2-2 G60 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUALPRODUCT DESCRIPTION CHAPTER 2: PRODUCT DESCRIPTION2The following single-line diagram illustrates the relay functionality using American National Standards Institute (ANSI)device numbers.Table 2-1: ANSI device numbers and functionsDevice number Function Device number Function21P Phase distance backup 51N Neutral time overcurrent24 Volts per hertz 59N Neutral overvoltage25 Synchrocheck 59P Phase overvoltage27P Phase undervoltage 59X Auxiliary overvoltage27TN Third harmonic neutral undervoltage 59_2 Negative-sequence overvoltage27X Auxiliary undervoltage 64F Field ground protection32 Sensitive directional power 64S Sub-harmonic stator ground protection40 Loss of excitation 64TN 100% stator ground46 Generator unbalance 67_2 Negative-sequence directional overcurrent49 Thermal overload protection (RTD) 67N Neutral directional overcurrent50BF Breaker failure 67P Phase directional overcurrent50G Ground instantaneous overcurrent 68 Power swing blocking50N Neutral instantaneous overcurrent 78 Out-of-step protection50P Phase instantaneous overcurrent 81O Overfrequency50SP Split phase protection 81R Rate of change of frequency50/27 Accidental energization 81U Underfrequency51G Ground time overcurrent 87RGF Restricted ground fault51PV Phase time overcurrent with voltagerestraint87S Stator differential
