OTC-25171-MS Investigation of Next Generation Subsea Power Distribution System Architectures Yao Duan, William Forrest, Xin Li, and Harald Bjørn Ulvestad Slide 2 Subsea Power Equipment in Subsea Processing • Main power equipment are motors for driving pumps and compressors – Multiphase/Single Phase Boosting Pump: 4-6kV, 3-6MW, up to 100Hz – Water Injection: 4-6kV, 1-3MW, up to 100Hz – Compressor: 6kV, 8-12MW, up to 200Hz Courtesy of FMC Technologies • Other power equipment – Electrical Heating (flowlines): 1-5MW – Subsea Uninterrupted Power Supply (UPS) for Magnetic Bearing Control System: 10 - 50kW – Subsea Chemical Injection Pumps: 40400kW Courtesy of Petrobras Courtesy of Statoil OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 3 How to Supply Power to Subsea Future: Subsea Power Distribution System Topside Topside power Present: Point-to-Point Connection Topside power Topside Subsea VSD Subsea Power umbilical Advantage of subsea power distribution system Power • Support more subsea power umbilical equipment cost effectively • Save topside space Subsea • Less maintenance Switchgear VSD 1 VSD 2 VSD 2 UPS ... Motor Motor 1 Motor 2 Motor 3 ... OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 4 Objective Study potential subsea power distribution system architectures based on simulation to investigate the direction of next generation subsea power system equipment developments OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 5 Investigation of Next Generation Subsea Power Distribution System Architectures • Four power system architectures are investigated – from “point to point” to “ring type distribution” Arch. I: point-to-point connection, topside VSD Arch. II: single subsea field with multiple subsea power loads Arch. III: single topside power source, multi-subsea fields with multisubsea power loads Arch. IV: multi-topside power sources, multi-subsea fields with multisubsea power loads • Steady state and transient simulation • Tools: ATP/EMTP software • Major findings discussed in this presentation 10.0 [kA] 7.5 5.0 2.5 0.0 -2.5 -5.0 -7.5 -10.0 0.070 0.096 0.122 (f ile Arch3Case1_f ullload_open.pl4; x-v ar t) c:X0053A-X0016A 0.148 c:X0053B-X0016B 0.174 [s] 0.200 c:X0053C-X0016C Contribution: identify power equipment requirements from a system level approach OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 6 Architecture I: Point to Point Power System Type 1 Power System Type 2 Topside power Topside power Topside VSD Courtesy of Petrobras Topside VSD Umbilical Topside Transformer Umbilical Courtesy of Oceaneering Subsea Transformer Subsea motor Subsea motor Courtesy of FMC Technologies OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 7 Architecture I: Point-to-Point Voltage Drop Main design factor: voltage drop from topside to subsea Exceed maximum voltage drop: need topside and subsea transformers 6 MW MPP 3 MW MPP 1 MW ESP Maximum Drop Step-Out Distance Main limitations of point-to-point architecture • • • Topside space for VSDs and their buildings Increasing umbilical cost with more subsea equipment Support capacity of host facility OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 8 Architecture II One topside power source, multiple subsea loads Topside power Topside transformer Topside swichgear Major challenges • Maintain subsea grid voltage • • Steady state Transient • System start up subsea side transient over-voltage Umbilical Subsea transformer Subsea switchgear Subsea VSD Subsea power load OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 9 Architecture II One topside power source, multiple subsea loads Challenge: subsea power loads operate at different levels Less voltage drop on umbilical Proposed Solution Topside transformer On-Load Tap Changers (OLTC) to adjust umbilical transmission voltage Higher subsea input voltage Tap pos. 1 Pump at lower power Assumed field data • • Tap pos. 2 Umbilical: 100 km, 95 mm2 Subsea power loads: • • • • 1 off 10 MW compressor 1 off 0.4 MW condensation pump 1 off 6 MW pump 1 off 3 MW water injection pump OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 10 Architecture II One topside power source, multiple subsea loads Challenge: One or more subsea power loads suddenly drop offline Static VAR Compensator (SVC) 15 Full load Load rejected • [kV] 10 5 • 0 -5 20 % increase of subsea power grid voltage Transformer OLTC slow response -10 -15 0.05 0.07 0.09 (f ile Architecture1_Load_Rejection.pl4; x-v ar t) v :X0043A 15 Full load 0.11 v :X0043B 0.13 [s] 0.15 v :X0043C Load rejected, SVC activated Proposed Solution [kV] voltage increase reduced to below 10 % by SVC in miliseconds 10 5 0 Assumed field data • • -5 Umbilical: 100 km, 95 mm2 Subsea power loads: • • • • -10 1 off 