Did you ever hear a discussion on whether there a point of low SF6 where internal flashover becomes a concern? I suppose in a well monitored breaker it is not realistic to go to 0 pressure without first getting an alarm and having time to isolate the breaker, but that is not the case here...
I know you do not operate an SF6 breaker if gas pressure is low, but assume dead tank SF switch where there is at least a little positive pressure:
a) Is there a gas pressure level where there a risk of an internal line to ground fault?
b) If the breaker is open, is there a gas pressure where...
My only notable experience with impedance relays seeing through a xfmr are in large auto-xfmrs where there are line relays on the remote side of the xfmr that can be relied upon to trip in less than a second (likely instantaneously in the reach of the xfmr relay). I seem to recall a case where a...
Overload protection is best done by design of the attached load, not by tripping fuses and relays. If you rely on fuses and relays to keep you from overloading the system, you have an unreliable system and a notable design problem.
Fuse amp rating is the current they can carry without damage...
With complex enough software models of the system, ground overcurrent is still used. I concur it would be nice to bypass the tedious checking of their coordination for a zillion different outages. I guess till all the old EM relays go away, they remain even in new uP relays, at least in the...
I am not going to put my brain through the strain of figuring out everyone's logic, but I see a basic problem statement error that makes this difficult for me:
In a delta system, loads are phase to phase, yet the problem starts my mentioning KVA on a single phase basis (phase A = ##kVA, phase B...
On David's comment of moving cables farther apart:
I d not think that will decrease phase to ground or phase to phase capacitance of sheilded cables, but I suppose it will increase inductance a tad.
On bacon4life comments:
Nice set of options. Increasing voltage rating of cable will force...
"Oh come on John". Hmmmm, Oh well, I will move on past what sounds like a bad attitude or an anger of some sort.
My suggestion was related to the fun of a young and bright mind fully understanding the physics of magnetics fields with earth and ground wire return, well enough to finding a set of...
Zero sequence of transmission lines. I tried to figure it out once, and was overcome by the complexity. Most of what people use is referred to as Carson's equations, but if you pull up a copy of Carson's paper, it provids un-derived equations that jump to results that I have never seen proven...
The voltage difference makes me wonder how much a fault at the end of say the 345kV line creates a current in the 115kV line, and vice versa. If there is low Io in the parallel line for a fault on the parallel line, then the parallel line would have low effect on the reach of the relays on the...
The way impedance relays looking into xfmrs are are set, load current is not really a problem. Assume xfmr Z = 9% per unit, and system impedance 1% on the xfmr base, for arguement and also a reasonable set of values. Through fault current is 10 x the load (self cooled MVA).
An impedance relay...
Reliance on lockout relays to prevent damage to high impedance bus diff relay from damage has been an industry standard since the invention of the high impedance bus relay (1930's?) and I am unaware of a concern about their failure and subsequent damage to the relay. Or maybe I am just unaware...
Can some of you more experienced people comment on whether I have mixed up additive and subtractive in the two bullets?
The two versions of the xfmr arise out of different approaches to making the winding polarity orientiation recognizable without having to look at the busihg polarity marks.
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I stand corrected again. One sample is not used in relays to trip. It takes a cycle's worth of data to accurately calculate RMS and fundamental frequency magnitude, though you can calculate either RMS or fundamental frequency data off of a quarter or half cycle of data if you assume that quarter...
