Use of FACTS and HVDC for Power System Interconnection · PDF fileUse of FACTS and HVDC for...

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Use of FACTS and HVDC for Power

System Interconnection and

Grid Enhancement

Günther Beck, Wilfried Breuer,

Dusan Povh, Dietmar Retzmann,

Erwin Teltsch

Siemens Power Transmission and

Distribution (PTD),

Germany

2 / 33

0. Overview Interconnection of power systems with either AC or DC links may offer important technical,

economical and environmental advantages. In the future of liberalised power markets, these

advantages will become even more important: pooling of large power stations, sharing of

spinning reserve, use of most economic energy resources, as well as ecological constraints:

nuclear power stations at selected locations, hydro energy from remote areas, solar energy

from steppes and deserts, and connection of large off-shore wind farms.

Examples of large interconnected systems are the Western and Eastern European systems

UCTE (installed capacity 530 GW) and IPS/UPS (315 GW), which are planned to be

interconnected in the future. Up to now, the power systems in China are more separated:

China with 7 large inter-provincial grids and India with 4 large regional grids. However,

interconnections by AC and increasingly by DC are in progress in Far East, too.

Since the 60s, FACTS (Flexible AC Transmission Systems) and HVDC (High Voltage Direct

Current) transmission have developed into a mature technology with high power ratings.

Transmission ratings of 3 GW over large distances with just one bipolar DC transmission

system are state of the art in many grids today. In China, however, there are new transmission

schemes in the planning phase with ratings of 4 - 6 GW (at +/- 800 kV DC and 1000 kV AC).

Reason for such high ratings is the need for bulk power transmission corridors with 20 GW

for system interconnection.

In general, for transmission distances above 700 km, DC transmission is more economical

than AC transmission (≥ 1000 MW). With submarine cables, transmission levels of up to 600

- 800 MW over distances of nearly 300 km have already been attained, and cable transmission

lengths of up to 1,300 km are in the planning stage. As a multi-terminal system, HVDC can

also be connected at several points with the surrounding AC networks. FACTS is applicable

in parallel connection (SVC, Static VAR Compensator – STATCOM, Static Synchronous

Compensator) or in series connection (FSC, Fixed Series Compensation - TCSC, Thyristor

Controlled Series Compensation – TPSC, Thyristor Protected Series Compensation) or in

combination of both (UPFC, Unified Power Flow Controller) to control load flow and to

improve dynamic conditions. Rating of SVCs is up to 800 MVAr, series FACTS devices are

implemented on 550 and 735 kV level to increase the line transmission capacity up to several

GW.

3 / 33

In the paper, benefits of FACTS and HVDC for system interconnection and for grid

enhancement are depicted, and preferences of applications are explained. Study and project

examples are given.

1. Development of Power Transmission

The development of power systems follows the requirements to transmit power from

generation to the consumers. With an increased demand for energy and the construction of

new generation plants, first built close and then at remote locations from the load centers, the

complexity of power systems has grown. This development is schematically shown in Fig. 1.

To transport the energy from generation to consumers, the development of power systems

considers locations of expected load requirements on the one hand, and the suitable location

of power stations on the other hand. However, on a long-term basis, it can be expected that

the transmission systems will stagnate in their development, since an increasing part of power

generation will be transferred into the distribution or low voltage networks in the future [1, 3].

Since the load flows existing today can change considerably, this altering environment

decisively influences further development and optimization of transmission networks. The

ancillary functions required for smooth operation of the networks, such as frequency control,

load-flow control, reactive-power and voltage control, as well as the responsibility for system

Fig. 1: Development of Power Systems and per Capita Consumption

Isolated smallGridsIsolated smallGrids

System Interconnections

Demand for Power Quality

Increased Automation

More Investments in DistributionDecentralized Power Supplies

High Energy Imports

Use of new Technologies

per CapitaPower Consumptionper CapitaPower Consumption

Developing Countries Emerging Countries Industrialized Countries

Long - DistanceTransmission(HVAC, HVDC)

Long - DistanceTransmission(HVAC, HVDC)

Introduction ofhigher VoltageLevels

Introduction ofhigher VoltageLevels

Lifetime Extension, Monitoring

Right of Way Problems, Transmission Bottlenecks

Least-CostPlanning

High Investments in Transmission Systems

4 / 33

security, are in the hands of the system operator. To support the operation and to increase the

reliability of heavily loaded networks, FACTS and HVDC need to be installed. Higher

investments into grid interconnections must be made to achieve cost benefits.

Based on a large number of studies on power system development in different world regions,

the following general trends can be expected:

As listed below, power system interconnections offer the necessary benefits regarding these

constraints. They are generally valid and do not depend on the kind of the interconnection.

With the size of interconnected systems, however, the technical and economical advantages

diminish and the required additional investments for system enlargements increase. In

addition to that, the transmission costs increase with the transmission distance. Considering

the current transmission costs of about 1-2 Cents per kWh and 1000 km, the advantages of the

energy taken from the interconnected systems over very long distances would not be

economical any more. The reasonable distance to transmit power still economically could be

therefore in the range of up to 3000 km. These conditions, however, could possibly change if

strong political efforts will support the use of renewable energy in remote areas in large scale,

independent from production and transmission costs. Strategies for the development of large

Increasing Power Demand - from 3,560 GW in 2000 to 5,700 GW in 2020

Strong Environmental Constraints – Limitation for Power Plant Expansions

Natural Energy Resources far away from Load Centers

Severe Right of Way Constraints A strong Issue in many Countries, especially in Europe

Possibility to use larger and more economical Power Plants

Reduction of the necessary Reserve Capacity in the System

Utilization of most favorable Energy Resources

Flexibility of building new Power Plants at favorable Locations

Increase of Reliability in the Systems

Reduction of Losses by an optimized System Operation

5 / 33

power systems go clearly in the direction of hybrid transmissions, consisting of HVDC and

HVAC interconnections among regional sub-systems. Such interconnected systems have

significant technical and reliability advantages [3-6].

Fig. 2 shows schematically such a hybrid system using HVDC and FACTS. Power exchange

in the neighboring areas of interconnected systems offering most advantages can be realized

by AC links, preferably including FACTS for increased transmission capacity and for stability

reasons. The transmission of larger power blocks over longer distances should, however, be

utilized by the HVDC transmissions directly to the locations of power demand. HVDC can be

realized as direct coupler without a DC line – the so-called Back-to-Back solution (B2) or as

point to point long distance transmission via DC line. The HVDC links can strengthen the AC

interconnections at the same time, in order to avoid possible dynamic problems which exist in

such huge interconnections [3, 6].

Long-term developments in power industry depend on expectations for future political,

financial and technical conditions. For the last decade, however, the developments have been

strongly driven by the globalization, leading to deregulation and liberalization. The world

markets have been gradually opened, with different speed in different countries. This

transition of economies brought many advantages, but also disadvantages in some fields. At

Fig. 2: Large Power System Interconnections – Benefits of Hybrid Solutions

Large System Interconnections, using HVDCLarge System Interconnections, using HVDC

SystemA

SystemC

SystemE

SystemF

High VoltageHVDC B2B

SystemB System

D

SystemG

and FACTS

AC Transmission- via AC Lines

DC – the Stability Booster and“Firewall” against “Blackout”

HVDC - Long Distance DC Transmission

“Countermeasures”against large Blackouts

& FACTS

Large System Interconnections, using HVDCLarge System Interconnections, using HVDC

SystemA

SystemA

SystemC

SystemC

SystemE

SystemE

SystemF

SystemF

High VoltageHVDC B2B

SystemB

SystemB System

DSystem

D

SystemG

SystemG

and FACTS

AC Transmission- via AC Lines

DC – the Stability Booster and“Firewall” against “Blackout”DC – the Stability Booster and

“Firewall” against “Blackout”

HVDC - Long Distance DC TransmissionHVDC - Long Distance DC Transmission



& FACTS& FACTS

6 / 33

the same time, social and environmental aspects became more and more important, even if

they are, in some way, in contradiction with the globalization of the economy.

