The eletromagnet cycram network refers to a ring network composed of transformers or electromagnetic coupling at different voltage levels.
In the early days of the emergence of a new higher voltage level in the power system, the network could not be very strong in structure, but it was gradually improved, strengthened, and reasonable. In this process of perfection and enhancement, in order to obtain large network transmission power, to rationally utilize cheap resources, and to meet users' requirements for maximum power usage, most of the power systems operate with one or more electromagnetic loops.
Electric power system electromagnetic ring network operation, usually refers to two adjacent voltage level electrical components linked into a ring network operation. Electrical equipment with more than two voltage classes forms an electromagnetic ring network operation. Only when the dispatcher handles the accident or shifts the load in a short period of time, there is no problem with the verification, and this transitional temporary extreme special power can be used. System operation mode.
1 The necessity of open-loop operation of the electromagnetic ring network In the operation of the power system, the operation of the electromagnetic ring network is often more taboo. According to statistics, from 1970 to 1990, there were a total of 187 power-angle-related and power-stability-related accidents in China in the period from 1970 to 1990. Among them, there were 55 accidents involving high- and low-voltage network structures, accounting for 20.2%. Overseas and electromagnetic ring networks Relevant blackouts are also common, such as the large power outage in the western United States on July 2, 1996. After the disconnection of the PACI (three 500 kV AC), a large number of currents flooded into the eastern 345/230 kV network, resulting in stable voltage destruction. The WSCC solution was divided into 5 islands, more than 2 million users were outages, and the loss load was 10,576 MW. The longest power outage time was 6.4 hours. On August 10 of the same year, similar accidents of the power system occurred again, power outage users, loss of load, The blackouts far exceeded the July 2 accident. Therefore, people tend to talk about ring discoloration. As long as possible, the electromagnetic ring network adopts an open-loop method.
Open loop operation has many advantages: it is stable and easy to control. Interference occurs in an open-loop network, and faulty components are often removed, supplemented by effective accident handling methods, and the developments can be calmed down. If a failure occurs in the ring network, the power transfer will be caused after cutting off the faulty components in many cases, so that non-faulty components will cause stable destruction through power overrun.
The real power (or power angle) and reactive power (or voltage) of the power supply at the sending end can achieve the purpose of adjusting the power flow. When the ring is closed, the power flow is naturally distributed within the ring network, and the control is difficult, and often the ring element passes power and full load or even overload, and some idle.
This is an important means of limiting the short-circuit capacity. Combined operation, because the integrated impedance is often smaller, the short-circuit capacity is relatively large. Busbars with large short-circuit capacity are busbars with more outgoing lines and concentrated power outlets. Failure of these busbars is often the culprit in triggering major power system accidents.
4' Simplify relay protection and safety automatic devices. The configuration of relay protection and stabilization measures in the ring network is much more complicated than the non-ring network, and it is more difficult to coordinate. The complexity and mismatch of protection and safety automatic devices are generally the direct or expanding causes of accidents.
5) In some ring networks, since there is no circulation problem in the open-loop operation, the transmission loss may be smaller than that in the closed-loop operation, which can improve the transmission efficiency.
2 The possibility of operation of the electromagnetic loop network In the actual operation of the power system, it does not exclude all the operating modes of the electromagnetic loop network. On the contrary, in some cases, it may take full use of resources, improve transmission reliability, reduce transmission losses, etc. in a period of time. Aspects of the electromagnetic ring network operation outweigh the disadvantages of open-loop operation.
The use of electromagnetic ring network operation should be careful, and adhere to the following principles:! In the event of an accident, any component in the ring network is mainly a disconnection of the high-voltage component. Even if power transfer occurs, it will not cause stable damage. ! When the electromagnetic ring network is in operation, relay protection configuration and setting coordination are good, and safety and stability measures are simple and reliable. ! After the operation of the electromagnetic ring network, the voltage level of the receiving terminal should not be substantially affected. ! Electromagnetic ring network operation, the increase of the short-circuit capacity of any bus should not cause the switch to be difficult to disconnect. ! Electromagnetic ring network operation, transmission losses should not be significantly increased.
If the above 5 principles are satisfied, the operation of the electromagnetic ring network should be acceptable. However, it must be pointed out that a large number of accidents are not completely within people's expectations. Therefore, when the power system adopts the electromagnetic ring network operation mode, it should prevent the accident interlock from occurring, cause large power transfer, and may cause stable damage. Or it may cause some reliable measures that reflect the protection of the load current and other erroneous actions.
3 Suggestions for the 500/220kV Electromagnetic Ring Network Operation Mode of Hunan Power System 3.1 The Hunan Power System has now formed a 500kV diamond single ring network; the 500kV and 220kV electromagnetic ring networks operate as shown. The power supply directly connected to the 500kV network is the Gegang Line and Wuqiangxi Power Plant linked to the Central China Power System. There are two-way power exchanges between the 500/220kV networks in Gangchang. Under normal circumstances, there is only one-way active power exchange between Loudi and Yuntian 500/220kV networks, that is, the 500kV network injects active power into the 220kV network.
3.2 In this complex electromagnetic loop network, there are the following two major problems: the "bottleneck" of Gangshi and Xidian 220kV eastbound.
