ZMaxEstimated maximum impedance value. An impedance that is higher than ZMax hasthe quality attribute as “Out of Range”.ZMinEstimated minimum impedance value. An impedance that is lower than ZMin hasthe quality attribute as “Out of Range”.7.2 Power swing detection ZMRPSB IP14499-1 v37.2.1 IdentificationM14853-1 v3Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberPower swing detection ZMRPSBZpsbSYMBOL-EE V1 EN-US687.2.2 Application IP14969-1 v17.2.2.1 General M13874-3 v3Various changes in power system may cause oscillations of rotating units. The mosttypical reasons for these oscillations are big changes in load or changes in powersystem configuration caused by different faults and their clearance. As the rotatingmasses strive to find a stable operate condition, they oscillate with dampedoscillations until they reach the final stability.The extent of the oscillations depends on the extent of the disturbances and on thenatural stability of the system.The oscillation rate depends also on the inertia of the system and on the totalsystem impedance between different generating units. These oscillations causechanges in phase and amplitude of the voltage difference between the oscillatinggenerating units in the power system, which reflects further on in oscillating powerflow between two parts of the system - the power swings from one part to another -and vice versa.Distance IEDs located in interconnected networks see these power swings as theswinging of the measured impedance in relay points. The measured impedancevaries with time along a locus in an impedance plane, see figure 66. This locus canenter the operating characteristic of a distance protection and cause, if nopreventive measures have been considered, its unwanted operation.Section 7 1MRK 505 393-UEN BImpedance protection134 Line differential protection RED650 2.2 IECApplication manual
