OPGW Installation Procedure

PURPOSE

Describe the system of installation and delivery of OPGW fibre optic cables.

GENERAL

In general, the system and the equipment used for installation of the OPGW are similar to those of the standard ground wire cable.

Nevertheless, there is an optical fibre core, fibres should be protected from suffering any damage by observing the minimum bending radius at all times. Therefore, specific components and machinery are used for the OPGW cable: pullers, tensioners, anti-twisting counterweights, swivels, pulling grips, pulley-blocks, self-gripping clamps, pulling ropes, pulling cables, etc.

PROCEDURES

Survey of the line

Prior planning for installation of the OPGW cable is performed by monitoring the line, taking into account the following parameters:

Length of each drum

The OPGW drum length is determined based on the following considerations: position of the tension towers, tower access, distance between supports and crossing with other lines, roads, railways, routes, services and other obstacles.

Splices

The position of the splices depends on the maximum available length of OPGW, on the position of the towers and the tower access.

Transport, loading, unloading and storage

The following procedures are recommended to prevent the cable from suffering damage during handling, transport and storage:

1. The drums should always be transported in vertical position with the cable ends fixed to prevent cable from slackening. All of the staves and safeguards should be maintained until the drums are situated for immediate installation.
2. After the transport, the drums should be inspected to verify that they have not been damaged and that none of the staves or safeguards is broken.
3. The drums should never, in any case, be thrown from the lorry during unloading, or moved by uncontrolled rolling.
4. Loading and unloading are performed so that the drum remains in vertical position and the sides of the drum are not damaged.
5. The drums can be moved by rolling a short distance ensuring that there are no objects that may damage the staves. The direction the drum turns should follow the instruction of the mark on the drum.
6. In any case the drum should not be stored horizontally.
7. The ends of the cable should be sealed to prevent water penetration.
8.  The drums should be stored on flooring that is strong enough to avoid sinking.
9. The drums should be stored to facilitate handling and loading, and should be located on a safe place where they will not be damaged.
   

Preparation for installation

Positioning the equipment

Drum

The drum is placed at the selected site (with the space required for its location) so that the cable outlet is on the upper part and aligned with the planned laying direction.

The drum must be located at a distance of 2 or 3 metres from the tensioner. The lifting components usually used are hydraulic jacks and a bar with the suitable dimensions inserted in the central opening of the drum.

The drum must be located at a height of 10 to 15 cm from the ground.

Puller and tensioner.

Either the puller or the tensioner must be placed at a minimum distance from the tower equal or more than twice of the tower’s height.

The tensioner as well as the puller should be placed aligned with the conductors. The maximum acceptable deviation angle is 30º. (< 30º)

If it is not possible to achieve this angle, the puller and tensioner are placed close to the following tower, using an additional pulling cable of the required length. At 90º or less angle, retracking of the optic cable is not allowed. The tensioner as well as the puller should be positioned at a minimum distance equivalent to twice the height of the support to which the cable is fastened. In the installation with retracking, the smallest angle must be more than 90º and the final pulley should be placed at a distance equal to twice of the tower’s height. In the tensioner, the first groove that the cable will pass through must be perpendicular to the axis of drum. The tensioner must be equipped with a dynamometer (i). Its reels must be protected with material that does not damage the outer layer of the OPGW cable. The puller must also be equipped with a dynamometer 1(i), with automatic disconnection in case of over tension on the cable. The pulling cable should be joined to the OPGW cable by a swivel and a pulling grip. The minimum diameter of the reels (where the OPGW is to be coiled) used during the installation should be at least 80 times the diameter of the OPGW cable. For example, the tensioner reels for a 15 millimeters cable should have a diameter of approximately 1.2 metres. Either the braking device or the puller has to be suitably connected to the ground by a system of moveable rollers such as that shown in the following picture. This also applies to the OPGW cable and the pulling cable, if it is a metal one.

Pulleys

The tower pulleys should have a minimum diameter of at least 0.8 metres in the following cases:

- In all towers with a change in laying direction equal to or greater than 15 degrees.

- In the first and in the last tower of a single installation.

- If the distance between the towers is greater than 600 metres.

In all the other cases pulleys with a diameter of 0.6 m can be used.

The pulleys have to be under good use conditions. The pulley groove should be protected with neoprene or other similar material.

