phase displacements

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bejoyengineer

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Hello ,
I am confused a bit with these questions

1. I have read that ??Transformer nameplates carry a vector group reference such at Yy0, Yd1, Dyn11 etc. This relatively simple nomenclature provides important information about the way in which three phase windings are connected and any phase displacement that occurs. Digit 0 means that the LV phasor is in phase with the HV phasor,Digit 1 that it lags by 30 degrees,Digit 11 that it leads by 30 degrees? I also read that? When viewing the voltage and current waveforms on an oscilliscope, the two curves would be on top of each other, in unison hence the name unity power factor.But when dealing with ac circuits you must also include a term called reactance (ac resistance) which can be composed of inductive loads and capactive loads. When viewing the voltage and current waveforms on an oscilliscope when reactance is involved, the two curves will be viewed as separate graphs. Either the voltage curve will lead the current curve (inductive type of loads), or the current curve leads the voltage curve(capactive loads).

1. So my question would be that when are the cases that the transformer is designed for different phase angles or in other words ? why and in which cases the transformer is designed for 30 degree lead and lags.
2. As explained above ??Digit 1 means that the LV phasor lags by 30 degrees
phase with the HV phasor and also as explained above ?the current curve will lag the voltage curve for inductive type of loads.? So does ?LAG? in both the cases have the same sense. Or in another words- the lag for the inductive load shows that the Power Factor is bad and so does it have the same meaning when it comes to the transformers i.e, lags by 30 degrees
phase with HV?
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You are mixing apples and oranges when you talk about transformer phase displacement and power factor. The transformer phase displacement is a phase difference between the primary and secondary voltage. Power factor phase displacement is between voltage and current.

A transformer with a delta winding and a wye winding inherently has a displacement between the primary and secondary because the primary and secondary windings of one phase have a common core and have the same voltage angle, but since one winding is connected ?-? and one connected ?-n, the ?-n voltages are some multiple of 30? out of phase with each other.
 
bejoyengineer said:
1. So my question would be that when are the cases that the transformer is designed for different phase angles or in other words ? why and in which cases the transformer is designed for 30 degree lead and lags.
Click to expand...
Phase angle "offset" of three-phase transformers is inherent with the configuration (winding connections). There are two basic configurations: Delta and Wye. When primary and secondary windings are configured the same (delta-delta, wye-wye), there is no shift between primary and secondary. When they are configured otherwise, such as delta-wye, there will be a 30 degree shift because of the ?-? one side while ?-N on the other. There is no shift in the primary and its mating secondary voltages... only the configuration changes the relationship.

For example, with a delta-wye xfmr, let's call voltage from Lines C to A the phasing 0? reference (actually xfmr connection diagrams use the center of the delta symbol, a virtual neutral point, to Terminal A (or H1) as the 0? reference... can discuss later if you like). The primary winding connected C to A powers the secondary winding connected N to A. So you now have Secondary Neutral to Line A is now at 0?. Then primary winding connected B to C (-240? volatge phase shift from 0? reference) powers the secondary winding connected N to C. Secondary Line C is now at -240?. Secondary Lines C to A voltage now has a phase angle of -30?, because line to line voltage angles of a wye secondary are 30? off the line to neutral voltage angles.

The letter designations you noted are just "shorthand" for the configuration:
Y is wye
D is delta
First is primary
second is secondary​
 
phase displacment

phase displacment

Hello
Thanks a lot for the informations.. it was true that i was mixing up things but now it's a little better. But just to get things better i was having a doubt on these quote"A transformer with a delta winding and a wye winding inherently has a displacement between the primary and secondary because the primary and secondary windings of one phase have a common core and have the same voltage angle, but since one winding is connected ?-? and one connected ?-n, the ?-n voltages are some multiple of 30? out of phase with each other. " 1. so now if the transformer is delta - wye - then there is going to be a phase shift of 30 degree - I agree. so when designing ,how do the designers come to a conclusion that they have to have the phase displacement at 11 O clock angle or the 1 O clock angle. is there any importance of this phase displacement when a contactor goes to purchase the transformer...
hope my questions are understandable.. if not, i will post the question one more time in an understanding way
 
bejoyengineer said:
1. so now if the transformer is delta - wye - then there is going to be a phase shift of 30 degree - I agree. so when designing ,how do the designers come to a conclusion that they have to have the phase displacement at 11 O clock angle or the 1 O clock angle. is there any importance of this phase displacement when a contactor goes to purchase the transformer...
Click to expand...

It is important if there is a chance for the secondary of one transformer to be connected to the secondary of another transformer. Both must be either Dyn1 or both Dyn11. Other than that, it is a matter of convention and standards.
 
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