CN113162094A

CN113162094A - Planning method of hybrid direct-current transmission system

Info

Publication number: CN113162094A
Application number: CN202011548900.1A
Authority: CN
Inventors: 朱刘柱; 马静; 叶彬; 陈煜�; 叶斌; 冯沛儒; 徐加银; 刘青
Original assignee: State Grid Anhui Zhongxing Electric Power Design Institute Co ltd; Economic and Technological Research Institute of State Grid Anhui Electric Power Co Ltd
Current assignee: State Grid Anhui Zhongxing Electric Power Design Institute Co ltd; Economic and Technological Research Institute of State Grid Anhui Electric Power Co Ltd
Priority date: 2020-12-24
Filing date: 2020-12-24
Publication date: 2021-07-23

Abstract

The invention discloses a planning method of a hybrid direct-current power transmission system, which comprises the following steps: 1) determining a boundary condition; 2) analyzing the current situation of a power grid and a power supply; 3) power grid development planning analysis; 4) analyzing the consumption of electric energy; 5) and confirming the direct current transmission scheme. The invention provides the main principle, the design content and the flow steps of the planning and design of the hybrid direct-current power transmission system based on the economic analysis of the hybrid direct-current power transmission system. Based on the proposed method, the design of the Chinese-Korean segment mixed direct current scheme of Mongolian-Zhonghan-Korea project is developed, and the feasibility of the proposed planning method is verified.

Description

Planning method of hybrid direct-current transmission system

Technical Field

The invention relates to the technical field of power transmission, in particular to a planning method of a hybrid direct-current power transmission system.

Background

With the increase of world economic development and population, global energy consumption continuously increases, a global energy internet is constructed, clean substitution and electric energy substitution are greatly promoted, global development, global configuration and continuous supply of clean energy are realized, and the method is a fundamental way for human beings to meet three challenges of global resource tension, environmental pollution and climate change and meet sustainable development. Clean energy is widely distributed in all continents, global land wind energy resources exceed 1 trillion kilowatts, solar energy resources exceed 100 trillion kilowatts, and abundant ocean wind energy, water energy, biomass energy, tide and geothermal energy resources can be converted into electric energy for utilization. Wind power and solar energy in the first-pole (north pole and equator) and hydropower of main watersheds of various continents are strategic key points of future energy development. The total amount of wind energy resources in arctic regions is the first global, and the technology development amount exceeds 300 trillion kilowatts and accounts for about 20 percent of the whole world; near the equator is the most global area with the most abundant solar energy resources, and land technology can be developed with the development amount of more than 1000 trillion kilowatts, which accounts for about 30 percent of the world. The full sphere water energy resource technology can be developed with 16 trillion kilowatts, and is mainly concentrated in Asia, Africa and south America. The development amount of global distributed wind power and solar power generation resources exceeds 10 trillion kilowatts. The clean energy of each continent is developed in an intensive scale, various distributed energy sources are developed flexibly and economically, multi-energy complementation, flexible mutual assistance and coordinated utilization are realized, and the future global energy demand can be completely met.

The ultra-high voltage power grid is a main grid frame of the global energy Internet, and all large clean energy bases and load centers in the world are in an ultra-high voltage transmission range. The arctic wind power can be transmitted to Asia, Europe and America through extra high voltage, and an Asia-Europe-America interconnected power grid is constructed; the solar energy of north africa and middle east can be transmitted to europe and asia by extra-high voltage to north, and an interconnection power grid of europe, africa and asia is constructed. Interconnection among other continents and between countries can be realized through multiple modes such as extra-high voltage. The cross-continent and cross-country power grid interconnection has obvious benefits of time zone difference, season difference and electricity price difference, the safety, economy and stability of clean energy are greatly improved, and the globalization of energy production, the globalization of configuration and the globalization of trade are realized. With the rapid increase of cross-continent and cross-country electric power trade, the role of the global energy internet in guaranteeing energy supply is more and more important.

With the rapid development of ultra-high voltage direct current and flexible direct current transmission technologies, the types of the converter stations in the direct current system and the connection relation between the converter stations are comprehensively determined according to the characteristics of an access system, the technical level and the like in the direct current system planning, and therefore the comprehensive technical economy optimization of the direct current system and the alternating current and direct current system becomes an important difficult problem in planning work.

