2017 2nd International Conference on New Energy and Renewable Resources (ICNERR 2017) ISBN: 978-1-60595-470-7

Analysis of Safety and Stability on Sending

and Receiving Ends of ±500kV DC

Mosi Liu, Zhiyuan Sun and Mingpo Li

ABSTRACT

The operation of HVDC transmission project shortened the transmitting distance between two power networks. While the change of power networks frame brought new diversification in the safe and stable operation of the sending and receiving ends of HVDC transmission. In this paper, ±500kV Jinzhong DC transmission project was taken as an example. By using PSD-BPA electromechanical transient software to simulate and analyze the sending and receiving ends faults after the operation of HVDC transmission, the influence of HVDC transmission project on the sending and receiving ends dynamic characteristics and the existing operational risk was studied. And then, corresponding control measures were put forward.

INTRODUCTION

The HVDC project of the hydropower station on the jinsha river starting point in Lijiang area of Yunnan Province, ending in district of , which voltage level is below 500kV, with capacity of 3200MW, a total of 1 HVDC lines, was put into operation in 2016. After that, AC/DC parallel operation grid has been formed in Guangxi power grid, which is not only a load center, but also a power transmission hub channel from west to east. The characteristics and mechanism of AC/DC interaction reflected by this particularity are different from those of Yunnan power grid and Guangdong power grid. Moreover, with the operation of Luoping back-to-back DC and the project of Guanyinyan HVDC, the Yunnan power grid and ______Mosi Liu, Zhiyuan Sun, Mingpo Li, Guangxi Electric Power Research Institute, Guangxi, China

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Guangxi power grid are interconnected asynchronously, and the characteristics of the grid are greatly changed. In this paper, the simulation analysis on the faults of sending and receiving ends of the HVDC has been carried out, and corresponding control measures are put forward.

±500KV JINZHONG HVDC PROJECT

Sending Converter Station of ±500kV Jinzhong DC

Jinguan station is the sending converter station of Jinzhong HVDC project connected to the system through 5 lines. The structure of the near area power grid of Jinguan converter station is shown in Figure 1. Jinguan station connected to Liyuan power plant with 1 line, connected to Ahai power plant with 2 lines, and connected to Taian station with 2 lines at present, eventually will connected to the system through 8 lines. The lines of sending transmission system connected to the system are 500kV Lia, 500kV Lijin, 500kV Ajin, 500kV Taijin, 500kV Taihuang.

Receiving Converter Station of ±500kV Jinzhong DC

Guizhong station in Guangxi Zhuang Autonomous Region is the ending point of the ±500kV Jinzhong HVDC, which connected to the system through 3 lines. The structure of the near area power grid of Guizhong converter station is shown in Figure 1. Guizhong station connected to Liudong station with 1 line, connected to Shatang station with 1 lines, and connected to station with 1 line, Combined with the commissioning of converter station, 2 sets of 1000MW transformers in the Guizhong station contacted with Guangxi power grid.

STABILITY ANALYSIS AND STRATEGY RESEARCH OF FAULTS ABOUT SENDING ENDS

Simulation Analysis of Bipolar Blocking of ±500kV Jinzhong DC

Liyuan Ahai

Longtan Liudong Shatang Jinguan Yantan Taian

Pingguo Guizhong Huangping Laibin

Baise Yongan

Figure 1. Schematic diagram of ±500kV Jinzhong DC project.

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TABLE I. SIMULATION RESULTS OF DC BIPOLAR BLOCKING IN DIFFERENT OPERATION MODES OF SENDING TERMINAL. active output power operation modes Stability Liyuan(MW) Ahai(MW) Normal operation model 2400 2000 Stable Unipolar maintenance 2400 1600 Stable Lia maintenance 1200 2000 Stable Lijin I maintenance 1200 1600 Stable Ajin maintenance 1800 800 Stable TaijinI maintenance 1800 2000 TaijinII overload Taihuang maintenance 1200 2000 Stable

The simulation results various maintenance methods are shown in TABLE I. On the normal operation mode of summer with heavy load, the system does not exist transient stability problems and meets the static security requirements. Bipolar blocking results in overload of the other line of Taijin, when Liyuan and Ahai generators operates at rated active power, and in the case of one line of Taijin maintenance.

Simulation Analysis About Three-phase Permanent Fault on A Single Line Leads to Double Line Tripping of a Jin Line

TABLE II. SYSTEM CONDITIONS AND MEASURES UNDER DIFFERENT MAINTENANCE MODES. active output power Control measures Stab- mode Reductions of Reductions of Liyuan(MW) Ahai(MW) ility Liyuan(MW) Ahai(MW) Unstable 600 1600 2400 2000 Unstable 0 2000 Unstable 1800 1200 Normal operation Unstable 600 400 1800 1600 model Unstable 0 800 Unstable 0 400 1200 1600 Unstable 600 0 1200 1200 Stable / / JinzhongDC 2400 2000 Unstable 1800 1600 transmission power of 2200MW 1200 1200 Stable / / Unipolar Unstable 1200 1200 2400 1600 maintenance Unstable 1800 800 Unstable 1200 1200 Taijin I maintenance 1800 2000 Unstable 600 1600 Taihuang 1200 2000 Unstable 600 1200 maintenance

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The simulation results are shown in TABLE II. Simulation analysis shows that, the fault is mainly caused Liyuan and Ahai unit losing synchronism with power systems. When the delivery section is above 2400MW of Liyuan and Ahai unit, the fault is mainly caused Liyuan and Ahai unit losing synchronism with main grid. The simulation results show that the DC operation power has some influence on the stability after the fault, The amount of cutting machine will increase when Liyuan and Ahai generators operates at rated active power and Jinzhong DC power down. The simulation results show that the measure of cutting the Ahai unit is more sensitive than the measure of cutting the Liyuan unit. When taking measures, priority shall be given to the Ahai unit[1-4].