Fig. 3 shows the typical sharing of investments in power generation, transmission and

distribution. These values depend, however, on the specific structure of the systems. The

estimation of the requested investments in the power industry for the next 30 years is US$ 10

trillion, or roughly US$ 350 billion per year. Based on this, about US$ 70 billion per year

should be invested in power transmission [1].

Fig. 3: Investments in Power Industry

Investments in Power IndustryInvestments in Power Industry

~ 40 %~ 40 %~ 40 %~ 40 %~ 20 %~ 20 %

Generation Transmission DistributionGeneration Transmission Distribution

Depending on Grid StructureDepending on Grid Structure

Fig. 4: Transmission Systems – The “VIPs” of the Power Market

GenerationGeneration

Regulated Markets:one Owner - the Utility

Regulated Markets:one Owner - the Utility

Deregulated Markets:different Owners & Players

Deregulated Markets:different Owners & Players

or -neck-neck

for Cash-Flow &Return on Investments

DistributionDistribution

Transmissioncan be

Transmissioncan be

7 / 33

Although the sharing of transmission investments is only 20 % of the total sum, its

importance is in fact high: transmission can be the key for cash-flow and return on

investments, or just a bottleneck causing limitations and supply interruptions. Thus,

transmission systems are the VIPs of the power market, as shown in Fig. 4.

Fig. 5 shows the perspectives of DC transmission capacity worldwide. It can be seen that

China alone will be contributing significantly to this development because of its large

increase of economy (GDP) per year.

In Fig. 6 and 7, the transmission grid developments in China and India are depicted, leading

to very large hybrid interconnections with AC and DC solutions.

A large number of different FACTS and HVDC have been put into operation either as

commercial projects or prototypes. Fig. 8 gives an example of the Siemens applications

worldwide. Thus it appears that some areas are still “blank”, which is expected to change in

the future. In the figure, the number and the increase of large HVDC long-distance

transmission projects are also indicated.

The different technologies with FACTS and HVDC for grid enhancement using modern high

power electronics, as indicated in Fig. 8, are explained more detailed in the next sections.

Fig. 5: Development of DC Transmission: Worldwide installed Capacity

1970 1980 1990 2000 2010

60

50

40

30

20

10

0

GW

An additional 48 GW are expected from Chinaalone until 2020 !

Worldwide installed HVDC “Capacity”: 55 GW in 2005Worldwide installed HVDC “Capacity”: 55 GW in 2005

Sources: IEEE T&D Committee 2000 - Cigre WG B4-04 2003

This is 1.4 % of the Worldwide installed Generation CapacityThis is 1.4 % of the Worldwide installed Generation Capacity

8 / 33

Fig. 6: China goes Hybrid: AC plus 20 HVDC Interconnections

Sources: SP China, ICPS - 09/2001; State Grid Corp. China, 2003

In to

tal:

20

HVD

C In

terc

onne

ctio

ns

3 x B2B11 x HVDC Long Distance Transmissions

plus

…

plus

…

2005: 12 GW2020: 60 GW

and

Russian Power Grid

North Power Grid

Center Power Grid

LanchangjiangRiver

JinshajiangRiver

NWCPG

NCPGWangqu Plant

Yangcheng Plant

NECPG

SPPG

CSPGThree Gorges

ECPG

CCPG

Tailand Power Grid

SCPG

South Power GridHPPG

Russian Power Grid

North Power Grid

Center Power Grid

LanchangjiangRiver

JinshajiangRiver

NWCPG

NCPGWangqu Plant

Yangcheng Plant

NECPG

SPPG

CSPGThree Gorges

ECPG

CCPG

Tailand Power Grid

SCPG

South Power GridHPPG

Gezhouba-ShanghaiTianGuang3G-ECPG IGuiGuang I3G-Guangdong

Initially:

GuiGuang II

Gezhouba-ShanghaiTianGuang3G-ECPG IGuiGuang I3G-Guangdong

Initially:

GuiGuang II

Fig. 7: Grid Extension in India - Hybrid AC plus DC

R O U R K E LA

R A IP U R H IR M A

T A L C H E R

J A IP U R

N E R

E RW R

N R

S R

B 'S H A R IF

A LL A H A B A D

S IP A T

G A Z U W A K A

J E Y P O R EC H A N D R A P U R

S IN G R A U LI

V IN D H Y A -

2000

MW

2000MW

3000M W

10 0 0M W

5 00 M W

LU C K N O W

D IH A N G

C H IC K E N N E C K

K R IS H N A

T E E S T A

T IP A IM U K HB A D A R P U R

M IS A

D A M W E

K A T H A L-G U R I

L E G E N D

7 65 K V L IN E S 4 00 K V L IN E S

H V D C B /B

H V D C B IP O LE

E X IS T IN G / X P LA N X I P LA N

Z E R D A

H IS S A R

B O N G A IG A O N

D E V E L O P M E N T O F N A T IO N A L G R ID

K O L H A P U R

N A R E N D R A

K A IG A

M A N G A LO R E

P O N D A

IX P LA N

M A R IA N I

N .K .

K A H A L G A O N

R A N G A N A D I

S E O N I

C H E G A O N

B H A N D A R A

D E H G A M

K A R A D

L O N IK A N D

V A P I

G A N D H A R /

T A LAA R U N

B A N G L A

B A LLA B G A R H A 'P U R(D E L H I R IN G )

B A N G A LO R E

K O Z H IK O D E

C O C H IN

K A Y A M K U LA M

T R IV A N D R U M

P U G A LU R

K A Y A T H A R

K A R A IK U D I

C U D D A L O R E

S O U T H C H E N N A I

K R IS H N A P A T N A M

C H IT T O O R

V IJA Y A W A D A

S IN G A R P E T

P IP A V A V

L IM B D I

K IS H E N P U R

D U L H A S T IW A G O O R A

M O G A

U R I

B H U T A N

R A M A G U N D A M

S A T LU JR A V I

JU LLA N D H A R

D E S HN A G A R

V A R A N A S I

/U N N A O

M 'B A D

P U R N E A

K O R B A

N A G D A

S IL IG U R I/B IR P A R A

P H A S E - III

NIC

OB

AR

AN

DA

MA

N A

ND

LAKSHAD

WEEP

T E H R I

M E E R U T

B H IW A D I

B IN A S A T N A

M A LA N P U RS H IR O H I

K A W A S

A M R A V A T I

A K O LA

(B y 2 0 1 2 )

A G R A

S IR S I

C H A L

J E T P U RA M R E LI

B O IS A RT A R A P U R

P A D G H E

D H A B O L

K O Y N A

/B A R H

G 'P U R

H O S U R

Similar Perspectives … as in China

Source: Power Grid Corporation of India, 2003

9 / 33

2. Transmission Solutions with FACTS and HVDC

FACTS and HVDC use power electronic components and conventional equipment which can

be combined in different configurations for switching or controlling reactive power, and for

active power conversion. Conventional equipment (e.g. breakers, tap-changer transformers)

offer very low losses, but the switching speed is relatively slow. Power electronics can

provide high switching frequencies up to several kHz, but with an increase in losses. A view

on the different kinds of semiconductors is given in Fig. 9. In Fig. 10, the stepwise assembly

of the thyristors in modules and valve groups is shown.

