7.2 Out-of-step protection OOSPPAM (78) GUID-8321AC72-187C-4E43-A0FC-AAC7829397C3 v17.2.1 IdentificationGUID-BF2F1533-BA39-48F0-A55C-0B13A393F780 v2Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberOut-of-step protection OOSPPAM<787.2.2 Application GUID-11643CF1-4EF5-47F0-B0D4-6715ACEEC8EC v6Under balanced and stable conditions, a generator operates with a constant rotor (power) angle,delivering an active electrical power to the power system, which is equal to the mechanical inputpower on the generator axis, minus the small losses in the generator. In the case of a three-phasefault electrically close to the generator, no active power can be delivered. Almost all mechanicalpower from the turbine is under this condition used to accelerate the moving parts, that is, therotor and the turbine. If the fault is not cleared quickly, the generator may not remain insynchronism after the fault has been cleared. If the generator loses synchronism (Out-of-step)with the rest of the system, pole slipping occurs. This is characterized by a wild flow ofsynchronizing power, which reverses in direction twice for every slip cycle.The out-of-step phenomenon occurs when a phase opposition occurs periodically betweendifferent parts of a power system. This is often shown in a simplified way as two equivalentgenerators connected to each other via an equivalent transmission line and the phase differencebetween the equivalent generators is 180 electrical degrees.SM1Synchronousmachine 1SM2E1 E2Synchronousmachine 2E1E2SM1Synchronousmachine 1Center of oscillationV, ISM2E1 E2Synchronousmachine 2E1E2ANSI10000107_3_en.vsdVoltages of all phasesto ground are zero inthe center ofoscillationANSI10000107 V3 EN-USFigure 47: The center of electromechanical oscillationThe center of the electromechanical oscillation can be in the generator unit (or generator-transformer unit) or outside, somewhere in the power system. When the center of the1MRK 511 364-UUS A Section 7Impedance protection103Application manual
