It’s a good time to raise power related questions, as many U.S. locations are right now experience deadly weather which could result in outages.
It’s a good time to raise power related questions, as many U.S. locations are right now experience deadly weather which could result in outages.
Several years ago we had a killer ice storm which dribbled late into the night at ground temperature of about 30-degrees, and besides trees toppling from ice weight, power transformers blew up. Skip ahead to the present, and after a whole day of rain at 29-degrees there are surprisingly few outages being reported on the utility website. Now the rain has turned to sleet.
Question: what is it about freezing rain that causes a power transformer to explode?
Why is sleet any different from rain as far as the transformers are concerned?
Another utility resource, the gas company, reports it is also ready for outages. What would cause a gas outage?
Bad Wx and Power
Carl,
I am not an expert on this but have a little industrial power distribution experience so take this as “educated guesses”.
Ice differs from rain in that it builds up layers on transformer insulators which then can arc over. Usually motorized switches and breakers can act to protect the transformer from electrical damage but ice can cause other damage to the outdoor switchgear and lines in a substation if it falls from structures onto conductors or gear. Large transformers are sometimes fan cooled and if ice gets in the fans cooling is compromised. I have been told by a local power company engineer that the transformers are running near capacity and there is not a lot of headroom for overloading.
Now here’s a wild guess. Gas distribution is controlled by pumps and valves. If power is gone it is possible that the valves close to “fail safe”. I don’t really know for sure but this would make sense. We have never lost gas pressure in my neighborhood.
Here, water systems use booster pumps to maintain pressure but if these lose power the head from the storage tanks can maintain a usable pressure.
I grew up in a rural setting and we could go indefinitely with no power because the heating was done with coal in a gravity convective furnace, cooking was on a wood fired stove, and water was hand pumped from a well. It was darn inconvenient but it was reliable and self sufficient. I don’t like the vulnerabilities of modern systems but they sure are convenient.
Anyway, stay warm and safe if you can.
Neil
Try It Now…
Although I have seen primary line insulators shoot sparks into the air due to salt buildup on them, transformers (pole or pad mount) have cutouts and fuses on the primary side. When those fuses blow it’s like a stick of dynamite. In the process the transformer may be damaged. The cause from ice is usually when the lines either cross or come down from the weight.
Substations usually have an auto-recloser on the primary line circuit breaker. When the breaker trips, it waits about 10 seconds and recloses. If the fault is still present the breaker opens and locks out the circuit until the fault is located and isolated and then manually reset. If the fault is something like a tree branch across the primary lines, it may just burn until the branch is clear or the lines come down as there was not sufficient current to trip the breaker.
About the gas lines, the big fire/explosion a week ago was do to debri and/or water in a pressure regulator on a distribution line. That caused the regulator to fail and the pressure went from a few ounces to about 10 pounds.
Ice accumulation
Ice accumulates and is heavy, rain however does not accumulate on wires and isnt heavy since it does not accumulate.
Ice can stick and seep where its not supposed to be
(ie, my weather station froze up because of the sleet, and upon freeing it, froze up again less that 20 minutes later)
freezing temperatures effects on wires/metal
Wire and metal become brittle at very cold temperatures. Connections can begin to arc which in turn will cause a power line to snap under its own tensions. Now add accumulated ice to the wire while under tension in the freezing conditions.
Normally the grid is designed to handle these situations. However in areas where sub zero temperatures are not normal, the grid infrastructure is not geared for the sudden temperature swings.
Usually it is the lower voltage lines that come down before the larger high voltage lines do because of over growth of trees dangling across the lines. When the ice builds up on the tree branches, might as well just take a metal rod across those power lines. With the amount of voltage and current potential on them, they will “flash” heat in a nanosecond and light up like one long heat filament, in turn creating another sudden temperature swing from freezing to burning hot. Naturally the metal will give and SNAP…there goes the power.
I am willing to bet that these areas hit by the unusual winter blizzards this year will take steps to beef up these power grids and start a campaign for the trimming of those over grown tree branches….as well as get more snow plows and de-icing pellets for the roads! 😀
RFB