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Prospects of Bulk Power EHV and UHV Transmission

V. Ramaswami, D. Retzmann*, K. Uecker

Siemens, Germany

ABSTRACT Deregulation and privatization pose new challenges for high voltage transmission systems. System elements are loaded up to their thermal limits, and power trading with fast varying load patterns is contributing to an increasing congestion. In this respect, interconnection of separated power systems may offer important technical, economical and environmental advantages. For the interconnections, innovative solutions will be essential to avoid congestion and to improve system stability. HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission Systems) provide the necessary features to avoid technical problems in the power systems, they increase the transmission capacity and system stability very efficiently and they help to prevent cascading disturbances. HVDC and FACTS will play an important role for the system developments, leading to “Smart Grids” with better controllability of the power flows.

For some countries, UHV transmission solutions with AC voltages of 1000 kV and DC systems with 800 kV are in the planning stage. This will increase the transmission capacity for AC links up to 10_GW and for DC systems up to 5 - 6 GW. UHV transmission will be applied in emerging countries like India and China, to serve their booming energy demands efficiently. In the paper, benefits of bulk power transmission solutions with HVDC and FACTS for system enhancement and grid interconnection are depicted and UHV technology issues for AC and DC are discussed. Prospects of high power electronics in future grid developments are presented.

KEY WORDS:

Power System Interconnection, System Stability, Blackout Prevention, Increase of Transmission Capacity, Prospects of UHV Solutions, Power-Flow Control, Short-Circuit Current Limitation, Parallel Operation of HVDC and FACTS

5th & 6th Feb, 2007 at India Trade Promotion Organisation - Pragati Maidan, New Delhi, India5th & 6th Feb, 2007 at India Trade Promotion Organisation - Pragati Maidan, New Delhi, India

*dietmar.retzmann@siemens.com

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1. PERSPECTIVES OF POWER SYSTEM DEVELOPMENTS

The development of power systems follows the need 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 and complexity of power systems have 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, ref. to Fig. 1.

Fig. 1: UCTE – Steps a) & b) for Interconnection of Zones 1, 2 and further Options c)

NORDEL

IPS/UPS

UCTE - 1

AL MAGHREB

TurkeyUCTE - 2

NORDEL

IPS/UPS

UCTE - 1

AL MAGHREB

TurkeyUCTE - 2

Zone 1 & 2 “resynchronized” since 10-10-2004 …Zone 1 & 2 “resynchronized” since 10-10-2004 …

Options for Grid InterconnectionOptions for Grid Interconnection

In synchronous Operation with 1st Zone

2nd UCTE Synchronous Zone

In synchronous Operation with 2nd Zone

1st UCTE Synchronous Zone

In synchronous Operation with 1st Zone

2nd UCTE Synchronous Zone

In synchronous Operation with 2nd Zone

1st UCTE Synchronous Zone

… since then, the Risk of large Inter-Area Oscillations in UCTE has been increased *

… since then, the Risk of large Inter-Area Oscillations in UCTE has been increased *

* depending on the actual Load Flow Situation

b)

c)

c)

a) The Interconnection CENTREL to UCPTE

… the 1st Step for System Extension… the 1st Step for System Extension

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Signals: simulated & measured by WAMS

UCTE Synchronous Interconnections:

Inter-Area Oscillations with Magnitudes up to 1000 MW

Damping Measures necessary

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However, with an increasing size of the synchronous interconnected systems, the technical and economical advantages diminish. This is related to problems regarding load flow, inter-area power oscillations ([1], ref. Fig. 1a) and voltage quality. If power is to be transmitted through the interconnected system over longer distances, transmission needs to be supported. This is, for example, the case in the UCTE system, where the 400 kV voltage level is in fact too low for large cross-border and inter-area power exchange. Bottlenecks are already identified, and for an increase of power transfer, advanced solutions using HVDC and FACTS need to be applied. 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 [3].

Such an enhancement scenario for power transmission systems is depicted in Fig. 2.

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 systems available [2].

