1 Use of FACTS for System Performance Improvement G. Beck, W. Breuer, D. Povh, D. Retzmann* Siemens, Germany ABSTRACT The performance of power systems decreases with the size, the loading and the 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, where contractual power flows do not follow the initial design criteria of the existing network configuration any longer. Power Systems have not been designed for “wide-area” energy trading with daily varying load patterns, and the systems are “close to their limits”. Flexible AC Transmission Systems (FACTS) based on power electronics have initially been developed to improve the performance of long distance AC transmission. Later, the technology has been extended to the devices which can also control power flow. Excellent operating experiences are available world-wide, and the technology became mature and reliable. FACTS are applicable in shunt connection, in series connection, or in a combination of both. In this paper, solutions with FACTS for system enhancement and for system interconnections are presented, and their advantages are explained. Examples of large project applications in Asia, America and Europe are depicted, including hybrid configurations with parallel operation of FACTS and HVDC (High Voltage Direct Current). KEY WORDS: System Stability, Blackout Prevention, Increase of Transmission Capacity, Power-Flow Control, Short-Circuit Current Limitation, Parallel Operation of FACTS and HVDC 1. INTRODUCTION 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 size of power systems has grown. 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 [1-3]. With an increasing size of the interconnected systems, the technical and economical advantages diminish. This is related to problems regarding load flow, power oscillations and voltage quality. If *[email protected]
Transcript
1
Use of FACTS for System Performance Improvement
G. Beck, W. Breuer, D. Povh, D. Retzmann* Siemens, Germany
ABSTRACT The performance of power systems decreases with the size, the loading and the 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, where contractual power flows do not follow the initial design criteria of the existing network configuration any longer. Power Systems have not been designed for “wide-area” energy trading with daily varying load patterns, and the systems are “close to their limits”.
Flexible AC Transmission Systems (FACTS) based on power electronics have initially been developed to improve the performance of long distance AC transmission. Later, the technology has been extended to the devices which can also control power flow. Excellent operating experiences are available world-wide, and the technology became mature and reliable. FACTS are applicable in shunt connection, in series connection, or in a combination of both.
In this paper, solutions with FACTS for system enhancement and for system interconnections are presented, and their advantages are explained. Examples of large project applications in Asia, America and Europe are depicted, including hybrid configurations with parallel operation of FACTS and HVDC (High Voltage Direct Current).
KEY WORDS:
System Stability, Blackout Prevention, Increase of Transmission Capacity, Power-Flow Control, Short-Circuit Current Limitation, Parallel Operation of FACTS and HVDC
1. INTRODUCTION
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 size of power systems has grown. 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 [1-3].
With an increasing size of the interconnected systems, the technical and economical advantages diminish. This is related to problems regarding load flow, power oscillations and voltage quality. If
power is to be transmitted through the interconnected system over long distances, transmission needs to be supported.
Fig. 1 and Fig. 2 summarize the perspectives of power system developments. In the future, an increasing part of the installed capacity, however, will be connected to the distribution levels (dispersed generation), which poses additional challenges on planning and safe operation of the systems, see Fig. 2. In such cases, power electronics can clearly strengthen the power systems and improve their performance [2].
Problems with congestion and transmission bottlenecks are even deepened by the deregulation of the electrical power markets, where contractual power flows do not follow the initial design criteria of the existing network configuration any longer. Large blackouts in America and Europe confirmed clearly that the favorable close electrical coupling might also include the risk of uncontrollable cascading effects in large and heavily loaded interconnected systems [2], see Fig. 3.
