# Clock face notation of a Transformer's "Vector Group"

#### jaus tail

Hi,
I'm studying transformer and am a bit confused. Say for vector group: Dy11, I guess it's the line voltage of LV leads the Line voltage of HV by 30 degrees. Book says phase angle. The phase angle is line voltage right,
since the phase voltage of HV and LV will always be in phase with each other.

I googled up for it, but everywhere it says phase angle. Just wanted to clarify whether phase angle is angle between line voltage of lv and hv side.

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#### Baluncore

The phase is measured between the three conductors on the primary or the three on the secondary. A 3PH transformer can be wound to generate any phase shift of the output required, but you can assume the secondary voltages will be in phase with the primary voltage. Only the inductive magnetising current will be at 90° to the phase voltage.

A three phase system has three single phases. The only difference between phases is that they are separated in time by a 120° phase shift. The three phase primary inputs have the same amplitude, or RMS voltages.
https://en.wikipedia.org/wiki/Three-phase

A phasor diagram of a 3PH system will show three vectors of equal length radiating from a neutral at the origin to a common circle. Those vectors rotate once on the diagram for each cycle of the AC supply. That is a Y connection.
https://en.wikipedia.org/wiki/Phasor#Phasor_diagrams

Notice that the vectors on the phasor diagram can be connected in an equilateral triangle that is closed, with all phasors summing to zero. That is a delta connection. There is no central neutral terminal. The circle that the three Delta terminals follow is smaller than the Y circle.

#### jaus tail

Yeah I've studied the equilateral triangle method and know the conventions of how to derive clock 11 or 1 or 0 or 6 from dot convention. But I guess the clock gives phase difference between line voltage of HV and LV. I'm confused here.
In star-delta transformer, there is 30 degree phase shift from HV line to LV line. This can be lead or lag depending on connections. So am I right in saying the clock(11 or 1) represents the phase difference between HV and LV line voltage?
I know that for delta we draw triangle and then take a neutral point at centre, join this with A2 to get other hand of clock.

#### Baarken

So am I right in saying the clock(11 or 1) represents the phase difference between HV and LV line voltage?
Correct.
From http://www.transformerworld.co.uk/vector.htm

The digits ( 0, 1, 11 etc) relate to the phase displacement between the HV and LV windings using a clock face notation. The phasor representing the HV winding is taken as reference and set at 12 o'clock. It then follows that:

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
etc

All references are taken from phase-to-neutral and assume a counter-clockwise phase rotation. The neutral point may be real (as in a star connection) or imaginary (as in a delta connection)

#### Baluncore

IEC 60076-1 Definitions ch.3.10.6
Phase displacement of a three-phase winding
The angular difference between the phasors representing the voltages between the neutral point (real or imaginary) and the corresponding terminals of two windings, a positive sequence voltage system being applied to the high-voltage terminals, following each other in alphabetical sequence if they are lettered, or in numerical sequence if they are numbered.
The phasors are assumed to rotate in a counter-clockwise sense

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Sorry,it has to be:

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#### jim hardy

Gold Member
2018 Award
Dearly Missed
Wow how'd i miss this thread ? Would have helped me in your homework thread, old jim

"Clock face notation of a Transformer's "Vector Group""

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