Transformer impedance is one of the important information that is needed for the transmission line modeling for power flow, short circuit and other various power system simulations, and protection coordination. However, unlike the transmission line that has a, more or less, standard design, thus easy to compute and obtain the equivalent model, modeling of the transformer is almost impossible without the percent impedance (%Z) information. Unfortunately, % impedance value is hard to generalize because it varies for every transformer model and ratings. Due to various parameters affecting the value of %Z, it is also hard to come-up even with a typical value. Even for transformers with same capacity and voltage ratings, %Z could still vary to some range.
This survey is an initial approach in making a study for good % impedance estimation for grid modeling (if information from the actual transformer is not available) based on the analysis of the surveyed actual % impedance that we personally gathered.
Below is the table of transformers that we, so far, gathered showing its essential ratings including the percent impedance or %Z;
|MVA rating||Cooling System||LV (In kV at nominal tap)||HV (In kV at nominal tap)||(Hz)||% Impedance||Cnxn||Loca- tion||Standard||Made by||Date Made|
|32/44.8/64||OA/FOA/FOA||13.2||230||60||13.63 at 64 MVA||Y-D||Ph||ANSI- C57-12||Mitsubishi||1976|
|70/100/125||OA/FA/FA||13.8||230||60||9.52 at 100 MVA||Y-D||Ph||ANSI- C57||ItalTraFo||1974|
|13.8||230||60||14.68 at 150 MVA||Y-D||Ph||ANSI- C57||Siemens||1998|
|70/100||OA/FA||13.8||230||60||17.57 at 100 MVA||Y-D||Ph||ANSI- C57- 12-1973||Pauwels Trasfo||1993|
|47.5||ONAN||13.8||138||60||11.73 at 47.5 MVA||Y-D||Ph||ANSI- C57- 12-1973||Fuji Electric||1973|
|12||ONAN||4.16||13.8||60||9.61 at 12 MVA||-||Ph||ANSI- C57- 12-1973||Fuji Electric||1973|
|1.8||ONAN||0.48||13.8||60||10.61 at 1.8 MVA||-||Ph||ANSI- C57- 12-1973||Fuji Electric||1973|
|OA/FA||13.8||69||60||4.97/5.72 at 13.33/15.33 MVA||Y-D||Ph||ANSI- C57- 12-1973||Meiden||1979|