A.01.13_TR_SS_Fault_Current_AMD0002.pdf

Table Rock MG Control Center Fault Current Calculation jfm 9-6-17

Notes & Assumptions

1) Both 480V feeders to the MG Control Center will have the same available fault current.

2) Worst case fault current will occur when both station service generators and the station service transformer are connected to the 480V system with the bus tie breaker closed.

3) The station service transformer is assumed to be connected to an infinite bus on the primary side.

4) There are no induction motor loads to contribute significant fault current.

5) Feeder impedence is assumed to be zero to give the most conservative results.

6) Station service transformer hi-side voltage is assumed to be 14.4KV as set by generator operating limits.

7) Station service generator voltage is assumed to be 528VAC (110%).

Figure 1 - MG Control Center 480V Feeders

Station Service Transformer Fault Current (ISST)

Nameplate Data:

13,2000V delta to 480V delta

1000MVA

Z = 11.24% (0.1124pu)

Rated 480V Current = 1000/.48/1.732 = 1203A PU Voltage = 14.4/13.2 = 1.09pu PU Fault Current = 1.09/.1124 = 9.71pu = 11681A = ISST

Station Generator Fault Current (ISSG)

Nameplate Data:

875KVA, 480V, 1052A

D-Axis Saturated Transient Reactance = 0.27pu

PU Voltage = 528/480 = 1.1pu PU Fault Current = 1.1/0.27 = 4.07pu = 4286A = ISSG

Total Fault Current = ISST + 2 x ISSG = 11681 + 2 x 4286 = 20,253A