Renewable Energy Resources at favorableLocations *Renewable Energy Resources at favorableLocations *

Transmission of large Power Blocks over long Distances * (Hydro Resources, Solar Energy)Transmission of large Power Blocks over long Distances * (Hydro Resources, Solar Energy)

Increased Power Exchange among the Interconnected SystemsIncreased Power Exchange among the Interconnected Systems

Extensions of Interconnected SystemsExtensions of Interconnected Systems

* by use of HVDC / FACTS for “remote” Infeed* by use of HVDC / FACTS for “remote” Infeed

Fig. 2: Enhancement of Transmission Systems

Fig. 3: Perspectives of Transmission and Distribution Network Developments

G

G

G

G

G

G

G

G

G

G

G

G

G

G

G

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G

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Today: Tomorrow:

Load Flow will be “fuzzy”Use of Dispersed GenerationUse of Dispersed Generation

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In the future, an increasing part of the installed capacity will, however, be connected to the distribution levels (dispersed generation), which poses additional challenges on planning and safe operation of the systems, see Fig. 3. In such cases, HVDC and FACTS can clearly strengthen the power systems and improve their performance.

2. SOLUTIONS FOR SYSTEM INTERCONNECTION The idea of embedding huge amounts of wind energy in the German grid by using HVDC, FACTS and GIL (Gas Insulated Lines) is depicted in Fig. 4. Goal is a significant CO2 reduction through the replacement of conventional energy sources by renewable energies, mainly off-shore wind farms. Main problem of such large scale wind energy integration is its fluctuating availability, as shown in Fig. 5. It means, a significant amount of reserve capacity will be needed somewhere in the system, and - by using HVDC and FACTS - both load and generation reserve sharing will be enabled [6].

However, this scenario needs further investigations regarding the investment costs and UCTE system stability.

Based on the global experience with large blackouts, strategies for the development of large power systems go clearly in the direction of hybrid transmissions, consisting of DC and AC interconnections, including FACTS [6].

Such hybrid interconnected systems offer significant advantages, both technically and in terms of reliability [5]. Fig. 6 shows schematically such a hybrid system using HVDC and FACTS. Power exchange in the neighboring areas of interconnected systems can be achieved by AC links, preferably including FACTS for increased transmission capacity and for stability reasons. The transmission of large power blocks over long distances should, however, be utilized by the HVDC transmissions directly to the locations of power demand [5].

HVDC can be implemented as direct coupler – the “Back-to-Back” solution (B2B) - or as point-to-point long distance transmission via DC line. The HVDC links can strengthen the AC interconnections

Fig. 4: Integration of large Off-Shore Wind Farms by means of HVDC and FACTS

Source: DENA Study 02-24-2005

platform

platform

platform

platform

platform

platform

AC or DCCables

AC or DCCables

2020 2020

Medium-term PlanningMedium-term PlanningGIL in Tunnel

to avoid 40-50 Cables nearby the Coasts

GIL in Tunnelto avoid 40-50 Cables nearby the Coasts

4 x GIL, 4 x SVC, 2 x HVDC4 x GIL, 4 x SVC, 2 x HVDC

incl. Baltic Sea &On-Shore

incl. Baltic Sea &On-Shore

Long-term: 30 - 50 GWLong-term: 30 - 50 GW

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at the same time, in order to avoid possible dynamic problems which exist in such huge interconnections. These options for HVDC application are depicted in Fig. 6.

Fig. 6: 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

Source: E.ON - 2003Problems with Wind Power Generationo Wind Generation varies stronglyo It can not follow the Load Requirements

Additional Reserve Capacity is requiredAdditional Reserve Capacity is required

This will be a strong Issue in the German Grid Development

Fig. 5: Network Load and aggregated Wind Power Generation during a Week of maximum Load in the E.ON Grid

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3. DEVELOPMENTS IN THE FIELD OF HVDC In the second half of last century, high power HVDC transmission technology has been introduced, offering new dimensions for long distance transmission. This development started with the transmission of power in an order of magnitude of a few hundred MW and was continuously increased to transmission ratings up to 3 GW over long distances by just one bipolar line. Transmission distances over 1,000 to 2,000 km or even more are possible with overhead lines. Transmission power of up to 600 - 800 MW over distances of about 300 km has already been implemented using submarine cables, and cable transmission lengths of up to about 1,300 km are in the planning stage. By these developments, HVDC became a mature and reliable technology. During the development of HVDC, different kinds of applications were carried out. They are shown schematically in Fig. 7. The first commercial applications were HVDC sea cable transmissions, because AC cable transmission over more than 60-80 km is technically not feasible due to reactive power limitations. Then, long distance HVDC transmissions with overhead lines were built because they are more economical than transmission with AC lines. To interconnect systems operating at different frequencies, Back-to-Back (B2B) schemes were applied. B2B converters can also be connected to long AC lines (Fig. 7a).

