Temporary Paralleling of Transformers

[dcdtn]

I am wanting to parallel a 150MVA with a 250 MVA transformer (both 161-46-kV) temporarily in the event that one needs to be taken out for maintenance. Normally, one bank is heavily loaded and the other lightly loaded and the 46-kV bus is split. My first question is what type of switch is needed to join the 46-kV buses, thus initiating the parallel operation. The second question is how long can these banks be operated in this temporary ,paralleled configuration. My last question is what type of switch is needed to deenergize one of the banks from the 46-kV side once the 161-kV breaker is opened (there is no breaker on the 46-kV side). Thanks in advance.

 

[dcdtn]

I would like to add a little to my original post. I have identified a breaker that can be used to tie the 46-kV buses together, so that is no longer a problem. I am still interested in knowing possible issues in paralleling these dissimiar transformers for short periods of time.

However, my main concern is that I will need to energize and deenergize the 150MVA bank from a newly installed switch on the 46-kV side. What is the minimum switch I will need (i.e. whip, vacuum, breaker, etc.)? And could there be voltage problems from energizing from the 46-kV side?

 

[mpparent]

Please make sure you are braced for paralleling, ie closed transition paralleling. If you are going open transition, then you should be ok. It's good to double check your bracing in either case.

Mike

 

[jbartos]

Suggestion: It is better to have one system grounding, i.e. at one transformer at a time.
Also, the secondary voltage should be exactly the same. The secondary windings are good to have protected at each transformer. Even a voltage regulator should be considered at each transformer to minimize currents between the transformers.