Sepam - HV/MV Protection and control units (ENG) - Trinet

Thermal overloadANSI code 49function n°OperationF431This function simulates the heat rise in the protectedequipment using the current measurements taken ontwo (I1 and I3) or three phases.It complies with theIEC 60255-8 standard.It monitors the heat rise and compares it with 2 setpoints OL1 and OL2:c according to the application, the first detectionset point is designed for alarm signaling(transformers, generators, capacitors) or detectionof hot status which is used by the starts per hourfunction (motors),c the second set point is designed for protection.The heat rise measurement may be accessedvia the via the pocket terminal or the communicationlink (Jbus/Modbus) even if the function is disabled.Taking into account of harmonicsHeat rise in equipment depends on the form of thecurrent flowing through it. Measurement of the rmsvalue of phase 1 current, which integratesthe influence of harmonics up to number 21,takes into account the wave form to calculate heatrise in balanced three-phase loads.Taking into account of negative sequence currentNegative sequence current is a significant factorin calculating heat rise in rotating machines.The rotating field that corresponds to the negativesequence current creates a double frequency rotatingcurrent that causes major losses.This is why the thermal overload function takesinto account the following equivalent current:Ieq 2 = I 2 + K.Ii 2I is the greatest of the following values:I1, I2, I3 et I1rmsIi is the current negative sequence.Adjust is the negative sequence factor(weighting coefficient).Operation curveThe protection gives a tripping order when the heat rise heating calculatedaccording to the measurement of an equivalent current Ieq is greater thanthe OL set point.The highest permissible continuous current is I = Ib e.The protection tripping time is set for the time constant T.The heat rise calculated depends on the current absorbed and the previous heatrise status.c The cold curve defines the protection tripping time according to a heat riseof 100%.10 1 cold curve1010 -110 -210 -3 0 510Influence of the time constantThe time constant depends on the equipment's thermal characteristics.It takes heat release and cooling into account.For a non-ventilated rotating machine, cooling is more effective when the machineis running than when it is stopped due to the ventilation caused by rotation.c Equipment running and stopping are calculated according to the current value:v running if I > 0.015Ib,v stopped if I < 0.015Ib.Two time constants can be set:c T1: heat rise time constant: concerns equipment that is running.The T1 thermal time constant is the time needed for the equipment under ratedload to reach 0.63 times the rated heat rise (obtained after an infinite time).c T2: cooling time constant: concerns equipment that is stopped.The T2 time constant is the time needed after stopping for the initial heat risein the protected equipment to drop to 0.36 times the rated heat rise.heating10.630T1Heat rise time constant.ttT = Loghot curvetT = LogleqIbleqIbleqIbleqIb22- OL2- 12- OLheating10.360T2Cooling time constant.tProtection functions2/21