Massive Integration of Offshore Using HVDC, 8th August 2012

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DecarbonisingthePowerSystem:
Santiago de Chile - Chile
Santiago de Chile
8th August 2012
Massive Integration of Offshore
Wind Power using HVDC
FranciscoM.Gonzalez-Longatt
@fglongatt@fglongatt
Department of Electrical Engineering
Coventry, United Kingdom
Asociacion Venezolana de Energia Eolica
Photo: http://www.bard‐offshore.de/media/fotos.html
Historical Perspective on HVDC Transmission
This section presents a brief history and facts
related to the HVDC transmission systems
AC versus DC

War of Currents: AC versus DC
War of Currents
• George Westinghouse and Thomas Edison became adversaries
due to Edison's promotion of direct current (DC) for electric
power distribution over alternating current (AC) advocated by
several European companies and Westinghouse Electric based in
Pittsburgh, Pennsylvania
George Westinghouse, Jr
(October 6, 1846 – March 12, 1914)
Thomas Alva Edison
(February 11, 1847 – October 18, 1931)
− Thomas Edison (DC) vs George
Westinghouse (AC)
− AC won…or so it seemed.
− Why?
However, AC transmission is hard to control
(power flows where it wants to flow)
High Voltage Direct Current (HVDC)
transmission is more efficient and more
controllable
“Take warning! Alternating currents are
dangerous, they are fit only for the
electric chair”, Thomas A. Edison
(1847-1931)
3
The beginning
• 1882 – First Demo of 1.5 kW HVDC
• Marcel Deprez was a Frenchman who created the DC
distribution system for the Exposition in Paris helped Miller
create the first long distance high voltage direct current
transmission ever.
• They transmitted 1,500 watts at 2000 volts over 35 miles from
Miesbach (the foothills of the Alps) to the Glaspalast in Munich.
Marcel Deprez (December 12, 1843 - October 13, 1918)
“The two systems shake hands fraternally in order to
give each other help and assistance…” (1889) R.
Thury
4

Thury Systems (1/2)
• 1889 – Rene Thury developed a
new 630 kW system transmitted
power at 14 kV DC over 120 km.
• He was known for his work with high
voltage direct current electricity
transmission and was known in the
professional world as the "King of DC.
Schematic diagram of a Thury HVDC transmission system
René Thury (August 7, 1860 – April 23, 1938)
In 1882, Thury's 6 pole dynamos were more compact than
Edison's. The small 1,300 kg (2,900 lb) version produced 22
kW at 600 rpm, while a larger 4,500 kg (9,900 lb) version
produced 66 kW at 350 rpm
5
Thury Systems (2/2)
• 1913 – fifteen Thury systems were in place up to 100 kV
• 1930 – Thury system were obsolete due the rotating
machinery required high maintenance and had high energy
loss.
Name
Converter
Station 1
Converter
Station 2
Cable
(km)
Overhead
line (km)
Voltage
(kV)
Power
(MW)
Year of
inaug.
Year of
decomm.
Remarks
Gorzente River -
Genoa DC
transmission scheme
Italy -
Gorzente
River
Italy - Genoa ? ? 6 ? 1889 ?
upgraded later
to a voltage of
14 kV, power
of 2.5 MW and
a length of
120 km,
dismantled
La Chaux-de-Fonds
DC transmission
scheme
Switzerland -
?
Switzerland -
?
? ? 14 ? 1897 ? dismantled
St. Maurice -
Lausanne DC
transmission scheme
Switzerland -
St. Maurice
Switzerland -
Lausanne
? ? 22 3.7 1899 ? dismantled
Lyon-Moutiers DC
transmission scheme
France -
Lyon
France -
Moutiers
10 190 ±75 30 1906 1936
Wilesden-Ironbridge
DC transmission
scheme
UK -
Wilesden
UK -
Ironbridge
22.5 ? 100 ? 1910 ?
Chambéry DC
transmission scheme
France - ? France - ? ? ? 150 ? 1925 1937
6

Early History
• 1906~1936 –Mountiers-Lyon System transmitted 8,600 kW
over 190km, 10km which was underground.
• 1932 – General Electric used mercury-vapor valves and a 12
kV DC transmission line in Mechanicville, New York.
• 1941- Berlin used a similar line underground, however,
project terminated due to the fall of government in 1945.
At the Moutiers power plant, there were four generators switched in series, whereby one turbine drove two
generators. As the power demand changed, the number of generator switched in series varied, and so did the voltage
in the transmission line.
The line was bipolar with a maximum of 75,000 volts to ground and so 150,000 volts between the conductors. The
line was 200 kilometres long, with 190 kilometres run overhead and 10 kilometres as paper insulated underground
cable. Originally the cable was rated for 75 A, but was later run with 150 A. Even after this increase in current the
cable was still in good condition when the scheme was dismantled in 1936
HVDC Mechanicville–Schenectady was the first experimental HVDC
transmission line in the United States. Built in 1932, the circuit traversed 37
kilometres (23 mi) from Mechanicville, New York to Schenectady, New York.
The system used mercury arc rectifiers at a voltage of 20,000 volts and a rated
power of 5 MW. The facility was dismantled after World War II.
Mechanicville Hydroelectric Station
7
Modern History
• 1950- First modern HVDC system was in service between
Sweden and the island Gotland (ASEA Swedish industry
company), rated 20MW, 100kVdc
• 1960- Three additional order were received by ASEA in New
Zeland, Sweden/Denmark, and Japan.
Mercury arc valve at Ygne, Gotland
Thyristor valves at Ygne converter station, Gotland
8

