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21 RAYTECH Switzerland
STEP BY STEP OPERATION: CON’T. 8 – 1
Understanding Three Phase Transformer results:
Testing three phase transformers with a single phase test system usually
requires additional calculations to determine the actual Turns ratio or
Voltage ratio. In some instances the reading on the single phase
ratiometer is neither the Voltage Ratio nor the actual Turns Ratio.
A simple chart below is given to allow easy calculation of either Voltage
or Turns Ratio from the displayed value on the TR-1 & TR-1P.
The only requirement to use this calculation chart is that the connections
to the transformer be made exactly as indicated in the previous charts
(See pages 15 to 20).
Config. Multiply reading
With this factor
to get Turns Ratio
multiply reading
with this factor
to get Voltage Ratio
multiply Turns Ratio
with this factor
to get Voltage Ratio
D: D 1 1 1
D: Yn 1 1/sqrt3 1/sqrt3
D: Y 1.5 sqrt3/2 1/sqrt3
D: Zn 2 2/3 1/3
Yn: D 1 sqrt3 sqrt3
Yn: Yn 1 1 1
Yn: Y 1.5 1.5 1
Yn: Zn 2 2/sqrt3 1/sqrt3
Y: D 2/3 2/sqrt3 sqrt3
Y: Yn 2/3 2/3 1
Y: Y 1 1 1
Y: Zn 1 1/sqrt3 1/sqrt3
Single 1 1 1
Sqrt 3= 1.732051
1/Sqrt 3= 0.57735
2/Sqrt 3= 1.1547
2/3= 0.66667
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