Grounding arrangement for medium voltage system of large offshore booster station

Abstract

The utility model discloses a ground arrangement structure of large -scale offshore booster station medium -voltage system, including first grounding device and second grounding device, the medium -voltage system includes at least one main transformer, the main transformer low -voltage side is connected A section bus and B section bus respectively, be connected with medium -voltage switch cabinet on the A section bus, the first grounding device is through cable access medium -voltage switch cabinet, the second grounding device is through cable access B section bus connected main transformer low -voltage side. The utility model large -scale offshore booster station every main transformer low -voltage side two section bus adopts different grounding mode grounding respectively, can guarantee offshore booster station medium -voltage system grounding mode reliability, flexibility when, maximum degree reduces grounding device, medium -voltage switch cabinet, cable and related equipment engineering quantity, reduces switch equipment, grounding device and cable laying occupies offshore booster station platform area, realizes the optimization of offshore booster station and reduces the design of the cost.

Description

Technical Field

[0001] This utility model belongs to the field of new energy technology, specifically relating to a grounding arrangement structure for a medium-voltage system of a large offshore substation. Background Technology

[0002] Offshore wind power, as a clean energy source, has developed rapidly in recent years, boasting advantages such as abundant wind resources, stable wind speeds, and a small footprint. Offshore substations, as the hub of the offshore wind power system, are responsible for receiving the electricity generated by the wind turbines and transmitting it to the onshore power grid after voltage enhancement. Optimizing the design of offshore substations is crucial for improving the efficiency and reliability of the entire wind farm and reducing project development and construction costs.

[0003] According to GB / T 51308-2019 "Design Standard for Offshore Wind Power Farms" and NB / T 31115-2017 "Design Specification for 110kV~220kV Offshore Step-up Substations for Wind Farm Projects", the neutral point grounding method on the low-voltage side of the main transformer should preferably be resistance grounding. When there is no neutral point lead-out on the low-voltage side of the main transformer, a grounding transformer and grounding resistor can be installed on each section of busbar or low-voltage outlet on the low-voltage side of the main transformer.

[0004] Offshore substation main transformers typically use a delta connection on the low-voltage side. In this case, the connection method where each busbar on the low-voltage side of the main transformer uses a grounding transformer and a resistor grounding system is generally as follows: the grounding transformer and the small resistor assembly are connected to the medium-voltage busbar of the medium-voltage switchgear via a medium-voltage cable. While this connection method provides some protection for the circuit, it has the following drawbacks because each busbar section requires a medium-voltage switchgear: 1. High equipment cost: Each busbar section requires an independent medium-voltage switchgear, which significantly increases the number of devices and directly drives up the initial investment cost.

[0005] 2. Large footprint: Medium-voltage switchgear is large in size, and the configuration of multiple busbars will significantly occupy the limited space resources of the substation, which may affect the overall layout and equipment installation. Utility Model Content

[0006] The purpose of this utility model is to overcome the shortcomings of the above-mentioned background technology and provide a grounding arrangement structure for a medium-voltage system of a large offshore substation.

[0007] The technical solution adopted in this utility model is: a grounding arrangement structure for a medium-voltage system of a large offshore substation, including a first grounding device and a second grounding device. The medium-voltage system includes at least one main transformer. The low-voltage side of the main transformer is connected to bus section A and bus section B respectively. A medium-voltage switchgear is connected to bus section A. The first grounding device is connected to the medium-voltage switchgear via a cable. The second grounding device is connected to the low-voltage side of the main transformer connected to bus section B via a cable.

[0008] Furthermore, the first grounding device includes a grounding transformer that also serves as a substation transformer and a first resistor. The high-voltage side of the grounding transformer that also serves as a substation transformer is connected to a medium-voltage switchgear via a cable, and the neutral point of the grounding transformer that also serves as a substation transformer is grounded via the first resistor.

[0009] Furthermore, the first grounding device is located inside the medium-voltage power distribution room where the medium-voltage switchgear is located.

