GE Multilin T60 Transformer Protection System 5-2615 SETTINGS 5.7 CONTROL ELEMENTS5(EQ 5.53)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.• En is the accumulated energy at index n.• En – 1 is the accumulated energy at index n – 1.The thermal overload protection element removes the THERMAL PROT 1 OP output operand when E < 0.05. In case ofemergency, the thermal memory and THERMAL PROT 1 OP output operand can be reset using THERM PROT 1 RESET setting.All calculations are performed per phase. If the accumulated energy reaches value 1 in any phase, the thermal overloadprotection element operates and only resets when energy is less than 0.05 in all three phases.The logic for the thermal overload protection element is shown below.Figure 5–147: THERMAL OVERLOAD PROTECTION SCHEME LOGICTable 5–25: TYPICAL TIME CONSTANTSPROTECTED EQUIPMENT TIME CONSTANT MINIMUM RESET TIMECapacitor bank 10 minutes 30 minutesOverhead line 10 minutes 20 minutesAir-core reactor 40 minutes 30 minutesBusbar 60 minutes 20 minutesUnderground cable 20 to 60 minutes 60 minutesE n E n 1–tΔt rst In( )---------------–=6(77,1*6(QDEOHG )XQFWLRQ2II %ORFN $1'6(77,1*,$5066RXUFH,%506,&5066(77,1*6,$!Nî,E.)DFWRU,%!Nî,E,&!Nî,F%DVH&XUUHQW25$1'6(77,1*7ULS7LPH&RQVWDQW581(!6(77,1*65HVHW7LPH&RQVWDQW581( 0LQLPXP5HVHW7LPH5HVHW(WR6(77,1*2II 5HVHW/DWFK655HVHWGRPLQDQW)/(;/2*,&23(5$1'7+(50$/352723)/(;/2*,&23(5$1'7+(50$/35273.3$&'5
