0
\$\begingroup\$

I have a step down 3 phase Delta/Wye transformer. 400 volts on the primary and 208 volts on the secondary. I have about 4 amps per phase on the primary and 13 amps on the secondary.

How is this possible? It should be around 8 amps on the secondary but the amperage has more than tripled. This means that the transformer is generating over 1 KW of power by itself.

Has anyone else seen this?

\$\endgroup\$
  • \$\begingroup\$ Can you post a picture of the transformer's rating plate or nameplate? \$\endgroup\$ – Li-aung Yip Sep 1 '15 at 14:48
  • \$\begingroup\$ Did you measure the actual voltage too? \$\endgroup\$ – Olin Lathrop Sep 1 '15 at 14:51
  • \$\begingroup\$ No, but it is a 50 KVA Delta/Wye K-13 xfmr. \$\endgroup\$ – Matt Wells Sep 1 '15 at 14:51
  • \$\begingroup\$ That is the actual voltage. \$\endgroup\$ – Matt Wells Sep 1 '15 at 14:52
  • 1
    \$\begingroup\$ Post a schematic as to how exactly it is hooked up. I will guarantee you though that the transformer is not generating any extra power. \$\endgroup\$ – R Drast Sep 1 '15 at 15:00
1
\$\begingroup\$

I think the 3-phase input complicates things so the calculation is not the same as for a "normal" (1 phase) transformer.

There's a calculator and some formulas here

If I fill in:

Three phase P = 4.8 kVA

Line to line voltage = 208 V

then I get the 13.3 A

BUT if I select:

Line to neutral voltage = 208 V

I get 7.7 A

So it depends on how you connect the loads to the transformer, see Three-phase power.

Also this might also help you understand.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.