8.5 Thermal overload protection, one time constant,Celsius/Fahrenheit LCPTTR/LFPTTR IP14512-1 v78.5.1 IdentificationM17106-1 v7Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberThermal overload protection, one timeconstant, CelsiusLCPTTR 26Thermal overload protection, one timeconstant, FahrenheitLFPTTR 268.5.2 Application M15283-3 v9Lines and cables in the power system are designed for a certain maximum loadcurrent level. If the current exceeds this level the losses will be higher thanexpected. As a consequence the temperature of the conductors will increase. If thetemperature of the lines and cables reaches too high values the equipment might bedamaged:• The sag of overhead lines can reach unacceptable value.• If the temperature of conductors, for example aluminium conductors, gets toohigh the material will be destroyed.• In cables the insulation can be damaged as a consequence of theovertemperature. As a consequence of this phase to phase or phase to earthfaults can occur.In stressed situations in the power system it can be required to overload lines andcables for a limited time. This should be done while managing the risks safely.The thermal overload protection provides information that makes a temporaryoverloading of cables and lines possible. The thermal overload protection estimatesthe conductor temperature continuously, in Celsius or Fahrenheit depending onwhether LCPTTR or LFPTTR is chosen. This estimation is made by using athermal model of the line/cable based on the current measurement.If the temperature of the protected object reaches a set warning level AlarmTemp, asignal ALARM can be given to the operator. This enables actions in the powersystem to be taken before dangerous temperatures are reached. If the temperatureSection 8 1MRK 511 407-UEN CCurrent protection158 Phasor measurement unit RES670 2.2 IECApplication manual