Modern History
• 1961 1st Cross Channel link from England to France rated
160MW, 100kVdc
The first HVDC Cross-Channel went into service in 1961 between static inverter plants at Lydd in England and Echinghen, near Boulogne-sur-Mer, in
France. This scheme was equipped with mercury vapour rectifiers. In order to keep the disturbances of the magnetic compasses of passing ships as small
as possible, a bipolar cable was used. The cable had a length of 64 kilometres (40 mi) and was operated symmetrically at a voltage of ±100 kV and a
maximum current of 800 amperes. The maximum transmission power of this cable was 160 megawatts (MW). The cable was built by ABB Group.
Anglo-French Interconnector Echinghen, near Boulogne-sur-Mer, France
Lydd in England
52km
225 kV, 60Hz
275 kV, 50Hz
Électricité de France
CEGB (the Central Electricity
Generating Board UK)
9
Modern History
• 1964 Volgograd-Donbass overhead line link rated 750MW
400kVdc and 450km long The HVDC Volgograd-Donbass is a high voltage direct
current line between the static inverter plants at
Volzhskaya (situated near the hydro-electric power plant
Volgograd) and Mikhailovskaya in the Donbass area,
which went into service in 1964.
It consists of a 475 kilometre long overhead line.
The static inverters of the HVDC Volgograd-Donbass
are equipped with mercury arc rectifiers for a voltage
of 100 kV and a maximum current of 940 ampere,
which were partly replaced at the beginning of the 90's
by thyristors.
The HVDC Volgograd-Donbass is a bipolar HVDC
with an operating voltage of 400 kV.
It can transfer a maximum power of 750 megawatts.
475 Km
10

Recent History
• 1969- First HVDC system to use solid state valves.
• 1970s – First HVDC system implemented within an AC
network (Los Angeles, California).
• 1972 Eel River Canada back-to-back rated at 320MW 1st
thyristor based link
• First microcomputer based control equipment for HVDC in
1979.
It is Commissioned in 1972, bwteween Hydro-Quebec (QHQ)
and the New Brunswick Electric Power Comission (NBEPC).
it supplies 320 MW at 80 kV d.c.
The link is of zero length and connects two a.c. systems of the
same nominal frequency (60Hz).
The largest thyristors used in converter valves have blocking
voltages of the order of kilovolts and currents of the order 100s
of amperes.
Source: HVDC Power Transmission Systems: Technology and System Interactions by K. R.
Padiyar
Eel River Controller
11
Recent History
• 1986 - 2nd Cross Channel link from England to France rated
2x1000MW 270kVdc – still the largest power cable link
“Interconnexion France Angleterre” (IFA)
Connection to France; Owned by National Grid and RTE
Because the first installation did not meet increasing
requirements, it was replaced in 1985–1986 by a new HVDC
line with a maximum transmission rate of 2,000 MW between
France and Great Britain, for which two new static inverter
plants were built in Sellindge (UK) and in Bonningues-lès-
Calais (Les Mandarins station), near Calais, (France).
The cable and substations were built by Areva.
This HVDC-link is 73 kilometres (45 mi) long in route, with
70 kilometres (43 mi) between the two ends.
The undersea section consists of eight 46 kilometres (29 mi) long 270 kV submarine cables (four pairs), laid
between Folkestone (UK) and Sangatte (France), arranged as two independent bipoles.
The landside parts of the link consist of 8 cables with lengths of 18.5 kilometres (11.5 mi) in England, and
6.35 kilometres (3.95 mi) in France
Interconnexion France-Angleterre : Station de conversion courant alternatif-courant continu des Mandarins (Pas de Calais)
http://www.rte-france.com/fr/mediatheque/medias/infrastructures-62-fr/interconnexions-interconnexions-fr
In 2006, 97.5% of the energy transfers have been made from France to
UK, supplying the equivalent of 3 million English homes. The link
availability is around 98%, which is among the best rates in the world.
The continued size and duration of this flow is open to some doubt,
given the growth in demand in Europe for clean electricity, and
increasing electricity demand within France
12

Recent History
• 1984-87 Itaipu Brazil 2x3150 600kVdc 800km overhead line
link
The HVDC Itaipu is a High Voltage Direct Current transmission line in Brazil from the Itaipu hydroelectric power plant to the region of São Paulo.
The project has two bipolar lines, which run from the generator site at Foz do Iguaçu in Paraná to the "load" (user) site Ibiúna near São Roque, São Paulo.
The lines were put in service in several steps between 1984 and 1987, and are among the major installations of HVDC in the world
Bipole 1.
1. stage: ± 300 kV, 1575 MW in July 1984
2. stage: + 300kV,2362.5 MW in April 1985
- 600 kV
3. stage: ± 600 kV, 3150 MW in May 1986
4.stage: ± 300 kV, 1575 MW { commissioned
Bipole 2.
5.stage: + 300 kV, 2362,5 MW { at the
- 600 kV { same time by
6.stage: ± 600 kV, 3150 MW { August, 1987
Simplified diagram of the Itaipu Transmission System
SOURCE: ITAIPU HVDC TRANSMISSION SYSTEM 10 YEARS OPERATIONAL EXPERIENCE,
http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/81f41178f000ca94c1256fda004aead6/$file/sepope2.pdf
Itaipu HVDC System main
circuit and evolution
13
Recent History
• First active DC filters for
outstanding filtering
performance in 1994.
• First Capacitor
Commutated Converter
(CCC) in Argentina-
Brazil interconnection,
1998
“Garabi” the Argentina – Brazil 1000 MW Interconnection Commissioning
and Early Operating Experience
Source: http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/336dd56474cadec5c1256fda004aeadd/$file/erlac01.pdf
60Hz
60Hz
50Hz
50Hz
14

Recent History
• First Voltage Source Converter (VSC) for transmission in
Gotland, Sweden , 50MW 80kVdc, 1999
Backs
Nas
Wind Farms
P = 50 MW
D = 70 km
Vdc = 80kV
Bipolar
15
Recent History
• 2010 Borwin 1 400MW 150kVdc, VSC 1st large offshore
wind farm connection
•By 2015, the DolWin2 wind farm will be connected with the
world’s largest offshore HVDC system.
http://www.tennettso.de
125 km sea cable
400 MW Offshore
converter
Source: ABB
400 MW HVDC Light® system off-shore
station on platform with sub-sea structure
80 Wind Turbines
40 m Deep
100 km
16

Recent History
• 2011 XianJiba- Shanghai 6400MW 800kVdc (next year there
will be a 7200MW link commissioned in China
2,071km
±800kV DC
Fulong
Substation
FengXiang
Substation
State Grid Corporation of China
Source: ABB
Source: ABB
17
Recent History: Evolution of Voltage
China 2011Evolution of the voltage level used on HVDC Systems
18

Development of HVDC Transmission
Worldwide installed
HVDC “Capacity”: 80
GW in 2005
1951, Kashira-Moscow
30 MW
This is 1.8% of the Worldwide
installed generation capacity
Sources: Cigre WG B4-04 2003 – IEEE T&D Committee 2006
Additionally, over 104
GW are expected from
China alone by 2020
Development of DC Transmission
Worldwide installed Capacity
19
HVDC Installation around the World
This section present a general picture of the
deployment of HVDC systems around the world.