Fig. 1: Trends in High Voltage Transmission Systems
PrivatisationGlobalisation/Liberalisation
Deregulation - Privatization: Opening of the Markets, Independent Transmission Companies ITCs, Regional Transmission Organisations RTOs
PrivatisationGlobalisation/Liberalisation
Deregulation - Privatization: Opening of the Markets, Independent Transmission Companies ITCs, Regional Transmission Organisations RTOs
PrivatisationBottlenecks inTransmission
Problem of uncontrolled Loop FlowsOverloading & Excess of SCC* LevelsSystem Instabilities & Outages
PrivatisationBottlenecks inTransmission
Problem of uncontrolled Loop FlowsOverloading & Excess of SCC* LevelsSystem Instabilities & Outages
System Enhancement & Interconnections:Higher Voltage Levels **New Transmission TechnologiesRenewable Energies
Investments inPower SystemsInvestments inPower Systems
* SCC = Short-Circuit Current** Example UCTE: 400 kV is actually too low** Example UCTE: 400 kV is actually too low
Fig. 2: Perspectives of Transmission and Distribution Network Developments
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Today: Tomorrow:
Load Flow will be “fuzzy”Use of Dispersed GenerationUse of Dispersed Generation
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Fig. 3: Blackouts 2003 - Example United States a) The Blackout Area - and a Satellite View b) Congestion and Loop Flows - Forecasting Studies and Cascading Events
Source: National Transmission Grid Study; U.S. DOE 5/2002 – “Preview”
Source: National Transmission Grid Study; U.S. DOE 5/2002 – “Preview”
Problems only in the synchronous interconnected Systems
Problems only in the synchronous interconnected Systems
* PTDF = Power Transfer Distribution Factor* PTDF = Power Transfer Distribution Factor
**
b)
Giant Loop Flows 2.2 - 4.8 GW
a)
Source: Blackout Summary, U.S./Canada Power Outage Task Force 9-12-2003
Blackout: a large Area is out of SupplyBlackout: a large Area is out of Supply
Before the Blackout Before the Blackout
However, some Islands still have local SupplyHowever, some Islands still have local Supply
Québec's HVDCs assist for Power Supply and System Restoration
Québec's HVDCs assist for Power Supply and System Restoration
Source: EPRI 2003
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Additional problems are expected when renewable energies such as large wind farms have to be integrated into the system, especially when the connecting AC links are weak and when there is no sufficient reserve capacity in the neighboring system available [3].
Based on the global experience with large blackouts [2], strategies for the development of large power systems go clearly in the direction of hybrid transmissions consisting of DC and AC interconnections including FACTS. Such hybrid interconnected systems offer significant advantages, both technical and in terms of reliability [2, 4]. Fig. 4 shows schematically such a hybrid system using FACTS as well as HVDC. Power exchange in the neighboring areas of interconnected systems offering most advantages can be achieved by AC links, preferably including FACTS for increased transmission capacity and for stability reasons [4]. The transmission of large power blocks over long distances should, however, be utilized by the HVDC transmissions directly to the locations of power demand. HVDC can be implemented as direct coupler – the “Back-to-Back” solution (B2B) – or as point-to-point long distance transmission via DC line. In addition to FACTS, 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]. The “Firewall” function of HVDC [2], as mentioned in Fig. 4, is explained in the next section.
2. ELIMINATION OF TRANSMISSION BOTTLENECKS BY MEANS OF POWER ELECTRONICS
Fig. 5 shows an “Application Guide” for grid enhancement with power electronics (ref. to Fig. 3 b). Depending on the grid structure, there are four basic cases:
• Load displacement in case of parallel lines by impedance variation (series compensation)
• Fast load-flow control in meshed structures with HVDC/GPFC (or very slow with phase shifting transformer)
• Voltage collapse: reactive/active power injection by means of FACTS/HVDC
• Excess of allowed short-circuit level: short-circuit current limitation (FACTS/HVDC)
Fig. 4: 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
“Countermeasures”against large Blackouts
“Countermeasures”against large Blackouts
& FACTS& FACTS
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GPFC (Grid Power Flow Controller) is a special DC back-to-back link which is designed for fast power and voltage control at both terminals [4]. The GPFC features are explained in the following.
The basic equation for power transmission (Fig. 6) explains the solutions for system enhancement in a more detailed way. The power transmitted between two subsystems depends on voltages at both ends of the connecting line, the line impedance and the phase angle difference between the connecting points. Power electronics can actively influence one ore more of these parameters and control or direct the power flow through the interconnection.
