stevenal
this is very complicated. I'm assuming UVW phase and phasor diagrams should be superimposed and rotated.
1U bus-fig.10 connect to bus 1U-fig. 11
2U bus-fig. 10 connect to bus 2U-fig. 11
1V bus-fig. 10 connect to bus 1V-fig. 11
2V bus-fig. 10 connect to bus 2V-fig. 11
1W bus-fig. 10 connect to bus 1W-fig. 11
bus 2W-fig. 10 connect to bus 2W-fig. 11
do not understand!
Preliminary remark:
any Ydx transformer fed by a negative sequence (1U=C, 1V=B, 1W=A) will work as Ydy (where y is the working vectorial group and it is x (nameplate vect. group) mirrored over the 12-6 clock axis).
i.e. an Yd1 fed by negative sequence will work as an Yd11; Yd3 as Yd9; Yd5 as Yd7; Yd7 as Yd5; Yd9 as Yd3; Yd11 as Yd1.
This can be demonstrated as shown by Stevenal in his FAQ.
Please name the phasors: A=12, B=4, C=8
Feed the Yd1 (let's name it TR-A) at 138kV by the direct sequence: 1U=12(A), 1V=4(B), 1W=8(C)
at 13.8kV you'll get: 2U=1(a), 2V=5(b), 2W=9(c)
Feed the Yd11 (let's name it TR-B) at 138kV by the negative sequence: 1U=8(C), 1V=4(B), 1W=12(A)
at 13.8kV you'll get: 2U=9(c), 2V=5(b), 2W=1(a)
Now, at 13.8kV, you can parallel the two transformer by means of connections as follow:
TR-A 2U with TR-B 2W
TR-A 2V with TR-B 2V
TR-A 2W with TR-B 2U
Please follow Stevenal's FAQ suggestions:
"To be safe, always test voltage across an open switch before completing the parallel"
and
"check if the impedances match"
If you have transformer differential protections it should be useful also to discuss about that....
Hope this can help.
Ciao
Erminio
The difference between overload and short circuit lies in the nature of the fault, not in the value of the current.
I'd been meaning to include a link in the FAQ to show the steps, so I've gone ahead and done so. The link is repeated below.
The FAQ was set up with H1, x2 type notation, so I've carried that through. No rotation is needed if you flip the paper over from left to right as I stated to get Fig 11b. 11c is a simple reordering of 11b with the text and arrow straightened out. The final step is to compare Fig 10 with Fig 11c. System phases are in the same positions, and rotation is the same. The only difference is which bushings the phases land on. Other phase swaps will also work, but the paper must be flipped diagonally or rotated afterward.
1 - Finally I understood. An image worth a thousand words!
Transformer T1 is connected Yd1-busbars:
H1 - A, H2 - B, H3 - C;
X1 - a , X2 - b, X3 - c;
Transformer T2 is connected Yd11-busbars:
H3 - A, H2 - B, H1 - C;
X1 - c, X2 - b, X3 - a;
2 - The annex shows the calculations I made to analyze the problem. These connections are in accordance with IEC 60076-8-1997 pag. 86 Fig 21 – reversed sequence
Thank you guys for more learning in electrical engineering!
