(Note this originally appeared as part of the discussion on the Claverton Energy Group email circulation list, but was judged to be sufficiently important to be published as a learned article on the main site. Preceding emails are appended at the end unedited. Feel free to join the circulation list…Ed.)
From Dr Gregor Czisch.
There are two subjects in Nigel Wakefield’s email I would like to address:
First Subject- Technical feasibility of complex multi-terminal HVDC systems:
Nigel Wakefield wrote
> One of the problems that needs addressing with HVDC is, I believe
> the problem of multi-nodal links. … However I understand that
> technology linking individual point supply into an HVDC link is
> not available yet.
Can anyone elucidate on this?
It is often claimed that HVDC is not ready for multi-terminal purposes.
This is as frequently claimed as it is wrong. I think the fact that it is repeated so often leads to the fact that it is widely believed even though it has been known more many years that multi-terminal systems are possible and every technology necessary is already available. I am not going to speculate on who is interested in keeping the misinformation on the technical unfeasibility alive but I want to contribute with some more technical “education”.
One of the “problems” often mentioned is the misinformation that HVDC circuit breakers are not available and therefore faults in complex HVDC systems could not be cleared (solved). This is absolutely wrong.
HVDC circuit breakers were built and tested in the mid 1980’s. The highly regarded HVDC expert Karl-Werner Kanngießer who was an employee of Calor Emag Schaltanlagen later ABB Calor Emag Schaltanlagen and also worked for Siemens wrote in [Kan99] about the HVDC circuit breakers.
“Untersuchungen  haben gezeigt, dass durch den Einsatz von HGÜ-Leistungsschaltern in parallel geführten Gleichstromleitungen die Klärung von transienten oder auch permanenten Leistungsfehlern in etwa 100 ms möglich ist, eine störende Auswirkung auf die angeschlossenen Drehstromsysteme somit praktisch vermieden wird. Nachdem der Prototyp eines 500 kV-HGÜ-Leistungsschalters gebaut und in einer bestehenden HGÜ-Anlage erfolgreich getestet worden ist , darf auch hier die Ausführbarkeit vorausgesetzt werden.”
My translation into English is as follows:
“Research  has shown that through the use of HVDC power circuit breakers in parallel operated direct current lines, clearing transient as well as permanent faults in about 100 ms is possible, and a disturbing effect on the connected AC systems can thus in fact be avoided. Since the prototype of a 500 kV HVDC-breaker has been built and successfully tested in an existing HVDC system , the executability can be seen as being assured.”
So there is no question that HVDC circuit breakers have been available since about 1985. It just has not been necessary to use them in point to point systems. But furthermore they would not definitely be necessary even in a complex HVDC system. This can be understood by reading the following explanations of Dr Uwe Radke a former member or E.ON Netz and participant of highly relevant feasibility studies about complex HVDC systems which have been elaborated with the participation of many big utilities and experts in the field of electricity transport (see e.g.
[BDE+98], [BDE+00], [Rad00a], [Rad00b]): Following statement was recently written by Dr Uwe Radtke about HVDC circuit breakers:
“The HVDC circuit breakers are able to interrupt a short circuit power flow in the range of milliseconds to separate a disturbed section of HVCD overhead lines or HVDC cable links with a minimum influence of the undisturbed transmission system. This kind of circuit breaker is not installed in any HVDC point-to-point links because it is not necessary. “
The same function to separate a disturbed section is also feasible with the thyristor valves in the converter station. In conjunction with disconnectors they are also able to separate a disturbed overhead line section in a sufficiently short time. After the thyristors have reduced the voltage on the disturbed line to null the disconnectors separate the disturbed line sections definitively. Disconnectors alone are not able the interrupt power flow.
For example if short circuit breakers are wished by the operators for meshed HVDC networks these circuit breakers could be compounded with existing devices. HVAC (alternating current) breakers of an industrial series production could be installed in connection with an oscillatory circuit to interrupt the short circuit power flow during the moment the voltage is null. As a consequence no device has to be developed, only devices from an industrial series production have to be installed. The principle of HVDC short circuit breaking was successfully tested many years ago.
