# Step up and step down transformers



## backstay (Feb 3, 2011)

The last step up trany I ordered from my SH was really a step down (480/240) I needed to go from 240 volt 3 phase to 480 volt 3 phase. It worked fine, I don't know if there is a difference.


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## sbrn33 (Mar 15, 2007)

I have always used the same tranny for either one. I do think they make a special one for step up but probably just a different label.


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## frenchelectrican (Mar 15, 2007)

Jimmymiranda said:


> Can anyone explain the difference between a step up and a step down transformer?


there is not much differnce between the step up or step down transfomer.

basically a primary winding ( coil ) turns is smaller than the secondary winding turn so it is a step up while the step down is reversed so primary coils are more than secondary coil.

this part is based on standard AC voltage but try to run that in DC it will NOT work at all.

Look back in alot of threads there are some subject been discussed before so you will find some of the answer there.


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## dtmartin408 (Nov 11, 2012)

Pretty much the same thing but you have to be careful with the capacity of the windings.


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## telsa (May 22, 2015)

To the OP:

You MUST be trolling us.

There can NEVER be any difference between a step-up and a step-down transformer.

See: Faraday, Clerk Maxwell, Tesla, and all the rest.

EM fields don't know which way they're going.

Our ENTIRE industry depends upon this.

Primary power is produced at MEDIUM voltages ... typically less than 10,000 volts. ( but not always )

Then the EMF is stepped up -- a LOT -- so that it, power, can be transmitted long distances. The rule of thumb is that 1,000 volts are needed for each mile.

So, if you want to send Big EMF 345 miles... you design for 345,000 Volts.

Such Long Distance distribution voltages are too much for ordinary switching gear.

So, Pocos drop the voltage down to ~ 35,000VAC to 12,000VAC for PRIMARY distribution... Typically as a Loop Circuit. ( aka Ring Circuit ) Each transformer is double-fed. This scheme increases reliability.

Only at the last leg is this voltage dropped down to utilization voltages:

208Y120
480Y277
240/120 single phase.

This is done at the 'pots', 'pad mounts' that you see everywhere across town.

The laws of electricity don't give a DANG whether you're going up voltage//reduced amps or down voltage and increased amps.

For obvious reasons, practicing electricians almost NEVER deal with increasing voltages.

For us, it's down voltage, all the way.

( Neon signage being the notable exception. We feed it 120VAC and see 35,000VAC coming out the other side. So many volts,... so few amps, though. )


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## micromind (Aug 11, 2007)

The vast majority of transformers can be used either way so there is no step-up or step-down. 

Some small transformers (less than 1KVA) however, have a turns ratio that will yield a slightly higher than nameplate voltage with no load. This is because they will have a certain amount of voltage drop when loaded. 

These units can be used either way but you'll get odd voltages if reverse fed. 

I've seen a few substation size transformers (more than 15,000KVA) that had tap changers and could not be reverse fed. This is because the tap changer can't handle the inrush if the low side is the primary. These models had fairly low Impedance compared to the ones that can be reverse fed.


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## MechanicalDVR (Dec 29, 2007)

Welcome aboard @Jimmymiranda!

Is this a hypothetical question or do you have a specific use in mind?


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## Electrical-EE (May 4, 2017)

I think this is a basic introductory question so I'd like to answer it from theoretical perspective instead.
A step-up transformer takes the lower input voltage at primary and steps it up to some higher value. For example, it can take 100 V and steps up to 1000 V, 500 V or some other level.

A step-down transformer takes higher input voltage at primary and steps down to some lower value, for example, it can take 500 V and will step it to 20 V, 50 V or some smaller value.


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## power (Feb 27, 2012)

There is no difference between step-up and step-down...as other people have already commented on.

Remember KVA in = KVA out........either direction.

However, do NOT think you can apply different voltages than the nameplate rated voltage. In other words, if you have a 240 - 120 xfmr.....DON'T think if you apply 120 to the H connection, that X will produce 60vac. Not true. Your meter might read that with no load, however, the core isn't saturated without sufficient winding voltage (either X or H windings) and will "drop-off" when load is added.

Apply the rated voltage to the xfmr, and it will work either way.

NOTE: Applying 3-phase 4-wire to the low side (X) will produce an ungrounded 3-phase 3-wire supply on the H side. This new system is now UNGROUNDED!!! You'll need ground indicating lights if it's a delta secondary.


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## frenchelectrican (Mar 15, 2007)

power said:


> NOTE: Applying 3-phase 4-wire to the low side (X) will produce an ungrounded 3-phase 3-wire supply on the H side. This new system is now UNGROUNDED!!! You'll need ground indicating lights if it's a delta secondary.


My SOP for step up transfomer in Delta - Wye system if reversed I typically grounded one phase and run in delta fashion. 

and put a warning sign about corner grounded delta so other personals will be aware of the set up.


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## splatz (May 23, 2015)

Jimmymiranda said:


> Can anyone explain the difference between a step up and a step down transformer?


Perspective


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