2015

Gargi Choudhury

8/29/2015

Cable Landing Station

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Contents 1. Cable Landing Station ........................................................................................................................... 3

1. Various Types of Submarine Cables ..................................................................................................... 4

2. Optical Submarine Cable Laying Procedure ......................................................................................... 6

4. Optical Submarine Cable Burial Method .................................................................................................. 7

5. Optical Submarine Cable Repair Method ............................................................................................... 10

6. Equipment in CLS ................................................................................................................................... 13

1. Power Feeding Equipment (PFE) ................................................................................................... 13

2. Submarine Line Terminal Equipment (SLTE) ................................................................................ 14

3. Optical Distribution Frame (ODF) .................................................................................................. 14

4. Submarine Interface Equipment (SIE) ............................................................................................ 14

5. Submarine Fiber Cables .................................................................................................................. 14

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1. Cable Landing Station

Cable Landing Station is one important component of a submarine cable system which

comprises of Wet Plant and Dry Plant.

The Dry Plant of a submarine cable system is a segment between the beach manhole and the

cable landing station, comprises of land cable, power feeding equipment (PFE) and submarine

line terminal equipment(SLTE), etc. The Wet Plant of a submarine cable system lies between the

beach manholes, consists of submarine cable, repeater/gain equalizer, branching unit. A typical

schematic of a submarine cable system is shown below.

Typical Schematic for a Submarine Cable System

The PFE and the SLTE of a submarine cable system are installed at the cable landing station. In

some cases, the PFE is installed at a cable landing station nearby the cable landing site, while the

SLTE may be installed in another cable landing station much faraway. For example, the terminal

station at Hillsboro for the SLTE of the TPE cable system is about 150 mile away from the cable

landing site at Nedonna Beach.

Multiple submarine cable systems may share the same cable landing stations. The submarine

cable system is connected with the terrestrial network at the cable landing station, through the so

called backhaul system.

The cable landing site is usually carefully chosen to be in areas:

that have little marine traffic to minimise the risk of cables being damaged by ship

anchors and trawler operations;

with gently sloping, sandy or silty sea-floors so that the cable can be buried to minimise

the chance of damage;

without strong currents that would uncover buried cables and potentially move cables.

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Multiple types of submarine cables may be used in a submarine cable system, subject to depth of

the seabed where the cable lies.

1. Various Types of Submarine Cables

There are four types of optical fibers which are used inside the sea. All fibers differ with each

other in just protection and uses in different conditions.

DA stands for Double armored optical fiber. DA is used in shallow water where cable is more

vulnerable for damage by environment or other factors. SA stands for Single armored optical

fiber. SA is used in less vulnerable but dangerous environment. SA has single armored layer

whereas DA has double armored layer around it.

SL Lightweight (LW) Cable

Light weight cable, and is used in deep sea areas of around 1,000m to 8,500m depth.

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Structure of light weight optical submarine cable

The other is an armored cable being attached a steel wire to the light weight cable, and is used in

a shallower area than about 1,000m depth.

Structure of single armored submarine cable

The other two fiber cables are used in deep water where optical fibers are less disturbed or less

vulnerable. LWP stands for Light Weight Protected optical fiber and LW stands for Light

Weight unprotected optical fiber.

The double armored submarine cable is used at the shore-end, terminated at the beach manhole

at the cable landing site, and is interconnected with much lighter land cable going onward to the

cable landing station.

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2. Optical Submarine Cable Laying Procedure

1. Towards the cable landing station A, one end of the cable is paid out by the cable ship and

landed. During this phase, the balloon buoys are attached along the cable to prevent possible

damages to the cable.

Finally, the buoys are detached, allowing the cable to sink to the seabed.

2. The ship lays the cable towards the opposite station B or the designated point in mid-ocean.

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3. At the designated point, the ship connects the cable with the end point of the previously laid

cable from the station B.