HVDC Installation around the World
21
UHVDC Prospects 600kV-800kV
22

UHVDC Prospects 600kV-800kV in China
23
Drivers of the Expansion on HVDC Market
• China is building vast quantities of generation in the west but most load is in
the east. By end of decade approx 20 HVDC links of 800kVdc 5GW+ rating
to be commissioned
• Brazil has major generation planned in the north but with major loads in the
south Offshore windfarms in Europe and North America
• Plans for multi-GW solar generation in N Africa to be transmitted to Europe
• Constraints on building transmission lines particularly in Europe
• Development of XLPE cables suitable for dc use.
MW Installed/ordered
Year
Power-MW
24

Alternatives of Power Transmission
This section discuses the alternatives of electric
power transmission
Alternatives for Power Transmission
• High Voltage (HV) and Ultra High Voltage (UHV) serves a dual
purpose:
– System interconnection: Operate the whole system in
perfect synchronism often prevents the transfer of power by
alternating current.
– Bulk energy transfer: there are various alternatives, not all
of them involving electric-power transmission, and an
economic assessment is essential in each case.
26
High Voltage AC High Voltage Direct Current
500 kV conventional as also series compensated
750 kV conventional as also series compensated
1200 kV conventional as also series
compensated
± 500 kV bipole
± 550 kV bipole
± 600 kV bipole
± 800 kV bipole

High Voltage Alternating Current: HVAC
• During the latter part of the 19th century, electricity started to
become increasingly important for society.
• The three-phase alternating current has been the dominant
option for the transmission of electric power over long distances.
• Developments led to higher voltages, increasing the scope for
the transmission of more power over greater distances.
Development of Voltages Levels
for AC Power Transmission
110 kV Lauchhamme–Riesa/Germany (1911)
220 kV Brauweiler-Hohenec/Germany (1929)
287 kV Boulder Dam/USA (1932)
380 kV Harsptanget-Halsberg/ Sweden (1952)
735 kV Montreal-Manicouagan/Canada (1965)
1 1200 kV Ekibastuz-Kokchetav (1985)
1
2
3
1
2
4
5
6
3
5
6
4
27
Resistance: 0.0107Ω/km
Reactance : 0.267 Ω/km
Capacitance: 14.15 nF/km
Surge Impedance: 245 Ω
Surge Impedance Load: 4080MW
Charging impedance load: 4.45MVAr/km
Maximum Surface gradient: 14.7 kV/cm
Voltage 1000 kV
Phase conductor wire 8x403/52 ACSR
Outer diameter 27.7 mm
Sub conductor spacing 400 mm
28

Bundle of 8
Conductors
1000 kV Test Line in China
Rated Voltage:
1000 kV
Maximum Operation
Voltage: 1100 kV
29
Limitation of HVAC
• Some limitation of HVAC systems are:
– Distance limitation: The power carrying capability of an AC
line is inversely proportional to the transmission distance
where as DC is not affected by the distance.
– Line compensation: AC transmission lines require
compensators which reduce the problem of charging currents
– Asynchronous connection: HVDC controllability allows to
connect AC grids of different frequencies.
– Frequent tripping: large power oscillations in the AC grid
can lead to frequent tripping and disturbances can be
transmitted from one system to another.
30

Limitation of AC transmission Line
System Modeling for Line Loadibility
Max Angular Displacement = 44º
Max Voltage Drop = 5%
Source: EPRI
31
Limitation of AC transmission Line
• Limitation of AC transmission line
Typical values of SIL for
overhead transmission lines
Note: No series or shunt compensation
LineLoadability-p.u.ofSIL
765 kV
1500 kV
Rated
voltage
[kV]
Thermal
Limit
[MW]
SIL
[MW]
230 400 135-145
345 1.200 325-425
500 2.600 850-1075
765 5.400 2.200-2.300
1100 24.000 5.200
32

Alternatives for Power Transmission
AC transmission is here to
stay …but is not perfect
33
Comparison between HVDC and HVAC
This section presents a simple comparison
between the HVDC and HVAC transmission
systems

Electric Power Transmission
HVAC HVDC
12 sin( )s R
s R
E E
P
X
  
2
12 cos( )s s R
s R
E E E
Q
X
 

 
Ud1 Ud2
R
2
1 2
12
d dU U
P
R


P
Rectifier Rectifier
+ -
+
-
+
-
1dU 2dU
RUI
1 2d dU U
I
R


1 1.dP U I 2 2.( )dP U I 
35
Electric Power Transmission using HVDC
10 Ω
1000 A
Inverter
300 kV 290 kV
10 Ω
2000 A
Inverter
310 kV 290 kV
10 Ω
1000 A
Rectifier
290 kV 300 kV
300 290 10
1000
10 10
kV kV kV
I A

  
 
1 300 .1000 300P kV A MW 
2 290 .( 1000 ) 290P kV A MW   
310 290 20
2000
10 10
kV kV kV
I A

  
 
1 310 .2000 600P kV A MW 
2 290 .( 2000 ) 580P kV A MW   
( 290 ) ( 300 ) 10
1000
10 10
kV kV kV
I A
  
  
 
1 ( 290 ).1000 290P kV A MW   
2 ( 300 ).( 1000 ) 300P kV A MW   
Inverter
Rectifier
Rectifier
300MW
600MW
290 MW
+
‐
+
‐
+
‐
+
‐
+
‐
+
‐
36

Economical Considerations
Comparison
Conclusions
• HVDC is more economical for transmission distances longer
than the break-even distance
• If capitalization of losses and right-of-way cost are included in
the cost comparison, the break-even distance is further reduced
Terminal Cost
Line Cost
Righ-of-Way-Cost
Higher
Lower
Lower
Lower
Higher
Higher
HVACHVDC
37
Capitalised Losses / Break-Even-Distance
• The AC system tend to be more economical for distances below
the breakeven distance and DC system become economical
above the break even distance.
• The breakeven distance depends on factors such as the
transmission medium and local factors.
38

