Raytech TR-1 - Page 19

Raytech USA, Inc. All rights reserved Ver. 1.13 18
Step By Step Operation: Con’t. 10 – 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 10 to 15).
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 / √ 3
1 / √ 3
D: Y
1.5
√ 3/2
1 / √ 3
D: Zn
2
2/3
1/3
Yn: D
1
√ 3
√ 3
Yn: Yn
1
1
1
Yn: Y
1.5
1.5
1
Yn: Zn
2
2 / √ 3
1 / √ 3
Y: D
2/3
2 / √ 3
√ 3
Y: Yn
2/3
2/3
1
Y: Y
1
1
1
Y: Zn
1
1 / √ 3
1 / √ 3
Single
1
1
1
√ 3 =
1.732051
1 /√ 3 =
0.57735
2 /√ 3 =
1.1547
2/3 =
0.66667
Example: Measuring a Y:D transformer:
The TR-1 Displays: 12.73
The Turns-Ratio is:
12.73 * 2 / 3 = 8.48667
( column 2 )
The Voltage-Ratio is:
12.73 * 2 / √ 3 = 14.6993
( column 3 )
or
The Voltage-Ratio is:
8.48667 * √ 3 = 14.6993
( column 4 )