Ratio and vector group test for trafo 2

[bangi]

we have two trafo for 2 arc furnaces rating 8.5MVA , 11KV /240V with on load tapchanger on HV side max 14 taps.Make AEG germany . Trafo vector group Yd11 , %z = 10

Siemens persons performed ratio and vetor group test with eqiupment :Tettax AG Model # 2791HR

1- They read out the reading from this equipment and divide it by factor 1.5 to get the actual ratio. As i red from my college for vector group YD11 we have
ratio for yd11= (Primary voltage / root 3) / secondary volatge , so the reading is divide by root 3 to get the actual ratio similarly for DY11 multiplied by root 3 to get the actual ratio. But this calcultaion confusing my concept i.e factor 1.5 what does it means .Is it root 3 * cos 30 = 1.5 for phase angle differnce or what ?

2- As far as vector group is concern they calculate it manually ?
i.e connect the U and u phase and applied voltage b/w UV, VW, WU and measure the following reading
W-v = W-w
V-v<U-V
V-v<U-w
I have no idea how these reslut are taken for knowing the vector group what about Dy11 is the same results?

 

[busbar]

 
If the primary-neutral terminal is accessible for ratio tests, no multiplier is used.

Use the site’s search function for ‘vector group’. There has been much discussion and a couple of applicable links. [Vector group for a particular transformer does not normally change from its installed configuration. You might ask Siemens for more information/recommendation.]

 

[bangi]

dear busbar

I have consult the Siemens experts and according to him 1.5 is the ratio meter factor .

Also as far as vector group is concern they provide follwoing infromations:

for vector group supripose the phase U and u on each other and measure all voltages w.r.t each other if

Cb= Cc Bb<Ab Bb <BC

Show Dy1 group

however if

Bb = Bc Cb > Cc Bc < BA

it is Dy11 group


where Captital letters are HV winding and small letters are LV winding


Can you help me how to draw the vector representation to calculate these values if we have no ratio meter arrangement .

What about YD11 and YD1 what will be voltage vlaues and how to compare these via vector representation

Nice Regrads

Bangi jord

 

[busbar]

 
Pardon me bangi, but I do not understand the meaning of

Cb= Cc Bb<Ab Bb <BC

Bb = Bc Cb > Cc Bc < BA

You may want to obtain a reference like IEC standard 60076-1 §6

 

[RalphChristie]

I am not familiar with the test equipment you mentioned.
But for quick tests:

For ratio test:
A low-voltage three-phase supply is applied to the HV-terminals. Measure voltage at LV-terminals. Determine ratio. (Vsupply / Vmeasured)

For polarity of windings and phasor group connections:

The HV and LV windings are connected together at one point as indicated. A low-voltage three-phase supply is then applied to the HV-terminals. Voltage measurements are then taken between various pairs of terminals as indicated and the readings obtained should be the phasor sum of the seperate voltages of each winding under consideration.

For Dy1:

Join:
A(HV) and b(LV)

Measure:
B(HV) and a(LV)
B(HV) and c(LV)
C(HV) and c(LV)

For Dy11

Join:
A(HV) and c(LV)

Measure:
B(HV) and b(LV)
C(HV) and b(LV)
C(HV) and a(LV)


Just remember:
A Dy1 trsf have this vector-group at a counter-clockwise phase rotation. (ABC)
If the phase rotation is clockwise (ACB) this transformer become a Dy11 trsf. (Even if the nameplate says it is a Dy1 trsf)



Regards

Ralph

 

[RalphChristie]

Sorry Bangi.

After reading again through your question, I saw you have Yd11 transformers.

Testing for polarity of windings and phasor group connections:

For a Yd1 trsf: Same as a Dy1 trsf
For a Yd11 trsf: Same as a Dy11 trsf


Regards

Ralph

 

[bangi]

Dear Ralph

Thanks for nice consideration my problem. As I asked from Siemens experts they suggest to connect phase A and a instead of your motioned cktry i.e A and b for Dy1 and A and c for Dy11.(although u know i have YD11 )

Also by measuring these voltages as u suggest what result I conclude. Is there any relation ship as I explain it before?

For Dy1 group voltage relation for HV and LV side

Cb= Cc
Bb<Ab
Bb <BC

For Dy11 group voltage relationship:
Bb = Bc
Cb > Cc
Bc < BA

or what vlaue i should get from measurment as I have Yd11 group

Is above vlaues are true for DY1 and DY11 or how I calculate these relationships, please explain me via some of your time consuming experience.