[0010] Furthermore, the second grounding device includes a grounding transformer, a disconnecting switch, and a second resistor. The high-voltage side of the grounding transformer is connected to one end of the disconnecting switch, and the other end of the disconnecting switch is connected to the low-voltage side of the main transformer connected to the B-section busbar via a cable. The neutral point of the grounding transformer is grounded through the second resistor.

[0011] Furthermore, the second grounding device is arranged on the second-floor platform of the offshore substation.

[0012] Furthermore, there are two main transformers, namely a first main transformer and a second main transformer. A bus tie switch is provided between the A section busbar on the low-voltage side of the first main transformer and the B section busbar on the low-voltage side of the second main transformer, and between the B section busbar on the low-voltage side of the first main transformer and the A section busbar on the low-voltage side of the second main transformer.

[0013] The beneficial effects of this utility model are as follows: Compared to the traditional grounding method where each busbar section is equipped with an independent medium-voltage switchgear, this utility model uses a first grounding device and a second grounding device connected to different busbars in different ways. This avoids setting up a medium-voltage switchgear on each busbar section, reducing the number of medium-voltage switchgear used, thereby reducing equipment procurement costs and effectively controlling initial investment. Since the number of medium-voltage switchgear is reduced, the space occupied by the medium-voltage switchgear in the substation is reduced accordingly, providing more space for the layout and installation of other equipment in the substation. This is conducive to optimizing the overall layout, improving space utilization, and making the substation structure more compact and reasonable.

[0014] This utility model's first grounding device adopts a design that combines the functions of a grounding transformer and a station service transformer, integrating the functions of both. This not only saves on the number of devices but also reduces the number of connecting cables and the floor space required, thus lowering equipment investment and installation costs. The high-voltage side of the grounding transformer / station service transformer is connected to the medium-voltage switchgear via a cable, and the neutral point is grounded through a first resistor. This simplified wiring method makes the system structure clearer, facilitating operation and maintenance personnel in operating and managing the system, and reducing the risk of misoperation due to complex wiring. Simplified system structure: This invention places the first grounding device inside the medium-voltage distribution room where the medium-voltage switchgear is located, shortening the electrical distance between the grounding transformer / station transformer and the medium-voltage switchgear, reducing line impedance, and improving system stability and reliability. In the event of a fault, the fault can be cleared more quickly, reducing the impact range of the fault on the system. At the same time, the grounding device and the medium-voltage switchgear are located in the same distribution room, which facilitates daily inspection, maintenance and repair work by operation and maintenance personnel, reduces the spatial distance between equipment, reduces the labor intensity of maintenance personnel, and improves work efficiency.

[0015] The second grounding device of this utility model includes a grounding transformer, a disconnecting switch, and a second resistor. The connection status between the grounding transformer and the low-voltage side of the main transformer can be flexibly controlled through the disconnecting switch. During normal operation, the disconnecting switch can be opened or closed as needed to meet different operating requirements.

[0016] This invention places the second grounding device on the second-floor platform of an offshore substation, making full use of the substation's three-dimensional space and avoiding interference with other equipment on the first floor. This arrangement allows for a more rational arrangement of other important equipment on the first floor, improving the overall space utilization efficiency of the substation. Furthermore, the second-floor platform typically has good ventilation, and placing the second grounding device here facilitates ventilation and heat dissipation. The grounding device generates heat during operation, and good ventilation can dissipate this heat in a timely manner, reducing the operating temperature of the equipment and extending its service life.

[0017] This utility model sets up two main transformers, and bus tie switches are installed between the A section busbar on the low-voltage side of the first main transformer and the B section busbar on the low-voltage side of the second main transformer, and between the B section busbar on the low-voltage side of the first main transformer and the A section busbar on the low-voltage side of the second main transformer. This design realizes mutual backup between the main transformers. When one main transformer fails or is under maintenance, the load can be switched to the other main transformer by closing the bus tie switch, thus ensuring the continuity and reliability of power supply. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the present invention.