10 MW compressor 1 off 0.4 MW condensation pump 1 off 6 MW pump 1 off 3 MW water injection pump -15 0.05 0.07 0.09 (f ile Architecture1_Load_Rejection.pl4; x-v ar t) v :X0046A 0.11 v :X0046B 0.13 [s] 0.15 v :X0046C OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 11 Architecture II One topside power source, multiple subsea loads Challenge: system startup • A hard startup by closing topside circuit breaker • Subsea end has more than 40 % transient over-voltage due to reflection waves Umbilical Voltage at subsea end 80 [kV] 60 40 20 0 -20 -40 -60 -80 0.00 • • Umbilical: 100 km, 95 mm2 Subsea power loads: • • • • 0.05 0.10 (f ile Architecture1_Sy stem_Start.pl4; x-v ar t) v :X0006A v :X0006C Assumed field data 1 off 10 MW compressor 1 off 0.4 MW condensation pump 1 off 6 MW pump 1 off 3 MW water injection pump 0.15 [s] 0.20 v :X0006B Proposed Solution Startup at lower voltage – wide tap settings of topside transformer OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 12 Architecture II One topside power source, multiple subsea loads Conclusion Major challenges Proposed Solutions Maintain subsea power On-Load Tap Changers system voltage at steady at topside transformer state Maintain subsea power system voltage during transient load rejection Topside Static Var Compensator (SVC) System start up transient over voltage Reduce voltage at start up OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 13 Architecture III One topside power source, multi – subsea fields with multi-subsea loads Major additional challenges: • Multi-subsea fields, fault-tolerant to increase system availability during ground fault • Maintain input voltages of multi- subsea fields with one topside transformer On Load Tap Changer OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 14 Architecture III One topside power source, multi – subsea fields with multi-subsea loads Challenge: fault tolerant Increase system availability during ground fault Field 1 Phase-to-Ground Voltage 25.00 [kV] 18.75 12.50 Proposed Solution Subsea transformer with multiple secondary windings and High Resistance Grounding (HRG) 6.25 0.00 -6.25 -12.50 -18.75 -25.00 0 10 20 30 (f ile Arch2Case2_f ullload_LG.pl4; x-v ar t) v :X0062A 40 v :X0062B 50 60 70 [ms] 80 v :X0062C Field 2 Phase-to-Ground Voltage 15 [kV] 10 5 0 -5 -10 -15 0 10 20 30 (f ile Arch2Case2_f ullload_LG.pl4; x-v ar t) v :X0063A 40 v :X0063B 50 60 70 [ms] 80 v :X0063C OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 15 Architecture III One topside power source, multi – subsea fields with multi-subsea loads Challenge: one topside OLTC to control voltages of two subsea fields Proposed Solution Increase umbilical transmission voltage Subsea transformer 20.0% Add subsea transformer for remote fields Voltage variation [%] 15.0% 10.0% Upper limit +6% 5.0% Field 1 0.0% -5.0% 0 0.2 0.4 0.6 0.8 1 Field 2 -10.0% -15.0% -20.0% Lower limit -10% Power [pu] OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 16 Architecture IV: Ring System Major additional challenges: • Synchronization of multi-topside power sources • Circuit breaker coordination OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 17 Architecture IV: Ring System Power Flow Field 1 Field 2 49.2 -j13.8 12 -j9 Challenges If the phase angles of the power sources are not synchronized, their output power will be unbalanced, or even power flow reversely 2.7 j2.1 37.5 -j4.3 14.7 -j6.9 12 -j9 21 -j10.8 12.5 -2.5 2.6 -0.5 Proposed Solution: Develop real-time communication and control between multiple power sources OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 18 Architecture IV: Ring System Short Circuit Challenge • • Higher short circuit current at subsea switchgear Circuit breaker coordination to prevent false tripping Proposed Solution Marinize topside circuit protection strategy for ring systems OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 19 Conclusion • Four power system architectures analyzed, from point-to-point to complex subsea power grid • With increasing subsea equipment, for subsea power distribution systems, the following power equipments needs to be applied: • On-Load Tap Changers • Static VAR Compensators • Subsea Multi-winding Transformers with high resistance groundings • Additional Subsea Transformers for remote fields • Synchronization of power sources and coordination of circuit breakers for ring systems • Control of all the additional topside and subsea power equipment OTC-25171-MS • Investigation of Next Generation Subsea Power Distribution System Architectures • Yao Duan Slide 20 Acknowledgements / Thank You / Questions Thanks to • FMC Technologies Subsea Processing group • Wensen Wang
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