Load Displacement by Series Compensation Load Displacement by Series Compensation Load Displacement by Series Compensation
Load Management by HVDCLoad Management by HVDCLoad Management by HVDC
*** Short-Circuit Current Limitation for Connection of new Power PlantsShort-Circuit Current Limitation for Connection of new Power PlantsShort-Circuit Current Limitation for Connection of new Power Plants
SVC & HVDC for Prevention of Voltage CollapseSVC & HVDC for Prevention of Voltage CollapseSVC & HVDC for Prevention of Voltage Collapse
* PTDF = Power Transfer Distribution Factor* PTDF = Power Transfer Distribution Factor
Fig. 5: Use of Power Electronics for System Enhancement
VV11 VV22
VV11 VV22
Parallel Compensation
VV11 VV22
VV11 VV22VV11 VV22
Parallel CompensationParallel Compensation
XX
XX
Series Compensation
XX
XX
Series CompensationSeries Compensation
sin (sin (δ 1 - δ 2)
Power-Flow Control
sin (sin (δ 1 - δ 2)
Power-Flow Control
PP
PP ==PP ==
G ~ G ~G ~G ~G ~ G ~G ~G ~
,, δ 2,, δ 1
Each of these Parameters can be used for Load-Flow Control and Power Oscillation DampingEach of these Parameters can be used for Load-Flow Control and Power Oscillation Damping
Fig. 6: Power Transmission – The basic Equation
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By using FACTS for reactive power compensation, the impedances and voltages of the system can be influenced: by adding series compensation (fixed or controlled) into the line, its reactance X can be reduced or modulated (for power oscillation damping, ref. to the equation); with FACTS parallel compensation, e.g. SVC (Static Var Compensator), the voltage can be stabilized (at constant values, or modulated for damping of oscillations). The transmission angle can be influenced by using HVDC for power-flow control. These methods are explained in Figs. 7-8.
Fig. 8 shows that HVDC is also well suitable for short-circuit current limitation (fault current blocking). Furthermore, in case of cascading events, HVDC acts like an automatic “Firewall” by fast decoupling of the interconnected systems during a disturbance and by immediate restarting power transmission after the fault. Systems directly coupled by AC links need time-consuming re-synchronization, which can take many hours. Alongside its main function of power-flow control, the HVDC incorporates also voltage control (by reactive power injection) for both sides of the system. It decouples the transmission equation by forcing the power to flow in a similar way like the well known phase-shifting transformer, however, much faster and independent from the frequencies and angles of the two coupled systems.
Using an extended control range of HVDC, the B2B can fully “feature” FACTS functions, e.g. fast voltage control, in the same way as an SVC. This new idea of GPFC as a “FACTS B2B” is explained in Fig. 9, in comparison to the “standard” HVDC control range. As indicated in the figure, these features have been successfully applied in a project at Lamar substation, USA.
Voltage Control
Parallel Compensation
Power-Flow Control
P P
Section of a Transmission Line
C >C >VV
VV
Series Compensation
C >C >
L L >>~ 1/X1/X
L L >>
Voltage ControlVoltage ControlVoltage Control
Parallel CompensationParallel Compensation
Power-Flow Control
P P
Power-Flow ControlPower-Flow Control
P P
Section of a Transmission LineSection of a Transmission Line
C >C >VV
VV
Series CompensationSeries Compensation
C >C >
L L >>~ 1/X1/X
L L >>Fig. 7: FACTS for Reactive Power Compensation
Slow FunctionsSlow Functions
Power & fast Voltage ControlFault-Current Blocking
Fast FunctionsFast Functions
V1 V2
Q2
L and C
Q1
L and C
G ~G ~
α and γ
PI2I1
V1 V2
Q2
L and C
Q1
L and C
G ~G ~
α and γ
PI2I1
V1 V2
Q2
L and C
Q1
L and C
G ~G ~G ~G ~G ~G ~
α and γ
PI2I1
Fault-Current Blocking
Fault-Current Blocking
Fig. 8: HVDC as Grid Power Flow Controller – The “FACTS” B2B
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3. FACTS TECHNOLOGIES AND APPLICATIONS
The main shunt connected FACTS application is the Static Var Compensator (SVC). SVC provides fast voltage control, reactive power control and power oscillation damping features. As an option, SVC can control unbalanced system voltages. World-wide, there are hundreds of these devices in operation. For decades, it has been a well developed technology, and the demand for SVCs is further increasing. For long AC lines, series compensation is used for reducing the transmission angle, thus providing stability enhancement. Fixed series compensation (FSC) is widely used to improve the stability and to increase the transmission capacity for long distance transmissions. A huge number of these applications are in operation. In case of more complex system conditions, Thyristor Controlled Series Compensation (TCSC) is used if fast control of the line impedance is required to adjust the load flow on parallel lines, or for damping of power oscillations. TCSC has already been applied in different projects for load-flow control, stability improvement and to damp oscillations in interconnected systems.