[0019] In the diagram, 1-First main transformer; 2-Second main transformer; 3-A section busbar; 4-B section busbar; 5-Medium voltage switchgear; 6-First grounding device; 6.1-Grounding transformer / station service transformer; 6.2-First resistor; 7-Second grounding device; 7.1-Grounding transformer; 7.2-Disconnecting switch; 7.3-Second resistor; 8-Bus tie switch; 9-Fan incoming line cabinet. Detailed Implementation

[0020] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding of this utility model, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0021] like Figure 1 As shown, this utility model provides a grounding arrangement structure for a medium-voltage system of a large offshore substation, including a first grounding device 6 and a second grounding device 7. The medium-voltage system includes two main transformers, which are low-voltage side double-split winding power transformers. The low-voltage side of each main transformer is connected to busbar A 3 and busbar B 4 respectively through branch switch cabinets. A medium-voltage switch cabinet 5 is connected to busbar A 3. Several fan terminal cabinets 9 are provided on both busbar A 3 and busbar B 4. The first grounding device 6 is connected to the medium-voltage switch cabinet 5 through a medium-voltage cable, and the second grounding device 7 is connected to the low-voltage side of the main transformer connected to busbar B 4 through a medium-voltage cable.

[0022] This utility model for large-scale offshore substations uses different grounding methods for the two busbars on the low-voltage side of each main transformer. This ensures the reliability and flexibility of the grounding method for the medium-voltage system of the offshore substation while minimizing the amount of engineering work for grounding devices, medium-voltage switchgear, cables and related equipment. It also optimizes the grounding transformer capacity and grounding resistance value, and reduces the area occupied by switchgear, grounding devices and cable laying on the offshore substation platform, thus achieving optimized and cost-reducing design for the offshore substation.

[0023] In some embodiments, the first grounding device 6 includes a grounding transformer / station transformer 6.1 and a first resistor 6.2. The high-voltage side of the grounding transformer / station transformer 6.1 is connected to the medium-voltage switchgear 5 via a cable, and the low-voltage side is connected to the low-voltage busbar of the corresponding low-voltage electrical equipment. The neutral point of the grounding transformer / station transformer 6.1 is grounded through the first resistor 6.2. That is, the grounding transformer / station transformer and the first resistor are connected to the A-section busbar through the medium-voltage switchgear. The first grounding device is arranged inside the medium-voltage power distribution room where the medium-voltage switchgear is located.

[0024] In some embodiments, the second grounding device 7 includes a grounding transformer 7.1, a disconnecting switch 7.2, and a second resistor 7.3. The high-voltage side of the grounding transformer 7.1 is connected to one end of the disconnecting switch 7.2, and the other end of the disconnecting switch 7.2 is connected via a cable to the low-voltage side of the main transformer connected to bus section B 4. The neutral point of the grounding transformer 7.1 is grounded through the second resistor 7.3. That is, the grounding transformer and the second resistor are connected to the low-voltage side of the main transformer connected to bus section B via the disconnecting switch. The grounding methods of the two bus sections are completely different. The second grounding device is arranged on the second-floor platform of the offshore substation and connected to the low-voltage side of the main transformer corresponding to the main transformer room on the first-floor platform of the offshore substation via a medium-voltage cable.

[0025] In some embodiments, the two main transformers are a first main transformer 1 and a second main transformer 2. A bus tie switch 8 is provided between the A section busbar on the low-voltage side of the first main transformer 1 and the B section busbar on the low-voltage side of the second main transformer 2, and between the B section busbar on the low-voltage side of the first main transformer 1 and the A section busbar on the low-voltage side of the second main transformer 2. That is, a bus tie switch is provided between the two busbars of the two main transformers with different grounding methods. The setting of the bus tie switch can ensure that when either main transformer fails, the busbar corresponding to the faulty main transformer can be connected to the busbar corresponding to the non-faulty main transformer, and the load can be switched to the other main transformer, thus ensuring the continuity and reliability of power supply.