Of course new HVAC breakers compounded by actual devices should be tested in an HV laboratory before they are installed in a transmission system.
Furthermore I think that meshed HVDC networks could be operated also without HVDC circuit breakers anyway only with required thyristor valves and disconnectors. This question of whether HVDC circuit breakers are necessary or not, finally depends on how the existing HVAC grid and the new HVDC network are connected with each other and how strong and fast the primary control of the power plants is. Primary control means a very fast power plant reserve capacity able to hold the frequency stable at rated frequency for example 50 or 60 Hz.
I think in any case network simulations of each situation are necessary to answer the question if HVDC short circuit breakers are necessary or not.
Summarizing I would like to say that a meshed HVDC network using currently available industrial produced equipment is technically feasible at the present state of the art.
So the alleged unavoidability of HVDC circuit breakers for multi-terminal HVDC systems as well as the alleged unavailability of HVDC circuit breakers are both false. They are simply not true. There is thus no real problem with HVDC circuit breakers.
There is a second myth about multiterminal HVDC systems. It is the myth about missing control methods. But there are methods to control even complex meshed HVDC systems. One was developed by Franz Karlecik-Maier an expert for control systems when he was working for Siemens. He invented the so called Combined and Coordinated Control Method (CCCM) which makes it possible to run big complex HVDC Systems. It is a method which permits operation of the system without a “master controller” (central control). At the least after its invention it could now be assumed that there is barely a technical limit in the number of converter stations in complex HVDC systems. Also this knowledge has been around for many years now. It is for example published in [BDE+00] [Rad00b]. (Some related patents of Franz Karlecik-Maier are [K-M08] [K-M97])
So, if anyone wanted to know about the existing – and already tested methods – they could easily have read about it.
Without CCCM – or another operational method with similar properties – the HVDC system would have to be divided into individual less complex subsystems, for example, ring systems, as investigated in [ABE +93], or in linear systems, such as described in [BHK +98] . This would increase the number of required converters. In the extreme and unnecessarily simplified case with just two converter stations at the two ends of point to point HVDC subsystems the number of required converter stations would nearly be doubled. Even this would not make the Supergrid unfeasible. But those speculations are in fact unnecessary because the control methods for complex multi-terminal HVDC systems are available as mentioned before.
Summarizing it can be stated that there is no reason at all why a complex multi-terminal HVDC system should not be feasible with today’s equipment. Multi-terminal HVDC systems are feasible with existing technology.
Second Subject – Political obstacles such as rising prices as a result new transmission lines
The point of rising prices in one market on one end of a new transmission system and the resulting rejection of the project (The UK Norway link) was addressed by Nigel Wakefield.
Nigel Wakefield wrote:
> However, I think the real reason was that UK prices were so much
> higher at the time than Nord Pool prices that the initial effect would
> have been a baseload export of 1200 MW to the UK. This would have
> raised wholesale prices in Norway (and likely across Scandinavia) by
> about 25% which would have been politically unacceptable……
I think this is a problem which is worth thinking about but which can be solved. In my statement for the hearing “Future energy and climate policy in Hessen” [Czi08] in the Hessian parliament I addressed it as follows:
“The large-scale electric power transmission can also raise legitimate fears on the consumer side. An example is the Norwegian electricity market. This marked is characterized by the production from storage hydropower plants and low electricity costs. The rated power of the storage hydropower plants exceeds the current network capacity between Scandinavia and Europe by about one order of magnitude. This means that the Norwegian market with its cheap electricity is only influenced relatively little by the European market in the south. But if the transmission capacity will be strengthened considerably, there is offered a very attractive market to Norwegian producers for the sale of their electricity – because of the high electricity prices. Because of the the character of storage hydropower – the Norwegian kind of electricity – the Norwegian electricity is particularly well-suited, to be placed as peak load electricity in the highest price segment in Europe. In the free play of market forces – without appropriate tools as counter measure – this would inevitably lead to an increase of electricity costs in Norway, while the Norwegian consumers would suffer from higher electricity prices. Even such mechanisms are thus to be taken into account while planning for the establishment of a powerful large-scale electricity transmission system in order to find solutions for the structural problems and in order to implement these in time”.
