8.5.1 IdentificationM17106-1 v7Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberThermal overload protection, onetime constant, FahrenheitLFPTTR 26Thermal overload protection, onetime constant, CelsiusLCPTTR 268.5.2 Application M15283-3 v8Lines and cables in the power system are designed for a certain maximum load current level. If thecurrent exceeds this level the losses will be higher than expected. As a consequence thetemperature of the conductors will increase. If the temperature of the lines and cables reaches toohigh values the equipment might be damaged:• The sag of overhead lines can reach unacceptable value.• If the temperature of conductors, for example aluminium conductors, gets too high thematerial will be destroyed.• In cables the insulation can be damaged as a consequence of the overtemperature. As aconsequence of this phase to phase or phase to ground faults can occur.In stressed situations in the power system it can be required to overload lines and cables for alimited time. This should be done while managing the risks safely.The thermal overload protection provides information that makes a temporary overloading ofcables and lines possible. The thermal overload protection estimates the conductor temperaturecontinuously, in Celsius or Fahrenheit depending on whether LFPTTR or LCPTTR (26) is chosen.This estimation is made by using a thermal model of the line/cable based on the currentmeasurement.If the temperature of the protected object reaches a set warning levelAlarmTemp, a signal ALARMcan be given to the operator. This enables actions in the power system to be taken beforedangerous temperatures are reached. If the temperature continues to increase to the trip valueTripTemp, the protection initiates trip of the protected line.8.5.3 Setting guideline IP14994-1 v1M15094-3 v7The parameters for the Thermal overload protection, one time constant, Fahrenheit/CelsiusLFPTTR/LCPTTR (26) are set via the local HMI or PCM600.M15094-5 v8The following settings can be done for the thermal overload protection.Operation:Disabled/EnabledGlobalBaseSel is used to select a GBASVAL function for reference of base values, primary current(IBase), primary voltage (UBase) and primary power (SBase).Section 8 1MRK 511 364-UUS ACurrent protection136Application manual
