Trans. phase rotation and vector group

[bdf5526]

Hi. I am doing vector group and ratio check on the 33kva, double secondary winding tx. The tx name rating as follows.

Primary: 21kv (delta)
1st Secondary : 6kv (star)
2nd Secondary 2: 4.7kv (star)
Vector group: Dyn1 - y1

For vector group test, when I applied 400V with phase A on primary and phase a' on secondary connected, I measured all the reading required and the vector group was correct. I measured the phase rotation as well. It was clockwise as primary. I did the same method for the Secondary winding no.2 as well. The phase rotation and vector group again was correct. (thanks for the previouse post in this site on vector group)

Now as per my understanding,if the vector grop is correct the phase rotation on secondary must be the same as primary. Am I correct?

 

[slavag]

Yes, of course.
But I don't understand exactly your test procedure.
Regards.
Slava

 

[bdf5526]

Hi Slavag,

Thanks fore the confirmation. The vector group test was actually carried out during commissioning of the Unit Auxilary Transformer and the transformer's secondary winding which rated for 6kv (Grounded neautral) will feed the utility and 4.7kv winding (no neutral terminal)will feed the Static Starting Device.

With link on the primary side opened from busduct, and cables from secondary sides opened from terminals. 400v applied to primary of the transformer with Phase A (primary) of the transformer and Phase a'(secondary) of the transformer shorted. Neutral was disconnected. Voltage measured with all the posibilities. But only two measurements used for the vector group determination. Phase A,B,C are primary; a'1, b'1,c'1 (secondary winding 1); a'2,b'2,c'2 (secondary winding 2).

Voltage between C and c'1 was almost equal to C and b'1
Voltage between B and b'1 smaller than B and c'1.

Same method was used for the secondary winding number 2.

One more question, during the ratio and vector group testing a friend of mine told me that the secondary winding terminals which is not under test need to be shorted if the ratio or vector group measurement is not as expected. When do we actually short the terminals in this way?. Thanks in advance.