East China UHV project short-circuit current exceeded

“After the East China UHV project was networked, the 500-kV line could be operated in a reasonably partitioned manner. This put a 500 kV 'hand-in-hand' line out of service. The resistance of this level was reduced, and all 500 kV plants were reduced. The short circuit current of the station can be controlled within the allowable value of the equipment.” Recently, Zhang Zhengling, deputy director of the Planning and Development Department of the State Grid Corporation of China, spokesperson Zhang Zhengling, “In the development process of the power grid, the systemic problem of large-scale outbreaks must rely on technology. upgrade."

The origin of short-circuit current exceeding the standard problem

The short-circuit current refers to the current in the short-circuit condition of the circuit. At this time, the resistance is zero and the current is increased. It is necessary to use the switch to cut off the faulty branch. The cut-off capability of the switch is certain. At present, the largest switch can cut 63 kA. If the short-circuit current is greater than this value, it will have an important destructive effect on the stability of the power grid. Zhang Zhengling said: "The development of power grids and the growth of short-circuit currents are a contradiction. To protect the load, one loop is not built enough for two loops, and two loops are not built enough for three loops. The more loops built the smaller the impedance and the greater the short-circuit current. During the development of a new voltage level, the short-circuit current will slowly increase, and individual points will not work. The switch will be turned off and finally it will increase to a large area."

It is understood that the problem of short-circuit current exceeding the standard in the East China region is outstanding. Nearly 30% of the plant stations have 500 kV short-circuit current exceeding the standard and the maximum short-circuit current exceeds 80 kA. To this end, the State Grid has taken a series of measures to control the short-circuit current, such as the suspension of the 500 kV line that has been built, the lap joint outside the line station, and equipment replacement. However, this is only an expedient measure and cannot fundamentally solve the problem. It also undermines the original strengthening of the power grid structure and brings potential safety and stability problems for the power grid. Moreover, with the increase of load density in East China, the problem of short-circuit current will further increase.

Zhang Zhengling explained further: “If we want to reduce the short-circuit current of a substation, we must evacuate. The two short lines become long lines and the resistance is large, but this also makes the original grid structure that needs to be strengthened destroyed. Therefore, to deal with this large The systemic problem of the outbreak of the area, 'headaches and foot aches and pains' is not enough, and we must rely on technological upgrading to solve it."

UHV networking can reduce short circuit current

Relevant calculations show that if the East China region adopts the 500 kV main grid scheme in 2020, there will be more than 44% of the substation short-circuit current exceeding the standard. If the East China UHV networking scheme is adopted, the 500 kV power grid is properly zoned and the short-circuit current of all 500 kV plant stations can be controlled within the allowable value of the equipment.

According to reports, the East China High-Voltage Network is mainly composed of three projects. The first is the 1000-kilovolt Huainan-Northern Zhejiang-Shanghai UHV AC project (the “Southern Semi-ring”), which is expected to be put into operation in October this year; the second is 1000-kV North Zhejiang. -The Fuzhou UHV AC project was just opened in April this year. The third is the 1,000 kV Huainan-Nanjing-Shanghai UHV AC project ("Northern Half Ring"), which is being evaluated by China International Engineering Consulting Corporation.

Zhang Zhengling emphasized: “Eastern China’s UHV network cannot be completed overnight, and it will take three years, five years, or even longer. Only after the East China UHV networked projects are put into operation to form a ring network can 500 kV lines be distributed. Reduce the resistance to each other.” That is to say, even when the “Southern Half Ring” of the East China UHV Network was put into operation this year, the original 500 kV line could not be solved, and the short-circuit current problem still existed. The short-circuit current formed by the new high-voltage line put into operation will probably increase the short-circuit current at this time.

The development of power grid has its objective law

It is understood that China's power grid has encountered similar problems in the process of upgrading from a 220 kV main grid to a 500 kV main grid. In the 1980s, with the increase in the power load, the original 220 kV line needed to be overlaid and reconstructed outside the line station, and the short-circuit current slowly increased. Finally, there was a systematic large-scale outbreak. The upgrade of the power grid became inevitable at this time, which promoted the development of 500 kV lines.

Some people think that if the short-circuit current exceeds the standard problem and the existing main grid and grid structure of the East China Power Grid are optimized, this can be done. In this regard, Han Feng, vice president of the Beijing Economic and Technical Research Institute of the State Grid, stated: “We have launched an UHV project that cannot be used to reduce short-circuit currents. The East China High-Voltage Network has formed a ring network structure. The need to improve the safety of the bearing, but also to strengthen the grid network, transfer DC power dispersion, etc."

In addition, Zhang Zhengling also introduced: “If we follow the existing 500 kV grid structure in East China, to reduce the short-circuit current, we must loosen the tight grid structure, which will reduce the safety of the load. But the load of East China Grid It's too big. I used to be able to afford it. Now my burden has increased tenfold, and I'm not able to back one up."