A further and for the future very important application of HVDC transmission is its integration into the complex interconnected AC system. Fig. 7c depicts this idea for both B2B – as Grid Power Flow Controller (GPFC) - and for long-distance point-to-point transmission. The reasons for these hybrid solutions are basically lower transmission costs as well as the possibility of bypassing heavily loaded AC systems.

Typical configurations of HVDC are depicted in Fig. 8. In Fig. 9, an overview of both standard and extended operating ranges of HVDC is given. While using the full control range of HVDC up to 90O, the B2B can “feature” FACTS functions, e.g. fast voltage control, in the same way as an SVC. As indicated in the figure, this new idea of GPFC as a “FACTS B2B” has been successfully applied in a project at Lamar substation, USA [4, 7].

The major benefit of the HVDC (in comparison with FACTS), both B2B/GPFC and LDT, is its incorporated ability for fault-current blocking, which serves as an automatic firewall for Blackout prevention in case of cascading events, which is not possible with FACTS.

Fig. 7: Types of HVDC Transmissions

Can be connected to long AC Linesa)

Can be connected to long AC Linesa)a)

b)b)

c)c)b) HVDC Long Distance Transmissiona) Back-to-Back Solution

c) Integration of HVDC into the AC System Hybrid Solution

b) HVDC Long Distance Transmissiona) Back-to-Back Solution

c) Integration of HVDC into the AC System Hybrid Solution

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c)

Fig. 8: HVDC Configurations a) Basic Scheme b) Technologies c) Control Features

a)

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:

HVDC-LDT - Long Distance Transmission

B2B - The Short Link

Back-to-Back Station

60 Hz 50 Hz

AC AC

B2B - The Short Link

Back-to-Back Station

60 Hz 50 Hz

AC AC

Back-to-Back Station

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

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

AC/DC and DC/AC Conversion by Power Electronics

HVDC PLUS (Voltage-Sourced Converter - VSC)

HVDC can be combined with FACTS

V-Control included

Slow FunctionsSlow Functions

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

Power & Voltage ControlFault-Current Blocking

The Firewallfor Blackout Prevention

The Firewallfor Blackout Prevention

Benefits ofHVDC in a synchronous AC System

Benefits ofHVDC in a synchronous AC System

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HVDC PLUS (Fig. 10) 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 using self-commutated voltage-sourced converters (VSC). Voltage-sourced converters do not have the

Fig. 9: HVDC Operating Ranges – and the new GPFC Solution as “FACTS B2B”

… with VSC Technology… with VSC Technology

Clean Energy from Platforms & Islands …Clean Energy from Platforms & Islands …

Fig. 10: DC with VSC – HVDC PLUS

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need for 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.

In Fig. 11, the benefits of using power electronics for system enhancement are summarized and a comparison of switching frequencies of line-commutated thyristor devices and self-commutated VSC are depicted. Conventional equipment (e.g. breakers, tap-changer transformers) offer very low losses, but the switching speed is very low. Power electronics can provide high switching frequencies up to several kHz, however, with an increase in losses. From Fig. 11, it can be seen that – due to less converter losses – the preferred solution for Bulk Power Transmission is in fact the line-commutated thyristor technology. The today’s losses of high power voltage-sourced converters with high switching frequencies are within the range of 4 - 5 %, which is too much for large bulk power DC transmission projects.

4. UHV TECHNOLOGIES FOR BULK POWER TRANSMISSION Bulk Power UHV AC and DC transmission schemes over distances of more than 2000 km are currently under planning for the connection of various large hydropower stations in China [4, 10, 11]. Ultra high DC voltage (up to 800 kV) and ultra high AC (1000 kV) are the preferred voltage levels for these applications to keep the transmission losses as low as possible.

In India, there are similar prospects for UHV DC as in China due to the large extension of the grid [4, 8, 9]. AC long distance transmission, however, will be implemented in India by EHV levels of up to 800 kV, including FACTS. The road-map for India’s hybrid bulk power grid developments are depicted in Fig. 12. India’s energy growth is about 8-9 % per annum, with an installed generation capacity of 124 GW in 2006 (92 GW peak load demand), ref. to [8, 9]. The installed generation capacity is expected to increase to 333 GW by 2017 [8].

