Introduction of HVDC
Advantages and disadvantages of HVDC
Introduction of FACTS Technology
Advantages of FACTS technology
Comparison of HVDC and FACTS
A high-voltage direct current (HVDC) electric power transmission
system uses direct current for the bulk transmission of electrical
power, in contrast with the more common alternating current (AC)
The longest HVDC link in the world is currently the Xiangjiaba–
Shanghai 2,071 km
HVDC allows power transmission between unsynchronized AC
For long-distance transmission, HVDC systems may be less
expensive and suffer lower electrical losses.
An HVDC link can be controlled independently of the phase angle
between source and load, it can stabilize a network against
disturbances due to rapid changes in power.
Various HVDC links in INDIA are:
± 500 kV , 1500 MWRihand – Delhi HVDC,814km
± 500 kV ,2000MW, HVDC Talchar – Kolar Transmission
•Perform AC to DC and DC to AC conversion
•HVDC converters are usually built as 12-pulse circuits.
•Consist of valve bridges and transformer
•High reactors with inductance as high as 1H in series with each pole.
•Decrease harmonics in voltage and current in dc lines.
•Prevent commutation failure in inverter.
•Converter generates harmonics in voltages and currents .These harmonics
may cause overheating of capacitors and nearby generators and interference
with Telecommunication systems, harmonic filters is used to mitigate these
REACTIVE POWER SUPPLIER
•Under steady state condition, the reactive power consumed by the converter is
about 50% of the active power transferred.
•Under transient conditions it could be much higher.
•For a strong AC power system, this reactive power is provided by a shunt
•Electrodes are conductors that provide connection to the earth for neutral
and they have large surface to minimse current and surface voltage gradients.
•They may be overhead lines or cables.
•DC lines are very similar to AC lines.
AC CIRCUIT BREAKER:
•They used to clear the faults in transformer and for taking DC link out of service.
•One pole, one set of conductor for transmission and current return path is
•Mainly used for submarine cable transmission
•Two poles, two set of conductors in transmission line, one positive with respect
to earth & other negative.
•The mid point of Bi-poles in each terminal is earthed via an electrode line and
•In normal condition power flows through lines & negligible current
through earth electrode. (in order of less than 10 Amps.)
BACK TO BACK HVDC LINK:
•Usually bipolar without earth return.
•Converter & inverters are located at the same place.
•No HVDC Transmission line.
•Provides Asynchronous tie between two different AC network
•Power transfer can be in either direction
•Chandrapur, connection between western to eastern region
•Three or more terminals connected in parallel, some feed power and
some receive power from HVDC Bus.
•Provides Inter connection among three or more AC network.
Advantages Of HVDC
No requirement of reactive power
Practical absence of transmission line length limitations
No system stability problems
Interconnection of asynchronously operated power
No production of charging current
No increase of short circuit power at the connection point
Independent control of AC systems
Fast change of energy flow i.e. Ability of quick and
bidirectional control of energy flow
Lesser corona loss and radio interference
Increase of transmission capacity
Can be used for submarine and underground
Low cost of DC lines and cables
Simple in construction
Low cost for insulators and towers
Less Line losses
Transmission line can be built in stages
Disadvantages Of HVDC
Use of converters ,filters etc increases the overall cost
DC circuit breakers are more expensive
HVDC converters have low overloading capacity
More maintenance is required for insulators
Voltage transformation is possible only on AC side
Definition of “Facts” & “Facts Controller”:
Alternating current transmission systems incorporating power
electronic-based and other static controllers to enhance controllability
and increase power transfer capability.
A power electronic-based system and other static equipment that
provide control of one or more AC transmission system parameters.
Basic Types of FACTS Controllers
FACTS controllers are classified as
Combined Series-Series Controllers
Combined Series-Shunt Controllers
General Symbol of FACTS
Advantages of FACTS technology:
Control of power flow to ensure optimum power flow.