The rating of shunt connected FACTS controllers is up to 800 MVAr, series FACTS devices are implemented on 550 and 735 kV levels to increase the transmission capacity of the lines up to several GW.
Fig. 10 shows the basic configurations of FACTS devices. The SVC uses 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 (Static Synchronous Compensator) using voltage-sourced converters (VSC, [4]). 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. 11. Special FACTS devices are UPFC (Unified Power Flow Controller) and the GPFC [4]. UPFC combines a shunt connected STATCOM with a series connected STATCOM (also named S3C, Solid-State Series
Fig. 9: HVDC Operating Ranges – and the new GPFC Solution as “FACTS B2B”
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Compensator), which can exchange energy via a coupling capacitor. GPFC is, at lower costs, less complex than UPFC. For most applications in AC transmission systems and for network interconnections, SVC, FSC, TCSC and GPFC/B2B are fully sufficient to match all requirements of the grid. STATCOM and UPFC are tailored solutions for special needs.
FACTS devices consist of power electronic components and conventional equipment which can be combined in different configurations. It is therefore relatively easy to develop new devices to meet extended system requirements.
Recent developments are the TPSC (Thyristor Protected Series Compensation, Fig. 10) and the Short-Circuit Current Limiter (SCCL) [4, 5], both innovative solutions that use high power thyristor technology.
Fig. 10: FACTS – Basic Configurations
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
FACTS - Flexible AC Transmission Systems: Support of Power Flow
SVC - Static Var Compensator (Standard for Parallel Compensation)
Figs. 12-13 show today’s FACTS applications including mechanically switched devices such as MSC/MSR, which are frequently used for voltage support and blackout prevention [2]. Actual ratings and voltage levels of the solutions are also indicated in the figures.
A large number of different FACTS and HVDC controllers have been put into operation either as commercial projects or as prototypes. Fig. 14 gives an example of the Siemens applications world-wide. Thus it appears that some areas are still “blank”, which is expected to change in the future. For comparison reasons, the number and the increase of large HVDC long-distance transmission projects are also indicated in the figure. The CSC (Convertible Synchronous Compensator), as mentioned in Fig. 14, uses a flexible combination of two STATCOMs, of which each controller (+/- 100 MVAr) can be switched individually from shunt to series mode. By these means, CSC provides a multiple of operation modes including UPFC operation for the two transmission lines passing Marcy substation in the area of New York, USA.
4. USE OF FACTS FOR TRANSMISSION ENHANCEMENT
In Great Britain, in the course of deregulation, new power stations where installed in the north of the country, remote from the southern load centers; and some of the existing power stations in the south were shut down due to environmental constraints and for economic reasons, see Fig. 15-1). To strengthen the transmission system, a total number of 27 SVCs have been installed because there was no right of way for new lines or higher transmission voltage levels [3]. Fig. 15-1c) shows the very effective power oscillation damping (main control function) with two of these SVCs, installed in Harker Substation in a parallel configuration. Additional SVCs were implemented in the southern part of the grid, of which Fig. 15-2) shows a view of one of the two Pelham SVCs (left side of the figure). The single line diagram for both Harker and Pelham SVCs is attached in the right part of Fig. 15-2).
An increasing number of SVCs are also going to be installed on other continents. In Fig. 16, an example of a large SVC in South America is depicted. The SVC was implemented to improve system stability of the extended transmission grid. The installed containerized solution offers additional benefits such as reduction in installation and commissioning time, as well as space and cost savings compared with conventional building technologies.