Disclosure of Invention

The invention aims to provide a planning method of a hybrid direct-current power transmission system, which can comprehensively and effectively plan and design the hybrid direct-current power transmission system.

In order to solve the technical problems, the invention adopts the following technical scheme:

a planning method of a hybrid direct current transmission system comprises the following steps:

1) determining a boundary condition;

2) analyzing the current situation of a power grid and a power supply;

3) power grid development planning analysis;

4) analyzing the consumption of electric energy;

5) and confirming the direct current transmission scheme.

As a further improvement of the above scheme:

the determining the boundary conditions specifically comprises:

the method comprises the steps of determining main boundary conditions and relevant principles of power transmission planning design of a power project matched with a hybrid direct-current power transmission system, determining a design level year, a distant view level year and a transition level of the hybrid direct-current power transmission system planning, and determining the range of the power transmission planning design.

The power grid and power supply current situation analysis comprises the following steps:

1) knowing the range of the involved power grid and its main characteristics;

2) knowing the current status of the power system includes:

21) installed capacity of a power grid, a power supply structure, generated energy, power consumption, maximum load, load characteristics and system peak shaving;

22) power grid conditions at and above 220 kv voltage levels;

23) the power transmission and receiving conditions of the regional power grid, the provincial power grid and the peripheral power grid;

24) the main power grid operation indexes comprise average coal price, electricity generation utilization hours and average on-line electricity price;

3) analyzing main technical indexes of the hybrid direct-current power transmission system, wherein the indexes comprise the following contents:

31) the geographical position, construction conditions, final scale capacity, staging construction capacity and the progress condition of earlier work of the project;

32) the main technical and economic indexes of the engineering project comprise annual matching power supply generating capacity, engineering utilization hours, static total investment and unit kilowatt investment;

if the matched power supply has a hydraulic power plant, the characteristics of the hydraulic power plant, the reservoir regulation performance, the guaranteed output, the annual average generated energy, and the predicted output, the average output and the forced output of each hydrological year can be known;

if the matched power supply has a wind power field, the wind resource condition, the characteristics of the wind power field, the output curve of each month, the typical output curve of each day, the output probability distribution and the output concurrence rate of the wind power field are also known;

if the matched power supply is a photovoltaic power station, the total annual amount of solar radiation, the peak sunshine hours, the characteristics of the power station, the output curve of each month and the typical output curve of the sun can be known.

The power grid development planning analysis comprises the following steps:

1) determining the load level of a transmitting-receiving end power grid according to a load prediction result of a regional power grid or provincial power grid development plan by combining the current economic development situation and the power load increase situation, and analyzing and proposing corresponding load characteristics;

2) analyzing the power supply construction planning, the power supply structure and the development change trend of the relevant areas, and listing the construction progress and the unit retirement plan of the newly added power plant in the planning period;

3) and analyzing and planning the development and planning of the power grids at the transmitting end and the receiving end in the planning period.

The electric energy consumption scheme analysis comprises:

1) analyzing the primary energy and the resource condition of the primary energy in the relevant area, and analyzing the reasonable flow direction of the energy and the market positioning of the power supply project;

2) determining boundary conditions and relevant principles of power and electric quantity balance;

3) selecting a representative year in a planning period of a relevant area to perform power and electric quantity balance calculation;

4) for a hybrid direct-current power transmission system for transmitting hydropower, the calculation of the substitution rate of thermal power, the electric quantity of abandoned water and the thermal power of a receiving-end power grid can be carried out; for a hybrid direct-current power transmission system for transmitting wind power or photovoltaic, peak-load balancing of a transmitting-receiving-end power grid is carried out, the absorption capacity of the transmitting-receiving-end power grid is analyzed, a power transmission curve is researched by combining the safety and the economy of power transmission, and a new energy and conventional power source configuration principle and proportion are provided;

5) considering the factors of power transmission cost and replacement capacity benefit, and providing a power supply range and a consumption scheme of the hybrid direct-current power transmission system through comprehensive economic comparison;

6) after the electric energy consumption scheme of the regional power grid is determined, the provincial consumption scheme is demonstrated and recommended according to needs.

