A three-phase, 6600-V main bus feeds a three-phase, 2-MVA, 6600/480-V transformer with 5% impedance. The transformer powers multiple loads, including a three-phase, 500-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 impedances are negligible, 

(2) The bus has multiple generators of large capacity (i.e., infinite bus), and 

(3) The motor delivering rated load before the fault with 92% efficiency and 90% pf lagging.

Transcribed Image Text:

Transformer 3-ph, 2-MVA, 5% Z IBus CB4 3-ph, 6600 VLL infinite bus CB3 CB2 CB1 480-V swbd 000 IMotor ITotal 460-V, 3-ph, 500-hp motor 120-V lighting loads 3-phasefault 460-V Loads