Most popular in 2018, multi DC feed into Jiangsu p

2022-09-23
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Analysis on the failure of cascading commutation of multi DC feed into Jiangsu planning in 2018

in recent years, with the friction construction of a large number of working pistons and force measuring pistons in China's HVDC transmission projects, load centers with large demand for electric energy are likely to have multiple DC drop points to form "multi DC feed into the receiving end". According to "Thirteen ˙ According to the "Five" plan, Jiangsu power will form a multi DC feed in power receiving terminal in 2018. The multi DC feed in system can better solve the problems of long-distance transmission of electric energy and power shortage, but the mixing of multi circuit DC and AC systems greatly increases the complexity of the electrical structure. The mutual coupling between DC and DC, AC and DC is likely to cause cascading faults, expand the scope of faults, and aggravate the consequences of faults

in the AC/DC hybrid power system with multiple DC drop points, the failure of the AC system or DC system at the receiving end may lead to the failure of multi circuit DC interlocking commutation, resulting in the reduction of DC voltage, the increase of current and the fluctuation of DC transmission power, causing a certain impact on the electricity. Interlocking commutation failure may also lead to more serious DC locking failure, DC power interruption and large-scale power flow transfer, endangering the voltage stability, power angle stability and frequency stability of the receiving end. Therefore, it is necessary to analyze the interlocking commutation failure of the actual multi infeed system and take preventive and control measures for the system

based on the Fengda operation mode of Jiangsu planned power in 2018, using the psd-bpa electromechanical transient program developed by China Electric Power Research Institute, aiming at the three-phase permanent short-circuit fault of the main 500kV AC line near the DC inverter station of the receiving AC system, considering the interaction between AC, DC and multi DC, this paper studies the causes of cascading commutation failure of Jiangsu multi DC feed in power, The problems needing attention in the use of miif and Vif are analyzed, which provides relevant references for the actual operation of Jiangsu electric power

2. Simulation of cascading commutation failure of Jiangsu multi DC fed DC transmission system

commutation failure of multi DC fed DC transmission system is mostly caused by the voltage reduction of the converter bus of DC inverter station caused by AC system failure. At present, there are two methods to judge commutation failure: the minimum voltage drop method and the minimum arc extinction angle method. The minimum voltage drop method is used in this paper. According to the actual project operation experience, when the voltage of the inverter side commutation bus drops to 0.8p u. Below and the change rate exceeds 0.3p u./s or voltage below 0.6p u. It is judged that the commutation failure of the DC system occurs, and the voltage recovers to 0.75p after the failure u. When, judge to restore normal commutation

in order to analyze the possibility of simultaneous or continuous interlocking commutation failure of DC system caused by AC system fault at the receiving end, simulate the most serious three-phase permanent short-circuit fault at the bus outlet of important 500kV AC lines near each DC inverter station at the receiving end. The fault is set at 10 cycles, and the fault line is cut off at 15 cycles. According to the structure diagram of Jiangsu planned power in 2018, taking the failure of Taizhou special side of Taizhou special Nanjing special side of the AC line near Taizhou converter station as an example, the simulation calculation results are shown in Figure 1, where Taizhou converter 1 and Taizhou converter 2 represent the 500kV and 1000kV converter buses of Taizhou converter station respectively

Figure 1 converter bus voltage after AC line fault at the receiving end

from the simulation results, it can be seen that when the AC line Taizhou special Nanjing special near Taizhou converter station has a three-phase permanent short-circuit fault on the Taizhou special side, the converter bus voltage of Zhengping Converter Station is still maintained at 0.8p u. Above, the voltage of the converter bus of Tongli converter station and Nanjing converter station is as low as 0.756p respectively u. And 0.706p u. The voltage of 500kV and 1000kV converter buses in Taizhou converter station after fault is as low as 0.557p, respectively u. And 0. Zhengping Converter Station will not have interlocking commutation loss, which is not greater than 0.5% of the load indication; Defeat. The interlocking commutation failure will occur in Tongli converter station and Nanjing converter station, but the voltage level can be quickly recovered after the AC fault is removed, so as to restore the normal commutation. The duration of commutation failure is less than 100ms. Taizhou converter station will have interlocking continuous commutation failure, and the fault duration is 100ms, which can be quickly recovered after the fault is cleared

