TITLE

UHV AC TRANSMISSION SYSTEMS

SCOPE

Standardization in the field of AC transmission technology for highest voltage of the system exceeding 800 kV, particularly the preparation of systems-oriented specifications such as those for planning, design, technical requirements, construction, commissioning, reliability, availability, operation, and maintenance. Development of processes for specifying requirements and demonstrating whether the required performance of UHV AC systems and specifying the system operation and control methods for UHVAC with consideration of the impact of renewable energy and UHVDC/HVDC interconnection is assured.

Responsibility for equipment standards remains with product TCs, except for specific equipment which is not within the scope of an existing TC but is nevertheless essential for the UHV transmission system. The UHV AC Transmission TC will consult and coordinate with the product TCs in all systems-related aspects of equipment standards.

BACKGROUND

Ultra High Voltage (UHV) AC transmission systems were developed in Italy, Russia, USA, and Japan in the 1970s and 1980s, to increase the bulk power transmission capability over long distances. The first commercial UHV transmission line, Ekibastuz – Kokchetav (1 150 kV, 500 km), was put into operation in the USSR in September 1985. In August 1988 it was prolonged by 410 km from Kokchetav to Kustanai, i.e. the full length became 910 km. The transmission line operated at 1 150 kV until January 1992 and then the voltage was reduced to 500 kV because there was no need to transmit the full power. As this line was unique it was not relevant to begin a standardization procedure in the IEC.

After that, UHV AC transmission technology was further developed and widely used in the 21st century. On the 6th of January 2009 the 1 100 kV UHV AC pilot project, Jindongnan-Nanyang-Jingmen, was put into commercial operation in China. More than 20 UHV transmission lines have been built and put into operation since then, and a UHV power grid has now been formed.

In 2012, India also put a 1 200 kV test station into trial operation at Bina, Madhya Pradesh.

Besides, some other countries began to think of the potential use of UHV AC transmission technology to realize bulk power transfer.

• Chair: Mr Bo Li (CN)

• Secretary: Mr Yoshimitsu Umahashi (JP)

• Assistant Secretary: Mr Rei Hemmi (JP)

• Assistant Secretary: Mr Toshiyuki Saida (JP)

• Technical Officer: Mr Svetozar Kapusta

• Standards Project Administrator: Mrs Lucie Constantin

• Editor: Mrs Lucy Sonner

• P-members: 7 countries

• Liaisons

TC 8, SC 8C, TC 11, TC 14, TC 17 TC 42, TC 99, TC 115, Liaison A: CIGRE/SC A2

• Working Groups

WG 1: System design

WG 2: Substation and Transmission Line Design

WG 3: Commissioning

WG 4: Maintenance

GENERAL

China is operating twenty-two 1 100 kV UHV AC transmission lines by 2024. UHV AC power grid and inter regional AC/DC hybrid power grid have been formed in China. Next some 1 100 kV UHV AC projects are under construction to improve UHV AC grid. Besides China, several other projects for 1 200 kV in India are also in planning and construction today.

In Brazil and South Africa planning has been started to consider the potential use of UHV DC and UHV AC systems, and it can be expected that in Europe and North America UHV AC systems may also be introduced, with the change in the power supply to a mix with large quantities of renewable power generation. In all these cases, the resources from wind, large hydro and solar will be located far away from the end users and bulk power transmission systems such as UHV will be required to connect the sources to existing power grids.

UHV in AC can be seen as an additional technical solution to long-distance UHV DC and HVDC bulk power transmission, potentially in a combined power network.

ECOLOGICAL ENVIRONMENT

The ecological impact of electric power transmission at UHV AC is low in general. The most critical impact is visibility of overhead lines which can have tower heights of 80 m to 140 m. Not all regions will accept such high towers for aesthetic reasons. AC underground systems are needed to offer solutions for UHV AC lines where such high towers cannot be built. Technical solutions are available, and rules need to be set up for when undergrounding is needed.

Electromagnetic fields along lines may also be critical and a reason to go underground with a fully earth system.

The noise of overhead lines or substations is another system aspect of UHV AC transmission which needs normative rules.

Also, there is a need for a consistent process to specify countermeasures to deal with ecological and environmental issues, and to verify them in a consistent manner.

The increase in electric power consumption world-wide and the concentration of electric load in megacities and industrial areas require higher capacities in power transmission lines. The required electric current in existing transmission lines in several locations of the world has reached rated current levels of up to 4 000 A and is reaching its technical limit at EHV. The only way to increase the bulk power transmission capacity in an AC system is to use higher transmission voltages (at the UHV level).

Using renewable energy sources on a large scale, in sites far away from the main load centres, e.g. in offshore wind farms, large hydro power plants or large photovoltaic installations in deserts, is also a driving force to introduce higher transmission voltages with acceptably low transmission losses, leading to a better economic balance.

Interconnecting existing AC transmission systems of 400 kV or 500 kV in various regions – Europe, Asia of the ASEAN countries, Africa south of the Sahara, North and South America and India – will also need the higher AC transmission voltage of UHV.

Furthermore, the number of countries to adopt UHV systems will grow and UHV AC interconnections between countries may be realized in future, which needs a globally agreed process to manage UHV AC systems at international level.

The Institute of Electrical and Electronic Engineers (IEEE) has already started standardization of UHV AC systems. CIGRÉ has also started technical work on UHV AC systems.

