2018 International Conference on Energy, Power, Electrical and Environmental Engineering (EPEEE 2018) ISBN: 978-1-60595-583-4

The Influence of Typhoon on the Power Grid and Countermeasures

1 2 1 3,* Tuan-jie GAN , Jian-feng WEN , Lian-dong HUANG and Xue-jiao HAN 1Jiangmen Power Supply Company of Guangdong Power Grid Co., Ltd Guangdong 529000, 2Guangdong Power Grid Co., Ltd Guangdong 510000, China 3Tsinghua University, Beijing 100084, China *Corresponding author

Keywords: Typhoon, Transmission line, Distribution line, Countermeasures of wind disaster.

Abstract. Guangdong affected by typhoon frequently, so power sectors pay high attention to the transmission line failure caused by the typhoon. Based on typhoon data in Guangdong, this paper gets characteristics of typhoon with a scientific method of the statistical analysis. By studying the loss of Jiangmen power grid caused by typhoon, this paper summarizes the cause of power accidents and puts forward countermeasures. It shows that typhoon mainly occurred between July and September in Guangdong, accounting for 72% of all the year round; Typhoon in Guangdong showed the tendency of reduced from west to east; Form 2008 to 2010, transmission line tripped 50 times caused by typhoon, and distribution circuit tripped 710 times in Jiangmen; The main reasons of breakdown are the mechanical overload, the flashover caused by wind age yaw and the reduction of air gap discharge voltage caused by lightning. This paper proposes to strengthen the early warning of typhoon, improve the design standard of transmission/ distribution line and develop new type tower material further study.

Introduction Guangdong is located in the main path for northwest Pacific Ocean and tropical cyclone to land in China [1], which is one of the provinces suffering from the worst typhoon disaster. Strong wind, heavy rain and storm surge generated by typhoon seriously threaten the security of power grid [2]. For example, the maximum wind speed of violent typhoon "Usagi" in 2013 reached 46.6m/s (grade 15), and the extreme wind speed was 60.7m/s (grade 17) [3,4], and 8 110kV and above overhead lines of Guangdong Power Grid Company suffered from wire breaking or tower breakdown accidents. No. 11 violent typhoon 'Utor' had maximum wind speed of 45.3m/s (grade 14), extreme wind speed was 60.5m/s (grade 17), and 500kV Yangwu AB line suffered from failure trip for 15 consecutive times. Statistical analysis method is used for studying violent typhoon weather characteristics in Guangdong, analyzing disaster reasons on power transmission and distribution lines, further proposing countermeasures of wind disasters, and ensuring safe and stable operation of power grid based on disaster data of typhoon landing on and affecting Guangdong, power grid failure statistical data and other data in the paper.

Tropical Cyclone Condition in Guangdong

Tropical Cyclone and Grading Thereof Tropical cyclone is a cyclonic circulation occurring on the sea surface of tropical and sub-tropical regions [5]. Tropical cyclone can be divided into different grades according to different maximum average wind speeds near the bottom center of tropical cyclone. Tropical cyclone in China forecast responsibility area is regulated as follows according to national

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standard (GB/T19201-2006): six grades of tropical low pressure, tropical storm, strong tropical storm, typhoon, violent typhoon and super-violent typhoon. Data of tropical cyclone landing in and affecting Guangdong from 1951 to 2010 are studied to summarize the characteristics of Guangdong typhoon in the paper. Inter-annual Change Feature There were 231 tropical cyclones landing in Guangdong from 1951 to 2010, 7 tropical cyclones landed in Guangdong at most in a year, and 1 tropical cyclone landed in a year at least as shown in figure 1. It can be seen from the figure that tropical cyclone landing in Guangdong generally presents a slight decreasing trend. More than 4 tropical cyclones landed in Guangdong in only 19 years. The annual tropical cyclone quantity is generally less than or equal to 4.

Figure 1. Quantity variation diagram of Guangdong tropical cyclone from 1951 to 2010.

