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## Analysis and Judgment of 110kV Transformer Low Voltage Short Circuit Impedance T

2020.09.08

A technician from our company went to a transformer substation in Zhejiang and performed a transformer with a rated voltage of 110/10.5kV, a rated capacity of 40000kVA, a high-voltage side current of 210A, an impedance voltage of 19.76%, and a wiring group of Ynd11. Use CT3600 transformer short-circuit impedance tester to conduct low-voltage short-circuit impedance test. The temperature of the transformer is 45℃. The test data is shown in the table. Transformer short-circuit test data table: Calculate according to the test data in the table:

⑴ First convert the test voltage of each phase to the impedance voltage under the rated condition

UKAB=UAB×(IN/IUAB)=420×(210/6.9)=12.783×103(V)

UKBC=UBC×(IN/IUBC)=415×(210/7.2)=12.104×103(V)

UKCA=UCA×(IN/IUCA)=423×(210/7.3)=12.169×103(V)

(2) Substitute UKAB, UKBC, and UKCA into the formula:

UK%=√3×[(UKAB＋UKBC＋UKCA)/3UN]×100%

＝√3×[(12.783＋12.104＋12.169)×103/(3×110×103)] ×100%

= 19.45%

(3) The impedance voltage measured by calculation is 19.45%, which is less than ±3% compared with the nameplate impedance voltage. Therefore, the impedance voltage of the transformer meets the requirements of the test standard, "transformer short-circuit impedance deviation ±10%".

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