Right-of-Way
50 m
± 500 kV DC
route width:50m
800 kV AC
route width:85m
110 m
2x500 kV AC
route width:110m
± 500 kV DC 800 kV AC 2x500 kV AC
Typical Transmission Line Structures for approx. 2000 MW
39
Applications of HVDC
This section presents an introduction of the most
frequent application of HVDC systems

Applications of HVDC
AC System 1 AC System 2
1U 1
1f
2U 2
2f
AC System 1
1U 1
1f
AC System 2
2U 2
2f
DC link in parallel with AC links
DC link between two AC networks
41
Emergency Frequency Control
Emergency frequency Control
• HVDC can rapidly increase or reverse
power flow direction to compensate
unbalance active power to recover system
frequency.
• When a large generator is tripped, the
system frequency falls down over acceptable
level.
42

Automatic Frequency Control
Automatic Frequency Control
• When you require to improve frequency deviation in normal operation
and after large disturbances, application of Automatic Frequency control
(AFC) function is recommended.
Frequency
Detector
Frequency
Detector
-
+
-
+
+
-
Converter Control
ObserverState Feedback
ServeFrequency
Reference
43
Power Swing Damping Control
Power Swing Damping Control
• The modulation control of the DC power improves power swing
stability and effectively dampes power oscillations, (this function is
not limited for HVDC-HVAC line in parallel, but also applies to
HVDC linked between two AC networks)
44

Commutation Techniques for HVDC
Converters
This sections introduces the commutation
techniques used on HVDC converters
Natural Commutated Converters (NCC) (1/2)
• This technique relies on the natural reversal of the sinusoidal ac
line voltage across the valves of the converter.
• Natural commutated converters are most used in the HVDC
systems as of today (LCC Systems).
• The component that enables this conversion process is the
thyristor, which is a controllable semiconductor that can carry
very high currents (4000 A) and is able to block very high
voltages (up to 10 kV).
8.5kV, 125mm thyristor
Thyristor column

Capacitor Commutated Converters (CCC)
• An improvement in the thyristor-based commutation, the CCC
concept is characterised by the use of commutation capacitors
inserted in series between the converter transformers and the
thyristor valves.
• The commutation capacitors improve the commutation failure
performance of the converters when connected to weak
networks.
Filter Series
Capacitor
Capacitor Commutated Converters (CCC)
• Reactive power through converter transformer is minimized which reduce
converter transformer rating.
• Current through commutation capacitors can be controlled by firing of the
valve.
• Voltage across capacitors is controlled by the current through the DC current.
• No AC side zero sequence current through capacitors - valve side of the
transformers winding are not grounded.
• Stresses of the commutation capacitors is reduced.
Reactive power ratings for a classic converter and a CCC
0.483filterQ 
0.127transfoQ  0.356vQ 
0Q 
0.13filterQ 
0.115transfoQ  0.358vQ 
0Q 
0.343cQ 
600 1.0 .P MW p u 

Forced Commutated Converters (FCC)
• The valves of these converters are built up with semiconductors
with the ability not only to turn-on but also to turn-off.
• Two types of semiconductors are normally used in the voltage
source converters: the Gate Turn-Off Thyristor (GTO) or the
Insulated Gate Bipolar Transistor (IGBT).
• Both of them have been in frequent use in industrial applications
since early eighties.
• They are known as Voltage Source Converters (VSC).
2.5kV, 3kA GTO Thyristor
3.3kV, 1.2 kA IGBT
GTO IGBT
• The operation of the converter is achieved by Pulse Width
Modulation (PWM).
• With PWM it is possible to create any phase.
• This type of converters introduces a spectrum of advantages, e.g.
feed of passive networks (without generation), independent
control of active and reactive power, power quality.
0
2
  3
2
 2
acU
2
dcU

2
dcU

acU
2
dcU

+
-
+
-
+
-
2
dcU

• Thus, PWM offers the possibility to control both active and
reactive power independently.
• This makes the PWM Voltage Source Converter a close to ideal
component in the transmission network.
• From a transmission network viewpoint, it acts as a motor or
generator without mass that can control active and reactive
power almost instantaneously.
tranfX lim
2
bX
1V 2V 3V
acI
Im
Re
1V
acI 3V
V

3 1
sin
V V
P
X

3 3
1
cosV V
Q V
X
  
  
 
Comparison of LCC and VSC
LCC HVDC
– Current-sourced
– Line-Commutated
VSC HVDC
− Voltage-Sourced
− Self-Commutated
+
‐
Idc

Comparison of LCC and VSC
LCC HVDC
•Use semiconductors which can withstand
voltage in either polarity
•Output voltage can be either polarity to
change power direction
•Current direction does not change
•Store energy inductively
•Use semiconductors which can turn on by
control action
•Turn-off and “commutation” rely on the
external circuit
VSC HVDC
•Use semiconductors which can pass
current in either direction a
•Output voltage polarity does not
change
•Current direction changes to change
Power direction
•Store energy capacitively
•Use semiconductors which can turn on or
off by control action
•Turn-off is independent of external
circuit
The Multi-Level Approach
2
dcU

+
-
-
2
dcU
+
acU +
-
Small Converter AC Voltage Steps
Low Rate of Voltage Rise

Modular Multilevel Converters (M2M)
• With advances in multilevel converters, the type of multilevel
converter that is attracting attention is the modular multilevel
converter (M2C).
acU +
-
+
-
dcU
Low Generation of Harmonics
Low Level of HF-Noise
Low Switching Losses
NO Snubbers required
Types of HVDC
This section presents several different types of
HVDC configurations

Types of HVDC Systems
Different common system configurations and operating modes
used for HVDC transmission
Monopole, Midpoint Grounded
(a) Monopole (b) Bipole
Bipole
(c) Multi-Terminal
Multiterminal
Bipole, Series-Connected
Converters
1. Monopole Link
• Monopolar systems are the simplest and least expensive systems
for moderate power transfers since only two converters and one
high-voltage insulated cable or line conductor are required.
• Monopolar link has one conductor and uses either ground and/or
sea return.
Since the corona effects in
a dc line are substantially
less with negative polarity
of the conductor as
compared to the positive
polarity, a monopolar link
is normally operated with
negative polarity.

