A method for configuring inductive reactive power decentralized compensation of offshore wind farm

Abstract

The application provides a method for configuring inductive reactive power compensation of offshore wind farms, comprising the following steps: calculating the inductive reactive power compensation demand of a sending system of a step-up transformer transmission system of an offshore wind farm to be compensated and the inductive reactive power compensation demand of a wind farm in a field area; determining half of the inductive reactive power compensation demand of the sending system as the configuration capacity of a land centralized control center reactor in the step-up transformer transmission system of the offshore wind farm; obtaining the capacity of a reactor of a box-type transformer at the side of each wind turbine according to half of the inductive reactive power compensation demand of the sending system and the inductive reactive power compensation demand of the wind farm in the field area; configuring the reactor for the land centralized control center according to the determined configuration capacity of the land centralized control center reactor; and configuring the reactor for each box-type transformer at the side of the wind turbine according to the determined capacity of the reactor of the box-type transformer at the side of the wind turbine. The application effectively solves the problem of excessive loss of the sending cable net of the offshore wind farm and the field area, and saves the area and investment cost of the offshore step-up station.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy and electric power, and particularly relates to a method for configuring inductive and capacitive reactive power dispersion compensation of an offshore wind farm. BACKGROUND

[0002] During operation, offshore wind farms will be accompanied by a large amount of power loss, and the annual average power loss accounts for about 3% to 5% of the total power generation. The existence of these additional power losses seriously restricts the power generation efficiency and economic benefits of offshore wind farms.

[0003] The collection line and the transmission line of the offshore wind farm generally use AC submarine cables. During operation, the AC submarine cables not only generate a large amount of charging power, which leads to an increase in line loss and occupies line capacity, but also cause a serious threat to the safe operation of equipment due to the problem of power frequency overvoltage. Therefore, it is necessary to configure reactive power compensation for the offshore wind farm access system to meet the requirements of local reactive power balance, power frequency overvoltage control, and voltage control during operation.

[0004] At present, the traditional method is to arrange high-voltage reactors on land, on the offshore booster station, or on the offshore booster station and the land centralized control center to absorb the reactive power of the transmission submarine cable, reduce the network loss of the transmission line, and improve the utilization rate of the submarine cable capacity. For example, the patent "A method for configuring reactive power compensation of an offshore wind farm access system and a system thereof" balances the capacitive reactive power generated by the transmission submarine cable by arranging reactors on the high-voltage side of the offshore booster station. The patent "A method for configuring reactive power compensation of an offshore wind farm transmission system" determines the required compensation value of the offshore high-voltage reactor of the land centralized control center according to the output change of the wind farm and the voltage change at the grid connection point. However, these schemes cannot balance the capacitive reactive power of the field area, resulting in excessive line loss and power frequency overvoltage, which affects the safe use of equipment. In addition, the configuration of high-voltage reactors on the offshore booster station also increases the area of the offshore booster station. SUMMARY

[0005] The purpose of the present application is to solve the problems in the background art. The present application provides a method for configuring dispersion reactive power compensation of an offshore wind farm. The method takes into account the reactive power generated by the collection line and the transmission submarine cable of the field area, and arranges the required reactors of the offshore wind farm between the high-voltage side of each wind turbine box-type transformer and the high-voltage side of the land centralized control center. This method not only solves the problem of excessive line loss of the offshore wind farm field area and the transmission submarine cable, but also saves a set of high-voltage reactors for the offshore booster station, which is helpful for the compact arrangement of the offshore booster station and saves the area and investment cost of the offshore booster station.

[0006] The technical scheme adopted by the present application is as follows: A method for configuring inductive and capacitive reactive power dispersion compensation of an offshore wind farm, comprising the following steps:

[0007] The sending system inductive reactive power compensation demand of the offshore wind farm booster transformer transmission system to be compensated and the field area wind farm inductive reactive power compensation demand are calculated;

[0008] Half of the sending system inductive reactive power compensation demand is determined as the land centralized control center reactor configuration capacity in the offshore wind farm booster transformer transmission system;

[0009] The sum of half of the sending system inductive reactive power compensation demand and the field area wind farm inductive reactive power compensation demand is divided by the number of the wind turbine side box transformer reactors in the offshore wind farm booster transformer transmission system, so as to obtain the capacity of each wind turbine side box transformer reactor;

[0010] According to the determined land centralized control center reactor configuration capacity, the land centralized control center is configured with a reactor;

[0011] According to the determined wind turbine side box transformer reactor capacity, each wind turbine side box transformer is configured with a reactor.