The process of confirming the direct current transmission scheme comprises the following steps:

1) according to the analysis result of the electric energy consumption scheme, the technical mode and the voltage level of the hybrid direct-current power transmission system are demonstrated and selected by combining the conditions of a power transmission corridor and the overall planning requirement of a power grid, and the drop points of the power grid at the transmitting end and the receiving end are analyzed;

2) a comparison and selection scheme and a necessary transition scheme are designed for the hybrid direct-current transmission system, electrical calculation is carried out on the designed scheme, the power flow distribution, the network loss, the transmission capacity, the power grid stability level and the short-circuit current level of each scheme are analyzed and compared, and after various influence factors are considered, a recommended scheme is provided through comprehensive technology and economic comparison.

Furthermore, after the dc power transmission scheme is confirmed, a technical and economic analysis of a planning scheme is also included, which includes:

1) performing typical mode electrical calculation on the recommended scheme;

2) carrying out investment estimation on the power transmission and transformation construction projects in the recommended scheme, and listing economic indexes, power transmission and transformation construction projects, subentry investment and total investment adopted by the investment estimation;

3) and (3) providing preliminary comments on system matching data required in the early research stage of the hybrid direct-current power transmission system, including the outlet voltage grade, the outlet loop number, main electrical equipment of a power supply project and parameter selection.

Furthermore, after the technical and economic analysis of the planning scheme, the planning, station selection and route selection are also included, which includes:

1) performing site reconnaissance on the planned station selection, and preliminarily analyzing station site construction conditions; the planning route selection should be carried out indoors by utilizing the former survey design results and satellite picture route selection as much as possible, and if necessary, the site survey can be carried out on the key road sections with the key paths or poor conditions, and the key road sections are primarily communicated with local government departments, so that the power transmission scheme is prevented from being overturned due to station sites or path reasons;

2) analyzing natural conditions of different power transmission corridors in the path scheme, wherein the natural conditions comprise geological landform, mineral distribution, traffic and weather; according to the development situation of the line selection work, special research on the planning of the power transmission corridor is developed when necessary.

Furthermore, after the station selection and route selection are planned, the method also comprises the power price competition analysis, which comprises the following steps:

1) calculating and listing the price of the power on the internet of the matched power supply project;

2) according to the electricity price policy, a power transmission electricity price measuring and calculating principle is provided, the power transmission electricity price of the recommended scheme is measured and calculated, and the power transmission electricity prices of other comparison schemes can be measured, calculated and analyzed if necessary;

3) carrying out sensitivity analysis on the influence of the change of the transmitted electric quantity on the power transmission price;

4) and measuring the arrival grid power price of the matched power supply project, and analyzing the arrival grid power price competitiveness so as to finally confirm the correlation coefficient of the hybrid direct-current power transmission system.

The invention has the beneficial effects that:

the invention provides main principles, design contents and flow steps of the planning and design of the hybrid direct-current power transmission system based on the economic analysis of the hybrid direct-current power transmission system. Based on the proposed method, the design of the Chinese-Korean segment mixed direct current scheme of Mongolian-Zhonghan-Korean-Japanese engineering is developed, and the feasibility of the proposed planning method is verified.

Drawings

FIG. 1 is a flow chart of the present invention.

Detailed Description

The present invention will now be described with reference to the accompanying drawings, wherein the specific embodiments described herein are merely illustrative and explanatory of the invention and are not restrictive thereof.

Referring to fig. 1, a method for planning a hybrid dc power transmission system includes:

1) determining a boundary condition;

2) analyzing the current situation of a power grid and a power supply;

3) power grid development planning analysis;

4) analyzing the consumption of electric energy;

5) confirming a direct current transmission scheme;

6) carrying out technical and economic analysis on the planning scheme;

7) planning station selection and line selection;

8) and (4) carrying out electric price competitive analysis.

Wherein the determining the boundary condition specifically comprises:

Wherein, electric wire netting and power current status analysis includes:

1) knowing the range of the involved power grid and its main characteristics;

2) knowing the current status of the power system includes:

22) power grid conditions at and above 220 kv voltage levels;

32) the main technical and economic indexes of the engineering project comprise annual matching power supply generating capacity, engineering utilization hours, static total investment and unit kilowatt investment; if the matched power supply has a hydraulic power plant, the characteristics of the hydraulic power plant, the reservoir regulation performance, the guaranteed output, the annual average generated energy, and the predicted output, the average output and the forced output of each hydrological year can be known; if the matched power supply has a wind power field, the wind resource condition, the characteristics of the wind power field, the output curve of each month, the typical sunrise output curve, the output probability distribution and the output concurrence rate of the wind power field are also known; if the matched power supply is a photovoltaic power station, the total annual solar radiation amount, the peak sunshine hours, the power station characteristics, the output curve of each month and the typical output curve of each month can be known.

