4–124 889 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALPROTECTION CHAPTER 4: SETPOINTSLogging this data into the CT sat tool, produces the following CT saturation waveform:The waveform shows that during this external bolted fault with maximum fault current of25 kA, the CT (3000:5) will saturate severely, and produce only a ¼ of a cycle saturationfree time. Break 2 must be set to a through fault current so that the CT (3000:5) produces atleast ½ cycle saturation free time. The solution is to change the fault current to 15000 kA.The waveform now shows a bigger part of the first cycle before saturation.The fault current of 15000 Amps would then be translated as 15000/3000 = 5 timeswinding 2 CT. Bringing this to the same scale with respect to winding 1 CT reference , i.e.multiplying by a magnitude of 0.4521, the Break 2 setting would be:Break 2 = 5 *0.4521 = 2.21 xCT (w1)
