INTERCONNECTION OF THE AEGEAN ISLANDSTO THE MAINLAND GRID

M. PAPADOPOULOS S. PAPATHANASIOU

National Technical University of Athens (NTUA)

MAIN PROFITS FROM THE POWER SYSTEM INTERCONNECTIONS

• The development of the Power Systems:- From autonomous to interconnecting systems - Better energy source exploitation, especially in case of intermittent

power generation

• Target of the interconnection of the islands today- Replacement of oil expensive products- Increased exploitation of the local RES

• Criteria for the interconnection of the islands- Technical feasibility- Economic viability: comparison of different electrification costs

ELECTRIFICATION OF ISLANDS _1ELECTRIFICATION OF ISLANDS _1

1. Autonomous development-RES are restricted to 10-15% of the consumption

2. Interconnection by two Submarine Cables (SC)-Security of supply is satisfied (“N-1 Criterion”)-Elimination of conventional Local Power Stations (LPS) is permitted-RES can reach twice the SC capacity(SC capacity may cover the load for 25 years after)

ELECTRIFICATION OF ISLANDS _2ELECTRIFICATION OF ISLANDS _2

3. Interconnection by one Submarine Cable (SC)- The capacity of the SC is selected to optimize the system, taking into account the RES capacity of the island -The capacity of the conventional Local Power Station (LPS), which is maintained, is equal to the maximum annual power demand-The base load is covered by the interconnection (IPS) and the rest may be covered by LPS

CAPACITY OF THE INTERCONNECTIONS

ΦορτίοΑ/ΓΑΣΠ

LoadWind

Power station

Load with Reserve

Wind power without reserveISLAND

MAIN LAND SYSTEM OR LARGE ISLAND

- Submarine cable sized for 20-25 years operation - If P0 the maximum demand of the island at t=0 and

5% is the rate of the load growth, than the demand at the end of the period t=23 will be:

P23=P0(1+0,05)23=3,0P0 - Consequently: One able capacity, equal to: 3,0Ρ0

Interconnection capacity: 2x3,0Ρ0=6,0Ρ0

- In case of Local Power Station: At t=0 ……… 0,30Ρ0t=23 0,3x3,0=0,90P0

INTERCONNECTIONS IN OPERATION

• HIGH VOLTAGEAll the Ionian Islands:

- Corfu (66 and 150kV) - Mainland - Lefkas – Kefalonia – Zakynthos – Mainland- Rio – Andirio and Evia- Greece – Italy (Conventional DC)

• MEDIUM VOLTAGEAbout 65 interconnections, to mainland and between islands

- 1960 – 1970 13 installations- 1971 - 1980 22- 1981 - 1990 20- 1991 – today 10

RECENT DEVELOPMENT OF THE SUBMARINE INTERCONNECTION TECHNOLOGIES

Pros and Cons of AC and DC Systems

• Extended use of plastic insulation HV cables, AC and DC

• Development of new type AC/DC or DC/AC converters “Voltage Source” instead of “Line commutated”

• Higher lengths can be obtained by DC transmissionOverhead HV lines on islands can be avoided

• Higher control capabilities may be obtained by DC transmission due to the flexibility of the converters

Very important in case of intermittent power generation

• AC systems remain usually more economic for distances up to about 60-70km

Extruded Insulation Cables

SUBMARINE CABLES SUBMARINE CABLES ((SCSC))

INTERCONNECTION STUDIES IN THE PLANNING STAGE

1. For CRETE ISLAND, 1988, by PPC – conventional technology

2. For CYKLADES ISLANDS, 1989 by PPC, partially constructed2004 by NTUA/RAE, Preliminary proposal2006 by, PPC, DESMIE, NTUA/RAE: Final planning

3. 2007-8, feasibility study for the interconnection of the most of the Aegean islands, in order to reduce the use of oil power products, by NTUA/RAE, including:- Extension of the Cyclades interconnection- Interconnection of the North Aegean islands to the mainland grid- Interconnection of Crete to the mainland system- Interconnection of the Dodecanese islands

