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Topic Title: Inter Bus Transformers
Topic Summary: common design in your country and considerations..
Created On: 14 June 2010 08:35 AM
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 14 June 2010 08:35 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

Hello, my name is Adityo, i am from Indonesia, South east Asia. I'm a undergraduate students who currently on internship program at transformers manufacturers, a joint venture company between local electricity provider company and Areva T&D, France.

In my internship programs, i am studying about the design criteria for Inter Bus Transformers. In my country, the local electricity provider company always use the tertiary winding in their transformers. Including the inter bus transformers. As far as i know, the tertiary winding is common in distribution transformers because of it's ability to eliminate third harmonic, improve voltage regulation if there are unbalanced line-to-ground loads etc.

For example, a Inter Bus Transformers that has been created here have following specification :
HV/MV/LV (Primary/Secondary/Tertiary) : 275/150/10 kV
90/90/30 MVA
Z(H/M) = 12.79%
Z(H/L) = 20.1%
Z(M/L) = 5.1%
Both side are solidly grounded

i want to ask, are providing tertiary winding in inter bus transformers is common in your country, if so, what is the consideration?

My goal is to show the electricity provider company that the tertiary winding isn't a must in every transformers. But i must have a strong argument to prove this.. and i need a comparison in other country whether they using tertiary winding.

Thanks for your comments, i will reply it as soon as possible because i'm still having a lot of question about this..

i hope you understand what i mean, sorry if my english is bad..
 15 June 2010 03:36 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

i recently read this thread on the forum : Link removed/forums/f...=2359&highlight_key=y

it's also talk about transformers tertiary winding..

some paper referred by the TS and responder are :

1. report dated July 9, 2002 by PS Technologies Inc. entitled "Loss of Electric Energy on the Colombian Electric System"
2. Star/Star transformer without Delta Tertiary By T Smith published in the Electrical Review 21July 1961.
3. The performance of Star Star transformer by Professor R. O. Kapp published in the IEE Journal Jan 1955.

i have found the 3rd paper.. but the second one it's difficult to find.. anybody can suggest me where to get the electrical review 21 July 1961?
 15 June 2010 10:43 AM
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westonpa

Posts: 1771
Joined: 10 October 2007

The tertiary winding is installed for several main reasons and thus you just need to prove that the transformer is being used for applications which do not require it, i.e., those things the winding seeks to solve are not an issue for that particular application. Thus you really need to look at, and understand, the applications. Alternatively you need to prove that there is another method for solving the application problems which does not require the tertiary winding.

However do appreciate that if you were for example producing 5000 transformers and 4750 were for applications which did require the tertiary winding and 250 were for applications which did not require it albeit it did not cause a problem for those applications by being fitted, then it would likely be uneconomical to change the production processes for such a short run.

Suggest you get this book:

J & P Transformer Book (Thirteenth Edition)

You can either view part of it via Google books......use IE and Firefox browsers because they allow you to access different pages and thus you get to view more. Alternatively you can access it via Science Direct at:

http://www.sciencedirect.com/s...ce/book/9780750681643

Either you would need to join or check if your university/college has educational access. Most UK universities do and thus UK students can access the book at no cost to themselves.

Regards.
 16 June 2010 08:25 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

Originally posted by: westonpa

The tertiary winding is installed for several main reasons and thus you just need to prove that the transformer is being used for applications which do not require it, i.e., those things the winding seeks to solve are not an issue for that particular application. Thus you really need to look at, and understand, the applications. Alternatively you need to prove that there is another method for solving the application problems which does not require the tertiary winding.



However do appreciate that if you were for example producing 5000 transformers and 4750 were for applications which did require the tertiary winding and 250 were for applications which did not require it albeit it did not cause a problem for those applications by being fitted, then it would likely be uneconomical to change the production processes for such a short run.



Suggest you get this book:



J & P Transformer Book (Thirteenth Edition)



You can either view part of it via Google books......use IE and Firefox browsers because they allow you to access different pages and thus you get to view more. Alternatively you can access it via Science Direct at:



Link removed/s...k/9780750681643



Either you would need to join or check if your university/college has educational access. Most UK universities do and thus UK students can access the book at no cost to themselves.



Regards.


Thanks for your reply, i really appreciate it.

For the J&P transformers hand books, i already have the 12th edition and i hope there is no major different between the 12th and the 13th one. I haven't finish the books yet, especially the 6th chapter that explain the operation and maintenance of the transformers. I'll read and try to understand it soon..

as far as i know, some main reason to provide the tertiary winding on a transformers are:
1. Improve voltage regulation if there are unbalanced line-to-ground loads
2. Protection of the system and transformers from excessive third harmonic voltages.
3. Facilitate the relaying of system faults

and from further study and discussion, i've some answer for those reason..
>for the first reason, because the transmission line do not supply any load directly, i assume there is no unbalanced line-to-ground loads.
>for the second reason, in those paper i've mentioned above, they had tested the harmonic on transformers without tertiary winding and the result shows that the 3rd harmonic voltage are less than 3%. So if we can accept those small ripple on the transmission line (the 150kV line do not directly supplying any load, and the distribution transformers always have the tertiary winding) we don't need the tertiary winding.
>for the third reason, my mentors say there is a method for detecting the earth fault current without tertiary winding. but i'm forget the method's name. It use the tank as a ground and the earth fault current detector is installed between the tank and earth (the tank is act as a tertiary winding)

please let me know if i have wrong perception.. by the way, is there any weakness of Star-Star Transformers?

and please share the common design for inter bus transformers in your country for my references..
 16 June 2010 05:50 PM
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westonpa

Posts: 1771
Joined: 10 October 2007

Your perception is ok and the book will also help you with respect to common designs.

