The Smart Grid, Part 1 - First Tell Me About LMP

I already know this won't be brief. No matter how much I say I'll try to keep it short, I can't. I talk too much and over-explain everything. Having accepted that, I sleep OK at night at peace with who I am.

With that out of the way....

Why do we need a "smart grid"?

If you've been following me for a while and have read the tutorials, you know the basic truth that AC power is generated exactly as it is consumed, with no practical storage applications. As demand goes up, frequency drops, and power plants increase output to match demand, and vice-versa. It is fluctuating every second. Thankfully, the smoothed out impacts of millions and millions of people turning lights and toasters and Blu Ray players on and off don't amount to much instantaneous fluctuation relative to the size of the interconnected grid. If you were trying to run a power grid of only five houses with a plant just barely big enough to do it, and they all happened to turn on a bunch of stuff at once, everyone would see a big dip and maybe low voltage damage - assuming it didn't trip the generator outright.

Following demand is not an efficient game. During high demand periods, power plants with expensive fuel sources have to run to keep supply up, raising the aggregate cost of power. During low periods, only the cheapest units run, lowering the aggregate cost, but when coal plants run below efficiency (usually under 80% or so), they create more pollution relative to power produced. Running thermal plants up and down every day for years wears them out, as the boilers and systems fatigue and break down from being heated and cooled over and over and over again. Overall energy costs go up not just from fuel costs, but repair and maintenance costs.

Despite real-time hourly changes in energy prices based on what power plants are running at that time of day, almost everyone at the consumer level pays a flat per-kilowatt hour charge for electricity. This is tricky for power companies, as they need to make their rate case with magic math that figures out how much revenue will be coming in based on which hours their systems are used and what energy costs actually are, with hopes that they get enough money to run the thing, but not so much that the consumers scream foul. It is frankly very easy to screw this up, and a couple of disastrous power market days with real-time energy prices increased by 1000% or more can take years for a company to recover from with their rate case locked-in usage fees.

The first step towards efficiency is to get all power companies in a large area to cooperatively control their power plants instead of playing the hourly market game. The Midwest Independent System Operator (MISO), a quasi-governmental reliability agency with authority over a huge footprint of power companies in the midwest, was the first to do this on a really large scale. Their coordinated control concept was based on a model called Locational Marginal Pricing (LMP).

Don't let these acronyms scare you, I'll try to keep it simple.

Let's say you have a self-contained power system with four power plants and no ties to the outside world. Your transmission lines are overbuilt and there are no restrictions on power flows anywhere in your system. Your customers pay for their electricity based on hourly usage instead of a flat round-the-clock average cost. Your power plants use different fuels and therefore have different costs. You run the cheapest unit until it reaches capacity, and then start the next cheapest unit. When #2 peaks, you start the third unit, etc. Figuring out your hourly energy costs are easy, it's basic math based on how much was produced from each plant for any particular hour, and everyone in your system is charged the same thing for any particular hour.

In this model, location means nothing. Pricing is flat across all areas by the hour. The wrinkle that screws everything up is constraints on the electric transmission system.

Back to the same model. Self-contained system with four plants, one in each quadrant. But this time, the transmission lines between the quadrants do not have unlimited capacity. As long as no lines are at their limits, the flat hourly pricing works fine. Let's say the cheapest unit is in quadrant 1. Now, as long as demand is low, that cheap unit can supply everyone fine, but as the day picks up, demand in quadrant 2 rises to the point that if the cheap unit in quadrant 1 keeps going up to cover, the power line between them will overload. Since the cheap plant cannot supply the demand in quadrant 2, the next-cheapest plant somewhere else will have to come online to make up the shortage.

At this point, you have locational marginal pricing, based on transmission (transportation) constraints. Back in quadrant 1, energy stays cheap, and only the people in quadrant 2 who did not have the foresight to increase their transmission line's capacity have to pay the averaged costs of what they could get from the cheap plant and the remainder they had to get from somewhere else. It's no different than living next to a bakery and getting cheap donuts, but over the hills where they have a small bakery that can't keep up and they can't ship enough donuts in from elsewhere on the only dirt road into town, the value of a donut logically goes up.