INTERCONNECTION OF CYCLADES ISLANDS APPLING THE USUAL PRACTICE

PROPOSED INTERCONNECTION OF CYCLADES

37.0 km

54.0 km

16.0 km

36.0 km

32.0 km

15.0 km

23.0 km15.0 km

HVDC~400 MW

~95 km

~50 km

~50 km

4 single-core cables

Ζεύξη-Υ/Σ

Υπάρχον δίκτυο 150kV

Επέκταση καλωδίων kVΓεωθερμικός Μήλου

Καλώδια 20kVΥπάρχον καλώδιο 66kV

INTERCONNECTION OF ALL AEGEAN ISLANDS BY GROUPS

INTERCONNECTION OF THE NORTH ISLANDS (DC and AC)

ONE LINE DIAGRAMME (DC and AC cables)

ΕΥΒΟΙΑ (Αλιβέρι)150kV

20 km υπόγειο καλώδιο 1000 mm2

Οξύλιθος

50 km υποβρύχιο καλώδιο(2+1)x280 MVA

ΣΚΥΡΟΣ

80 km υποβρύχιο καλώδιο

(2+1)x280 MVA

100 MVAR

ΨΑΡΑ

40 km υποβρύχιο καλώδιο

2x400mm2

2x140 MVA

ΧΙΟΣ

80 km υποβρύχιο καλώδιο

2x630mm2

2x280 MVA

ΛΕΣΒΟΣ

ΦΟΡΤΙΑ ΝΗΣΙΩΝ (MW)Μέγιστο 2010 2035Χίος 53 132Λέσβος 78 181Ψαρά - -Σκύρος 5 13(Ελάχιστο = 20% Μεγίστου)150 MVAR

40 MVAR60 MVAR

Α/Γ ΝΗΣΙΩΝ (MW)2010 2035

Xίος-Ψαρά 50 130Λέσβος 75 180Ικαρία 15 30Σάμος 50 110

-100/+100 MVAR

SVC

Προσθήκη το 2020

R (Ω/km) X (Ω/km) C (nF/km) Imax (A)ΥΠΟΒΡΥΧΙΑ ΚΑΛΩΔΙΑ 390 MVA (350 MW) 0,04 0,1 240 1500280 MVA (250 MW) 0,06 0,125 180 1078140 ΜVΑ 0,08 0,14 140 539

ONE LINE DIAGRAMMEOnly AC cables

SOME CHARACTERISTIC RESULTSInstalled Wind Power (WP): 25% or 100% of the year maximum (Pm)

TOTAL ELECTRIFICATION COST OF THE ISLAND (in per cent)Without WP With WP

Autonomous operation (WP=0,25Pm) 100 97Interconnection to grid (WP=1,0Pm) 78 75

WIND ENERGY CONTRIBUTIONEnergy Conventional Wind

Autonomous operation 100% 89% 11%Interconnection 100% 46% 54%

INTERCONNECTION OF CREETE

INTERCONNECTION OF DODECANESES

150 kV ΑC submarine cable 2x280 MVA

INTERCONNECTION OF CRETE AND DODECANESE TO THE MAINLAND GRID

The conventional power stations on Crete and Rodos are maintained

SUMMARY AND CONCLUSIONS

• TECHNICALAll Aegean islands seems to be technically possible to be interconnected to the mainland grid applying new technologies

• ECONOMICThe economic viability of the required interconnection investments is clearly feasible in some cases, or marginal in the rest, taking into account only the reduced electrification cost, compared to the one obtained by the autonomous power station using oil products

• RENEWABLE ENERGY SOURCE DEVELOPMENTConsidering that in the most of the Aegean islands, wind power at least equal to the maximum demand of the island can be installed without inadmissible environmental impact, it is clear that the existing excellent wind capacity can be exploited, covering a large part of the island needs.Further development can be obtained by the development of off-shore wind parks or on uninhabited roc-islands.

ROCK ISLANDS