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Phase angles on DYN11 transformers
4

Phase angles on DYN11 transformers

Phase angles on DYN11 transformers

(OP)
Dear all,

I have an interesting problem, that I cannot explain:
We have three transformers vector group DYN11, 10/0.4kV. All three transformers are supplied from the same medium voltage substation and each of them feeds one low voltage distribution. The star points of the transformers are connected to ground on the low voltage side.

A measurement on the low voltage site of the three transformers (between the transformers) results as follows:
Rotating field in all three low voltage distrubutions is equal!
U Tr1 - U Tr2 : 0V
V Tr1 - V Tr2 : 0V
W Tr1 - W Tr2 : 0V
(That seems OK so far)
U Tr1 - U Tr3 : 230V
V Tr1 - V Tr3 : 230V
W Tr1 - W Tr3 : 460V
U Tr2 - U Tr3 : 230V
V Tr2 - V Tr3 : 230V
W Tr2 - W Tr3 : 460V

It seems to me, as Tr3 is not connected in a proper way. But what might be the cause? A false vector group (DYN5 instead DYN11) would cause a 180° angle and therefore the difference in all phases should be 460V (correct?). A confusion on two phases (e.g. on the primary side) would cause a change of sense in the rotation field, which is not the case.

Any ideas?

RE: Phase angles on DYN11 transformers

A client had one of the tranformer fault and needed rebuilt.  They got the rebuilt tranformer back and put it back in service.

We were installing a tie switch between this and another transformers.  As part of commissioning, we noticed a similar problem.  As a last resort, since it was just rebuilt, we consulted the rebuilder of the transformer.  They picked it up right away.  They had crossed the phasing inside the transformer.  I do not remember our readings exactly, but yours sound familiar (there are several connections that will result in numerous combinations).  The fact that the differnece is common to #1 and #2, I say #3 is improperly phased inside.

RE: Phase angles on DYN11 transformers


Sketch six phasors 60° apart.  

0° - U1 - 3 o’clock
60° - U3 – 1 o’clock
120° - W1 – 11 o’clock
180° - V3 – 9 o’clock
240° - V1 – 7 o’clock
300° - W3 - 5 o’clock
  

RE: Phase angles on DYN11 transformers


Reversing two primary connections of one ∆-Y transformer with respect to the other may produce the described secondary-voltage relationship with 'normal' secondary-winding  internal connections.  

Are R-S-T the corresponding primary designations?
  

RE: Phase angles on DYN11 transformers

Not only the two connection have to be reversed, but also there has to be a 30 degree phase shift between T3 and other two tranfromers which will have the phasor diagram described by 'busbar' and the reading you are getting.

T3 internal connections are not the same as T1 and T2, regardless of what the namepate reads.

RE: Phase angles on DYN11 transformers

Hi Area,

From your voltage measurements it can be proved that ONE transformer- ONLY ONE- is fed by the reverse phase sequence on the primary. As a result you have got a 3-vector set similar to an inverted star, which gives a hexagon with 230 V on each side. Therefore the remedial action should be to provide the “faulty” transformer with the standard sequence on the primary.

How to correct this in the field? My suggestion is this.

The most convenient way is to use a phase sequence meter connected to each secondary of the transformer out put terminal and identify which one is giving the reverse sequence. ( If the transformers are labeled properly then it is again easy to identify the u,v,w on the secondary bushings. Otherwise you have to stand facing the HV SIDE and then identify the corresponding u,v,w terminals on the secondary ) After identifying the reversed one, correct it ONLY from the primary and then confirm that all three are fed with the standard sequence of supply. Finally your voltage measurements should be all zero!!

Good Luck!

Kiribanda  

RE: Phase angles on DYN11 transformers

One more piece of info needed:

Are all three transfromers fed from the same primary bus/feeder or different feeders?

If on different feeders, it is possible that one the T3 feeder has 30 degree phase shift, because of different trasnformation.

