edges of both sides of transformer compartment unit 104 are welded with 160*80*5mm square tube beams, which are fully welded to the corner pieces at the front and rear ends of the compartment to serve as the main load-bearing structure. The left and right edges of both sides are welded with 120*80*6mm square tube columns, which are fully welded to the upper and lower beams at their upper and lower ends, respectively. The stainless steel mesh door is made of 304 stainless steel and is hinged to the columns by hinges. The mesh door is equipped with a door lock with a padlock, which can increase the natural heat dissipation area of ​​the transformer. The top left and right main crossbeams of transformer compartment unit 104 are made of 160*80*5mm square tubing, with both ends fully welded to the corner pieces at the front and rear ends of the compartment. Cross-shaped reinforcing ribs are set between the main crossbeams. The transverse reinforcing ribs are made of 120*80*6mm square tubing, with both ends fully welded to the left and right main crossbeams. The longitudinal reinforcing ribs are made of 120*80*6mm square tubing, with both ends fully welded to the top crossbeams at the front and rear ends of the compartment. On the basis of the cross-shaped reinforcing ribs, external cross-shaped diagonal reinforcing ribs are set. The diagonal reinforcing ribs are made of 120*80*6mm square tubing, and are fully welded from the intersection of the cross-shaped reinforcing ribs to the corner pieces at the four top corners.

[0024] The low-voltage compartment unit 105 is a sealed cabin structure. The front of the cabin is equipped with a double-opening maintenance door, with an observation window and a door lock. The door lock is interlocked with the low-voltage incoming circuit breaker, and the cabinet door cannot be opened when the circuit breaker is closed. The bottom of the cabin is equipped with a cable inlet hole with a waterproof gland. The interior of the cabin is equipped with a low-voltage cabinet mounting base, which is fully welded to the bottom frame of the cabin.

[0025] The three-winding transformer module 2 is used for voltage conversion, stepping up low-voltage photovoltaic power to high-voltage power. The three-winding transformer module 2 includes a core assembly 201, a low-voltage winding assembly 202, a high-voltage winding assembly 203, a main air-circuit insulation structure 204, an oil tank assembly 205, an oil conservator assembly, and a temperature control assembly 206.

[0026] The core assembly 201 uses high-permeability grain-oriented cold-rolled silicon steel sheets and adopts a fully oblique joint stacked structure without punching. The core adopts a three-phase three-column structure, and the yoke section is stepped, matching the yoke section with the core column section.

[0027] The low-voltage winding assembly 202 includes a first low-voltage winding and a second low-voltage winding. The two windings are arranged symmetrically up and down along the axial direction of the iron core column. The high-voltage winding is arranged outside the two low-voltage windings. A grounded metal partition is provided between the two low-voltage windings. The two low-voltage windings have the same number of turns, wire gauge and impedance. The two windings are electrically independent and are used to connect to different photovoltaic sub-arrays respectively.

[0028] like Figure 2As shown, the main air channel insulation structure 204 is disposed between the low-voltage winding and the high-voltage winding. The total thickness of the main air channel is 16.5mm. From the low-voltage winding side to the high-voltage winding side, the following are arranged in sequence: first support bar 2041, first cardboard layer 2042, soft corner ring assembly, second cardboard layer 2045, and second support bar 2046, with a winding margin of 0.5mm reserved.

[0029] The opening of the U-shaped soft corner ring 2043 faces the low-voltage winding side and wraps around the upper ends of the first cardboard layer 2042 and the second cardboard layer 2045. The two sides of the U-shape are respectively attached to the surfaces of the first cardboard layer 2042 and the second cardboard layer 2045. The horizontal side of the L-shaped soft corner ring 2044 is clamped at the lower ends of the first cardboard layer 2042 and the second cardboard layer 2045, and the vertical side is attached to the outer surface of the second cardboard layer 2045. The outer end of the soft corner ring extends and is laid on the upper and lower end faces of the high-voltage coil, which can enable the axial coil to form a stable axial tension force and improve the axial resistance to short-circuit impact force of the coil.

