400kv 2 x 1000mw submarine cable crossing...
TRANSCRIPT
400KV – 2 X 1000MW SUBMARINE CABLE CROSSING OF THE DARDANELLES STRAIT IN TURKEY
GÜLNAZİ YÜCE
Turkish Electricity Transmission
Corporation - TEIAS
Turkey
CELALETTİN ULUBALCI
Turkish Electricity Transmission
Corporation -TEIAS
Turkey
SUMMARY
The article outlines and describes the planning, design, installation and commissioning of
the double circuit 400 kV, 2x1000MW XLPE insulated and copper armoured submarine cable
crossing of the Dardanelles Strait in Turkey.
TEİAŞ has planned submarine cable projects considering to;
increase the demand and security of our electricity supply system
complete The Marmara ring network via the Western corridor (Trakya)
include the power plants located in the southern Marmara Sea
provide alternative connections to İstanbul and around
This 400 kV Lapseki- Sütlüce Submarine Cable Connection; together with the connecting
OHL electricity produced by the power plants the south of Marmara Sea shall be transferred
to Istanbul region.
The construction of the cable system and the associated 400 kV OHL TLs have been
economically justified for the transmission to Istanbul.
For these purposes; TEIAS has planned two Submarine Cable Projects which are 400 kV,
Lapseki 1 -Sütlüce 1 and 400 kV, Lapseki 2 -Sütlüce 2.
TEIAS has planned&designed the system, carried out the Dardanelles crossing site
selection, carried out submarine cable route survey with service procurement method and
prepared technical specification.
Lapseki 1 - Sütlüce 1 power transmission system was commissioned in April 2015 (6 XLPE
insulated cables + 1 spare cable). This project is one of the very few 400 kV submarine ones
with extruded insulation worldwide. Lapseki 2 - Sütlüce 2 power transmission system is 2nd
similar adjacent 2x1,000 MW – 400 kV is under construction at the time of writing.
KEYWORDS
Submarine cable, Grid Planning, Submarine Cable Design, Laying, Installation and Protection
2-03
SEERC First South East European Regional CIGRÉ Conference, Portoroz 2016
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1. INTRODUCTION
The Turkish Power System has undergone rapid development for several decades driven
by mass development of the Industry.
Figure 1
In Turkish Transmision Power Network; end of 2015 There are;
- 18.400 km 400 kV Overhead Lines
- 37.800 km 170 kV Overhead Lines
- 84,5 km 220 kV Overhead Lines (Georgia, Armenıa)
- 5010 km 66 kV Overhead Lines
- 250 km 170 kV XLPE Insulated Underground Power Cable Connection
- 65 km 400 kV XLPE Insulated Underground Power Cable Connection
The summer peak power demand has been 43,300MW and yearly energy demand 264
TWh. The TPS supplies a population of 75 million in a national territory of 780,000 km2.
The objective of this project is the provide power to megacity Istanbul with min. 14 m
population demanding more than 10.000 MW.
TEIAS activities described in the paper are the following:
Obtainment of the permits from the related Authorities, considering the high
international maritime traffic on the Dardanelles Strait, and the need to cross 7 existing
fibre optic cables laid along the Strait. The consequentially applied protection against
cable damages from boat anchors and fishing trawlers are reported in the paper.
Avoidance of interference with other planned infrastructures, in particular the planned
bridge across the Strait in close proximity of the cable route.
The technical specification for the turn-key design, fabrication, testing, installation and
commissioning of the submarine cables and of the cable – OHL transition stations.
Technical Study for integration of submarine link to the National Network.
The cable differential protection installed in the transition OHL – cable stations at the
two sea shores, which in case of a cable fault ensures the fast transfer tripping of the
400kV circuit breakers at the ends of the OHL sections, via optical ground wires
(OPGWs) and also block the single-pole reclosure.