Increase the loading capability of of lines to their
thermal capabilities, including short term and
seasonal. This can be achieved by overcoming other
limitations, and sharing power among lines according
to their capability.
Increase the system security by raising the transient
Provides greater flexibility in siting new generation.
Reduce reactive power flows, thus allowing the lines to
carry more active power.
ADVANTAGES OF HVDC OVER HVAC
USING FACTS TRANSMISSION
ASYNCHRONOUS OPERATION POSSIBLE BETWEEN
REGIONS HAVING DIFFERENT ELECTRICAL
NO RESTRICTION ON LINE LENGTH AS NO
REACTANCE IN DC LINES
LONG DISTANCE OVERHEAD
• If the overhead transmission is long enough, say 1500 Km, the saving in
capital costs and losses with a dc transmission line may be enough to pay for
two converters. This distance is known as break-even distance.
• This break-even distance is very subject to many factors including the
cost of the line, right-of-way, and often most important the politics of
obtaining permission to build the line.
• But it is important to recognize that while FACTS can play an important
role in an effective use of ac transmission, it probably does not have too
much influence on the break-even distance.
COST: AC vs DC Transmission
Line Cost AC
Line Cost DC
Terminal Cost DC
Terminal Cost AC
Break Even Distance
HVDC IN INDIA
HVDC LINK CONNECTING
Vindyachal North –West 2 x 250
Chandrapur West – South 2 x 500
Vizag – I East – South 500
Sasaram East – North 500
Vizag – II East – South 500
1)Both are complementary technologies
2)The role of HVDC is to interconnect ac systems where a reliable
ac interconnectionwould be too expensive
Independent frequency and control
Lower line cost
Power control, voltage control and stability control possible
3) The large market potential for FACTS is within AC system on a value
added basis where
The existing steady-state phase angle between bus node is
The cost of FACTS solution is lower than the HVDC cost
The required FACTS controller capacity is lesser than the
FACTS IN INDIA
In india,FACTS has received much attention in the last 2 decades
The 1st FACTS device installed in india is Thyrister Controlled
Series Capacitor(TCSC) with Fixed Series Compensation(FSC)
at 400 KV transmission line between Kanpur(UP) and
Ballabgarh(Haryana) in the Northern grid.
Some more existing FACTS devices projects which work
succesfully in india are :
Ranchi-Sipat 400 KV D/C
376 Km transmission line with 40% FSC at Ranchi end
364 Km transmission line in Andra pradesh
FSC-TCSC installed in Kalpakam-Khammam 400 KV D/C
HVDC PROJECTS: APPLICATIONS
Cables have a large capacitance and hence ac cables require a large
charging current (reactive power) an order of magnitude larger than
that of overhead lines. As a result, for over a 30 Km or so stretch of ac
submarine cable, the charging current supplied from the shore will
fully load the cable and leave no room for transmitting real power.
The charging current flowing in the cables can only be reduced by
connecting shunt inductors to the cable at an intervals of 15-20 Km.
But with HVDC cable, distance is not a technical barrier and also the
cost of dc cable transmission is much lower than that of ac.
FACTS technology can provide an improvement by controlling the
magnitude of one end of the voltages so as to keep it identical to that of
the other one. In this way, the effective length of the cable from the
standpoint of the charging current can be halved.
•Because of the high cost of underground cables, the break-even
distance for HVDC is more like 100 Km as against 1500 Km for
•Again FACTS technology probably does not have much influence
in the break-even distance.
CONNECTING AC SYSTEMS OF DIFFERENT OR
•For historical reasons, the oceans in effect separate the globe’s electric systems
into 50 Hz and 60 Hz groups.
•The 60 Hz normal frequency pervades all the countries of the Americas,
excepting Argentina and Paraguay. Those two countries and all the rest of the
world have a 50 Hz frequency except Japan, which is partly 50 Hz and 60 Hz.
•In general, the oceans are too huge and deep to justify interconnections of 50 Hz
and 60 Hz systems. Thus, there is a limited market for HVDC for connecting 50
and 60 Hz systems.