- Thread starter philhanna@comcast.net
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- wire pulling grunt

That is boosted load rating

basically 14 v x 93 A

edit not sure you have the right transformer

Group 2 3 phase 208/222 multiple choices based on kva

http://www.temcoindustrialpower.com...?p=buck_boost_transformer_selection_guide#III

http://attachments.temcoindustrialpower.com/Wiring_diagram/buckboost_wiring_8.pdf

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- Location
- Placerville, CA, USA

It is perfectly reasonable to connect the neutral side of each transformer with #12 wire, since no direct load current will be flowing through that wire, only the primary current corresponding to the 93A on the secondary side.

I would expect one terminal of the autotransformer to be directly connected to the phase conductor though, and that will carry all of the load current plus some of the primary current.

What is the input? Wye or delta

same output?

load kva?

you want to step up 208 to 220-230 range?

Delta: All the loads are three phase motor loads and they are rated at 220v. My input is three phase delta 208v

There is no neutral as all the loads are motors. here is the wiring diagram for the two 1.5 kva transformers

It is perfectly reasonable to connect the neutral side of each transformer with #12 wire, since no direct load current will be flowing through that wire, only the primary current corresponding to the 93A on the secondary side.

I would expect one terminal of the autotransformer to be directly connected to the phase conductor though, and that will carry all of the load current plus some of the primary current.

http://attachments.temcoindustrialpower.com/Wiring_diagram/buckboost_wiring_8.pdf

The transformer size would normally bother me, but the literature states that it only handles a small portion of the load current. Unfortunately the wiring diagram looks as if two of the x windings on each transformer handle the full load current.That is boosted load rating

basically 14 v x 93 A

edit not sure you have the right transformer

Group 2 3 phase 208/222 multiple choices based on kva

http://www.temcoindustrialpower.com...?p=buck_boost_transformer_selection_guide#III

http://attachments.temcoindustrialpower.com/Wiring_diagram/buckboost_wiring_8.pdf

I was wrongThe transformer size would normally bother me, but the literature states that it only handles a small portion of the load current. Unfortunately the wiring diagram looks as if two of the x windings on each transformer handle the full load current.

I was thinking it was an autotransformer type

I believe yours should be rated fr the full load kva ~ 35 kva or so

I would go for 40

edit:

OK I see now

your 1.5 rating is not from the chart ( on the chart it is 36)

when you click the link for the associated transformer the data shert comes up

1.5 kva http://www.temcoindustrialpower.com/products/Transformers_-_General/FT0167.html

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You need to have a 222V, 3-phase from 208V, 3-phase?

Connect the two transformers in open-delta. The common winding should be wired 240V (series 120V windings) while the series windings connected 16V (parallel 16V).

there is a link for connection details http://attachments.temcoindustrialpower.com/Wiring_diagram/FP-Buck-Boost.pdf

Only the wires that carry the differential are #12

1500/208 or 7 A

Your winding wiring diagram looks like the one I have, but I don't understand how the x windings of the 1.5 kva transformers can carry 93 amps. What am I missing?You need to have a 222V, 3-phase from 208V, 3-phase?

Connect the two transformers in open-delta. The common winding should be wired 240V (series 120V windings) while the series windings connected 16V (parallel 16V).

View attachment 15134

- Location
- Placerville, CA, USA

You are missing that it is 93A at only 16V.Your winding wiring diagram looks like the one I have, but I don't understand how the x windings of the 1.5 kva transformers can carry 93 amps. What am I missing?

If I have ten 12V batteries in series delivering 10A, each battery only supplies 120W.

without getting into phasors and suchYour winding wiring diagram looks like the one I have, but I don't understand how the x windings of the 1.5 kva transformers can carry 93 amps. What am I missing?

there are 2 coils in parallel

each carry 1/2 or 47 A

each coil contributes 14 V

2 x 14 x 47 ~ 1.3 kva

rated at 16 V per the data sheet

close to 1.5 kva

93A (technically 1500VA/16V = 93.75A) is the rated full-load current of your 16V secondary winding (2 windings in parallel, each 16V winding capable of providing 93.75/2 = 46.875A).Your winding wiring diagram looks like the one I have, but I don't understand how the x windings of the 1.5 kva transformers can carry 93 amps. What am I missing?

Take note that the paralleled 16V-windings are connected in series with the common winding (2-120V windings wired in series)! That would mean that the secondary current will have to be limited to the secondary current-carrying capacity of 93A. So the line current of your 222V output should be this value = 93A!

If you might wonder, your kVA capacity is not 63kVA, as you posted! Why? It's because 93 x 1.732 x 222 = 36,048 VA ~36kVA! You should have chosen a 2 x 3kVA boost transformer.

In their selection guide93A (technically 1500VA/16V = 93.75A) is the rated full-load current of your 16V secondary winding (2 windings in parallel, each 16V winding capable of providing 93.75/2 = 46.875A).

Take note that the paralleled 16V-windings are connected in series with the common winding (2-120V windings wired in series)! That would mean that the secondary current will have to be limited to the secondary current-carrying capacity of 93A. So the line current of your 222V output should be this value = 93A!

If you might wonder, your kVA capacity is not 63kVA, as you posted! Why? It's because 93 x 1.732 x 222 = 36,048 VA ~36kVA! You should have chosen a 2 x 3kVA boost transformer.

208-222

36 kva load

2 x 1.5 kva xfmrs are selected

Does the phasor relationship make the 93 amps appear to be less as it passes through the transformer? It seems strange to connect a #2 wire to 2#12 wires on the primary and 2# 10 wires to a #2 on the secondary.without getting into phasors and such

there are 2 coils in parallel

each carry 1/2 or 47 A

each coil contributes 14 V

2 x 14 x 47 ~ 1.3 kva

rated at 16 V per the data sheet

close to 1.5 kva

NopeDoes the phasor relationship make the 93 amps appear to be less as it passes through the transformer? It seems strange to connect a #2 wire to 2#12 wires on the primary and 2# 10 wires to a #2 on the secondary.

pretty much the 93 or 45 each

the make #12 rated for >55A for applications like this

Sorry I'm a bit late to this discussion, but let me jump in here...Does the phasor relationship make the 93 amps appear to be less as it passes through the transformer? It seems strange to connect a #2 wire to 2#12 wires on the primary and 2# 10 wires to a #2 on the secondary.

Where are you getting the idea there are #12 and #10 wires involved here?

Assuming a full load of ~94A is flowing through the secondaries, the equivalent is 94A*222V/208V=105A on the 208V primary conductors at 208V. Under the NEC, the conductors must be rated for this current, basically. However, we're talking motor loads, so there's a possibility the conductor ampacities can be lower. Missing details. How many motors and the ratings of each? Any short-circuit and ground-fault protection or controller(s) after the transformer?

While these are constructed as isolation transformers, they are being connected as autotransformers, so the autotransformer rules apply...

- Location
- Massachusetts

I am fairly certain the OP is talking about the factory installed leads on the buck boost transformers.Where are you getting the idea there are #12 and #10 wires involved here?