GE Multilin C70 Capacitor Bank Protection and Control System 5-2435 SETTINGS 5.7 CONTROL ELEMENTS5To 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 5.23)In the above equation,• τrst = thermal protection trip time constant• Tmin is a minimum reset time settingFigure 5–112: 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:(EQ 5.24)t rstτrstkI B( )2I2 kI B( )2–----------------------------- ln× T min+=0.1 1 10 100I / Ipkpt (min)0.010.1110100τ = 30rstτ = 30opT = 10min827724A1.CDRE n E n 1–tΔt op In( )---------------+=
