“Physics Forums (Forums > Engineering > Electrical Engineering)
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Impedance voltage is relative short circuit voltage, when secondary of a transformer is short circuited, and we are slowly raising the primary voltage "Vpr" until the current at the secondary reaches its nominal value. The ratio of the "Vpr" and nominal voltage of the transformer is called impedance voltage. It usually goes from 3% to 20%.
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I know its a strange name, we call it relative short circuit voltage (in my country).”
( https://www.physicsforums.com/threads/impedance-voltage-of-a... )


„Fakultet elektrotehnike i računarstva, Zagreb
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Energetski transformatori
Relativni napon kratkog spoja
napon kratkog spoja (uk)
- Prirodna karakteristika svakog transformatora koja proizlazi iz njegove izvedbe (geometrije)
- Određuje se pokusom kratkog spoja
- uk se obično izražava u postotku nazivnog napona
- U normalnom pogonu povoljniji je manji uk (manji pad napona)
- U uvjetima kratkog spoja povoljniji je veći uk (manja struja kratkog spoja)
- Normalno se kreće između 3 i 20%(od manjih prema većim snagama)“
( https://www.fer.unizg.hr/_download/repository/ElPos_predavan... )