RE: Phase angles on DYN11 transformers

2
A 30° phase shift wouldn't produce the reported voltages.  Reverse phase sequence on one of the transformers as noted by Kiribanda would.  This results in a 60° phase shift on the secondary.  This is probably the cause - two phases are reversed on the primary of one of the transformers.

RE: Phase angles on DYN11 transformers

jgrisht:

There has to be a 30 degree shift AND reversal of two phases to get his 'steady' voltage results,as posted in previous posts.

Just reversing two phases will produce 0 volts in the between the phase that is not reversed and 460 in the other two.
(assuming fed from the same bus, so frequecny is locked)

RE: Phase angles on DYN11 transformers

Suggestion: Three identical transformers connected the same way on the primary should have 0V readings among exactly corresponding secondary terminals. This is necessary requirement for transformers direct paralleling. The transformer winding termination at the transformer terminals should follow the specific industry standard.
Which industry standard are those transformers built to?

RE: Phase angles on DYN11 transformers

I'll go along with busbar and jghrist on this. Been there and done it. Winding is okay, high side connection isn't. If we had a phasor diagram of this thing, we could tell you which two to swap.

RE: Phase angles on DYN11 transformers

Maybe I can tell you anyway. Locate phasor W on wye side of your transformer phasor diagram. Find the phasor that parrallels it on the delta side. Reverse the two leads that connect to this winding on transformer three.

RE: Phase angles on DYN11 transformers

U1: 3 o'clock (0 deg)
W3: 1 o'clock (60 deg)
V1: 11 o'clock (120 deg)
V3: 9 o'clock (180 deg)
W1: 7 o'clock (240 deg)
U3: 5 o'clock (300 deg)

As seen here, the voltages read between two trfs are 230, 230 and 460.

RE: Phase angles on DYN11 transformers

If the primary is the normal (UVW) counterclockwise phase rotation, the vectors given by saltan indicate that transformers 1 and 2 have their primary phases swapped.  This makes the secondary (UVW) clockwise phase rotation.  Only transformer 3 has UVW counterclockwise rotation on the secondary.

RE: Phase angles on DYN11 transformers

My apologies. Firstly, the vector diagram is drawn correctly and even the voltages are correct but anlges mentioned  were wrong.

The phase difference has to be 60 degrees and which will be created by phase reversal on the primary side AND in order to correct the rotation the secondaries are  reversed therefore creating a 60 degree phase shift between two of the phases and 180 on the third. This will give you the 230, 230, 460V results.

I will update my diagram.

RE: Phase angles on DYN11 transformers

Suggestion: Visit
http://www.emsyst.com/products/netvision.htm
for an opposite rotation on the meter, namely, U1, U2, U3 in clockwise direction instead of A, C, B in clockwise direction.
http://www.themeterguy.com/Theory/therules.htm
Reference:
1. William D. Stevenson, J.R., Elements of Power System Analysis, 3rd Edition, McGraw-Hill Book Company, 1975,
page 27 Figure 2.14 and Figure 2.15
indicate the phase rotation in clockwise direction as A, B, C.

RE: Phase angles on DYN11 transformers

Rbulsara,

Try drawing the delta side first, and reversing the connections there. Then carry it over to the wye side. Simply swapping two leads on the delta side will give you the 60 degree shift and phase reversal shown in your last diagram.

RE: Phase angles on DYN11 transformers

Stevenal:

Let us review it again.

Remember, you need to SUBTRACT the phasors not 'add' (we measuring the differnce in voltage at two points) as it is misleading to look at the phasors with 60 degree difference and just add them.  

A simple phase revesal on the primary side, should and would give a simple phase revrsal on the secondary side!!
That will give you the voltage readings of 0, 400 and 400V. As seen in the second picture on the top (on the right)in my diagram.

You have to reverse phasing again on the secondary side to get my last diagram.

RE: Phase angles on DYN11 transformers

Thanks for the review, rbulsara, but I wasn't adding anything. I use a simple graphical approach.

