Sizing primary & secondary XFMR protection

[l3city]

Hi, this is the first time I been involved in working with high voltage XFMRS.
I'll appreciate any help from any of you.
I have two different XFMRs

1)12.47KV-4160V, 750KVA, 3Ph
2)4160V-120/208V, 150KVA, 3Ph
This is a big solar array project, and I am going from 208V to 4160V, then from 4160V to 12470V

any comments, tips, calcs)

 

[davidbeach]

Why make the intermediate step of 4160V? Extra transformers would just result in more losses. If you're a utility, you should have standards to work with. If non utility and in the US, you have the NEC requirements to comply with, otherwise you will have some other local code requirement.

 

[l3city]

davidbeach, well this is what I been given by the Elect. contractor who hired us. know that you respond, I think there are also special typoe of cable used for this hogh voltages, any ideas??

 

[swn1]

Medium voltage cable is indeed a different kind of thing, requiring specialized termination kits and a properly trained installer. A bad termination may last a while but it will eventually fail.

You didn't really say what you are tring to do to or with this system. What kind of "tips" or "calcs" do you want?

In answer to the "why" question: this kind of two-stage system is common, though usually with bigger transformers, in industrial plants. The utility distribution network has the same architecture. It minimizes the total life cycle cost of the system.

How? Keeping the required conductor size in the 4/0 to 1500 MCM range minimizes the combined cable + switchgear + transformer cost. Too high a voltage and the insulation costs too much for the value of the energy delivered. Too low and the copper costs too much.

 

[l3city]

swn1:
Thanks for responding, we solve the "problem" (Well after all, seemed to be hard, ended-up easy) Anyways, we got it done. I was trying to get ideas on sizing fuses and disconnects for the XFMR's used. WE ended-up using a big sidemounted switchgear next to the 12470V XFMR, from there we went to the smaller XFMRS (each with its own disconnect, so they can be serviced in case they needed)
What's the project about..? Well, it's a big solar array project, generating "tons" of power (you were right, this type of XFMR's and cables where for "high power" stuff)
thanks for replying

 

[wfowfo]

Out of curiousity, was the 12.5/4.16 Kv transformer a wye/wye or delta/wye?