Tap changing? 1

[cctdiag]

Normally we tap change our 11000/415v transformers isolated
(as recommended), however due to a high authority supply voltage we had to do a change on a transformer energised but with no load.(load supported via generators) Can anybody advise if this could of had a detrimental affect on the transformer?

thanks

 

[jwerthman]

You are quite lucky that the tap changer didn't fail catastrophically. No load tap changers should never be operated with voltage applied. The contacts are not made to interrupt any current - even the no-load magnetizing current of the transformer. Since it didn't fail, you probably did no damage, but I would strongly recommend against doing that again. You might not be so lucky the next time.

 

[nbucska]

There is a Russian patent for this : they add a relative long stock of E & I cores (i.e. closed core with two parallel channels. The transformer taps are placed altarnatingly in one or the other channel. The inductance
of a full turn is in series with the short circuit between
adjacent taps during switching. <nbucska@pcperipherals.com>

 

[electricpete]

jwerthman is definitely correct.

The term &quot;no-load tapchanger&quot; is a little misleading... perhaps might be misunderstood to mean that the only requirement for changing the tap is removing the load... this is definitely NOT the case.

 

[cctdiag]

Gents

Many thanks for the confirmation, i have passed this onto the the person who carried out the change. He did mention the Transformer did not like the switching action by the noise it made. I think the comment 'catastrophic' has hit home and a lesson been learned, he will not do this again.

Thanks

 

[busbar]

cct — Seems like an apt description of a classic &quot;near miss.&quot; Some sounds leave magnificently sobering impressions.