In case of sharp angles, the pulley must be placed so that the cable always passes through the centre of the groove

If the angles are greater than 30 º, a dual pulley system must be used in order to increase the bending radius during the installation. The diameter of each pulley should be at least 0.6 m

Anti-twisting devices

When a single or double layer OPGW cable is installed, an anti-twisting device is required to compensate the inherent effect of torque of the OPWG cable. This device is always positioned at the pulling head of the

OPGW cable and equipped with two counterweights placed at a distance that is at least 3 meters one from the other. In this way that when one counterweight goes through the pulley the other is operative.

Another anti-twisting device is installed at the end of the OPGW cable just before it leaves the tensioner.

The weight of the anti-twisting devices has to be high enough to prevent OPGW cable rotation. The minimum values recommended for each counterweight are as follows:

- Spans 300 m 12 kg

- Spans 300 m - 700 m 15 kg

- Spans 700 m 20 kg

For Installation length longer than 4000 metres these values should be increased by 5 kg.

After the counterweights have been installed, they should not be removed until the cable is secure and cannot rotate.

Special precaution must be taken so that the cable does not rotate inside the counterweights, due to unsuitable cable dimensions or incorrect tightening.

Auxiliary components

The swivel is specifically designed for OPGW cables. They are of the suitable size for the cable to beinstalled and in optimum condition for use

The pulling grip for OPGW cable stringing must be at least 1.5 metres long and specifically designed for stringing OPGW cables. Moreover, it should be of the suitable dimensions and in optimum condition for use.

The clamps used during stringing operations have to be specifically designed for OPGW cables and must be suitable for the OPGW cable diameter.

If preformed fittings are used, these should be specifically designed for the OPGW cable to be installed. The diameter as well as the length and material of these components must be suitable for the OPGW cable.

The torque wrenches used must be reliable and calibrated on a regular basis. If a fall or accidental damage occurs, the calibration must be verified.

Pulling rope

The pulling rope has to be specifically designed for cable stringing. As stringing is performed on a power line that is out of service we recommend the rope to be a metallic one. The minimum breaking load must be 5000 kg. This value can be higher depending upon the OPGW cable mechanical characteristics and at least equal to 2.5 times the maximum stringing load. If an old earth cable must be used as a pulling rope, ensure that it is not damaged and that its weight is lower than the OPGW cable one that is going to be installed. The pulling cable must be joined to the optical cable by a swivel and a pulling grip. The swivel is necessary to prevent any twisting of the cable when stringing is performed. As a rule, one drum at a time of OPGW cable is installed.

Installation of OPGW

Important factors to be taken into account during stringing

Basic controls

Strict controls must be established during installation to ensure that it is performed correctly, without excess tension, twist of the OPGW, unsuitable compression, regulating a correct sagging. Neither the fibres nor the tube will be damaged.

The tensioner and the puller should be placed at a distance from the first tower pulley which is equivalent to at least twice the height of the pulley.

Intermediate control points should be established, with the necessary precautions that are required at critical points during installation (beginning/end of drum, angles, etc.).

During installation, the OPGW cable should not strike nor graze any objects other than the pulleys. No obstacles must prevent the pulleys from rotating in the correct way.

The minimum bending radius must be controlled during all installation operations.

Ensure that the metal part of the pulleys do not make contact with the cable to prevent it from being  damaged.

Stringing speed

The maximum permissible stringing speed is 40 metres per minute. It always depends on the stringing conditions and must be reduced to avoid damages to the optical fibres, the tube and the OPGW cable.

Pulling tension

The recommended pulling tension shall be lower than 1.5 times the weight (kg) of 1 km OPGW cable length.

In case that higher pulling tensions are required, further information should be asked to ZHC supervisor in order to know the maximum permissible pulling tension for such particular installation.

Minimum bending radius

The minimum bending radius is as follows:

- on tensioner reels 40 times the cable diameter

- during installation 400 mm

- after installation 20 times the cable diameter

Communications during stringing

The personnel located at the puller, the tensioner, the pulley crossings and the cable ends are in communication at all times by communication system.

Sagging of the cable

Generally, the methods used to obtain the correct sag values of the OPGW cables are the same used for conventional ground wire cables. The specific recommendations are as follows:

Pulling is performed by a preformed fitting or tension clamp (in intermediate spans) or with the pull jacket at the end.

Sagging of the cable and fittings installation are always performed after stringing. At this time, the attachment fittings are also installed to prevent damage to the OPGW cable.