Fig. 13 depicts how the ideas of hybrid bulk power interconnections are reflected in China's UHV grid developments. Focus is on interconnection of 7 large inter-provincial grids of the Northern, Central and Southern systems via three bulk power corridors which will built up a redundant “backbone” for the whole grid. Each corridor is planned for about 20 GW transmission capacity which shall be realized with both AC and DC transmission lines with ratings of 4 - 10 GW each (at +/- 800 kV DC

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

More Dynamics for better Power Quality:

Use of Power Electronic Circuits to control 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 %

The Solution for Bulk Power Transmission The Solution for Bulk Power Transmission

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Fig. 12: Grid Developments in India [8, 9]

a) System Overview – including the “Chicken Neck Area” b) Hybrid Solutions in the Chicken Neck – including UHV DC

and 1000 kV AC, ref. to the figure). Therefore, each corridor will have a set-up with 2 - 3 systems for redundancy reasons. With these ideas, China envisages a total amount of about 900 GW installed generation capacity by 2020. For comparison, UCTE and IPS/UPS together sum up to 850 GW today.

EXISTING

CHICKEN NECK AREA

800 kV DC800 kV DC

800 kV DC800 kV DC

800 kV DC800 kV DC

800 kV DC800 kV DC

6-7 x 6 GW DC

DEVELOPMENT OF CHICKEN NECK AREA

Up to 10 GW AC

50 GW Hybrid:≈ 10 GW AC≈ 40 GW DC

FUTURE

b)

HVDC SYSTEMS BY 2011-12

NER

ER

NR

WR

SR

LEGEND

500MW

500 MW

MW1000

2X500MWGAZUWAKA

BHADRAVATI

VINDHYACHAL

SASARAM

HVDC BACK-TO-BACK

AN

DA

MA

N &

NIC

OB

AR

LAKSHADW

EEP

TALCHER

KOLAR

HVDC BIPOLE2000

MW

CHANDRAPUR

PADGHE

MW1500

RIHAND

DADRI

1500MW

1000 MWKOLHAPUR

BHIWADI

BALIA

2500 MW

BISHWANATHCHARIYALIAGRA

6000 MW

HVDC SYSTEMS BY 2011-12

NER

ER

NR

WR

SR

LEGEND

500MW

500 MW

MW1000

2X500MWGAZUWAKA

BHADRAVATI

VINDHYACHAL

SASARAM

HVDC BACK-TO-BACK

AN

DA

MA

N &

NIC

OB

AR

LAKSHADW

EEP

TALCHER

KOLAR

HVDC BIPOLE2000

MW

CHANDRAPUR

PADGHE

MW1500

RIHAND

DADRI

1500MW

1000 MWKOLHAPUR

BHIWADI

BALIA

2500 MW

BISHWANATHCHARIYALIAGRA

6000 MW

• Back-to-Back: 6 x (Σ 4,000 MW)

• Bipole : 6 x (Σ 13,500 MW)

Main GridDC

• Back-to-Back: 6 x (Σ 4,000 MW)

• Bipole : 6 x (Σ 13,500 MW)

Main GridDC

Source: “Brazil-India-China Summit Meeting on HVDC & Hybrid Systems – Planning and Engineering Issues”, July 2006, Rio de Janeiro, Brazila)

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The benefits of the large hybrid power system interconnections in India and China are clear:

• Increase of transmission distance and reduction of losses - using UHV and EHV • HVDC serves as stability booster and firewall against large blackouts • Use of the most economical energy resources - far from load centers • Sharing of loads and reserve capacity • Renewable energy sources, including large wind farms and solar fields can much more easily

be integrated

However, using the 1000 kV AC lines, there will be in fact stability concerns: if for example such an AC line - with up to 10 GW transmission capacity - is lost during faults, large inter-area oscillations might occur. For this reason, additional large FACTS controllers on the UHV AC lines for stability support are in discussion in China.

