A three-phase, 4.16-kV main bus feeds a three-phase, 5-MVA, 4.16-kV/480-V transformer with 6% impedance. The transformer powers multiple loads, including a three-phase, 1000-hp motor as shown in the following figure. Determine the symmetrical rms fault current through CB1, CB2, CB3, and CB4 under a three-phase fault at the spark location assuming: 

(1) All cable impedance is negligible, 

(2) The bus has multiple generators of large capacity to make it an infinite bus, and

(3) The motor delivers rated load before the fault with 90% efficiency and 0.85 pf lagging.

Transcribed Image Text:

Transformer 3-ph, 5-MVA, 6% Z ele IBus 3-ph, 4.16 KVLL infinite bus CB4 CB3 CB2 CB1 480-V swbd ele IMotor 460-V, 3-ph, 1000-hp motor ITotal 120-V Lighting loads 3-phasefault 460-V Loads