Fig. 14: FACTS & HVDC worldwide – Example Siemens (ref. to Text)
SeriesFSC
NGH
TPSC
TCSC
SeriesFSC
NGH
TPSC
TCSC
2, 2 Tian Guang 2003Kayenta 1992
Serra de Mesa 1999Imperatriz 1999
Fortaleza 1986••
•
•Samambaia 2002
•
Virginia Smith 1988
•Welsh 1995
•Acaray 1981
•••Dürnrohr 1983
Etzenricht 1993Wien Südost 1993
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Bom Jesus da Lapa 2002
•
Limpio 2003
•
Ibiuna 2002
•3 Vincent 2000
•Jacinto 2000
•Funil 2001
2 Pelham, 2 Harker, 2 Central, 1991-1994
•Clapham 1995,Refurbishment
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Atacama 1999
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P. Dutra 1997
•Cerro Gordo 1999
•Chinú 1998
•Impala
•2 Adelanto 1995
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•3 Montagnais 1993
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2 Kemps Creek 1989
•Brushy Hill 1988
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•
Campina Grande 2000
2 Zem Zem 1983
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••
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Rejsby Hede 1997
•Sullivan 1995
•Paul Sweet 1998 •
Inez 1998
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2 Marcy 2001-2003
Military Highway 2000
•Kanjin (Korea) 2002
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Lugo 1985
Laredo 2000
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Spring Valley 1986
••IllovoAthene•
Muldersvlei 1997
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2 Tecali 20023 Juile 2002
•Barberton 2003•
Maputo 2003
• Milagres 1988
• 2 Yangcheng 2000
•2 Hechi 2003
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•
Eddy County 1992
2 Dominion 2003
2 Chuddapah 20032 Gooty 2003
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Lamar 2005
2 Midway 2004 Seguin 1998•
1994-1995
Porter 2006Dayton 2006
Nine Mile 2005
ParallelSVC
MSC/R
ParallelSVC
MSC/R
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.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
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••• Châteauguay 1984
Ahafo 2006•
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2 Lucknow 2006
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3 Puti 2005
• Iringa, Shinyanga 2006
3, 2 El Dorado2006
STATCOMFlicker STATCOMSTATCOMFlicker STATCOM
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Radsted 2006
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• 2 Sabah 2006
Nebo 2007,Refurbishment
9 Powerlink 2007,Refurbishment
Devers 2006
Benejama,Saladas 2006
La Pila 1999
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•• •• ••
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
Jember 1994
Load FlowB2B/GPFC
Load FlowB2B/GPFC
UPFCCSCUPFCCSC
•Nopala 2006
••
Sao Luiz 2006Sinop 2006
2 Fengjie 2006•
… and over 110 Industry SVCs all over the World… and over 110 Industry SVCs all over the World
Status: 12-2005 In total: over 150 SVCs
In total: over 150 SVCs
••
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Fig. 15: Europe - UK goes ahead with FACTS - 27 SVCs 1) Harker Substation, 1993 – 2 SVCs for Power Oscillation Damping 2) Pelham Substation, 1991 - 2 SVCs for Voltage Control (ref. to Text)
The Transmission System:
BenefitsBenefits
Results of Dynamic System Tests:a) No SVC connectedb) Both SVCs in
In Figs. 17-19, the features and cost savings of series compensation due to grid enhancement are summarized. The mentioned SSR (subsynchronous resonances) topic is a crucial issue for large thermal generators with long shafts [5].
The flexibility of modern FACTS technologies under extremely harsh environmental conditions is indicated in Figs. 18-19: the operating range for FSC begins at -500 C, for TCSC it can reach up to +850_C. This is necessary due to the outdoor installation on high voltage potential, with the isolated platform mounted directly in series with the transmission line.
In Fig. 20, two projects with series compensation in China are presented. Picture a) gives a view of one phase element of the two Pingguo TCSCs. The 3D view b) and the photo c) (from Barberton FSC, RSA) demonstrate how easily series compensation can be mounted to the existing line: when the equipment installation is finished but not yet connected to the line, a line interruption and a jumper connection from the line to the platform is made with a short interruption of power transmission of 1-3 days only.