A. Monopole, Ground Return
• The power is transmitted from one converter station to another
station through one conductor (positive or negative polarity) and
return is grounded at both stations
Low-voltage electrode lines and sea electrodes to carry the return
current in submarine cable crossings
I
I
I
A. Monopole, Metallic Return
• The power is transmitted from one converter station to another
converter station through one conductor and metallic conductor
is used as return and grounded at one end.
A metallic return can also be used where concerns for harmonic
interference and/or corrosion exist.
In applications with dc cables (i.e. HVDC Light), a cable return is
used.
I
I

B. Monopole, Midpoint Grounded
• This is an economic alternative to a monopolar system with
metallic return.
• The midpoint of a 12-pulse converter can be connected to earth
directly or through an impedance and two half-voltage cables or
line conductors can be used.
• The converter is only operated in 12-pulse mode so there is never
any stray earth current.
I/2
I/2
I I
C. Back-To-Back
• Both rectifier and inverter stations are located at same place.
• The normal configuration is to use monopolar blocks, but several
converter blocks can be installed in parallel, each with separated
dc circuit.
In this arrangement
there is no dc
transmission line and
both converters are
located at one site.

C. Back-To-Back
• The purpose of this kind of configuration is to connect two
asynchronous systems.
• It reduces the total system cost, due to absence of lines/cables;
current rating of the system shall be increased with reduced
voltage.
• Thus, transformer size could be reduced.
60Hz 50Hz
e.g. Itaipu Brazil (60Hz)-Paraguay (50Hz)
2. Bipolar Link
• Bipole has two conductors, upper pole is operating in positive
current and positive voltage and lower pole is operating in
negative voltage and negative current.
• Both poles transmit a power in same direction.
• It is grounded at both stations.
I
I
+
-
+
-

2. Bipolar Link
• Both poles are operating at equal currents during steady state,
therefore zero current through the ground.
• It can be operating as a single pole during fault at another pole.
I
I
I=0I=0
The most common configuration for modern overhead HVDC transmission lines is bipolar with a single 12-
pulse converter for each pole at each terminal.
A. Bipolar Link: Outages
• Monopolar earth return operation, often with overload capacity,
can be used during outages of the opposite pole.
I
I=0
II

B. Bipole, Metalic Return
• Metallic return operation capability is provided for most dc
transmission systems.
• This not only is effective during converter outages but also
during line insulation failures where the remaining insulation
strength is adequate to withstand the low resistive voltage drop in
the metallic return path.
I
I
2I
C. Bipole, Series Connected Converters
• For very-high-power HVDC
transmission, especially at dc
voltages above ±500 kV (i.e.,
±600 kV or ±800 kV), series
connected converters can be
used to reduce the energy
unavailability for individual
converter outages or partial line
insulation failure.
Converters
Operating in this mode also avoids the need to transfer to
monopolar metallic return to limit the duration of emergency
earth return.
Series Connected Converters. two
series-connected converters per
pole in a bipolar system, only one
quarter of the transmission
capacity is lost for a converter
outage or if the line insulation for
the affected pole is degraded to
where it can only support half the
rated dc line voltage.

Components of HVDC Systems
This section presents a brief introduction of the
components involved on HVDC systems
Elements of HVDC System
• The three main elements of an HVDC system are: the converter
station at the transmission and receiving ends, the transmission
medium, and the electrodes.
Terminal A Terminal B

Overview and Organization of HVDC Systems
• Basic structural diagram of a bipolar HVDC system.
Monitoring, Control, Protection
Pole 2
Pole 1
To/From
other
terminal
1. AC Swichyard
2. AC Filters
3. Transformers
4. Converter Valves
5. Smoothing
Reactors and DC
Filters
6. DC Swictyards
Types of HVDC Systems
• The detailed structure and components of a HVDC system
depend on the configuration and operating mode.
Monopole, Midpoint Grounded
Bipole
Multiterminal
Converters
Different common system configurations and operating modes used for HVDC transmission

Basic HVDC Single Line Diagram
• Basic HVDC Single Line Diagram
HVDC Converter Station Design
Shunt
Capacitor
bank
AC filter
banks
AC Switch
yard
Converter
building
DC Switch
yard
AC
Filter
DC
Filter
DC
Filter
Source: ABB
Improvement: FGL
Source: ABB
Improvement: FGL
Approximately 80 x 180 meters

Longquan Converter Station, Panorama View
The Longquan HVDC converter
station in China (above) is similar to
the converter stations ABB will
deliver in Brazil. Converter stations
of this type are used in large
hydopower transmission projects, in
China and other countries.
Source: ABB
Converter Station size:600m x 360m
The 500kV Longquan
Converter Station is one of
supporting the power
transmission project for Three
Gorges Dam Power Delivery
in China.
The construction site is
located in Xiangyanshi
Village of Longquan Town of
Yichang County in Hubei
Province. Project was
completed on June 30, 2002
500KV DC bipolar, transmission
capacity of 3000MW, 2 × 6 groups
complete duplex valve blocks, each
pole with a 12-pulse valve block, 12
units of converter transformers (plus
2 backup), and 8 groups of AC filter
for a total 1076Mvar.
Three Gorges –Guangzhou, Jingzhou
Source: ABB
Two converter stations for the 3,000
MW HVDC power link to transmit
electricity from the Three Gorges
hydropower plant in central China to
the Guangdong province.

