Sample TCC curve image with annotations showing coordination between relay, recloser, and fuse.
to ensure the protection system knew which way the "river" was flowing. electrical distribution system protection pdf
. This was the "proper" part of the system. He had programmed the devices so they operated in a specific hierarchy: should blow before the trips for a permanent fault on a branch. should trip before the Substation Breaker Sample TCC curve image with annotations showing coordination
The primary objective of protection is not merely to prevent damage, but to ensure . A protection system must detect a fault, isolate only the faulted section, and leave the rest of the system operational. This concept, known as "selectivity," is the cornerstone of modern relay coordination. This was the "proper" part of the system
| | Primary Protection | Backup Protection | Common Relay ANSI Codes | |---------------|------------------------|------------------------|-------------------------------| | Transformer (<5 MVA) | Fuse or breaker | None (or fuses primary) | 51, 50 | | Transformer (>5 MVA) | Differential | Overcurrent | 87, 51, 50G | | Feeder (MV) | Overcurrent | Directional OC | 51, 67, 50N | | Motor (>500 HP) | Overload + short | Ground fault | 49, 50, 51G | | Capacitor Bank | Overvoltage + overcurrent | Unbalance | 59, 50, 60 |