Some power line device questions

Line caps typically start at about 50 kVAR per can. That works out to about 2.1 uF for your line voltage.

More likely its a current limiting fuse. It limits the peak fault current to the cap. Normal overcurrent fuses don't open fast enough to limit the first half cycle current peak.

Maybe current transformers?

Typically, reclosers count the number of station breaker trips and recloses. The furthest one out will be set to open after the first trip. If the breaker recloses and trips again, the next recloser in, being set to two counts, opens, If the station breaker closes and trips again, the next recloser in opens after three trips. No fancy communications infrastructure required.

Just to add to Paul's comments a little. Many protective relaying schemes use 'distance relays'. These devices can 'measure' the distance/direction between them and the fault. Their contacts are coordinated with the overcurrent relays to provide selective tripping. If a high current fault is outside the distance relay's range, then the instantaneous tripping is blocked so that a substation closer to the fault can trip it and clear the fault. The inverse time tripping is still left active, so if the nearest substation *doesn't* clear the fault, then the inverse time delay relaying at the next station (the one whose distance relay blocked instantaneous tripping) will time out and try and clear the fault. Misadjustment of the distance that distance relays are set for can cause problems though, if too short, you have some portion unprotected, if too long, then faults near the second substation can trip two substations.

Recloser will happen *after* the fault is cleared the first time (usually several seconds). Which ever station cleared the fault will 'reclose' after a time delay to try and reenergize the line. Fast-recloser is an exception in that they will reclose in just a cycle or two. Fast-reclosure is used for stability in parallel lines where lightning strikes can cause flashover of lightning protectors. I think flashovers (either lightning protectors or line-line in high winds) are about the only type of fault that can clear itself fast enough for fast-reclosures.

Some substation protective relaying at the higher end of power transmission

*do* use line signaling between stations ('tone' equipment). Often this is for backup protection if the station nearest the fault cannot clear it, tone equipment will signal other stations in a multiple-feed system.

As for power, many protective relaying schemes use line power (auctioneered from either line coming into station is common). But so are 'station' batteries that provide DC when extreme reliability is needed (generating stations and major yards).

daestrom

On distribution systems, capacitor "cans" come in 50, 100, 150 and 200 Kvar sizes (at least that is what we use). The "round" devices you see could be current limiting fuses, or oil/vacuum switches for opening and closing the banks. On systems that use PLC (power line carriers)for communications (such as load shedding and automated meter reading), there is often a choke in series with the capacitors to block them from shunting the high frequency signals to ground. Relcosers in series all see the same fault current, but they typically all have inverse time tripping characteristics. This means that the higher the fault current, the faster they trip. If the system is designed correctly, the one closest to the fault will have the quickest trip time, so it will open before the upstream devices do. If it fails to operate, the next one in line will catch it. No communication neccessary. In newer loop schemes, where a line can be fed from several sources, utilities are using the newer relays that are basically programmable logic controls. They can sense current and voltage, what direction the fault is in, and send communications to other relays to trip or block tripping according to the protection scheme devised. Communications can be fiber, radio, etc. depending on the speed of the switching required.