HVDC Classic Converter Station
• HVDC-CSC
Converter
Transformer
Smoothing Reactor
AC Filters
DC Filters
Converter
DCDC
ACAC
Thyristor Valves
OutdoorOutdoor
IndoorIndoor
Outdoor
Indoor
Source: ABB
Source: ABB
HVDC Classic
HVDC Classic
Thyristor valves
Thyristor modules
Thyristors
Line commutated
Thyristor Module
3 phase arrangement inside a valve hall
(500 kVdc / 825MW)
One valve module, including
thyristors, RC snubber circuits and
reactors
Valve Arrangement
Direct Light Triggered Thyristor (LTT) and fiber
optic connectors
ThyristorSingle
Valve
Quadruple
ValveDoble
Valve
Source: Siemens
Source: Siemens
Source: Siemens

HVDC VSC Converter Station
• HVDC-VSC
OutdoorOutdoor
IndoorIndoor
Outdoor
Indoor
IGBT Valves
HVDC Light Converter Station
Source: ABB
Source: ABB
Shoreham HVDC Light
converter station overview.
Shoreham, NY, USA.
HVDC Light®
HVDC Light®
Coolers
AC filters
Phase
Reactor
IGBT Valve
Enclosures
StakPak™ IGBTs with six and four sub-
modules
The HVDC Light® converter station consists
of four parts:
1. The DC yard, with DC filtering and
switches;
2. The converter, with the IGBT valves and
the converter reactors;
3. AC filter yard;
4. The grid interface, with power transformer
and switches.
Source: ABB

HVDC Light®
HVDC Light
IGBT valves
IGBT valve stacks
StakPaks
Submodules
Self commutated
Two of three thyristor valve
stacks used for long distance
transmission of power from
Manitoba Hydro dams
IGBT Valve Stacks
StakPak™
Submodule
Chip
Solid-state converter development
Source: ABB

Solid-state converter development
Voltaje (kV)
Current (kA)
4 inch 5 inch
6 inch
New Generation of Thyristors
6” Thyristor (8 kV /4.5 kA) for
XJB-SHA UHVDC Project
Suspended Valve: AREVA
Source: Areva
Source: Areva
Source:Areva

Valve Hall
Converter Transformer
Suspended Valvue
Wall Bushing
Source: Siemens
Source: Siemens
Valvues Hall
Source: ABB
Double Valves 500 kV DC, Zhengping
Chandrapur site
Converter Housing
AC
Filter
DC
Filter
DC
Filter

Baltic Cable, DC yard
Source: ABB
Wall Bushing
Converter Bulting
DC Yard
HVDC Terminal Requirements
AC Switchyard
Connects the Terminal to the AC System
AC
Filter
DC
Filter
DC
Filter

Chandrapur AC yard
Source: ABB
AC Yard
Baltic cable, ac side
Source: ABB
AC
Filter
DC
Filter
DC
Filter
Source: ABB
Improvement: FGL

AC
Filter
DC
Filter
DC
Filter
AC Filters, Capacitor Banks
Reactive Power Supply
Filter harmonic Currents
Longquan AC Filters
Source: ABB
AC
Filter
DC
Filter
DC
Filter
Capacitor
Reactors

New Zealand, ac filters
Source: ABB
Shunt Capacitor
Source: ABB

Converter Transformers
• Obtain the AC Voltage needed for the required DC Voltage
• Obtain 12-Pulse Operation (Star and Delta Connection)
• Allow for Series Connection of 6-Pulse Bridges
AC
Filter
DC
Filter
DC
Filter
Source: Siemens
Smoothing Reactors and DC Filters
• Smoothen the DC Current
• Avoid Resonance with DC Line
• Limit Interference caused by DC Side Harmonics
DC Switchyard
• Achieve required DC Side Transmission Configuration
AC
Filter
DC
Filter
DC
Filter

New Zealand, dc filter
Source: ABB
AC
Filter
DC
Filter
DC
Filter
Source: ABB
Improvement: FGL
New Zealand, smoothing reactor
New Zealand, DC Filter
New Zealand, sound barriers
Source: ABB
AC
Filter
DC
Filter
DC
Filter
800kV HVDC Smoothing Reactor 4000A 75mH
Sound Barriers

DC Smoothing Reactors
•Connected in series in each converter with each pole
• Decreases harmonic voltages and currents in the DC
line
• Smooth the ripple in the DC current and prevents the
current from becoming discontinuous at light loads
• Limits crest current (di/dt) in the Rectifier due to a
short circuit on DC line
• Limits current in the bypass valve firing due to the
discharge of the shunt capacitances of the dc line.
•Two Smoothing Reactors per pole
•Inductance - 125mH
•Nominal DC Voltage – 500KV
•Max DC Voltage – 515KV
•BIL – 950/1425KV
(Typical Value for 2000 MW
± 500 KV Bipole HVDC
Link)
Wall Bushing
Smoothing
Reactor
DC Filters
Source: ABB

DC High Speed Switches
DC Switch
Snubber Capacitor Snubber Reactor
Arrester
HVDC CONTROLS SYSTEM
GENERAL CONTROL CONCEPTS
This section present an introduction of the general
concepts used to control HVDC systems

HVDC Control: General Concept
What are the basic principles of HVDC Controls?
P
Rectifier Rectifier
+ -
+
-
+
-
1dU 2dU
RUI
1 2d dU U
I
R


1 1.dP U I 2 2.( )dP U I 
HVDC Control: General Concept
• What are the basic principles of HVDC Controls?
• Id in one direction only.
• Magnitude of Id or power is
controlled depending on the
difference in the terminal
voltages (Ud1, Ud2)
•Direction of power is
controlled depending on the
polarity of the terminal voltages
(Ud1, Ud2)
d1 d2
P
2dU1dU
2dU
1dU
P

HVDC Control
I
V
V
I
I
dI
I
V
V
I
General Control Loops for Classical HVDC
Multi-Terminal HVDC Systems
• Future Electricity Network use the concept of Multi-
Terminal HVDC Systems
Multiterminal

Practical Multi-Terminal HVDC
Control Strategies for MTDC
Schematic representation of MTDC control system hierarchy
VSC dcn
iP ,dc iP
,dc iUiV
,g iP
,l iP
1gP
1lP
Time
Scale
The terminal controllers
determine the behavior of the
converter at the system bus.
They are designed for the main
functions for
controlling: active power (P),
reactive power (Q), AC and the
DC voltage (Vac, Udc)
The master control optimizes the overall performance of the
MTDC by regulating the DC side voltage.
It is provided with the minimum set of functions necessary for
coordinated operation of the terminals in the DC circuit, i.e.
start and stop, minimization of losses, oscillation damping and
power flow reversal, black start, AC frequency and AC voltage
support.
sec
<s
ms
s

refQ
Q
acV
,ac refV
*
qi *
di
refP
P
dcU
,dc refU
,ac CtrlV
CtrlQ
,dc CtrlU
CtrlPTerminal Controller
Terminal Controllers are
based on locals actions and
measurements.
Wide-area measurement and
control can improve the
system performance.
refQ
Q
acV
,ac refV
*
qi *
di
refP
P
dcU
,dc refU
,ac CtrlV
CtrlQ
,dc CtrlU
CtrlP
 
refQ
Q
,
,
i Q
p Q
K
K
s
 *
qi
maxi
maxi
  ,
,
i Udc
p Udc
K
K
s
 *
di
maxi
maxi,dc refU
dcU 
acV
,ac refV ,
,
i Vac
p Vac
K
K
s
 *
qi
maxi
maxi
 
refP
P
,
,
i P
p P
K
K
s
 *
di
maxi
maxi





 