Specific issues for the necessary UHV technology developments are depicted in the following, as seen from the Siemens perspective [4, 12]. It is obvious that the UHV insulation requirements will lead to a huge increase of the mechanical dimensions of all equipment, including PTs, CTs, breakers, disconnectors, busbars, transformers and reactive power equipment. Some main equipment does not require detailed investigations since existing technology basically enables to extrapolate from lower voltage applications. An example for this type of equipment is the DC thyristor valve which is based on a modular design. Additional thyristor levels to be connected in series are well feasible and do not require any conceptual changes. However, for other equipment it has to be verified to which extent existing technology and know-how are adequate for design and manufacturing process. This includes the following equipment:

• AC grid transformers and DC converter transformers including bushings • AC and DC wall bushings

Fig. 13: Perspectives of Grid Developments in China - AC & DC Bulk Power Transmission from West to East via three main Corridors [12]

Sources:

North Corridor

Central Corridor

South Corridor

3 x 20 GW3 x 20 GW

… the installed Generation Capacity will be 900 GW

… the installed Generation Capacity will be 900 GW

Transmission Capacity of each Corridor will be 20 GW in 2020 …

Solutions:800 kV DC & 1000 kV AC

Solutions:800 kV DC & 1000 kV AC

AC: 6-10 GW

DC: 4-6 GW

n xn xn x

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• DC smoothing reactors • AC reactive power equipment, including FACTS • AC breakers and disconnectors • DC bypass switches and DC disconnectors • AC and DC measurements

Regarding shunt-connected FACTS controllers, there are no specific additional efforts necessary for the medium voltage equipment at the secondary side of the grid transformers. For series connected FACTS, if applied, efforts will be needed for a robust construction of the platforms matching the required seismic performance.

Converter transformers are one of the very important components for UHV DC application. It is well understood that the existing technology and know-how of converter transformers can manage higher DC voltages. Yet, there are critical areas which need careful consideration and further development in order to keep the electrical stresses at a safe level. Above all the windings and the transformer internal part of bushings on the valve side of the converter transformers with the barrier systems and cleats and leads require very careful attention.

In the following, design aspects for key UHV DC equipment are outlined. From Figs. 14-15 it can be seen that for transformers the bushings will be a major issue with regard to mechanical dimensions, including transportation to site.

An example of the complete HVDC station layout is given in Fig. 16. Main idea of this concept is to use two 12-pulse converters with 400 kV DC operating voltage each and then to connect them in series in order to achieve the desired 800 kV arrangement.

A major benefit of this solution will be a smaller size of the converter transformers, if transportation restrictions exist. Furthermore, it increases the redundancy of the transmission: each of the 4 converters of plus and minus pole can be bypassed and the assigned DC line will be operated at 400_kV reduced voltage level.

Due to this, the single line diagram of +/- 800kV UHV DC converter station will be mostly the same as a +/- 500kV HVDC converter station. A configuration of two 12 pulse-groups per pole has also a long term operation experience worldwide. It means there is no basic new concept to be developed.

The arrangement of the valve-units in two 400 kV valve halls per pole is outlined in Fig. 17.

Works for 800 kV DC TransformerWorks for 800 kV DC Transformer

Existing Technology and Know-How can well manage higher DCVoltage Stresses Transformers for 800 kV HVDCSystem are within existingManufacturing CapabilitiesTransportation Limits and ConverterConfiguration will determine Type and SizeR&D in Progress in specific Fields

Fig. 14: Transformer for UHV DC – In the State of Development

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Main benefit will be the use of proven modular technologies by just expanding them to the new application.

This is also valid for the AC and DC control and protection schemes. However, the measurements will need to be adapted to the higher voltage level.

The 800 kV DC concept can be summarized as follows:

Based on the above discussions and descriptions, the following conclusions can be made for the design of UHV AC and DC bulk power transmission systems:

Regarding the main equipment, UHV DC systems of up to 800 kV and UHV AC systems of up to 1000 kV are technically feasible

In general, UHV equipment can be designed and manufactured on the basis of existing technologies

For most of the station equipment only some or even no R&D is anticipated

UHV DC applications are also in discussion for bulk power long distance transmission projects in other regions of the world, e.g. South America and South Africa [12].