[0026] In some embodiments, the length of the medium-voltage submarine cable connected to the low-voltage side busbar of each main transformer is counted, the capacitive current of the low-voltage side busbar of each main transformer is calculated under different operating modes, and the grounding resistance and the capacity of the grounding transformer or grounding transformer combined with station service transformer are designed.

[0027] (1) Normal operating conditions The low-voltage side bus capacitance current Ic1 of each main transformer section i It can be estimated using the following formula: Ic1 i =(95+1.44S) / (2200+0.23S) * U N L i =62A.

[0028] Where S is the cross-sectional area of ​​the submarine cable, in mm. 2 U N Rated line voltage of the submarine cable, in kV; L i The length of the medium-voltage submarine cable connected to each section of the low-voltage busbar of the main transformer is in km; i is the number of the low-voltage busbar of the main transformer.

[0029] Considering the current capacity and development needs of the equipment within the station, a factor of 1.13 is taken. Therefore, the maximum system capacitance Ic1 under normal operating conditions is... imax =1.13*Ic1 i .

[0030] Under this operating condition, the required compensation current Ir1 for each section of the low-voltage busbar of the main transformer is... i Grounding resistance R1 I Grounding transformer capacity S1 i It can be estimated using the following formula: Ir1 i =K x Ic1 imax .

[0031] R1 I =(U N / √3 / Ir1 i ) x 1000.

[0032] S1 i =U N x Ir1 i / (√3x10.5).

[0033] The value of K is usually between 2 and 4.

[0034] (2) Single main transformer failure and out of operation The low-voltage side bus capacitance current Ic2 of each main transformer section i It can be estimated using the following formula: Ic2 i =(95+1.44S) / (2200+0.23S) * U N (L) i + L j =124A.

[0035] Among them, L j The length of the medium-voltage submarine cable connected to the low-voltage side busbar of the i-th main transformer via the bus tie switch between the two busbars is in km; j is the number of the low-voltage side busbar of the faulty main transformer.

[0036] Considering the current capacity and development needs of the equipment within the station, and taking a factor of 1.13, the maximum system capacitance Ic2 under the condition of a single main transformer failing and being taken out of operation is then calculated. imax =1.13*Ic2 i .

[0037] Under this operating condition, the required compensation current Ir2 for each section of the low-voltage busbar of the main transformer is... i Grounding resistance R2 I Grounding transformer capacity S2 i It can be estimated using the following formula: Ir2 i =K* Ic2 imax .

[0038] R2 I =(U N / √3 / Ir2 i ) * 1000.

[0039] S2 i =U N * Ir2 i / (√3*10.5).

[0040] (3) Control method and grounding transformer capacity configuration Under normal operating conditions, the bus tie switch between the two busbar sections on the low-voltage side of each main transformer and the two busbar sections on the low-voltage side of the adjacent main transformer is in the open state, and the grounding transformer and the station service transformer are independently connected to the low-voltage side busbar of each main transformer.

[0041] When a single main transformer fails and is taken out of service, the bus tie switch is closed, and the two sections of the low-voltage busbars of the main transformer that are taken out of service are connected to the low-voltage busbars of the main transformer that are in normal operation through the bus tie switch. At the same time, the grounding transformer and the second resistor connected to the low-voltage side of the main transformer through the isolating switch are disconnected to ensure that there is only one grounding point on the low-voltage busbar of the same section of the main transformer.

[0042] Under the above control method, the first grounding device connected to the low-voltage side busbar of the main transformer via the medium-voltage switchgear, and the capacity of the grounding transformer / station service transformer are calculated according to S2. i The first resistor value is set according to R2. I Calculation; the second grounding device connected to the low-voltage side of the main transformer via the disconnecting switch, the grounding transformer capacity is calculated according to S1. i The resistance value of the second resistor is determined according to R1. I calculate.