4. After the final splice, the cable is released on the seabed.

4. Optical Submarine Cable Burial Method

In the water area shallower than the depth of 1,000 meters, cables are buried under the seabed

mainly by two ways in order to protect them from damages, which might be caused by fishing

activities or anchors of large vessels.

The one is to use the towed type burying machine, PLOW-II, which performs the simultaneous

operation of cable laying and burial.

PLOW-II makes the installation period shorter because of the simultaneous operation of cable

laying and burial, and is suitable for new and long distance operations.

Since PLOW-II is towed by the vessel on the seabed after threading the cable through it, it

cannot be used for the burial operation after laying(burial after laying).

The working area of PLOW-II is limited depending on the seabed form or the slope.

The other is burial by ROV(MARCAS-III, MARCAS-IV).

ROV digs, by blasting waterjet into the seabed, a trench with the targeted burial depth by coming

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and going several times at the same section, and drops the cable into the trench. Because of this

method, the construction efficiency of ROV is not better than PLOW-II. However, ROV has the

capability that it can float and move around on the sea bed, and ROV can work for the carved

cable section which was caused by the final bight release, or in the area where PLOW-II can not

be operated due to severe condition of the seabed.

Example of Cable Searching and Burial after Laying by ROV

1. Launching ROV and Localizing Failure Point

The cable ship arrives at the cable failure point which is estimated by the electrical and optical

measurement from the cable landing station in advance. The ship launches ROV onto the seabed.

The precise cable failure location is specified by using the subsea cameras and cable sensors

system of ROV.

2. Cable Cutting and Cable Recovery

ROV cuts the cable failure section by the manipulator and cutting tool. It attaches the cable

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holding tool(gripper) to either cable end. After connecting the gripper with the rope paid out

from the ship by the manipulator, the cable is recovered onto the ship. The transponder is

installed around the other cable end, and ROV is recovered onto the ship.

3. Buoy Installation, Cable Search and Recovery

The buoy is attached to the cable on the ship, and is released once on the sea. Again, ROV is

launched on the seabed, and searches the cable's other end relying on the transponder previously

installed. By the same procedure as above item 2, the cable is recovered on the ship.

4. Insertion of Spare Cable and Cable Jointing

The recovered cable in above item 3 and the spare cable in the ship are jointed. After the

jointing, the ship approaches to the buoy in the item 3 laying the spare cable, and recovers the

buoy and cable. After jointing the laying spare cable and the recovered cable, the cables are

released to the seabed.

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5. Cable Burial after Laying

The attached spare cable and the exposed cable on the seabed due to the repair work are buried

under the seabed by the waterjet of ROV

5. Optical Submarine Cable Repair Method

There is a case in which an optical fiber cable is cut or damaged due to ocean earthquakes and

fishing gears etc..

In the situation, the cable ship is urgently dispatched to the cable failure site and repairs the

cable.

The cable repair procedure normally consists of the followings:

1) Localization of the cable failure point.

2) Recovery of the failure cable onto the ship

3) Cutting and removal of the cable failure section

4) Jointing of the recovered cable and the spare cable in the cable tank of the ship

5) Confirmation test and reburial of the cable

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Optical Submarine Cable Repair Procedure

1. The distance of the cable failure location from the landing station is estimated by several tests

in advance. The cable ship is navigated to the location by DGPS. At the place, the tool for cable

search and cutting, which is attached to the rope end, is paid out to the sea. By dragging the

grapnel tool on the seabed, the cable is cut.

2. The rope with the grapnel at its end is paid out from the ship, and one end of the cut cable is

caught by the grapnel(Cable Catch), and is recovered to the ship(Cable Recovery). It might take

more than one day to recover the cable from the sea of 8,000m depth. The optical fiber test and

electrical test of its power feed conductor is carried out. If there is still a failure, the cable is

recovered further, the failure section is cut and removed.

