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Single Phase Rating Page - Open Delta Transformer Editor
The single phase transformer ratings and impedances can be entered by clicking the Per Transformer button on the open delta transformer editor rating or impedance page.
Rated MVA
The single phase transformer T1 is the bank connected to the phase A at the Wye connected side. The single phase transformer T2 is the bank connected to the phase B at the Wye connected side. The single phase transformer T3 is the bank connected to the phase C at the Wye connected side. One of the 3 single-phase transformers will be hidden for the open delta transformer.
The equivalent power ratings of the Open Delta transformer are 2 times of the smaller power ratings between the two available single phase transformers. Note that the equivalent power ratings are not the required de-rated power ratings for operating. The factor of 0.87 may be taken for a 3-phase load at the Delta connected side to avoid the overloading of the transformer.
The Class 2 and Class 3 power ratings (when they are available) are calculated and displayed only when the Per Standard button is selected in the Open Delta transformer editor rating page. The User-Defined option must be selected in the Open Delta transformer editor rating page in order for them to be editable.
Note : the equivalent power ratings and impedances of the Open Delta transformer are not used in the calculations. The phase-by-phase model is used for the Open Delta transformer instead.
FLA
This displays the primary winding and secondary winding full load amperes corresponding to the smallest and the largest power ratings for each single-phase transformer.
kV
Enter primary and secondary line-to-neutral voltage ratings of each single-phase transformer in kilovolts.
Impedance
Enter the positive sequence impedances at the nominal tap setting, in percent, with the transformer MVA and kV ratings as the base values. Click the appropriate button to obtain the typical single-phase transformer impedance together with X/R ratio, or X/R ratio only.
The impedance and X/R ratio of the equivalent Open Delta transformer are calculated from the 2 single-phase transformer impedances and X/R ratios.
Typical Z and X/R and Typical X/R
Click the appropriate button to obtain the typical single-phase transformer impedance together with X/R ratio, or X/R ratio only. The typical impedance and X/R ratio data for ANSI 2-winding transformers are based on two sources: American National Standard C57.12.10 and Industrial Power System Handbook by Beeman.
The Industrial Power System Handbook by Beeman (page 96) specifies typical data for transformers that has rating not larger than 500 kVA and primary voltage not higher than 12.47 kV.
Typical Impedance for Transformer Less Than or equal to 500 kVA:
- Group 1: Transformers with high voltage windings of less than or equal to 8.32 kV
- Group 2: Transformers with high voltages of greater than 8.32 kV and less than or equal to 12.47 kV
American National Standard C57.12.10 specifies impedance values for transformers larger than 500 kVA.
Typical Impedance for Transformer More Than 500 kVA:
** Self-cooled transformers with greater than 5000 kVA values are the same as those for 23 kV high voltage.
Typical X/R Ratios for Transformer More Than 500 kVA:
Rating Group 1* (^) Group 2+ % Z X/R % Z X/R kVA ≤ 5 2.3 0.88 2.8 0. 5< kVA ≤ 25 2.3 1.13 2.3 1. 25< kVA ≤ 50 2.6 1.69 2.4 1. 50< kVA ≤ 100 2.6 1.92 3.7 2. 100< kVA ≤ 167 4.0 3.45 3.7 3. 167< kVA ≤ 500 4.8 4.70 5.2 5.
High Voltage Side Low Voltage Side < 2.4 kV
Low Voltage Side ≥ 2.4 kV Without LTC With LTC kV ≤ 13.8 5.75** 5.5** 13.8 < kV ≤ 23 6.75 6.5 7. 23 < kV ≤ 34.5 7.25 7.0 7. 34.5 < kV ≤ 46 7.75 7.5 8. 46 < kV ≤ 69 8.0 8. 69 < kV ≤ 115 8.5 9. 115 < kV ≤ 138 9.0 9. 138 < kV ≤ 161 9.5 10. 161 < kV ≤ (230) 10.0 10.
Rating X/R Rating X/R MVA ≤ 1 5.790 8 < MVA ≤ 10 15. 1 < MVA ≤ 2 7.098 10 < MVA ≤ 20 18. 2 < MVA ≤ 3 10.67 20 < MVA ≤ 30 23. 3 < MVA ≤ 4 11.41 30 < MVA ≤ 40 27. 4 < MVA ≤ 5 12.14 40 < MVA ≤ 50 29. 5 < MVA ≤ 6 12.85 50 < MVA ≤ 100 34.