Fig. 8: FACTS & HVDC worldwide – Example Siemens (ref. to Text)

SeriesFSC

NGH

TPSC

TCSC

SeriesFSC

NGH

TPSC

TCSC

Load FlowB2B

UPFC

CSC

Load FlowB2B

UPFC

CSC

2, 2 Tian Guang 2003Kayenta 1990

Serra de Mesa 1999Imperatriz 1999

Fortaleza 1986

••

•

•Samambaia 2002

•

Virginia Smith 1987

•Welsh 1995

•Acaray 1981

•••Dürnrohr 1983

Etzenricht 1993Wien Südost 1993

•Bom Jesus la Lapa 2002

•

Limpio 2003

•Ibiuna 2002

•3 Vincent 2000

•Jacinto 2000

•Funil 2001

2 Pelham, 2 Harker, 2 Central, 1991-1994

•

Nopala 2006

•

Atacama 1999

•

P. Dutra 1997

• Cerro Gordo 1999

•Chinú 1998

•Impala

•2 Adelanto 1995

•

Jember 1994

•3 Montagnais 1993

•

2 Kemps Creek 1989

•Brushy Hill 1988

•

•

Campina Grande 2000

2 Zem Zem 1983

•

••

•

•

Rejsby Hede 1997

•Sullivan 1995

•Paul Sweet 1998 •

Inez 1998

•

2 Marcy 2001-2003

Military Highway 2000

•Kanjin (Korea) 2002

•

Lugo 1985

Laredo 2000

•

Spring Valley 1986

••IllovoAthene•

Muldersvlei 1997

•

2 Tecali 2002

3 Juile 2002

•Barberton 2003•

Maputo 2003

•Milagres 1988

• 2 Yangcheng 2000

•2 Hechi 2003

•

•

Eddy County 1992

2 Dominion 2003

2 Chuddapah 20032 Gooty 2003

•

Lamar 2005

2 Midway 2004 Seguin 1998•

1994-1995

Porter 2006Dayton 2006

Nine Mile 2005

ParallelSVC

MSC/R

ParallelSVC

MSC/R

.

.Moyle MSC 2003Willington 1997

Hoya Morena,Jijona 2004

.Baish 2005,Samitah 2006 .

K.I. North 2004

Kapal 1994

Ghusais,Hamria,Mankhool, Satwa

1997

.

Siems 2004

Cano Limón 1997

• 2006

••

2, 2 Purnea2, 2 Gorakhpur

Status: 10-2005

•

••• Châteauguay 1984

Ahafo 2006

•

•

2 Lucknow 2006

•

3 Puti 2005

• Iringa, Shinyanga 2006

•

3, 2 El Dorado2006

STATCOMFlicker STATCOMSTATCOMFlicker STATCOM

•

Radsted 2006

•

• 2 Sabah 2006

Nebo 2007

9 Powerlink,Refurbishment2007

Devers 2006

•Benejama,Saladas 2006

La Pila 1999

•

•• •• •

•

Plus 16 Projects for HVDC Long Distance Transmission …

Plus 16 Projects for HVDC Long Distance Transmission …

8 alone between 2000 &2005 in 4 Continents8 alone between 2000 &2005 in 4 Continents

Fig. 9: High Power Semiconductors

Pellet of LTT Thyristor

Pellet ofGTO / IGCT

Assembly ofChips in IGBT

IGCT = Insulated Gate commutated Thyristor

IGBT = Insulated Gate bipolar Transistor

LTT = Light triggered Thyristor

10 / 33

Fig. 11: Use of Power Electronics for FACTS & HVDC - Transient Performance and Losses

More Dynamics for better Power Quality:

Use of Power Electronic Circuits for Controlling P, V & QParallel and/or Series Connection of ConvertersFast AC/DC and DC/AC Conversion

ThyristorThyristor

50/60 Hz

ThyristorThyristor

50/60 Hz

GTOGTO

< 500 Hz

GTOGTO

< 500 Hz

IGBT / IGCT

Losses

> 1000 Hz

IGBT / IGCT

LossesLosses

> 1000 Hz

Transition from “slow” to “fast”

Switching Frequency

On-Off Transition 20 - 80 ms

Transition from “slow” to “fast”Transition from “slow” to “fast”

Switching Frequency

On-Off Transition 20 - 80 ms

1-2 %1-2 %

4-5 %4-5 %

ThyristorThyristor

ModuleModule

Valve Group - Example Indoor for HVDC

ThyristorThyristor

Module

Valve Group - Example Outdoor for FACTS

Fig. 10: HVDC and FACTS - Advanced Power Electronics for High Voltage Systems

11 / 33

The dependency between transient performance and losses is depicted in Fig. 11. An example

of actual losses in a large HVDC project is given in section 5, Fig. 26.

Flexible AC Transmission Systems (FACTS) based on power electronics have been

developed to improve the performance of long distance AC transmission. The technology has

then been extended to the devices which can also control power flow. Excellent operating

experiences are available worldwide, and FACTS technology also became mature and

reliable.

Fig. 12 shows the principal configurations of FACTS devices. Main shunt connected FACTS

application is the Static Var Compensator with line-commutated thyristor technology, where

the maximum switching frequency in each phase element is limited by the “driving” system

frequency.

A further development is STATCOM using voltage sourced converters. Both devices provide

fast voltage control, reactive power control and power oscillation damping features (POD). As

an option, SVC can control unbalanced system voltages. The developments of FACTS

technologies are depicted in Fig. 13. Static Var Compensation is mainly used to control

system voltage. There are hundreds of these devices in operation worldwide. For decades, it

has been a well developed technology, and the demand on SVC is further increasing.

Fixed series compensation is widely used to improve the stability by reducing the

transmission angle in long distance transmissions. A huge number of these applications are in

operation. If system conditions are more complex, Thyristor Controlled Series Compensation

Fig. 12: FACTS - Flexible AC Transmission Systems: Support of Power Flow

SVC - Static Var Compensator (Standard for Parallel Compensation)

STATCOM - Static Synchr. Compensator (Fast SVC, Flicker Compensation)

FSC - Fixed Series Compensation

TCSC - Thyristor Controlled Series Compensation

TPSC - Thyristor Protected Series Compensation

GPFC - Grid Power Flow Controller (FACTS-B2B)

UPFC – Unified Power Flow Controller

TCSC/TPSC

FSC

60 Hz 60 Hz

ACAC

60 Hz 60 Hz

ACACACAC

GPFC/UPFC

AC AC

50 or 60 Hz60 Hz

GPFC/UPFC

AC AC

50 or 60 Hz60 Hz

ACAC ACAC

50 or 60 Hz60 Hz

/ UPFC

/ TPSC

/ STATCOMSVC

60 Hz60 Hz

ACAC

SVC

60 Hz60 Hz

ACAC

60 Hz60 Hz

ACAC

60 Hz60 Hz

ACACACAC

12 / 33

is used. TCSC has already been applied in different projects for load-flow control, stability

improvement and to damp oscillations in interconnected systems.

Special FACTS devices are UPFC (Unified Power Flow Controller) and GPFC (Grid Power

Flow Controller) [2, 5]. UPFC combines a shunt connected STATCOM with a series

connected STATCOM (= S3C, Solid State Series Compensator), which can exchange energy

via a coupling capacitor. The CSC (Convertible Synchronous Compensator) in Fig. 8 uses a

UPFC which can be switched over into different applications with either two STATCOMs or

two S³Cs. GPFC is a special DC back-to-back link, which is designed for fast power and

voltage control at both terminals. In this manner, GPFC is a “FACTS Back-to-Back”, which

is less complex and expensive than the UPFC.