[0012] In the above technical solution, the sending system inductive reactive power compensation demand is calculated according to the charging power of the sending submarine cable, the reactive power loss of the sending submarine cable, the reactive power loss of the offshore booster station main transformer, and the principle that the sending system reactive power charging power is equal to the reactive power loss.

[0013] In the above technical solution, the field area wind farm inductive reactive power compensation demand is calculated according to the charging power of the field area submarine cable, the reactive power loss of the field area submarine cable, the reactive power loss of the field area box transformer, and the principle that the field area reactive power charging power is equal to the reactive power loss.

[0014] In the above technical solution, the reactor configured for the wind turbine side box transformer is arranged on the wind turbine platform and connected to the corresponding wind turbine side box transformer high voltage side bus through an alternating current cable.

[0015] In the above technical solution, the offshore wind farm booster transformer transmission system to be compensated includes an offshore wind farm, an offshore booster station, a wind turbine side box transformer, a field area submarine cable, a sending submarine cable and a land centralized control center; the offshore wind farm is connected with the offshore booster station through a plurality of groups of wind turbine side box transformers; each group of wind turbine side box transformers includes a plurality of sub-box transformers connected in series through the field area submarine cable; the offshore booster station includes a plurality of main transformers; each main transformer is electrically connected with the land centralized control center through a corresponding sending submarine cable; and the land centralized control center is electrically connected with the power grid.

[0016] In the above technical solution, the sending system inductive reactive power compensation demand Q p感 Calculation formula:

[0017]

[0018] Wherein Q p容Q p损 Q z损 S T U T B T X T L T Ns zi I0 k I

[0019] Q c感 The calculation formula is:

[0020]

[0021] Wherein Q Q S i B i X i L i Ns i I0 I z0 I zk I

[0022] Q z The calculation formula is:

[0023]

[0024] Wherein, each sub-box type transformer in each group of wind turbine side box type transformers is configured with an electric reactor; the electric reactor configuration capacity Q z is evenly divided by the electric reactors of the corresponding sub-box type transformers

[0025] The beneficial effects of the present application are: the present application disperses the electric reactors at the high-voltage side of the box-type transformer and the land centralized control center, although the investment cost of the electric reactors is increased, but through analysis and calculation, the present application can obviously reduce the system network loss, and the comprehensive economic benefits are still very obvious, specifically, taking a 400MW wind farm as an example, although the investment cost of the electric reactors of the present application is increased by 6 million, the loss of the generated power of the wind farm in 10 years of operation can compensate for this part of the cost. The present application can reduce the investment of the offshore booster station, save the cost of a set of high-voltage electric reactors and cabinets of the offshore booster station by about 1.5 million, reduce the platform area of the offshore booster station by 80 square meters, which can help the compact arrangement of the offshore booster station and save the investment cost of the booster station. The present application can improve the voltage quality of the field area and ensure the safe operation of the field area equipment.

[0026] Further, the present application provides a sending system inductive reactive power compensation demand calculation method taking the principle that the reactive power charging power and the reactive power loss of the sending system are equal, which can effectively prevent the operation safety of the sending electrical equipment of the offshore wind farm from being affected by the power frequency overvoltage problem, and realize the best operation state through the local reactive power balance of the offshore wind farm. Meanwhile, the calculation method fully considers the working characteristics of the main transformer of the offshore booster station and the sending submarine cable in the sending system, ensures the calculation accuracy, and further improves the compensation accuracy.

[0027] Further, the present application provides a field area wind farm inductive reactive power compensation demand calculation method taking the principle that the reactive power charging power and the reactive power loss of the field area are equal, which can effectively prevent the operation safety of the field area electrical equipment of the offshore wind farm from being affected by the power frequency overvoltage problem, and realize the best operation state through the local reactive power balance of the field area of the offshore wind farm. Meanwhile, the calculation method fully considers the working characteristics of the box-type transformer at the fan side and the field area submarine cable in the field area wind farm, ensures the calculation accuracy, and further improves the compensation accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a method flowchart of the present application;

[0029] Figure 2 It is a system diagram of the inductive reactive power compensation configuration of the offshore wind farm of the present application. DETAILED DESCRIPTION

[0030] The present application will be further described in detail below in combination with the drawings and specific embodiments, so as to be clearly understood by the present application, but they do not constitute limitations to the present application.

[0031] As shown in the drawings, Figure 1 The present application provides a kind of inductive reactive power dispersion compensation configuration method of offshore wind farm, comprising the following steps:

[0032] The sending system inductive reactive power compensation demand of the offshore wind farm booster voltage transmission system to be compensated and the inductive reactive power compensation demand of the wind farm in the field are calculated.

