HVDC Transmission SystemElectrical Engineering Seminar
September 2, 2008 14.00-16.00 Hrs. Faculty of Engineering
King Mongkut’s University of Technology North Bangkok
Presented byNitus Voraphonpiput, Ph.D.
Engineer Level 8 Technical Analysis – Foreign Power Purchase Agreement Branch
Power Purchase Agreement DivisionElectricity Generating Authority of Thailand
2
Aims To introduce basic concept of the High Voltage Direct Current (HVDC)
transmission systems. To present applications and
technologies of the High Voltage Direct Current (HVDC) transmission
systems.
3
Content Introduction Why uses HVDC? Applications of HVDC Future Trends Conclusion
Introduction
5
Power transmission was started in the early 1880s using direct current (DC).
With the development of transformers, induction motors and synchronous generators, the DC transmission systems were replaced by AC
Transmission system.
Nowadays, due to successful development of HV converters (rectifiers and inverters) based on
Silicon Controlled Rectifiers (SCR), the High Voltage Direct Current (HVDC) transmission systems become an economic and attractive
technology.
Introduction
6
HVDC is the abbreviation of High Voltage Direct Current.
Beginning of HVDC Transmission System Marcel Deprez put his experiment (1881) to
practice in 1882. a 1.5 kW at 2 kV over a distance of 35 miles was operated.
In 1889, R. Thury continued the D. Marcel work, he used DC generators connected in series to generate high voltage and sent 20 MW at 125
kV over a distance of 230 km (Moutiers-Lyon) in France.
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Part I: Mercury Arc Valve
The first commercial HVDC in Europe was Gotland in Sweden (1954).
Cross Channel -1961; 160 MW, 64 km cable between England and France (ASEA)
Volgorod – Donbass - 1965; 720 MW, 470 km in Russia Sardinia; 1967; 200 MW, 413 km between Sardinia and Italian
mainland (GEC England) New Zealand – 1965; 600 MW between the south and north
islands (ASEA) Konti-Scan I – 1965; 250 MW, 180 km between Sweden and
Denmark (ASEA) Sakuma - 1965; 300 MW frequency converter in Japan (ASEA)
Vancouver I - 1968; 312 MW, 69 km between BC and Vancouver island (ASEA)
Pacific HVDC Inter-tie – 1970; 1440 WM, 1362 km overhead line between Oregon and Los Angeles (JV between ASEA and GE)
8
Part II: Thyristor Valve
Gotland Extension – 1970; Adding 50kV and 10 MW to the Gotland scheme using thyristors (ASEA)
Eel River – 1972; 320MW first all thyristor asynchronous link in Canada (GE)
……………………..(more than ten projects)…………. Haenam-Cheju – 1993; +/- 180 kV, 300 MW, south Korea
(English Electric) Baltic Cable Project – 1994; 450 kV and 600 MW (Sweden
Germany) Kontek HVDC Interconnection - 1995; 400 kV, 600 MW,
Denmark Scotland-N.Ireland – 1996; 250 kV and 250 MW
Leyte-Luzum -1997; 400 kV; 1600 MW; 440 km, Philippines. Chandrapur-Padghe – 1997; +/- 500 kV; 1500 MW; 900 km, India
Greece-Italy – 1997; 500 kV EGAT-TNB – 2001; 300kV and 300 MW, 110 km thyristors
(Siemens) ………
9
Main components of a HVDC transmission
Cooling system
10
Main components of a HVDC transmission
Converter stations connected to the AC bus via transformers.
Two-winding or three-winding transformers, in which a 30 degrees phase shift is required between the
converter units because of the 12-pulse connection selection of vector groups.
The on-load tap changer of the transformer Filters and capacitor banks.
Converter bridges, usually two six-pulse bridges in series, equipped with controls of their own enables
independent operation Cooling system
11
Main components of a HVDC transmission
Firing pulses of the thyristors are usually passed via optical fibers.
Control system. Smoothing inductors (act as filters harmonics in DC
and limits the rate of current change.) DC Filters (on overhead lines).
A cable or an overhead line as a transmission path for the current passing through sea or earth, also
electrodes are required.
