16.7 Hz - The Missing Link?

16.7 Hz - The Missing Link? Prof. István Erlich University of Duisburg-Essen Bremen, January 2014

Current Concept 2

Current Concept Offshore Onshore WP1 33 kv AC, 50 Hz WP-Plattform WP-Plattform 150 kv AC, 50 Hz HVDC-Plattform 50 Hz DC 1000 MW 300 kv DC DC 50 Hz 400 kv AC WP2 Separate platform for each wind farm plus one additional HVDC Platform, both offshore 150 kv AC for wind farm connections voltage too low for considerable power transmission Converter technique is located offshore reliability concerns 3

Alternative Concept 16⅔ Hz Offshore Onshore WP-Plattform WP1 500-600 MW 16 2/3 Hz 50 Hz 400 kv AC 33 kv AC, 16 2/3 Hz WP2 WP3 WP-Plattform WP-Plattform 220 kv AC, 16 2/3 Hz 220 kv AC, 16 2/3 Hz 500-600 MW 500-600 MW 16 2/3 Hz 50 Hz 16 2/3 Hz 50 Hz 400 kv AC 400 kv AC 220 kv AC cable for power transmission to onshore 220 kv AC suitable for a mashed North Sea grid Separate platform for each wind farm but no need for HVDC platform No converter offshore 4

Cable Losses at Low Frequency Losses at I n_50hz =2483 A 70 W/m 60 50 40 P c ~ P s P d P 30 20 P c 10 0 50 Hz 16,7 Hz 1 Hz 5

Alternative Concept 16⅔ Hz Converter onshore: Converter is not separated in offshore and onshore but back-to-back Not affected by sea climate Maintenance fast and to lower costs possible Mashed offshore grid easy to establish Quelle: Siemens 6

Wind Turbines Full rated WT Type 4 DFIG Type 3 Speed control Pitch and Power GB CR Speed control Pitch and Power GB ASG P ref SG/ ASG P ref MSC control P Q,cos,VG Thru fast current control MSC C MSC control VT MSC C CH LSC control U DC (Q,cos,V G ) LSC CH L LSC V G LSC control P VT U DC Q,cos,VG Thru fast current control L VG Change to 16⅔ Hz is difficult, 16⅔ Hz DFIG is too heavy Change to 16⅔ Hz is easily accomplished 7

16⅔ - 50 Hz Converter Already developed for single phase Example Datteln 50 Hz side: 4x103 MW With overload: 138 MW Nominal: 413 MW 103 (138) MW unit 8

245 kv Cable 245 kv Submarine Cable 1200 mm 2 Cu/RM 245 kv three phase XLPE submarine cable up to 2000 mm 2 Al and 1600 mm 2 Cu are available or can be built 9

245 kv Cable 245 kv Submarine Cables 2000 mm 2 Al/RE 1200 mm2 Cu/RM Parameter 50 Hz 16⅔ Hz 50 Hz 16⅔ Hz I max / ka 1.3 1.6 (1.5) 1.3 1.6 (1.5 S n /MVA 498 623.8 504.1 610 R /m /km 38 22.2 31.9 20.4 L /mh/km 0.34 0.34 0.37 0.37 X /m /km 107 37 117 39 C /nf/km 227 227 191 191 G /ns/km 71 22 60 20 10

Calculation of Transmission Capacity Wind Farm P Wind Q Wind Shunt Reactor X R Offshore Cable, 100 sections Shunt Reactor X R P Grid Q Grid Onshore Grid Shunt reactors are calculated for full compensation of the cable 1 under no load conditions X R 2 2 f C Example: 1200 mm 2 Cu/RM Cable, 400 km distance ' cable l P Wind 617 MW Q Wind 0 Mvar 1.7 ka 1.65 1.6 Voltage 245 kv 240 235 P Grid 561 MW Q Grid 94 Mvar 1.55 1.5 Hotspot I=Imax=1600 A Current 230 225 1.45 220 1.4 215 0 50 100 150 200 250 300 350 400 11 Distance

Calculation of Transmission Capacity Wind Farm P Wind Q Wind Shunt Reactor X R Offshore Cable, 100 sections Shunt Reactor X R P Grid Q Grid Onshore Grid Shunt reactors are calculated for full compensation of the cable 1 under no load conditions X R 2 2 f C Example: 1200 mm 2 Cu/RM Cable, 400 km distance ' cable l P Wind 643 MW Q Wind 53 Mvar 1.7 ka 1.65 1.6 Voltage 245 kv 240 235 P Grid 584 MW Q Grid 53 Mvar 1.55 1.5 Hotspot I=Imax=1600 A Current 230 225 1.45 220 1.4 215 0 50 100 150 200 250 300 350 400 Distance 12

Calculation of Transmission Capacity Wind Farm P Wind Q Wind Shunt Reactor X R Offshore Cable, 100 sections Shunt Reactor X R P Grid Q Grid Onshore Grid 1200 mm 2 Cu/RM Cable, Imax=1500 A, 400 km distance Var demand supplied solely from the grid side Transmission Capacity: P Wind 589 MW P Loss 8.1% P Wind 589 MW Q Wind 0 Mvar 1.7 ka 1.6 Hotspot I=Imax=1500 A Voltage 245 kv 241 P Grid 541 MW Q Grid -84 Mvar 1.5 237 1.4 Current 233 1.3 229 0 50 100 150 200 250 300 350 400 Distance 13

