3.1.4 Insulated Cross Arm
1.Basic Structure and Function of Insulated Cross Arm
(1)Basic structure
Insulated cross arms are generally composed of glass fiber boards and metal accessories.In recent years,insulated cross arms made of FRP and composite materials have appeared.They all have the characteristics of light weight,strong insulation,corrosion resistance and small volume.
The composite insulated cross arm consists of a glass fiber epoxy core rod,a silicone rubber skirt,a front end link fitting and a connecting flange,as shown in Fig.3-10.The core rod and the fittings are connected by a cementing process,and the core rod and the skirt are integrally molded by one-time forming injection process.The core rod has high mechanical strength and high tensile strength compared to ordinary steel.
Fig.3-10 Composite Insulated Cross Arm
(2)Basic function
The main role of the insulated cross arm is to support the conductors and keep the conductors insulated from the pole and tower.It is widely used in the straight line cross arm operation of the live replacement of 10 to 35kV distribution line pole and tower,as well as the steel cross arm of replacement of 110kV-220kV transmission line steel tube pole.
2.Classification and Technical Specifications of Insulated Cross Arms
(1)Classification
①According to the composition of materials,it can be divided into glass fiber board insulated cross arm,FRP insulated cross arm,composite insulated cross arm and so on.
Fig.3-11 shows the glass fiber board insulated cross arm,Fig.3-12 shows the used FRP cross arm,and Fig.3-13 shows the composite insulated cross arm.
Fig.3-11 Glass Fiber Board Insulated Cross Arm
Fig.3-12 FRP Cross Arm
Fig.3-13 Composite Insulated Cross Arm
②According to the shape and use,it can be divided into insulated branch cross arm,temporary pole cross arm,rubber rod auxiliary cross arm,and three-phase insulated branch cross arm for pole,as shown in Fig.3-14.
Fig.3-14 Insulated Cross Arm for Distribution Lines
1-insulated branch cross arm;2-temporary pole cross arm;3-three-phase branch cross arm for pole(https://www.daowen.com)
(2)Performance specification
See Table 3-3 for the technical specifications for the most commonly used FRP insulated cross arms for live replacement of linear cross arms.
Table 3-3 Specifications for FRP Insulated Cross Arms and Insulated Pedals
3.Inspection Items of the Insulated Cross Arm
(1)Insulated cross arms must be visually inspected before use.Mainly inspect the insulating main material(or insulating rod)and metal parts;inspect whether the insulation part is reliable(with relevant instruments),and whether the metal parts are deformed or damaged;whether the connection of metal parts is firm and reliable.
(2)In addition to checking whether the surface of the FRP insulated cross arm is broken or dirty,it must be checked before use for stress,and it can be used without any problem.Short circuit of the FRP cross arm shall be strictly prevented.
(3)The composite insulated cross arm must be checked before use to see if the skirt,the core rod and the front and rear end link fittings are broken and damaged.The load test and power frequency withstand voltage test must be carried out.
4.Usage of Insulated Cross Arms
(1)The insulated branch cross arm used in the distribution line is mainly used for rewiring or maintenance of single-phase and three-phase conductor support frames.The temporary pole cross arm is mainly used as the temporary cross bar frame to be connected with live cables when replacing the electric pole cross arm.The three-phase branch cross arm for poles is mainly used for replacing electric poles,brackets and insulated porcelain insulators,etc.
(2)FRP insulated cross arm is used for live replacement of the cross arm for the 10 to 35kV line.It has the characteristics of having no need to move the conductor,keeping the conductor at the original position,and operating more simply and reliably.
(3)Composite insulated cross arm is a cross arm made of a new type of material.It is small in size,light in weight,excellent in electrical and mechanical properties,and is used as the cross arm on 110kV and 220kV double-circuit steel tube poles,which can further reduce the line corridor.
In addition,the insulated cross arm can also be used in the straight rod and strain rod operations in the charged state.
5.Precautions for Storage of Insulated Cross Arms
The insulated cross arm shall be placed on the shelf in a room for special tools for live working,which is dry and well ventilated with suitable temperature.Fig.3-15 shows the storage of the insulated cross arm.
Fig.3-15 Storage of Insulated Cross Arm
6.Preventive Test of Insulated Cross Arms
The preventive test of the insulated cross arm includes the following items.
(1)Electrical test.It shall pass the corresponding 45kV or 95kV short-duration power-frequency withstand voltage test at the voltage class of 10kV and 35kV(qualified if there is no breakdown,flashover and obvious heat),and the test cycle is 1 year.
(2)Mechanical test.Including static and dynamic load tests.The test cycle is 2 years.