Hypothetical Transformer Question

electrofelon said:
I don't think there is a way without a more advanced meter. Would need watts, or power factor. My amprobe ACDC-54NAV could do it.
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My Amprobe circuit tracer could. The signal would go back to the source only. So if it is a step down transformer, the signal would also show up on the 480 side if connected to the 120 side. If it is a step up, no signal on the 480 side when connected to the 120 side.
 
TwoBlocked said:
I have had a new thought, though. If the transformer has a load on it, there will be a voltage loss due to heat. So if the high voltage side is less than it would be with a theoretical, lossless transformer, then it is a step up transformer. And if the low voltage side is less than it would be with a theoretical, lossless transformer, then it is a step down transformer.
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TwoBlocked said:
Is measuring the amps necessary? See what I posted on #15.
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Your post 15 could work out if there is enough load to drop the voltage from the transformer to make it apparent the drop is beyond just transformer tolerances.

If you had two meters, one on each side of the transformer, and quite a bit of time observing voltage drops from changing loads, you might be able to identify which side had a higher percentage change. That would be the output side due to the transformer's impedance.
This could be tried with one meter, but it would take a lot of back and forth to separate voltages changes due changing loads from posible changes on the source voltage. Doesn't sound like fun.
 
hillbilly1 said:
The signal would go back to the source only.
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I have used a similar tracer to find the feeder breaker for a 480 to 208Y/120 volt transformer.
That one pulled a small amount of current from the circuit in a pulse. That pulse also appears on the primary side of the transformer, if you have connected the tracer to the secondary side. The signal is much reduced on the primary side, but was always detectable when I did that.
 
don_resqcapt19 said:
I have used a similar tracer to find the feeder breaker for a 480 to 208Y/120 volt transformer.
That one pulled a small amount of current from the circuit in a pulse. That pulse also appears on the primary side of the transformer, if you have connected the tracer to the secondary side. The signal is much reduced on the primary side, but was always detectable when I did that.
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Yep, I've been able to trace signals all the way to a 4160V breaker.
 
hillbilly1 said:
Amprobe circuit tracers uses a current pulse, not an injected signal. The current will flow from the point of connection back to the source only. Where cheaper tracers inject a signal which travels both ways and give false readings.
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Ok I see what you are saying. It draws current from the source so you can tell where the source is. I have an amprobe circuit tracer, one of the $500 ones, but I havent used it much.
 
electrofelon said:
Ok I see what you are saying. It draws current from the source so you can tell where the source is. I have an amprobe circuit tracer, one of the $500 ones, but I havent used it much.
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You will see the pulse on both sides of the transformer, but the signal will be attenuated on the supply side if you have connected the tracer to the load side. The attenuation of the single may be enough to identify the source side, but not sure.
 
TwoBlocked said:
I have had a new thought, though. If the transformer has a load on it, there will be a voltage loss due to heat. So if the high voltage side is less than it would be with a theoretical, lossless transformer, then it is a step up transformer. And if the low voltage side is less than it would be with a theoretical, lossless transformer, then it is a step down transformer.

Other than that, if you could control an additional load on one side or the other at a disconnect, the amps would change on the conductors from where the power is coming from. Yes, you would need to use a clamp-on amp meter.
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Meter accuracy to see for use in field enough to detect voltage difference
Second case add load violate initial premise of problem non-invasive meter only approach
 
Just for my curiosity. And I think it's illegal now but Would a wye wye xfmr work correctly if it was wired backwards?
 
qcroanoke said:
....but Would a wye wye xfmr work correctly if it was wired backwards?
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Yes it does. I have used them with alternative energy source interconnects. Attention must be paid to any grounding of the wye points and it's affect on any building GF systems.
 
electrofelon said:
I don't think there is a way with just a basic clamp meter. If there was a high steady load on it, perhaps you could measure current, adjust for voltage ratio and go off transformer losses, but power factor can trip you up.
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The transformer would also need to be near full load or the losses might not be noticeable.
 
don_resqcapt19 said:
You will see the pulse on both sides of the transformer, but the signal will be attenuated on the supply side if you have connected the tracer to the load side. The attenuation of the single may be enough to identify the source side, but not sure.
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Mine works fine through transformers with no signal loss. It can even trace which poco pad mount it comes from, if there happens to be multiple. Computers operate at close to the same frequency, so they can make it difficult to distinguish due to their noise covering up the pulse.
 
don_resqcapt19 said:
You will see the pulse on both sides of the transformer, but the signal will be attenuated on the supply side if you have connected the tracer to the load side. The attenuation of the single may be enough to identify the source side, but not sure.
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Actually if it is a step-up transformer and the signal tracer is put on the higher voltage side, the signal will be stronger on the low voltage side because the current on the signal will increase. I am thinking I did that, but am not remembering the details.
 
TwoBlocked said:
This was posed to me by and excellent apprentice a few years ago:

Let's say you go into a room and there is a transformer there. Conduits going to disconnects and continuing out of the room. You open the disconnects, look at the wiring, take voltage readings, and determine that the transformer is 480/277 3ph on one side and 208/120 3ph on the other, both with grounded neutrals, but not grounded in the transformer nor in the disconnects, but somewhere outside of the room.

With no more information, and without opening the circuit on either disconnect, and with just a normal meter, can it be determined if this is a step up or a step down transformer? In other words, is the power coming from the 480V or the 208V side?

I can think of a way with additional equipment, but not with just a regular meter, but that doesn't mean there isn't a way.
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Check the Data Plate on the TX. LOL
 
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