[0033] Half of the sending system inductive reactive power compensation demand is determined as the land control center reactor configuration capacity in the offshore wind farm booster voltage transmission system.

[0034] The sum of half of the sending system inductive reactive power compensation demand and the inductive reactive power compensation demand of the wind farm in the field is divided by the number of the wind turbine side box-type transformer in the offshore wind farm booster voltage transmission system, so as to obtain the capacity of the reactor of each wind turbine side box-type transformer.

[0035] According to the determined land control center reactor configuration capacity, the reactor is configured for the land control center.

[0036] According to the determined capacity of the wind turbine side box-type transformer reactor, the reactor is configured for each wind turbine side box-type transformer.

[0037] The principles of the present application are further illustrated below in combination with specific embodiments.

[0038] As shown in Figure 1 , the offshore wind farm distributed inductive reactive power compensation configuration method of the present embodiment comprises the following steps:

[0039] Step 1, determine the offshore wind farm booster voltage transmission system to be compensated, wherein the booster voltage transmission system mainly comprises: an offshore wind farm, an offshore booster station, a wind turbine side box-type transformer, a field cable, a sending cable and a land control center; the offshore wind farm is electrically connected with the offshore booster station via a plurality of groups of wind turbine side box-type transformers; each group of wind turbine side box-type transformers comprises a plurality of sub-box-type transformers connected in series through the field cable; the offshore booster station comprises a plurality of main transformers; each main transformer is electrically connected with the land control center through a corresponding sending cable; and the land control center is electrically connected with the power grid.

[0040] Step 2, calculate the charging power of the sending cable, the reactive power loss of the sending cable and the reactive power loss of the main transformer of the offshore booster station; in order to prevent the operation safety of the sending electrical equipment of the offshore wind farm from being affected due to the problem of power frequency overvoltage, the best operation state is that the reactive power of the offshore wind farm is balanced on site, that is, the principle of equalizing the reactive power charging power and the reactive power loss of the sending system is used to obtain the inductive reactive power compensation demand Q p感 of the sending system, half of which is compensated by the land control center reactor and the other half is compensated by the wind turbine side box-type transformer. According to the demand capacity, the land control center reactor configuration capacity is determined as

[0041] Step 3, calculate the charging power of the field area submarine cable, the field area submarine cable reactive loss, the field area box transformer reactive loss, to prevent the offshore wind farm field area electrical equipment from being affected by the operation safety due to the problem of power frequency overvoltage, the best operation state is the reactive power balance of the offshore wind farm field area, that is, the principle of equalizing the field area reactive charging power and the reactive loss to obtain the inductive reactive power compensation demand Q of the field area wind farm c感 , which is compensated by the box transformer on the fan side.

[0042] Step 4, summary and Q c感 , obtain the required configuration of inductive reactive compensation capacity of all box transformers on the fan side, and divide the capacity to each box transformer on the fan side to determine the configuration capacity of the reactor of each box transformer on the fan side.

[0043] Step 5, according to the determined configuration capacity of the reactor of the land centralized control center, configure the high-voltage reactor for the land centralized control center; according to the determined capacity of the reactor of the box transformer on the fan side, configure the reactor for each box transformer on the fan side. Each sub-box transformer in each group of box transformers on the fan side is configured with a reactor; the configuration capacity Qz of the reactor of each group of box transformers on the fan side is divided by the corresponding sub-box transformer. The configuration distribution is shown in Figure 2 .

[0044] The distributed inductive reactive power compensation configuration method of the offshore wind farm is further designed that the inductive reactive power compensation demand Q p感 of the step 2 is calculated by the following formula:

[0045]

[0046] , wherein Q p容 is the charging power of the sending system, Q p损 is the reactive loss of the sending submarine cable, Q z损 is the inductive reactive loss of the main transformer of the offshore booster station. S T is the sending capacity of the sending submarine cable T, U T is the rated voltage of the sending submarine cable T, B T is the unit electric capacity of the sending submarine cable T, X T is the unit electric reactance of the sending submarine cable, L T is the length of the sending submarine cable T, Ns is the number of the sending submarine cable, Nz is the number of the main transformer, S zi is the capacity of the main transformer z i , I0 is the main transformer no-load current percentage, U k is the main transformer short-circuit impedance voltage percentage. The sending system refers to the sending submarine cable from the offshore booster station to the land centralized control center. 2 main transformers can correspond to only 1 sending submarine cable.

[0047] The offshore wind farm distributed inductive reactive power compensation configuration method is further designed that the reactive power compensation demand Q c感 The calculation method is:

[0048]

[0049] Wherein is the charging power of the cable i in the field area, is the reactive power loss of the cable i in the field area, is the reactive power loss of the transformer i. U i is the rated voltage of the cable i in the field area, B i is the unit electric capacity of the cable i in the field area, X i is the unit reactance of the cable i in the field area, L i is the length of the cable i in the field area, N is the number of transformers, S i is the capacity of the transformer i, is the reactance of the transformer z i I. z0 is the no-load current percentage of the transformer, U zk is the short-circuit impedance voltage percentage of the transformer.

[0050] The offshore wind farm distributed inductive reactive power compensation configuration method is further designed that the reactance of each transformer reactor configuration capacity is:

[0051]

[0052] The following takes an actual offshore wind farm as an example to verify the superiority of the inductive reactive power compensation configuration method.

[0053] Taking a 400MW offshore wind farm as an example, a certain offshore wind farm has 100 wind turbines with a single machine capacity of 4MW. The booster station contains 2 main transformers, each with a capacity of 280MW. The wind farm has 10 sets of 4MW wind turbines per 10 sets of 4MW wind turbines. There are 10 sets of power collection lines, and the voltage grade of the power collection line is 35kV. The medium voltage cable model in the power collection line is: HYJQF41-F 48 / 66kV 3×300mm 2 The outgoing cable adopts 2 sets of HYJQF41-F127 / 220kV 3×500mm2 high-voltage cable, and the cable and transformer specifications are shown in Tables 1 and 2.

[0054] Table 1 35kV power collection line cable parameters

[0055]

[0056] Table 2 220kV outgoing cable parameters

[0057]

[0058] Table 3 main transformer parameters

[0059] Number of main transformers Main transformer capacity MVA Main transformer voltage kV Main transformer short circuit impedance 2 2×280 220 / 35 14％

[0060] Table 4 box transformer parameters

[0061]

[0062] The equivalent unit cable length of the power collection system of the offshore wind farm is The equivalent unit cable parameters are as follows:

[0063]

[0064] In the formula, r is the equivalent unit resistance, L is the equivalent unit inductance, C is the equivalent unit capacitance, i is the serial number of the single chain branch, m is the maximum value of the single chain branch, j is the serial number of the wind turbine in the branch, n is the number of the wind turbine in the single chain branch, a is the power passing through the jth cable in the ith link, which is a multiple of the unit wind turbine output power, r, L, and C are the unit resistance, inductance, and capacitance values of the jth cable in the ith link, and l is the length of the jth cable in the ith link. m ij ij ij ij ij

[0065] As Figure 1 ​​​​​​As shown, first, the offshore booster station booster transformer power transmission system is constructed, the charging power of the outgoing sea cable, the outgoing sea cable reactive loss, the offshore booster station main transformer reactive loss are calculated, and the outgoing system inductive reactive power compensation demand is obtained. The charging power of the field area sea cable, the field area sea cable reactive loss, the field area box transformer reactive loss are calculated, the field area wind farm inductive reactive power compensation demand is obtained, and finally the land centralized control center and each box transformer reactor configuration capacity are obtained. After calculation, the capacitive charging power of each outgoing sea cable is 49.02 MVar, the inductive loss is 4.305 MVar, and the inductive loss of 2 main transformers is 0.4536 MVar. The capacitive charging power of the field area sea cable is 9.25 MVar, the inductive loss of the field area sea cable is 3.54 MVar, and the inductive loss of the box transformer is 0.11 MVar. After calculation, the reactor capacity of 44.5 MVar needs to be configured on the land centralized control center side, and the reactor capacity of 0.5 MVar needs to be configured on the high voltage side of each box transformer. The cost of the reactor of 44.5 MVar is about 3.2 million, and the cost of the reactor of 0.5 MVar is about 60,000, so the cost of the reactor of 100 box transformers is about 6 million. As can be seen from Table 5, compared with the offshore wind farm without reactor scheme, the network loss of the offshore wind farm when full load is reduced from 2.4 MW to 1.3 MW, although the investment cost increases by 9.2 million, considering various operating conditions of the offshore wind farm, the network loss power is reduced by about 3300 MWh per year, considering the on-grid electricity price of 0.4 yuan / kWh, the network loss cost is reduced by about 1.32 million yuan per year, the network loss cost is reduced by 33 million yuan in 25 years of operation, and the comprehensive economic benefit is about 23.8 million yuan. Compared with the traditional reactor configuration in the offshore booster station scheme, although the investment cost increases by 6 million, the network loss is reduced from 1.8 MW to 1.3 MW, the network loss power is reduced by about 1500 MWh per year, the network loss cost is reduced by about 0.6 million yuan per year, the network loss cost is reduced by 15 million yuan in 25 years of operation, and the comprehensive economic benefit is 9 million yuan. At the same time, the reactor is dispersedly arranged at the land centralized control center and the high voltage side of the box transformer of the wind turbine, which can improve the field area power frequency voltage quality, reduce 1 high voltage reactor of the offshore booster station, reduce the platform area of the offshore booster station by about 80 square meters, save the cabinet and reactor cost of the offshore booster station by about 1.5 million, and realize the compact arrangement of the offshore booster station.

