GE Multilin L60 Line Phase Comparison System 5-2755 SETTINGS 5.6 CONTROL ELEMENTS5Figure 5–140: 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 5.30)When current is less than the dropout level, I n > 0.97 × k × I B, the element starts decreasing the thermal energy:(EQ 5.31)In the above equations,• ∆t is the power cycle duration.• n is the power cycle index.• top(In) is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations.• trst(In) is the reset time calculated at index n as per the reset time equation.• In is the measured overload RMS current at index n.0.1 1 10 100I / Ipkpt (min)0.010.1110100τ = 30rstτ = 30opT = 10min827724A1.CDRE n E n 1–tΔt op In( )---------------+=E n E n 1–tΔt rst In( )---------------–=
