Siemens 7UT51

Contents 7UT51 v3
4 PRIM-2330C
4 Transformer Differential Protection (87T and 87HS).................................................................. 39
4.1 Method of Operation...................................................................................................................................39
4.1.1 Matching Currents ......................................................................................................................................39
4.1.2 Handling Non-Ideal Behavior......................................................................................................................41
4.2 Describing the Transformer ........................................................................................................................43
4.2.1 Type of Transformer ...................................................................................................................................44
4.2.2 Normal Operational Status .........................................................................................................................44
4.2.3 System Frequency......................................................................................................................................44
4.2.4 Rated Phase-to-Phase Voltage ..................................................................................................................45
4.2.5 Rated Apparent Power ...............................................................................................................................45
4.2.6 Phase Shift Between Windings ..................................................................................................................45
4.3 Describing the CT Scheme......................................................................................................................... 48
4.3.1 Nominal Secondary Rating of CTs..............................................................................................................48
4.3.2 Nominal Primary Rating of CTs ..................................................................................................................48
4.3.3 Three-Winding Transformers with Considerably Different Rated Powers ..................................................48
4.3.4 Orientation of CTs.......................................................................................................................................49
4.3.5 Processing the Zero Sequence Current .....................................................................................................49
4.3.6 Zero-Sequence Current Elimination vs. Correction Mathematical Illustration ............................................50
4.3.7 Using a Ground or Neutral Current CT.......................................................................................................54
4.4 Trip Characteristic.......................................................................................................................................55
4.4.1 Minimum 87T Trip Threshold......................................................................................................................56
4.4.2 High Set (87HS) Trip Threshold ................................................................................................................. 56
4.4.3 Lower Slope of Pickup Characteristic.........................................................................................................57
4.4.4 Upper Slope of Pickup Characteristic.........................................................................................................58
4.5 Through-Fault Restraint..............................................................................................................................58
4.6 Second-Harmonic Restraint .......................................................................................................................59
4.7 Higher-Harmonic Restraint .........................................................................................................................60
4.8 Blocking by Frequency Variance ................................................................................................................ 61
4.9 Time Delays................................................................................................................................................61
4.10 Events and Actions.....................................................................................................................................62
4.11 Single-Phase Transformers ......................................................................................................
..................66
5 Motor or Generator Differential Protection (87M/G)................................................................... 67
5.1 Method of Operation...................................................................................................................................67
5.2 Describing the Protected Motor or Generator.............................................................................................67
5.2.1 Type of Protected Object ............................................................................................................................ 68
5.2.2 Normal Operational Status .........................................................................................................................68
5.2.3 System Frequency......................................................................................................................................68
5.2.4 Motor/Generator Information ......................................................................................................................68
5.3 Describing the CT Scheme......................................................................................................................... 69
5.3.1 CT Orientation ............................................................................................................................................69
5.3.2 Nominal Primary Rating of CTs ..................................................................................................................71
5.3.3 Nominal Secondary Rating of CTs..............................................................................................................71