For Thyristor Protected Series Compensation TPSC, innovative developments in Thyristor-Technology have been applied: LTT (Light-triggered Thyristors, now state-of-the-art for FACTS and HVDC) by applying a special heat-sink to enable very fast self-cooling of the valves, within half a
Fig. 17: 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:
Increase of Transmission Capacity
Fig. 16: 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
2002
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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 (metal 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. Therefore, 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. 21 shows a site-view of one of the 5 TPSCs installed at 500 kV in California, USA.
Fast-growing generation in high load density networks on one hand, and interconnections among the systems on the other hand, increase the short-circuit power. If the short-circuit capacity of the
Fig. 19: 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 hrs would cost 840,000 US$ *
Up to 500 PODOperations per Dayfor saving the System Stability
A System Outage of 24 hrs 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
1999
Fig. 18: FSC at EHV 735 kV plus harsh Environment
Poste Montagnais, Canada - FSCPoste Montagnais, Canada - FSC
- 50 o C- 50 o C
1993
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equipment in the system is exceeded, the switchgears must be uprated or replaced, which is a very cost and time-consuming procedure. In such cases, short-circuit current limitation offers clear benefits. Limitation by passive elements, e.g. reactors, is a well known practice. It reduces, however, the system stability, and there is an impact on the load flow.
By combining the proven TPSC application with an external reactor (see Fig. 22), 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, 5]).
Fig. 23 shows the basic function and the operating principle of the SCCL, including a 3D view of the SCCL. In comparison with the TPSC site photo, it can be seen that the TPSC is complemented by just an additional reactor for current limitation. Further details on the SCCL solution are described in [5].
This new device operates with zero reactance in steady-state conditions, and in case of short-circuit it is switched over to the current limiting reactance within a few ms.
Fig. 24 depicts an example of an on-site fault recording of one of the Vincent TPSCs. The measured currents and the calculated junction temperature rise of the valve in Phase B for a line fault in phase BC are recorded. The figure shows that there is still a huge margin for higher current stresses.
Fig. 20: 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 2 x 600 MVAr, Line Compensation Level 35% c) Demonstration of the FSC-Jumper Connection to the Line - from Barberton FSC, RSA
… Example Barberton –RSA*, 2003
How to “loop” the FSC into the Line …
Commercial Operation in June 2006Commercial Operation in June 2006
Enhancement of Chinas “Central Transmission Corridor”Enhancement of Chinas “Central Transmission Corridor”
quite easyquite easyPower Outage between 1 & 3 Daysonly
* RSA = Republic of South Africa
b)
c)
a)
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In Fig. 25, a brief overview on today’s solutions for fault-current limitation is given, including the new SCCL. Basically, there are two methods for fault-current reduction: limitation and interruption. The constraints and the benefits of the different solutions are indicated in the figure.
It can be seen that the SCCL offers numerous advantages.
A comparison of the new SCCL with the conventional solution using a current limiting reactor is depicted in Fig. 26. The main concerns are related to a risk of voltage collapse in case of dynamic system conditions, which can lead to cascading disturbances (blackout).
Fig. 21: TPSCs Vincent & Midway/USA: five Systems at 500 kV - fully proven in Practice, plus two new Projects (El Dorado)
Outdoor Valves on a PlatformLTT Thyristors, self-cooled
TPSC Technology: Outdoor Valves on a PlatformLTT Thyristors, self-cooled
TPSC Technology:
Fig. 22: SCCL - an Innovative FACTS Solution using TPSC
Thyristor Protected Thyristor Protected Series CompensationSeries CompensationThyristor Protected Thyristor Protected Series CompensationSeries Compensation
The new Idea !The new Idea !
Use of proven TechnologyUse of proven Technology
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K]
Valve-Temperature Rise only 11 oValve-Temperature Rise only 11 o
A huge Margin for higher Valve Currents - up to 110 kA peakA huge Margin for higher Valve Currents - up to 110 kA peak
Fig. 24: TPSC and SCCL – up to 110 kA
Fig. 23: 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
Just one additional X !Just one additional X !
