Parallel Connection of 4-Wdg Transformers

[Kiribanda]

Hi all members,

This is a question based on a parallel connection of two four winding transformers and how they can be modeled in any load flow & short circuit software.

Recently I have seen the following 4-winding power transformer connection with closed buses in a large industrial plant. May be they are operating when everything is fine. Please visualize a situation where,

Four winding transformer A :
50/30/30 MVA/ 132-11 kV, Yyyd, OLTC on 132 kV side with usual 16 steps of +/- 1.25%.
Secondary S1, Tertiary T1 with a separate DELTA stabilizing winding.
S1 is connected to 11 kV secondary Bus B1A
T1 is connected to 11 kV secondary Bus B2A

Four winding transformer B :
50/30/30 MVA/ 132-11 kV, Yyyd, OLTC on 132 kV side with usual 16 steps of +/- 1.25%.
Secondary S2, Tertiary T2 with a separate DELTA stabilizing winding.
S2 is connected to 11 kV secondary Bus B1B
T2 is connected to 11 kV secondary Bus B2B

Bus Section Details:
11 kV Bus sections B1A & B1B are normally CLOSED by a 11 kV TIE circuit breaker.
11 kV Bus sections B2A & B2B are normally CLOSED by a 11 kV TIE circuit breaker.
But 11 kV Buses B1A/ B1B and B2A/ B2B are physically separated apart by about 10 m in the same 11 kV substation.

My concerns are,

1)How does the voltage is regulated on each 11 kV bus at 11 kV nominal with this parallel 4-winding transformer connection?

2)Is it reasonable to model this configuration as it is, in a load flow/ short cct software program?

3)Is this a standard connection/configuration? Any advantages and disadvantages or any practical difficulties?


Comments are welcome!

Regards!
Kiribanda

 

[jbartos]

Suggestions marked ///\\1)How does the voltage is regulated on each 11 kV bus at 11 kV nominal with this parallel 4-winding transformer connection?
///It depends. Are you developing one line and preparing the paralleled transformer connections? It appears that if you parallel the 50MVA transformers with 11kV secondary, the MVAsc may be too high for standard rated buses 1500MVA max. Notice that 100MVA/[.1x.1/(.1+.1)]=2000MVAsc, for example.\\2)Is it reasonable to model this configuration as it is, in a load flow/ short cct software program?
///It depends. If it is homework, anything can be done to show the theory understanding and the software skill.\\3)Is this a standard connection/configuration? Any advantages and disadvantages or any practical difficulties?
///The connection may be standard; however, the 11kV voltage will probably cause practical difficulties because of high MVAsc level.\\\

 

[stevenal]

See

http://www.beckwithelectric.com

for information on paralleling load tap changing transformers. Indepedant load tap changer controls will fight each other without a paralleling scheme.