So there are solutions which can be found for this problem (providing rigorous adherence to rigid and irrational market dogmas are abandoned….as they have been recently in banking..Ed) But this does not have to be very difficult. One just has to combine the construction of the transmission systems with the formulation and signing of appropriate contracts, which regulate the electricity prices. This sounds like a simple approach as long as one does not take into account the market ideologists who politically still are very influential and dislike this kind of approach. But especially the huge hydropower potentials with their huge storage volume in Norway could be extremely helpful in order to come to a reliable end affordable electricity supply totally from renewable energies. Therefore it is worthwhile to search for solutions even if it might be necessary to overcome some mental and ideological barriers.
[ABE+93] ASAL, H. ; BRUMSHAGEN, H. ; EROULT, M. ; HASSON, B. ; KULA, M.
V. ; PIRET, J.-P. ; RIPPAR, G. ; SEIPEL, E. ; SMIRNOV, I. ; SOULIS, E. ; VERGELLI, L.: Elements for the development of a future European power system / Union der Elektrizitätswirtschaft (Eurelectric). 1993 ( 04002Ren9326).
[BDE+98] BELENERGO ; DC BALTIJA ; EESTI ENERGIA ; LATVENERGO ; LIETUVOS ENERGIJA ; PPGC ; PREUSSENELEKTRA ; RAO EES ROSSIJ ; VEAG, Autoren n. b.: TEN-Energy Study East-West High Power Electricity Transmission System – Baltic Route – Phase I / European Commission: Trans-European Energy Networks.
Gelsenkirchen, April 1998. – Executive Summary. conveyed by Uwe Radtke, E.ON Netz, Lehrte
[BDE+00] BELENERGO ; DC BALTIJA ; EESTI ENERGIA ; LATVENERGO ; LIETUVOS ENERGIJA ; PPGC ; PREUSSENELEKTRA ; RAO EES ROSSIJ ; VEAG, Autoren n. b.: TEN-Energy Study East-West High Power Electricity Transmission System
– Baltic Route – Phase II / European Commission: Trans-European Energy Networks.
Gelsenkirchen, Mai 2000. – Executive Summary. conveyed by Uwe Radtke, E.ON Netz, Lehrte
[BHK+98] BRUNTT, M. ; HANSSON, B. ; KNUDSEN, L. ; NURMINEN, H. ; RADTKE, U. ; STØVRING-HALLSSONAND, S.: Baltic Ring Study, Power System Analysis Report:
Multiterminal HVDC Systems / Baltic Ring Electricity Co-operation Committee (BALTREL). 1998. – Forschungsbericht. Veröffentlichung auf CD-Rom
[Czi08] Czisch, G.: Stellungnahme zur Anhörung “Zukünftige Energie- und Klimaschutzpolitik in Hessen” des Ausschusses für Umwelt, ländlichen Raum und Verbraucherschutz, im Hessischen Landtag, 2. bis 4. September 2008, Kassel, August 2008
[Kan99] KANNGIESSER, K.-W.: Nutzung regenerativer Energiequellen Afrikas zur Stromversorgung Europas durch Kombination von Wasserkraft und Solarenergie. In:
BRAUCH, H. (Hrsg.) ; CZISCH, G. (Hrsg.) ; KNIES, G. (Hrsg.):
für Europa durch Fernübertragung elektrischer Energie. Moosbach :
September 1999 (1). – ISBN 3-926979-71-2, S. 111-122
[K-M08] Karlecik-Maier, F.: Patent: Control Method for Direct-Current Transmission by Means of a Plurality of Converters, Agents: LERNER GREENBERG STEMER LLP, Assignees: SIEMENS AKTIENGESELLSCHAFT, Origin:
HOLLYWOOD, FL US, IPC8 Class: AH02M710FI, USPC Class: 363 68, 2008
[K-M97] Karlecik-Maier, F.: Patent: PROCESS AND DEVICE FOR REGULATING N POWER CONVERTER STATIONS OF A MULTIPOINT HVDCT NETWORK, International Application No.: PCT/DE1996/002186 Publication Date:05.06.1997
[Rad00a] RADTKE, U.: TEN-Energy Study East-West High Power Electricity Transmission System – Baltic Route: Main Results and Conclusions of the Final Report Phase II, Executive Summary Working Group 4 “Environmental and Routing” / European
Commission: Trans-European Energy Networks. 2000. – presentation on CD, conveyed by Uwe Radtke, E.ON Netz, Lehrte
[Rad00b] RADTKE, U.: TEN-Energy Study East-West High Power Electricity Transmission System – Baltic Route: Main Results and Conclusions of the Final Report Phase II Working Group 1 “Technical Aspects” / European Commission: Trans-European Energy Networks. 2000. – presentation on CD, conveyed by Uwe Radtke, E.ON Netz, Lehrte
 Kanngießer, K.W.; Wolters, I.: “Comparative performance of an HVDC transmission system with d,c, breakers for clearing d.c. line faults”.
