First South East European Regional CIGRÉ Conference, Portoroz KV 2 X 1000MW SUBMARINE CABLE CROSSING OF THE DARDANELLES STRAIT IN TURKEY

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First South East European Regional CIGRÉ Conference, Portoroz 2016 SEERC 2-03 400KV 2 X 1000MW SUBMARINE CABLE CROSSING OF THE DARDANELLES STRAIT IN TURKEY GÜLNAZİ YÜCE Turkish Electricity

1 First South East European Regional CIGRÉ Conference, Portoroz 2016 SEERC KV 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 gulnazi.yuce@teias.gov.tr

2 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; km 400 kv Overhead Lines km 170 kv Overhead Lines - 84,5 km 220 kv Overhead Lines (Georgia, Armenıa) km 66 kv Overhead Lines 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 km 2. The objective of this project is the provide power to megacity Istanbul with min. 14 m population demanding more than 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, 1

3 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 : 1600mm 2 Underground Cable : 2000mm 2 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 : 1600mm 2 Underground Cable : 2000mm 2 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 2

4 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 OHL cable 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 3

5 Lapseki 4.6 km Sutluce to Bekirli (36 km) 4.6 km to Gelibolu (15 km) disconnecting switch earthing switch current transformer surge arrester 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 OHL cable OHL 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 mm 2 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 mm 2 copper conductor cross section with 4

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.

6 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 VSD-Group Approx. Overall Diameter : 157 mm Approx. Weight in Air : 60 kg/m Approx. Weight in Water : 41 kg/m 400 kv, 1x1600 mm 2 Cable Construction 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 semiconducting screen layer to conductor wires (avoid interlayer contamination) - Provides mountability VSD-Group 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 5

400 kv, 1x1600 mm 2 Cable Conductor Construction Semi Conducting

outer metallic layers - To avoid space between conductor and

electrical field on the insulation layer and provide homogeneous

provide longitudial water barrier between outer semiconducting

over the cable core as metallic screen and radial water barrier

Armour - Provides mechanical protection against to external effects

a degree of abrassion protection and to reduce cable/skid friction

7 400 kv, 1x1600 mm 2 Cable Conductor Construction 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 semiconducting screen and metallic sheath VSD-Group 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 6

8 CONSTRUCTIONAL DATA 1 - Mechanical Forces Unit Value - Maximum straight pull tension kn 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 Conductor short circuit current for 1 s ka Metallic sheath nominal phase-to-ground short circuit current (for 0.65 s) ka Metallic sheath nominal phase-to-ground short circuit current (for 0.4 s) ka Power Core Electrical Data - Conductor DC electrical resistance at 20 C /km Conductor AC electrical resistance at 90 C /km Cable capacitance (nominal) F/km Cable inductance (nominal) mh/km kv, 1x1600 mm 2 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 mm 2. 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 semiconducting 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. 7

9 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 7 th 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

10 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. Figure 5 System Map of Dardanelles Area 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 9

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.

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.

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.

11 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 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) OHL Interface center (Asia) Submarine cable laying Figure 6 Submarine and land cables installation 10

12 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. EUROPE ASIA 400 kv network AC Double circuit OHL Land cables Submarine cables Double circuit OHL 15 km 0.7 km 4.0 km 35 km AC Circuit breaker current Open-end voltage [A] [kv] ,00 0,05 0,10 0,15 0,20 0,25 [s] 0,30 (f ile Kannak_L10pcSA_04_TD01c.pl4; x-v ar t) c:x0001a-x0345a ,00 0,05 0,10 0,15 0,20 0,25 [s] 0,30 (f ile Kannak_L10pcSA_04_TD01c.pl4; x-v ar t) v :X0349A 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, These projects are technical proof that TEİAŞ is ready to manage similar projects in the future. 11

13 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 CIGRE TB 490 Recommendations for testing of long AC submarine cables with extruded insulation for system volt 12

OFFSHORE WIND FEASIBILITY STUDY APPENDICES Appendix C.2 Subsea Cable Data Sheets

OFFSHORE WIND FEASIBILITY STUDY APPENDICES 10-7 10.3.2 Appendix C.2 Subsea Cable Data Sheets Design data for TFVA 36 kv 3x1x240 mm 2 KQ Metallic Laying up Inner sheath Bedding Armor Diameter of conductor