Schweitzer Engineering Laboratories SEL-251 - Page 14

ii Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Transformer Blown-Fuse Detection........................................................................................... 2-27
What Happens When a High-Side Fuse Blows?................................................................ 2-28
How Does the SEL-251 Relay Detect Transformer Fuse Operations?.............................. 2-28
Use the Detection Logic to Trip or Indicate....................................................................... 2-29
Demand Ammeters..................................................................................................................... 2-29
Fault Locator.............................................................................................................................. 2-30
Nomographs........................................................................................................................ 2-31
Event Report............................................................................................................................... 2-32
Event Report Triggering..................................................................................................... 2-32
Time-Overcurrent Element Curve-Timing and Time Delay Reset Equations........................... 2-33
TABLES
Table 2.1: Trip Circuit Monitor Alarm (TCMA) Truth Table............................................................... 2-10
Table 2.2: SEL-251 Relay Word............................................................................................................ 2-14
Table 2.3: Setting Group Selection Input Truth Table........................................................................... 2-21
Table 2.4: Power Supply Self-Test Limits............................................................................................. 2-23
Table 2.5: Self-Test Summary................................................................................................................ 2-25
FIGURES
Figure 2.1: SEL-251 Relay Conventional Terminal Block Model Inputs, Outputs, and Targets
Diagram ......................................................................................................................... 2-5
Figure 2.2: SEL-251 Relay Plug-In Connector Model Inputs, Outputs, and Targets Diagram ................ 2-6
Figure 2.3: Time Delayed 52A and 52B Functions................................................................................... 2-9
Figure 2.4: Trip Circuit Monitor (TCM) DC Voltage Connections ......................................................... 2-9
Figure 2.5: Trip Circuit Monitor Alarm (TCMA) Logic ........................................................................ 2-10
Figure 2.6: SEL-251 Relay SELOGIC Control Equations Block Diagram.............................................. 2-13
Figure 2.7: Relay Word Bit Realizations ................................................................................................ 2-15
Figure 2.8: Relay Word Bit Realization.................................................................................................. 2-16
Figure 2.9: SEL-251 Relay Front Panel Target LEDs ............................................................................ 2-17
Figure 2.10: Sequence Coordination, Ground/Residual Overcurrent Elements ..................................... 2-19
Figure 2.11: Distribution Transformer Bank Protected by High-Side Fuses.......................................... 2-28
Figure 2.12: Current-Limiting Reactor and Line Impedances ................................................................ 2-30
Figure 2.13: Nomograph for Fault Locating ........................................................................................... 2-32
Figure 2.14: Moderately Inverse Curves................................................................................................. 2-34
Figure 2.15: Inverse Curves .................................................................................................................... 2-34
Figure 2.16: Very Inverse Curves ........................................................................................................... 2-34
Figure 2.17: Extremely Inverse Curves................................................................................................... 2-34
Figure 2.18: SEL-251 Phase Overcurrent Logic Diagrams..................................................................... 2-35
Figure 2.19: SEL-251 Negative-Sequence Overcurrent Logic Diagrams............................................... 2-36
Figure 2.20: SEL-251 Ground/Residual Overcurrent Logic Diagrams................................................... 2-37
Figure 2.21: SEL-251 Overcurrent and Undervoltage Elements ............................................................ 2-38
Figure 2.22: SEL-251 Transformer Blown-Fuse Detection Logic.......................................................... 2-39
Figure 2.23: SEL-251 Demand Ammeters.............................................................................................. 2-40
Figure 2.24: SEL-251 Programmable Trip Logic Diagram .................................................................... 2-41
Figure 2.25: SEL-251 Close Logic Diagram........................................................................................... 2-41