The ImpedanceZC is the forward impedance giving the borderline between zone 1and zone 2. ZC should be equal to the transformer reactance ZT. The impedance isgiven in % of the base impedance, see equation 425.The angle of the impedance line ZB – ZA is given as AnglePhi in degrees. Thisangle is normally close to 90°.StartAngle: An alarm is given when movement of the rotor is detected and the rotorangle exceeds the angle set for StartAngle. The default value 110° is recommended.It should be checked so that the points in the impedance plane, corresponding tothe chosen StartAngle does not interfere with apparent impedance at maximumgenerator load.TripAngle: If a pole slip has been detected: change of rotor angle corresponding toslip frequency 0.2 – 8 Hz, the slip line ZA – ZB is crossed and the direction ofrotation is the same as at start, a trip is given when the rotor angle gets below theset TripAngle. The default value 90° is recommended.N1Limit: The setting N1Limit gives the number of pole slips that should occurbefore trip, if the crossing of the slip line ZA – ZB is within zone 1, that is, thenode of the pole slip is within the generator transformer block. The default value 1is recommended to minimize the stress on the generator and turbine at out of stepconditions.N2Limit: The setting N2Limit gives the number of pole slips that should occurbefore trip, if the crossing of the slip line ZA – ZB is within zone 2, that is, thenode of the pole slip is in the external network. The default value 3 isrecommended give external protections possibility to split the network and thuslimit the system consequencies.ResetTime: The setting ResetTime gives the time for (PSPPPAM) function to resetafter start when no pole slip been detected. The default value 5s is recommended.8.16.3.1 Setting example for line application SEMOD172162-25 v3In case of out of step conditions this shall be detected and the line betweensubstation 1 and 2 shall be tripped.IEDZB Line impedance = ZCZA = forward source impedanceIEC07000014_2_en.vsdIEC07000014 V2 EN-USFigure 233: Line application of pole slip protectionIf the apparent impedance crosses the impedance line ZB – ZA this is the detectioncriterion of out of step conditions, see figure 234.Section 8 1MRK 506 369-UEN BImpedance protection428 Line distance protection REL670 2.2 IECApplication manual