Fig. 15: UHV DC Bushing at Test Lab TU Graz – Austria

800 kV DC Bushing in Test Field800 kV DC Bushing in Test Field

UHV DC Valves using proven modular Designbased on existing Technology and Know-How for DC Voltage 800 kVValve Tower Configuration: Double or Quadruple Valve Proven existing LTT Technology

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Transformer BushingsTransformer Bushings

400 kV DC400 kV DC 800 kV DC800 kV DC

400 kV-Valve Group400 kV-Valve Group 800 kV-Valve Group800 kV-Valve GroupDC NeutralDC NeutralDC LineDC Line

N-1 Criteria: Redundancy through Bypass-BreakersN-1 Criteria: Redundancy through Bypass-Breakers

Each PoleEach Pole can be operated with can be operated with 400 kV DC400 kV DCEach PoleEach Pole can be operated with can be operated with 400 kV DC400 kV DC

Fig. 16: Fully redundant HVDC Scheme – with two 400 kV 12-Pulse Converters per Pole

Fig. 17: Valve Hall Configuration – for 800 kV HVDC

800 kV Valve Hall800 kV Valve Hall

to 800 kV DC Lineto 800 kV DC Line400 kV DC400 kV DC

400 kV Valve Hall400 kV Valve Hall

DC NeutralDC Neutral

400 kV DC400 kV DC

“Ready for Transmission”“Ready for Transmission”

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5. PROJECTS FOR SYSTEM ENHANCEMENT WITH HVDC

5.1. Gui-Guang HVDC Project – China The 3000 MW +/-500kV bipolar Gui-Guang HVDC system (Fig. 18) with a transmission distance of 980 km was build to increase the transmission capacity from west to east [12]. It is integrated into the large AC interconnected system. In the same system there is also an already existing HVDC scheme in operation. Both DC systems operate in parallel with AC transmission in this grid.

In addition to that, Fixed Series Compensation (FSC) and Thyristor Controlled Series Compensation have been used in the system. Due to long transmission distances, the system experiences severe power oscillations after faults, close to the stability limits. With its ability to damp power oscillations, HVDC essentially contributes to reliable operation of the system [4, 12].

5.2. HVDC Project Neptune - USA After the 2003 blackout in the United States, new projects are smoothly coming up in order to enhance the system security.

One example is the Neptune HVDC project. Siemens PTD has been awarded a contract by Neptune Regional Transmission System LLC (RTS) in Fairfield, Connecticut, to construct an HVDC transmission link between Sayreville, New Jersey and Long Island, New York. Because new overhead lines can not be built in this high density populated area, power should directly be brought to Long Island by HVDC cable transmission, by-passing the AC sub-transmission network.

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 one single source, Siemens is providing seamless coverage of 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.

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 completed 6 Months ahead of Schedule by Sept. 2004Project completed 6 Months ahead of Schedule by Sept. 2004

2004

Fig. 18: Geographic Location and Main Data of Gui-Guang HVDC Project - China

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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. 19, highlights of this innovative project that are typical for future integration of HVDC into a complex synchronous AC system are depicted

5.3. East-South Interconnector - India The grid in India has been developed to regional power systems which were operating asynchronously [6]. Later interconnections between regional systems have been made by AC and Back-to-Back HVDC. The first HVDC long distance transmission was Rihand-Delhi which is integrated into the 400_kV AC system. The HVDC East-South interconnection (commercial operation in 2003) uses both advantages, the avoidance of transmission of additional power through the AC system and the interconnection of power areas which can not be operated synchronously. Fig. 20 shows the geographical location of the DC Interconnector and its main data. A view of the HVDC northern terminal in the state of Orissa is given in Fig. 21. In April 2006, Siemens has been awarded an order by Powergrid Corporation of India to increase the transmission capacity of the East-South DC transmission from 2000 MW to 2500 MW. After the upgrade is completed, it will be possible to make maximum use of the system’s overload capacity. To increase the capacity of the link, the Siemens experts have developed a solution known as Relative Aging Indication and Load Factor Limitation (RAI & LFL). By these means, it will be possible to utilize the overload capacity of the system more effectively without having to install additional thyristors.

Fig. 19: Geographical Location and Main Data of Neptune HVDC - 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”

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Fig. 20: Geographic Map and Main Data of Indian East-South Interconnector

Kolar

Talcher

Kolar

Talcher

2003

Fig. 21: Site View of Indian East-South Interconnector – DC Station Talcher

DC Station Talcher – State of Orissa2003 2000 MW

2500 MWRAI & LFL: full Use of Overload Capacity –without additional Thyristors

RAI & LFL: full Use of Overload Capacity –without additional Thyristors

2007

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5.4. Basslink HVDC - Australia Fig. 22 gives an overview of the Basslink project in Australia, which transmits electric power from wind- and hydro sources very cost-efficiently from George Town in Tasmania to Loy Yang in Victoria and the same way back. This happens by means of HVDC via a combination of submarine cable (with

Hydro Plants for:Base Load andEnergy Storage

Hydro Plants for:Base Load andEnergy Storage

Plus Wind Power Plus Wind Power

Covering Base and

Benefits of HVDC:Clean Energy CO2 ReductionCost Reduction

“flexible”

“fuzzy”

Peak-Load Demands

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

2005

Fig. 22: Basslink HVDC – for a “Smart” and flexible Grid

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295 km the longest submarine cable in the world up to now), land cables (8 km for reasons of landscape protection) and overhead lines over a total transmission distance of 370 km. The nominal power is 500_MW at a DC Voltage of 400 kV and a current of 1250 A. The overload capacity of the transmission system is 600 MW during 10 hours per day.