For most applications in AC transmission systems and for network interconnections, SVC,

FSC, TCSC and GPFC/B2B are fully sufficient to match the essential requirements of the

grid. STATCOM and UPFC are tailored solutions for special needs.

The basic configurations of HVDC are depicted in Fig. 14 and 15. HVDC operates as power

flow controller; it “forces P to flow”. In hybrid system configurations with synchronous

frequencies over the whole grid, HVDC offers a highly effective control of power flow. In

addition to that, in case of system faults, HVDC can either support the grid recovery, or it can

automatically split the systems like a “Firewall”, which is very helpful for Blackout

1st Generation

MechanicallySwitched Devices

1st Generation

MechanicallySwitched Devices

VSC TechnologyGTO, IGBT, IGCT

3rd Generation

VSC TechnologyGTO, IGBT, IGCT

3rd Generation

Thyristor ControlledComponents

2nd Generation

Thyristor ControlledComponents

2nd Generation

Breaker DelayBreaker Delay 2 - 3 Cycles 2 - 3 Cycles 1- 2 Cycles 1- 2 Cycles Response TimeResponse Time V-Control

I-Control:< 1 Cycle

Slow VARsSlow VARs Fast VARsFast VARs

Fig. 13: FACTS – Technology Developments

13 / 33

prevention in case of cascading events [3]. For bipolar applications, a second set of converters

with negative voltage plus coupling transformers is provided.

For system interconnections, an additional benefit of the HVDC is its incorporated fault-

current limitation feature. HVDCPLUS is the preferred technology for interconnection of

islanded grids to the power system, such as off-shore wind farms. This technology provides

the so-called “Black Start” feature by use of voltage sourced converters. Voltage sourced

Fig. 15: HVDC - High Voltage DC Transmission: It forces P to flow

HVDC-LDT - Long Distance Transmission

B2B - The Short Link

Back-to-Back Station

60 Hz 50 Hz

AC AC

B2B - The Short Link


60 Hz 50 Hz

AC AC


60 Hz 50 Hz

ACAC ACAC

DC Cable

AC AC

Submarine Cable Transmission

DC Cable

AC AC

DC Cable

ACAC ACAC

Submarine Cable Transmission Long Distance OHL Transmission

DC Line

AC AC

Long Distance OHL Transmission

DC Line

ACAC ACAC

HVDC - High Voltage DC Transmission: It forces P to flowStandard with Thyristors (Line-commutated Converter)

AC/DC and DC/AC conversion by Power Electronics

HVDCPLUS (Voltage-Sourced Converter - VSC)

HVDC can be combined with FACTS

V-Control included

130 ≤ kV ≤ 800300 ≤ MW ≥ 4000

130 ≤ kV ≤ 800300 ≤ MW ≥ 4000

Rating LDT:

130 ≤ kV ≤ 800300 ≤ MW ≥ 4000

130 ≤ kV ≤ 800300 ≤ MW ≥ 4000

Rating LDT:

up to 1000 - 4000 km

... or with Cable/Line - the Long Distance Transmission

up to 1000 - 4000 km

... or with Cable/Line - the Long Distance Transmission

Filters Filters

Back-to-Back - the short Link ...Back-to-Back - the short Link ...

fA = 50 Hz Example fB = 60 HzfA = 50 Hz Example fB = 60 Hz

Power & Voltage ControlFault Current Blocking

13,8 ≤ kV ≤ 55030 ≤ MW ≤ 1200

13,8 ≤ kV ≤ 55030 ≤ MW ≤ 1200

B2B - Rating:

13,8 ≤ kV ≤ 55030 ≤ MW ≤ 1200

13,8 ≤ kV ≤ 55030 ≤ MW ≤ 1200

B2B - Rating:

Fig. 14: High Voltage DC Transmission – Basic Configurations

14 / 33

converters do not have the need of a “driving” system voltage; they can build up a 3 phase AC

voltage via the DC voltage at the cable end, supplied from the converter at the main grid.

3. Phase Shifting Transformer versus HVDC and FACTS

Phase shifting transformers have been developed for transmission system enhancement in

steady state system conditions. The operation principle is voltage source injection into the line

by a series connected transformer, which is fed by a tapped shunt transformer, very similar to

the UPFC, which uses VSC-Power Electronics for coupling of shunt and series transformer.

This way, overloading of lines and loop-flows in Meshed Systems and in parallel line

configurations can be eliminated. However, the speed of phase shifting transformers for

changing the phase angle of the injected voltage via the taps is very slow: typically between 5

and 10 s per tap, which sums up for 1 minute or more, depending on the number of taps.

As a rule of thumb for successful voltage or power-flow restoration under transient system

conditions, a response time of approx. 100 ms is necessary with regard to voltage collapse

phenomena and “First Swing Stability” requirements. Such fast reaction times can easily be

achieved by means of FACTS and HVDC controllers. Their response times are fully suitable

for fast support of the system recovery. Therefore, dynamic voltage and load-flow restoration

is clearly reserved to power electronic devices like FACTS and HVDC.

In conclusion, phase shifting transformers and similar devices using mechanical taps can only

be applied for very limited tasks with slow requirements under steady state system conditions.

4. FACTS Technologies and Applications

In this section, a more detailed description of FACTS technologies is given. Fig. 16 and 17

show the full range of applications, including actual ratings and voltage levels of today’s

solutions, as listed in Fig. 8.

Fig. 18 shows a site view of one of the 27 SVCs, which have been installed in the UK to

overcome transmission bottlenecks caused by deregulation [3]. The SVC control functions,

including options for specific tasks, such as unbalance control (not necessary in UK), are also

indicated in the figure. An increasing number of SVCs are also going to be installed in other

continents. In Fig. 19, an example of an SVC in South America is given. The SVC was

implemented to improve system stability of the large transmission grid. The installed

containerized solution offers additional benefits, such as reduction in installation and

15 / 33

commissioning time, as well as space and cost savings compared to conventional building

technologies.

Fig. 17: FACTS for Series Compensation

FSC

~

220 ≤ kV ≤ 800200 ≤ MVAr ≤ 800

Fixed Series Compensation

Protection

Circuit BreakersArresters

Capacitors

FSC

~

220 ≤ kV ≤ 800200 ≤ MVAr ≤ 800

Fixed Series Compensation

Protection

Circuit BreakersArresters

Capacitors

TCSC

~

220 ≤ kV ≤ 800100 ≤ MVAr ≤ 200

Thyristor Controlled Series Compensation

Thyristor ValvesControl & Protection

α

Capacitors

Circuit Breakers

TCSC

~

220 ≤ kV ≤ 800100 ≤ MVAr ≤ 200

Thyristor Controlled Series Compensation

Thyristor ValvesControl & Protection

α

Capacitors

Circuit Breakers

TPSC

~

220 ≤ kV ≤ 800100 ≤ MVAr ≤ 500

Thyristor Valves

Thyristor Protected Series Compensation

Protection

ILim

Capacitors

Circuit Breakers

TPSC

~

220 ≤ kV ≤ 800100 ≤ MVAr ≤ 500

Thyristor Valves

Thyristor Protected Series Compensation

Protection

ILim

Capacitors

Circuit Breakers

MSC / MSR

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 500

Mechanical SwitchedCapacitors / Reactors

Reactors

SwitchgearCapacitors

MSC / MSR

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 500

Mechanical SwitchedCapacitors / Reactors

Reactors

SwitchgearCapacitors

STATCOM

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 800

Static Synchronous Compensator

GTO/IGBT ValvesControl & ProtectionTransformerDC Capacitors

STATCOM

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 800

Static Synchronous Compensator

GTO/IGBT ValvesControl & ProtectionTransformerDC Capacitors

SVC

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 800

Static Var Compensator

Reactors

Thyristor Valve(s)Control & ProtectionTransformerCapacitors

SVC

~

52 ≤ kV ≤ 80050 ≤ MVAr ≤ 800

Static Var Compensator

Reactors

Thyristor Valve(s)Control & ProtectionTransformerCapacitors

Fig. 16: FACTS for Parallel Compensation

16 / 33

In Fig. 20-21, the features and cost savings of series compensation due to grid enhancement

are summarized. The mentioned SSR (sub-synchronous resonances) topic is a critical issue

for large thermal generators with long shafts [7]. The flexibility of modern FACTS

technologies under extremely harsh environmental conditions is indicated in Fig. 21-22: the

operating range for FSC begins at -500 C, for TCSC it can reach up to +850 C. This is

