5-244 G30 Generator Protection System GE Multilin5.7 CONTROL ELEMENTS 5 SETTINGS5• IB = protected element base (nominal) currentTo ensure element accuracy for high overcurrent conditions, the maximum value of I/(k x I B) is limited to 8, even when real-istically it is exceeding this value.The reset time of the thermal overload protection element is also time delayed using following formula:(EQ 5.58)In the above equation,• τrst = thermal protection trip time constant• Tmin is a minimum reset time settingFigure 5–115: IEC 255-8 SAMPLE OPERATE AND RESET CURVESThe thermal overload protection element estimates accumulated thermal energy E using the following equations calculatedeach power cycle. When current is greater than the pickup level, In > k × IB, element starts increasing the thermal energy:t rstτrstkI B( )2I2 kI B( )2–----------------------------- ln× T min+=0.1 1 10 100I / Ipkpt (min)0.010.1110100τ = 30rstτ = 30opT = 10min827724A1.CDR