The installer is responsible for any damage to the OPGW cable that may occur due to failure cause by incorrect application of the previous points.

If the tension and sags are different from the expected values, the stringing or sagging should be halted.

The Zhongtian Hitachi supervisor and the project leader will be consulted in order to safely continue the installation operations.

Installation of fittings and accessories

The fittings: tension clamps, suspensions, earthing clamps, dampers, etc. should be installed in accordance with the manufacturer’s instructions and using the appropriate tools.(see part 5)

Personnel training

All personnel who participate in the installation of the OPGW cable should be informed of handling problems and installation procedures for the OPGW cable.

Fiber Optic Communication Lines for OHTL

Nowadays fiber optic cables (FOC) are widely used for fast-speed communication lines.

For data transmission glass or plastic fibers are used. Laser-type source transmits light waves along the fiber. Fiber optic cables provide high security of transmitted data, wide bandwidth and require little space. May be viewed as physical means of ground communication in future.

In the world there are used six types of cables for OHTL:

OPGW - FOC in ground wire

OPPC - FOC in phase conductor

Wrap GW - FOC wrapped around ground wire

Wrap PC - FOC wrapped around phase conductor

Externally attached FOC

ADSS - All-Dielectric Self-Supporting Cable

For fiber optic communication lines on OHTLs OPGW cable is used most often. In this case FOC has two functions: lightning protection of OHTL and provision of telecommunication.

Usage of FOC on OHTLs eliminates emissions and all other types of pollutions of the environment. It does not require additional natural resources, apart from the territories and air space already occupied by OHTLs.

Brief description of the technology of erection of OPGW used by the JSC "UralElektroSetStroi"

OPGW is erected on the towers of OHTL by means of modern technology of "under the tension" stringing:

Pulleys with pilot line are suspended at the ground wire peaks of the towers of OHTL being erected (at working OHTLs the existing ground wire may serve as pilot line). Special antitwisting braided rope or nylon rope is used as pilot line for stringing OPGW.

On both sides of the section being strung one puller and one tensioner machines by "Tesmec" with built-in dynamometers are placed.

Before stringing the pilot line is connected with the OPGW with swivel joint and sock joint. For prevention of OPGW twisting during stringing operations counterweights are used at the end of pilot line.

the stringing of the OPGW along the section is performed with the help of puller machine which spools the pilot line. Speed and tension of stringing are chosen in accordance with OPGW characteristics, properties of the OHTL and project requirements. The tensioner machine governs the working tension to provide constant sagging force.

After stringing of the section, OPGW is fixed with the tension clamp at the tower from the tensioner side. Free ends of the OPGW at each side of the section are left of sufficient length for welding the optic fibers in the connector on the ground.

After clamping of the OPGW at the tensioner side it is sagged and clamped with the tension clamp at the puller side of the section. Then it is transferred from pulleys to the suspension clamps on suspension towers.

Connection of OPGW is performed in specialized mobile laboratory (mobile laboratory for erection and testing MLET). Complete connectors are fixed to the towers.

What is OPGW?

An optical ground wire (also known as an OPGW or, in the IEEE standard, an optical fiber composite overhead ground wire) is a type of cable that is used in the construction of electric power transmission and distribution lines. Such cable combines the functions of grounding and communications. An OPGW cable contains a tubular structure with one or more optical fibers in it, surrounded by layers of steel and aluminum wire. The OPGW cable is run between the tops of high-voltage electricity pylons. The conductive part of the cable serves to bond adjacent towers to earth ground, and shields the high-voltage conductors from lightning strikes. The optical fibers within the cable can be used for high-speed transmission of data, either for the electrical utility's own purposes of protection and control of the transmission line, for the utility's own voice and data communication, or may be leased or sold to third parties to serve as a high-speed fiber interconnection between cities.

The optical fiber itself is an insulator and is immune to power transmission line and lightning induction, external electrical noise and cross-talk. Typically OPGW cables contain single-mode optical fibers with low transmission loss, allowing long distance transmission at high speeds. The outer appearance of OPGW is similar to ACSR cable usually used for shield wires.