Benefits:o Improvement of Voltage Qualityo Increased Stability

Voltage Control Reactive Power ControlPower Oscillation DampingUnbalance Control (Option)

Voltage Control Reactive Power ControlPower Oscillation DampingUnbalance Control (Option)

Fig. 18: SVC Pelham, NGC, UK - 400 kV/14 kV, -75/+150 MVAr

Fig. 19: SVC Bom Jesus da Lapa, Enelpower, Brazil - 500 kV, +/-250 MVAr Containerized Solution

Valves & ControlValves & Control Benefits:

o Improvement of Voltage Qualityo Increased Stabilityo Avoidance of Outages

17 / 33

necessary due to the outdoor installation on high voltage potential, with the isolated platform

mounted directly in series with the transmission line.

Fig. 21: 500 kV TCSC Serra da Mesa, Furnas/Brazil – Essential for Transmission

Current Control Impedance ControlPower OscillationDamping (POD)Mitigation of SSR(Option)

Current Control Impedance ControlPower OscillationDamping (POD)Mitigation of SSR(Option)

Benefits:o Increase of Transmission Capacityo Improvement of System Stability

Benefits:o Increase of Transmission Capacityo Improvement of System Stability

Up to 500 PODOperations per dayfor saving the System Stability

A System Outage of 24 h hours would cost 840,000 US $ *

Up to 500 PODOperations per dayfor saving the System Stability

A System Outage of 24 h hours would cost 840,000 US $ *

* 25 US $/MWh x 1400 MW x 24 hrs

> + 60 o C

up to 85 o

> + 60 o C

up to 85 o

Fig. 22: FSC at EHV 735 kV plus harsh Environment

Poste Montagnais, Canada - FSCPoste Montagnais, Canada - FSC

- 50 o C- 50 o C

Fig. 20: FACTS - Application of Series Compensation

TCSC/TPSCTCSC/TPSC FSCFSCα

~ ~

TCSC/TPSCTCSC/TPSC FSCFSCα

~ ~

α

~~~ ~~~~Damping of Power OscillationsLoad-Flow ControlMitigation of SSR

Controlled Series Compensation:

Damping of Power OscillationsLoad-Flow ControlMitigation of SSR

Controlled Series Compensation:Controlled Series Compensation:

Fixed Series Compensation:

Increase of Transmission Capacity

Fixed Series Compensation:Fixed Series Compensation:


18 / 33

For Thyristor Protected Series Compensation TPSC, innovative developments in Thyristor-

Technology have been applied: Light-triggered Thyristors (now state of the art for FACTS

and HVDC) by means of a special heat-sink to enable a very fast self-cooling of the valves

within half a second only. By these means, TPSC is fully suitable for multiple fault

conditions, as it is often the case under hot climate conditions due to brush-fires leading to

repetitive line faults. In the TPSC, the thyristor replaces the conventional MOV (zinc oxide

arrester) for fast capacitor protection against over voltages due to short-circuit currents.

During faults, the MOV heats up heavily. Due to an upper temperature limit, the MOV must

cool down before the next current stress can be absorbed. Cool-down requires a substantial

amount of time, time constants of several hours are typical. During this time, the series

compensation must be taken out of service (bypass-breaker closed) and consequently the

power transfer on the related line needs to be reduced dependent on the degree of

compensation, leading to a significant loss in transmission capacity. Thus it appears that by

using the TPSC with fast cooling-down time instead of conventional series compensation with

MOV, a significant amount of money for each application can be saved.

Fig. 23 shows a site-view of one of the 5 TPSCs, installed at 500 kV in California, USA (ref.

to Fig. 8).

In Fig. 24, two projects with series compensation in China are presented. The picture a) gives

a view of one phase element of the two Pingguo TCSCs. The 3D view b) demonstrates how

Fig. 23: TPSCs Vincent and Midway/USA: 5 TPSC Systems at 500 kV - fully proven in Practice

Outdoor Valves on a PlatformLTT Thyristors, self-cooled

TPSC Technology: Outdoor Valves on a PlatformLTT Thyristors, self-cooled

TPSC Technology:

19 / 33

easily series compensation can be mounted to the existing line: when the installation is

finished (besides the line), a line interruption and a jumper connection to the platform is

made, with an actual power transmission interruption of only 1-3 days.

5. HVDC for Interconnection and Transmission Optimization

During the developments of East-West Grid interconnection in Europe, three B2B projects

have initially been installed. One of them is shown in Fig. 25. All 3 projects led to fast and

more than full return on investments by energy trading. With the upcoming synchronous

extension of UCTE, however, they were taken out of service.

The low losses of the thyristor technology in comparison with VSC devices (ref. to Fig. 11),

are depicted in Fig. 26 for the Etzenricht installation shown in Fig. 25. Similar – and even

lower – losses have been achieved with the new HVDC installations. Especially in very large

DC transmission projects with 3 GW and more, minimal losses are an important issue for the

investors.

Fig. 24: China goes ahead – Transmission Enhancement with FACTS a) Photo of Pingguo TCSC, commissioned in June 2003 b) 3D View on Fengjie 500 kV Fixed Series Compensation, China 2x 600 MVAr, Line Compensation Level 35%

Commercial Operation in June 2006Commercial Operation in June 2006

Enhancement of Chinas “Central Transmission Corridor”Enhancement of Chinas “Central Transmission Corridor”

b)

a)

20 / 33

After the Blackout in the United States, new projects with high voltage power electronics are

smoothly coming up. Siemens PTD has been awarded a contract by Neptune Regional

8000 kW of Losses equals1.33% of 600MW

3%3%3%3%4%4%

37%37%

53%53%

AuxiliariesSmoothing ReactorFilter Circuits

Converter Valves

Converter Transformers

this sums up to …this sums up to …

Total B2B Losses: close to 1 % onlyTotal B2B Losses: close to 1 % only

Fig. 26: HVDC Losses – Example B2B Etzenricht

Fig. 25: Etzenricht, one of the initial Steps for East-West System Interconnection in Europe with 3 B2Bs – now replaced by synchronous Links (ref. to Text)

HVDC B2B - as Interconnector or Power-Flow Controller: Etzenricht, an Example from Germany

System Data:Rated Power: 600 MWDC Voltage: 160 kV DCDC Current: 3750 A AC Voltage: 420 kV

21 / 33

Transmission System LLC (RTS) in Fairfield, Connecticut, to construct an HVDC

transmission link between Sayreville, New Jersey and Long Island, New York. Neptune RTS

was established to develop and commercially operate power supply projects in the United

States. By delivering a complete package of supply, installation, service and operation from a

single source, Siemens is providing seamless coverage for the customer’s needs. The

availability of this combined expertise fulfills the prerequisites for financing these kinds of

complex supply projects through the free investment market. Siemens and Neptune RTS

developed the project over three years to prepare it for implementation. In addition to

providing technological expertise, studies, and engineering services, Siemens also supported

its customer in the project’s approval process. In Fig. 27, highlights of this innovative project

are depicted.

Another highlight of HVDC project development is shown in Fig. 28. Basslink HVDC

