Lightning protection solutions for overhead insula

Lightning protection solutions for overhead insulated conductors

I. advantages of overhead insulated conductors

1.1 good insulation performance

compared with bare conductors, overhead insulated conductors have superior insulation performance, which can reduce the distance between lines, reduce the insulation requirements for line supports, improve the number of circuits of lines on the same pole, and prevent phase to phase short circuit caused by foreign objects

1.2 little corrosion

the overhead insulated conductor has more plastic sheath, which is less subject to oxidation corrosion than the bare conductor and improves the service life of the line

1.3 simplify the tower structure

it can simplify the tower structure of the line, and even lay along the wall, which not only saves the line materials, but also beautifies the city streets

1.4 go deep into the load center

it is convenient for high-voltage to go deep into the load center, reduce the power supply radius of low-voltage lines, and improve the voltage quality

1.5 it is conducive to urban greening

it is conducive to urban construction and greening, and reduces the pruning amount of offline trees

1.6 reducing the line corridor

saves the space occupied by overhead lines, facilitates overhead lines to cross in narrow channels, and reduces the line corridor. Compared with overhead bare lines, the line corridor can be reduced a lot

1.7 extending the maintenance period

due to the improvement of line technical conditions, the maintenance workload is reduced, the maintenance period is extended, and the time of power failure due to maintenance is reduced. II. Application of overhead insulated conductors

2.1 applicable to densely populated and prosperous places

2.2 applicable to places with narrow line corridors

2.3 applicable to places with fast growth of trees

2.4 applicable to places with more salt fog pollution

2.5 applicable to places where balloons and colored belts fly

2.6 reducing the tripping probability of lines in typhoon season

III Problems needing attention

3.1 problems in planning and design

1) the span of overhead insulated lines should not be greater than 50m, and the length of tension section should not be greater than 1km. The distance between overhead insulated lines shall not be less than 0.4m, and the compact erection with insulating support shall not be less than 0.25m

2) if aluminum or aluminum alloy core insulated wire is used, the design minimum cross-section of main line is 150mm2 and branch line is 50mm2

3) at both sides of the interconnection switch, the place where the joints of the branch pole and the tension pole have increased by about 22.5% year on year and the conductor of the branch line point where the reverse power transmission is possible shall be set with the power failure working grounding point; When the line is in normal operation, the grounding point for power failure shall be equipped with an insulating cover

4) special insulation cover should be set at the connection between the terminal of fuse, lightning arrester, transformer and insulated conductor for insulation sealing

3.2 problems of material selection

1) overhead insulated conductors shall comply with the provisions of gb14049, and relevant supporting materials shall be selected according to the use requirements of insulated conductors

2) insulators shall comply with the provisions of gb1000, and the use of insulators, fittings and insulating parts shall comply with the following requirements. Insulated distribution line: composite pin insulator should be used for straight pole (for example: fpq-10/1: what is the classification and working principle of fatigue testing machine? 4); A composite tension insulator (e.g. FNB － 10/70) and insulated tension clamp (nej Series) should be used for the tension rod

IV. lightning protection of lines

at present, the erection of most overhead insulated conductors has not taken corresponding lightning protection measures, resulting in lightning stroke overhead insulated conductor disconnection accidents from time to time, which has seriously affected power safety and economic development

3.4.1 cause of disconnection

the lightning stroke disconnection principle of insulated conductor is obviously different from that of bare conductor. When the insulator flashover is caused by direct lightning strike or induced lightning overvoltage acting on the bare conductor, the connected power frequency short-circuit current arc moves along the conductor away from the power supply under the action of electric force, and the probability of serious conductor burn is very small. However, the insulated conductors are different. When lightning strikes the insulated conductor, the lightning overvoltage first breaks through the insulation layer, which then causes insulator flashover. The broken insulation layer is in a pin hole shape. The continuous power frequency short-circuit current is blocked by the surrounding insulation. The arc root can only burn at the pin hole, and the conductor will be neatly burnt out in a very short time. Therefore, the insulated conductor is easier to burn out than the bare conductor after lightning strike. In addition, the insulator on the line may flashover or burst due to lightning strike, and even cause accidents such as wire fusing

3.4.2 lightning protection measures

1) preferred lightning protection measures:

according to the principle of lightning disconnection of insulated conductor, the recommended method of corresponding preventive measures is to install lightning protection clamp of overhead insulated wire on insulated conductor near insulator. The function and principle of the clamp are as follows: the clamp with puncture structure is used to penetrate the insulation layer of the conductor and make close electrical contact with the insulated conductor; The lower part of the clamp is provided with an arc resistant electrode, and another arc striking electrode is installed on the iron cross arm under the insulator and well grounded; Adjust the distance between the arc striking electrode and the arc striking electrode so that in case of lightning, the arc resisting electrode and the arc striking electrode discharge, and fix the power frequency arc root generated by lightning on the arc resisting electrode for combustion, so as to protect the conductor from burns. Because the product adopts a puncture structure, it is easy to install; If equipped with specially developed flame-retardant insulation protector, the safety of the line can be further improved. Installation method: select the corresponding model fhjc insulated wire lightning protection clamp according to the nominal cross-sectional area of the conductor. When it is used for one-way power supply line, it is installed on the load side (away from the power side) of the insulator. If it is used for two-way power supply line, it is recommended to install one on both sides of the insulator. See the product operation manual for the specific installation method

2) other lightning protection measures:

a. install corresponding lightning wires above overhead insulated conductors; Composite pin and tension insulators (e.g. fpq-10/4 or FNB － 10/70) are used as insulators on the line

b. in heavily mined areas, a group of lightning arresters shall be installed every 150m on the road (e.g. hy5ws － 12.4/50); Or adopt lightning protection pin insulator

c. reinforced concrete poles in residential areas should be grounded, iron poles should be grounded, and the grounding resistance should not exceed 30 Ω

d. the overhead insulated distribution line with load carrying line shall be grounded, and its grounding resistance shall not be greater than 30 Ω. V. performance requirements for lightning protection clamp of overhead insulated conductor

as lightning protection clamp of overhead insulated conductor is a new product developed in recent years, there is no national standard, but according to its use requirements and with reference to the national standards of similar products, our company has developed the following internal control standards in the industry of experimental machines in China for several decades

a. lightning impulse discharge test:

after the product is installed according to the use status, test the wiring according to figure 1 to check whether the flashover is clamped on the arc resistant electrode under the action of lightning impulse and whether the power frequency arc path can be effectively located

b. power frequency arc test:

after the product is installed according to the use status, test the wiring according to figure 2 to check whether the power frequency freewheeling arc root after lightning flashover can be fixed on the arc resistant electrode for combustion, the degree of arc resistant electrode burns and whether the conductor can be effectively protected from burns

c. connection resistance of clamp:

after installing the clamp, the connection resistance shall not be greater than 1.2 times of the conductor of the same length

d. damage to the conductor:

after installing the clamp, the breaking force of the conductor shall not be less than 95% of the specified breaking force of the conductor

e. flame retardancy of insulation shield:

in the power frequency arc test, the insulation shield shall not ignite and expand the combustion range

VI. conclusion

the advantages of overhead insulated conductor different from ordinary overhead bare conductor make its application value more and more obvious. It will be more and more common to replace ordinary overhead bare conductor with overhead insulated conductor. However, if the lightning protection measures for overhead insulated conductors are lack or improperly used, it will not only affect the project quality and operation management, but also leave many hidden dangers of accidents