Trans Bay Cable A Breakthrough of VSC Multilevel Converters in HVDC Transmission Siemens AG Power Transmission Solutions J. Dorn, joerg.dorn@siemens.com CIGRE Colloquium on HVDC and Power Electronic Systems Wednesday March 7 through Friday March 9, 2012 Hotel Nikko, San Francisco, California, USA
Content Overview Operational Experience Further Development Aspects Impressions of Trans Bay Cable
Overview Operational Experience Further Development Aspects Impressions of Trans Bay Cable
Trans Bay Cable - The Initial Situation Situation before Trans Bay Cable: Bottlenecks in the Californian grid Problem: No right of way for new lines or land cables The solution:
Trans Bay Cable Key Data Converter: Modular Multilevel HVDC PLUS Converter Rated Power: 400 MW @ AC Terminal Receiving End DC Voltage: ± 200 kv Submarine Cable: Extruded Insulation DC Cable Start of Commercial Operation November 2010 Potrero Substation San Francisco Pittsburg Pittsburg Substation < 1 mile 1 mile 53 miles 1 mile < 3 miles 115 kv Substation AC Cables AC/DC Converter Station Submarine DC Cables AC/DC Converter Station AC Cables 230 kv Substation
HVDC PLUS Modular Multilevel Converter Basic Scheme SM 1 SM 1 SM 1 SM 2 SM 2 SM 2 SM n SM n SM n SM U d SM 1 SM 1 SM 1 SM 2 SM 2 SM 2 SM n SM n SM n Phase Unit
Overview Operational Experience Further Development Aspects Impressions of Trans Bay Cable
Operational Experience: AC Under-Voltage Fault
Operational Experience: Step Response in terms of Converter Arm Energies 1,5 Eingangs- und Ausgangsstrom i [pu] AC Currents (normalized) Converter Arm Energies (normalized) Zweigenergie w [pu] 1 0,5-0,5 0 0,05 0,07 0,09 0,11 0,13 0,15 0,17 0,19 0,21 0,23 0,25-1 -1,5 1 0,95 0,9 0,85 0,8 0,75 0,7 0,65 Zeit t [s] Step Response of vertical balancing control in terms of converter arm energies. No influence on AC currents! 0,6 0,05 0,07 0,09 0,11 0,13 0,15 0,17 0,19 0,21 0,23 0,25 Time (sec)
1,5 Operational Experience: Step Response in terms of Converter Arm Energies Eingangs- und Ausgangsströme i [pu] AC Currents (normalized) Converter Arm Energies Zweigenergien (normalized) w [pu] 1 0,5 0 0,25 0,27 0,29 0,31 0,33 0,35 0,37 0,39 0,41 0,43 0,45-0,5-1 -1,5 1 Zeit t [s] 0,95 0,9 0,85 0,8 0,75 0,7 Step Response of horizontal balancing control in terms of converter arm energies. No influence on AC currents! 0,65 0,6 Time (sec) 0,25 0,27 0,29 0,31 0,33 0,35 0,37 0,39 0,41 0,43 0,45
Operational Experience: Harmonics: Converter phase to ground voltages Equivalent disturbing current in the range from 60 Hz to 5.1 khz.
Operational Experience: Harmonics: DC current Total harmonic distortion of converter phase to ground voltages in the range from 120 Hz to 3 khz clearly below 1%.
Operational Experience: Losses Total losses between the two AC systems within the specified limits.
Overview Operational Experience Further Development Aspects Impressions of Trans Bay Cable
Further Development Aspects: Increase of Current Capability Half Bridge Submodule with parallel connection of IGBTs to increase the current capabability
Further Development Aspects: Full Bridge Submodules SM 1 SM 2 SM n SM 1 SM 2 SM n SM 1 SM 2 SM n AC voltage instead of DC voltage possible u DC pole-to-pole fault can be turned off by IGBTS SM 1 SM 2 SM n SM 1 SM 2 SM n SM 1 SM 2 SM n Higher losses compared to half bridge submodules
Further Development Aspects: Clamp-Double Submodule Double voltage capability compared to half bridge submodule and full bridge submodule Capability to turn off a DC pole-to-pole fault with IGBTs but Lower losses than full bridge Submodule
Further Design Aspects: Requirements for Offshore Wind Grid Access Wind turbines have only 100... 200ms Fault Ride Through (FRT) capability Onshore Grid Codes, however, require interruption capability of > 1s Main goal: Keep windfarm operational at all costs / prevent wind turbine shutdown Windfarm output power has to be kept up during this period There are no feasible means of storage for the excess power, so where to put it?
Possible solution: DC braking chopper Further Design Aspects: Braking Chopper Submodule for Grid Access absorbs dynamic excess power generated by the windfarm during onshore grid interruptions Windfarm will take no notice of short onshore grid interruptions For enduring grid faults, the windfarm may be throttled down in usual order, via windfarm power control no emergency shut-down The chopper is installed at the onshore converter station, the offshore station s footprint is not enlarged.
Further Design Aspects: Series Connection of Power Semiconductors Usually, a semiconductor device failure does not lead to a discharge of the capacitor. But: A faulty semiconductor has to have the capability for load current Or: Bypass device Short circuit of a whole half bridge shall be considered (impact on neighbored submodules)
Overview Operational Experience Further Development Aspects Impressions of Trans Bay Cable
Trans Bay Cable Some Impressions
Trans Bay Cable Some Impressions
Trans Bay Cable DC Yard
Trans Bay Cable AC Yard
Trans Bay Cable Converter Hall
Thank you very much for your attention!