[0030] The first support bar 2041 is arranged on the main air passage near the low-voltage winding side, and the second support bar 2046 is arranged on the main air passage near the high-voltage winding side. The support bars form an axially connected heat dissipation oil passage, and the transformer oil flows in the oil passage to carry away the heat generated by the coil.

[0031] A 0.5mm winding allowance is reserved to compensate for the looseness that occurs during the winding of the multi-layer insulation structure, and to avoid deviation between the inner diameter of the high-voltage coil and the theoretical design value after winding.

[0032] The oil tank assembly 205 adopts a corrugated oil tank structure. The oil tank and the mounting base of the transformer room are fixedly connected by bolts. Each oil tank is equipped with 8 fixing points. The top of the oil tank is equipped with a high-voltage bushing and two low-voltage bushings. The high-voltage bushing is a 35kV oil-immersed bushing and is connected to the high-voltage switch module 3. The two low-voltage bushings are 0.8kV high-current bushings with a rated current of 4000A and are connected to the two incoming line cabinets of the low-voltage power distribution module 4 respectively.

[0033] The temperature control component 206 uses a platinum resistance temperature sensor, which is set at the upper and lower ends of the three-phase winding and in the upper layer of oil in the oil tank. It has 6 temperature measurement points. The temperature sensor is connected to the intelligent measurement, control and protection module 5 to monitor the winding temperature and oil temperature. When the temperature exceeds the set value, it will trigger an alarm and trip protection.

[0034] The high-voltage switch module 3 is used for grid connection control, electrical isolation, and fault protection on the 34.5kV high-voltage side. The high-voltage switch module 3 includes a vacuum circuit breaker 301, a disconnecting switch 302, a grounding switch 303, a surge arrester 304, a voltage transformer 305, a current transformer 306, a five-proof interlocking mechanism 307, and a high-voltage cabinet 308.

[0035] The high-voltage cabinet 308 adopts a metal armored removable structure and is installed on the mounting beam of the high-voltage compartment and fixed by bolts. The interior of the cabinet is divided into circuit breaker compartment, busbar compartment, cable compartment and instrument compartment according to function, and the compartments are separated by steel plates.

[0036] The high-voltage bushing of the three-winding transformer is connected to the incoming terminal of the disconnector switch 302 via a copper busbar. The outgoing terminal of the disconnector switch 302 is connected to the incoming terminal of the vacuum circuit breaker 301. The outgoing terminal of the vacuum circuit breaker 301 is connected to the grid-connected cable via a copper busbar to form a high-voltage main circuit. The surge arrester 304 is connected in parallel to the outgoing side of the vacuum circuit breaker 301, and its grounding terminal is connected to the cabin grounding system for overvoltage protection. The voltage transformer 305 and the current transformer 306 are respectively installed on the busbar side and the outgoing side for the acquisition of voltage and current signals. The acquired signals are connected to the intelligent measurement and control and protection module 5.

[0037] In the five-prevention interlocking structure, mechanical interlocks are set between disconnecting switch 302, grounding switch 303, high-voltage compartment cabinet door, and circuit breaker trolley. The specific interlocking logic is as follows: when vacuum circuit breaker 301 is in the closed state, disconnecting switch 302 cannot be opened or closed, and the circuit breaker trolley cannot be moved; when disconnecting switch 302 is in the closed state, grounding switch 303 cannot be closed, and the high-voltage compartment cabinet door cannot be opened; when grounding switch 303 is in the closed state, disconnecting switch 302 cannot be closed, and the circuit breaker trolley cannot be pushed into the working position; when the high-voltage compartment cabinet door is not closed, the circuit breaker cannot be closed. This meets the five-prevention requirements and prevents safety accidents such as accidental entry into energized compartments and misoperation.

[0038] Vacuum circuit breaker 301 is equipped with overcurrent, instantaneous trip, overvoltage, undervoltage, zero sequence, temperature, and gas protection.

[0039] In this embodiment, the low-voltage power distribution module 4 is used to collect the electrical energy from both low-voltage sides and connect it to the photovoltaic branch. The low-voltage power distribution module 4 includes two low-voltage incoming cabinets 401 and one busbar transition cabinet 402, with the three cabinets arranged in a triangular pattern in the low-voltage room.