the simulation calculation results of the converter bus voltage after the failure of important AC lines near the DC inverter station at the receiving end of Jiangsu electric power are shown in the table, in which the failure occurs at the bus outlet at the head end of the circuit

Table 1 converter bus voltage after AC line failure near Nanjing converter station

Table 2 converter bus voltage after AC line failure near Tongli converter station

according to the simulation results in the table, the following conclusions can be drawn:

(1) Nanjing converter Sanchawan, Nanjing converter Anlan, Anlan Nanjing After the three-phase short circuit from Sancha bay to akito, it will lead to the short-term commutation failure of Nanjing converter station and the adjacent Taizhou converter station

(2) the three-phase short-circuit fault of AC lines near Tongli converter station Tongli exchange Mudu, Tongli exchange Wujiang, Tongli exchange Chefang, Mudu Meili, Mudu Chefang, Wujiang Chefang will lead to the short-term commutation failure of Tongli converter station and adjacent Zhengping Converter Station

(3) AC lines near Zhengping Converter Station Zhengping exchange Yixing, Zhengping exchange Wunan, Wunan Huiquan Yixing Minzhu three-phase short-circuit fault will lead to short-term commutation failure of Zhengping Converter Station and adjacent Tongli converter station "to create a stable, practical and visually attractive top pillar module for production.

(4) The three-phase short-circuit fault of Taizhou 1-fengcheng, Taizhou 1-shuangcao, Taizhou 1-qijie, Fengcheng Zhongyang and Shuangcao Dafeng AC lines near Taizhou converter station will lead to short-term commutation failure of Taizhou converter station. The three-phase short-circuit fault of Qijie Shuyang will lead to short-term commutation failure of Taizhou and Nanjing converter stations, Nanjing Taizhou, Suzhou Taizhou The three-phase short-circuit fault of Taizhou converter 2 - Taizhou special will lead to the simultaneous commutation failure of Tongli, Nanjing and Taizhou converter stations

Table 3 converter bus voltage after AC line failure near Zhengping Converter Station

Table 4 converter bus voltage after AC line failure near Taizhou converter station

in addition, the above DC system interlocking commutation failure caused by AC system failure can quickly return to normal commutation after the AC fault is cleared, and the duration of commutation failure does not exceed the fault duration of 100ms, which is the same as that after the three-phase short circuit between Taizhou and Nanjing. According to the configuration of DC protection in the current actual operation, when the commutation failure caused by external AC fault is detected, the protection delay of 300ms will block the DC to prevent the continuous commutation failure from damaging the inverter. Therefore, for the 2018 Jiangsu planning power, the AC line failure at the receiving end will only cause the short-term commutation failure of the DC and industrial current system, and will not lead to more serious DC blocking

3. Cause analysis of Jiangsu electric interlocking commutation failure

in the AC/DC hybrid system with DC drop point, DC commutation failure is one of the more common faults. For the single feed DC system with only one DC drop point, when the AC fault of the receiving system leads to the reduction of the voltage of the converter bus, the converter valve cannot recover the positive blocking ability in time when exiting the commutation, resulting in the failure of DC commutation. The main factors inducing commutation failure include the strength of AC system at the receiving end, fault location, fault severity, reactive power support strength at the commutation bus, etc; For the multi infeed DC system with multiple DC drop points, the mechanism of cascading commutation failure caused by AC fault is more complex. Compared with the single infeed system, the distance between multiple DC drop points and the coupling relationship between them have different degrees of influence on whether cascading commutation failure will occur

