Utility Recloser "Problem"

| 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

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.

I am single phase and the transformer is on a pad behind my house and underground to the house as well as the neighborhood. The overhead lines are outside the neighborhood, so I assume the fault was on those lines. We do have some sort of loop arrangement in the underground feed in the neighborhood. I am not sure but think there is a programmed swich of the loop at around same time every night 11:00PM or midnight depending on season. I hear all my UPS' chirping at same time. The recloser probably is on the overhead lines feeding ours and other neighborhoods.

That could be a capacitor bank at the distribution substation switching in (or out). This can cause momentary voltage transients.

Yes. Its not normal to protect underground only systems with a reclosing function (recloser or station breaker). Typically, when underground systems fault, its permanent. The trip-reclose is used to automatically restore an overhead system that might have experienced a momentary fault due to tree limbs or the like.

| Yes. Its not normal to protect underground only systems with a reclosing | function (recloser or station breaker). Typically, when underground | systems fault, its permanent. The trip-reclose is used to automatically | restore an overhead system that might have experienced a momentary fault | due to tree limbs or the like.