The situation that the unreasonable design of grounding reconstruction in the hydropower station,and grounding resistance greatly exceeds the specified value are analyzed comprehensively.Through test and investigation on the factors such as the geography,geology and soil resistivity,and combined with regulations and actual conditions the program of underwater grounding grid extension in a reservoir is proposed to reduce the target value by this effective method.When the program is completed,the grounding resistance is measured.Finally,the measurement is compared with the calculated value of underwater grounding resistance,the accuracy of the analytical algorithm on the underwater ground resistance is verified.

A specific lightning strike fault happened on a 110 kV double circuit transmission line in the Shaoguan area is analyzed,it is concluded that the main reason caused back flashover happened on 110 kV line is the low lightning withstand level,and the lightning and tripping out occurred in the same time usually caused by small difference between the lightning withstand level of double circuit line.Based on the theoretical analysis and combined the actual situation,some measures are proposed to improve the lightning withstand level and increase the difference between the lightning withstand level of double circuit line,such as reduce the grounding resistance of the tower,adopt a balanced high insulation and erection of coupling line.In addition,a new lateral rod with griding ball is used to avoid the lightning shielding failure,there is better disperse effect after lightening current crossed the griding ball.Theoretical analysis shows that these measures can receive a better lightning protection effect.

The phenomenon that a large number of grounding resistance exceeded was analyzed, and it was concluded that the main reason result in a lot of grounding resistance exceeded was improper design,designers did not fully take into account the specific circumstances of each tower and gave only a single grounding type.Based on the analysis of the reason that a lot of grounding resistance exceeded, this paper used a tower as an example to investigate the transform program of the tower,the analysis showed that it can play a good reduction in resistance.

220 kV Ma-mo transmission line is one of the key lines of shaoguan district,there have been many lightning accidents since the transmission line puts into operation.The author analyzes the existing lightning protection measures and the cause of lighting accident of Ma-mo 220kV transmission line and also calculates the lightning withstand level of the line using the existing parameter of the lightning protection measures of the accident tower.It is concluded that the lightning accident of the line is mainly caused by strike back of lightning strike on tower or lightning wire.Based on accident analysis,the transmission line has been reconstructed by decreasing grounding resistance of tower to avoid the defects and problems of the existing lightning protection measures.Because of the terrain of the tower is special,the traditional reduction resistance measures cannot reduce the grounding resistance to the theory value,the author analyzs SYJ type grounding device and designs the specifications of the device according to the target value.In addition,the author adopts installation of transmission line arrester and setting up coupling line as the supplementary measures for line reconstruction.After the measures mentioned in the paper were implemented,the lightning protection effect is better.

The present situation of lightning protection of a 35 kV line in the guangning area is analyzed,concluded that it is not ideal to improve the lightning protection performance only by reducing the grounding resistance of the towers.Line transformation is suggested carried out by the insulator string in parallel with a kind of adjustable protection gap.The principle and structure of the adjustable protection gap are analyzed: the distances of the protection gap for 3 and 4 pieces is obtained by a good deal of lightning impulse tests: 345.12 mm for 3 pieces is,440 mm for 4 pieces,and the effectiveness of the protection device is verified,this device can be applied to other 35 kV overhead lines.The results of contrast test and data calculate shows that,the lightning protection capability of the line can be improved by increasing the number of the insulator to four,and the lightning protection capability of the protection gap will not be affected.