Polarity of tranformers

Here's something I showed a young ape last night, polarity.

It was somewhere around 1980 or so a standard was set to standardize the polarity of transformers.

below 8660 volts AND 200kva below is an additive polarity
above 8660 volts is a subtractive polarity

So a 7620 225kva transformer is a subtractive polarity and a 14400 15kva is a subtractive polarity.

left to right X3 X2 X1 - additive
right to left X1 X2 X3 - subtractive

Old transformers like 1950's it could either be subtractive or additive, only true way to tell in such case (don't trust the name plate) is to run a test. I'll have to bust out a book on how to do it, involves putting voltage and running a jumper on the bushings. Get to that later.

Anyways polarity because important to know when building banks or paralleling transformers. You can in a sense change the polarity when working with 2 high side bushing transformers, comes in handy at times when building open delta banks running your tie buss jumpers. More on that later.

rcdallas wrote:Here's something I showed a young ape last night, polarity.

It was somewhere around 1980 or so a standard was set to standardize the polarity of transformers.

below 8660 volts AND 200kva below is an additive polarity
above 8660 volts is a subtractive polarity

So a 7620 225kva transformer is a subtractive polarity and a 14400 15kva is a subtractive polarity.

left to right X3 X2 X1 - additive
right to left X1 X2 X3 - subtractive

Old transformers like 1950's it could either be subtractive or additive, only true way to tell in such case (don't trust the name plate) is to run a test. I'll have to bust out a book on how to do it, involves putting voltage and running a jumper on the bushings. Get to that later.

Anyways polarity because important to know when building banks or paralleling transformers. You can in a sense change the polarity when working with 2 high side bushing transformers, comes in handy at times when building open delta banks running your tie buss jumpers. More on that later.

Is this true of padmounts? Or maybe even those individual three phase pole mounted trnsfrmrs?

Ya know I've heard that before; someone saying padmounts are subtractive. Dammit I'm just going to have to see it for myself. Never have seen a brand new 3Ø overhead unipot. Just a handful of them out in the field. Matter of fact I came across my first open-wye open delta unipot just 2 weeks ago. Old sumbiitch.

I'd get a pic but someone decided it's not economically freezable to store a padmount or two in our headquarters anymore (a long with a few other things!)?? I'll have to find one out in the area!

Now you hafta follow through!

Looking at some specifications on line. According to this all transformers in Mexico are subtractive and all transformers in Canada are additive. Not all the detailed things to remember as American transformers.

wtdoor67 wrote:Looking at some specifications on line. According to this all transformers in Mexico are subtractive and all transformers in Canada are additive. Not all the detailed things to remember as American transformers.

Tequila, Corona, and now a simpler standard for transformers! Man Mexico's gonna surpass us soon!!

Mike, I came across this 25kva and it's additive polarity. It's not listed where I would think it'd be on the name plate up toward the top portion...it's listed just below the schematic of the coils.

Though I suppose really it doesn't matter as every padmount I've come across always had the secondary labeled. X1,X2,X3 or maybe X0,X1,X,2,X3 or even X1,X2,X3,X4. Couple of places you might see where two of them are banked together. I think it'd be cool to bank 6 of them together

Now one other thing I learned awhile back; it's not exactly industry standard but manufactures were making an effort to differentiate underground and overhead just by the way the voltages are listed on the name plate. 7200/12470 would be overhead and 12470/7200 is underground.

rcdallas wrote:Mike, I came across this 25kva and it's additive polarity. It's not listed where I would think it'd be on the name plate up toward the top portion...it's listed just below the schematic of the coils.

Though I suppose really it doesn't matter as every padmount I've come across always had the secondary labeled. X1,X2,X3 or maybe X0,X1,X,2,X3 or even X1,X2,X3,X4. Couple of places you might see where two of them are banked together. I think it'd be cool to bank 6 of them together

Now one other thing I learned awhile back; it's not exactly industry standard but manufactures were making an effort to differentiate underground and overhead just by the way the voltages are listed on the name plate. 7200/12470 would be overhead and 12470/7200 is underground.

The order of the voltage rating numbers indicate the number of bushings of the transformer. If for example it says 7200/12470, then the pot has 2 primary bushings. If the numbers are in the order of 12470/7200, then it has only one primary bushing. This applies to single phase pots, I don't recall the rule for 3 phase pots.

watertightdoor67 - Ok Cowboy wrote:
The order of the voltage rating numbers indicate the number of bushings of the transformer. If for example it says 7200/12470, then the pot has 2 primary bushings. If the numbers are in the order of 12470/7200, then it has only one primary bushing. This applies to single phase pots, I don't recall the rule for 3 phase pots.

When I went to SLTC; if I reckon the order defined underground vs overhead and when I went through the CAPS classes for my apeship I'd bet my poker chips that was brought up then too.

BUT

Who knows; I'll keep an eye out for what your saying. Next time I get around a transformer dock I'll have a gander. Maybe different manufacturers do different things.