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Dr. Sood's Discussion---part2

(2007-12-27 20:29:20)
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教育

 

My echoes:

Excellent topic

I think the EHVDC is a mature technology. Not like what you said "the technologies of the HVDC are not mature". The UHVDC is not a mature technology, aslo the CCC-HVDC and CSCC-HVDC are not.

China now has grasped the point technology of HVDC. Nowadays, BDCC can finish the SYSTEM DESIGH independently. However there are also some technologies we must learn and some key equipment we must buy from SIENMENSE and ABB.

I don't agree with planning and building so many UHVDC links before we have enough operation experience. Recently I know that the project of "Ningxia East to Shandong" is modified to 660kV/3kA/4000MW.

Also I don't agree with the opinion of Dr. Sood " CCC-HVDC will be developed a lot and widely used between the year from 2000 to 2020. and VSC-HVDC will be widely used after 2020."

Does anyone agree with me?

I am so glad to read your post, can you give your E-mail?

John’s echoes:

Thank you for your time

 

But I am not quite familar with HVDC topic, because my research topic is UVLS.I already forwarded your comments to Dr. Sood; hopefully, we can have his response soon

"Dear Dr. Sood,

I am glad to report you that we already received the first comments on the BBS, which was posted by a Ph.d student inside China.……………………………………………………………………………………

If you have some words to say, you can Email me or comment on the BBS directly

Thank you for your time.

if possible, can you send me your PPT file or some other files to me, then I can post on BBS.

 

My comments to John:

Thanks john cheng!

Yes, China is now planning to build about 15 UHVDC projects until 2020. You can find these plans in the internet. And Jiangsu province belonging to State Grid and Guangdong province belonging to South Grid will be two multi-infeed system. Especially in Shanghai, the received end is electrically approximal. The interaction of HVDC is a troublesome problem. I think we should put much attention on these problems and give practical methods to meet the safety requirements of our power system.

I suggest that you can find some materials to understand the reason why China will planning so many UHVDC. There are some reports about the reason. But I don't have them.

 

Dr. Sood’s echoes:

Thank you for your comments, and Dr.Sood is very interested, I will post his response as below

 

"Cheng

    That is helpful definitely.I can make some comments:

    "HVDC is a mature technology now and much has been learnt from the mistakes of the past. However, each link has its own particularities, and there can be some new aspects to learn. Suitable simulation and other studies can help tremendously in doing a good planning.

Manufacturers like Siemens and ABB have tremendous experience, and it is necessary to have their input into these projects. Their expertise lies in their capabilities to design and manufacture equipment to stringent specifications.

    Too many HVDC links is also a potential problem. There are difficulties in tapping power from HVDC links. They are very good for point to point transmission, but future modifications to adapt to changing needs is not so evident. However, the econonics of planning take this into consideration, and a 30-40 year scenario is often studied; if the link is economical, then why not build it?

    The future challenges of tapping HVDC links are being studied, and with developments in force commutated converters will lead the way. The dc breaker technology is advancing also, and will play a role in this. The CCC will assist in commutation, and provide an option for multi-terminal operation. The VSC HVDC will be extremely useful in inter-connections in urban environments, not for long distance transmission. The increasing use of wind power generation will require VSC HVDC technology."

Thanks for your help

Vijay Sood"

 

My echoes and Dr. Sood’s echoes:

Thanks Dr. Sood and Mr. John Cheng

Dr. Sood and Mr. John Cheng,

    Thanks the time of Dr. Sood and Mr. John Cheng took. I am very excited to hear about the opinion of Dr. Sood.

    Thanks Dr. Sood to explain the reason why he wrote in the book of "Applications Of Static Converters In Power Systems" as follows:

    "The first 25 years of HVDC transmission were sustained by converters having mercury arc valves till the mid-1970s. The next 25 years till the year 2000 were sustained by line-commutated converters using thyristor valves. It is predicted that the next 25 years will be dominated by force-commutated converters [4]. Initially, this new force-commutated era has commenced with Capacitor Commutated Converters (CCC) eventually to be replaced by self-commutated converters due to the economic availability of high power switching devices with their superior characteristics."