provides a submarine cable link across the Bass Strait between Tasmania and the state of

Victoria on the Australian mainland. Basslink Pty Ltd. was specially formed by National Grid

Transco (the world's largest independent transmission network operator) to run the project

titled Basslink. The advantages of this link lie on both sides of the water: gaining access to the

Australian electricity market, Tasmania can supply Victoria at peak load times with power

from hydro generating plants. Tasmania can top up its base load from the mainland grid and

Fig. 27: New HVDC Cable Link Neptune RTS, USA

Customer:

End User:

Location:

Project

Development:

Supplier:

Transmission:

Power rating:

Transmission dist.:

Neptune RTS

Long Island Power

Authority (LIPA)

New Jersey: Sayreville

Long Island: Duffy Avenue

NTP-Date: 07/2005

PAC: 07/2007

Consortium

Siemens / Prysmian

Sea Cable

600/660 MW monopolar

82 km DC Sea Cable

23 km Land Cable

Customer:

End User:

Location:

Project

Development:

Supplier:

Transmission:

Power rating:

Transmission dist.:

Neptune RTS

Long Island Power

Authority (LIPA)

New Jersey: Sayreville

Long Island: Duffy Avenue

NTP-Date: 07/2005

PAC: 07/2007

Consortium

Siemens / Prysmian

Sea Cable

600/660 MW monopolar

82 km DC Sea Cable

23 km Land Cable

Ed Stern, President of Neptune RTS: “High-Voltage Direct-Current Transmission will play an increasingly important Role, especially as it becomes necessary to tap Energy Reserves whose Sources are far away from the Point of Consumption”

Ed Stern, President of Neptune RTS: “High-Voltage Direct-Current Transmission will play an increasingly important Role, especially as it becomes necessary to tap Energy Reserves whose Sources are far away from the Point of Consumption”

22 / 33

also secure the base load in drought periods, when reduced hydro power is available. In

addition to that, Tasmania plans to set up wind farms to improve the production of electrical

power from regenerative sources further, ref. to Fig. 28.

The Basslink HVDC project shows that HVDC is fully suitable to match complex

transmission requirements even under environmental sensitive conditions. In Fig. 29 it is

shown that a combination of land cable, sea cable and overhead line was selected to match

both environmental constraints and cost issues.

For a long time, China has been benefiting from HVDC transmission by connecting clean and

low cost energy sources to the remote load centers, as indicated in Fig. 30 for the Tian-Guang

project (1800 MW) in South China. In Fig. 31 it is shown that a project termination for Gui-

Guang I (3000 MW) could be achieved 6 months ahead of schedule, which provides a large

amount of additional return on investments to the customer.

Fig. 28: Innovative Transmission Technologies for long Distances - Basslink HVDC

Benefits of HVDCBenefits of HVDC

Clean & Low Cost Energyover Long Distance – suitable

for Peak-Load Demand

Clean & Low Cost Energyover Long Distance – suitable

for Peak-Load Demand

Improvement of PowerQualityImprovement of PowerQuality

Improvement of localInfrastructuresImprovement of localInfrastructures

HVDC Cable (400 kV / 1500 mm2)

Metallic Return Cable (12/20 kV / 1400 mm2)

FO Cable (12 Fibers)

HVDC Cable (400 kV / 1500 mm2)

Metallic Return Cable (12/20 kV / 1400 mm2)

FO Cable (12 Fibers)

System Data:Rating 500 MWVoltage 400 kV DCThyristor 8 kV LTTTransmissionlength 370 km

System Data:Rating 500 MWVoltage 400 kV DCThyristor 8 kV LTTTransmissionlength 370 km

Cable Laying Vessel“Giulio Verne“

23 / 33

As a follow-up of the Gui-Guang I project, which is in full commercial operation, a new

contract for Gui-Guang II has been awarded to Siemens and its local partners with equal

transmission capacity of 3000 MW. Examples of system studies for projects with HVDC and

FACTS for system stability improvement in China and other continents are depicted in the

next section.

Sea Cable

Underground Cable

Converter Station

500 kV Substation

3.2 km 57.4 km 295 km

Transition Station

6.4 km

Underground Cable

Converter Station

Transition Station

220 kV Substation

1.7 km 2.1 km8.9 km

McGauransBeach

Five Mile Bluff

Bass Strait

Loy Yang Georgetown

Sea Cable

Underground Cable

Converter Station

500 kV Substation

3.2 km 57.4 km 295 km

Transition Station

6.4 km

Underground Cable

Converter Station

Transition Station

220 kV Substation

1.7 km 2.1 km8.9 km

McGauransBeach

Five Mile Bluff

Bass Strait

Loy Yang Georgetown

Fig. 29: Basslink HVDC - Optimization of the Transmission System

Operated by:South China Electric Power JVC (SCEP)

System Data:Rating 1800 MWVoltage +/-500 kVDCThyristor 8 kVLine Length 960 km

BenefitsBenefitsUse of Clean &Low CostEnergy

Use of Clean &Low CostEnergy

TianshengqiaoTianshengqiao

Guangzhou BeijiaoGuangzhou Beijiao

The Task: Connection of Hydro Generation to Remote Load Centers

Tian Hydro StationTian Hydro Station

Fig. 30: HVDC Long Distance Transmission Tian-Guang

24 / 33

6. System Studies for large Transmission Projects with HVDC and FACTS

Fig. 32-33 give an example of a large power system simulation of the Chinese grid [2], in

which both FACTS and HVDC have been integrated for grid interconnection and point to

point long distance transmission in a hybrid way.

Fig. 31: HVDC Long Distance Transmission Gui-Guang I

Rating: 3000 MWVoltage: ± 500 kV

Contract: Nov. 1, 2001Project terminated 6 Months ahead of Schedule by Sept. 2004

Thyristor: 5" LTT with integrated Overvoltage Protection

View of the Thyristor-Module

Project terminated 6 Months ahead of Schedule by Sept. 2004

Fig. 32: Use of HVDC and FACTS in a hybrid System in China

GuiyangNayong

AnshunAnshun

Huishui

Hechi

Lubuge

TSQ-ILuoping

HVDC TSQ

LiudongYantan

TCSC & FSCPingguo

Baise

TSQ-II

Nanning

Yulin

Laibin

Hezhou

Gaomin

Luodong

ZhaoqingConv. Stat.

BeijiaoConv. Stat.

Guangzhou

Wuzhou

TSQ Conv. Stat.

Yunnan

Guangxi

Guizhou

Guangdong

HVDC GuiGuang

AnshunConv. Stat.

Liuzhou

Zhaoqing

Beijiao

Zhengcheng

Guangxi

Pingguo

FSC

HVDC Converter Station

TCSC FSC

HVDC Converter Station

TCSCTCSC FSCFSC

Hydro Power StationHydro Power Station

Thermal Power StationThermal Power Station

25 / 33

Because of the long transmission distances, the system experiences severe power oscillations

after faults, close to the stability limits. In the recordings in Fig. 33 (upper part) oscillations

are depicted. The first case given is HVDC transmitting power in constant power mode, see

curve a. It can be seen that strong power oscillations occur. If, however, damping control of

HVDC Gui-Guang is activated (curve b ), the oscillations are damped very effectively. Using

series compensation with two TCSCs and two FSCs at Pingguo substation, the stability of the

overall system can be further increased (curve c ). The lower part of Fig. 33 shows that

without HVDC, the Pingguo TCSCs need more actions for damping: 1a) compared to 2a)-b).

Without series compensation and without HVDC damping, such a large power system would

be unstable in case of fault contingencies, thus leading to severe outages (Blackout) [3].

