8.5.6 Monitored dataTable 95:TRPTTR Monitored dataName Type Values (Range) Unit DescriptionTTRIP REAL - - Estimated time to trip (inmin)TTRIPCAL INTEGER - - Calculated time status totrip: not active/long time/activeTRESCAL INTEGER - - Calculated time status toreset: not active/longtime/activeTRESLO REAL - - Estimated time to reset ofthe function (in min)HEATCONT REAL - % Percentage of the heatcontent of thetransformerI-MEASUR REAL - % Current measured by thefunction in % of the ratedcurrent8.5.7 Operation principleThe sampled analogue phase currents are pre-processed and for each phase current thetrue RMS value of each phase current is derived. These phase current values are fedto the Thermal overload protection, two time constants (TRPTTR).From the largest of the three phase currents a relative final temperature (heat content)is calculated according to the expression:2finalrefIIæ öQ = ç ÷ç ÷è øEQUATION1171 V1 EN (Equation 49)where:I is the largest phase currentIref is a given reference currentIf this calculated relative temperature is larger than the relative temperature levelcorresponding to the set operate (trip) current a start output signal START is activated.The actual temperature at the actual execution cycle is calculated as:1MRK 504 135-UEN A Section 8Current protection175Technical manual