Wherein the power grid development planning analysis comprises:

Wherein the power consumption scenario analysis comprises:

Wherein the process of confirming the direct current transmission scheme is as follows:

Wherein the technical and economic analysis of the planning scheme comprises:

1) performing typical mode electrical calculation on the recommended scheme;

Wherein, the planning station selection and line selection comprises:

Wherein the electricity price competitiveness analysis comprises:

The project planning design work is carried out by taking the project of China-Korean section, which has the fast working progress in the early stage of project of planned Mongolian-ZhongHan-Ri, as an example. The method mainly aims at relevant contents of a mixed direct current technical scheme in a power transmission planning scheme to carry out key research and analysis. According to the preliminary research conclusion, the direct current engineering of China-Korean district is in the Korea Renchuan region of Shandong province, China, and the receiving end.

First, boundary condition

1. China Shandong electric network

At present, the alternating current maximum voltage level of the China power grid is 1000 kilovolts, a structure of five synchronous power grids operating in North China-China, east China, northeast China, northwest China and south China is formed, and national power grid interconnection except Taiwan province is realized. The Shandong power grid is an important component of the power grid in North China, and 17 cities are covered by 500 kV power grids to form a main grid frame structure with five transverse lines and two longitudinal lines.

By 2018, the total installed capacity of the power grid in Shandong is 12556 ten thousand kilowatts, wherein 8 ten thousand kilowatts of hydropower station account for 0.06%; the pumped water energy storage is 100 ten thousand kilowatts and accounts for 0.8 percent, and the thermal power is 9768 ten thousand kilowatts and accounts for 77.8 percent; wind power 1061 ten thousand kilowatts, account for 8.5%; the photovoltaic 1052 ten thousand kilowatts accounts for 8.4 percent. In 2018, the power consumption and the maximum load of the Shandong power grid in the whole society reach 5430 hundred million kilowatt hours and 8930 ten thousand kilowatts respectively.

2. Korean electric network

Approximately 40% of the load in korea is concentrated in the central urban area, and large power plants are mainly distributed in coastal areas. The korean power grid consists of 15 areas: seoul, choiseer, renchuan, beijing plasma chambers, kyongplasma chambers, jiangyuan, zhongqing north, da-zhou south, duqiu, qingshang north, cauldron mountain-weishan mountain, qing south and jizhou. At present, a main grid frame of 345 kV alternating current power grid covering the whole country is formed in Korea, and an 765 kV power transmission channel crossing things is built in the north.

By the end of 2018, the installed capacity of the national power generation in korea reaches 11691 ten thousand kilowatts. Wherein, the hydropower 649 ten thousand kilowatts accounts for 5.6 percent; fire coal 3671 ten thousand kilowatt, accounts for 31.4%; the fuel oil accounts for 3.6 percent and is 416 ten thousand kilowatts; fuel gas 3784 ten thousand kilowatts, account for 32.4%; nuclear power 2253 ten thousand kilowatts, accounting for 19.3%; the other 919 ten thousand kilowatts account for 7.9 percent. In 2017, the Korea Hooker uses 5078 hundred million kilowatt hours of electricity and 8510 ten thousand kilowatts of maximum load. By 2017, the length of a power transmission line of a Korean power grid is 33955 kilometers, wherein the direct current transmission line is 231 kilometers, and the transformation capacity is 31200 ten thousand volt-ampere.

Second, electric energy consumption scheme

The results of the power balance calculation according to the power grid in Shandong, Korea, Renchuan, China are shown in the table below.

Table 1 influence of access system conditions on technical routes of converter stations

According to the current balance result, 230 million kilowatts of surplus power exists in Shandong of China in 2025, and 140 million kilowatts of market space exists in Korea Renchuan, so that China-Korea networking projects are built in 2025, the cross-country interconnection of China and Korea power grids is realized, the interconnection of the power grids among countries in northeast China and the construction of power infrastructure can be promoted, the power utilization pressure of load centers of Churl, Kenruan and peripheral areas in northwest of Korea can be relieved, and the energy substitution and transformation pace in northwest of Korea can be promoted.