Fig. 33: China - Benefits of active Damping with HVDC & FACTS

2b)

2a)

1a)

POD Output Signal (pu) TCSC 1 (= TCSC 2)


POD Output Signal HVDC (%)

Fast and strong Action of HVDC with POD

HVDC not activeMore Action of TCSC required

Less Action of TCSC required HVDC active

2b)

2a)

1a)



POD Output Signal HVDC (%)

Fast and strong Action of HVDC with POD

HVDC not activeMore Action of TCSC required

Less Action of TCSC required HVDC active

5 10 15 200

0

600

900

1200

1500

-600

300

-900

-300

Time (s)

Powe

r flo

w in

one

line

Huish

ui-H

echi

(MVA

)

a

b

5 10 15 200

0

600

900

1200

1500

-600

300

-900

-300

Time (s)

Powe

r flo

w in

one

line

Huish

ui-H

echi

(MVA

)

a

b

Time / s

ab

c

5 10 15 200

0

600

900

1200

1500

-600

300

-900

-300

Time (s)

Powe

r flo

w in

one

line

Huish

ui-H

echi

(MVA

)

a

b

5 10 15 200

0

600

900

1200

1500

-600

300

-900

-300

Time (s)

Powe

r flo

w in

one

line

Huish

ui-H

echi

(MVA

)

a

b

Time / s

aabb

cc

Power Flow in one Line Huishui-Hechi (MW)

Dynamic Results

a – without Power Modulationb – with Power Modulation

of HVDC Controlc – further Improvements with

Pingguo TCSC/FSC

26 / 33

Similar studies have been carried out for large transmission projects worldwide. An example

of such studies is described in the following.

With the Mead-Adelanto and the Mead-Phoenix Transmission Project (MAP/MPP), a major

500 kV transmission system extension has been carried out to increase the power transfer

opportunities between Arizona and California, USA. The extension includes two main series

compensated 500 kV line segments and two equally rated Static Var Compensators, supplied

by Siemens, at the Adelanto and Marketplace substations - ref to Fig. 34. The SVCs enabled

the integrated operation of the already existing highly compensated EHV AC system and two

large HVDC systems. The SVC installation was an essential prerequisite for the overall

system stability at an increased power transfer rate.

An example of the intensive project testing with computer and real-time simulator facilities is

given in Fig. 35 for a fault application at Marketplace 500 kV bus. The figure shows the

computer test results with both SVCs active. The influence of the HVDC can be seen from

Fig. 34: HVDC plus SVC: Mead-Adelanto - USA


Improvement of System Stability


Improvement of System Stability

Upgrade of a large AC and DC TransmissionSystem with 2 SVCs& FSCs

Each SVC: 388 MVAr for Voltage and POD ControlEach SVC: 388 MVAr for Voltage and POD Control

27 / 33

the DC voltage E dc. Figure a) is with both SVCs only in voltage control mode (PSDC

blocked); Figure b) shows an improved damping with the PSDC function enabled.

In Fig. 36, a new FACTS application with SVC in combination with HVDC in Germany is

shown [2]. It is actually the first high voltage FACTS controller in the German network.

Reason for the SVC installation at Siems substation nearby the landing point of the Baltic

Cable HVDC were unforeseen right of way restrictions in the neighboring area, where an

initially planned new tie-line to the strong 400 kV network for connection of the HVDC was

denied. Therefore, with the existing reduced network voltage of 110 kV (see the dotted black

lines in Fig. 36, only a limited amount of power transfer of the DC link was possible since its

commissioning in 1994, in order to avoid repetitive HVDC commutation failures and voltage

problems in the grid. In an initial first step for grid access improvement, an additional

transformer for connecting the 400 kV HVDC AC bus with the 110 kV bus (see the figure)

was installed. Finally, in 2003 with the new SVC, equipped with a fast coordinated control,

the HVDC could fully increase its transmission capacity up to the design rating of 600 MW.

In addition to this measure, a new cable to the 220 kV grid was installed, to increase the

system strength with regard to performance improvement of the HVDC controls. In Fig. 37, a

photo of the Siems SVC in Germany is given.

1100

1000

900

800

700

400

200

0

1.4

1.2

1.0

0.8

0.6

400

200

0

E dc Adelanto (volts) Mkplc 500kV Bus Vlt (pu)

Adel Bsvc (Mvar) Mkplc Bsvc (Mvar)

a)E dc Adelanto (volts)

Mkplc 500kV Bus Vlt (pu)

Adel Bsvc (Mvar) Mkplc Bsvc (Mvar)

1100

1000

900

800

700

1.4

1.2

1.0

0.8

0.6

400

200

0

400

200

0

0 0 1010 2020Time (sec) Time (sec)

b)

a) Both SVCs in Voltage Control Mode

b) Both SVCs in Coordinated Voltage & Power Oscillation Damping Control Mode

Design by Computer StudiesDesign by Computer Studies

Fig. 35: Mead-Adelanto Studies – Comparison of SVC Voltage- and POD-Control Mode

28 / 33

In the same way as in the previous project cases, intensive studies, first with computer and

then with real-time simulator by using the physical SVC controls and simplified models for

the HVDC, have been carried out prior to commissioning.

Essential for enhanced Grid Access of the HVDCEssential for enhanced Grid Access of the HVDC

Fig. 37: The Solution – the first HV SVC in the German Grid at Siems Substation

Fig. 36: The Problem – no Right of Way for 400 kV AC Grid Access of Baltic Cable HVDC

Initially planned Connection

Grid Access denied

1

2

1 Initial Step for Grid Access Enhancement

2 and a new 220 kV Cable

2

2

Final Solution: new SVC with TCR & TSC100 MVar ind.200 MVar cap.

Now, the HVDC can operate at full Power Rating

Initially planned Connection

Grid Access denied

11

22



2 and a new 220 kV Cable22 and a new 220 kV Cable

22

22



Now, the HVDC can operate at full Power Rating

2003

1994

29 / 33

In conclusion of the previous sections, Table 1 summarizes the impact of FACTS and HVDC

on load flow, stability and voltage quality when using different devices. Evaluation is based

on a large number of studies and experiences from projects.

7. Innovative Transmission Solutions using High Voltage Power Electronics

Increasing generation in high load density networks on the one hand, and interconnections

among the systems on the other hand, increase the short-circuit power. If the short-circuit

current rating of the equipment in the system is exceeded, the equipment must be uprated or

replaced, which is a very cost- and time-intensive procedure. Short-circuit current limitation

offers clear benefits in such cases. Limitation by passive elements, e.g. reactors, is a well

Table 1: FACTS & HVDC – Overview of Functions & “Ranking”

HVDC (B2B, LDT)

UPFC(Unified Power Flow Controller)

MSC/R(Mechanically Switched Capacitor / Reactor)SVC (Static Var Compensator)STATCOM (Static Synchronous Compensator)

Load-Flow Control

Voltage Control: Shunt Compensation

FSC (Fixed Series Compensation)TPSC (Thyristor Protected Series Compensation)TCSC (Thyristor Controlled Series Compensation)

Variation of the Line Impedance: Series Compensation

Voltage QualityStabilityLoad Flow

SchemeDevicesPrincipleImpact on System Performance

Influence: no or lowsmallmediumstrong

Based on Studies & practical Experience

30 / 33

known practice. It reduces, however, the system stability, and there is an impact on the load-