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3. At the end of the cable from which the failure section is removed, the waterproof treatment is

carried out. After the attachment of the mooring rope and buoy to it, the cable is once dropped in

the sea. The cable ship moves for searching the other end of the cable, and repeats the same

procedure as above item 2.

4. The optical fiber test and electrical test of its power feed conductor on the recovered cable is

carried out in the same way as above item 2. If there is a failure, the failure section is cut and

removed. The cable is jointed with the spare cable which is stored in the cable tank(normally,

Universal Joint technology is used). The cable ship approaches to the previously installed buoy

together with paying out the spare cable.

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5. Holding the spare cable, the cable ship recovers the cable attached to the buoy again, and

joints it with the opposite end of the spare cable. For the final confirmation, the test is held

between two cable landing stations of the cable. After the confirmation of the communication

normality, the on-board cable is released to the seabed, and the repair work is completed.

6. Equipment in CLS

1. Power Feeding Equipment (PFE)

The power feeding equipment supplies constant DC current to the submarine repeaters. To

improve the reliability of the system power feeding, power feeding equipment sets with the

capability of feeding all of the system voltages requirement are installed at landing station at

both ends of the system. The voltages to be supplied to the submarine repeaters are allocated to

supply the power feeding equipment at both ends. All PFE’s are duplicated, i.e. they consist of

two suites of generator units. In normal operation, the load is shared between them, but if one

unit were to fail the remaining one will take up the load. A suite can be equipped with up to four

generator units, thus providing up to 10 KV.

Figure 2 shows an example of voltage allocation for a case in which power is fed from both

stations. Usually, each of the two landing stations feeds both positive and negative voltage

corresponding to 1/2 of the total system voltage. If a fault occurs in either of the power feeding

equipments, the one at the opposite landing station feeds the total system voltage in order to

enable a constant current supply to the submarine repeaters. This system redundancy is intended

to improve the system reliability.

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2. Submarine Line Terminal Equipment (SLTE)

SLTE is the equipment where the double armored submarine fiber cable ends towards the CLS.

At SLTE optical fiber separates from conductor cable. Conductor cable is connected to PFE.

SLTE comprises of the latest technologies (DWDM, SDH, etc.) depending upon the make and

model. SLTE is the equipment which multiplexes the optical signal. The capacity of the optical

link depend on the capacity of the SLTE.

3. Optical Distribution Frame (ODF)

Optical distribution frame is a fiber optic management unit used to organize the fiber optic cable

connections. The optic distribution frame is usually used indoor and the ODF could be very big

size frame or small size similar like the patch panel boxes. All the testing can be done at ODF so

that no other part of the equipment is disturbed at that time.

4. Submarine Interface Equipment (SIE)

Submarine Interface Equipment is used at the end where optical fiber is connected towards

terrestrial network. In other words SIE is the interface between subsea network and terrestrial

network. One more ODF is used after SIE for easy arrangement of fiber connections at the

equipment and for testing purpose. i

5. Submarine Fiber Cables

The inner most component of the cable are optical fibers, covered by unit fiber structure. The

fiber structure is then wrapped around by strength wires which give strength to sustain from

tension and pressure under the sea. The strength wires are then covered by copper sheath or

copper wires which are used for transmitting electricity for the repeaters and branching unit.

copper wires are then covered by insulation jacket which is then covered by armored protection

layer.

There are four types of optical fibers which are used inside the sea. All fibers differ with each

other in just protection and uses in different conditions.

DA stands for Double armored optical fiber. DA is used in shallow water where cable is more

vulnerable for damage by environment or other factors. SA stands for Single armored optical

fiber. SA is used in less vulnerable but dangerous environment. SA has single armored layer

whereas DA has double armored layer around it.

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The other two fiber cables are used in deep water where optical fibers are less disturbed or less

vulnerable. LWP stands for Light Weight Protected optical fiber and LW stands for Light

Weight unprotected optical fiber.

Structure of Land Cable

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Structure of Single Armored Submarine Cable

i Cable landing station