HVDC
Dr. Osama Abdulrahman Al-Naseem
Electrical Engineering Department
Kuwait University
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EE551
Introduction to HVDC
Dr. Osama A. Al-Naseem, EE Dept, KU
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In 1941, the first contract for a commercial HVDC
system was signed in Germany: 60 MW were to be
supplied to the city of Berlin via an underground
cable of 115 km length. The system with ±200 kV
and 150 A was ready for energizing in 1945.
It was never put into operation.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Nowadays, the GCC Interconnection is the
biggest back-to-back HVDC station in the
world with capacity of (3×600MW) 1800MW
and it is the first of its kind in the region.
Dr. Osama A. Al-Naseem, EE Dept, KU
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The GCC Interconnection grid consists of over 900km of
double circuit 400 kV back bone of overhead line links
from Kuwait, through Saudi Arabia with taps to Bahrain
via Submarine cable, and Qatar and also is extending to
the Emirates and Oman.
Seven main 400kV substations were also built to link the
four countries of Phase 1 of the Project.
Dr. Osama A. Al-Naseem, EE Dept, KU
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400 kV double-circuit transmission line 292 km long from Al Zour (Kuwait) to AlFadhili (Saudi Arabia).
400 kV double-circuit transmission line 114 km between Al-Fadhili and Ghunan
substation close to the city of Dammam in Saudi Arabia.
Back-to-Back HVDC interconnection between the 50 Hz interconnector to the
Saudi Arabia 380 kV, 60 Hz system at Al Fadhili Substation
400 kV double-circuit interconnection comprising overhead lines and submarine
link from Ghunan to Al Jasra (Bahrain) and the associated substations.
400 kV double-circuit transmission line 288 km long between Ghunan to Salwa
(Saudi Arabia) and the associated substations.
400 kV double-circuit transmission line 97 km long from Salwa to Doha South
(Qatar) and the associated substations.
Dr. Osama A. Al-Naseem, EE Dept, KU
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400 kV double-circuit transmission line from Salwa (Saudia Arabia) to Al-Silaa
(UAE) and the associated substations.
Double and a single-circuit 220 kV transmission lines between Al-Fouha (UAE)
to Mhadha (Oman) and the associated substations.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Dr. Osama A. Al-Naseem, EE Dept, KU
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HVDC Converter Station: Areva T&D and Cogelex
were awarded two contracts worth US$234
million.
Areva delivered the region’s first Back-to-Back
1800 MW HVDC converter station. The station
consists of three 600 MW converters including
thyristor valves, 375 MVA converter transformers
in addition to 380 kV and 400 kV circuit breakers.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Dr. Osama A. Al-Naseem, EE Dept, KU
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Costs of d.c. and a.c. transmission
If undersea crossings greater than around 50km are required, then, because of
the capacitive charging current of a.c. cables, d.c. is the only option.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Dr. Osama A. Al-Naseem, EE Dept, KU
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Key HVDC Attributes
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per conductor
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Dr. Osama A. Al-Naseem, EE Dept, KU
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Dr. Osama A. Al-Naseem, EE Dept, KU
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Dr. Osama A. Al-Naseem, EE Dept, KU
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Current Source Converter ∗
Used extensively for point-point transmission of bulk power and are
available at d.c. voltage ratings of up to 800kV and are able to transmit
6500MW over a single overhead h.v.d.c. link.
Thyristors are used and light-triggered on by a gate pulse.
They turn off when the current through them falls to zero. Thus current
source converters are also called line (or naturally) commutated converters.
It can be made up to very high power and d.c. voltage ratings and the
thyristors are comparatively robust with a significant transient overload
capability.