[0043] Example Taking the 400MW offshore substation as an example, the main transformers of the offshore substation adopt two 240MVA low-voltage side double-split winding power transformers. The 220kV main transformer model is SFZ11-240000 / 230, with a connection form of YN, d11-d11, and a rated voltage ratio of 230±81.25% / 35-35kV. Each main transformer adopts two busbars on the low-voltage side, and bus tie switches are installed between the two busbars on the low-voltage side of each main transformer and the two busbars on the low-voltage side of the adjacent main transformer.

[0044] The low-voltage side A section (or I section) busbar of each main transformer is grounded by a grounding transformer that also serves as a station service transformer via a first resistor. One set of grounding transformer that also serves as a station service transformer and the first resistor complete set of equipment is connected to the A section busbar via a medium-voltage cable to a medium-voltage switchgear. The low-voltage side B section (II section) busbar of each main transformer is grounded by a grounding transformer via a second resistor. One set of grounding transformer and the second resistor complete set of equipment is connected to the low-voltage side of the main transformer connected to the B section busbar via a medium-voltage cable and a disconnecting switch.

[0045] The length of medium-voltage submarine cable connected to the low-voltage side busbar of each main transformer section is counted. The capacitive current of the low-voltage side busbar of each main transformer section is calculated under different operating modes. The grounding resistance and the capacity of the grounding transformer combined with the substation are designed.

[0046] The total length of the 35kV submarine cable in the offshore wind farm area is approximately 30.47km, including 3×95 mm... 2 2.05km in length, 3×120 mm 2 1.38km long, 3×185 mm 29.17km long, 3×400 mm 2 The length is 17.87km, and it is assumed that the submarine cable will be connected to four 35kV busbars on average.

[0047] All grounding transformer capacities are considered based on the condition of a single main transformer failing and being taken out of operation, i.e., Ic1=124A, Ic1 max =140A, take the compensation current Ir1=400A, the grounding resistance R1=50.5Ω, and the grounding transformer capacity S1=1000kVA.

[0048] Calculations based on the design scheme proposed in this utility model: (1) Normal operating conditions The low-voltage side bus capacitance current Ic1 of each main transformer section i It can be estimated using the following formula: Ic1 i =(95+1.44S) / (2200+0.23S) *U N L i =62A Where S is the cross-sectional area of ​​the submarine cable, in mm. 2 U N Rated line voltage of submarine cable, in kV, L i The length of the medium-voltage submarine cable connected to each section of the low-voltage busbar of the main transformer is expressed in km, and i is the number of the low-voltage busbar of the main transformer.

[0049] Considering the current capacity and development needs of the equipment within the station, a factor of 1.13 is taken. Therefore, the maximum system capacitance Ic1 under normal operating conditions is... imax =1.13 *Ic1 i =70A.

[0050] Under this operating condition, the required compensation current Ir1 for each section of the low-voltage busbar of the main transformer is... i Grounding resistance R1 I Grounding transformer capacity S1 i It can be estimated using the following formula: Ir1 i =K *Ic1 imax =200A R1 I =(U N / √3 / Ir1 i ) * 1000 = 101Ω S1 i =U N * Ir1 i / (√3 * 10.5) = 500kVA (2) Single main transformer failure and out of operation The low-voltage side bus capacitance current Ic2 of each main transformer section i It can be estimated using the following formula: Ic2 i =(95+1.44S) / (2200+0.23S) * U N (L) i + L j =124A Among them, L j The length of the medium-voltage submarine cable connected to the low-voltage side busbar of the i-th main transformer via the bus tie switch between the two busbars is expressed in km, and j is the number of the low-voltage side busbar of the faulty main transformer.

[0051] Considering the current capacity and development needs of the equipment within the station, and taking a factor of 1.13, the maximum system capacitance Ic2 under the condition of a single main transformer failing and being taken out of operation is then calculated. imax =1.13 *Ic2 i =140A.

