In our lives, we are always inseparable from electricity. Ice is one of the most serious threats to the current power grid. With the start of the “freezing” model this winter, temperatures in the southern regions of Guangdong, Guangxi, and Guizhou have continued to decline, and some alpine regions are snow-capped. To protect the security of electricity supply, China Southern Power Grid launched the first round of this year's melting ice.
Under what conditions is it necessary to carry out ice melting in the grid? What measures are generally taken to melt ice in power grids? What "black technology" do we have?
Hazard of ice covered with snow
---- The "disease" of safe operation of the power grid
According to the "Analysis Report on the Influence Trend of Low Temperature Frozen Weather in the Southern Region of 2018 and the Spring of 2019" compiled by China Southern Power Grid Corporation, it shows: In this winter and the next spring, the low-temperature freezing weather in Guangdong, Guangxi, Yunnan, and Guizhou is generally a slightly lighter year. However, there are still some possibility of strong ice icing in some areas such as Guangxi, Yunnan and Guizhou.
With the rapid development of electric power, ice accidents on transmission lines have occurred at some times. In 1932, the transmission line was covered with ice in the United States. In 1994, the transmission lines and power-related equipment in the eastern and southern parts of the United States suffered severe ice-covered accidents. Since China recorded the first power grid ice fault in 1954, ice and snow have been seriously jeopardizing the safe operation of the grid. The most serious power grid ice icing accident occurred in 2008, and some parts of the south suffered the worst cold snow and ice disaster in 50 years. Rare ice disasters have led to accidents involving ice-collapsed towers and broken transmission lines in 12 provinces and cities such as Hunan, Guizhou, Jiangxi, Zhejiang, and Fujian. The power grid has a large area of power outages and power cuts.
According to statistics, at that time, the amount of power supply dropped to 14% of the power supply before the disaster. More than 100 million people in the country were affected, and the direct losses exceeded 100 billion yuan.
DC melting ice
----- Solve the large-scale frozen disaster of the power grid
Statistics show that as of December 9 this year, China Southern Power Grid Corporation has 270 ice-covered lines on 10 kV and above, and 32 ice-covered ratios over 0.3. Guangxi Power Grid Engineer Feng Bo introduced that the ice coating ratio is the value of the actual ice thickness measured by the designed wire to withstand the ice thickness. If it exceeds 0.5, it is necessary to implement ice melting measures.
However, experts from the China Electric Power Research Institute told the Science and Technology Daily reporter that due to the variety, randomness and unpredictability of natural ice coating, in addition, the specific conditions of each region are different, and the micro-topography and micro-meteorology have serious impacts. Therefore, the ratio of ice-covered ratios determined by each region to implement ice-melting measures is different.
The way the power grid is protected against ice and de-icing, people used to climb onto the poles and manually remove them with a hammer and a hammer. But now, anti-ice technology has been upgraded, including fixed DC ice melting, AC ice melting transformers, ice melting knife brakes, automatic mechanical device melting ice, air bomb vibration deicing, pulley melting ice. Jiang Qingliang, a professor at Chongqing University, said that ice coating is an extremely complicated international problem. After the large-scale ice disaster in the south in 2008, China has carried out extensive research, and DC ice melting is currently the only feasible method to solve the large-scale freezing disaster of the power grid.
DC melting ice is mainly a method of applying a DC voltage to a transmission line and short-circuiting at the end of the transmission line, cause the wires to heat up to melt ice on the transmission line. The fixed (SCR) DC ice-melting device adopts a 10 kV power supply that is introduced into the substation. After passing through the three-winding rectifier transformer, it is fed with a 12-pulse thyristor, and after rectification, it outputs a DC of 3000 volts/1400 amps. In this regard, the power expert explained that the current is similar to the water flow, the thyristor is similar to the controllable gate, through the three-winding rectifier transformer, the 10 kV high-voltage electricity is converted into a relatively low-voltage current, and then through the 12-pulse wave The thyristor rectifier eliminates harmonic interference and the like. Melting ice is not a quick heating of the transmission line, but a little bit of warming, generally speaking, it is enough to warm up to about 1 degree Celsius. Therefore, it is necessary to convert the high-voltage power output of the substation into a low-voltage direct current through a rectifier before it can be used.
