The electromagnetic ring network (eletromagnetcycolramanetwork) of the power system refers to a ring network composed of transformers or electromagnetic coupling of transmission lines of different voltage levels.
In the early days of the emergence of a new, higher voltage class for power systems, the network could not be structurally strong, but rather refined, strengthened, and sensible. In this perfect and intensified process, in order to obtain large network transmission power, to rationally utilize cheap resources, and to meet users' requirements for maximum power consumption, most of the power systems have one or more electromagnetic ring networks running.
The operation of the electromagnetic loop of the power system usually means that two electrical components of adjacent voltage levels are connected to operate in a ring network. The electrical equipment of two or more voltage levels forms the operation of the electromagnetic ring network. Only when the dispatcher handles the accident or the load is transferred for a short time, the verification is no problem, and the transitional temporary extreme special power can be used. How the system works.
1 The necessity of the open loop operation of the electromagnetic ring network In the operation of the power system, the operation of the electromagnetic ring network is often taboo. According to statistics, in China from 1970 to 1990, there were 187 times of power angle and voltage stability damage (stability destroy) related to power grid structure, of which 55 times related to high and low voltage network structure, accounting for 20.2%. Foreign and electromagnetic ring network Related large blackouts are also common. For example, on July 2, 1996, the US power system blackouts occurred. When PACI (three 500 kV AC) was disconnected, a large number of tidal currents rushed to the eastern 345/230kV network, causing voltage stability and destruction. WSCC was demarcated into five islands, and more than 2 million users had power outages, with a loss of 10,576 MW and a maximum power outage of 6.4 h. On August 10 of the same year, accidents of the same nature in the power system occurred again, power outages, loss of load, The blackout time far exceeded the July 2 accident. Therefore, people tend to “talk about the color changeâ€, and whenever possible, the electromagnetic ring network adopts an open loop method.
There are many merits for open loop operation: stability is easy to control. Interference occurs in the open-loop network, often the faulty components are removed, and supplemented by effective accident handling means, the situation can be calmed down. If a fault occurs in the ring network, in many cases, after the faulty component is removed, power transfer will occur, causing the non-faulty component to pass the power limit and cause stable damage.
The active (or power angle) and reactive (or voltage) of the power supply of the whole delivery end can achieve the purpose of adjusting the power flow. When the ring is closed, the current is naturally distributed in the ring network, and the control is difficult. It often happens that the ring network components are fully loaded or even overloaded by power, and some are idle.
Line is an important means of limiting short circuit capacity. Combined loop operation, because the integrated impedance is often small, the short circuit capacity is relatively large. Busbars with a large short-circuit capacity are busbars with more outlets and concentrated power outlets. The failure of these busbars is often the culprit triggering a major power system accident.
4' Simplified relay protection and safety automatics. The configuration of relay protection and stability measures of the ring network is much more complicated than that of the non-ring network, and it is difficult to cooperate. The complication and mismatch of protection and safety automatic devices is generally the direct or expanding cause of accidents.
5) In some ring networks, because there is no circulation problem in the open loop operation, the transmission loss may be smaller than that in the closed loop operation, thereby improving the transmission efficiency.
2 The possibility of electromagnetic loop operation in the actual operation of the power system does not exclude all electromagnetic ring network operation modes. On the contrary, in some cases, it may take full advantage of resources, improve transmission reliability, reduce transmission loss, etc. for a period of time. In terms of the electromagnetic ring network operation is more beneficial than the open loop operation.
Use electromagnetic ring network operation, should be cautious, and adhere to the following principles:! In the case of an accident, any component in the ring network is mainly a high-voltage component 'disconnected, even if power transfer occurs, it will not cause stable damage. ! When the electromagnetic ring network is running, the relay protection configuration and setting are well coordinated, and the safety and stability measures are simple and reliable. ! After the electromagnetic ring network is operated, the voltage level at the receiving end should be basically unaffected. ! The operation of the electromagnetic ring network, the increase of the short-circuit capacity of any busbar, should not cause the switch to be difficult to interrupt. ! When the electromagnetic ring network is operated, the transmission loss should not increase significantly.
If the above five principles are met, the electromagnetic loop network operation should be acceptable. However, it must be pointed out that a large number of accidents are not completely expected by people. Therefore, when using the electromagnetic ring network operation mode, the power system should prevent accidental interlocking, resulting in large power transfer, which may cause stable damage. Or cause some reliable measures to reflect the protection error of the load current.
3 Hunan Power System 500/220kV Electromagnetic Ring Network Operation Mode Recommendations 3.1 Hunan Power System has now formed a 500kV diamond-shaped single-ring network; 500kV and 220kV electromagnetic ring network operation, as shown. The power supply directly connected to the 500kV network has the Gegang Line and Wuqiangxi Power Plant connected to the Central China Power System. There is power bidirectional exchange between the 500/220kV networks in the postal city. Under normal circumstances, there is only one-way active power exchange between the Loudi and Yuntian 500/220kV networks, that is, the 500kV network injects active power into the 220kV network.