*
dv
*
qv
,d refi
,q refi
di
qi
dv
qv
,
,
i id
p id
K
K
s

,
,
i iq
p iq
K
K
s

L
L
Q Controller P Controller
Udc ControllerVac Controller
Idq Controller
Terminal Controller

(i) Voltage Margun Method (VMM)
,AdcU
AP
dcU
upperPlowerP
When the active power is to be transmitted
from Terminal B to Terminal A (PA<0,
PB>0), the voltage margin (Udc) is
subtracted from the DC reference voltage
for Terminal A.
(i) Voltage Margin Method (VMM)
(ii) Voltage-Droop Method (VDM)
,AdcU
AP
mc
dcU
upperPlowerP
,
a
dc refU
b
refP
b
refU
a
refP
(ii) Voltage-Droop Method (VDM)
When Udc drops the slack converter station
(VSCA) will increase the active power
injection in the DC grid PA until a new
equilibrium point.

OffShore Wind Power: Motivation
This section presents a set of driver to use HVDC
in the integration of offshore wind power
Context: Where Decarbonise?
Roadmap 2050: A practical Guide to a Prosperous, Low-Carbon Europe
80% CO2 EMISSION REDCUTION
95%
5.9 GtCO2/yr
5.2 GtCO2/yr
1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 20402030 2050
Oil
Gas
Coal
Hydro
Nuclear
Solar
Wind
Geothermal
Biomass
CCS
BillionBarrelsofOilEquivalentperyear
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
The 80% CO2
reduction overall
implies 95%
reduction
in Power
Roadmap 2050: A
practical Guide to a
Prosperous, Low-
Carbon Europe
Energy Supply in 2050
(High Res Pathway)
Historical
Roadmap 2050
1970 1980 1990 2000 2010 2020 2030 2040 2050
0
10
20
30
40
50
60
70
80
90
100
All RES
Wind
EU Energy Policy to 2050, EWEA

North Sea National Targets 2030
UK Wind Farms: East Anglia
IR ISH SEA
ENGLISH CHANNEL
BELG
UNITED
KINGDOM
IRELAND
IR ISH SEA
ENGLISH CHANNEL
BELG
UNITED
KINGDOM
IRELAND

Firth of Forth
Phase 1
1075 MW
Firth of
Forth
Phase 3
790 MW
Firth of Forth
Phase 2
1820 MW
Forth Array
Neart na
Gaoith
Inch Cape
Bell Rock
UK Wind Farms: Dogger Bank, HornSea, Firth of Forth
IR ISH SEA
ENGLISH CHANNEL
BELG
UNITED
KINGDOM
IRELAND
IR ISH SEA
ENGLISH CHANNEL
BELG
UNITED
KINGDOM
IRELAND
"They could see gross value added to the UK economy of £7 billion and a
cumulative cost-reduction impact of £45 billion for the whole offshore wind
sector in UK waters by 2050,"
Wind farm 'may save £45bn' in costs
Offshore wind could boost GDP by “huge” 0.6%
The figures build on 2010 research from the Offshore Valuation Group
which found that by harnessing less than a third of the UK’s offshore wind
resource, the UK could generate the equivalent of
one billion barrels of oil a year by 2050
Integration of Wind Power using HVDC
This section presents a introduce of use HVDC
technologies to integrate offshore wind farms

Connections for offshore wind farms
Electrical view of an offshore wind farm
• Schematic layout of an offshore wind farm; the collecting point
can be an offshore substation.
PCC: point of common coupling
Use of DC or AC
Single/Multiple
Use of DC or
AC even low frequency
Single/ Multiple
Collecting point
Multiples AC or DC
technologies
Single/ Multiple
Interface
Single/ Multiple
NKT Anholt cable

Offshore Substations
Possible layout for a 980MW (196x5MW) offshore
wind farm
(a) Alternative A
(b) Alternative BOSS: Offshore Substation
Offshore Wind Farms
• Structure of Typical Electrical Infrastructure used on offshore
wind farm: High Voltage AC approach
Transmission
System
POI
Transformer
substation
Collecting point Local WT collector system
...
...
...
...
...
...
...
...
...
...
...
Terminal
Substation
Integration
system
Wind Turbine
MV Distribution
system
HV Transmission
system

High Voltage Alternate-Current Transmission
• The basic configuration of 600 MW wind farm with a high-
voltage alternating-current (HVAC) solution.
SVC: static VAR compensator; XLPE:
polyethylene insulation sources.
30 kV
300 MVA
400 kV
Onshore
network
600 MVA
150 kV
150 kV, XLPE cable
Rating 200 MW
Onshore converter
station
30 kV
30 kV
30 kV
300 MVA
150 kV
SVC
150 kV, XLPE cable
Rating 200 MW
150 kV, XLPE cable
Rating 200 MW
SVC
HVACHVAC
Siemens: 20 (AC) offshore substations so far
Copyright © Siemens all rights reserved
1st Generation

Siemens: 1st Generation
Siemens: 2nd Generation
2nd Generation

Siemens: 2nd Generation
• Compact Design
Thanet 300 MW grid connection June 2010
Prof. Francisco M. Gonzalez‐Longatt at Thanet Wind Farm

Thanet 300 MW grid connection June 2010
Thanet Wind Farm
• 100 wind turbines each with a
control
• loop which has:
– Feedback
– Gain
– A finite delay
– A sampling frequency
• Set in an array of 100 cables
of
• assorted lengths and cross
sections
– every joint is a reflective node
– outages create thousands of
states
• Fed from the grid where the
source
• impedance / fault level may
change
• May need to allow for filters