ReactanceX
ReactanceX
Zero Ohm for best Load Flow
Fast Increase of Coupling Reactance
t
17
In the next section, examples for parallel operation of FACTS and HVDC in large interconnected transmission systems are depicted.
5. FACTS AND HVDC IN PARALLEL OPERATION With the Mead-Adelanto and the Mead-Phoenix Transmission Project (MAP/MPP), a major 500 kV transmission system extension was carried out to increase the power transfer opportunities between Arizona and California, USA [3]. 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. 27.
The SVCs enabled the integrated operation of the already existing highly compensated EHV AC system and the large HVDC system. The SVC installation was an essential prerequisite for the overall system stability at an increased power transfer rate.
Fig. 25: FCL (Fault Current Limiters) - Principles and Applications
SCCL: no ConcernsSCCL: no Concerns
Difficult or impossible at High Voltage LevelsDifficult or impossible at High Voltage Levels
Fault Current LimitationConventional Solution: Reactor
Not available for HV Levels plus Concernsabout Reliability and Protection Co-ordination
Not available for HV Levels plus Concernsabout Reliability and Protection Co-ordination
Fig. 26: SCCL versus Conventional Reactor
Only Current Limiting Reactor ?Voltage Drop - needs Compensation
SCCL - The better Alternative:No Risk of Voltage Collapse
Reactive Power remains balanced
No Impact on Grid Load Flow
No Impact on First Swing Stability
Mechanically or ThyristorSwitched Capacitor will be necessary
Bus 1
ACAC
Bus 2Bus 1
ACACACAC
Bus 2
Bus 1 Bus 2
AC AC
Bus 1 Bus 2
ACAC ACAC
18
Fig. 27: HVDC plus SVC - Mead-Adelanto, USA
Increase of Transmission Capacity
Improvement of System Stability
Increase of Transmission Capacity
Improvement of System Stability
Upgrade of a large AC and DC Transmission System with 2 SVCs & FSCs
Each SVC: 388 MVAr for Voltage and POD ControlEach SVC: 388 MVAr for Voltage and POD Control
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. 28: Mead-Adelanto Studies – Comparison of SVC Voltage- and POD-Control Mode
19
An example of the intensive project testing with computer and real-time simulator facilities for a fault application at Marketplace 500 kV bus is given in Fig. 28. The figure shows the computer test results with both SVCs active. The influence of the HVDC can be seen from the DC voltage E dc. Figure a) is with both SVCs only in voltage control mode (POD blocked); Figure b) shows an improved damping with the coordinated POD function enabled.
In Fig. 29, a view on the SVC installation in Marketplace is given.
Similar studies have been carried out for a number of large transmission projects world-wide. In Figs. 30-32, an innovative FACTS application with SVC in combination with HVDC for transmission enhancement in Germany is shown [3, 6].
It’s a matter of fact that this project is the first high voltage FACTS controller in the German network. The 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. 31), 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 step towards grid access improvement, an additional transformer for connecting the 400 kV HVDC AC bus to the 110 kV bus was installed (see the figure). Finally, in 2004, 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. 32, a view of the Siems SVC in Germany is depicted.
Fig. 29: Static Var Compensators Mead-Adelanto – View on Marketplace Substation
1995Features:o Coordinated Voltage Control &o Damping of Power Oscillations
Features:o Coordinated Voltage Control &o Damping of Power Oscillations
Benefits:
Increase of Transmission Capacity
Improvement of System Stability
Support of existing HVDC
Benefits:
Increase of Transmission Capacity
Improvement of System Stability
Support of existing HVDC
20
Prior to commissioning, intensive studies have been carried out; first with the computer program NETOMAC and then with the RTDS real-time simulator by using the physical SVC controls and simplified models for the HVDC [3].