12
6-pulse Bridge Circuit
Thyristor valveComponents of the thyristor m
odules
13
A Thyristor valve
Thyristor Module
2x 6-bridge
Symbol
Thyristor valves
EGAT-TNB HVDC 300 MW 300 kV
14
YY
Converter Transformers
Transformer
EGAT-TNB HVDC 300 MW 300 kV
Converter Transformers
15
Switchyard, Capacitor Banks and AC Filters DC Tower and DC Line
EGAT-TNB HVDC 300 MW 300 kV
16
Smooth Inductor
(smoothing reactor)DC Active Filter
EGAT-TNB HVDC 300 MW 300 kV
17
HVDC Transmission System (electrical system)
18
Electric Power Transmission
R
UUP dd 2
21
12
HVAC HVDC
jX RES ER Ud1 Ud2
RSRSS
RSRS
X
EEEQ
X
EEP
cos
sin
2
12
12
19
IUP
IUPR
UUI
d
d
dd
.
.
22
11
21
Rectifier Inverter
+ UR -
AC system
AC system
Electric Power Transmission using HVDC
20
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Electric Power Transmission using HVDC
21
Converter Operation
Voltage and current waveform of HVDC converters
22
30
VI.cos
I
I.sin
30
866.02
)2515cos(15cos
2
)cos(coscos
Rectifier Operation of the 6-pulse bridge converter
Assume = 15 and = 25
The converter operates in rectifier mode. It transmits active power while consumes reactive power.
Converter Operation
23
145
VI.cos
II.sin
145
823.02
)25135cos(135cos
2
)cos(coscos
Inverter operation of the 6-pulse bridge converter
Assume = 135 and = 25
The converter operates in inverter mode. It receives active power while
consumes reactive power.
Converter Operation
24
Alternatives for the implementation of a HVDC transmission system
i) Mono-polar Configuration
ii) Bipolar Configurationa) Earth Return
b) Metallic Return
iii) Homo-polar Configuration
25
Alternatives for the implementation of a HVDC transmission system (continued)
26
This configuration can be found as early as 1954, there was no interest in its commercial use until the 1990s because the control and protection equirements were considered to be exce
ssively complex.
The first commercial application, taken into full service in June 2000, is a 1100 MW asynchronous back-to-back link betwee
n Argentina and Brazil
Source: Alstom
Capacitor Commutated Converter HVDC (CCC-HVDC)
Why uses HVDC?
28
Why uses HVDC?The reasons that HVDC have been used
are:1. An overhead DC transmission line with its towers can be designed to be less costly per
unit of length.2. It is not practical to consider AC cable systems exceeding 50 km (due to capacitive
current charging of the cable).3. Some AC electric power systems are not synchronized to neighboring networks even though their physical distances between
them is quite small. (Interconnection problem)
29
Less cost/unit length
Source: Siemens and Jos Arrillaga’s book (1998)
30 300 km 300 km 300 km
900 km
HVDC
HVAC
Less cost/unit length
31 Source: ABB
Less cost/unit length
32
System Modeling for Line Loadability
Line model
Source: EPRI
Limitation of AC transmission line
33
Typical values of SILfor overhead transmission lines
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
Note: No series or shunt compensation
Constant line voltage drop 5%
Steady state stability limit (30% margin)
Source: EPRI
Thermal Limit
HVDC can utilize line up to thermal limit.
Limitation of AC transmission line
34
Limitation of AC cableGeneral AC Cable Technologies Pipe-type
Coated and protected steel pipe houses the cable and dielectric fluid
Dielectric fluid is maintained under pressure Insulation material is Kraft paper or laminated
paper-polypropylene Self-contained, fluid-filled (SCFF)
Insulation impregnate is a low viscosity liquid which must be maintained under pressure internally
Conductor has central fluid duct Extruded cross-linked polyethylene (XLPE)
Solid dielectric insulation, no fluid, no pressurizing plant
Limited applications above 230 kV to dateSource: ABB
35
1.SCFF for AC or DC 2.MI for DC
3.Single-core XLPE for AC 4.Three-core XLPE for
5.Extruded HVDC Light for DC 6.Extruded HVDC Light for DC
Source: ABB
36 Source: ABB
Limitation of AC cables
37 Source: ABB
HVDC can utilize cable up to thermal limit.
Limitation of AC cables
38
Limitation of AC Interconnection
It is impossible to connect two (or more) different system frequencies via HVAC.
Without control center to take care off whole system frequency, it is impossible to connect two (or more) systems through HVAC event
their system frequencies are equal.
Difficult to control power flow between areas without special equipment such as phase
shifting transformer.
But HVDC can overcome these problems.
