8.11 Directional overpower protection GOPPDOP8.11.1 IdentificationFunction description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberDirectional overpower protection GOPPDOPP >2DOCUMENT172362-IMG158942V2 EN328.11.2 FunctionalityThe task of a generator in a power plant is to convert mechanical energy available asa torque on a rotating shaft to electric energy.Sometimes, the mechanical power from a prime mover may decrease so much that itdoes not cover bearing losses and ventilation losses. Then, the synchronous generatorbecomes a synchronous motor and starts to take electric power from the rest of thepower system. This operating state, where individual synchronous machines operateas motors, implies no risk for the machine itself. If the generator under considerationis very large and if it consumes lots of electric power, it may be desirable to disconnectit to ease the task for the rest of the power system.Often, the motoring condition may imply that the turbine is in a very dangerous state.The task of the reverse power protection is to protect the turbine and not to protect thegenerator itself.Figure 197 illustrates the low forward power and reverse power protection withunderpower and overpower functions respectively. The underpower IED gives ahigher margin and should provide better dependability. On the other hand, the risk forunwanted operation immediately after synchronization may be higher. One should setthe underpower IED to trip if the active power from the generator is less than about2%. One should set the overpower IED to trip if the power flow from the network tothe generator is higher than 1%.When IED with a metering class input CTs is used pickup can be set to more sensitivevalue (e.g.0,5% or even to 0,2%).1MRK502052-UEN B Section 8Current protection427Technical manual
