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Electric Power Distribution Engineering, 3rd Edition by Turan Gonen

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10.12 Fault-Current Calculations in Per Units

Fault currents can also be determined by using per unit values rather than actual system values, of course. For example, Anderson [3] gives fault-current formulas that use per unit values, as shown in Table 10.12.

Table 10.12

Fault-Current Formulas in Per Unit

Fault Type

Fault-Current Formula

Source Connection

I ¯ f,3ϕ = V ¯ f Z ¯ sys + Z ¯ T + Z ¯ ckt + Z ¯ f

Delta or grounded wye

L-L

I ¯ f,b = I ¯ f,c = j 3 × V ¯ f 2( Z ¯ sys + Z ¯ T + Z ¯ ckt )+ Z ¯ f

Delta or grounded wye

L-G

I ¯ f,a =0

Delta or

I ¯ f,a = 3 V ¯ f 2 Z ¯ sys +3 Z ¯ T +6 Z ¯ ckt +3 Z ¯ f

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