Applications of HVDC
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Applications of HVDC
41
Emergency Frequency ControlWhen a large generator is
tripped, the system frequency falls down over an acceptable level.
HVDC can rapidly increase or reverse power flow direction to
compensate unbalance active power to recover system frequency.
42
Automatic Frequency ControlWhen you require to improve frequency deviation in normal
operation and after large disturbances, application of Automatic Frequency Control (AFC) function is recommended.
Source TMT&D, Japan
43
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.)
Source TMT&D, Japan
44
Starting Up the Generator
When an HVDC system is connected to the isolated generator at the sending end, the system has to be started up in coordination with the governor action of the generator. The bipoler operation is available, overall transmitted power can be built up smoothly from zero to the rated value by having two poles transmit power in opposite dire
ctions.
Source TMT&D, Japan
45
Usage of HVDC in USA (same frequency)
46
Usage of HVDC in Japan (two different system frequencies)
Source: Toshiba
47 Usage of HVDC in India.
48
Usage of HVDC in China
49
Itaipu, Brazil
Brazil decided to build a HVDC transmission system from Itaipuhydro power plant to SãoPaulo to meet the rapidly growing
power demand in 1978. A 3150+3150 MW ±600 kV HVDC power link between Itaipu and SãoPaulo brings power generated at 50 Hz (in
Itaipuhydropower plant) to the 60 Hz network in SãoPaulo. This project was commissioned in 1984-1987.
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Québec -New England, Canada -US
This project was commissioned in 1990-1992. It is a 2000 MW ±450 kV multi-terminal HVDC power link.
The HVDC multi-terminal system brings power from La Grande II hydro power station to loads in Montreal, Québec, Canada
and to Boston, Massachusetts, USA
51
Baltic Cable, Sweden -Germany
A 600 MW 450 kV HVDC sea cable system links between Germany and Sweden to enable further integrate power systems of the Baltic Sea region. This project was commissioned in 1997 and it
is an economic exchange between a thermal power system and a hydro/nuclear power system
52
Brazil -Argentina Interconnection
This project links Argentina (50 Hz) and Brazil (60 Hz) to utilize their electricity resources more efficiently and cost effectively.
It providers import and export power to take advantage of peaks demand between Brazil’s and Argentina’s asynchronous
networks. It is a CCC-HVDC (2200 MW 140 kV (±70 kV) back-to-back system).
53
HVDC has been integrated. Because of long transmission lines, the AC system experiences severe power oscillations after systems faults, close to the stability limits. In first case, HVDC is transmitting power in constant power mode (curve a). ,the power oscillations occur.
With daming control of HVDC, the oscillations are damped very effectively (curve b). Without HVDC, e.g. with a fully synchronous interconnection, such a large power system would be unstable in case of faul
t contingencies, thus leading to blackout.
HVDC GuiGuang, China
54
Hokkaido-Honsyu HVDC (Japan)
Source: Toshiba
55
EGAT-TNB HVDC, Thailand
In 2003, a mono-polar 300 MW 300 kV HVDC transmission system was installed between Thailand and Malaysia. This HVDC offers an
important option in economic operation of the Thailand power system. It transfers economical energy between two countries. This HVDC provides
four enhanced stability functions for AC system. One of these is Power Swing Damping (PSD) function. This function was designed to damp inter-
area oscillation on the tie transmission line linking Central system and Southern system.
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January 13, 2005, TNB experienced the separated system event between the Northern part and the Southern part. It resulted in over-frequency
in the Northern part and low frequency in the Southern part due to over generation (in north) and lower generation (in south) respectively. Frequency Limit Control (FLC) function of the HVDC increased power into EGAT system
from 300 MW to 406 MW to stabilize frequency in TNB system.