for multi infeed DC system, miif index is mainly used to analyze the operation characteristics and mutual influence relationship of AC and DC system at present. The main factor affecting the failure of multi DC interlocking commutation lies in the coupling relationship between multiple DC, so miif can be used to analyze the cause of interlocking commutation. Miif refers to the voltage drop of converter bus J and its ratio when the symmetrical three-phase reactor is put into converter bus I to reduce the bus voltage by 1%. The calculation of this index is relatively complex. The voltage drop of the converter bus is equivalent to the change of the node injection current, and the analytical calculation of the index can be realized by using the node impedance matrix. The miif is extended to any AC node, and the Vif is proposed. The calculation formula is as follows:

use the above formula to calculate the fmiifji of each DC fed into Jiangsu power to analyze the cascading commutation failure of Jiangsu power. The calculation results are shown in Table 5

table 5: Jiangsu electric power's DC fmiifji

the results show that there are a total of 20 fmiifs between the four DC converter buses fed into Jiangsu electric power, only 8 of which exceed 0.1, and 6 of which exceed 0.15. It can be seen that the voltage fluctuation of a certain DC circuit of Jiangsu electric power at the converter bus has little impact on the voltage of the other DC converter buses, and the correlation between the four DC circuits is generally weak

according to the actual fault simulation results of Jiangsu electric power, for the DC converter bus with fmiifji 0.15, when a three-phase short circuit occurs at the converter bus and the voltage drops to 0 for a short time, the voltage of the corresponding other converter bus will drop significantly, resulting in interlocking commutation failure. The fmiifji of Nanjing converter to Taizhou converter 1 is 0.149, close to 0.15. Therefore, when a three-phase short circuit occurs at the converter bus of Nanjing converter station, the voltage drop to 0 will also cause a large drop in the voltage of Taizhou converter 1 converter bus, resulting in interlocking commutation failure. The fmiifji of Taizhou converter 2 converter bus to Tongli converter bus is only 0.077, but the transmission power of the two DC circuits is quite different, so the fmiifji can not well distinguish the connection between the two DC circuits. In fact, when the voltage of Taizhou converter 2 converter bus drops to 0, it will also lead to short-term commutation failure of Tongli converter station

based on the above analysis, the main reason for the interlock commutation failure caused by the three-phase short circuit of Jiangsu planning power at the converter bus of DC inverter station in 2018 is that the fmiifji between some converter buses is large, which cannot be treated as a single feed DC. There is a large interaction between DC. When a three-phase short circuit fault occurs at a converter bus, the voltage will instantly drop to 0, making the commutation failure of this DC, And because the voltage drop is very large, it will also make the corresponding voltage of another commutation bus have a large drop, which will lead to interlocking commutation failure

4. Conclusion

based on the Fengda operation mode of multi DC feeding into Jiangsu planned power in 2018, the simulation analysis of the cascading commutation failure of Jiangsu power is carried out for the 500kV AC line fault near the DC inverter station. The research results show that:

(1) in the four loop direct current fed into Jiangsu power, the 500kV converter bus and 1000kV converter bus of Tongli converter station and Zhengping Converter Station, Taizhou converter station The 1000kV converter bus of Taizhou converter station and Nanjing converter station are closely related to each other, and the voltage interaction of the converter bus is strong. When a three-phase short-circuit fault occurs at the converter bus of one DC inverter station, the interlocking commutation failure of this DC and the corresponding other DC will occur

(2) Taizhou Nanjing and Taizhou Suzhou are very important AC channels of Jiangsu planned power in 2018. When three-phase short-circuit fault occurs, it will lead to the failure of three circuit DC simultaneous interlocking commutation, which will have a great impact on the power. Therefore, sufficient attention should be paid to the actual operation and scheduling

(3) due to the strong reactive power support ability of Jiangsu electric power, the DC can resume normal commutation after the AC fault is cleared, and the commutation failure lasts

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