Old
Postings:
·
Reading Material for Power System Protection:
Link to the C.R. Mason's Text
http://www.geindustrial.com/industrialsystems/pm/notes/artsci/index.htm
*The
video clip shows a three phase air disconnect switch attempting to open the high
voltage supply to a large three phase 33 Million Volt Ampere Reactive
(MVAR) shunt line reactor. The reactor is the huge transformer-like
object behind the truck at the far right at the end of the clip. The clip was
believed to be part of the 500 kV
Normally, pressurized sulfur hexafluoride (SF6) gas "puffer"
interrupters, just to the right of the air break switches, will first
de-energize the circuit so that the air break switches can the open with no
current flowing. The actual switching elements for the interrupters are hidden
inside the horizontal bushings. However, as the interrupters open, a high
voltage switching surge causes one of the interrupter bushings to flash over.
Since this phase remains energized, the air break switch for this phase opens
"hot", and it continues arcing as the switch swings to the fully
"open" position. The arc continues to grow upward, driven by rising
hot gases and writhing from small air currents, until it easily exceeds 50
feet. Long arcs usually terminate before by connecting to an adjacent phase or
to ground, causing a detectable fault which then trips out the circuit. This
particular arc could have persisted for quite some time, but the utility
manually commanded an upstream Oil Circuit Breaker (OCB) to open, abruptly
extinguishing it.
As impressive as this may be, the air switch was NOT disconnecting a real load.
The arc is "only" carrying the relatively low (perhaps ~20 amp)
magnetizing current associated with the line reactor. The 94 mile transmission
line associated with the above circuit normally carries over 1,000 megawatts
(MW) of power between