TNB frequency
DC Power to EGAT
K u a h
M e la k a
S e re m b a n
G e o rg e to w n
K o ta B h a ru
K u ala T e re n g g a n u
Ip o h
K u an ta n
S h a h A la m
A lo r S e ta r
K a n g a r
J O H O R
P A H A N G
M E L A K A
N E G E R I S E M B IL A N
S E L A N G O R
P E R A K
K E D A H
P U L A U P IN A N G
K E L A N T A N
T E R E N G G A N U
P E R L IS
W IL A Y A HP E R S E K U T U A N
L A N G K A W I
M E L A K A
B E R S IA
K E N E R IN G
T E M E N G O R
K E N Y IR
S G P IA H U P P E R
S G P IA H L O W E R
J O R
W O H
O D A K
C H E N D E R O H
P E R G A U
MAIN GRID INPENINSULAR MALAYSIA
N
L e g e n d
H y d ro P o w e r S ta t io n
T h e rm a l P o w e r S ta t io n
S ta te C a p ita l
E x is t in g P la n n e d
5 0 0 k V O v e rh ea d L in e
2 7 5 k V O v e rh ea d L in e
2 7 5 k V C ab le
J o h o r B a h ru
P R A I
G E L U G O R
S E G A R I
C O N N A U G H T B R ID G E
S E R D A N G
K A P A R
P O W E R T E K
P D P O W E R
G E N T IN G S A N Y E N
P O R T D IC K S O N
Y T L
P A S IR G U D A N G
P A K A
Y T L
A y e r T a w a r
B a tu G a ja hP ap a n
K u a la K a n g s a r
B u k it T a m b u nJ u n ju n g
B u k it T en g a h
G u ru n
B e d o n g
K o ta S et ar
C h u p in g
B u k i t T ar ek
K L (N )K L (E )
H ic o m G
K L (S )
S a la k T in g g i
M ela k a
K g A w a h
S c u d a i
T elo k K a lo n g
T an a h M e ra h
J A N A M A N J U N G
M a jo r T N B S u b s ta t io n
Y A N
Y o n g P e n g (N )
B u k it B a tu
S ed il i
L e n g g e n g
Y o n g P e n g (E )
3 0 0 k V H V D C L in e
EGAT-TNB HVDC, Malaysia
Future Trends
58 Source: ABB
59
Voltage-sourced converter based HVDC systems are called HVDC Light (ABB) or
HVDC Plus (Siemens) become new trend of HVDC due to
Converters do not require reactive power. Suitable both for submarine and land cable connecti
ons. Advanced system features.
Small footprint (e.g. 550 MW): 120 x 50 x 11 meters. Black Start Capability Short delivery time.
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Voltage-sourced converters (VSC) operate with a smooth dc voltage provided by a
storage capacitor. The fast switching capability of the IGBT allows to create a
pulse width modulated (PWM) AC voltage.
The converter can operate in 4 quadrants of the active power and reactive power plane.
The commutation does not depend on the ac network voltage. Thus it can connect to very weak
power systems. The ac output voltage of the converter can be
changed extremely quickly.
61
However, the voltage and power ratings of IGBTs are as yet far below those of
thyristors and so applications with voltage-sourced converters are limited to low and
medium power. The first commercial project was once more
commissioned on Gotland and taken into service in November 1999. A power of 50 MW is transferred
through two underground cables of 70 km length at a voltage level of ±80 kV from the south of the
island to the north. A similar installation (3X60 MW, ±80 kV) was
commissioned and brought into operation in 2000 to connect the grids of Queensland and New South
Wales, Australia.
62
Power rating of Switching devices
Source: ABB
63 Source: ABB
64 Source: ABB
65 Source: Siemens
Conclusion
67
Advantages of HVDC DC lines can be loaded up to
the thermal limit. Power flow control.
Does not increase the short-circuit currents in the AC
network. No capacitive charging
current on DC lines. Ground or sea can be used
as a return conductor. Fast control of power and
stabilizing of AC system. N-1 criteria may not be
required. Economic for long
transmission line and bulk energy.
Interconnection between two AC systems is possible.
Disadvantages of HVDCElectric Field can cause a
problem to human.Converter stations are
expensive and complex arrangements when
compared with the stations in an AC system.
Conventional Converters (rectifier and inverter)
require reactive power. Converters produce
harmonics both in the AC network and the DC side.In mono-polar links, the return current passing through ground causes
corrosion in metal objects.Sensitive to fault in AC network near converter.
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Long distance over land
Long distance over sea
Inter-connection
asynchronous network
Wind Turbine
connection to network
Feed
a small isolated
loads
HVDC
+ OH line HVDC
+ Cable CCC
B2B CCC
+OH line CCC
+ Cable VSC
B2B VSC
+ Cable
69
In emerging countries, power systems will grow (very) fast. Because of reliability and economic reasons. HVDC will play a signific
ant role in the future (such as China and Indian).
Conventional HVDC still uses in power system. It is a proven technology.
In future, VSC-HVDC and polyethylene DC cables will made Economic at lower power levels (down to 200 MW) Economic at short distance (60 km).
70
Thank you
ขอบคุ�ณคุรั�บ
Questions and discussions are very welcome.