Intermonth Change Feature Guangdong may be affected by tropical cyclone all year round according to the historical data of previous years [6]. Concrete distribution is shown in figure 2. Figure 2 shows that the distribution trends of tropical cyclones affecting and landing in Guangdong are roughly the same. Tropical cyclones affecting Guangdong are the most in August, which are followed by September and July. Guangdong is also affected by tropical cyclone in June, October, November and May, but the probability is relatively small. The tropical cyclones are rare in December (there was only one typhoon in the record, namely No. 27 typhoon in 1974). The probability is extremely low from January to April, and only one typhoon is available. Tropical cyclone activities are frequent from July to September as a whole, which account for 72% of the whole year. Therefore, typhoon prevention work should be strengthened from July to September.

2 1.5 1 0.5 0 1 2 3 4 5 6 7 8 9 10 11 12

Figure 2. Intermonth change diagram of tropical cyclone average quantity in Guangdong (full line is influence quantity, and dotted line is landing quantity).

Landing Feature of Tropical Cyclone in Guangdong The sources of typhoons landing in and affecting Guangdong are studied. It is discovered that about 19% typhoon sources come from South China Sea and 81% typhoon sources come from the northwest Pacific Ocean (see table 1) [7]. The coastal areas of Guangdong are divided into three regions, including West Guangdong Province (-Xuwen), Central Guangdong Province (Huidong-Taishan) and East Guangdong Province (Raoping-Haifeng)[8]. The specific distribution of tropical cyclones landing in the three coastal areas each month is shown in Table 2. Table 2 shows that the tropical cyclones landing in West Guangdong Province, Central Guangdong Province and East Guangdong Province are

242 decreased in turn. Namely the influence of tropical cyclone on Guangdong is decreased from west to east, wherein West Guangdong Province is affected by tropical cyclone most seriously, accounting for 45% of the total number. Analysis table 2 also shows that the tropical cyclones landing in coast areas of Central Guangdong Province are more than that of other regions in May and December. The tropical cyclones landing in the coastal area of West Guangdong Province are the most in June, July, August, September, October and November [9]. Table 1. Source regions of typhoon landing in Guangdong at different months (1949~2010). Month Pacific Ocean South Total China Sea 5 1 3 4 6 9 4 13 7 24 6 30 8 16 6 22 9 30 3 33 10 11 1 12 11 5 0 5 12 1 0 1 Total 97 23 120 Table 2. Quantity distribution table of tropical cyclone landing in three coastal regions of Guangdong at different months (1949~2010). May Jun July Aug Septem Octob Novem Decem Total e ust ber er ber ber West 0 13 27 29 24 9 3 0 105 Guangd ong Province Central 4 9 16 21 17 6 1 1 75 Guangd ong Province East 2 5 17 8 16 2 1 0 51 Guangd ong Province

Influence of Typhoon on Guangdong Power Grid

Hazard of Typhoon on Power Transmission and Distribution Lines Power transmission line, especially overhead power transmission line, is seriously affected by severe weather disasters due to its long exposure [10]. Powerful disasters such as typhoons, etc. have caused great damage to power transmission line particularly. In general, the wind disaster accidents of overhead power transmission line can be roughly divided into the following categories [11]: jumper (including jumper string) windage yaw flashover trip, suspension string windage yaw flashover tripping, strand breaking, wire breaking, string breakage, tower breakdown, etc. [12]. (1) Line mechanical overload accident: The damages of power transmission line facilities caused by mechanical overload accident are mainly shown as the following four categories: pole bending distortion and falling; tower head (crossarm) damage; wire breaking, insulator and hardware damage, etc.; pole base slanting and removal. (2) Trip accident caused by windage yaw flashover: The reason for windage yaw flashover lies in air gap distance reduction of power transmission line, which does not meet the design requirements. The line contains large span, large pitch and large sag wires or wires in micro topography and microclimate zones. It is easy to produce larger monsoon under the effect of strong wind. The minimum air gap distance of wire on pole is reduced after monsoon, which does not meet the

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requirements on power frequency voltage, operation over-voltage as well as thunder and lightning overvoltage. Wires discharges to tower body, and such circumstances account for absolutely high portion. Secondly, wires discharges to near buildings, trees, other crossed lines and other obstacles due to insufficient electric distance. The majority of windage yaw flashovers occur under the working voltage, and reclosure cannot succeed generally, thereby leading to line operation stop. The typical windage yaw flashover is shown in figure 3.

