Today, let Martin, hengfengshuai electrical engineer, lead you to understand the common sense of 20kV distribution network:
The purpose of 20kV Voltage Level in the world is to improve the primary distribution voltage. Its function is to replace 10kV / 35kV, 11 / 33kV and other voltages, directly form 110 / 20 / 0.4kV, 220 / 20 / 0.4kV, 330 / 20 / 0.4kV power supply system, reduce line loss and improve power supply stability.
1、 Global development of medium voltage distribution network
At present, dozens of countries and regions in the world have taken 20kV voltage level as the standard voltage of medium voltage distribution network and listed it in the standards of International Electrotechnical Commission, with very mature technology and experience. As early as the early 1960s, the line loss rate of urban power grids such as South Korea and Singapore was as high as 29.4%. After taking measures to increase the transmission voltage, strengthen monitoring and anti-theft electricity, and further taking measures to increase the primary distribution voltage, the line loss decreased to 5.9% after increasing the original 3.3 and 6.6kV distribution lines to 22.9kv. This is mainly because 20kV is compared with 10kV / 11kv, Its power supply radius and capacity are almost double that of the latter, reducing the loss, construction funds and maintenance costs per unit capacity. Technical and economic comparisons abroad have proved that the 20kV scheme is superior to the 10kV / 11kv scheme.
Note: at present, 80% of countries in Europe (Germany, France, Italy, Spain, etc.) and 14 countries and regions in Asia (Singapore, Japan, South Korea, Taiwan, etc.) all or in urban areas adopt 20kV as the standard voltage level of urban power distribution.
2、 Disadvantages of 10 kV / 11 kV distribution network
① Small transmission capacity: on the premise of ensuring the terminal voltage and line loss of 10kV / 11kv line, 10kV / 11kv can only transport loads below 1mkw.
② Short transmission distance: with the development of industrialization, the load density is increasing. The transmission distance of 10kV / 11kv is changed from 10km to 2 ~ 3km, which greatly reduces the power supply radius.
③ . the substation is too dense: with the increasing load density, the distribution of 10kV / 11kv substation is becoming more and more dense, wasting land resources.
④ Capacity increase: with the development of industry, the capacity of lines and transformers has greatly increased, resulting in some unnecessary power grid losses and a waste of many renewable resources.
3、 Advantages and characteristics of 20kV distribution network
- Multi circuit, high reliability and low loss: when the same power is transmitted on the same conductor, compared with the 10kV / 11kv voltage level, the 20kV power supply radius is increased by 60%, the power supply range is expanded by 1.5 times, the power supply capacity is increased by 1 time, and the transmission loss is reduced by 75%.
- Low investment and land saving: 20kV distribution network is adopted for power supply, which can reduce investment and save land for customers with large capacity, and provide optimal power supply mode. At the same time, the operation and maintenance cost is basically equivalent to 10kV / 11kv.
- Large power transmission capacity and wide power supply range: the power transmission capacity is about twice that of 10kV / 11kv line, and the power supply range is about 2.5 times that of 10kV / 11kv line.
- Long distance transmission: the advantages and potential of power supply in remote rural areas are huge. The use of 20kV long-distance power supply can reduce loss, alleviate the problem of excessive voltage, and give full play to the advantages of long-distance transmission in low load density areas.
4、 At present, the 20kV medium voltage distribution systems in operation in China include:
- The South Asia company in Kunshan uses 20kV distribution voltage level;
- Shanghai rail transit, Metro and light rail adopt 20kV, and the actual operation is in good condition;
- 20kV has been used for 45km to the east of Qingqiupu in Suzhou Industrial Park for many years;
- On March 27, 2003, the secondary substation in Nanfen area of Benxi, Liaoning Province was put into operation after reconstruction. Six 20 kV distribution lines were in operation. Since the operation of two main transformers and 199 distribution transformers, there has been no single line grounding fault;
- In 2007, Jiangsu Electric Power Company suggested that major cities in the province should establish at least one 20kV experimental area in the next 1-2 years. In 2008, some projects in Suzhou, Wuxi, Nanjing and other regions have been completed and put into operation and successfully connected to power, realizing reliable operation.
- The “double petal” distribution automation system of the Beijing Hangzhou Grand Canal, which was put into operation in May 2018, ensures that there are power supplies from three different directions, and the power supply reliability rate exceeds 99.9999%! The average annual outage time of users is less than 21 seconds, which is 9 seconds less than the average household outage time in Singapore!