Simulation Analysis About Three-phase Permanent Fault on A Single Line Leads to Double Line Tripping of Taijin Line

The simulation results are shown in TABLE III. Liyuan, Ahai unit and Jinguan converter formed island operation. According to the tide of Jinguan converter before the failure occurs, there will be the problem of high frequency or low frequency in the island after the failure occurs. And the failure does not affect the stability of the main grid of Southern Power Grid. when the sending power is large from the Jinguan section, The island frequency increases more than 0.5Hz. There will be high frequency problems in the island, needed to take measures to cut off Liyuan and Ahai units after the failure occurs. When the switching power of the sending section is smaller, which is less than 500MW, the frequency of the isolated island can be kept stable by the function of DC FLC modulation and the speed control function of the unit after the fault[5]. The highest frequency inside the island is 55Hz after the fault when the active power of 500kV Taijin line reach 2150MW. It is suggested that the transmission power of the Taijin line will be no more than 1500MW considering the DC FLC function.

TABLE III. THE ISLANDING FREQUENCY STABILITY AFTER TAIJIN N-2 FAULT CONSIDERING THE DC FLC. Active output power Resection volume Limit frequency（Hz） Liyuan (MW) Ahai (MW) Taijin(MW) Liyuan (MW) Ahai(MW) 2400 2000 1150 0 0 51.60 2400 2000 2150 0 0 55.00 2400 2000 1150 600 400 50.65 1800 2000 560 0 0 50.65 1200 1200 -820 0 0 49.15

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TABLE IV. MULATION RESULTS OF STABILITY ANALYSIS AND STRATEGY RESEARCH OF RECEIVING END. fault type Stability Stability control measures Laozhongjia and Pingnan line Cut down the DC power of Jinzhong and cut the PinglaiN-2 overload Longtan unit ShaliuN-2 Liuzhongjia line overload Cut down the DC power of Jinzhong Pingnan and Wuchong line Cut down the DC power of Luxi and cut the BaiyongN-2 overload Longtan unit YongnanN- Pingnan and Wuchongline Cut down the DC power of Luxi and cut the 2 overload Longtan unit Laozhongjia and Pingnan line Cut down the DC power of Jinzhong and cut the PinglaiN-2 overload Longtan unit

STABILITY ANALYSIS AND STRATEGY RESEARCH OF RECEIVING END

The commissioning of the Jinzhong DC plant affected the power of Longtan Power Plant and Yantan Power Plant, and exacerbated the trend of the adjacent lines, the simulation results are shown in TABLES IV. The results show that there is no transient stability problem for the terminal power grid after the HVDC operation, but affected the overload of the 500kV line. N-2 principle means any two components in the power system are outage. 500kV Pinglai N-2 fault will cause the 500kV Laozhongjia and Pingnan line overload, To eliminate the overload of 500kV line, the effect of return Jinzhong DC power is remarkable. Therefore, it is suggested that the Guizhong converter station needs to add a new safety and stability control device to solve the overload problem caused by Pinglai N-2 fault and return down the Jinzhong DC transmission power. 500kV Shaliu N-2 can lead the overload of Liuzhongjia line. After lowering the Jinzhong DC power, the overload is eliminated. It is suggested to further reduce the Jinzhong DC transmission power, so that no measures can be taken after the failure.

CONCLUSIONS

In this paper, the simulation analysis of the structure and stability of sending and receiving ends of HVDC transmission is carried out. The main simulation results and measures are as follows: 1.The failure of the AC power network will cause the transient instability of the unit, which can be solved by the cutting unit. 2.The fault of the AC power network at the receiving end is likely to cause the overload problem, which can be solved by the pre control DC power and down DC power, respectively.

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REFERENCES

1. CSG Research Institute. China Southern Power Grid Security Strategy of Rolling in 2015, In Chinese. 2. ZJ Jun, Y S Su, H T Liu, YZhang and J S Li 2010 Study on the Bipolar Operation Mode of Yunnan-Guangdong ±800 kV DC System (Southern Power SystemTechnology vol 4) chapter 4 pp 29-31, In Chinese. 3. T X Zhu, CWu and C Wang 2009 Influence of AC System Fault on HVDC System and Improvement Suggestions (Automation of Electric Power Systems vol 33) chapter 4 pp 93-98, In Chinese. 4. X M Mao and X C Wu 2004 Analysis On Operational Problems In South China AC-DC Hybrid Power Grid (Power System Technology vol 28) chapter 2 pp 6-13, In Chinese. 5. H F Zhang and T X Zhu 2007 Influence of rectifier AC fault on HVDC transmission system(Relay vol 35) chapter 15 pp 24-28, In Chinese.

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