Cooperating on UHV
Jean Kowal Secretary of Cigre

(Nov. 28th 2006)

Introduction

It is clear to everyone that access to energy is vital for the future of our World, and that electricity is the main vector for the use of electricity.

Electricity access today means mechanical power, light, health (with refrigeration for meals and drugs), education. It is the key which opens the World of Economy.

The needs will increase dramatically in the coming years irrelevant of the differing conditions in the World:

? Around 1.5 billion people do not event have minimum access to electricity and we must be able to meet their basic needs

? In developing countries the level of energy use per capita is much lower than in developed countries and though improvements in efficiency can be expected, consumption should increase significantly

? In developed countries new needs are emerging, resulting from the ??digital society?? and developments are expected both in quantity and quality.

Meeting the needs is a tremendous challenge as energy supply must meet three requirements: it must be accessible, affordable, acceptable - the famous 3As of the World Energy Council.

The stakes are very high and cooperation should be the rule. From this point of view this Workshop is a good illustration and also a well-timed event.

Generation??The Constraints

To supply electricity the primary condition is to generate as much power as is required by the load. It is a necessary condition, but not the only one??

There is today a consensus that generation should be a mix of primary energy: coal, hydro, nuclear, oil??wind. Apart from concerns over pollution emissions, which can determine the location of power plants, these show specific constraints:

? hydro : is tied to geographic features

? coal: means moving huge quantities of material, via railroad, trucks??, for which the appropriate infrastructure is required

? nuclear: implies cooling conditions??.

? Wind power: in addition to geographic requirements, also means non guaranteed generation (same as hydro in some cases); hence must be complemented with some other generation means.

Making these different sources efficiently exploitable is the miracle of the network. On this account the US National Academy of Engineering declared that ??the vast networks of electrification are the greatest engineering achievement of the 20th Century??.

When we think of it, we must recognize that this statement is perfectly accurate; developments such as telecommunications, electronics???? could not be if there were no power systems.

The Grid

The grid has two main functions: transmission and interconnection. The transmission function consists in wheeling energy from one point to another: from generation to leads, in one direction only. Interconnection is the second function; this allows mutual assistance, providing compensation in case of outage of a plant or line.

Equipment of the grid will contribute to the two functions, but there are cases when the role of the line is purely transmission: for example the line which connects a power plant to the general grid, for which the flow of power is always in the same direction, with a well defined value. The actual flow on an equipment will be the addition of the transmission flow and of the interconnection flow, the value of which is on the average nil.

The interconnection function allows saving in investment, on the generation side as well as on the transmission side: without interconnection continuity of supply will imply full redundancy of the equipment (less investment, less reserve). It also allows using, at any time, the most advantageous generation ?C from the point of view of environment considerations - , proceeding to maintenance work, accommodating fluctuating generation, such as wind power.

AC is quite favourable for interconnection, as the mutual compensation is up to a certain point inherent to AC. On the other hand, interconnection in AC will not prevent the spreading of faults ?C the recent near black-out in Western Europe is an example.

DC is more favourable than AC for transmitting power over long distances, as it does not have to face the problem of voltage support, stability?? So a combination of both techniques can be the right answer for huge systems.

In both cases, AC and DC, going to higher voltages is technically positive: increase of transmission capacity, better use of space, extension of the efficient transmission distance, reduction of transmission, increase of the robustness of the interconnection?? So, looking at higher voltages when volumes and distances are increasing is a natural step.

Challenges for UHV

In a nutshell we can state that there is no technical feasibility problem in going to 1000 kV or 1200 kV. This was the position of the Ad Hoc Working Group on UHV in its report in 1972.

The 1000 kV project headed by Italy (and Brazil), the 1200 kV line built in Russia, and the 1000 kV system built by TEPCO in Japan support this position, even if the latter systems are not presently operated at this voltage.

As for the underground cable, the Italian development included a 1100 kV project, feasibility of which was demonstrated, for the cable as well as for the accessories, joint and termination.

These developments provided the Companies and their experts with opportunities to investigate various issues: auto-reclosing, temporary overvoltages, compensation, switching overvoltages, insulation behaviour, pollution problems, noise, corona, EMF..., structural and mechanical problems, conductor bundles, for lines, substation lay-out, transformers, switching devices, surge arresters, testing conditions. Investigations were also carried out on HVDC.
The consensus is that the problem is related to the optimisation of the system and to its economy.

Involvement of Cigre

CIGRE has been very active in the area of UHV, at least up until the years 1990.

As mentioned earlier an Ad Hoc group was set up in 1969, to answer a suggestion from IEC to the President of CIGRE: ??study the technical aspects which determine the economics of UHV?? and determine the voltage beyond which an increase will not result in further cost reduction??. The purpose was to supply IEC with information toward standardisation of the next voltage levels, above 765 kV. The report was published in 1972.

Over the period from 1968 to 2006, 102 papers were issued by CIGRE, mostly Session papers, which can be found in the CIGRE Library. They represent a tremendous amount of knowledge and information, available to all.

This year IEC approached CIGRE with quite a similar suggestion to that put in 1969: holding of a Symposium to expose the present state of the art in UHV, and the issues still pending, in view of a standardisation action on UHV.

CIGRE has agreed to organise this event with IEC, and will be in charge of the presentation of the scientific and technical challenges in UHV, AC and DC. The main issues addressed will be, for AC:

System aspects: insulation coordination; system technical performance ?C reactive power, stability, secondary arc, system protection??

? Lines

? Substations

? Equipment

? Measuring and Testing

For DC, similar issues will be considered.

Working Groups devoted to issues specific to UHV will be started shortly after the conclusion of this Joint IEC-CIGRE Symposium (one such Working Group has already been operating for a year on 800kV DC ?C Technical Assessment of 800 kV HVDC Applications).

Conclusion

The development of needs for energy is unavoidable and especially the need for electricity. This development which has to take into account environmental constraints cannot be achieved without new technologies and without a wide cooperation.

Exploring UHV technology will prove very profitable and will certainly result in important technical breakthroughs.

When technology, knowledge and cooperation are involved CIGRE will be contributing.

The workshop is an efficient platform to collect information and exchange ideas. I am sure that it will prove a success and I hope that other such events will follow.


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