| Several nights ago, our power suddenly failed, then cam back on, failed
| again, and came right back on. So far so good, I am used to this
| recloser action. Then moments later, the exhaust fan in the bathroom
| sounded like it was labored, running fast and the CFL lamp in the
| fixture lit up twice as bright as normal. I was concerned about this
| apparent over voltage condition and called the utility agter turning off
| some stuff. Next morning the lineman came by to say my voltage was
| normal but that a tree limb had fallen and that they had a "recloser
| problem". What would cause a surge lasting a few seconds?
I'm assuming your service is single phase and your service drop transformer
is connected line-to-nuetral.
A fault between one of the other phases and the neutral would pull the neutral
towards that phase. The voltage drop due to this fault current along the
neutral wire back to the source transformer at the substation would now be
additional voltage (need to figure vector sums to get the exact voltage and
phase change) applied to the primary of your service drop transformer. If
that distribution neutral were opened, you'd see the worst case scenario of
a 73% increase in voltage, minus any saturation effects on your service drop
transformer. But even with the neutral intact, a solid fault current will be
high and result in some significant voltage drop that could give you a 10% to
30% voltage increase.
Think of it is the faulted wiring trying to migrate the service transformer
from its line-to-neutral wiring partially over to line-to-line (fully if
the nuetral opens). Transformers that are wired for line-to-line would see
the reverse effect (a voltage sag).
I have seen voltage swells like this a couple times. In both cases it was
during severe weather when it would be expected for trees to contact power
lines. But otherwise I was never able to confirm any particular cause.
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
Click to see the full signature.