 --------------------in my opinion, I think the LCC, CCC (CSCC) and VSC-HVDC is not the relationship of replacement each other. they are the relationship of complement each other. VSC-HVDC can't instead of LCC-HVDC. I think that's the reason why China now builds so many EHVDC and UHVDC, although we are doing some research of VSC-HVDC.

 

    I also have some questions about the comments of Dr. Sood as follows:

    1, Dr Sood wrote that "each link has its own particularities, and there can be some new aspects to learn", Can Dr. Sood give some examples about the new aspects?

    Each new link has its own special problems. Some may be related to resonances, others to operational characteristics depending on the AC network they are feeding into. Specially, China with its many links will be facing problems due to interactions between different ties which are in close proximity to each other. The cheapest version is LCC. If there are commuation problems due to weak AC system, then CCC can be used. If the power capability is low (less than 300 MW) then light HVDC can be used for high quality power. Again, it all depends on the attached AC system.

   China is going for EHVDC because of bulk power (6000MW), point-to-point transmission only. Economics is a big reason for this

_________________________________________________________________________

 

    2, "Suitable simulation and other studies can help tremendously in doing a good planning"----I agree with Dr. Sood very much. I want to know why Dr. Sood does not use the electromagnetic transient software of PSCAD/EMTDC. Also how to define the "Suitable simulation", and how to verify the validity and adaptive of HVDC models which you represented. Dr. Sood give some examples about the dynamic analysis of HVDC in the chapter of 10, "TYPICAL DISTURBANCES IN HVDC SYSTEMS", I do not know how to determine the parameters of KP, KI and some measurement time constant like UD, ID. The step response is just to verify whether they can meet the requirements of system design. Does Dr. Sood have some other solution to determine the parameters? like frequency domain analysis or root locus analysis? And how to use the small signal analysis determining the parameters independently and collectively?

    I use the EMTP RV program which is similar to EMTDC, or I should state that EMTDC is similar to EMTP. The new version of EMTP RV is vastly enhanced (graphical user interface, machine models, VSC Converter models etc). The tools are all based on the Dommel algorithm. I encourage the reader to visit the website of www.emtp.com <http://www.emtp.com>

    The determination of gain parameters is complicated. The theoretical calculations are only approximations based on the data available of the system. The calculations have to be supplemented with simulation studies, and then by actual measurement. There are solutions available to calculate these parameters based on root locus analysis. And I do use them. I supplement these claculations with simulation studies for faster results.

 

    3, I don't think that the multi-terminal HVDC is a promising technique in China because of the distance of resource and load center. Also the technique is not flexible in system operation and too complicated in system control. What's the opinion of Dr. Sood?

    Three terminal operation is feasible, and we have shown that in Quebec (1600 kms, 2000MW). However, it is more complicated control than two terminal transmission. More than 3 terminals is very risky, and not recomended. Again, HVDC is useful and used only in particular circumstances, not in ALL circumstances. HVDC will complement AC transmission, not supplant it

 

    I will read the Dr. Sood's book again; I think it is beneficial for me to learn more from that book and this discussion. Thanks Dr. Sood again.

    Now I am focusing on modeling HVDC system detaildly just for ABB tech and SIENMENSE tech. Could Dr. Sood give me some suggestions?

    Also I want to know the opinion of Dr. Sood about the tool of simulation. Now China focuses on modeling the detailed model in electromagnetic transient software PSCAD/EMTDC, and modeling the model on the RTDS. Could Dr. Sood give some suggestions about this? Also I focus on modeling these for BTB-HVDC, EHVDC, UHVDC and EHVAC and analyzing the interaction of AC/DC.

    I do the same. The models are getting better all the time.

 

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