Regards.
 18 June 2010 04:09 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

Thanks,

will you share the common design for transformers in your country? does it have the tertiary winding or not?

regards,
 18 June 2010 11:18 AM
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westonpa

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Joined: 10 October 2007

 29 June 2010 12:17 PM
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jafarpour

Posts: 198
Joined: 14 August 2005

1- Regarding high voltage protection concerning, please note dangerous resonance or Ferro resonance is subjected to voltage harmonics not current harmonics. The third- harmonic voltage in wye - wye connection without star grounding (regardless of additional delta connection) is possible strongly; because there are not any path for flow of third-harmonic currents, indeed If the transformer neutral is not grounded, the third-harmonic voltage at the neutral point will be additive for all three phases, and the neutral voltage will oscillate around the zero point at three times the system frequency. Third harmonic voltages are also created on the lines, which can subject the power system to dangerous over voltages due to resonance with the line capacitance. This is particularly true for shell-type three phase transformers, five-limb core-type transformers, and three-phase banks of single-phase transformers.

2-If the transformer and source neutrals are grounded, third harmonic currents will flow that can create interference in telephone circuits which can be trapped by delta connection winding. For any three-phase connection of three-limb core-form transformers, the impedance to third harmonic flux is relatively high on account of the magnetic coupling between the three phases, resulting in a more stabilized neutral voltage. A delta tertiary winding can be added on wye - wye transformers to provide a path for third-harmonic and zero-sequence currents and to stabilize the neutral voltage and also trapping of third-harmonic which can create interference in communication systems.

3- Generally delta-connected tertiary winding is provided to reduce third-harmonic voltages (refer to article 1 above), to permit the transformation of unbalanced three-phase loads, and to enable the use of supply-station auxiliary load or power-factor improvement equipment. The tertiary winding must be designed to accept all of these external loads as well as the severe short-circuit currents and forces associated with three phase faults on its own terminals or single line-to-ground faults on either the primary or secondary terminals.

4- In my country (IRAN) the delta-star connection is normal practice for interconnection.


--------------------------------
Creative thinking is breezy, Then think about your surrounding things and other thought products. http://electrical-riddles.com
 30 June 2010 09:31 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

Originally posted by: jafarpour

1- Regarding high voltage protection concerning, please note dangerous resonance or Ferro resonance is subjected to voltage harmonics not current harmonics. The third- harmonic voltage in wye - wye connection without star grounding (regardless of additional delta connection) is possible strongly; because there are not any path for flow of third-harmonic currents, indeed If the transformer neutral is not grounded, the third-harmonic voltage at the neutral point will be additive for all three phases, and the neutral voltage will oscillate around the zero point at three times the system frequency. Third harmonic voltages are also created on the lines, which can subject the power system to dangerous over voltages due to resonance with the line capacitance. This is particularly true for shell-type three phase transformers, five-limb core-type transformers, and three-phase banks of single-phase transformers.



2-If the transformer and source neutrals are grounded, third harmonic currents will flow that can create interference in telephone circuits which can be trapped by delta connection winding. For any three-phase connection of three-limb core-form transformers, the impedance to third harmonic flux is relatively high on account of the magnetic coupling between the three phases, resulting in a more stabilized neutral voltage. A delta tertiary winding can be added on wye - wye transformers to provide a path for third-harmonic and zero-sequence currents and to stabilize the neutral voltage and also trapping of third-harmonic which can create interference in communication systems.



3- Generally delta-connected tertiary winding is provided to reduce third-harmonic voltages (refer to article 1 above), to permit the transformation of unbalanced three-phase loads, and to enable the use of supply-station auxiliary load or power-factor improvement equipment. The tertiary winding must be designed to accept all of these external loads as well as the severe short-circuit currents and forces associated with three phase faults on its own terminals or single line-to-ground faults on either the primary or secondary terminals.



4- In my country (IRAN) the delta-star connection is normal practice for interconnection.





--------------------------------

Creative thinking is breezy, Then think about your surrounding things and other thought products. Link removed


Thanks for your response, in the transformers that i study has grounded neutral on the both side . How can i know whether the third harmonic currents will interference in telephone or radio equipment? are the effect very intolerable?

from those reason that you mention in #3, maybe the most worrying problem are the third harmonic voltage. Because the tertiary are not subject to supply any load at the site and i guess there is no unbalance load in that transformers voltage level (275/150kV). and we also consider the protection problem for the tertiary because sometimes the fault are happen in the tertiary bus or the tertiary cannot hold up the fault current occurred until it's blow up. Any comment for the protection issues?

4. what the voltage level that your delta-star transformers operating? and what the main consideration that you taken to choose the star-delta configuration?

Regards.
 06 July 2010 04:25 AM
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adityokusumo

Posts: 8
Joined: 11 June 2010

please also take a look to my other topic that still related to this topic :
inter bus transformer
IET » Energy » Inter Bus Transformers

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