Tettex 2293 - 14 Short Circuit Impedance; Overview; Theory; Definitions

Short circuit impedance
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14 Short circuit impedance
14.1 Overview
The unit can perform the short circuit impedance test of a transformer at reduced voltages, the
short circuit impedance in a transformer is quite linear with the voltage and therefore an
extrapolation to the nominal voltage can be perform for comparison.
This optional feature is enabled using the license manager. This process only needs to be
completed the first time magnetic balance is used. For instruction how to enable a feature please
read Chapter 16 Optional Features activation.
14.2 Theory
14.2.1 Definitions
The short-circuit impedance (Z
short-circuit
) is defined as the impedance corresponding to the voltage
(U
cc
) that must be connected to one pair of terminals of a transformer, with terminals of other side
shorted, which causes rated current (I
rated
) to flow on the two sides of the transformer.
LV
HV
I
rated
U
CC
rated
cc
CC
I
U
Z 
For single phase transformers, the sort circuit impedance in % (
cc
) can be easily calculated after
the Z
cc
has been measured according the formula
100
2

U
S
Z
mcc

Where:
cc

Short circuit impedance in %
U
cc
Short circuit voltage in V
S apparent power in VA from nameplate