Fig. 31: The Problem – no Right of Way for 400 kV AC Grid Access of Baltic Cable HVDC - and Solutions
11
22
1 Initial Step for Grid Access Enhancement
11 Initial Step for Grid Access Enhancement
2 and a new 220 kV Cable22 and a new 220 kV Cable
22
Initially planned Connection
400 kV Grid Access denied HVDC
Signals
220 kV Land Cable350 MVA, 11 km220 kV Land Cable350 MVA, 11 km
Now, the HVDCcan operate at full PowerRating
Now, the HVDCcan operate at full PowerRating
19941994only
110 kV
22
Final Solution: new SVC with TCR & TSC100 MVAr ind.200 MVAr cap.
Final Solution: new SVC with TCR & TSC100 MVAr ind.200 MVAr cap.
20042004
Fig. 30: SVC Siems, Germany - Support of HVDC Baltic Cable
HVDC and FACTS in parallel OperationHVDC and FACTS in parallel Operation
Source:Source:
21
6. POWER ELECTRONICS FOR HVDC AND FACTS – MARKET EXPECTATIONS AND RELIABILITY ISSUES
Table 1 summarizes the market expectations for FACTS and HVDC solutions today and in the future. Today, the market for series compensation, for SVC and for B2B/GPFC for load-flow control is in fact large and, as a result of liberalization and deregulation in the power industry, is developing fast in the future. Further, the market in the HVDC long distance transmission field is progressing fast. A large number of high power long distance transmission schemes using either overhead lines or submarine cables have been put into operation or are in the stage of installation.
Fig. 32: The Solution – the first HV SVC in the German Grid at Siems Substation
Essential for enhanced Grid Access of the HVDCEssential for enhanced Grid Access of the HVDC
2004Verified by Computer and Real-Time Simulation …Verified by Computer and Real-Time Simulation …
… fully confirmed by Site Experience… fully confirmed by Site Experience
Table 1: 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
22
Concerning reliability of high voltage power electronics, Table 2 gives an example of two SVC projects installed in South Africa. The same high reliability is also achieved for HVDC as 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.
7. 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 contribute to an increasing congestion. To keep the power supply reliable and safe, system enhancement will be essential.
In conclusion to the previous sections, Table 3 summarizes the impact of FACTS on load flow, stability and voltage quality when using different devices. The evaluation is based on a large number of studies and experiences from projects. For comparison, HVDC as well as mechanically switched devices (MSC/R) are included in the table.
As a consequence of “lessons learned” from the large blackouts in 2003, FACTS and HVDC will play an important role for the system developments, leading to “Smart Grids” [4] with better controllability of the power flows.
High voltage power electronics provide the necessary features to avoid technical problems in the power systems, they increase the transmission capacity and system stability very efficiently and they assist in prevention of cascading disturbances.
Table 2: Availability of Power Electronics - Example FACTS: close to 100 % - same for HVDC
8. REFERENCES [1] W. Breuer, X. Lei, D. Povh, D. Retzmann, E. Teltsch: “Role of HVDC and FACTS in future Power Systems”; 15th CEPSI, October 18-22, 2004, Shanghai, China [2] G. Beck, D. Povh, D. Retzmann, E. Teltsch: “Global Blackouts – Lessons Learned”; Power-Gen Europe, June 28-30, 2005, Milan, Italy [3] G. Beck, D. Povh, D. Retzmann, E. Teltsch: “Use of HVDC and FACTS for Power System Interconnection and Grid Enhancement”; Power-Gen Middle East, January 30 – February 1, 2006, Abu Dhabi, United Arab Emirates [4] U. Armonies, M. Häusler, D. Retzmann: “Technology Issues for Bulk Power EHV and UHV Transmission”; HVDC Congress 2006 – Meeting the Power Challenges of the Future using HVDC Technology Solutions, July 12-14, 2006, Durban, Republic of South Africa [5] 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, Paris [6] H. Waldhauer: “Grid Reinforcement and SVC for full Power Operation of Baltic Cable HVDC Link”; The 38th Meeting and Colloquium of Cigré Study Committee B4 “HVDC and Power Electronics”, Technical Colloquium, September 25, 2003, Nuremberg, Germany
Influence: *
no or lowsmallmediumstrong
Based on Studies & practical Experience
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
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
