a3_302_2012
TRANSCRIPT
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Suitability evaluation of improved high vo ltage circuit breaker design with
drastically reduced environmental impact
PETER SDERSTRM JOHAN LIDHOLM ULF KESSONVattenfall AB ABB AB ABB AB
Sweden Sweden Sweden
SUMMARY
The vendors research and development strategies had to focus on improved mechanicalsolution, isolation media to withstand the dielectric requirements and also keep or improve the
arc extinguishing capability depending of voltage level. The performance of the SF6 circuitbreakers is outstanding and the reliability has reached a level where very few arcing chambers
are used in series even for the high voltages which results in a minimum need of maintenance.The environmental focus and demand have increased from governments all over the world
and the grid owners have started to follow. By this the demand with reduced environmental
impact of high voltage equipment the pressure on vendors has focused their research and
development efforts been to reduce the environmental impact of the high voltage circuit
breakers as one of all equipments in the electrical grid.Many life cycle assessments have been performed to show the circuit breakers impact on theenvironment by calculating the CO2release. Independently if it is metal clad circuit breakers (in gas
insulated substation or dead tank) or air insulated circuit breaker it is some areas in the design parts
that have the highest impact on CO2release in addition to the raw material impact. The isolating gasSF6 leakage rate (SF6 which is a classed greenhouse gas), the main current path contact resistance,
tank and cabinet heaters which all three gives power losses.
During the past ten years the best practise developments have been to integrate more functions of thesubstation equipment in the same product. Good examples have been the disconnecting circuit breaker
which has reduced the losses in the main contact system by removing the disconnectors from the
substation with the result of increased availability reduced power losses and use of less raw materials
and of course maintenance. Another good example in addition the design of the circuit breakers hasimproved to double motion breaking chambers which reduced the needed energy in the drives and so
forth fewer raw materials.To adapt to the environmental demands even more a new design of the circuit breaker has beendeveloped addressing improvements to all the main contributors to the CO2release in the design. The
life cycle assessment shows improvement of 15 - 20% of the CO2release over life time. From the grid
owner point of view these steps in developing the product have been asked for a long time. The circuit
breaker has been evaluated after initial type testing by trial operation in a field installation where thecircuit breaker had the opportunity to function as both line circuit breaker and capacitor bank circuitbreaker. The evaluation shows that the improved design give good possibilities to reduce the
21, rue dArtois, F-75008 PARIS A3-302 CIGRE 2012http : //www.cigre.org
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environmental impact drastically for circuit breakers both in common climates with no extreme
requirements and also in very cold climates.
KEYWORDS
Sulphur Hexa Fluoride, Carbone Di Oxide, High Voltage, Circuit Breaker, Environmental
Impact
Historical backgroundThe historical development of circuit breakers has been in purpose to increase reliability and improvebreaking current performance. In the past the circuit breakers were the one of the weakest spots for life
length and the highest need of maintenance. The air blast circuit breakers where replaced by oil circuitbreakers which were a large technology step and the reliability were improved drastically. Today still
many oil-minimum circuit breakers are in service. The technology of SF6circuit breaker has reducedthe number of parts in a high voltage circuit breaker by the high dielectric performance and current
breaking capability to an optimum. The circuit breakers are not the most maintenance driven productanymore and has a very high reliability.
The development of the SF6circuit breaker has continued to improve performance of current breaking
capability and be more efficient with less gas and higher current ratings in parallel with especially hightransient recovery voltage requirements. The energy demands on the drives have been reduced bymodified breaker chamber technology to double motion techniques.The technical development has not only been in a performance respective of breaking current and
withstand voltages, development has an environmental profile also included in the strategy. Since the
vendors are aware of the draw backs of SF6environmental aspects. A strong focus has been toimprove the needed amount of gas to use within the circuit breakers, reducing the gas containervolume, independent if it is an AIS solution or GIS solution. Secondly where allot of efforts have been
in to reduce the SF6leakage to a minimum.Not only has the circuit breaker itself been room for environmental driven development. Other
substation equipment has been reviewed. The disconnecting switch function has been incorporatedinto the circuit breaker, named as disconnecting circuit breaker. That development has increased the
reliability allot in the substation, since theSF6 circuit breaker were developed the disconnectingswitch has been the more maintenance demanded then the circuit breaker. More over the
environmental impact has been reduce drastically, just by using less material.
Global environmental demandsIn the Kyoto protocol from 1997 [1] the SF6gas were labeled as one of the global warming gases.Since then the SF6 gas emission has been monitored. Other legal organisations, countries and
companies has defined their directives and legislations how to handle SF6 and other green housegases.The European Union have directives and regulations for instance 305/2008 and 842/2006, as
minimum a demand of recognised announcement of certification of personal for recycling of some
fluorine greenhouse gases for high voltage circuit breakers.Several countries has announced rules to follow in the purchasing situation and handling of equipment
containing SF6including recycling, Australia for instance have introduced a kg tax for SF6 gas. Therequirement within each country and legal region puts requirements on the developer, vendor andowner of high voltage circuit breakers.
Some grid owner and utilities have defined own strategic rules for the environmental requirements of
SF6and equipment that utilise SF6that is higher than the country rules. Vattenfall Distribution
Operations Nordic has a target of less than 0.25% SF6leakage over one year. Their own demands areincreasing yearly.