HVDC: LCC + STATCOM
• Basic configuration of 500MW wind farm using a line-
commutated converter (LCC) high-voltage direct-current
(HVDC) system with a STATCOM (for a configuration for a
1100MW wind farm using an LCC HVDC system with diesel
generators on the offshore substation.
F: filter; HFF: high frequency filter; the statcom can be replaced with a diesel generator.
HVDCHVDCOffshore wind farm
145 kV, 50 Hz Statcom
F
HFF
Offshore substation
Three-phase
Two-winding
Converter
transformer
Integrated return
cable 500 MW
500 kV
1000 A
HFF
F
F
F
F
380 kV
Single-phase
Three-
winding
Converter
transformer
380 kV, 50 Hz
Onshore converter
station
Voltage Source Converter based HVDC
• A 600 MW wind farm using two voltage source converter
(VSC); high-voltage direct-current (HVDC) systems, each
converter station with a 300 MW rating.
Source: based on Eriksson et al, 2003

• A 500 MW wind farm using one VSC HVDC system based on a
converter station with a 500 MW rating.
BorWin 1, 400 MW HVDC Light
Standardisation
•Consistent block sizes for wind farms
• Allow suppliers to compete head to head
Best practice design

Siemens: 3rd Generation
Source: ABB
400 MW HVDC Light® system off-shore
station on platform with sub-sea structure
Onshore station at E.ON substation Diele
Cables
DC cable submarine (2x125km)
DC cable on land (2x75km)
Fibre optic cable (200 km)
Source: ABB
Comparison: Rating
• Presently, AC cables have a maximum rating of about 200MW per three-
phase cable.
• This rating is based on a voltage level of 150–170 kV, compensation at both
ends of the cable and a maximum cable length of around 200 km.
• For shorter distances, voltage ratings may increase to 245 kV, which would
raise the maximum rating to 350MW over a maximum of 100 km, or 300MW
over 150–200km.
Number of cables needed for different wind farms and different technical
solutions
Note: CS ¼ converter station; HVAC: high-voltage alternating-current; HVDC: high-voltage direct-current; LCC: line-commutated
converter; VSC: voltage source converter

Comparison: Losses
• The losses of HVDC connections show only a very limited correlation with
the length of the cable, depending on the efficiency of the converter stations.
• The efficiency of LCC stations is usually higher than that of VSCs. This
means that for short distances the losses from a HVAC link are lower than
those from a HVDC connection, owing to the comparatively high converter
losses.
• There is, however, a distance X where the distance-related HVAC losses reach
similar levels to those of HVDC links
Comparison of losses for
high-voltage alternating
current (HVAC) and
high-voltage
direct current (HVDC)
Selection of Transmission Technology
• Choice of transmission technology for different wind farm
capacities and distances to onshore grid connection point based
on overall system economics (approximation); economics of
high-voltage alternating-current (HVAC) links, line-commutated
converter (LCC) based high-voltage direct-current (HVDC) links
and voltage source converter (VSC) based HVDC link.
50 100 150 200 250 300
100
200
300
400
500
600
700
800
900
HVAC
(up to 170 kV)
HVAC or
VSC
based
HVDC
HVAC (245 kV) or
VSC based HVDC
VSC based HVDC
VSC based HVDC
LCC based HVDC
VSC based HVDC or LCC based HVDC
HVAC (245 kV) or
VSC based HVDC

System Solution
Use of Low Frequency
• Connection of an offshore wind farm using a low AC frequency.
PCC: point of common coupling.
Source: based on Schutte, Gustavsson and Strom, 2001.
2/3
2/3
Frequencies lower than 50 or 60 Hz are currently used mainly in electrified railway
systems. The railway systems in Germany, Switzerland, Austria, Sweden and Norway,
for instance, use 16 2/3 Hz at 15 kV, Costa Rica uses 20 Hz and the USA mainly 25 Hz.
DC internal Collector System
• DC wind farm design based on wind turbines with AC
generators.
Source: based on Martander, 2002.

Use of DC Generators
• DC wind farm design based on wind turbines with DC
generations (DCGs)
Source: based on Lundberg 2003
Multi-terminal VSC HVDC network
• The MTDC transmission system can connect several large
offshore wind farms distantly located and export the wind power
to several onshore grids widely dispersed.
offshore onshore

Topologies of multi-terminal VSC-HVDC
transmission for large offshore wind farms
This section shows some of the candidatee
topologies to be used on the massive integration of
wind power
Two WFVSC link to Single GVSC
• Two WFVSC link to Single GVSC The DC tie-cable
interconnecting offshore
substations or onshore
substations can provide
system redundancy and
control flexibility.
offshore
onshore
if the distance between offshore
substations is less than onshore
substations, the tie-cable will be
built offshore

Single WFVSC link to two GSVCs
• Single WVVS link to two GVSCs The DC tie-cable
interconnecting offshore
substations or onshore
substations can provide
system redundancy and
control flexibility.
if the distance between onshore
substations is less than offshore
substations, the tie-cable will be
built onshore
offshore
onshore
2 WFSCs link to 2GVSCs
• Two WFVSCs link to correspondent GVSCs with an onshore tie-
line
offshore
onshore

2 VFVSCs link to 2 GSVCs
• Two WFSCs link to correspondent GSVCs with an offshore tie-
line
offshore
onshore
3 WFVSC link to 3 GVSCs
• Three WFVSCs link to correspondent GSVCs with wind farms
ring
offshore
onshore
onshore
The wind farms ring
topology can withstand
different faults without
losing wind power using
minimal number of HVDC
circuit breakers

Conclusions
This section presents a general conclusion…
Multi-Terminal HVDC Systems
Future Electricity Networks will be
radically different to the present

Santiago de Chile
8th August 2012
Massive Integration of Offshore
Wind Power using HVDC
FranciscoM.Gonzalez-Longatt
@fglongatt@fglongatt
Department of Electrical Engineering
Coventry, United Kingdom
Asociacion Venezolana de Energia Eolica
Photo: http://www.bard‐offshore.de/media/fotos.html
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