OPGW fiber optic cable manufacturer introduce OPGW cable

Optical fiber applies the refractive index difference between the core material and its cladding material to accomplish light transmission along optical fiber, which is a major revolution in the history of communication. Fiber optic light weight, small volume, has been widely used in the power system in the substation and dispatching between transport dispatching telephone, remote signal, relay protection, television images of information. In order to improve the stability and reliability of optical fiber and cable, the cable and wire, overhead ground wire and electric cable are developed. OPGW fiber optic cable as a result of metal wire wrapped, so that the cable is more reliable, stable and strong, due to the overhead ground wire and cable composite as one, compared with the use of other means of cable, both to shorten the construction period and save construction costs. In addition, if the OPGW, which is made of aluminum or aluminum alloy wire, is equivalent to a good conductor, can be received to reduce the electric current, reduce the power frequency overvoltage, improve the power line interference and the risk of the communication lines, and other benefits.

Several Different Style of OPGW

Several different styles of OPGW are made. In one type, between 8 and 48 glass optical fibers are placed in a plastic tube. The tube is inserted into a stainless steel, aluminum, or aluminum-coated steel tube, with some slack length of fiber allowed to prevent strain on the glass fibers. The buffer tubes are filled with grease to protect the fiber unit from water and to protect the steel tube from corrosion, the interstices of the cable are filled with grease. The tube is stranded into the cable with aluminum, aluminium alloy or steel strands, similar to an ACSR cable. The steel strands provide strength, and the aluminum strands provide electrical conductivity. For very large fiber counts, up to 144 fibers in one cable, multiple tubes are used.

In other types, an aluminum rod has several spiral grooves around the outside, in which fibers in buffer tubes are laid. The fiber unit is covered with a plastic or steel tape, and the whole surrounded with aluminum and steel strands.

Individual fibers may be in "loose buffer" tubes, where the inside diameter of the tube is greater than the fiber outside diameter, or may be "tight buffered" where the plastic buffer is coated directly on to the glass. Fibers for OPGW are single-mode type

OPGW cable installation guide--Part 1(handling)

Visual inspection  After the delivery of ptical ground wire (hereinafter referred to as OPGW cable), deal with cable appearance inspection, to ensure that it is not damaged in transit. Confirm information on the nameplate of the cable drum, such as drum number, length and diameter of the cable and other details, to make sure the delivered materials are consistant with the orders.

The transportation cable drum should be placed vertically, not permitted to be placed horizontally and piled up. Forklift should handle the cable drum from the side face, and it is definitely prohibited to roll cable drum using the forklift. If crane is applied to handle cable drum, a strong steel axle shaft hole should be used to prevent the chain from destroying cable drum. Every time only one drum should be lifted. If crane is not available, steel sleepers shall be used to hold the rim of the drum to help roll it down slowly. It is not allowed to roll down or drag down the cable drum directly from the vehicle. The OPGW cable drum should be rolled following the rotating direction arrow marked on the drum, Fiber optic cable outlet direction and its opposite. The storage temperature should be controlled in the range of +60oC ~ -40 oC. If the cable drum should be stored for a long period of time before the installation starts, it should be stored in the indoor room to protect the fiber optic cable and cable drum.

Optical ground wire(OPGW)

Introduction

The OPGW cable ( short for optical ground wire or, in the IEEE standard, an optical fiber composite overhead ground wire) is a type of cable that is used in the construction of electric power transmission and distribution lines. Such cable combines the functions of grounding and communications. An OPGW cable contains a tubular structure with one or more optical fibers in it, surrounded by layers of steel and aluminum wire. The OPGW cable is run between the tops of high-voltage electricity pylons. The conductive part of the cable serves to bond adjacent towers to earth ground, and shields the high-voltage conductors from lightning strikes. The optical fibers within the cable can be used for high-speed transmission of data, either for the electrical utility's own purposes of protection and control of the transmission line, for the utility's own voice and data communication, or may be leased or sold to third parties to serve as a high-speed fiber interconnection between cities.

