The Valleyist Papers
A COLLECTION OF ESSAYS WRITTEN IN FAVOUR OF THE IMPROVEMENT OF STEPHENS VALLEY
Author – William Ray
Edition 4. Issue 11.
This issue is a rewrite of a very early issue of The Valleyist. Since every power interruption of any type causes a lot of questions from the SV residents, and since a lot of new folks have arrived in the four years since we last addressed the subject, perhaps it is timely to revisit this.
Everyone in SV gets their electricity from Nashville Electric Service (NES). In turn, NES buys that power wholesale from Tennessee Valley Authority (TVA) at several substations around middle Tennessee. We are very lucky to have TVA as the power supplier to NES. TVA has a very diverse set of generation resources they use to supply electricity to its 153 local power companies, like NES. They use area dams to generate hydroelectric power (the original renewable energy resource for electricity generation) and those dams provide about 11% of the power we use here, they use nuclear plants to produce about 39% of our energy, they burn natural gas to get about 26% of our needs, they still burn coal to produce 19% of our energy, the rest comes from wind, solar and energy efficiency programs. It is great to have so much diversity on our supply because if something crazy happens to one source, or fuel, it doesn’t cripple TVA.
TVA was born of the Great Depression and FDR’s intent to make the economy and living conditions of the southeastern US better by seeing to it that electric power was democratized – made cheap and available to all. TVA is also tasked with managing the flow of the Tennessee River system, and the economic and environmental stewardship of the region. TVA is owned by the United States, but they get no financing from the public coffers. They raise their own capital completely apart from the federal government, and they pay their debt service with revenues they generate. You can read a lot more about TVA at www.tva.gov. NES was created in 1939 and is a non-profit, owned by Nashville Metro. NES policies are set by a Board consisting of five members, appointed by Nashville’s Mayor. You can read more about them and sign up to see their meetings at https://www.nespower.com/about-nes/.
NES is one of the largest municipally owned utilities in the US. They serve 420,000 meters over a 700 square mile area, using 5,900 miles of transmission and distribution lines in the process. But once NES purchases this TVA power and uses its distribution circuits to transport it, how does the power get to our homes in Stephens Valley?
Though NES hasn’t shared their mapping with us, by riding around and observing, we can tell that SV is normally served by a high voltage circuit that originates at the NES McCrory Lane substation. The good part about that is we are not too far from the source substation. The bad part is that a lot of that circuit comes down McCrory Lane, which is completely infested with trees that are looking for an opportunity to fall and damage the overhead circuit! To put this in context, just go down Highway 100 and turn right on McCrory Lane just past Loveless Cafe, and drive a few miles north while looking at the trees. See the problem?
As that circuit comes up Pasquo Road, there is one pole in front of the SV West project where the circuit goes underground to serve us. There is another pole near the original SV entrance on Sneed Road where the other half of the SV underground distribution starts. Both of these points are normally served by the same circuit out of the McCrory Substation, so when that circuit fails, all of SV is in the dark. This is still a good design that NES has implemented. Underground cables can fail, and the repair time can be many, many hours. Having redundant feeds into SV means that NES could reconfigure a failed underground component and get nearly all customers back on while repairs are taking place. This is a good thing! However, these additional connection points do introduce a certain number of potential problems. Many in SV just experienced a several hour outage due to the failure of a switch mechanism within one of those pad-mounted green boxes wherein underground cables connect to each other. Those switches a mechanical devices that include moving parts, and they can fail. But that is rare. In the last 60 months, SV has experienced only one such failure.
We're only discussing about 8 miles of NES grid here around SV. Since NES has about 5,890 other miles of plant to maintain, it is clear we are way out on the edge of their system. For now, being on the edge isn’t what we really want, but as the electric grid changes over the next few years, perhaps we will wind up in a very good position. Maybe we will discuss future possibilities for taking advantage of our remote location in a future issue.
You’ve likely noticed that we do have sporadic power outages in SV. The most common interruption to our electricity is a simple momentary interruption. Those are the events that send us scurrying to re-boot computers and reset the time on our garage door openers. These occurrences are from transient faults on the McCrory Lane circuit. A tree branch, an animal contact (think birds and squirrels), a lightning strike, or a car accident causes fault current to flow to ground. Outages to our power in SV can come from any and all of these hazards, and more. We don't have to be experiencing violent weather for our circuit to trip due to a fault. This fault current is recognized by a relay at the substation and the circuit breaker at the substation opens (just like a circuit breaker in our garages) the circuit to eliminate the overload. Now, when that happens at a substation the relays are fast and smart, and they immediately tell the circuit breaker to reclose. When that happens, and if the fault is gone, we only experience a sub one second blink. Of course, when one of our garage breakers trips, we must go find it and physically reset it. That normally takes a bit longer, but the principle is identical.
The NES record of service reliability in SV is quite good, by comparative industry standards, for a rural community outside of any city.
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