GE Multilin L30 Line Current Differential System 5-2415 SETTINGS 5.7 CONTROL ELEMENTS5f) THERMAL OVERLOAD PROTECTION (ANSI 49)PATH: SETTINGS CONTROL ELEMENTS MONITORING ELEMENTS THERMAL OVERLOAD PROTECTION THERMALPROTECTION 1(2)The thermal overload protection element corresponds to the IEC 255-8 standard and is used to detect thermal overloadconditions in protected power system elements. Choosing an appropriate time constant element can be used to protect dif-ferent elements of the power system. The cold curve characteristic is applied when the estimated Ip current is less than10% of the base current. If I p current is greater or equal than 10% than the base current, then the hot curve characteristic isapplied. Ip current is estimated with a fixed time constant for both cooling and heating that reaches to the final value in twoseconds on a step change (either step up or step down) signal.The IEC255-8 cold curve is defined as follows:(EQ 5.24)The IEC255-8 hot curve is defined as follows:(EQ 5.25)In the above equations,• top = time to operate• τop = thermal protection trip time constant• I = measured overload RMS current• Ip = measured load RMS current before overload occurs• k= IEC 255-8 k-factor applied to I B, defining maximum permissible current above nominal current THERMAL PROTECTION 1THERMAL PROTECTION 1FUNCTION: DisabledRange: Disabled, EnabledMESSAGE THERMAL PROTECTION 1SOURCE: SRC1Range: SRC 1, SRC 2MESSAGE THERMAL PROTECTION 1BASE CURR: 0.80 puRange: 0.20 to 3.00 pu in steps of 0.01MESSAGE THERMAL PROTECTION 1k FACTOR: 1.10Range: 1.00 to 1.20 in steps of 0.05MESSAGE THERM PROT 1 TRIPTIME CONST: 45 min.Range: 0 to 1000 min. in steps of 1MESSAGE THERM PROT 1 RESETTIME CONST: 45 min.Range: 0 to 1000 min. in steps of 1MESSAGE THERM PROT 1 MINIMRESET TIME: 20 min.Range: 0 to 1000 min. in steps of 1MESSAGE THERM PROT 1 RESET:OffRange: FlexLogic operandMESSAGE THERM PROT 1 BLOCK:OffRange: FlexLogic operandMESSAGE THERMAL PROTECTION 1TARGET: Self-resetRange: Self-reset, Latched, DisabledMESSAGE THERMAL PROTECTION 1EVENTS: DisabledRange: Disabled, Enabledt opτopI2I2 kI B( )2–-------------------------- ln×=t opτopI2 I p2–I2 kI B( )2–-------------------------- ln×=