Now, the MISO did exactly this, back in about 2003 or so, but on a GRAND scale. Covering all or parts of 11 U.S. States and the Canadian Province of Manitoba, with 35 power companies owning transmission assets and another 98 companies owning generation and/or serving load, they coordinate over 130,000 megawatts of energy generation from hundreds of power plants. In real time, pulsing power plants to move up and down to live within the cheapest-power-possible-to-where-you-are LMP model every few seconds.

How do they set prices? The generation owners bid the units into the MISO system, with costs based on output. They even have allowances for efficiency bandwidths, so you can say your power plant costs 'x' from 200-400MW, 'y' from 401-475Mw, 'z' 476-510MW, etc. The MISO super AGC computer sees real-time demand across their entire footprint, determines when generation needs to increase, and finds the next cheapest unit anywhere in their entire area to go up. Except that the MISO super AGC computer also knows what the real-time flows on all of the transmission lines are, and knows how moving any generator up or down will impact every transmission line. So it doesn't just grab the next cheap unit in the stack, it grabs the next cheap unit that can increase without overloading any power lines anywhere else.

This creates hundreds of pricing bubbles in the MISO footprint based on LMP restrictions. The MISO super AGC computer measures consumption at thousands of points on the system and knows which power company is the consumer at every given point. Knowing how much energy you used at any given consumption point every hour, and knowing the energy cost in that bubble for that hour, it is no great leap to figure out what to charge you for the energy based on your usage at all of your consumption points. So, in effect, the MISO "buys" the energy using cheapest-possible source from the bidding process and influenced by the LMP model, and then sells the energy back to the members with pricing based on their usage and location, keeping a cut to operate their massive bureaucracy.

This effectively killed the hourly power market in MISO, as it completely ended the hourly guessing game. Your units ran if you priced them low enough to get picked up and had transmission availability out of your system, and you know you always got the cheapest energy possible that was offered. If your costs seem too high, build more power lines into your system or help your neighbors build lines that will help you get more cheap stuff. The day of the energy trader making hourly deals like working Wall Street ended in MISO.

It was gigantic gain in efficiency, as you no longer run your own units up and down to meet only your local demand. Cheap units run pretty much full power all day, and the load increases and decreases at scales large enough that it is unlikely that the stack will land on any one unit and run it up and down for hours. Increased demand flies through the stack quickly enough that your unit running at minimum waiting get picked up gets the signal to go to full and then stays there for hours.

MISO is not the only one playing the LMP game in the U.S., but they are the largest and did it best first (though not without some noteworthy hiccups worth another post another day). And while efficiency was vastly improved, it did not address any of the problems of meeting demand when things really go bad on the system, or how to manage the somewhat uncontrollable "green power" resources such as wind and solar. They still flex the system to work around those, and stress the system when a big contingency hits somewhere. MISO's LMP manages generation pretty well, but what it doesn't really do at all is manage the other side.... it doesn't manage load. Imagine how much nicer it would be if you could prevent donut riots on the other side of the hills by magically influencing how badly those people wanted donuts on any particular day? That is the foot in the door for the Smart Grid.

Another post, another day.

So..... did any of this make sense?

Tutorial 10: System Protection, Part III

OK, we're back for another rare installment of the tutorials that make up "Grid 101: Introduction to How The Power Grid Works", or "What Is This Confounded Sorcery?"

You don't have to re-read all the tutorials for this to make sense, but I would suggest you at least go over Tutorial 9: System Protection, Part II.

First is the detection relays. I explained that the relays watch for faults and decide what to do about them, but did not expand on how this magic works.

Remember that electricity flows can be compared to water flows that you fireman-types can relate to. Voltage is equal to water pressure, Amperage is equal to flow rate, and Resistance (Ohms) is equal to friction loss.

Resistance is hard-calculated much like water friction loss. We know the more-or-less fixed value of water psi loss for a given section of 1.75" hose and associated appliances. Similarly, power system engineers can calculate the resistance that a given power line of x distance and y conductor size will create. So file that away for a moment.

