- Advantages of the technology
Sometimes the simple way is the most effective. This is especially true in the field of OPGW. In generations of constructions it has been an unwritten law that an OPGW has to consist of two parts: a central optical core and an armouring applied over that. With the steel tube technology this times are past because it is now possible to build up an integrated solution. Retaining the rope structure of a usual earth wire only one or more wires in the first armouring layer are substituted by stainless steel tubes with optical fibres. This gives the advantage of an OPGW structure which combines superior optical transmission characteristics with all advantages of a rope like design and behaviour.
- Structure of Stainless Steel Tube
The optical unit consists of optical fibres which are loosely housed in a jelly filled tube made of laser welded stainless steel. The well known advantages of a loose structure such as de-coupling from outer forces and low attenuation are combined with perfect protection and water and steam tightness of the tube. For best welding seam quality all steel tubes are measured with an eddy current fault detector during production.
- Cable Structure
Basis for the construction is the usual rope which mostly consists of a steel core made of a central wire and one layer of wires stranded around this. In this layer one or more steel wires can be substituted by steel tubes. To protect the steel tubes from radial pressure the coverage in this layer is optimised. Like in standard conductors the core structure is greased for corrosion protection. One, two or more layers of aluminium (alloy) wires are stranded around this core construction to give the OPGW the right conductivity.
- What are the Advantages of this Construction?
- Stranded loose tube design
- low attenuation because fibres are free of stresses
- no change in attenuation due to different temperatures and additional loads
because of a strain margin of at least 0,5%
- no influence of vibrations or other motions because fibres are embedded
in filling jelly
- Rope like design
- mechanical and electrical characteristics like usual ground wire with similar
diameter and weight
- additional loads very similar to replaced ground wire
- behaviour and flexibility very similar to usual ground wire
- no anti-torque equipment for installation necessary
- Modular design
- change of characteristics just by replacing components
- rise of fibre count by filling up the steel tube and by additional tubes possible
- Fully metal design
- no degradation of plastic materials due to UV radiation or temperature
- high overloads in case of short circuit currents possible (no melting of plastic)
- Modular Structure of Steel Tube OPGW
All in all only four materials are used for the armouring of OPGW world-wide i. e. aluminium clad steel (ACS), galvanised steel (St), aluminium (Al) and aluminium alloy (AA). This materials are standardised in national, European and IEC standards. With wires of this materials the cables can be build up in following combinations: Al/ACS, Al/St, AA/ACS and AA/St. Most common in the field of OPGW is the combination AA/ACS because of best mechanical properties and corrosion protection.
With steel tubes of different sizes it is possible to build up different cable cores. Every cable core can be applied with one or two (or more) layers of aluminium (alloy). The sum of constructions that can be built up with one core is called an OPGW family. On the following pages these families are presented in detail. By means of mechanical, electrical and other properties the right OPGW for almost every application can directly be taken from the tables.
- What if the right OPGW cannot be found in the standard tables?
No problem! The modularity of the steel tube construction gives the possibility to built up sub families in addition to the standard cables. Changing the construction by simple substitution of elements raises the number of constructions into never known dimensions. By this our expert team is in the position to find the right solution for you.
The following illustration shows an example of an OPGW variation on basis of a standard type. Although the variations are limited to the exchange of elements in the cable core it results in not less than 14 new sub types. The influence on RTS and short time current capacity is shown in the diagram. Such variations are possible with all standard types in the tables on the following pages. Taking into account that the second and if existing a third layer can also be modified the number of OPGW constructions with stainless steel tubes is nearly unlimited.
Figure : Variations of OPGW type ASLH-D(S)bb 1x24E9/125 (AA/ACS 56/36-8,2)