Thanks for nice coordination
Best Regards

Bangi

 

[RalphChristie]

Bangi

The test-method in my previous answer came out of the J&P Transformer Book pg310 (12th edition)

I've taken a small 3-phase, 1200/380V 4kVA trsf (Dy11) and have done a few tests with a voltmeter to determine vector-groups. I've swapped connections to get other groups. Here are the test method and results. (Values in brackets is the measured values)

Capital Letter = Primary side
Small letters = Secondary side

Connect A - a

Supply primary side with 3ph Low-voltage source.

Measure in following order with voltmeter:

A - B - reference
B - b
C - c
B - c
C - c

For Dy1:

A - B - reference (389V)
B - b - reading less than reference (290.7V)
C - c - reading less than reference (288.3V)
B - c - near reference (413V)
C - c - reading less than reference (288.3V)

For Dy3:

A - B - reference (389V)
B - b - near reference (409V)
C - c - near reference (408V)
B - c - reading more than reference (500V)
C - c - reading less than reference (287.6V)

For Dy5:

A - B - reference (389V)
B - b - reading more than reference (506V)
C - c - reading more than reference (503V)
B - c - reading more than reference (503V)
C - c - near reference (409V)

For Dy7:

A - B - reference (389V)
B - b - reading more than reference (500V)
C - c - reading more than reference (496V)
B - c - near reference (410V)
C - c - reading more than reference (498V)


For Dy9:

A - B - reference (389V)
B - b - near reference (410V)
C - c - near reference (410V)
B - c - reading less than reference (287.6V)
C - c - reading more than reference (504V)

For Dy11:

A - B - reference (389V)
B - b - reading less than reference (287.5V)
C - c - reading less than reference (287.5V)
B - c - reading less than reference (313.5V)
C - c - near reference (405V)

You can also draw a vector-diagram to determine the voltages
Star/Delta will be the same

I hope it is of some help to you.


Failure seldom stops you, it is the fear for failure that stops you - Jack Lemmon


Regards

Ralph

 

[RalphChristie]

Just another point:

Remember to disconnect the neutral point.


Regards

Ralph

 

[bangi]

Dear Ralph

again need some help from you :

1- what do you mean by swapping the connection i.e here we connect A-a wether you connect A-b and so on for vector groups as mentioned in J & P book or something else ?

2- As you metioned the pairs :

A - B - reference
B - b
C - c is it Correct or C-b
B - c
C - c


Thanks alot for your nice suggestions and deeply help

 

[RalphChristie]

Bangi

Firstly, my apologies (have to review my answers in future)
I've tried the J&P Book's method, but couldn't succeed. (was not sucessful with the metod they decribe) Use the method on my last answer.

A - B - reference
B - b
C - c
B - c
[red]C - b[/red]

If the notation on a trsf specify a certain vector-group, it means it is true if you connect your red phase on the A-bushing, Yellow phase on the B-bushing and Blue phase on the C-bushing. The same on the LV-side. But, if for some reason, you change your phase-rotation or connections, you effectively change your vector group.

Example:

For Yd1 on nameplate
[red]A[/red] = [red]RED phase HV[/red]
[yellow]B[/yellow] = [yellow]YELLOW phase HV[/yellow]
[blue]C[/blue] = [blue]BLUE phase HV[/blue]
[red]a[/red] = [red]red phase LV[/red]
[yellow]b[/yellow] = [yellow]yellow phase LV[/yellow]
[blue]c[/blue] = [blue]blue phase LV[/blue]

but if change phase-rotation on HV and LV it becomes a
Yd11
[red]A[/red] = [red]RED phase HV[/red]
[yellow]B[/yellow] = [blue]BLUE phase HV[/blue]
[blue]C[/blue] = [yellow]YELLOW phase HV[/yellow]
[red]a[/red] = [red]red phase LV[/red]
[yellow]b[/yellow] = [blue]blue phase LV[/blue]
[blue]c[/blue] = [yellow]yellow phase LV[/yellow]

By using different connections you can change a Yd1 to a Yd3, Yd5, Yd7, Yd9 and a Yd11. It just depend on your actual connections on your bushings.
The same will happen with a Dy-vector.

Failure seldom stops you, it is the fear for failure that stops you - Jack Lemmon



Regards

Ralph

 

[bangi]

Dear Ralph

Thanks for your nice detailed help to resolve my commissioning problems


Thanks a lot!

Bangi