Analysis of Four Technical Problems of UHV Transmission

In December 1880, New York, USA, provided a true utility service for utility lighting , a transmission line constructed by Brush ElectricCompanys, powered by several streets in Manhattan, only 3.2 km away; in 1889, Portland, Oregon, GE created 14 kilometers of transmission distance, rated power 4 kilowatts, to create a world-wide power transmission "high pressure" miracle.

Today 125 years later, in China, Henan has been connected to Xinjiang via an 800 kV HVDC transmission line. Each year, it can receive 37 billion kilowatt-hours of electricity from Xinjiang. The total length of its line is 2,192 kilometers. It passes through Xinjiang, Gansu, Ningxia and Shaanxi provinces Shanxi, Henan six provinces (districts). Since 2009, the national grid has been completed and put into operation two exchanges and three UHV DC transmission electrician process.

How do power scientists move from a distance of 3.2 km to more than 2000 km? Or the next 5,000 km? The technical secret is to increase the transmission voltage. To this end, scientists are making unremitting efforts to increase the level of transmission voltage that can neither be seen nor touched: the history of power grid construction, the transmission voltage from 10 kV, 35 kV, 110 kV, 220 kV, 330 kV, 500 kV, 750 kV, up to 1000 kV.

However, every time the voltage is increased, the power transmission technology is hampered. AC transmission voltage is generally divided into high pressure, high pressure and UHV, the international high voltage usually refers to 35-220 kV voltage; EHV usually refers to 330 kV and above, 1000 kV and below voltage; UHV refers to 1000 kV And above the voltage. Each increase in the level of a transmission voltage, are facing technical breakthroughs and challenges.

One of the problems: to raise the voltage and suppress the voltage

Chen Weijiang is an expert in the field of UHV transmission research and is the deputy director of the State Grid Corporation of China for Exchange and Construction. He is also the main builder of UHV AC test base in Wuhan, China. He plays an important role in the research of major key technologies for UHV transmission. When a reporter asked in a meeting room of the State Grid Office building what is the biggest difficulty in the UHV technology breakthrough, he answered: "The primary solution is to solve the voltage control problem."

UHV, as its name implies, is a high-voltage transmission. Scientists do everything possible to increase the voltage transmission level. Why is the primary consideration? How to control voltage? Voltage control is an important concept in power transmission technology. It means that when the power supply voltage exceeds its rated value Voltage control, including three aspects: the first is to run the voltage control, the second is the internal over-voltage control (including temporary over-voltage, operating over-voltage and fast transient over-voltage), the third is lightning over-voltage control Overvoltage).

When the grid is operating normally, the line voltage of 50 Hz sine wave is the operating voltage, such as 1000 kV UHV line, the normal line voltage is 1000 kV, 500 kV UHV line, the operating voltage is 500 kV, the operating voltage Also known as steady-state voltage; and over-voltage is a transient voltage, only suddenly appear in a moment, rather than the sine wave as repeatedly. Over-voltage than the operating voltage is much higher, if analog audio equipment, playing the normal volume can be regarded as operating voltage, and when plugging the signal line is issued an instant pounding noise can be regarded as over-voltage. Daily lines in the power grid, transformers , shunt reactors switching, sub-closing, and even line failures, etc. will cause the line over-voltage, collectively referred to as the internal over-voltage. The lines, towers, ground lightning lines were caused by natural lightning over-voltage known as lightning over-voltage.

From the ultra-high voltage 500 kV to UHV 1000 kV, the voltage level has doubled, the control voltage allows the value is a simple multiple relationship? Chen Weijiang said "no." He introduced: In fact, UHV allows the operating voltage rise of the over voltage margin has become smaller. Based on the operating voltage is 1 times the overload voltage at 110 kV, 220 kV when there are three times the margin when the voltage is 500 kV is 2.0 times 750 kV is 1.8 times to 1000 kV When only 1.6 times the margin. Margin, refers to the degree of leaving a certain amount of room.

"Demand is to increase the voltage transmission level, because of the energy of UHV transmission, long distance; but from the technical requirements point of view, the higher the voltage level, the operating voltage allows the smaller multiple, which means that the voltage control more difficult "Said Chen Weijiang.

What measures to use to suppress the internal voltage overvoltage and lightning overvoltage it? From 2004 onwards, the China Electric Power Research Institute has dozens of researchers to do 1000 kV UHV AC transmission system over-voltage research, research topics include the standard voltage Selection, over-voltage and insulation coordination, lightning protection, on-line double circuit system circuit breaker transient, steady-state over-voltage and electromagnetic transient optimization of more than 10 studies. The scientific and technological achievements urgently needed by these projects, especially after the relevant parameters have been calculated and verified through experiments, have strongly supported the development and selection of UHV equipment.

To suppress the temporary over-voltage, for example, the most important equipment is the reactor, which is also one of the most important UHV equipment, because the line load in the event of failure or failure caused by a sudden increase in voltage, the amplitude is Second calculation, only through the high-capacity high-voltage reactor effectively limit the power frequency over-voltage amplitude. In Xi'an, Vice President and Chief Engineer of China XD Group Corporation, Mr. Chuan Chuan-Long's office, he briefed reporters on the process of developing and manufacturing chokes. Mr. Chuanlong won the 2012 National Science and Technology Progress Grand Prize and ranked third.

Reactor manufacturing is the strength of the West.宓 Chuan-Long did not hide the technical advantages of the West, the last century they have developed for the Three Gorges ± 500 kV DC transmission converter transformers and smoothing reactors, the end of China's large-scale electrical equipment such dependence on imports. In 2008, XD undertook the development of the UHV shunt reactor with a capacity of 1000MV 320Mvar and 240Mvar (a compensation unit of reactive power compensation device) for the first UHV AC pilot project in China.

Reactors, also known as inductors, function primarily to ensure the maximum power delivered by the line and to limit the effects of voltage abrupt changes in the network and current surges caused by overvoltages, since the reactor is rated at 1100 kV and is rated at a voltage of 1000 kV In comparison, the insulation level of UHV reactors is about 5% higher than high-voltage transformers, "he said.

The development of the first UHV reactor in China by the West Power Development Project was very smooth: first, the main design plan and the relevant parameters were worked out, and then the plan of the electric plan and the structural plan was formulated. How to validate the parameters, such as heavy insulation parameters, during the development of the program? They made a small scale on a pro-rata basis, simulating the product shock wave through a crest-measuring experiment and measuring how the heavy-insulated electric field of each coil is distributed. After finishing the data and calculated values ​​are compared to see how much the similarity? Where the voltage difference more. Then do the experiment, then verify. When repeated comparison did not

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