Both Victoria and Tasmania profit from the interconnection of their networks:

During times of peak load Tasmania delivers “green energy” from its hydro power stations to Victoria, while Tasmania can cover its base load demands out of the grid of Victoria during dry seasons when the hydro-reservoirs are not sufficiently filled. Furthermore, the island of Tasmania receives access to the power market of the Australian continent.

Tasmania intends to install additional wind farms to increase its share in regenerative energy production. The figure shows that hydro power is perfectly suitable to be supplemented with the rather “fuzzy” wind energy – in terms of base load as well as through its ability to store energy for peak load demands. Insofar, the DC link can contribute still more to the reduction of CO2 through the combined use of regenerative energy sources.

6. CONCLUSIONS Deregulation and privatization pose new challenges on high voltage transmission systems. System elements are loaded up to their thermal limits, and wide-area power trading with fast varying load patterns will contribute to an increasing congestion.

Environmental constraints will also play an important role. The loading of existing power systems will further increase, leading to bottlenecks and reliability problems. As a consequence of “lessons

Power System Expansion …

Fig. 23:

HVDC PLUSHVDC PLUSHVDC PLUSHVDC PLUS

… with Advanced Transmission Solutions

From Congestion, Bottlenecks and Blackouttowards a “Smart Grid”

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learned” from the large blackouts in 2003, HVDC and FACTS will play an important role for the system developments, leading to “Smart Grids” (see Fig. 23) with better controllability of the power flows.

UHV bulk power DC long distance transmission will be the preferred solution for emerging countries like India and China to serve their booming energy demands efficiently.

7. REFERENCES

[1] H. Breulmann, E. Grebe, M. Lösing, W. Winter, R. Witzmann, P. Dupuis, P. Houry, T. Pargotin, J. Zerenyi, J. Dudzik, L. Martin, J. M. Rodriguez, “Analysis and Damping of Inter-Area Oscillations in the UCTE/CENTREL Power System”; Report 38-113, CIGRE Session 2000, Paris

[2] M. Luther, U. Radtke, “Betrieb und Planung von Netzen mit hoher Windenergieeinspeisung” ETG Kongress, October 23-24, 2001, Nuremberg, Germany

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

[4] U. Armonies, M. Häusler, D. Retzmann: “Technology Issues for Bulk Power EHV and UHV Transmission”; HVDC 2006 Congress – Meeting the Power Challenges of the Future using HVDC Technology Solutions, July 12-14, 2006, Durban, Republic of South Africa

[5] D. Povh, D. Retzmann, E. Teltsch, U. Kerin, R. Mihalic: “Advantages of Large AC/DC System Interconnections”; Report B4-304, CIGRE Session 2006, Paris

[6] W. Breuer, D. Povh, D. Retzmann, E. Teltsch: “Trends for future HVDC Applications”; 16th CEPSI, November 6-10, 2006, Mumbai, India

[7] G. Beck, W. Breuer, D. Povh, D. Retzmann: “Use of FACTS for System Performance Improvement”; 16th CEPSI, November 6-10, 2006, Mumbai, India

[8] R.P. Singh, “New Projects on HVDC in India”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil

[9] R.P. Sasmal, “Planning Issues on HVDC Systems in India”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil

[10] W. Ma, “Main Aspects of UHVDC System Planning and Design”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil

[11] Y. Zeng, “Chinese CSG Experience on HVDC Transmission”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil

[12] W. Breuer, M. Lemes, D. Retzmann, “Perspectives of HVDC and FACTS for System Interconnection and Grid Enhancement”; Part 1 – DC and AC Technology Issues for Bulk Power EHV and UHV Transmission; Part 2 – Power System Expansion with Advanced Technologies – Solutions for a “Smart Grid” Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil