Tricks A Dumb Grid Can Play


Inauguration Day
in Brookville, Pennsylvania arrived with a bang. Within minutes after Donald
Trump swore to preserve, protect, and defend the constitution of the United
States, the 911 calls began.  In
one house, light bulbs were exploding. 
Another resident reported that a power strip was smoking.  At another house, the siding was on
fire, and at yet another the electric meter was engulfed in flames.  The main radio transmitter at the
police station tripped out, so the 911 call center was unable to contact them until
the dispatcher used his battery-powered radio to make contact.  In all, about 400 residents of the
small western Pennsylvania town of 3800 suffered some type of damage, ranging
from singed carpets to fried computers and exploding fluorescent light fixtures.

The power surge
had nothing directly to do with Donald Trump.  A quick investigation by Penelec, the local electric
utility, revealed that an insulator on a power line had failed.  What follows here is my extrapolation
from the limited details in the Associated Press wire story, but represents
what I think is a good guess.

Electric power
networks are divided into transmission lines and distribution lines.  The transmission lines are the tall
steel-framed towers that span many miles across the countryside, and are the
interstate highways of the electric grid, transmitting megawatts of power from
generating plants to substations many miles away.  To transmit this much power efficiently, the voltage of
these lines is generally above 100,000 volts (100 kV).  For example, there is a 138-kV
transmission line that connects Brookville with the rest of the power grid in
western Pennsylvania, and there may be others at even higher voltages.

           

Once power arrives
at a substation, it is stepped down in voltage with large, expensive units
called transformers to a lower voltage suitable for distribution locally.  Distribution lines, the neighborhood
streets of the network, carry voltages in the range of 12 kV to 35 kV, or
occasionally higher in rural areas. 
My guess is that Brookville has at least two or three separate
distribution circuits with voltages in the 25-kV range.  The familiar wooden power poles that
carry telephone and cable TV lines also support power-distribution cables,
always suspended on the highest point of the poles.  Every few hundred feet, a “pole pig” (distribution
transformer), usually a metal can a couple of feet tall, lowers the voltage
still more to 240 V or less for delivery to commercial and residential
customers. 

What probably
happened was this.  One of the
high-voltage insulators on a transmission line carrying in excess of 100,000
volts failed mechanically, dropping its conductor on or near enough to one of
the town’s distribution lines to allow a flashover (an arc) to jump from the
100+ kV transmission line to a 25-kV distribution line.  All power-line insulators are built
with a safety margin.  That is, an
insulator for a 25-kV line may be able to withstand 50 or even 100 kV, which
can happen during situations such as lightning surges and so on.  This is good in normal circumstances,
but in this case it backfired.

The insulation of
the 25-kV distribution line held just long enough for the high voltage, four or
five times normal, to get into the distribution transformers and ultimately the
houses of about ten percent of the town. 
So for a few seconds or maybe even longer, equipment designed for 120 V
was receiving, say, 500 or 600 V. 

There are kooks
on YouTube who delight in taking innocent electric appliances such as razors,
clocks, toasters, light bulbs, and so on, and connecting them to high-voltage
power sources just to see what happens. 
They are never pretty. 
Every electric appliance has a maximum rated voltage, and when you
exceed it by 500% you either blow a fuse or, in the case of equipment that
doesn’t have fuses such as light bulbs, the excess heating makes something melt
or vaporize or explode. 

Many power strips
have surge-arresting devices in them meant to absorb fast transient surges
caused by lightning.  But those surges
usually last only milliseconds, and a surge of several seconds overheats such a
device, making it smoke, which explains the reports of smoking power
strips. 

Why didn’t all
the protective devices that a utility normally uses, such as fuses and circuit
breakers, operate right away? 
Because they are designed primarily for lightning strikes, not an
overvoltage that lasts many seconds. 
And the fuses probably didn’t blow right away because a fuse only
slightly over its rated current takes a considerable time to melt. 

Penelec has
announced that they will compensate those who have suffered losses as a result
of the surge.  Fortunately, no one
was injured, but a considerable amount of property was damaged and the mess
will take weeks or months to clean up. 

The “dumb
grid” in the title refers to the fact that most electric utilities still
use protective technology that was developed prior to World War I, for the most
part:  fuses and electromechanical
relays.  Innovative “smart
grid” technology connecting the power grid to the Internet and replacing
many electromechanical controls with faster-acting solid-state devices promises
a number of good things, mainly pertaining to increased efficiency and
reliability.  But it’s also
possible that if Brookville’s grid was smarter—that is, if it could have
figured out within milliseconds what happened and cut off the surge then—none
of the bizarre damage might have occurred.

Admittedly,
situations in which a transmission line arcs over to a distribution line are
rare.  But as Brookville shows,
they can happen.  If the new Trump
administration wants to improve America’s infrastructure, encouraging utilities
to take the smart-grid path is one way to do it.  Whatever Washington does about it, though, it’s too late for
a few hundred residents of Brookville, who are still replacing siding, light bulbs,
and computers as a result of a freak accident that shows we still have a ways
to go in improving electric utility safety and reliability.



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