[0052] Under this operating condition, the required compensation current Ir2 for each section of the low-voltage busbar of the main transformer is... i Grounding resistance R2 I Grounding transformer capacity S2 i It can be estimated using the following formula: Ir2 i =K * Ic2 imax =400A R2 I =(U N / √3 / Ir2 i ) *1000=50.5Ω S2 i =U N * Ir2 i / (√3 * 10.5) = 1000kVA (3) Control strategy and grounding transformer capacity configuration Under normal operating conditions, the bus tie switch between the two busbar sections on the low-voltage side of each main transformer and the two busbar sections on the low-voltage side of the adjacent main transformer is in the open state, and the grounding transformer and the station service transformer are independently connected to the low-voltage side busbar of each main transformer.

[0053] When a single main transformer fails and is taken out of service, the bus tie switch is closed, and the two sections of the low-voltage busbars of the main transformer that are taken out of service are connected to the low-voltage busbars of the main transformer that are in normal operation through the bus tie switch. At the same time, the grounding transformer and the small resistance complete set of equipment connected to the low-voltage side of the main transformer through the isolating switch are disconnected to ensure that there is only one grounding point on the low-voltage busbar of the same section of the main transformer.

[0054] Under the above control strategy, the grounding transformer / station service transformer and the first resistor assembly connected to the low-voltage side busbar of the main transformer via the medium-voltage switchgear have a grounding transformer capacity of S2. i =1000kVA, grounding resistance R2 I =50.5Ω; The grounding transformer and the second resistor assembly connected to the low-voltage side of the main transformer via the disconnecting switch, with a grounding transformer capacity S1 i =500kVA, grounding resistance =101Ω.

[0055] The above are merely specific embodiments of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Contents not described in detail in this specification belong to prior art known to those skilled in the art.

Claims

1. A grounding arrangement structure for a medium-voltage system of a large offshore substation, characterized in that: The medium-voltage system includes a first grounding device (6) and a second grounding device (7). The medium-voltage system includes at least one main transformer. The low-voltage side of the main transformer is connected to bus section A (3) and bus section B (4) respectively. A medium-voltage switchgear (5) is connected to bus section A (3). The first grounding device (6) is connected to the medium-voltage switchgear (5) via a cable. The second grounding device (7) is connected to the low-voltage side of the main transformer connected to bus section B (4) via a cable.

2. The grounding arrangement structure of the medium-voltage system of a large offshore substation according to claim 1, characterized in that: The first grounding device (6) includes a grounding transformer that also serves as a substation transformer (6.1) and a first resistor (6.2). The high-voltage side of the grounding transformer that also serves as a substation transformer (6.1) is connected to the medium-voltage switchgear (5) via a cable, and the neutral point of the grounding transformer that also serves as a substation transformer (6.1) is grounded via the first resistor (6.2).

3. The grounding arrangement structure of the medium-voltage system of a large offshore substation according to claim 1, characterized in that: The first grounding device (6) is located inside the medium-voltage power distribution room where the medium-voltage switchgear is located.

4. The grounding arrangement structure of the medium-voltage system of a large offshore substation according to claim 1, characterized in that: The second grounding device (7) includes a grounding transformer (7.1), a disconnecting switch (7.2), and a second resistor (7.3). The high-voltage side of the grounding transformer (7.1) is connected to one end of the disconnecting switch (7.2), and the other end of the disconnecting switch (7.2) is connected to the low-voltage side of the main transformer connected to the B section busbar via a cable. The neutral point of the grounding transformer (7.1) is grounded through the second resistor (7.3).

5. The grounding arrangement structure of the medium-voltage system of a large offshore substation according to claim 1, characterized in that: The second grounding device (7) is arranged on the second-floor platform of the offshore substation.

6. The grounding arrangement structure of the medium-voltage system of a large offshore substation according to claim 1, characterized in that: The main transformer is provided in two units, namely the first main transformer (1) and the second main transformer (2). A bus tie switch (8) is provided between the A section bus (3) on the low voltage side of the first main transformer (1) and the B section bus (4) on the low voltage side of the second main transformer (2), and between the B section bus (4) on the low voltage side of the first main transformer (1) and the A section bus (3) on the low voltage side of the second main transformer (2).

Images