Type B voltage regulator range of -8.6% 1

[bacon4life]

Why do ANSI type B voltage regulators have a range of +10% to -8.6% per slide 15 of Regulators-D.Wareham.pdf when the nameplate states +10%/-10%? I can see why they would have a range of +11.1% to -9.1% if the series winding is 10%. I cannot figure out where the 8.6% comes from.

 

[argotier]

Very interesting question, it got me thinking for the past two days.

ANSI world is always a strange world for me and I'm not really experienced with voltage regulators, but lacking other answers I will try a theoretical approach.

First of all, standards recognize that Type B regulators have indeed a lower range for the lower side of the regulation and specify that the 10% amount for the raise side must be the nominal value. I'm checking C57.15-2009 / IEC 60076-21-2011, I believe there is a newer version but I don't have it. I don't think this in particular would change.

Now, as you said, if the series winding represents the 10% the range would be +11.1% to -9.1%.

But, if we modify the series winding to give the nominal regulation for the raise side (10%) as the standard specifies, you end up with -8.3% in the lower side. You said -8.6% but the slide says -8.3%. If 8.6% is the correct value, then nothing I'm putting here is valid.

Here a couple of examples to illustrate that (there are some things in grey just for my curiosity, disregard them):

With 10% series winding:

Spoiler

With modified series winding:

Spoiler

I'm not very satisfied with my answer to your problem but perhaps it will trigger better answers. On my end I'm still with some doubts about the whole thing (ANSI world remains a strange place).

Hope it helps.

 

[bacon4life]

Oh, your explanation make sense. I wonder if we can revise the ANSI standard to require the nameplate to state +10%/-8.3% instead of +10%/-10%.

Sorry for the confusion, the field measured value on the extreme lower tap was -8.6%. I assume the regulator actually matches the value of 8.3% posted in the slides.