Adjusting transformer tap changers

[hallmg]

Hi,

My query is:-

There are two transformers feeding a distibution board.

I wish to increase the voltage slightly by adjusting the tap settings on the transformers.

How could this be accomplished? I assume you cannot have two transformers feeding a common board with different tap settings?

Any suggestions would be very much appreciated.

Regards,
Hallmg.

 

[waross]

When you change one tap changer the voltage difference will be partly absorbed by a circulating current and partly by a small shift in load sharing.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

For the amount of unbalance loading etc please refer to IEC 60076-8.Usually OLTC will be configured to operate one as master and other as follower so that tap changing will be initiated together.

 

[Mbrooke]

Not sure if these will help, but its a try.

https://www.beckwithelectric.com/docs/app-notes/appn-13.pdf

https://beckwithelectric.com/docs/tech-papers/advxpara.pdf

https://www.google.com/url?sa=t&rct...rFHXhdzkxr5EDWe55uoRiQ&bvm=bv.149760088,d.cGc

 

[crshears]

Hmmm...

When I read the OP I took it to be referring to two transformers in parallel with multiple taps on their headboards, and thus took the question to be asking whether it is acceptable to permanently wire two transformers together with a one-tap spread between them.

Then Bill answered as if this question was in regard to two transformers with ULTCs operating in parallel, which made me wonder if I had misunderstood the OP...and the following responses accorded with Bill's...

Either way, Bill is spot-on with his response.

As to tap spreads between banks with ULTC's, in my utility we often enough end up running with significant to unbelievable tap spreads between such banks because of the spread in place when one of them breaks; outages to repair such equipment can sometimes be difficult to arrange due to loadings, etc., and we end up having to unwillingly live with these nasty spreads for some time, hoping no contingency occurs which will mean having to leave customers interrupted due to not being able to supply voltage within the acceptable range...and as the old-time operators are teaching the up and coming controllers, "having no voltage at all is better than having low voltage."

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Andiri812]

The circulating currents between 2 or more paralleled trafos on different taps tend to cause additional heat build up over and above that of normal loading and effectively reduces the usable capacity of the trafo.

We have a substation with 4 x 2,5MVA 30//6,6kV paralleled trafos of which 1 is 2 taps above the rest. A little testing proved that 1 trafo seems to be connected differently at its tapchanger or the handle & indicator were incorrectly installed. When each trafo was energised seperatley and the output voltage measured 3 were the same at the same tap and the 4th only produced the same voltage at 2 taps higher. We tested them all again on the other taps too and the relationship stayed the same.The current on each transformer stays the same when loaded individually and when paralleled the secondary loads are equal... been opperating like that for over 20 years and nothing funny has stuck its head out yet.