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
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

►
Operational Experience
Further Development Aspects
Impressions of Trans Bay Cable
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

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:
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable – Key Data
Potrero
Substation
•
•
•
•
•
•
•
•
•
•
Converter: Modular
Rated Power:
DC Voltage:
400 MW @ AC Terminal Receiving End
± 200 kV
Submarine Cable: Extruded Insulation DC Cable
Start of Commercial Operation November 2010
San
Francisco Pittsburg
Pittsburg
Substation
< 1 mile 1 mile 53 miles 1 mile < 3 miles
AC
Cables
115 kV
Substation
AC/DC
Converter
Station
Submarine DC Cables
AC/DC
Converter
Station
AC
Cables
230 kV
Substation
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

HVDC PLUS
Modular Multilevel Converter – Basic Scheme
SM 1
SM 2
SM 1
SM 2
SM 1
SM 2
SM n SM n SM n
SM
U d
SM 1
SM 2
SM 1
SM 2
SM 1
SM 2
SM n SM n SM n
Phase Unit
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

►
Overview
Further Development Aspects
Impressions of Trans Bay Cable
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Operational Experience:
AC Under-Voltage Fault
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Operational Experience:
Step Response in terms of
Converter Arm Energies
1,5
1
0,5
0
0,05
-0,5
0,07 0,09 0,11 0,13 0,15 0,17 0,19 0,21 0,23 0,25
-1
Step Response of vertical balancing control in terms of converter arm energies.
Zeit t [s]
0,95
0,9
0,85
0,8
0,75
0,7
0,65
0,6
0,05 0,07 0,09 0,11 0,13 0,15
Time (sec)
0,17 0,19 0,21 0,23 0,25
No influence on AC currents!
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Operational Experience:
Step Response in terms of
Converter Arm Energies
1,5
1
0,5
0
0,25
-0,5
-1
0,27 0,29 0,31 0,33 0,35 0,37 0,39 0,41 0,43 0,45
Step Response of horizontal balancing control in terms of converter arm energies.
-1,5
1
0,95
0,9
0,85
0,8
0,75
0,7
Zeit t [s]
No influence on AC currents!
0,65
0,6
0,25 0,27 0,29 0,31
Time (sec)
0,33 0,35 0,37 0,39 0,41 0,43 0,45
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Operational Experience:
Harmonics:
Converter phase to ground voltages
Equivalent disturbing current in the range from
60 Hz to 5.1 kHz.
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

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%.
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Operational Experience:
Losses
Total losses between the two AC systems within the specified limits.
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

►
Overview
Operational Experience
Impressions of Trans Bay Cable
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Further Development Aspects:
Increase of Current Capability
Half Bridge Submodule with parallel connection of IGBTs to increase the current capabability
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Further Development Aspects:
Full Bridge Submodules
SM 1
SM 2
SM n
SM 1
SM 2
SM n
SM 1
SM 2
SM n
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
• Higher losses compared to half bridge submodules
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

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
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

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?
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Further Design Aspects:
Braking Chopper Submodule for Grid Access
Possible solution: DC braking chopper 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.
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

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)
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Overview
Operational Experience
Further Development Aspects
►
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable
Some Impressions
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable
Some Impressions
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable
DC Yard
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable
AC Yard
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Trans Bay Cable
Converter Hall
Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012

Cigre Colloquium on HVDC and Power Electronics Systems
March 7 through 9, 2012