At present, China has pre-installed a fixed DC ice melting device on many “backbone power grids”, the mobile DC ice melting device is composed of a rectifying component, a transformer component, an induced voltage suppressing component, an output combination knife gate, and the like, it can be installed directly on the trailer and can be scheduled for use at any time. "But the implementation of DC ice melting requires power outages and manual interventions. The operation is complicated and the ice melting time is long. This is the key technology that needs to be solved.” Jiang Qingliang said that interventional anti-icing and melting ice are the current development trends at home and abroad. The power grid anti-ice disaster reduction should be fundamentally changed from ice-melting measures with high cost, low reliability and power interruption to ice disaster prevention methods with no power outage, non-human intervention, intelligence, low cost and high reliability, but this remains to be further research and engineering application proof.
------Using Spitfire UAV and Lidar
“Now, when we sit in front of the computer, we can see the whole process of melting ice from power grid equipment thousands of miles away, which was previously unimaginable.” Niu Baohong, the safety director of China Southern Power Grid Corporation, said that through the Internet of Things and telecommunications technology, the command center can remotely program the deicing and melting equipment, and realize the combination of various means such as drones, large-scale, cross-regional, Automated inspections, etc., improve efficiency and avoid the safety risks of personnel operations.
In addition to DC melting ice, the grid is still experimenting with other "black technologies" in deicing and melting ice. For example, China Southern Power Grid has made new breakthroughs in non-contact melting ice technology such as fire-breathing drones, laser dampers and laser radar scanning, and laser radar for field de-icing operations. Guangdong Power Grid Corporation of China Southern Power Company took the lead in attempting to de-ice the high-voltage line ground in the domestic fire-breathing drone, and accelerated the melting of ice in the heavy ice area of the ground line by 8 times of fire-breathing within 5 minutes; the laser clearing device is a product independently developed by Dongguan Power Supply Bureau of China Southern Power Grid Corporation. It can clear the line floating objects in a timely, fast and safe way. In the test applied to melt ice, the ultra-long-range laser energy was used to successfully remove the ice layer with a total thickness of 12 cm in the most severe section of the ground wire in 8 minutes.
"In the past, ground deicing was mainly labor-based, not efficient, and it was dangerous. Since the conventional ground wire is not energized, the ice coating will be more serious, and the DC melting operation cannot be performed. The ground melting ice has become a major problem in the power industry. ” Yang Ting, director of the Power Transmission Management Office of Dongguan Power Supply Bureau of China Southern Power Grid, said that the field test application of two non-contact ice melting technologies, such as laser damper and fire-breathing drone, will change the original mode of traditional artificial de-icing, reducing the risk of electric workers taking risks in the bad weather, it is also expected to solve the problem that the overhead line of the power industry cannot be melted by current short circuit due to multi-point grounding.
“The research on melting ice technology was first in Canada, but the world’s first DC ice melting device was actually used in Guizhou.” Li Licheng, an academician of the Chinese Academy of Engineering and chairman of the Expert Committee of China Southern Power Grid Corporation, said that the controllable current source ice melting device should become the standard type of a new generation of ice melting devices. Scientists have also made new progress in the research and application of anti-icing materials for power grids. For example, stranded carbon fiber composite core conductors have better compressive capacity, overall stability, and fracture resistance. They can be used in medium-weight ice areas and strong winds. District, improve the anti-icing and disaster prevention capabilities of the transmission line body. In the anti-icing coating, the surface of the superhydrophobic coating has a micro-nano roughness structure, which can effectively reduce the contact area and adhesion between the ice layer and the coating layer, and realize easy ice removal; there is an air layer between the coating and the coating surface. Blocks the heat transfer when the droplets freeze, reaching the effect of delaying icing.
Jiang Qingliang said that ice coating is a common phenomenon faced by various structures, not only the power grid, wind turbines, airplanes, high-speed rails, etc. are facing the danger of ice coating. Ice disaster prevention is a major scientific and technological problem and key technology in many fields. The scientific and technological achievements obtained by the ice melting of the power grid can be applied to aircraft and high-speed rail in the future.