Prysmian has performed with a turnkey contract the design of the cable system,
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manufacturing, testing, laying in sea bottom, protection against external damages and
commissioning. The marine survey of the cable route has been performed by a Turkish
company before the tendering stage and repeated again in details by Prysmian before cable
laying.
2. PLANNING OF THE SUBMARINE CABLE CROSSING
400 kV Lapseki 1 – Sütlüce 1 Submarine Cable Project’s main features as following.
Power & Voltage : 2000MW, 400KV AC
Routh Lenght : 3,9 km at Sea, 0,75 km at land
Cable amount : 2 circuit, 6 phase + 1 spare phase
Submarine : 27,3km,
Underground : 5,25km,
Cable Cross Sections
Submarine Cable : 1600mm2
Underground Cable : 2000mm2
Cable Type : XLPE, Cu
400 kV Lapseki 2 – Sütlüce 2 Submarine Cable Project’s main features as following.
Power & Voltage : 2000MW, 400KV AC
Routh Lenght : 4,1 km at Sea, 0,25 km at land
Cable amount : 2 circuit, 6 phase
Submarine : 24,6km,
Underground : 1,5km,
Cable Cross Sections
Submarine Cable : 1600mm2
Underground Cable : 2000mm2
Cable Type : XLPE, Cu
Since it was not possible to build OHL due to heavy population of the shore areas and busy
ferry and ship traffic, the shortest feasible route was chosen for the submarine crossing with
approximate distance of 3,6 kms. The max. water depth is 98 mts and the cables were spaced
by 75 mts to 250 mts. The primary burial method was by Jetting with the target depth of 1,5
mts.
The submarine crossing survey has been performed by an ad hoc equipped Turkish vessel
on a swath of ~1500 m. Scope of work was: water depth; seabed morphology and geology;
cable burial assessment; sea bottom soil sampling; landing and inshore water survey. The
survey has been checked and extended by the project turnkey contractor during
implementation, and showed favourable conditions for EHV cable lying: stable sea bottom
with regular profile and moderate water stream; feasibility of cable burial at 1.5 m by water
jetting almost on the whole crossing routes; absence of obstacles.
There are along the Dardanelles Strait 4 fibre optic telecommunication cables laid on sea
bottom, which had to be over-crossed by all the 400 kV cables. Agreements have been
reached with the owners of the fibre optic cables on the crossing procedures and cable
protections. Information thereof are provided in section 3.2.
Permissions have been requested and obtained from 15 State, Provincial and Municipal
Entities, including the Energy Market Regulation Authority, 5 Ministries, 4 General
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Directorates, 3 Provincial Directorates and 2 Municipalities.
The specified main technical characteristics of the submarine and land 400 kV cables and
of the fibre optic cables are reported in section 3.1.
The single line diagram of the OHLcable transition switchyards in the European and
Asiatic sides is shown in Figure 2 and Figure 3. Each transition bay includes: a motor
operated disconnecting switch: earthing switches on the OHL and cable sides; current
transformers for the supply of the dedicated differential protection of the cables; surge
arresters; cable terminals.
Figure 2 Single-line diagram of the Southern Marmara Sea 400 kV network
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4.6 kmLapseki Sutluce
4.6 km
to Gelibolu(15 km)
to Bekirli(36 km)
disconnecting switch
current transformer
earthingswitch
surgearrester
Figure 3 Single-line diagram of the transition OHL-cable switchyards
The spare cable is laid between the two cable circuits and is terminated to a busbar
tensioned transversally over the 400 kV equipment bays. This layout allows the fast
connection of the spare cable with pre-fabricated down leads for replacing any one of the six
cables.
Each mixed OHLcableOHL is protected at the terminal substations of Bekirli and
Gelibolu by distance teleprotections operated with the directional comparison scheme and by
a differential protection using fibre optic telecommunications (optical ground wires (OPGW)
in the OHL sections). The single-pole high-speed reclosure is applied, as usual in the 400 kV
OHLs in Turkey.