The optical fiber itself is an insulator and is immune to power transmission line and lightning induction, external electrical noise and cross-talk. Typically OPGW cables contain single-mode optical fibers with low transmission loss, allowing long distance transmission at high speeds. The outer appearance of OPGW is similar to ACSR cable usually used for shield wires

An optical ground wire (also known as an OPGW or, in the IEEE standard, an optical fiber composite overhead ground wire) is a type of cable that is used in the construction of electric power transmission and distribution lines. Such cable combines the functions of grounding and communications. An OPGW cable contains a tubular structure with one or more optical fibers in it, surrounded by layers of steel and aluminum wire. The OPGW cable is run between the tops of high-voltage electricity pylons. The conductive part of the cable serves to bond adjacent towers to earth ground, and shields the high-voltage conductors from lightning strikes. The optical fibers within the cable can be used for high-speed transmission of data, either for the electrical utility's own purposes of protection and control of the transmission line, for the utility's own voice and data communication, or may be leased or sold to third parties to serve as a high-speed fiber interconnection between cities.[1]

The optical fiber itself is an insulator and is immune to power transmission line and lightning induction, external electrical noise and cross-talk. Typically OPGW cables contain single-mode optical fibers with low transmission loss, allowing long distance transmission at high speeds. The outer appearance of OPGW is similar to ACSR cable usually used for shield wires

History

An OPGW cable was patented by BICC in 1977 and installation of optical ground wires became widespread starting in the 1980s. In the peak year of 2000, around 60,000 km of OPGW was installed world-wide. Asia, especially China, has become the largest regional market for OPGW used in transmission-line construction.

Construction

Several different styles of OPGW are made. In one type, between 8 and 48 glass optical fibers are placed in a plastic tube. The tube is inserted into a stainless steel, aluminum, or aluminum-coated steel tube, with some slack length of fiber allowed to prevent strain on the glass fibers. The buffer tubes are filled with grease to protect the fiber unit from water ingress and to protect the steel tube from corrosion, the interstices of the cable are filled with grease. The tube is stranded into the cable with aluminum, aluminium alloy or steel strands, similar to an ACSR cable. The steel strands provide strength, and the aluminum strands provide electrical conductivity. For very large fiber counts, up to 144 fibers in one cable, multiple tubes are used.

In other types, an aluminum rod has several spiral grooves around the outside, in which fibers in buffer tubes are laid. The fiber unit is covered with a plastic or steel tape, and the whole surrounded with aluminum and steel strands.

Individual fibers may be in "loose buffer" tubes, where the inside diameter of the tube is greater than the fiber outside diameter, or may be "tight buffered" where the plastic buffer is coated directly on to the glass. Fibers for OPGW are single-mode type.

Comparison with other methods

Optical fibers are used by utilities as an alternative to private point to point microwave systems, power line carrier or communication circuits on metallic cables.

OPGW as a communication medium has some advantages over buried optical fiber cable. Installation cost per kilometre is lower than a buried cable. Effectively, the optical circuits are protected from accidental contact by the high voltage cables below (and by the elevation of the OPGW from ground). A communications circuit carried by an overhead OPGW cable is unlikely to be damaged by excavation work, road repairs or installation of buried pipelines. Since the overall dimensions and weight of an OPGW is similar to the regular grounding wire, the towers supporting the line do not experience extra loading due to cable weight, wind and ice loads.

An alternative to OPGW is use of the power cables to support a separately-installed fiber bundle. Other alternatives include fiber-bearing composite power conductors (OPCC), wrapped fibre optic cable (SkyWrap or OPAC), or using transmission towers to support a separate All-Dielectric Self-Supporting fiber cable with no conductive elements.

Application

A utility may install more fibers than it needs for its internal communications both to allow for future needs and also to lease or sell to telecommunications companies. Rental fees for these "dark fibers" (spares) can provide a valuable source of revenue for the electrical utility. However, when rights-of-way for a transmission line have been expropriated from landowners, occasionally utilities have been restricted from such leasing agreements on the basis that the original right of way was only granted for electric power transmission.

Lower-voltage distribution lines may also carry OPGW wires for bonding and communications; however, utilities may also install all-dielectric self-supporting (ADSS) cables on distribution pole lines. These cables are somewhat similar to those used for telephone and cable television distribution.

While OPGW is easily installed in new construction, electrical utilities find the increased capacity of fiber to be so useful that techniques have been worked out for replacement of ground wires with OPGW on energized lines. Live-line working techniques are used to re-strand the towers with OPGW replacing the all-metal type of overhead shield wires.

Installation

Installation of OPGW requires some additional planning because it is impractical to splice an OPGW cable in mid-span; the lengths of cable purchased must be coordinated with the spans between towers to prevent waste. Where fibers must be joined between lengths, a weatherproof splice box is installed on a tower; a similar box is used to transition from the OPGW to an outside plant fiber-only cable to connect the fibers to terminal equipment.