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Re: 1350 KVA Current limiting

Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>

Tesla list wrote:

Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>
My 15KV neon sign transformer finally gave out, so I pulled three new Staco 5.5KV transformers out of their packaging and wired the secondaries in series. I knew the label said the transformers were rated for 450KVA each, but I thought I must be reading it wrong or a period was missing in front of the digits. But it turns out that they really are rated for 450KVA and 5.5KV each. Now my 10KVA variac is way inadequate to handle the power. I've got a bunch of very large power resistors in my collection of parts. Can I put the resistors in series with transformer secondary output to reduce the current from 1350KVA to below 10KVA? I've never placed resistors on a high potential line before and want to learn as much about it before I do.

Hi Dave,

What is the Staco model number? And, how much does each one weigh?

I strongly suspect that you actually have transformers rated for 450 VA (0.450 kVA). If you did, in fact, have 450 kVA transformers, each would weigh in the range of 1500 - 2500 pounds apiece. If yours aren't nearly this big, then the faceplate may be in error (i.e., simply missing a period). This is not all that uncommon...

You can limit current to ANY sized transformer by adding inductance in series with the LV side primary. This works irrespective of the actual KVA rating of the transformer(s), and is a simpler, safer, more efficient, and usually much more cost effective way than trying to limit current on the HV side.

You can add a number of MOT primaries in series or series/parallel (with the HV sides shorted), one or more spools of #10 or #12 AWG house wire, or use an AC welder (output shorted) to add inductive reactance that will limit the current to the range of your variac stack. You can also check the Pupman archives for "ballast" to find these, and other ideas.

Good luck and best regards,

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