The lead sheets of the submarine cables are specified and designed to carry, in case of
fault, without damage the maximum short circuit current of 50 kArms for no more than 0.4s.
The high-speed reclosure must be blocked in case of a fault on a cable, for not doubling in
close sequence the fault clearing time and because it is an useless stress for equipment. A
dedicated differential protection has therefore been installed for the cables, which sends trip
signals to the line circuit breakers in Gelibolu and Bekirli substations, as well as blocking
signals of the reclosure of the mixed line. This differential protection is supplied by the
current transformers in the transition switchyards and uses the fibre optic cables laid along the
400 kV cables. The auxiliary power is provided by a MV/LV transformer supplied by the
local distribution network, backed by a small diesel generator. A 48 V DC battery and battery
charger have also been installed.
3. CABLE SYSTEM DESIGN, QUALIFICATION, INSTALLATION AND
COMMISSIONING
3.1. Submarine and Land Cables Design and Qualification
The submarine XLPE insulated cables have 1600 mm2 copper conductor cross section
designed to reduce power losses. The conductor design includes an inner aluminium rod and
an outer layer made of compacted copper wires, water blocked by water swelling material.
The metallic screen is made of lead sheath protected by a polyethylene anticorrosion sheath.
The armour is made of one layer of round copper wires providing a sufficiently low resistance
path for the ac current and the necessary mechanical performances.
The land XLPE insulated cables have 2000 mm2 copper conductor cross section with
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milliken design. The metallic screen is made of longitudinally welded aluminium sheath
protected by a polyethylene anticorrosion sheath.
Fibre optic cables with 48 fibres each have been laid. Each fibre optic cable was bundled
with one of the submarine power cable. Optical fibres are single mode type and comply with
ITU-T, Rec.G652-D
Submarine Cable Design
Inner to Out Layers
1 – Central Rod / Aluminum
2 – Conductor / Stranded Copper
3 – Binder / Semi – Conducting Tape
4 – Insulation / XLPE
5 – Insulation Screen / Semi- Conducting Polymer
6 – S.C. Water Barrier / Water Swelling Tapes
7 – Metallic Sheath / Lead Alloy Sheath
8 – Outer Serving / Semi Conductive PE Layer
9 – Bedding / Polypropylene Strings
10 – Armour / Copper Wires
11 – Corrosion Protection / Bitumen Layer
12 – Serving / Polypropylene Strings
• Approx. Overall Diameter : 157 mm
• Approx. Weight in Air : 60 kg/m
• Approx. Weight in Water : 41 kg/m
400 kV, 1x1600 mm2 Cable Construction
VSD-Group
VSD-Group
Conductor - Stranded copper with annealed plain copper wires - With aluminum central rod (in order to reduce conductor loses) - Conductor filled with water blocking medium (to limit water propagation) Semi Conducting Tape - In order to avoid entering the extruded inner semi-conducting screen layer to conductor wires (avoid inter-layer contamination) - Provides mountability Semi Conducting Layer(Inner) - To make smooth interface between conductor and insulation - To avoid space between conductor and insulation layer, prevents partial discharges - To limit radial electrical field on the insulation layer and provide homogeneous distribution - Creates a thermal barrier Insulaton - It is electrically inslulated to condcutor from the outer
layers
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400 kV, 1x1600 mm2 Cable Conductor Construction
VSD-Group
Semi Conducting Layer(Outer)
- To make smooth interface between insulation and outer
metallic layers
- To avoid space between conductor and insulation layer,
prevents partial discharges
- To limit radial electrical field on the insulation layer and
provide homogeneous distribution
- Creates a thermal barrier
Water Swelling Tape
- To provide longitudial water barrier between outer semi-
conducting screen and metallic sheath
Metallic Sheath
- To provide over the cable core as metallic screen and
radial water barrier
Core Jacket
- To protect the metallic sheath against to corrosion
Armour
- Provides mechanical protection against to external
effects
Polypropylene Strings
- Provides mechanical protection
- To provide a degree of abrassion protection and to
reduce cable/skid friction during laying