As the thyristors switch off only when the current through them has dropped
to zero, switching losses are low.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Voltage Source Converter ∗
Advantages:
1. can operate at any combination of active and reactive power
2. have the ability to operate into a weak grid and even black-start an a.c.
network
3. have fast acting control
4. can use voltage polarized cables
5. produce good sine wave-shapes in the a.c. networks and thus use small filters
Disadvantages:
1. presently their rating is very much lower than CSC h.v.d.c. schemes
2. their power losses are higher
Dr. Osama A. Al-Naseem, EE Dept, KU
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The Thyristor
(a) Structure of a four-layer thyristor
(b) Symbol
(c) Thyristor characteristic
Dr. Osama A. Al-Naseem, EE Dept, KU
Gate is light-triggered
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Three-Pulse Rectifier ∗
Dr. Osama A. Al-Naseem, EE Dept, KU
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Three-Pulse ∗
Rectifier Output
Waveform
showing the ∗
effect of delay
angle alpha
Dr. Osama A. Al-Naseem, EE Dept, KU
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Three-Pulse Rectifier ∗
Output Waveform
showing the effect of ∗
commutation due to
source inductance
Dr. Osama A. Al-Naseem, EE Dept, KU
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Six Pulse Current Source Converter
α is called the delay angle
Thyristor firing Sequence: 1,2 – 2,3 – 3,4 – 4,5 – 5,6 – 6,1
Dr. Osama A. Al-Naseem, EE Dept, KU
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Six-Pulse ∗
Rectifier Output
Waveform
showing the ∗
effect of delay
angle alpha
Dr. Osama A. Al-Naseem, EE Dept, KU
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Six Pulse Current Source Converter
AC Line Current Harmonics
IN GENERAL:
Harmonic order is mp ± 1
Where m is an integer and p is the number of pulses
Dr. Osama A. Al-Naseem, EE Dept, KU
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Series Twelve Pulse Current Source Converter
Dr. Osama A. Al-Naseem, EE Dept, KU
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Series Twelve Pulse Current Source Converter
Dr. Osama A. Al-Naseem, EE Dept, KU
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Converter Equivalent Circuit
For six pulse converter
Dr. Osama A. Al-Naseem, EE Dept, KU
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Complete DC Link Model
α is called the delay angle
;
β = (180⁰ - α) is called the angle of advance
δ is called the extinction angle.
γ = β – δ is the commutation overlap angle due to the source inductance
The current, and thus the power flow, is controlled by means of the
difference between the controlled voltages.
The current direction is fixed and the power direction is controlled
by means of the voltage polarity.
Dr. Osama A. Al-Naseem, EE Dept, KU
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Complete DC Link Model
Dr. Osama A. Al-Naseem, EE Dept, KU
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HVDC System Control
Minacont
Dr. Osama A. Al-Naseem, EE Dept, KU
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HVDC System Control
In the upper half, station A
is rectifier and station B is
inverter.
Also Vdr_A and Vdi_B
are both positive, so power flows
from station A to B.
In the lower half, station B
is rectifier and station A is
inverter.
Also Vdr_B and Vdi_A
are both negative, so power flows
from station B to A.
Dr. Osama A. Al-Naseem, EE Dept, KU
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HVDC System Control
Dr. Osama A. Al-Naseem, EE Dept, KU
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Main Types of HVDC Schemes
1. Back-to-Back (B2B) Converters eat
2. Monopolar Long-Distance Transmissions
A. Monopole with ground return path
B. Monopole with metallic return path
3. Bipolar Long-Distance Transmissions
A. Bipole with Ground Return Path
B. Bipole with Dedicated Metallic Return Path for Monopolar
Operation
C. Bipole without Dedicated Metallic Return Path for Monopolar
Operation
4. Homopolar
Dr. Osama A. Al-Naseem, EE Dept, KU
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Main Types of HVDC Schemes
A
Rectifier
cheaper
B
Dr. Osama A. Al-Naseem, EE Dept, KU
f
Lessresistance
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Main Types of HVDC Schemes
of
bipolar
case
mono scheme survives
In
2
Double power
Dr. Osama A. Al-Naseem, EE Dept, KU
a
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Main Types of HVDC Schemes
Dr. Osama A. Al-Naseem, EE Dept, KU
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HVDC Station Schematic
DC side Voltage
AC current
6pm
up
imper
31in
360
6pulse
too
360
reuse
Lessharmonics
Dr. Osama A. Al-Naseem, EE Dept, KU
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