Tap Changing Transformer S.C Voltage

"...I am surprised to see this. What is the reason if so?..."

1. Why are you surprised to see this?

2. What is the reason why you are surprised?

Perhaps you should tell us what your issue is with the original German, we cannot read your mind (there are other forums for that).

Be simple and brief.

reply 1: I read for the first time as I implied above the relation between voltage levels of a tap change levels and short circuit voltage

reply 2: the same words mot-a-mot as the ones written above...

by the way, I had explained what these lines narrate in my original post. I guess you did not understand what I wrote.

Do you expect us members of this forum to understand French , German, Russian, Chinese , or Hindi? Most of us understand English only. So we expect you to explain your question in English please( if you do not mind) otherwise we cannot reply.

Do you know what the %Z means or how this value is determined?

exactly know. Just can not see why we must select the magnitude of the levels of the tap changing system since we change it in no-load condition. Even in under load condition it would be not reasonable to make this design since I can not see a relation between these two issue. (s.c voltage & tap levels)

Your translation from the German, "... that the level difference in a tap-changing transformer is equal to the short circuit voltage.."

Google's translation, "...May only take place in the off state, the switchover. The voltage differences, eg 20800 V-20000 V = 800 V, corresponding to the impedance voltage of the three-phase transformer..."

Don't know how old the book is, but I suspect it's a typo, the missing word is "unterschied" or "differenz", difference in English; i.e., "...corresponding to the difference in the impedance voltages between taps ..." If it's a modern book contact the author and report back what he said.

I agree with RAMConsult. This isn't talking about the transformer impedance, but about the difference in voltage between the taps of the no-load tap changer. It would help if you provided a bit more of the quote, to show what is said next. From what I interpret (my German is limted and rusty, but my NLTC knowledge is sufficient), this is a warning not to change the NLTC taps while energized. Of course, you do know why this is so, correct??? The contacts of the NLTC are not designed and constructed to make and break the load current of the transformer.

I think your reference to the transformer impedance is throwing you off. When I did a Google translation on this, the terminology that comes out is "short-circuit voltage." There does not appear to be a direct reference to the impedance here. The danger with switching the NLTC under load is that the arc drawn would first be due to the load current across the opening contacts of one tap. Then, if the switching action continued, this could escalate to a turn-to-turn short between taps, at the associated voltage difference between taps. Not a pretty thing.

excuse me, Forgive me if I am wrong but my german is well enough. This passage states that the difference between primary voltage tap-changing level magnitude = 800 volt is equal to the short circuit voltage of the transformer. This statement is very very strange to me:)

why people are sticking to the "german part" of the issue :)

the difference between steps in tap voltages is 5% because that is what purchasers of tap-changing transformers want and specifiy. once a voltage is 5% too low, we want to be able to increase it to nominal. we would specify smaller steps if useful and cost effective. at the consumer level, plus or minus 10% is usually the maximum acceptable voltage range, so at the HV level, plus or minus 5% easily keeps consumers voltage within that range.