Design of three-phase direct current transmission scheme

1. Voltage class

According to the preliminary research result of Mongolian-Zhonghan-Japanese engineering, the preliminary engineering planning scheme is that the power is transmitted from Mongolia to China according to the design of 1000 ten thousand kilowatts, the path length from Mongolia converter station to China Tianjin converter station is considered to be about 1250 kilometers, and the Mongolian-China engineering is preliminarily planned to adopt +/-800 kilovolt high-voltage direct current.

For the projects of China-Korea sections, according to the power balance result of 2025 years of project operation years, the length of a project path is considered to be about 380 kilometers, the project is recommended to adopt +/-500 kilovolts in the current period, and the rated power transmission capacity is considered to be 240 ten thousand kilowatts (the direct current is 2400 amperes). At the initial stage of project operation, collecting power from a Shandong power grid and sending the power to a Kenchuan region of Korea; in the long term, with the multi-end production of the korean to japanese section projects and the gradual production of the power supply in the vicinity of the Mongolian converter station, the power transmission capacity and the power transmission requirement of the china to korean section projects will gradually increase. In the future, projects in China-Korea sections have the requirements of being expanded to +/-800 kilovolts and having power transmission capacity exceeding 400 ten thousand kilowatts.

2. DC technical scheme

21. Technical route of sending end converter station

(1) The power supply is mainly a conventional power supply. A power supply installation machine in a Shandong power grid mainly adopts thermal power, a large number of nuclear power generating units are also arranged in the vicinity of the West sea of the east, and although a Chinese converter station at the transmission end of China-Korean projects has no specific matched power supply temporarily, the network collection power of the converter station is mainly provided by the thermal power generating units and the nuclear power generating units in the vicinity.

(2) The converter station is connected to 500 KV main network in Shandong. According to the consideration of the maximum power transmission scale of 200 ten thousand kilowatts in the current period of the projects from China to Korea, the China converter station should adopt 500 kV voltage level and is connected to a 500 kV alternating current main network in Shandong, the power grid strength is high, and the reactive voltage supporting capability is strong.

(3) Sea cable engineering. The maximum voltage grade of the sea cable suitable for the LCC/VSC converter station is 700 kilovolts at present, and the maximum through current is 2560 amperes; the existing submarine cable equipment can meet the engineering technical requirements by combining the current transmission capacity of 240 ten thousand kilowatts of engineering from China to Korea and adopting the LCC technology in a converter station.

(4) And (5) subsequent extension requirements. After the future expansion of the engineering from China to Korea, if only the converters are connected in parallel without increasing the rated direct current voltage, the through-current capacity of the direct current submarine cable designed in this period will seriously restrict the improvement of the subsequent transmission capacity of the engineering. In combination with the development of direct current cables/submarine cables with higher voltage level, which are developed worldwide, the current converter series connection scheme is recommended in the long-term Chinese-Korean projects, and outgoing lines with higher voltage level are added, so that the power transmission requirement of later projects is met.

22. Technical route of receiving end converter station

(1) The converter station is connected to 345 kV power grid near Kenchuan in Seoul. 345 kilovolt areas in the Kenchuan region have a strong power grid structure, 63 transformer substations are arranged in the system, the total length of a power transmission line is 1208 kilometers, and the total transformation capacity is 2390 kilovolt-ampere; in 2017, the maximum load of the RENCHUAN power grid is 686.4 thousands kilowatts, and surplus power of the regional power grid is transmitted to the surrounding regions through 66/154/345 kilovolt lines.

(2) Sea cable engineering. The submarine cable engineering analysis is the same as the analysis of the front-end converter station.

(3) And (5) subsequent extension requirements. The transmission capacity of the project in this period from China to Korea is about 240 ten thousand kilowatts, and the total load of the Kenchuan power grid is 1/3, and the project in this period can adopt LCC or VSC technology in consideration of the power grid structure and voltage level in the Kenchuan area; after future engineering extension is considered, if the load is estimated according to the engineering transmission capacity of 400 ten-thousand kilowatts, the load occupies 2/3 in the Kenchuan area, and the gradual decommissioning of the fire coal thermal power generating units in the Noseoul, Kenchuan and the peripheral areas is considered, the support capability of the Kenchuan power grid on the converter station is obviously reduced. And comprehensively considering the near-term and long-term engineering scale and the system condition, and the receiving end converter station can adopt VSC and LCC technical routes.

