Which one is the best connection for high voltage step-down transformers? 1

[usercan]

I know star-star and star-delta transformers are used in utility systems as a step down transformer due to their low costs. But which one is best for a 420/33 kV transformer? What would be the advantages/ disadvantages of each?

 

[crshears]

It depends . . . what is your situation? Without some background the answer will be too generic to be useful.

Better information yields better answers!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[davidbeach]

There is no universally "right" answer. The "best" choice for any given application would be to match what's being done in similar installation in the neighborhood. If that transformer is going to be networked on both sides, it absolutely has to have the phase shift that matches the existing phase shift; that immediately eliminates one of the choices. If your particular 33kV isn't networked, but there is networked 33kV in the area you'll still be better off if you match the phasing.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[prc]

The majority of step-down transformers that I came across were YN/yn connected. There were few locations or countries where the connection was Yn/d with grounding transformers at both sending and receiving ends of LV lines.

 

[usercan]

It depends . . . what is your situation? Without some background the answer will be too generic to be useful.

Better information yields better answers!

I'm not sure what kind of specific information you request but It will be a step-down transformer connected to distribution network. HV and LV sides will be both grounded. Zigzag Grounding transformer will be used for the delta connection.

 

[usercan]

The majority of step-down transformers that I came across were YN/yn connected. There were few locations or countries where the connection was Yn/d with grounding transformers at both sending and receiving ends of LV lines.

Some people say star-delta connected step-down transformers are becoming more important with the increase in distributed generation. Would you agree?

 

[RRaghunath]

Typically, the grid authorities insist on having one side Delta connected windings for the transformer. The reason is to prevent earth faults in downstream system affecting the grid.
Having Delta at transmission level increases the cost of transformer substantially and hence the only option is YNd connection.
I have seen YNyn0 transformers used within the T&D system. But these are typically where transmission and distribution are owned by one and the same agency.

 

[prc]

In distributed generation projects,these are called collector transformers and are not step down transformers,but step up transformers. In India,we have standardised YNyn transformers for this duty. Probably the reason for selecting YNd for this duty is other end (HV side of photovoltaic transformer) is delta connected with grounding transformer on the bus.