Calculation of Transmission Capacity Wind Farm P Wind Q Wind Shunt Reactor X R Offshore Cable, 100 sections Shunt Reactor X R P Grid Q Grid Onshore Grid 1200 mm 2 Cu/RM Cable, Imax=1500 A, 400 km distance Var demand distributed equally to both ends Transmission Capacity: P Wind 604 MW P Loss 8.4% P Wind 604 MW Q Wind -45 Mvar 1.7 ka 1.65 1.6 1.55 Hotspot I=Imax=1500 A Voltage 250 kv 245 240 235 P Grid 553 MW Q Grid -45 Mvar 1.5 230 1.45 Current 225 1.4 220 0 50 100 150 200 250 300 350 400 14 Distance

Calculation of Transmission Capacity Wind Farm P Wind Q Wind Shunt Reactor X R Offshore Cable, 100 sections Shunt Reactor X R P Grid Q Grid Onshore Grid 1200 mm 2 Cu/RM Cable, Imax=1500 A, 400 km distance optimized operation for max. active power transmission Transmission Capacity: P Wind 610 MW P Loss 8.5% P Wind 610 MW Q Wind -58 Mvar 1.7 ka 1.65 1.6 1.55 U=Umax=245 kv Hotspot I=Imax=1500 A Voltage Hotspot I=Imax=1500 A 250 kv 245 240 235 P Grid 558 MW Q Grid -34 Mvar 1.5 230 1.45 Current 225 1.4 220 0 50 100 150 200 250 300 350 400 Distance 15

Compensation Demand Qc at both ends (Mvar) Transmission Characteristic 245 kv Submarine Cable 2000 mm 2 Al/RE Voltage and voltage angle transmission of 600 MW over 400 km Compensation demand 0 km Voltage offshore 1.2 V real in p.u. 1 0.8 Voltage onshore 400 km 800 700 600 500 Grid PCC Q c Submarine Cable Q c Offshore Wind PP 9.56 deg 0.6 400 300 50Hz 16,7Hz 0.4 200 100 0.2 V imag in p.u. 0-0.1-0.05 0 0.05 0.1 0 0 100 200 300 400 Cable Length (km) 16

Hypothetic Nord Sea Grid Meshed North Sea Grid with 16⅔ Hz at 220 kv level would be possible! 17

Power Flow in the North Sea Grid Assumed total generation power: 5000 MW Acceptable voltage drops Voltage angle differences are small Losses are acceptable 18

16⅔ Hz Transformer Experience in building 16⅔ transformers are available Weight is about 2x more than that of 50 Hz transformers 16⅔ Hz Transformer, 15 MVA; 120/17,25 kv, ONAN-Hermetik; Ii0 (Quelle: Alstrom) 19

Transmission Capacity of 400 kv Overhead Lines 3000 MW Power Transmission Capacity 2600 2200 50 Hz 16⅔ Hz 1800 1400 1000 0 100 200 300 400 500 600 700 length (km) Conductor: 4xAl/St 550/70 R = 0,01315 Ohm/km ; X = 0,26 Ohm/km ; C = 0,014 F/km I max =4080 A 20

Transmission Capacity of 500 kv Overhead Lines 3800 MW 3400 Power Transmission Capacity 3000 2600 50 Hz 16⅔ Hz 2200 1800 1400 1000 0 100 200 300 400 500 600 700 800 length (km) Conductor: 4xAl/St 550/70 R = 0,01315 Ohm/km ; X = 0,26 Ohm/km ; C = 0,014 F/km I max =4080 A 21

Dynamic Simulation P + jq P + jq 16.7 Hz Offshore Grid R16.7Hz L16.7Hz MMC 300 km - B1 Submarine Cable B2 B3 50 Hz Utility Grid Active Power Controller + Reactive Power Controller 16.7Hz Grid Side Converter (GSC) Udc MMC 50Hz Grid Side Converter (GSC) L50Hz R50Hz DC Voltage Controller (Udcref = 400 kv) + Reactive Power Controller 16.7 Hz Offshore Grid Onshore Frequency Converter + 50 Hz Grid Active Power(MW) Reactive Power (Mvar) 600 500 400 300 200 100 600 MW 80 Mvar 400 MW Active Power Pref Rective Power Qref 50 Mvar Reactive Power (Mvar) 120 100 80 60 40 20 100 MW 0 0.5 1 1.5 2 2.3 2.5 Time (s) (a) Reference Power Flow in 16.7 Hz Grid 0 0.5 1 1.5 2 2.3 2.5 Time (s) (b) Reference Reactive Power Flow in 50 Hz Grid

Simulation Results 16.7 Hz side Sending End

Simulation Results 50 Hz side

Conclusions The integration of offshore wind farms by three phase 16⅔ Hz technology and setting up a 16⅔ Hz offshore grid is a favorable alternative to DC links Converter are only onshore, easy to acces and not affected by serious weather conditions No need for HVDC platform offshore Offshore are only approved technologies like transformer and switch gears Due to meshed 220 kv grid (n-1) security is possible Extention to 400 kv (500 kv) onshore overlay grid is possible by 16⅔- Hz technology 25

Thank you for your attention! Thank you for your attention! 26