This phenemonon puzzeled me when I first encountered it. Phasing sticks read line to ground and double line to ground voltages across an open switch. While I was still scratching my head, operations rolled two high side connections and cleared the problem. Determined to avoid that particular embarassment again, I sketched out the phasors. The drawing is a tool I keep handy for when it reoccurs. Unfortunately, it has reoccured, but at least I had an answer. Not really the answer my boss wanted to hear, but correct anyway. You may persist in your attempts to prove that bumblebees can't possibly fly, but I prefer to understand how they do fly.

Get it fixed yet Area?

RE: Phase angles on DYN11 transformers

rbulsara,

As Stevenal says, you have to go back to the delta primary.  Your diagrams do not show the proper phase relationships between the delta and wye sides.  Try this:

Turns ratio n = 10000/230

Primary side voltages:

VA = 5774@0°
VB = 5774@-120°
VC = 5774@120°
VAC = VA-VC = 10000@-30°
VBA = VB-VA = 10000@-150°
VCB = VC-VB = 10000@90°

Secondary side voltages:

Va = VAC/n = 230@-30°
Vb = VBA/n = 230@-150°
Vc = VCB/n = 230@90°

This is the normal Dyn11 (US Std) connection.  Now if we reverse voltages B & C:

Primary side voltages:

V'A = 5774@0°
V'B = 5774@120°
V'C = 5774@-120°
V'AC = V'A-V'C = 10000@30°
V'BA = V'B-V'A = 10000@150°
V'CB = V'C-V'B = 10000@-90°

Secondary side voltages:

V'a = V'AC/n = 230@30°
V'b = V'BA/n = 230@150°
V'c = V'CB/n = 230@-90°
 
The secondary side voltages are now reverse rotation acb counterclockwise 60° shifted from before and:

V'a-Va = 230@90°
V'b-Vb = 230@90°
V'c-Vc = 460@-90°

RE: Phase angles on DYN11 transformers

Nice work jghrist. Note that V'c to Vc has the largest error, like phases W3 and W1 in the question. Vc is at 90 degrees, corresponding to VCB on the primary, and C and B are the swapped phases. Likewise Area just needs to swap whichever two primary phases line up with W.

RE: Phase angles on DYN11 transformers

stevenal/jghrist:

Your explantion explains voltages, except the last line of the original question by 'Area' that "A confusion on two phases (e.g. on the primary side) would cause a change of sense in the rotation field, which is not the case."

So if he just reverses two phases on the primary only, what happens to any motor rotations (if any connected to T3) that are running in 'correct' direction now?



RE: Phase angles on DYN11 transformers

Question to the original posting: Please, would nameplate data of each transformer be available?

RE: Phase angles on DYN11 transformers

To jghrist:
I think Dyn1 is the standard delta-wye transformer connection in the U.S.A. In Dyn1, VAN leads Van by 30 degrees.

RE: Phase angles on DYN11 transformers

Rbulsara,

They would reverse of course. I would suggest Area recheck this part. I can see no combination of correctly rotating phasors that will give these magnitudes.

RE: Phase angles on DYN11 transformers

mvcjr,

You're right.  And, my calculations are for a Dyn1 connection.  For a Dyn11 connection:

VA = 5774@0°
VB = 5774@-120°
VC = 5774@120°
VAB = VA-VB = 10000@30°
VBC = VB-VC = 10000@-90°
VCA = VC-VA = 10000@150°

Secondary side voltages:

Va = VAB/n = 230@30°
Vb = VBC/n = 230@-90°
Vc = VCA/n = 230@150°

This is the normal Dyn11 connection.  Now if we reverse voltages B & C:

Primary side voltages:

V'A = 5774@0°
V'B = 5774@120°
V'C = 5774@-120°
V'AB = V'A-V'B = 10000@-30°
V'BC = V'B-V'C = 10000@90°
V'CA = V'C-V'A = 10000@-150°

Secondary side voltages:

V'a = V'AB/n = 230@-30°
V'b = V'BC/n = 230@90°
V'c = V'CA/n = 230@-150°
 
The secondary side voltages are now reverse rotation acb counterclockwise 60° shifted from before and:

V'a-Va = 230@-90°
V'b-Vb = 460@90°
V'c-Vc = 230@-90°

RE: Phase angles on DYN11 transformers

You can find a UVW dy11 phasor diagram here: http://www.riedel-trafobau.de/english/pd...

