30 degree phase shift

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mpross

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I know there is a 30 degree phase shift when going from delta to wye, and also the other way around. Is the high side always advanced, or does it depend on delta or wye?

I have the phrase "highjack" in my head, so my feeling about this is that the high side is always advanced by 30 deg. ?

Thanks.
 
mpross said:
I know there is a 30 degree phase shift when going from delta to wye, and also the other way around. Is the high side always advanced, or does it depend on delta or wye?

I have the phrase "highjack" in my head, so my feeling about this is that the high side is always advanced by 30 deg. ?

Thanks.
Click to expand...

I know the answer, but I don't quite understand the question. What do you mean by "high side"?
 
high side

high side

as in case of going from a generator to transmission, the transmission would be the high side.

MP
 
The standard is to have the high voltage side lead the low voltage side with a positive sequence connected to H1, H2, H3.

If you connect a negative sequence to a standard transformer Then the high voltage side will lag the low voltage side.


The best way to determine how a transformer is wired internally is to refer to the nameplate. They should have the vector relationships of the terminals along with the rotation.
 
mpross said:
I know there is a 30 degree phase shift when going from delta to wye, and also the other way around. Is the high side always advanced, or does it depend on delta or wye?

I have the phrase "highjack" in my head, so my feeling about this is that the high side is always advanced by 30 deg. ?

Thanks.
Click to expand...

According to C57.12.00:

5.7.2 Angular displacement (nominal) between voltages of windings for three-phase transformers
The angular displacement between high-voltage and low-voltage phase voltages of three-phase transformers with Δ-Δ or Y-Y connections shall be zero degrees.
The angular displacement between high-voltage and low-voltage phase voltages of three-phase transformers with Y-Δ or Δ-Y connections shall be 30?, with the low voltage lagging the high voltage. The angular displacement of a polyphase transformer is the time angle expressed in degrees between the line-to-neutral voltage of the reference identified high-voltage terminal H1 and the line-to-neutral voltage of the corresponding identified low-voltage terminal X1.

However, transformers can be specified to be other then this, and therefore it is imperative that on existing installations nameplates be checked. If you plan on tying into one system into another system, you also need to check the phasing of each system before doing so. Mis-matches can, and do occur.
The text also confirms that the appropriate way to discuss sides of a transformer are by HV and LV, or H and X, NOT by terms such as primary and secondary as this can become confusing. The high voltage side is not always the primary side, i.e. a generator step-up transformer has the low voltage side as the primary side.

It is a good idea to do a phasing diagram when large systems are being modified, and many levels of transformation exist.
 
King, I am confused. How can we define the neutral point of a delta? Seems to me that the L-L voltages in the wye side always lag the corresponding L-L voltages in the delta side irrespective of the voltage levels.
 
Provided below are the choices available. The chart is taken from IEC (international) standards, but it is very illustrative when it comes to the choices you have and it also shows the winding connections:

View attachment 146
View attachment 147
View attachment 148
View attachment 145
View attachment 144

The capital I, II, III, is high voltage, which also corresponds to the Capital Y, or D. The low voltage is the lower case i, and corresponding lower case y or d.
For convenience, I penciled in the degree shift, 0, 30, 60, 120, etc.
 
kingpb, that is a great way to show the phase relationships between primary and secondary windings that I have never thought of. I have always drawn the two phasor diagrams side by side and it is much more difficult to see the phase relationships.
 
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