[0040] Two low-voltage incoming line cabinets 401 are respectively arranged on the left and right sides of the low-voltage room, and the busbar transition cabinet 402 is arranged in the middle of the rear side of the two incoming line cabinets. The three cabinets are arranged in a triangular shape to improve space utilization. The three cabinets are separated by a grounding metal sealing plate shell with a thickness of 2mm or more.

[0041] The low-voltage incoming line cabinet 401 has a single rated current of 4000A, which is used to adapt to the large current connection of the 0.8kV low-voltage side of the transformer. Each incoming line cabinet is internally divided into two independent spaces, upper and lower, completely separated by a grounded metal partition with a thickness of 3mm or more. The upper space is the busbar incoming unit, with an installation height of 1200mm or more, used to install 4000A low-voltage universal circuit breakers and the incoming bus system. The incoming terminals of the circuit breakers are directly connected to the low-voltage bushings of the three-winding transformer via copper busbars. The upper circuit breakers of the two incoming line cabinets are respectively connected to the two independent low-voltage windings of the transformer. The lower space is the photovoltaic branch access unit, with an installation height of 1200mm or more, used to install photovoltaic incoming molded case switches and cable terminals. The molded case switches are arranged in two rows, upper and lower, front and back, in the lower space. A single incoming line cabinet can accommodate up to 16 circuits, and two incoming line cabinets can accommodate a total of 32 circuits. The incoming terminal of each molded case switch is connected to the output terminal of the photovoltaic inverter via a cable, and the outgoing terminal is connected to the incoming bus system via a copper busbar.

[0042] Busbar transition cabinet 402 is located behind the two incoming line cabinets and is reliably connected to the busbar system of the two incoming line cabinets via copper busbars. The lower space of busbar transition cabinet 402 is reserved for the installation of 6 320A low-voltage incoming molded case switches, and the installation holes, busbar connection points and cable wiring space are prefabricated.

[0043] Each incoming line cabinet is equipped with a universal circuit breaker with long-delay, short-delay, instantaneous, and ground fault protection. Each branch circuit breaker is equipped with overload and short-circuit protection, achieving hierarchical protection. In case of a fault, only the faulty branch is disconnected.

[0044] In this embodiment, the intelligent measurement, control and protection module 5 is used for the system's electrical quantity acquisition, status monitoring and operation and maintenance. The intelligent measurement, control and protection module 5 includes a high-voltage side measurement, control and protection unit 501, a dual low-voltage side independent measurement, control and protection unit 502, a transformer temperature control unit 503, a communication management unit 504, a human-machine interaction unit 505, and a remote operation and maintenance interface 506.

[0045] The intelligent measurement, control and protection module 5 adopts a hierarchical distributed architecture. The high-voltage side measurement, control and protection unit 501, the dual low-voltage side measurement, control and protection unit, and the transformer temperature control unit 503 are connected to the communication management unit 504 through the RS485 bus. The communication management unit 504 is connected to the human-machine interaction unit 505 and the remote operation and maintenance interface 506 through the Ethernet interface.

[0046] The first low-voltage circuit and the second low-voltage circuit are each equipped with an independent measurement and control protection unit. Each unit is equipped with an independent current transformer 306, voltage transformer 305, power acquisition unit, and energy meter. It independently collects and calculates the branch current, voltage, power, and energy of the two circuits, which facilitates the power station's refined management of the dual photovoltaic sub-arrays.

[0047] The protection logic is divided into three levels. The first level is branch-level protection, which provides overload and short-circuit protection for low-voltage branch molded case switches, and only disconnects the faulty branch. The second level is incoming line-level protection, which provides graded protection for low-voltage incoming line circuit breakers and overcurrent protection for high-voltage circuit breakers, and disconnects the faulty incoming line circuit. The third level is system-level protection, which provides transformer gas protection, temperature protection, high-voltage side instantaneous trip protection, and zero-sequence protection, and disconnects the main power supply of the system to ensure equipment safety.