The "bottleneck" sent by the 220kV substation in Gang City. The power transmission to the 220kV network by Gang Substation is limited by the transmission capacity of three 220kV tie-lines (Gang Ti, Kong De, Kong Ying). Three transmission line transmission power and system-wide load level, Jiangyan and Shimen, Wuqiangxi power plant output, Gezhouba power plant south to send power, Mingshan, Panshan, Mocheng, Wusheng Palace four 220kV substation load size, etc. related. The power generation capacity connected to the 220kV busbar on the Gangshi City is 900MW. In some cases, it is necessary to receive some of the Wuqiangxi Power Plant and Gezhouba Power Plant to send power through the main transformer. For the maximum and minimum load of the system in 2000, the maximum load and minimum load of four 220kV substations such as Mingshan, Panshan, Mouteng, and Wushenggong were only 250MW and 120MW, respectively. Therefore, three times of 220kV lines are often operated under heavy loads. , And has become a "bottleneck" sent by 220kV substation in Gang City. ! From Yiyang to Changsha, the "bottleneck" of West Power Transmission to the East. The 220kV systems of Changde and Yiyang have access to a power generation capacity of nearly 1,570MW, of which hydropower capacity is nearly 970MW. In the area (including Zhangjiajie, Hucheng, and plant power supply, the maximum and minimum load in 2000 were only 770MW and 340MW, respectively. The maximum load of 260MW and the minimum load of 120MW in Jishou and Huaihua areas are also the maximum load of 1030MW, and the minimum load of 460MW, that is, 540*1110MW must be sent through the two main transformer substations in Gangshi and the two 220kV lines from Yiyang to Changsha. The variable capacity is only 500,000 kV*A, and the total capacity of the two 220 kV connecting lines from Yiyang to Changsha cannot exceed 350 MW according to the stability requirement. Therefore, the West-East electricity transmission is seriously hindered when the load is low.
(2) In the following cases, if the measures are not effective, the 220kV system may be stably destroyed and the power may be cut off in a large area. ! The main transformer substation trips in Gang City; one trip in the two 220 kV connection lines from Yiyang to Changsha;! The southerly transmission power of the Gegang line is relatively large, and with the full-fledged Wuqiangxi power station, any 500kV line in the 500/220kV ring network trips and power is transferred.
3.3 Before Changsha, Yiyang 500kV substation and Gang-Yi-Chang-Yun 500kV line are put into operation, in order to enable the 500/220kV electromagnetic ring network to operate more reliably, the following measures must be taken: Strictly monitor and limit the power generation output in the western region so that after the load is balanced in the region, there will be no change to the post-change and post-transmission of 220kV Gangde, Kongtie, Gang (Tai) Line and Yiyang to Changsha. The power exceeds the stability limit.
The main transformer station in Gangchang City and the 220kV Gangde, Gangtie, Gang (Tai) Yingxian and Yiyang-Changsha two-way 220kV tie-line tripped, installed far-reaching western generating units or reduced power or local/distantly cut Changsha and other loads. Central area load.
3.4 Shimen Power Plant (Jiangyan Power Station), Panshan Transformer, Hucheng Transformer, Kiln Slope Change, Mingshan Change, Wushenggong Change Gangchang City Change 220kV Same Bus, Busbar Switching Separately, Jingkong City Change Main Transformer Operation on 500kV System .
This open electromagnetic ring network operation program is so feasible because:! Changes in Panshan, Hucheng, Yaopo, Mingshan, and Wushenggong Shimen Power Plant in 2000, the maximum and minimum loads were 283MW and 158MW, respectively, which means that 300MW of Jiangyan Power Station must be sent through Gangchang Substation. It is feasible to send out a three-phase 220kV line with the help of Gangde, Gangtie, and Gang (Tai).
In Changde, Yiyang, Zhangjiajie, Jishou and Huaihua regions in 2000, the maximum and minimum loads were 800MW and 350MW, respectively, after deducting Panshan, Kuangpo, Mingshan, and Wushenggong, and that was Fengtan, Jiangyan, Lingjin. When the beach is full, it must send 170*620MW on two 220kV lines from Yiyang to Changsha and 270MW on low valleys. If you consider the maintenance or shutdown of one unit of the Shimen Power Plant during the Daxifa Hydropower Development period, the The problem was solved by connecting to the 220kV busbar of the 500kV system in the main town of Jinggang. However, during the trough load, the total output power of the two 220kV lines from Yiyang to Changsha reaches a stable control power of 350MW, and any one trip must be far away from the Fengtan or Lingjintan units.
3.5 After the Yiyang, Changsha 500kV transformers and the Gangyi, Yichang and Changyun 500kV lines are put into operation, the 220kV Tian Ying and Tian (Yu) yarns should be opened after the addition of Konggang City's variable open loop points. As a result, the history of the operation of the western electromagnetic loop network has ended.
4 Conclusion In the operation of the power grid, electromagnetic loop network operation should be avoided as far as possible. As a last resort, we must do our utmost to meet the operating conditions of the electromagnetic ring network. In the current situation, the western electromagnetic grid of Hunan Power Grid can be operated in open loop on the 220kV busbar in Gangchang. After the Yiyang and Changsha 500kV transformers and the Gangyi, Yichang and Changyun 500kV lines are put into operation, in addition to maintaining the open market to 220kV bus open loop, the 220kV Tian Ying and Tian (Yu) yarns should also be opened.
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