MGVCL Exam Paper (30-07-2021 Shift 3)
Determine the ohmic value of the current limiting reactor per phase external to a 40 MVA, 15 kV, 50 Hz, three phase synchronous generator which can limit the current on short circuit of 6 times the full load current. The reactance of the synchronous generator is 0.06 pu.
The ratio of full load current to short circuit current = 1/6 Xsc = j/(1/6) External reactance required = j*((1/6) - 0.06)) = j*0.106 pu Full load current = (40*1000)/(√3*15) = 1539.6 A Per unit reactance = j*0.106 = (I*Xr)/V j*0.15 = (1539.6*Xb)/((15/√3)*1000)) = 0.60 ohm
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1.6 inches = 1.6 inches x 1,000 mils per inch = 1,600 mils 0.25 inch = 0.25 inch x 1,000 mils per inch = 250 mils Area = 1,600 x 250 = 400,000 square mils