3. Converter station access system scheme

31. Sending end converter station

The sending end converter station is positioned in the Weihai area of Shandong province in China, and 2 access system schemes are provided.

(1) Scheme 1: the converter station is connected to the Kunze 500 kV station through a double-circuit 500 kV line. The length of 500 KV line is 2X 40 km, and the line conductor model is temporarily in accordance with LGJ-4X 630.

(2) Scheme 2: the converter station is connected with the Kunze 500 kV station through a 1-loop 500 kV line, and is lapped with the planned 1-loop 500 kV line from the Shijie bay to the Kunze station through another 1-loop 500 kV line. The length of a 500 kilovolt line is 2 multiplied by 40 kilometers, and the line conductor model is temporarily in accordance with LGJ-4 multiplied by 630.

According to the load flow calculation result: scheme 1 tidal current flows reasonably, and the wiring is clear. Therefore, scheme 1 is temporarily recommended as a sending-end stream switching station access system scheme.

32. Receiving end converter station

The receiving-side converter station is located in korea renchuan area, and the access system considers the following 2 schemes.

(1) Scheme 1: and the receiving end converter station and the Nassah 345 kV transformer substation are built together.

(2) Scheme 2: the receiving end converter station is 8 kilometers away from the Narcissus 345 kV transformer station, and is connected to the Narcissus transformer station through a double-circuit 345 kV line.

Through comprehensive comparison, the scheme 1 has reasonable trend flow direction, clear wiring and investment saving. Therefore, the scheme 1 is recommended as a receiving end converter station access system scheme.

Four, electric calculation

1. Load flow calculation

11. Sending end system

Carrying out load flow calculation aiming at the project sending end systems from China to Korea, and displaying the result: the power flow of a near-area power grid of the transmitting-end converter station is uniformly distributed in a large mode and a small mode, the voltage level meets the requirements, and an alternating current circuit and a transformer are not overloaded in an N-1 mode and an N-2 mode.

12. Receiving end system

Carrying out load flow calculation aiming at the engineering receiving end systems from China to Korea, and displaying the result: the tidal current distribution is uniform under the large and small modes of the Kenchuan power grid, and the voltage and the line load level meet the requirements.

2. Transient stabilization

21. Sending end system

The transient stability calculation analysis result of the sending end system in the large and small modes shows that: when 500 KV lines N-1 and N-2 or direct current single and double pole blocking faults exist in the near area of the converter station, measures are not needed, the system can be kept stable, and voltage and frequency fluctuation meets requirements.

TABLE 2 stability calculation results of the sending end system

22. Receiving end system

The transient stability calculation analysis result of each scheme shows that: the receiving end system can be kept stable under the fault, and the voltage and frequency fluctuation meets the requirements.

TABLE 3 Renchuan electric network transient stability calculation results

3. Short circuit current

31. Sending end system

(1) Short circuit current

Aiming at the short-circuit current calculation carried out by the Chinese-Korean engineering sending end system, the calculation result shows that: the short-circuit current of the 500 kV bus in the near area of the converter station is within 63 kiloamperes, and the requirement of the rated breaking current of the circuit breaker is met.

TABLE 4 short-circuit current calculation results of sending end system

Serial number	500 KV bus name	Short-circuit current (Qian' an)
			1	Weihai convertor station	15.9
2	Kunzui	23.8
			3	Mou Ping	25.6
4	Shidao bay	25.0
			5	Cyanea sicca	38.7

(2) Short circuit ratio/equivalent short circuit capacity

The Chinese-Korean engineering adopts a system-level end-to-end hybrid structure, so that only one type of direct current transmission technology exists for the sending end converter station, and under the condition, the short circuit ratio index is consistent with the equivalent short circuit capacity index.

According to the short circuit calculation result, the following results are shown: under 2025 years of small-mode operation of a Shandong power grid, the short-circuit capacity of the converter station is 1444 million volt-ampere. According to the calculation of 240 ten thousand kilowatts of project in the current period, the short circuit ratio level of the convertor station is 5.4; if the short circuit ratio of the converter station is measured according to 400 ten thousand kilowatts in a long period, the short circuit ratio of the converter station is 3.01.

