reactor for SVC

[Pafi]

Hello!
I wonder if someone on the forum knows the role of the second much smaller reactor in series connection with each branch of TCR reactor. The TCR reactor is made up from 3 air core reactors - one for each phase. Each phase reactor is devided into 2 equal halves but - at least for this particular SVC - there is also a small air core reactor in series with each main phase TCR reactor. The value of TCR reactor is 2x25mH and this small reactor is only 0.4mH, it is smaller than the tolerance of main TCR reactor. I cannot see the reason for it?
Problem is that this customer replaced one phase of TCR reactor with a reactor manufactured by an other manufacturer (other than the original manufacturer of TCR) and after that began to have problems with the thyristors groups - burned thyristors, etc. Wonder what problems could occur ?

Thanks for any oppinion.
Pafi

 

[Skogsgurra]

That sounds like a commutation reactor that is connected in series with the thyristors. Its purpose is to limit the di/dt so that the thyristors aren't locally overloaded (it takes some time for the conduction zone to spread across the Silicon tablet).

Have those reactors been removed? No wonder the thyristors burn out.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[mikekilroy]

One of my favorite sayings is "Usually the last thing we did is the cause of a new problem."

You say:
- Each phase reactor is devided into 2 equal halves
- there is also a small air core reactor in series with each main phase TCR reactor.
- The value of TCR reactor is 2x25mH
- this small reactor is only 0.4mH
- Problem is that this customer replaced one phase of TCR reactor with a reactor manufactured by an other manufacturer and after that began to have problems

hmmmm.... see a relationship here?

Posting a schematic of this wired up would help us understand better.

We used to use center tapped inductors on SCR drive outputs, and folks easily bought wrong inductance replacements not understanding that L goes up by the square of the turns. example: "9mh CT" inductor on common core is equiv to 2pc of 3mh individual ones in series. Is your replacement inductor maybe wrong inductance? Reducing the L would likely lead to such problems.

http://www.KilroyWasHere<dot>com

 

[Pafi]

Thanks for your answers!

The replacement reactor had exactly the same parameters - in terms of L. Trench received the technical file of the original. It is not, obvious, exactly the same, it is heating a little more, but the dimensions have been very close. But Trench sent the results of tests and the reactor is in tolerance. And the customer replaced only this main TCR reactor, the smaller one remained in place. Don't think they made any mistake in wiring, they have experience as they replaced one time this reactor with an original one (made by Nokian), after 2 years of erection - reactor burned exactly after the warranty period. The reason they didn't want to buy an other from Nokian is that the replaced reactor burned again after 2 years, this time inside the warranty, they received a new one free of charge but the confidence, of course, is gone. And the new one from Trench should be a spare part, just in case. They put it to test, after one week had problems with thyristors and the fear was that it is something wrong with the reactor.
What I don't understand is what is the role of the small reactor because in in series connection with one half of the main TCR reactor and it's value is so small comparing with the value of TCR reactor.
Also, the 3 TCR reactors work independently per phase, how much would matter a small difference in L value so much? That is, 1-2% difference in L value/ per phase?
I shall give you in attachment the copy of electrical schematic and a picture from Alsthom (Nokian) where such a small reactor can be seen, tomorrow, when I go to work.

Thanks again!
Pafi

 

[Pafi]

I have attached 2 links, one with the schematic and the second it is a page from Alstom document where at the bottom there is a picture where the main TCR reactor(made from 2 halves) and the much smaller series reactor can be seen.

thanks!
Pafi

 

[Pafi]

And the second link

 

[mikekilroy]

Any chance you installed the replacement coil backwards polarity? Being as close as they are in the picture, seems that the magnetic field of each would interact since they are not turned 90 degrees from each other. If one is backwards maybe some of its L is being cancelled out by the other magnetic field? Far out thought but worth asking?

http://www.KilroyWasHere<dot>com