Why Scott T

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roger

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A facility that we contract to called and had a machine with a 35KVA Scott T 3 ? - 2 ? 240/90V four wire and they needed a replacement. The machine was built in the 70's and they had contacted the manufacturer who was wanting two prices for a new transformer, we found them one for half the price.

The 90 volt 2 ? output is 17.5 KW each and feeds heating elements.

My question is, what would have been the advantage of the Scott T 3 ? / 2 ? verses say a Delta / Delta transformer wound for the 90 volt output voltage?


Roger
 

jim dungar

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Wisconsin
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PE (Retired) - Power Systems
A delta-delta is a three phase to three pase conversison.
A Scott-T is a three phase to two phase conversion.

The configuration of the loads would need to be changed to use something other than two phase.
 

kwired

Electron manager
Location
NE Nebraska
A facility that we contract to called and had a machine with a 35KVA Scott T 3 ? - 2 ? 240/90V four wire and they needed a replacement. The machine was built in the 70's and they had contacted the manufacturer who was wanting two prices for a new transformer, we found them one for half the price.

The 90 volt 2 ? output is 17.5 KW each and feeds heating elements.

My question is, what would have been the advantage of the Scott T 3 ? / 2 ? verses say a Delta / Delta transformer wound for the 90 volt output voltage?


Roger

If there are no two phase motors, you got me, the heaters will not care if it is single, two or three phase applied.
 

roger

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A delta-delta is a three phase to three pase conversison.
A Scott-T is a three phase to two phase conversion.

The configuration of the loads would need to be changed to use something other than two phase.
Jim, that's the kicker, I don't know why they couldn't build the machine with elements sized and configured for a three phase (more common) system but, you may have the reason.

Roger
 

ronaldrc

Senior Member
Location
Tennessee
Hello Roger

The scott T gives them a balanced load on the Electrical system across all three phases
as opposed to an unbalanced load with two separate Transformers or a Three phase transformer
using two phase of the three.

That would be the only advantage I see.


Ronald
 

Jraef

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San Francisco Bay Area, CA, USA
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Hello Roger

The scott T gives them a balanced load on the Electrical system across all three phases
as opposed to an unbalanced load with two separate Transformers or a Three phase transformer
using two phase of the three.

That would be the only advantage I see.


Ronald
Same thing I was thinking, but seems to me they would have to be some really powerful heater elements to make that worth it. 15.5kW at 90V 1 phase would be around 194A. Hardly worth it if you ask me, but maybe the original intent was for this thing to be connected to a small supply where 194A on only 2 of 3 phases might cause a severe imbalance. Spread it across a 2 phase setup and it becomes 138A per phase on all 3 (plus the transformer losses), but balanced.
 

steve66

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Illinois
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Engineer
Is this "machine" a simple motor, or something more complex?

If its something more complex, maybe they had a reason they wanted the two phases with the 90 deg. phase difference.
 

roger

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Fl
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Is this "machine" a simple motor, or something more complex?

If its something more complex, maybe they had a reason they wanted the two phases with the 90 deg. phase difference.
Steve, I think Jraef nailed. It is basically a big kiln or oven with no moving parts just heating elements. It just seems they could have used few more smaller elements with a three phase configuration and have still balanced everything.

Hello Ronald.


Roger
 

Jraef

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Steve, I think Jraef nailed. It is basically a big kiln or oven with no moving parts just heating elements. It just seems they could have used few more smaller elements with a three phase configuration and have still balanced everything.

Hello Ronald.


Roger
Sometimes if the elements on the kiln are embedded and hard to get to, they can use the same design as it is. For single phase supplies they just connect directly to the erlements, then use the Scott-T xfmr if it is a 3 phase supply and needs balancing, but either way they don't have to have two different heater element configurations inside the kiln.
 

roger

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Fl
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Retired Electrician
Sometimes if the elements on the kiln are embedded and hard to get to, they can use the same design as it is. For single phase supplies they just connect directly to the erlements, then use the Scott-T xfmr if it is a 3 phase supply and needs balancing, but either way they don't have to have two different heater element configurations inside the kiln.
And that makes sense.

Roger
 
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