According to the calculation result, for the projects from China to Korea, the near-term and the far-term of the power grid at the Shandong transmitting end are strong systems, so that the converter station recommends to adopt the LCC technology.

32. Receiving end system

(1) Short circuit current

Short-circuit current calculation is carried out aiming at the engineering receiving end systems from China to Korea, and the calculation result shows that: the short-circuit current of 345 kilovolt buses in the near region of the converter station is within 63 kiloamperes, and the requirement of rated breaking current of the circuit breaker is met.

TABLE 5 short-circuit current calculation results of receiving end system

Serial number	500 KV bus name	Short-circuit current (Qian' an)
			1	Shin-Incheon	45.6
2	West-Incheon	44.2
			3	Shin-Sihwa	39.2
4	Shin-Kimpo	48.3
			5	Shin-Kajwa	33.1

(2) Short circuit ratio

China-Korea projects adopt a system-level end-to-end hybrid structure, so that only one type of direct current transmission technology exists for a receiving end converter station, and under the condition, the short circuit ratio index is consistent with the equivalent short circuit capacity index.

Effective short circuit ratio analysis is carried out aiming at the engineering receiving end converter stations from China to Korea, and the calculation result shows that: under the condition of conveying 240 million kilowatts in the project in the period, the effective short circuit ratio of the Renchuan power grid in a small mode is 3.04, and the system is a strong system; if the long-term engineering transmission capacity is expanded to 400 ten thousand kilowatts for measurement, the effective short-circuit ratio of the Renchuan power grid is about 1.83, and the system is extremely weak.

From the calculation results, for the projects from china to korea, although the receiving-end bengchua power grid has better system conditions recently, the system strength is remarkably reduced and becomes a weak system after the direct current project is expanded. And comprehensively considering the near-term adaptability and the long-term adaptability and considering the station site construction conditions in the Seelnakawa area, and the VSC technology is recommended to be adopted by the receiving end converter station.

Investment estimation

1. Estimated range of investment

The investment estimation range comprises a converter station project, a submarine cable project, a landing cable project, a land overhead line project and a matched alternating current net rack reinforcing and access system project.

The converter station engineering comprises a Chinese Weihai converter station and a Korean Renchuan converter station. The landing cable engineering comprises landing section cable engineering from each cable terminal station at sea. The land overhead line engineering comprises overhead line engineering from each sea-entry cable terminal station to a converter station.

2. Principle of investment estimation

(1) Construction engineering cost: the price levels of manpower, materials, construction machinery and the like which are different in China and various countries in Korea are considered.

(2) Equipment purchase cost: the specific cost adopts the quotation list provided by the production companies such as a converter valve, a submarine cable and the like.

(3) Engineering installation cost: the price levels of manpower, materials, construction machinery and the like which are different in China and various countries in Korea are considered.

In addition, exploration design costs, preparation costs, and other costs are also considered in the investment estimation.

3. Investment estimation

(1) Converter station investment estimation

And aiming at the 2 types of main wiring schemes, carrying out investment estimation on the converter stations in different schemes, wherein specific calculation results are shown in the following table.

TABLE 6 Chinese-Korea DC engineering investment estimation

Unit: hundred million yuan

From the estimation result of the investment of the converter station: the transmitting end and the receiving end adopt a scheme 1 of LCC technology, and the investment of a converter station is 5.9 hundred million dollars; and the transmitting end adopts a scheme 2 of LCC and the receiving end adopts VSC, and the investment of the converter station is 6.4 hundred million dollars.

(2) Submarine cable investment estimation

And the engineering construction characteristics of each country, sea area conditions and the like are comprehensively considered, and the XLPE-LCC model is selected for the submarine cable equipment, so that the investment of the submarine cable engineering is 19.25 hundred million dollars.

(3) Total investment of project

After the investment of the converter station and the investment of the submarine cable are comprehensively considered, the investment estimation result of the project from China to Korea in the current period is as follows:

(1) the sending end and the receiving end adopt a scheme 1 of LCC technology, and project investment in the current period is 25.15 hundred million dollars;

(2) the sending end adopts LCC, the receiving end adopts VSC scheme 2, and the project investment of this period is 25.65 hundred million dollars.

