Three Winding Transformer 1

[bhks]

Working on the design of power distribution in an industrial plant, we are debating whether to use two winding transformers or three winding transformer with identical LV windings. We have the otion of using either TWO 25kV-480V 2MVA 2-winding transformers or ONE 25kV-480V/480V 4MVA 3-winding transfomer. Obviously, the use of 3-winding trasfomer reduces real estate requirement and capital outlay. However, there are disadvantages as well - more eggs in one basket, increased short circuit availability (increased arc-flash concerns), limited manufacturing experience (most leading manufacturers will like to stay away from 3-winding design for this size of transformers).
Has anyone got any experience in the use of three winding transformers of similar sizes and configuration? Your thoughts and advice would be highly appreciated. -bhks

 

[dpc]

Based strictly on economical analysis, the three-winder should be less expensive. We have worked for several clients who have 3-winders at various industrial facilities and power plants.

In the long run, most people tend to wish they had standard two-winding units for increased reliability and backup capability. This is especially true if they've ever had a 3-winder fail. Not much available in the "pre-owned" market and delivery times are pretty long.

I wouldn't think you'd have much trouble getting bids for a new three-winding - any major transformer manufacturer will have the necessary knowledge to build them.

 

[bhks]

Thanks for your response, dpc. We intend to use these transformers in secondary redundant system. You are right that transformer failure event would have greater adverse effect on redundancy. Talking to various manufacturers, I understand that most of them are not equipped to perform a heat run test on three winding transformers. Thus, you are forced to relax FAT requirements or narrow down your choice of manufacturers. Have you experienced such difficulties? Are there any manufacturers who will meet this requiremnt?
Regards