Presented by:

Pooja Bisi

Pravudatta Patel

Pritesh Priyadarshi

Priti Sucharita Tripathy

CONTENTS

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 transmissionsystem uses direct current for the bulk transmission of electricalpower, in contrast with the more common alternating current (AC)systems

HVDC allows power transmission between unsynchronized ACtransmission systems

An HVDC link can be controlled independently of the phase anglebetween source and load, it can stabilize a network againstdisturbances due to rapid changes in power.Various HVDC links in INDIA are:± 500 kV , 1500 MW Rihand – Delhi HVDC,814km± 500 kV ,2000 MW, HVDC Talchar – Kolar TransmissionLink, 1450km

The longest HVDC link in the world is currently the Xiangjiaba–Shanghai 2,071 km

HVDC TRANSMISSION

For long-distance transmission, HVDC systems may be lessexpensive and suffer lower electrical losses.

CONVERTERS•Perform AC to DC and DC to AC conversion•HVDC converters are usually built as 12-pulse circuits. •Consist of valve bridges and transformerSMOOTHING REACTORS•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.HARMONIC FILTERS•Converter generates harmonics in voltages and currents .These harmonicsmay cause overheating of capacitors and nearby generators and interferencewith Telecommunication systems, harmonic filters is used to mitigate theseharmonics.REACTIVE POWER SUPPLIER•Under steady state condition, the reactive power consumed by the converter isabout 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 shuntcapacitor.ELECTRODES•Electrodes are conductors that provide connection to the earth for neutraland they have large surface to minimse current and surface voltage gradients.

DC LINES:•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.

MONOPOLAR LINKBIPOLAR LINKHOMOPOLAR LINK

MONOPOLAR LINK:•One pole, one set of conductor for transmission and current return path is through earth. •Mainly used for submarine cable transmission

BIPOLAR LINK:

•Two poles, two set of conductors in transmission line, one positive with respectto earth & other negative.•The mid point of Bi-poles in each terminal is earthed via an electrode line andearth electrode.•In normal condition power flows through lines & negligible currentthrough earth electrode. (in order of less than 10 Amps.)

•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

BACK TO BACK HVDC LINK:

•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.

MULTI-TERMINAL SYSTEM

Advantages Of HVDCTechnical advantages:

No requirement of reactive power

Practical absence of transmission line length limitations

No system stability problems

Interconnection of asynchronously operated power

systems

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

Greater reliability

Increase of transmission capacity

Can be used for submarine and underground

transmission

Economic Advantages:

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 HVDCUse 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”: FACTS:(IEEE Definition)

Alternating current transmission systems incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability.

FACTS Controller:A power electronic-based system and other static equipment that provide control of one or more AC transmission system parameters.

Basic Types of FACTS ControllersFACTS controllers are classified as

Series Controllers

Shunt Controllers

Combined Series-Series Controllers

Combined Series-Shunt Controllers

General Symbol of FACTS controller

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 stability limit.

Provides greater flexibility in siting new generation.

Reduce reactive power flows, thus allowing the lines to carry more active power.

CONTROLLED POWER

ASYNCHRONOUS OPERATION POSSIBLE BETWEEN

REGIONS HAVING DIFFERENT ELECTRICAL

PARAMETERS(I.E FREQUENCY)

NO RESTRICTION ON LINE LENGTH AS NO

REACTANCE IN DC LINES

ADVANTAGES OF HVDC OVER HVAC

USING FACTS TRANSMISSION

LONG DISTANCE OVERHEAD TRANSMISSION:

• 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

Terminal Cost AC

Terminal Cost DC

Line Cost DC

Line Cost AC

Break Even Distance

HVDC IN INDIABack-to-BackHVDC LINK CONNECTING

REGION

CAPACITY

(MW)

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 reliableac interconnection would 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 reasonable

The cost of FACTS solution is lower than the HVDC cost

The required FACTS controller capacity is lesser than the transmission rating

FACTS IN INDIAIn 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: APPLICATIONSSUBMARINE CABLES:

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.

UNDERGROUND TRANSMISSION:

•Because of the high cost of underground cables, the break-even distance for HVDC is more like 100 Km as against 1500 Km for overhead lines.

•Again FACTS technology probably does not have much influence in the break-even distance.

CONNECTING AC SYSTEMS OF DIFFERENT OR INCOMPATIBLE FREQUENCIES:

•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.