Looks U and W are reversed on winding 1 (high side) in Area's case.

Don't know why I'm bothering. No responses from Area. Probably had it fixed long ago.

RE: Phase angles on DYN11 transformers

(OP)
Dear all,

sorry for the late reply, but I was out off the office for some days and did not have the possibility to check the internet.
Special thanks to stevenal for all the bothering, I really appreciate it. Sorry again for the late reply.

Hope I can answer all your questions so far:

To rbulsara: Yes all transformers are connectet to one (the same) medium voltage busbar. But each transformaer is connected to this busbar via his own short circuit breaker.
I tried to open your sketch, unfortunately our network adimistrator seems to have banned geocities from our proxy server; I only receive a proxy error.

To jbartos: Unfortunately, all three transformers are under tension, meaning that the nameplate is not accessible. I have to wait for the next plant shutdown (mid of October)

To jghrist: Thanks a lot for the phaser description. Excellent work. It is very helpfull. I did not know how to transfer the phasers from the primary to the secondary voltage side. I was also not aware, that a DYN1 vector group exists: As also mentioned in the file that stevenal is referring in his last post, I only knew DYN5 and DYN11 vector groups, where the phase angle between primary and secondary side is -150 / -300 degree. I did not know, that also a DYN1 exists.
It explains perfectly the voltages that me measured, unfortunately, as also mentioned by rbulsara, it does not explain the non-reversed sense of rotation.

So today, we checked again the sense of rotation with an external consultant.(I did not trust in our own measurement any longer). But he came to the same result. We also checked the busbar connection between the low voltage side of the transfomers and the distribution panels: There seems to be a reversed phase on the low voltage side of the faulty transfomer, as the busbar is connected in a different way. The consultant explained me, that we also have a reversed phase on the medium voltage side. This would explain the right sense of rotation.

To stevenal: I fully agree with you, that the phases on the secondary side must be reversed, if a phase on the primary side is reversed. I have now two good explanations:
The phasor diagram of jghrist and the explantion/observation of the consultant. Unfortunately, they do not match. If we have a double reversing of phases, and the phasor diagram of jghrist is correct (what I believe) I would expect to have 400V between U-U, 400V V-V and 460V between W-W.

It still remains I mistory to me. I can reassure you stevenal, problem is not solved yet. I will again contact our consultant and confront him with the diagram of jghrist.

Nevertheless, thanks so far to everybody for the interesting discussion and help.

RE: Phase angles on DYN11 transformers

The only difference between a Dyn1 and a Dyn5 is what you call the secondary phases.  The difference between a Dyn11 and a Dyn1 is that the primary phases are reversed internally, producing a 60° phase shift on the secondary.  The same thing would occur if you externally reverse the phases on a Dyn11 connection.

RE: Phase angles on DYN11 transformers

I think it takes more than two dimensions to explain these readings. The S plane is no longer a plane. Have you checked phase to phase across the tie point? U1 to V3, U1 to W3, V1 to W3 and so on? I assume that all phase to phase and phase to neutral readings are normal on T3?

Is transformer 3 presently powering three phase motors?

RE: Phase angles on DYN11 transformers

Hi everyone

I am sorry to jump in after the discussion is probably over but after reading it I am a bit confused.
 
as recommended by stevenal (Electrical) I visited the following site and looked ath the phasor diagram of dy11 etc.
http://www.riedel-trafobau.de/english/pd...

In Protection Relay Application Guide - Alstom, a completely different figure and connection has been given for the same vector group. It also says " The Power transformer vector group references correspond to those specified in IEC 76:1967 and BS 171:1970."

I shall be very thankful if anyone could please claify this.

With kind regards
isoA120

RE: Phase angles on DYN11 transformers

Hi everyone

Pls ignore my question. I just made a mistake reading the PRAG.

Regards
IsoA120

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