Phase Matching Transformer Secondaries

[millerbitte]

How do you phase match the secondaries of two three phase delta/wye transformers fed from the same source? I have seen a document before describing the relationship between the primary and secondary phasing but am not able to locate it.

 

[gar]

110322-2341 EDT

Connect the neutrals together. Any two phases with about zero voltage difference between them belong together.

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[hurk27]

I have never cared for paralleling transformer, as if one fails the other one gets the full load and is the reason for each transformer to have its own over current protection before the tie point (see 450.7)

But as long as L1 connects to H1 and L2 connects to H2 Etc... and X1 to X1 and X2 to X2 Etc... I would believe they should be in phase?

But Gar is right, there should be 0 volts between the two in-phase lugs if the X0's are connected, I'm just not keen at trying to get this reading on two hot transformers, as this could be dangerous.

One way would be to connect a smaller wires to X1 and X1 to a meter, then energize the transformer, repeat for X2, if these so ok then you will know the last is X3 to X3.

 

[mivey]

In addition to being from the same source, there is a little more involved than just matching the voltages. You must also consider the kVA rating, X/R ratio, turns ratio, and impedance.

Ideally you would want these to be the same but impedance and turns ratio being the more important. If not, you can have excess circulating currents (like over 10%, due to unequal ratios) and unequal load sharing (due to unequal kVAs or impedances) that can overload one of the transformers.

What is your application?

 

[powerqualityworld]

In our case, we use high voltage testers... If the voltage between the test phases is zero, then they should be of the same phase (equal or have close values in both magnitude and angle)...

We normally do this before we parallel substation transformers to avoid customer interruption during transfer switching... Phasing-out is the most important aspect to verify when considering paralleling of transformers...

 

[powerqualityworld]

We use high voltage testers to determine if two phases are in-phase... If the voltage between them is zero then we can say that their voltages are of the same magnitude and angle.

Normally, we conducting phase testing before temporary paralleling our substations in order to avoid customer interruption...

However, I'm not sure if this answer your question since you mentioned about phasing the primary and secondary of the transformer...