- Yellow/Black pattern is applied in order to give high
visibility to the cable
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CONSTRUCTIONAL DATA
1 - Mechanical Forces Unit Value
- Maximum straight pull tension kN 160
- Maximum tension on MBR kN 92
- Tensile force during laying (ELECTRA n.171) kN 62
2 – Power Core Thermal Data
- Maximum continuous conductor temperatures (normal service) °C 90
- Maximum continuous conductor temperatures (short circuit) °C 250
- Conductor short circuit current for 1 s kA 230
- Metallic sheath nominal phase-to-ground short circuit current
(for 0.65 s) kA
41.6
- Metallic sheath nominal phase-to-ground short circuit current
(for 0.4 s) kA 52.3
3 – Power Core Electrical Data
- Conductor DC electrical resistance at 20 °C /km 0.0113
- Conductor AC electrical resistance at 90 °C /km 0.0168
- Cable capacitance (nominal) F/km 0.194
- Cable inductance (nominal) mH/km 0.24
400 kV, 1x1600 mm2 Cable Construction
1-Conductor:
Conductors is of a compacted circular design, constructed from annealed plain copper
wires and filled with a water blocking medium to limit water propagation in case of cable
severance. They have a copper nominal cross sectional area of 1600 mm2. In order to reduce
conductor losses the central part of the conductor is made with an aluminium rod.
2-Conductor screen, Insulation and Insulation screen:
The insulation system consists of an inner semi-conducting screen layer, the insulation
compound and an outer semi-conducting extruded insulation screen, extruded in a triple
process in order to avoid inter-layer contamination.
The insulation is composed of XLPE EHV compound.
3-Water swelling tape:
One layer of semi-conducting water-swelling tape is applied between the outer semi-
conducting screen and the metallic sheath as longitudinal water barrier.
4-Metallic sheath:
An extruded lead alloy sheath is provided over the cable core as metallic screen and radial
water barrier.
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5-Core jacket:
An extruded layer of semiconductive polyethylene compound is provided over the lead
alloy sheath, acting as anti-corrosion protection.
6-Armouring:
The “armouring” includes the bedding, the armour and the serving application in one
common process.
A polypropylene string layer or synthetic tapes will be applied over the assembly as
bedding for the armour wires.
One layer of copper armour wires is applied over this bedding.
The application of bitumen is provided over the armour layer as further anti-corrosion
protection and to aid the adhesion of the overall serving.
Two layers of polypropylene strings are applied over the armour as cable serving, to
provide a degree of abrasion protection and to reduce cable/skid friction during lay.
The polypropylene serving is applied with a black and yellow pattern in order to give high
visibility to the cable and enable monitoring of cable horizontal movement by ROV cameras.
Metal Screen Bonding Scheme
Cables metallic screens bonding has been implemented to cope with the existence of a 7th
spare cable in terms of maximum induced voltages and current rating. Submarine cables metal
screens have been earthed at both ends while each of the land cable sections has metal screens
bonded to local earth in one point only with the other side connected to surge arresters. The
metal screens bonding scheme is shown in Figure 4.
The cable system has been qualified according to CIGRE TB 490 and IEC 62067.
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Figure 4 Metal screens bonding scheme representing one cable circuit
3.2. Submarine and Land Cables Installation
Submarine cables have been manufactured and installed without any intermediate joint in
one laying campaign.
Installation was carried out through the Dardanelles Strait by the Giulio Verne cable laying
ship. Maximum spacing between two of the intermediate couples of adjacent submarine
cables reaches 250 m in correspondence to the maximum water depth which is 100 m.
Cables have been protected against external damages by burial in the seabed at the target
depth of 1.5 m in 80 % of total laid length.
The main cable protection methodology used was burial by jetting, using specialized
subsea machines. In short hard soil areas and at crossings with existing telecommunication
cables concrete mattresses have been used to protect 20 % of the cable routes.