CIGRE-Symp. 200-05, Boston 1987.
 Bachmann, G.; Mauthe, G.; Ruoss, E.; Lips, H.P.; Porter, J.; Vithayathil, J.: “Development of a 500 kV airblast HVDC circuit breaker”. IEEE trans. power app. a, syst. PAS-104 (1985) S.2460.
PREVIOUS EMAILS – READ FROM BOTTOM UP
Dave Andrews schrieb:
> Nigel – many thanks for this.
> Gregor – or anyone else got any knowledge on the last point in Nigel’s
] Sent: 29 January 2009 17:20
> Subject: RE: [Claverton-Group] Interconnector – intercontinental?
> Norway UK / UK Iceland link?
> I would hesitate to call myself an expert on the costs, though I
> looked at the North Sea Interconnector iin 1999. At the time the
> forecast cost was £450 million for a 1200 MW line of about 600 miles
> in length.
> There were many reasons it did not go ahead but I think the main one
> stated was that the two grid companies could not agree on a joint
> balancing code for real-time operation (their “gate closure”
> procedures were very different and neither wanted to change). However,
> I think the real reason was that UK prices were so much higher at the
> time than Nord Pool prices that the initial effect would have been a
> baseload export of 1200 MW to the UK. This would have raised wholesale
> prices in Norway (and likely across Scandinavia) by about 25% which
> would have been politically unacceptable……
> I think prices for HVDC cable got close to the $1 million per km mark
> at the height of the market. I suspect they will be considerably
> cheaper now with all commodity markets suffering due to the recession.
> From that perspective, now is a great time to be buildnig these links
> since commodity prices are only likely to be in this low range for a
> couple of years at best.
> Iceland to nearest UK landfall (northern Scotland in the Dounreay
> area) would be about 500 miles. However, landing a meaningful quantity
> of power there would mean a very expensive and NIMBY-resisted upgrade
> to the grid all the way down to the England / Scotland border. It
> would probably be better to run a line down the seabed on the Scottish
> west coast and make landfall at somewhere like Sellafield, Heysham,
> Wylfa, etc….
> One of the problems that needs addressing with HVDC is, I believe, the
> problem of multi-nodal links. A west coast link running from Iceland
> would, in theory, be able to pick up a lot of otherwise stranded wind
> and tidal current energy along the way. However I understand that
> technology linking individual point supply into an HVDC link is not
> available yet. Can anyone elucidate on this?
>> >> Subject: RE: [Claverton-Group] Interconnector – intercontinental?
> Norway UK / UK Iceland link?
>> Date: Thu, 29 Jan 2009 09:58:44 +0700
>> Hi Nigel, don’t you have some knowledge of the costs of the proposed
>> / UK HVDC link? I assume this would be pretty much the same as the
> cost of
>> a link from Iceland to UK? Perhaps you could remind us of the costs
> and why
>> it didn’t go ahead?
>> There was a proposal to link Iceland directly to Holland at one point.
>> Kind Regards
>> Dave A
>> Ps George – for year I thought Iceland was the size of the Isle of
> Wight –
>> but in fact it is pretty much the same size as the UK……
>> Why not go across the top from Russia across the Barents Sea to US?
> This has
>> been talked about……..
> From: Nigel Wakefield [