(a) Flashover trace on the wire (b) Discharge trace to tower body Figure 3. Field photo of typical windage yaw flashover. The main failure forms of overhead distribution line under typhoon weather include large-scale pole falling, pole slanting, wire breaking, etc. The typhoon wind speed higher than design standard is the main reason of large scale pole falling and wire breaking on the distribution line [13]. Distribution line destructive failure caused by typhoon usually has large influence scope and long duration, and huge economic loss is brought to the society [14]. The basic characteristics of power distribution equipment damage caused by typhoon are shown as follows [15]: (1) Disaster scope and severity of power distribution facilities are mainly related to typhoon landing location and development path. Coastal area suffers from typhoon face-to-face landing, the terrain is empty, and it is prone to wind disaster, thereby the disaster level is more serious. (2) The damage of distribution line pole is mainly concentrated on concrete pole falling and pole breaking. 10kV and lower low voltage lines have large scale and severe damage. Poles of 35kV and lower distribution lines are mainly made of cement. Angle iron towers and steel pipe poles are rarely used. Pole damage is also mainly concentrated on cement poles. (3) Old lines suffer from the most severe pole falling and breaking. Damaged lines were mostly operated before 2000, which have been operated for more than 10 to 20 years, pole falling and breaking are especially more concentrated in old lines without modification. Lines operated in recent five years also suffer from pole damage phenomena, but the quantity is relatively small. (4) Pole falling and breaking are most common in straight poles without drawing line. The straight poles with drawing line are damaged rarely, and the tension poles are damaged minimally. The damage proportion of straight poles without drawing lines is 93%, the damage proportion of straight poles with drawing line is 4%, and the damage proportion of tensile poles is 2% according to Maoming statistics. (5) Distribution line poles suffer from direct wind load overload and indirect influence of typhoon. For example, trees around the line are toppled due to typhoon attack, trees are collapsed on the lines to produce pole falling and pole breaking. The strong precipitation accompanied by typhoon leads to the collapse of pole foundation or soil and water loss pole falling and breaking. The thunder and lightning process accompanied by typhoon lead to lightning stroke damage of power distribution facilities, etc. Accidents of Power Grid Due to Typhoon in Guangdong Since typhoon has large randomness of disaster, the statistics of power grid accidents are incomplete, the power grid failure in Jiangmen is described with an example in the section. There were frequent typhoons from 2008 to 2010, such as "Kammuri", "Nuri", "Hagupit", "Molave", "Goni", "Koppu", "Conson" and "Chanthu", etc., which threatened the safe and stable operation of power grid in Jiangmen seriously. Typhoon disasters are accompanied by strong wind and storm, which cause many tripping accidents in main power distribution network, and even pole breaking and tower breakdown. The main network line in Jiangmen suffered from a total of more than

244 50 tripping accidents, and power distribution grid lines suffered from a total of 710 tripping accidents due to typhoon in recent three years (please see Figure 9 and 10). Concrete distribution is shown in table 3 and 4: Table 3. Statistical table of tripping frequency of main network lines due to typhoon from 2008 to 2010. Voltage grade 2008 2009 2010 100kV 0 11 0 220kV 26 13 0 500kV 0 0 0 Total 26 24 0 Proportion in 31% 44% 0% total tripping accidents Table 4. Statistical table of tripping frequency of distribution network line due to typhoon from 2008 to 2010. Accident trip rate (time/per Tripping Grounding Households during power Year hundred km.year) frequency frequency failure (house.household) Finished Indicator (time) (time) 2010 2.96 10.73 86 14 3319.351 2009 7.4 8.9 203 51 10709.483 2008 15.44 16.72 421 58 23937.517

Figure 4. Main network and distribution network trip condition.