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Life cycle assessmentThe importance to overview the total life of the products environmental impact cannot be enough
stressed. There have been many statements and comparisons in different reports that have been
published by Cigre. Comparison of a SF6circuit breaker and SF6 disconnecting circuit breaker [1]shows much lower environmental impact over life for disconnecting circuit breaker not for the used
amount of SF6 but the amount ofE1) MaterialE2) Transportation
E3) Load losses
E4) HeatingThe main contributors mentioned above can be improved in a high degree by the developers, some of
course to a higher initial purchasing cost and some by changing technology.
The amount of material (E1) is mainly inventors owe the possibility to improve. Equally thetransportation (E2) can be much improved to use less equipment and also how much the product is
pre-mounted on one hand make an easy installation but on the other hand increase the transportation
volume.The utilities can contribute to reduce the load losses (E3) during purchasing phase by applying penalty
cost evaluating the offers. Some already does. It is important utilise evaluation method to boost the
development to reduce the environmental footprint. The last area mentioned above is the heating (E4),it is for live tank breakers a necessity to overcome condensation in the closed drive cabinet and forcold climates additional heating for the auxiliary circuit equipment also in the drive cabinet which
could be used more efficient. For dead tank circuit breakers additional heating is applied on the tank
containing the breaking chamber with purpose to reduce the SF6 gas condensation, tank heatersstrongly increase the CO2 foot print over life.
Technology improvementA strong focus from development over many years has resulted in other solutions of arc interruptingmedia with different technologies. Vacuum interrupters have existed for many years in the medium
voltage segment and stretching of the technology has been done to reach the lower end of the high
voltage segment. It is not uncommon to see different vendors showing up results from testing and newpilot installations with vacuum interrupters for 72 kV some even for 145 kV [1]. Other explored area
is to change the SF6gas to some other gas. The obvious required properties of a gas to replace SF6 is
mainly cooling effect, dielectric withstand capability and also liquidation point. Gas mixtures areachievable most times for 2 of the criteria. Some of the more promising gases are the CO2gas. The
CO2gas has been explored by many research institutes and product developers showing results in
comparison to SF6 [1], [2], [3].The gas mixture of CO2 gives a high good dielectric withstand capability, the cooling effect
compared to SF6 is less but in most cases enough. The liquidation point is very low for CO2which
gives opportunity to meet all requirements in the world and to reduce the needed amount of tankheating.
Figure 1, Environmental impact comparison between SF6and CO2 circuit breaker
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ValidationTo emphasise the importance of an environmental friendly products, the CO2gas has been exploredand verified all summarized in this section. To really show the potential of the CO2gas the aim was toachieve a circuit breaker with performance at 145 kV voltage level. The very best knowledge gained
in development of SF6gas circuit breakers were used and adopted and optimised to the CO2gasproperties. Development tests of the single element circuit breaker have shown a good performance
considering an increased gas pressure compared to SF6. A full type test series were performed withsuccessful result. The dielectric performances were interesting, extremely good performance even atdisconnecting circuit breaker level for the LIWL at 750 kV. The draw backs with reduced heat
dissipation performance of the CO2 gas could be seen with increased temperature, approximately 10%,in the temperature rise test with the same design.
Figure 2, Comparison of SF6and CO2temperature rise at 4000 A.
The environmental initiative was not only addressed with the respect to SF6-free circuit breaker butalso with respect to the load losses (E3) mainly to show the possibilities by utilising larger currentpaths the load losses could be decreased by approximately 10%.
ExperienceTo gain experience a pilot installation has been running for more than 2 years utilising the 145 kV,
31,5 kA, 3150 A, 50 Hz CO2circuit breaker.Positioned as a busbar circuit breaker the circuit breaker has been serving as a capacitor bank circuit
breaker, switching a 24 Mvar shunt capacitor bank, part time of the year and the rest of the year as aline circuit breaker. By this it has been feasible to achieve experience of daily operations and also
being connected with nominal current for longer times.
The operation results show a very good performance, no issues reported from the grid owner. Meantime inspection showed also normal conditions inside the circuit breaker.
Figure 3, Pilot installation of LTB 145D1 CO2circuit breaker
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ConclusionsTo meet the demands from users and country regulation of environmental impact it is necessary totake a major technology step. The compact solutions have existed for more than 10 years. Obviously
the lower voltage range will be affected first in the high voltage segment. The show case defines that it
possible to take the step for higher voltages then 72 kV. The CO2based technology circuit breakers
will give good performance and reliability to the utilities/users to a lower environmental impact.Utilising a compact solution as disconnecting circuit breaker with built on earthing switch will reducethe environmental impact another 50%.The doubts are cleared technology wise the critical areas found in development has been explored and
verified, now the utilities have the opportunity to go for SF6free solutions to use more environmental
friendly high voltage circuit breakers.
End of text
BIBLIOGRAPHY
[1] H Okubo, A Beroual Recent Trend and Future Perspectives in Electrical Insulation Techniques inRelation to Sulfur Hexafluoride (SF6) Substitutes for High Voltage Electrical Power Equipment (IEEE
Electrical Insulation Magazine 0883-7554/07, Vol. 27 No.2)[2] S. Okabe, H. Goshima, A. Tanimura, S. Tsuru, Y. Yaegashi, E. Fujie, and H. Okubo. Fundamental
insulation characteristic of high-pressure CO2gas under actual equipment conditions. (IEEETransactions on Dielectrics and Electrical Insulation. 14 (1). 2007)
[3] T. Uchii, Y. Hoshina, H. Kawano, K. Suzuki, T. Nakamoto M. Toyoda Fundamental Research On SF6-
free Gas Insulated Switchgear Adopting CO2Gas and Its Mixutres (ISETS07 2007)