3.1.3 Insulated Insulator Cradle
1.Basic Structure and Function of the Insulated Insulator Cradle
(1)Basic structure
Insulated insulator cradle is an important tool for live replacement of tension and linear insulator strings on power transmission line.Both of its sides are composed of oval hollow pipe or rectangular insulating plate,and its main materials are connected by several curved plates,on which 2-3 insulating pipes are fixed to facilitate string movement of insulator.Fig.3-5 shows the insulated insulator cradle.
Fig.3-5 Insulated Insulator Cradle
(2)Basic function
The insulator string is held in the operation of replacing the strain insulator string to keep it in a relaxed state,so as to facilitate the replacement of the insulator string.
2.Classification and Technical Specifications of the Insulated Insulator Cradle
(1)Classification
Insulated insulator cradle can be classified as linear insulator cradle and tension insulator cradle according to the function.Fig.3-5 shows the insulated linear and strain insulator cradle.
Fig.3-6 Insulated Linear and Strain Insulator Cradle
a-insulated linear insulator cradle;b-insulated strain insulator cradle
(2)Technical specifications
①The metal accessories at both ends of the insulated insulator cradle shall be treated with chrome plating and other surface anti-corrosion.After the parts of the insulating laminated materials are formed,the machined surface shall be insulated,that is,the joints at the inner holes of the interface shall be filled with high-strength insulating adhesive.The surface shall be coated with the insulating paint.
②After the components of the insulated insulator cradle are formed,the machined surfaces shall be regularly flat.
③The spacing between insulating supports in insulated insulator cradle(insulator cradle with voltage level of 220kV and below)is generally about 500mm(the height of 3 pieces of insulators),and that of the insulator cradle with the voltage class of 330kV and above should generally be about 600～800mm(height of 3 to 4 insulators).
④The width of the two upper connecting rods in the insulated insulator cradle shall be compatible with the disk diameter of the insulator.The distance(depth)of the upper and lower connecting rods shall be more than half of the disk diameter of the insulator.
3.Inspection Items of the Insulated Insulator Cradle(https://www.daowen.com)
(1)The surface of the insulated insulator cradle shall be smooth,free from air bubbles,wrinkles and cracks.The glass fiber cloth and the resin are well bonded,and the rods,segments and plates are firmly connected.
(2)The insulated insulator cradle shall be inspected for insulation before use,as shown in Fig.3-7.
(3)When the insulated insulator cradle is used,the electrical and mechanical test certificates shall be checked for validity period.The insulated insulator cradles beyond the validity period cannot be used.
Fig.3-7 Insulated Insulator Cradle
4.Usage of the Insulated Insulator Cradle
(1)Visual inspection must be carried out before use of the insulated insulator cradle to check whether its main materials,curved plate and insulating pipe are deformed or slackly connected.
(2)When replacing insulator strings,it is necessary to pay attention to the match of clamps to ensure that the connection is firm and reliable,and the impact test shall be carried out to verify the connection.
(3)In the course of delivery,attention shall be paid that the insulator cradle shall not collide with the tower and fittings,which may lead to damage.Fig.3-8 shows the replacement of the insulator string with an insulated insulator cradle.
Fig.3-8 Replacement of the Insulator String with the Insulator Cradle
5.Storage of the Insulated Insulator Cradle
The insulated insulator cradle shall be stored in a well-ventilated room for special tools for live working.If the storage period exceeds the production date by 12 months,the electrical performance test shall be carried out according to relevant standards.The insulated insulator cradles shall be transported in special tool bags,tool cases or special tool cars to protect them from moisture and damage.Fig.3-9 shows the storage of insulated insulator cradles on shelves.
Fig.3-9 Storage of Insulated Insulator Cradles on Shelves
6.Preventive Test of the Insulated Insulator Cradle
The preventive test of the insulated insulator cradle includes the following items.
(1)Electrical test.Power frequency withstand voltage test and operating impulse withstand voltage test:Short-duration power frequency withstand voltage test is carried out for test samples with voltage class of 220kV and below,and long-duration power frequency withstand test and operating impulse withstand voltage test are carried out for test samples with voltage class of 330kV and above.The test cycle is 1 year.
(2)Mechanical test.The mechanical test items include a bending static load test and a bending dynamic load test.The test cycle is 2 years.