3.2 In this complex electromagnetic ring network, there are two main problems: Gangshi and Xidian 220kV east to send "bottleneck"
The "bottleneck" sent by the 220kV in the substation of Gang City. The power transmission from the Gangshi Substation to the 220kV network is limited by the transmission capacity of the three 220kV tie lines (gang iron, Gangde, Gang Ying). The power transmission capacity of the three-line line and the whole system load level, the output of Jiangyan and Shimen, Wuqiangxi Power Plant, the power transmission capacity of Gezhouba Power Plant, the load of four 220kV substations in Mingshan, Panshan, Hucheng and Wusheng Palace, etc. related. Connected to the Gangshi 220kV bus, the installed capacity of power generation is 900MW. In some cases, it is necessary to receive some power from the Wuqiangxi Power Plant and Gezhouba Power Plant through the main transformer. When the maximum and minimum load of the system in 2000, the maximum load and minimum load of the four 220kV substations such as Mingshan, Panshan, Hucheng and Wushenggong are only 250MW and 120MW respectively. Therefore, the three 220kV lines are often operated under heavy load. And became the "bottleneck" sent by the 220kV of the substation in Gangshi. ! Yiyang to Changsha's West Power East sent a "bottleneck." The 220kV system of Changde and Yiyang has a power generation capacity of nearly 1 570 MW, including hydropower capacity of nearly 970 MW. The area (including Zhangjiajie, Hucheng and plant power) has a maximum and minimum load of 770 MW and 340 MW respectively. The maximum load of 260MW and the minimum load of 120MW in Jishou and Huaihua are only 1030MW and the minimum load is 460MW. That is, 540*1110MW must be sent through the main transformer of Gangshi Substation and the 220kV tie line of Yiyang to Changsha. The variable capacity is only 500,000 kV*A, and the total capacity of the two 220kV tie lines from Yiyang to Changsha cannot exceed 350MW according to the stability requirement. Therefore, the west power transmission is severely blocked during the low valley load.
(2) Under the following circumstances, if the measures are not effective, the 220kV system may be stably damaged and the power will be cut off in a large area. ! The main transformer of the Gangshi Substation failed to trip; one of the two 220kV tie lines from Yiyang to Changsha tripped; The Gegang line has a large power transmission south, and the Wuqiangxi power station is full, and any 500kV line in the 500/220kV ring network trips and power is transferred.
3.3 Before the Changsha, Yiyang 500kV substation and Gang-Yi-Chang-Cloud 500kV line are completed and put into production, in order to make the 500/220kV electromagnetic ring network operate reliably, the following measures must be taken: Strictly monitor and limit the power generation in the western region, so that after the load in the balance area, it will not cause the main city to change and the 220kV Gangde, Gangtie, Gang (Tai) line and the two 220kV tie lines of Yiyang to Changsha The power exceeds the stability limit.
Ganggang changed main transformer and 220kV Gangde, Gangtie, Gang (Tai) Yingxian and Yiyang to Changsha two 220kV tie lines tripped, installed far-cut western generator set or reduced force or local / remote cut Changsha load The load in the central area.
3.4 Shimen Power Plant (Jiangsu Power Station), Panshan Substation, Hucheng Substation, Kiln Slope Change, Mingshan Substation, Wusheng Palace changed the post city to 220kV the same busbar, the busbar switch is separated, and the post-change main transformer changes to 500kV system operation .
This operation scheme for opening the electromagnetic ring network is feasible because:! In the year of 2000, the maximum and minimum loads were 283 MW and 158 MW, respectively, and the power consumption of the Shimeng Power Plant was increased to 283 MW and 158 MW, respectively. It is feasible to send out the 220kV lines of Gangde, Gangtie and Gang (Tai).
In Changde, Yiyang, Zhangjiajie, Jishou and Huaihua districts in 2000, the maximum and minimum loads were deducted from Panshan, Kiln, Mingshan and Wusheng, respectively, and were 800MW and 350MW. That is, Fengtan, Jiangyan and Lingjin. When the beach is full, it must send 170*620MW through the two 220kV lines from Yiyang to Changsha, and 270MW during the low valley load. If one unit of Shimen Power Plant is overhauled or shut down during the hydropower generation period, the Jiangyan Power Station will also be used. The problem was solved after connecting the 220kV busbar of the 500kV system on the main post of the postage city. However, during the low valley load period, the total output power of the two 220kV lines from Yiyang to Changsha reached a stable control power of 350MW, and any tripping trip must be far away from the Fengtan or Lingjintan units.
3.5 After the Yiyang and Changsha 500kV transformers and the Gangyi, Yichang and Changyun 500kV lines are put into operation, the 220kV Tianying and Tian (Jade) wool yarns should be opened in addition to the postal opening of the postal city. Thus, the history of the operation of the western electromagnetic ring network has come to an end.
4 Conclusion In the operation of the power grid, when there are conditions, the electromagnetic ring network should be avoided as much as possible. As a last resort, every effort should be made to meet the conditions for the operation of the electromagnetic ring network. Under the current circumstances, the western electromagnetic ring network of Hunan Power Grid can be opened in the 220kV busbar of Ganggang City. After the Yiyang and Changsha 500kV transformers and the Gangyi, Yichang and Changyun 500kV lines are put into operation, in addition to maintaining the opening of the 220kV busbar in the postal market, the 220kV Tianying and Tian (Jade) yarns should be opened.
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