Analysis of Accident Reasons According to the characteristics of typhoon disaster and power grid failure data analysis. The following 4 accident causes can be obtained according to typhoon disaster characteristics and analysis on power grid failure data: (1) Strong winds cause mechanical overload and windage yaw flashover; typhoon meteorological disasters are accompanied by thunderstorms, high winds and storm surges. When real-time wind speed exceeds the design wind speed of poles, accidents such as pole falling and pole breaking, etc. will occur. (2) Wind deflection discharge is caused by small design margin. The following parameters are gradually improved with constant deepening of the study, such as the recurrence period of power transmission line, maximum design wind speed, wind pressure unbalance coefficient, etc. Compared with the actual situation, the existing parameters are relatively small, and it is the internal cause of wind deflection discharge, thereby leading to insufficient ability of existing power transmission line to resist strong winds. (3) Thunder and lightning storm reduce the discharge voltage of air gap. The typhoon process often brings thunderstorm disaster. The rainstorm forms a directional intermittent waterline along the wind direction under the action of strong winds. When the waterline and flashover path are in the same direction, the power frequency discharge voltage between wire and pole is sharply reduced, thereby further causing line deviation trip failures. (4) Influence of micro topography and micrometeorology on disaster aggravation; Terrain and geomorphology are complex, and there are many kinds of micro topography and micrometeorology in Guangdong. The terrain is flat, and there are no tall trees and other obstacles in the channel; the

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confluence of canyon, the funnel-shaped trough with narrow tube effect, wind position at the top of the mountain with relative high altitude, etc. are special geographical position prone to failure line pole.

Measures to Prevent Typhoon Guangdong power grid must actively adopt measures aiming at such frequent typhoon disasters, thereby reducing the loss on the power grid. Typhoon prevention measures mainly include the following three aspects: (1) Typhoon warning work should be strengthened. The damage caused by typhoon to the power system can be reduced if disaster warning can be implemented before the loss is caused aiming at sudden and extremely strong typhoon disasters. Relevant studies on typhoon wind field and the data of power system failure are regarded as basis for establishing failure model of power transmission and distribution lines under violent typhoon disaster weather. Meanwhile, a disaster assessment system and pre-disaster warning system is also established, corresponding emergency repair measures are set up subsequently, thereby ensuring safe operation of power grid before, during and after disaster. (2) The power transmission and distribution line design standards should be improved. The typhoon resistance design of existing power transmission and distribution line is generally 25-35 m/s, which is far lower than the maximum typhoon wind speed. Therefore, it is necessary to improve the design of power transmission and distribution line wind speed in the areas with frequent typhoon. The wind speed changes of Guangdong coastal area are obtained through calculation under general condition according to medium and long-term typhoon wind field analysis and numerical simulation calculation of wind speed. The design standards of power transmission and distribution line is improved, thereby naturally enhancing the typhoon resistance ability of the lines, and further guaranteeing the line power supply reliability under typhoon disaster. (3) Research on novel pole material: the old poles are affected by typhoon disasters most seriously. Meanwhile, cement pole is also prone to pole falling and breaking. Study on high strength novel pole material can improve the problem of pole falling breaking to some extent. For example, fiber reinforced composite materials are more suitable for the material of power transmission pole and tower due to its excellent performances in light quality, high strength, high rigidity, superior insulation performance, corrosion resistance, etc. It is especially suitable for wind and corrosion prevention work in coastal areas of Guangdong. Meanwhile, superior electrical insulation performance of the fiber reinforced composite material can greatly reduce or even avoid the flashover problem of poles caused by wind deviation. Currently, more and more attention has been paid to the composite materials with constant deepening of the research. The research on pole materials should be strengthened, which will lay a foundation for Guangdong coastal areas to resist typhoon disasters.

Conclusion (1) Tropical cyclone landing in Guangdong from 1951 to 2010 generally shows a slight decreasing trend. Guangdong suffered from less than or equal to 4 tropical cyclones a year under general condition, tropical cyclones are mainly concentrated from July to September, accounting for 72% of total tropical cyclones in the whole year. (2) About 19% of the typhoons landing in and affecting Guangdong were originated from the South China Sea, and 81% were originated from the northwest Pacific Ocean, and a trend of increasing from east to west is shown. (3) There were 50 tripping accidents in the main network line in Jiangmen due to typhoon from 2008 to 2010. The distribution network line suffered from a total of more than 710 times. Causes of the accidents include the follows: mechanical overload and windage yaw flashover are caused by strong winds, wind deviation discharge is caused by small design margin, discharge voltage reduction

246 of air gap is caused by thunder and lightning storm, and microtopography and micrometeorology aggravate disaster influence. (4) The following 3 typhoon prevention measures can be summarized: strengthening of typhoon warning work; improvement of power transmission and distribution line design standard; research on novel pole material.

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