In the shallow water sections (up to 10 m water depth) at both ends, characterized by the
presence of Cymodocea prairies, a dredging system run by divers has been used.
Four in service optical submarine cables have been crossed on the Dardanelles Strait. At
Figure 5 System Map of Dardanelles Area
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the crossing locations, “uraduct” plastic shells have been fitted to 400kV submarine cables on
board during the cable laying to provide the physical separation between energy and optical
cables. Post-lay matresses have been installed to cover the crossing area to protect the 400kV
submarine cables. Power cables routes have an angle with the crossed in service cables higher
than 70°. All the seven complete length of submarine cables have been tested in the factory
for 30 minutes at 470 kVrms before armouring and at 440 kVrms after armouring.
The cable system was commissioned in April 2015. After installation the cables have been
tested at 330 kVrms for 60 minutes by means of resonant systems. Testing frequency was 34
Hz with 54 A conductor to screen current. Partial Discharges have also been measured by
means of Pry-cam grids system.
Integrity of PE anticorrosion sheath and Sheath Voltage Limiters (SVLs) have been
verified by a DC test after installation at 10 kV and 15 kV, respectively.
Some pictures of submarine and land cables installation are shown in
Figure 6.
Land cables installed in tunnel (Europe)
Submarine cable laying
OHL Interface center (Asia)
Figure 6 Submarine and land cables installation
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4. SWITCHING AND TEMPORARY OVERVOLTAGE ANALYSIS
A switching and temporary overvoltages analysis with the ATP – EMTP program, jointly
performed by TEIAS and Prysmian, has been necessary because the cable crossings are the
intermediate section of mixed OHL – cable lines, causing a concern on the resonance on
harmonics and some switching operations.
A statistic overvoltage study of hybrid line energization has been carried out with 1000
cases simulated with random timing in circuit breaker poles closure.
Different network configurations have been investigated, including the ones with low short
circuit power.
Maximum calculated switching overvoltage was 759 kVpeak which corresponds to 2.21
p.u. This result is well within tolerable range of the mixed line and associated equipment.
A typical no-load energization case of the 400 kV the mixed OHL – cable line is shown in
Figure 7.
(f ile Kannak_L10pcSA_04_TD01c.pl4; x-v ar t) v :X0349A
0,00 0,05 0,10 0,15 0,20 0,25 0,30[s]-600
-400
-200
0
200
400
600
[kV]
Open-end voltageCircuit breaker current
(f ile Kannak_L10pcSA_04_TD01c.pl4; x-v ar t) c:X0001A-X0345A
0,00 0,05 0,10 0,15 0,20 0,25 0,30[s]-1500
-1000
-500
0
500
1000
1500
[A]
AC AC400 kV
network
EUROPE ASIA
15 km 35 km
Double circuit OHL Double circuit OHL4.0 km
Submarine cables0.7 km
Land cables
Figure 7 Typical no-load energization of the 400 kV the mixed OHL – cable line
5. CONCLUSIONS
400 kV Lapseki-Sütlüce 1 Submarine Cable Project was commissioned in April 2015 and
is one of the very few 400 kV submarine ones with extruded insulation worldwide. This
project is first submarine Cable Project which is connecting Europe and Asia in Turkey.
400 kV Lapeki-Sütlüce 2 Submarine Cable Project is under construction and it will be
commissioned in January 17, 2017. These projects are technical proof that TEİAŞ is ready to
manage similar projects in the future.
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BIBLIOGRAPHY
1. TEIAS Technical Specification of 400 kV Submarine Cable Project
2. IEC 62067: "Power cables with extruded insulation and their accessories for rated
voltages above 150 kV (Um = 170 kV) up to 500 kV (Um = 550 kV) - Test methods and
requirements”, Nov 2011
3. CIGRE TB 490 “Recommendations for testing of long AC submarine cables with extruded
insulation for system volt