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transformer vector group
Transformer vector group

why we need to specify the transformer vector group in substation design. If the vector grp of a generating transformer is changed from yd11 to yd1 how it will be going to affect in synchronising the generator

1 out of 1 members thought this post was helpful...

Responding to Krishna's queries:

Q1) Why is vector group important?
A1) Because it determines the phase angle displacement between the primary (HV) and secondary (LV) windings.

Q2) If the vector-group is changed from Yd11 to Yd1, how will it affect generator synchronization?
A2) The Yd11 has an HV to LV phase angle displacement of plus 30, while that of the Yd1 is minus 30. Synchronization could be done if the HV and LV configurations were reversed, i.e., Yd11 and Dy1 in parallel. But, it is not possible if the Yd1 were to be paralleled with a Yd11 if the primary of both transformers were supplied from the same source.

The response might be different if you could furnish additional system detail! I may have misinterpreted your system layout regarding the number of gensets!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[tal-2@webtv.net] (Cepsicon@aol.com)

I'd like to have information-like text book, hand book etc.- about vector group design. I know, what it means but physically not. Which one is lagging or leading: current or voltage or both?

1 out of 1 members thought this post was helpful...

Responding to ucf's Thu, Oct 13, 1:01am query:

Typically, Vector-Group specification of power transformers is not used by USA manufacturers. Nevertheless, because English and German trafo manufacturers do, I suggest you contact those manufacturers or their world-wide affiliates.

Failing that you can contact me for specific info!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[tal-2@webtv.net] (Cepsicon@aol.com)

> Typically, Vector-Group specification of power transformers is not used by USA manufacturers. Nevertheless, because
> English and German trafo manufacturers do, I suggest you contact those manufacturers or their world-wide affiliates.

> Failing that you can contact me for specific info!

>Phil Corso, PE

sir, i have one doubt is there any possibilities to make a transformer YNd5 with + or - 5 & 10% tappings on LV side

1 out of 1 members thought this post was helpful...

Kani... are you referring to an existing transformer, or one being proposed for a new project?

Regards, Phil Corso

By William Hinton on 10 July, 2005 - 3:21 pm

The vector group denotes the way in which the windings are connected and the phase position of their respective voltage vectors. It consists of letters identifying the configuration of the phase windings and the number indicating the phase angle between the phase-to-neutral voltages of the windings.

The ANSI notations are not identical to the IEC marketplace (See ANSI/IEEE Std C57.70). For the IEC marketplace the winding connections are categorized as follows:

a) Delta (D,d)
b) Start (Y,y)
c) Interconnected Star (Z,z)
d) Open (III, iii)

IEC NOTATION:

Capital Letter = HV winding, lower case letter = MV or LV winding.
Number = multiple of 30o denotes the angle by which the vector of LV winding lags that of the HV winding

See the enclose site for additional reference

www.riedel-trafobau.de/english/pdf_eng/b/gen_e.pdf

1 out of 1 members thought this post was helpful...

A small, albeit important technical correction of William Hinton's Sun, Jul 12, 2005, 3:20pm comments:

Your observation regarding phase-angle (displacement) between primary phase-to neutral and secondary phase-to-neutral voltages for the Yy case is correct. But, the same cannot be said for the Yd case.

For the case of the Yd1 the primary phase-neutral voltage leads the corresponding secondary phase-neutral voltage. For the Yd11 case the secondary leads the primary. However, because the neutral-point of the delta secondary is non-existent, then, one must use the phase-to-phase
measurement. For the Yd1 case, the primary phase-to-neutral voltage A-N, is in phase with the secondary a-b voltage. Conversely, for the Yd11 case, the primary voltage A-N, is in phase with the secondary a-c
voltage.

Consequently, it is obvious that the Yd11-Yd1 substitution can not be made without affecting PT and CT protective relaying and metering circuits!

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[tal-2@webtv.net] (Cepsicon@aol.com)

The new transformer secondary will lag by 30 degrees, while the old transformer will lag by 330 degrees. Incorrect phase information will be supplied to the synchronising equipment. By changing external connections you may be able to use the new transformer without changing other equipment. You can find more information on vector groups here: http://wiki.myelectrical.com/index.php?title=Vector_Group.

While paralleling two transformers the vector group should be same hence we can make sure that phase angle differnce between them are zero.

If you parrallel Dy1 Tr. with Dy11 transformer the phase angle differece between them will be 60digree which will result circulating current betwee these transformers.

Regards
Sunil Kumar (sunil_thisha@yahoo.com)

I had one of my biggest headache of my life when I faced this problem. Especially when the experts and professors have different thoughts than you.

You may need to rephrase your question on whether you are paralleling the transformers OR synchronize a generator step up transformer to the grid in which many transformers are connected in parallel. Both terms are different.

In the case of substituting a generator step up transformer from Ynd11 to Ynd1, there would be no problem as long as the generator LV is not connected in parallel with any other generators. To be safe during synchronizing, please ensure that the synchronization circuit consist of 2 phase sensing.

I have replaced one of my failed generator step up transformer from Ynd1 to Ynd11 for period of 3 months while waiting for my replacement transformer is delivered. No problem ;)

Yes there will be no problem, but your synchronizing circuit should be in such a way that it would sense and verify the actual phase angle and voltage of each phase with actual reference to the Y side. Your d side have an actual phase difference of around 60 degrees between d11 and d1 and you must compensate for this difference.

A DY1 transformer can be parralleled with a DY11 transformer.... here's how...

Roll the HV (swap two phase leads)
Roll the LV (swap two phase leads).

This changes the phase rotation through the transformer... the 30 lead (lag in the other tx) is in the opposite direction due to the change in rotation.

Caution... If your metering (protection) CT's & VT's are outside the roll you will never get unit protection to 'line up'... Best to have these inside the rolls.