4. Technical economic analysis

(1) Comparison of techniques

Due to the proposed class 2 main wiring scheme, the scheme such as power flow distribution, transient stability, short-circuit current, short-circuit ratio and the like can meet the requirements of relevant engineering design.

If the long-term engineering extension requirement and the receiving end station site condition are considered, the receiving end adopts the scheme 1 of the LCC technology, the supporting capability of a receiving end system to the converter station is obviously reduced, and the short-circuit ratio of the converter station cannot meet the design requirement more than 3; compared with the scheme 2 that the receiving end stream switching station adopts the VSC technology, the scheme 2 has better long-range adaptability.

(2) Economic contrast

According to the investment estimation result of the class 2 main wiring scheme, the project investment of the scheme 2 is higher than that of the scheme 1 by 0.5 hundred million dollars and is about 2 percent because the receiving end adopts VSC technology.

(3) Economic analysis of integrated technology

Considering the class 2 main connection scheme comprehensively, although the investment of the scheme 2 is slightly higher, the scheme 2 has better adaptability in terms of the operation and the extension of a long-term converter station, and the like, so the scheme 2 is recommended to be used as a main connection design scheme of the project of the segments from China to Korea, namely that the transmitting end China Wicycle station adopts the LCC technology and the receiving end Korea Kenzuan station adopts the VSC technology.

Claims

1. A planning method for a hybrid direct current transmission system is characterized by comprising the following steps:

1) determining a boundary condition;

2) analyzing the current situation of a power grid and a power supply;

3) power grid development planning analysis;

4) analyzing the consumption of electric energy;

5) and confirming the direct current transmission scheme.

2. A planning method according to claim 1, wherein the determining of the boundary conditions is specifically:

3. The planning method according to claim 1, wherein the power grid and power source status analysis includes:

1) knowing the range of the involved power grid and its main characteristics;

2) knowing the current status of the power system includes:

22) power grid conditions at and above 220 kv voltage levels;

31) the geographical position, construction conditions, final scale capacity, staging construction capacity and the progress of earlier-stage work of the project;

if the matched power supply has a wind power field, the wind resource condition, the characteristics of the wind power field, the output curve of each month, the typical sunrise output curve, the output probability distribution and the output concurrence rate of the wind power field are also known;

4. The planning method according to claim 1, wherein the grid development planning analysis comprises:

5. The planning method of claim 1 wherein the power consumption plan analysis comprises:

4) for a hybrid direct-current power transmission system for transmitting hydropower, calculation of the thermal power substitution rate, the water-abandoning electric quantity and the thermal power variable cost of a receiving-end power grid is carried out; for a hybrid direct-current power transmission system for transmitting wind power or photovoltaic, peak-load balancing of a transmitting-receiving-end power grid is carried out, the absorption capacity of the transmitting-receiving-end power grid is analyzed, a power transmission curve is researched by combining the safety and the economy of power transmission, and a new energy and conventional power source configuration principle and proportion are provided;

6. The planning method according to claim 1, wherein the process of confirming the dc power transmission scheme is:

2) a comparison and selection scheme and a necessary transition scheme are drawn up for the design of the hybrid direct-current transmission system, electrical calculation is carried out on the drawn up scheme, the power flow distribution, the network loss, the transmission capacity, the power grid stability level and the short-circuit current level of each scheme are analyzed and compared, and after various influence factors are considered, a recommended scheme is proposed through comprehensive technology and economic comparison.

7. The planning method according to claim 1, wherein after the confirmation of the dc power transmission scheme, a technical-economic analysis of the planning scheme is further included, which includes:

1) performing typical mode electrical calculation on the recommended scheme;

8. The planning method according to claim 7, further comprising planning station selection and route selection after the technical and economic analysis of the planning scheme, comprising:

1) performing site reconnaissance on the planned station selection, and preliminarily analyzing station site construction conditions; the planning route selection is carried out indoors by utilizing the previous survey design result and satellite picture route selection as much as possible, the on-site survey can be carried out on the important road sections with the important paths or poor conditions if necessary, and the initial communication is carried out with local government departments, so that the power transmission scheme is prevented from being overturned due to station sites or path reasons;

9. The planning method according to claim 8, further comprising a price competition analysis after the station selection and route selection, the price competition analysis comprising: