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L7 - ECE 524 Transients in Power Systems Session 7 Page 1/9...

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ECE 524: Transients in Power Systems Session 7; Page 1/9 Spring 2012 Transient R-L Circuit Example Given a 230kV:34kV, -Ygrounded, 100MVA transformer supplied supplied by a source with a short circuit MVA of 2000. The transformer has a per unit reactance of 0.1pu on its ratings base. Both the transformer and the source impedance have an X/R ratio of 12. Calculate the complete phase A fault current if a fault occurs on the LV side of the transformer at 70 degrees past the voltage peak. Define Units: MVA 1000kW  S BASE 100MVA  pu 1  Transformer parameters: S rated 100MVA  XoverR 12  V hv 230kV  V lv 34.5kV  X trans 0.1pu  R trans X trans XoverR  R trans 0.01 pu Find the transformer impedances referred to the LV side since the fault occurs on that side. Z BLV V lv 2 S rated  Z BLV 11.9 Ω R transLV R trans Z BLV  R transLV 0.0992 Ω X transLV X trans Z BLV  X transLV 1.19 Ω L transLV X transLV 2 π 60 Hz  L transLV 3.157 mH
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