[0066] Table 5 wind farm network loss

[0067]

[0068]

[0069] The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A method for configuring a dispersed compensation of inductive and capacitive reactive power for an offshore wind farm, characterized in that: The method comprises the following steps: calculating the sending system inductive reactive power compensation demand of the offshore wind farm booster transformer transmission system to be compensated and the field area wind farm inductive reactive power compensation demand; determining half of the sending system inductive reactive power compensation demand as the configuration capacity of the land centralized control center reactor in the offshore wind farm booster transformer transmission system; dividing the sum of half of the sending system inductive reactive power compensation demand and the field area wind farm inductive reactive power compensation demand by the number of the wind turbine side box-type transformer in the offshore wind farm booster transformer transmission system to obtain the capacity of the reactor of each wind turbine side box-type transformer; configuring the reactor for the land centralized control center according to the determined configuration capacity of the land centralized control center reactor; configuring the reactor for each wind turbine side box-type transformer according to the determined capacity of the wind turbine side box-type transformer reactor; wherein the reactor configured for each wind turbine side box-type transformer is arranged on the corresponding wind turbine platform and is connected to the high-voltage side bus of the wind turbine side box-type transformer through an AC cable; calculating the sending system inductive reactive power compensation demand according to the charging power of the sending submarine cable, the reactive power loss of the sending submarine cable, and the reactive power loss of the offshore booster station main transformer, and taking the principle that the sending system reactive power charging power is equal to the reactive power loss; calculating the field area wind farm inductive reactive power compensation demand according to the charging power of the field area submarine cable, the reactive power loss of the field area submarine cable, and the reactive power loss of the field area box-type transformer, and taking the principle that the field area reactive power charging power is equal to the reactive power loss; The offshore wind farm booster transformer transmission system to be compensated comprises an offshore wind farm, an offshore booster station, a wind turbine side box-type transformer, a field area submarine cable, a sending submarine cable, and a land centralized control center; the offshore wind farm is connected to the offshore booster station through a plurality of groups of wind turbine side box-type transformers; each group of wind turbine side box-type transformers comprises a plurality of sub-box-type transformers connected in series through the field area submarine cable; the offshore booster station comprises a plurality of main transformers; each main transformer is electrically connected to the land centralized control center through a corresponding sending submarine cable; and the land centralized control center is electrically connected to the power grid. Sent-out system inductive reactive compensation demand Q p感 Calculation formula: where Q p容 is the charging power of the sending-out system, Q p损 is the reactive power loss of the sending-out submarine cable, Q z损 is the inductive reactive power loss of the main transformer of the offshore booster station; S T is the sending-out capacity of the Tth submarine cable, U T is the rated voltage of the Tth submarine cable, B T is the unit electric susceptance of the Tth submarine cable, X T is the unit electric reactance of the Tth submarine cable, L T is the length of the Tth submarine cable, Ns is the number of the sending-out submarine cables; Nz is the number of the main transformers, S zi is the capacity of the zith main transformer, I0 is the no-load current percentage of the main transformer, U k is the short-circuit impedance voltage percentage of the main transformer; The field area wind farm reactive power compensation demand Q c感 The calculation formula is: wherein Qi is the charging power of the i-th field area submarine cable, Xi is the reactive loss of the i-th field area submarine cable, Ui is the reactive loss of the i-th wind farm side box transformer; U i Vi is the rated voltage of the i-th field area submarine cable, B i Xi is the unit susceptance of the i-th field area submarine cable, X i Li is the unit reactance of the i-th field area submarine cable, L i Li is the length of the i-th field area submarine cable, N is the number of wind farm side box transformers, S i Qi is the capacity of the i-th wind farm side box transformer, Xi is the reactance of the i-th wind farm side box transformer; I z0 Qi is the no-load current percentage of the box transformer, U zk Qi is the short-circuit impedance voltage percentage of the box transformer; The capacity Q of the reactor of the box-type transformer on the side of each group of fans z is: Wherein, each sub-box transformer in each group of fan-side box transformer is configured with a reactor; the reactor configuration capacity Q of each group of fan-side box transformer z Is divided by the reactor of its corresponding sub-box transformer.

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