flow.

By combining the previously mentioned 500 kV TPSC application with an external reactor

(see Fig. 38), whose design is determined by the allowed short-circuit current level, this

device can also be used very effectively as short-circuit current limiter (SCCL, ref. to [4, 7]).

This new device operates with zero impedance in steady-state conditions, and in case of short-

circuit it is switched within a few ms to the limiting-reactor impedance.

Fig. 39: FCL - Principles and Applications

Not available for HV Levels and Constraints on Protection Co-ordination

Not available for HV Levels and Constraints on Protection Co-ordination

Difficult or impossible at High Voltage LevelsDifficult or impossible at High Voltage Levels

Fault Current LimitationConventional Solution: Reactor

The new FACTS Solution: SCCL

Future Option: High-Temperature Superconducting FCL

Fault Current InterruptionIs-Limiter

Electronic Devices (“Small FACTS”)

Risk of Voltage CollapseRisk of Voltage Collapse

SCCL: no ConstraintsSCCL: no Constraints

Fig. 38: SCCL - an Innovative FACTS Solution using TPSC

Bus 1 Bus 2

AC AC

Bus 1 Bus 2

ACAC ACAC

SCCL SCCL SCCL SCCL SCCL SCCL

TPSCTPSCTPSCTPSCTPSCTPSC + ReactorReactor+ ReactorReactorReactorReactor

Thyristor Protected Thyristor Protected Series CompensationSeries CompensationThyristor Protected Thyristor Protected Series CompensationSeries Compensation

Use of proven TechnologyUse of proven Technology

The new Idea !The new Idea !

31 / 33

Fig. 39 gives a brief overview on today’s solutions for fault-current limitation, including the

new SCCL. Basically, there are two methods for fault-current reduction: limitation and

interruption. The constraints and benefits of the different solutions are indicated in the figure.

Fig. 40 shows the basic function and the operating principle of the SCCL, including a 3-D

view of the SCCL. In comparison with the TPSC site photo, it can be seen that the TPSC is

just complemented by an additional reactor for the current limitation. Further details on the

SCCL solution are described in [7].

8. Market and Reliability Issues

Table 2 summarizes the market expectations for FACTS and HVDC solutions today and in

the future. The market for series compensation, for SVC and for B2B for load-flow control is

actually large today and, as a result of liberalization and deregulation in the power industry, is

developing fast in the future. The market in the HVDC long distance transmission field is

further progressing fast. A large number of high power long distance transmission schemes

using either overhead lines or submarine cables projects have been put into operation or are in

the stage of installation.

Fig. 40: SCCL - Short-Circuit Current Limitation with FACTS

To Bus 2

Reactor

Thyristor Valve Housing

BYPASS Breaker

Capacitor Bank

To Bus 1

Communication

To Bus 2

Reactor

Thyristor Valve Housing

BYPASS Breaker

Capacitor Bank

To Bus 1

Communication

ImpedanceX

Zero Ohm for best Load Flow

Fast Increase of Coupling Impedance

t

ImpedanceX

ImpedanceX

Zero Ohm for best Load Flow

Fast Increase of Coupling Impedance

t

Just one additional X !Just one additional X !

32 / 33

Concerning reliability of high voltage power electronics, Table 3 gives an example of two

SVC projects installed in South Africa. Same high reliability is also achieved for HVDC as

Table 2: Markets for FACTS and HVDC

HVDC

UPFC

TCSC / TPSC

FSC

STATCOM

SVC

Series Compensation

Shunt Compensation

Combined Device

Power Transmission

MSC/R

HVDC

UPFC

TCSC / TPSC

FSC

STATCOM

SVC

Series Compensation

Shunt Compensation

Combined Device

Power Transmission

MSC/R

Excellent Market Upcoming Market Small Market

Table 3: Availability of Power Electronics – Example FACTS: close to 100 %- same for HVDC

Recordings from NATAL SVCs / RSA (2 TCR & 3 Filter)Guarantied Availability: 98 - 99 %

1h0036h409h402h13MDT in hrs

03h002h0010h15On-line Maintenance

162h00102h2680h000hOff-line Maintenance

1252Forced and deferred Outages

10010099.4599.9Availability (%)

1998199719961995Illovo SVC


03h002h0010h15On-line Maintenance

162h00102h2680h000hOff-line Maintenance


10010099.4599.9Availability (%)

1998199719961995Illovo SVC


0001h00On-line Maintenance

60h1562h0081h004h00Off-line Maintenance


99.7799.9299.7199.78Availability (%)

1998199719961995Athene SVC


0001h00On-line Maintenance

60h1562h0081h004h00Off-line Maintenance


99.7799.9299.7199.78Availability (%)

1998199719961995Athene SVC

33 / 33

the technology applied uses the same components. Excellent on-site operating experience is

being reported, and the FACTS and HVDC technology became mature and reliable.

9. Conclusions

Deregulation and privatization is posing new challenges on high voltage transmission

systems. System elements are going to be loaded up to their thermal limits, and wide-area

power trading with fast varying load patterns will cause congestion. System enhancement will

be essential to keep the supply reliable and safe. Interconnection of power systems offers

many benefits for the operation of the grids. The performance of power systems, however,

decreases with size, loading and complexity of the networks. This is related to problems with

load flow, power oscillations and voltage quality. Such problems are even deepened by the

changing situations resulting from deregulation of the electrical power markets. The power

systems have not been designed for wide-area power trading with daily varying load patterns,

where power flows do no more follow the initial planning criteria of the existing network

configuration. Large blackouts in America and Europe confirmed clearly that the favorable

close electrical coupling might also include risk of uncontrollable cascading effects in large

and heavily loaded interconnected systems. FACTS and HVDC, however, provide the

necessary features to avoid technical problems in the power systems, and they increase the

transmission efficiency.

10. References

[1] U. W. Niehage, “Future Developments in Power Industry”, Key-Note Adress at AESIEAP, 28-05 September 2005, New Delhi, India

[2] L. Kirschner, D. Retzmann, G. Thumm, “Benefits of FACTS for Power System Enhancement”, 14-18 August, 2005, IEEE/PES T & D Conference, Dalian, China

[3] G. Beck, D. Povh, D. Retzmann, E. Teltsch, “Global Blackouts – Lessons Learned”, Power-Gen Europe, 28-30 June 2005, Milan, Italy

[4] W. Breuer, D. Povh, D. Retzmann, V. Sitnikov, E. Teltsch, “Benefits of Power Electronics for Transmission Enhancement”, 10-11 March 2004, Moscow, Russia

[5] W. Breuer, X. Lei, D. Povh, D. Retzmann, E. Teltsch, “Role of HVDC and FACTS in future Power Systems”, 18-22 October 2004, 15th CEPSI, Shanghai, China

[6] W. Breuer, X. Lei, D. Povh, D. Retzmann, E. Teltsch, “Solutions for large Power System Interconnections”, 18-22 October 2004, 15th CEPSI, Shanghai, China

[7] V. Gor, D. Povh, Y. Lu, E. Lerch, D. Retzmann, K. Sadek, G. Thumm, “SCCL – A new Type of FACTS based Short-Circuit Limiter for Application in High Voltage Systems”, CIGRÉ Report B4-209, Session 2004.

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