For clause E. SDGs below: TC 122 focuses on standardization in the field of AC transmission technology for highest voltage of the system exceeding 800 kV. This field totally supports reducing carbonization with very highly efficient AC transmission system.

1. UHV AC transmission system will lead to connect the clean energy to wide area by highly efficient and low losses system.
2. UHV AC transmission system is very important infrastructure on energy system and will lead innovative development with industry.
3. Highly efficient and low loss of the UHV AC transmission will improve climate change with reducing carbonization.

TREND IN TECHNOLOGY

The equipment technology of circuit breakers, disconnectors, earth switches, current and voltage transformers, bushings, power transformers, gas-insulated switchgear (GIS) and transmission lines has already extended product standards to UHV AC. For underground cables and gas-insulated transmission lines, series compensators and controllable shunt reactors, the development of product standards for UHV AC is under way.

The successful application of all these products to UHV AC systems will need UHV AC system standards to give rules for interconnecting UHV AC lines on a world-wide standardized basis. This is important for equipment manufacturers to be able to standard-design and manufacture of products since the development costs are very high. A standardized market and systems requirement is the most efficient way to reduce costs.

Also, in order to initiate and maintain a stable power supply, standards to define appropriate processes to verify the required performance of UHV AC systems are needed, in addition to individual system-related standards.

New challenges to be solved by international standardization are:

1. interoperability of equipment following standardized testing requirements;

2. environmental impact of UHV AC systems: since this can be considerable, normative rules are needed for noise, electromagnetic fields and visual impact;

3. control and protection of UHV AC, which require rules for high power reliability and network stability;

4. efficient operation of AC UHV systems, which needs normative rules for power factor compensation;

5. handling of network failures such as earth or line faults;

6. interaction of UHV AC lines with regional power transmission, which requires grid connection codes;

7. proper management of a UHV power system from concept planning to decommissioning, to ensure that required performance is achieved and maintained through its lifecycle.

The main activity is seen in the following areas:

1. general system-related specifications for the design of substations and transmission lines;

2. harmonizing of system-related aspects for on-site acceptance tests of electrical equipment and system commissioning of UHV AC;

3. reviewing all the phases of UHV power systems and developing a consistent approach to specifying their requirements, to demonstrate that proper performance is properly fulfilled and maintained.

To introduce UHV AC on a world-wide basis will need new system-oriented international standards. This is the only way to reduce the high system cost, achieve the necessary reliability/availability requirements and tackle expensive product development.

TREND IN THE MARKET

The biggest market trend for UHV AC is towards long-distance bulk power transmission and interconnection with existing power systems; there is also a trend towards building strong power reception grids to receive more large-scale power feed-in. The grid changes are driven by fast-growing power consumption in load centres of emerging countries and by structural changes of coal, gas, and nuclear power generation towards full renewable power generation with wind, solar, large hydro, and others at far-away generation locations.

With increasing renewable power generation, mainly from wind, large hydro and solar, electrical energy will be competitive with oil, gas, and coal sources, but it will need new AC transportation systems to cope with the needs foreseen.

AC transmission lines or corridors of 5 GW to 10 GW will be needed, which is more than double today’s 3 GW to 4 GW at 400 kV or 500 kV. Doubling the AC transmission voltage to 1 000 kV can solve this in an efficient and economic way. UHV AC provides reliable, safe, and efficient bulk power transmission over long distances to get energy into load centres or to interconnect regions to balance load and generation.

On the other hand, the characteristics, such as its large power flow mentioned above, of UHV AC system may have a serious impact on existing power grids and their operation if, for example, severe transmission faults occur on the UHV AC lines built without the proper consideration and evaluation.

TC 122 dealing with UHV AC transmission systems will mainly act as a coordinator of systems aspects in connection with the relevant product and horizontal committees.

The focus of standards to be developed by this TC will be purely system-related and they will be established in coordination with related product standards and horizontal standards.

In this TC, based on the communication with relevant TC/SCs, all the stages in a UHV project from concept planning to design, installation, operation, maintenance, and others will be reviewed to provide an appropriate management approach through its life.

The related TCs and SCs could be:

TC 7         Overhead electrical conductors

TC 8         Systems aspects of electrical energy supply

SC 8C       Network Management in Interconnected Electric Power Systems

TC 11        Overhead lines

TC 14       Power transformers

TC 17       High-voltage switchgear and controlgear

SC 17A     Switching devices

SC 17C     Assemblies

TC 20       Electric cables

SC 22F     Power electronics for electrical transmission and distribution systems

TC 33       Power capacitors and their applications

TC 36       Insulators

SC 36A    Insulated bushings

TC 37       Surge arresters

TC 38       Instrument transformers

TC 42       High-voltage and high-current test techniques

TC 57       Power systems management and associated information exchange

TC 73       Short-circuit currents

TC 77       Electromagnetic compatibility

TC 85       Measuring equipment for electrical and electromagnetic quantities

TC 95       Measuring relays and protection equipment

TC 99       Insulation co-ordination and system engineering of high voltage electrical power installations above 1,0 kV AC and 1,5 kV DC

TC 115     High Voltage Direct Current (HVDC) transmission for DC voltages above 100 kV

CISPR      International special committee on radio interference

Additionally, this TC will cooperate with ISO and related groups in IEEE and CIGRE.

TC 122 does not have any publications to be used for IEC Conformity Assessment Systems.