[0048] The communication management unit 504 supports multiple communication protocols such as Modbus-RTU, Modbus-TCP, and IEC60870-5-104. It can be connected to the SCADA system of photovoltaic power plants, local monitoring platforms, and cloud-based operation and maintenance platforms to perform four remote functions: telemetry, remote signaling, remote control, and remote adjustment. It can monitor equipment status and provide fault warnings, and remotely set parameters and remotely control start and stop.

[0049] The Human-Machine Interface Unit 505 uses a 10-inch color touch screen, which is installed on the instrument door of the low-pressure room to display data such as system voltage, current, power, energy, temperature, switch status, and fault information.

[0050] In this embodiment, the heat dissipation and protection module 6 is used to regulate the temperature of each compartment. The heat dissipation and protection module 6 includes a transformer room natural heat dissipation unit 601, a high and low voltage room forced ventilation heat dissipation unit 602, a condensation control unit 603, a grounding protection unit 604, and a fire protection unit 605.

[0051] The transformer room natural heat dissipation unit 601 adopts an open mesh door structure for the transformer room and a natural heat dissipation solution for the corrugated oil tank. Natural air convection is achieved through the stainless steel mesh doors on both sides, combined with the large heat dissipation area of ​​the corrugated oil tank.

[0052] In the high and low pressure forced ventilation and heat dissipation unit 602, two axial flow fans are installed on the top of the high pressure chamber and the low pressure chamber respectively, and air inlet louvers are set at the bottom of the chamber. The louvers are equipped with dust filters. When the temperature inside the chamber exceeds 40°C, the fans are started, and when the temperature is below 30°C, the fans are stopped.

[0053] In the condensation control unit 603, two condensation controllers and heaters are installed in the high-pressure chamber and the low-pressure chamber, respectively. When the relative humidity in the chamber exceeds 75%, the heater is activated to reduce the humidity in the chamber.

[0054] In the grounding protection unit 604, the container frame 101, each cabinet, transformer oil tank, high-voltage switchgear, cable shielding layer, and the grounding terminal of surge arrester 304 are all connected to the grounding grid.

[0055] In fire protection unit 605, the steel plate separating the transformer room and the high and low voltage rooms is lined with Class A fireproof and heat-insulating cotton. The transformer room is equipped with smoke detectors and aerosol fire extinguishing devices. When smoke is detected, an alarm is triggered and the aerosol fire extinguishing device is activated to extinguish the fire. Example

[0056] like Figure 4 As shown, a control method for a large-capacity three-winding photovoltaic containerized transformer system includes the following steps: S1. Initialize the system and configure parameters; S2. Perform balanced control on the dual low-voltage windings; S3. Monitor operational data and issue early warnings; S4. Implement graded fault protection and handling.

[0057] In step S1, the system is initialized and parameters are configured, including the following steps: S101. After power-on, the system performs a self-test on the hardware status, communication status, and sensor signal status. Once all tests pass, the system enters the running state. After power-on, a self-test is performed, which includes hardware status, communication status, and sensor signal status. If any self-test item fails, the system will not enter the running state. If all self-test items pass, the system will enter the running state.

[0058] S102. Configure and store system operating parameters; The system operating parameters are configured through the human-machine interface unit 505 or a remote platform. The operating parameters include rated voltage, rated capacity, protection settings, temperature threshold, communication parameters, etc. The parameters are stored after configuration.

[0059] In step S2, equalization control is performed on the dual low-voltage windings, including: Balanced current shunting control is implemented for the dual low-voltage windings. The output current and output power of the two low-voltage circuits are collected, and the inverter output of the two photovoltaic subarrays is adjusted to achieve balanced heating of the two windings. The expression is as follows:

[0060] In the above formula, This represents the difference in output power between the two low-voltage circuits. These are the real-time output power of the first low-voltage circuit and the second low-voltage circuit, respectively. This refers to the rated capacity of a single low-voltage winding. These are the real-time output currents of the first low-voltage circuit and the second low-voltage circuit, respectively. In this embodiment... It has a capacity of 4 MVA.

[0061] In step S3, monitoring operational data and issuing alerts includes the following steps: S301. Collect electrical quantity data; Collect electrical quantity data for the entire system, including voltage, current, power, energy, power factor, and frequency on the high-voltage side and both low-voltage sides.

[0062] S302. Collect device status data; Collect equipment status data, including transformer winding temperature, oil temperature, oil level, high and low voltage switch status, fan and heater operating status, and cabinet door status.

[0063] S303. Issue an early warning when the data approaches 80% of the protection threshold; The collected data is analyzed for trends. When the data approaches 80% of the protection threshold, an early warning signal is triggered, and the warning information is pushed through the human-machine interface and remote platform.

[0064] For example, when the top oil temperature of the transformer reaches 70°C, the tripping threshold is 85°C, triggering a high temperature warning.

[0065] In step S4, graded fault protection and handling are performed, including the following steps: S401. Implement three-level protection in case of a fault; When a system fault occurs, protection is provided according to a three-level protection logic. The first level is branch-level protection, which includes overload and short-circuit protection for the molded case switches of low-voltage branches, cutting off only the faulty branch. The second level is incoming line-level protection, which includes graded protection for low-voltage incoming line circuit breakers and overcurrent protection for high-voltage circuit breakers, cutting off the faulty incoming line circuit. The third level is system-level protection, which includes transformer gas protection, temperature protection, high-voltage side instantaneous trip protection, and zero-sequence protection, cutting off the main power supply of the system to ensure equipment safety.

[0066] S402. When one low-voltage circuit is disconnected due to a fault, the other circuit operates under rated load. When one of the low-voltage circuits fails, the corresponding incoming circuit breaker trips to disconnect the faulty circuit, while the other low-voltage circuit continues to operate under rated load. At the same time, the operating parameters are adjusted to ensure safe and stable operation.

[0067] S403. Record and upload the fault time, type, and data; After a fault occurs, record the fault time, fault type, and fault data to facilitate maintenance personnel in troubleshooting the cause of the fault.

[0068] The system operation data is uploaded to the power plant's SCADA system and cloud-based operation and maintenance platform via a remote communication interface for remote monitoring.

[0069] This invention enables 34.5kV grid connection, reducing losses. Simultaneously, the dual low-voltage circuits are electrically independent and magnetically decoupled, allowing for single-sided maintenance without interrupting operation. The transformer's main circuit employs a segmented layered insulation structure, combined with U-shaped and L-shaped soft corner rings, and a double-sided support structure for heat dissipation and winding margin, enhancing short-circuit withstand capability and improving the transformer's long-term operational reliability. A triangular arrangement of three low-voltage switchgear units improves space utilization. The cabinets have a double-layer structure; the two incoming line cabinets can accommodate up to 32 320A molded case switches, and with the 6 expansion switches reserved in the transition cabinet, the total number of connected branches can reach 38, significantly improving system scalability. Furthermore, operation can be performed inside the cabinet, avoiding the impact of outdoor weather on equipment and operations, thus enhancing operational safety. On-site installation requires only hoisting, cable connection, and grid connection commissioning, shortening the installation cycle. Equipped with five-proof interlocking and a remote maintenance interface 506, it can be connected to the photovoltaic power station's SCADA or cloud platform for unattended operation, improving applicability.

[0070] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Clearly, those skilled in the art can make various alterations and variations to the invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of equivalents of the invention, the invention is also intended to include these modifications and variations.

Claims

1. A high capacity three winding photovoltaic container transformer system, characterized by, include: The container cabin module is internally divided into a high-voltage compartment unit, a transformer compartment unit, and a low-voltage compartment unit; The three-winding transformer module is located in the transformer room unit. The three-winding transformer module includes an iron core, a high-voltage winding wound on the iron core, and two low-voltage windings that are symmetrically arranged vertically along the iron core axis and electrically independent. The high-voltage switch module is located in the high-voltage compartment unit and is electrically connected to the high-voltage side of the three-winding transformer module. The low-voltage power distribution module is located in the low-voltage room unit and includes two low-voltage incoming cabinets, which are electrically connected to the two low-voltage windings of the three-winding transformer module respectively. The intelligent measurement, control and protection module is connected to the three-winding transformer module, the high-voltage switch module and the low-voltage power distribution module respectively, and is used for electrical quantity acquisition, status monitoring and hierarchical protection control; The heat dissipation and protection module is used to provide heat dissipation and protection for the various units within the container cabin module.

2. A large capacity three winding photovoltaic container transformer system according to claim 1, characterized in that, The container cabin module's cabin frame is formed by welding steel profiles. The high-voltage chamber unit and the transformer chamber unit, as well as the transformer chamber unit and the low-voltage chamber unit, are separated by welding cold-rolled steel plates, and fireproof and heat-insulating cotton is installed on the separating steel plates.

3. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, In a three-winding transformer module, the high-voltage winding is arranged outside the two low-voltage windings. In the main air-channel insulation structure between the high-voltage winding and the low-voltage winding, a support bar, a cardboard layer, a soft corner ring assembly, a cardboard layer, and a support bar are arranged sequentially from the low-voltage winding side to the high-voltage winding side. The soft corner ring assembly includes a U-shaped soft corner ring and an L-shaped soft corner ring.

4. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, The high-voltage switch module includes a vacuum circuit breaker, a disconnecting switch, a grounding switch, and a five-proof interlocking mechanism. The five-proof interlocking mechanism forms a mechanical interlock between the vacuum circuit breaker, the disconnecting switch, the grounding switch, and the high-voltage compartment door.

5. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, The low-voltage power distribution module also includes a busbar transition cabinet, and two low-voltage incoming cabinets are arranged in a triangular pattern with the busbar transition cabinet in the low-voltage compartment unit; Each low-voltage incoming switchgear is internally divided into an upper-level busbar incoming unit and a lower-level photovoltaic branch access unit. The upper-level busbar incoming unit is equipped with an incoming circuit breaker and connected to the corresponding low-voltage winding, while the lower-level photovoltaic branch access unit is equipped with multiple photovoltaic branch molded case switches.

6. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, The intelligent measurement, control and protection module includes independent measurement, control and protection units corresponding to the high-voltage side, the first low-voltage circuit and the second low-voltage circuit, as well as a communication management unit and a transformer temperature control unit connected to each measurement, control and protection unit.

7. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, The intelligent measurement, control, and protection module is configured to perform three levels of protection: The first level is overload and short-circuit protection for the molded case switch of the photovoltaic branch in the low-voltage power distribution module; The second level is the graded protection of the low-voltage incoming line cabinet circuit breaker and the overcurrent protection of the high-voltage switch module circuit breaker. The third level is the gas and temperature protection of the three-winding transformer module, as well as the instantaneous overcurrent and zero-sequence protection on the high-voltage side.

8. A large capacity three winding photovoltaic container transformer system as claimed in claim 1, wherein, The heat dissipation and protection module includes: The transformer room's natural heat dissipation unit is achieved through the mesh door structure set in the transformer room unit and the corrugated oil tank of the three-winding transformer module; The high and low pressure chamber forced ventilation and heat dissipation unit includes an axial flow fan and air inlet louvers installed in the high pressure chamber unit and the low pressure chamber unit; The condensation control unit includes a condensation controller and a heater located in the high-pressure chamber unit and the low-pressure chamber unit.

9. A control method of a large-capacity three-winding photovoltaic container transformer system, applicable to the large-capacity three-winding photovoltaic container transformer system of any one of claims 1-8, characterized in that, Includes the following steps: S1. Initialize the system and configure parameters; S2. By collecting the output current and power of the two low-voltage circuits, adjust the output of the corresponding photovoltaic sub-array inverters so that the difference in output power between the two low-voltage circuits does not exceed the preset percentage of the rated capacity of a single circuit, and the output current tends to be consistent. S3. Collect system electrical quantities and equipment status data, and issue early warnings for data approaching protection thresholds; S4. When a fault occurs, the protection action is executed according to the preset three-level protection logic.

10. The control method of a large-capacity three-winding photovoltaic container transformer system according to claim 9, characterized by, In S4, when one of the low-voltage circuits fails and is disconnected, the other low-voltage circuit is controlled to continue operating under rated load, and the operating parameters are adjusted.

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