Voltage (pressure) is measured by potential transformers (PT). These are everywhere, nearly always attached to any buses as well as on the line-side of any breakers at the station. They serve to detect the presence of voltage as well as its strength. Their output is fed to the relays.

Amperage (flow) is measured by current transformers (CT). These are located anywhere an overload flow condition could arise that would need to be cleared, such as above and below every substation transformer and also on the line-side of any breakers at the station.

The differential protection mentioned in Tutorial 9 is made possible by the CTs on both (or all) sides of a given section, providing the measurements that should sum to zero indicating that everything going in is also going out, which is a good thing.

For each line out of the station, the values from the PT and CT are fed to the relays. For decades, relays were electromechanical solid-state devices, and specific electrical signals from the CT/PT would cause one or more contacts in the relay to close, enabling a trip signal to be sent to the necessary circuit breaker(s). In the past fifteen years or so, digital relays have arrived, and they have uber-fast computers that analyze the CT/PT inputs and decide what to do about it.

In all cases, electromechanical and digital relays have to be programmed or tuned by relay technician engineers who input tolerable levels of flow and voltage based on engineering system studies. Being a relay tech is fascinating work. Not only does each sold state relay need to be set up to do its thing, it also needs to be able to detect that its requested action happened or not and be able to send a trip signal to the next thing upstream if necessary. Digital relays too, but it is much easier to program that aspect than fine-tune the mechanicals.

The reclosing ability of lines and feeders relies on PT inputs to help the relay decide whether it should try or not. If a line trips and a reclose is permitted, the relay will first check the upstream PT for the presence of voltage. If no voltage upstream (bus is dead), there is no benefit to reclosing, and it won't happen.

Often, transmission line reclosing is staged so that the test is performed from the strongest side, so that a repeated fault doesn't disrupt a larger area or a generation plant. For an "auto-first" recloser, the automatic recloser will reclose into a dead line if the bus behind it is hot (PT senses voltage). An "auto-second" recloser waits for both the line and bus to be hot, meaning that the line was successfully tested OK by the other side. Auto-second is found at all power plants, and at weaker substations. A third variety, less common, is where a recloser sees a hot line and a dead bus. If the bus was merely de-energized by a large scale outage and never suffered a clearing fault, the breaker will close to pick up the bus, at which point any auto-first reclosers will see the bus pick up and try their lines. Of course, reclosers can be set up to operate at the direction of the relays in multiple or all of these situations.

Random amusing unrelated picture, to interrupt the long post.

Seriously, it's OK if you want to go refill your coffee at this point.

OK, all rested up? Onward.

So, we know that relays process input from PTs and CTs to decide if there is a fault, and how bad it is. Take it back to fire flows and it makes sense. If you have high water flow but water pressure is good, that is probably OK. Likewise, if water pressure is a little low and water flows are also low, it isn't ideal but doesn't indicate a major problem either. Conversely, if your water flow suddenly surges while water pressure plummets, you have a pretty clear indication of a burst hose. Translated to the PT/CT inputs, high amps and volts are OK, as are low amps and volts, relatively speaking, but sudden high flows with plummeting voltage is a clear indication of a line fault.

Within the transmission protection zones, relays watch the line from both ends, and can use the PT/CT inputs to not only detect a fault but also figure out with fairly good accuracy how far out the fault is from the station. The location of the fault is important, and influences the behavior of the relay.

A relay looking out into a line for a fault typically has three zone of protection in regard to the line. Zone 1 watches for faults from the breaker on out to cover 80-90% of the line. Zone 2 over-reaches Zone 1 by 10-25% and can see faults in or near the remote bus of the next station past the far breaker of the monitored line. Zone 3 looks backwards from the breaker into its own local buswork. See the illustration below for the protection zones watched by the relays assigned to circuit breaker "A" at West Substation (in blue), and the zones for circuit breaker "B" at East Substation (in green).

A fault in Zone 1 is indisputably on the protected line and will be cleared without delay by the breaker that sees it, usually within about 3 cycles (0.05 seconds). Most of the line is covered by both Zone 1's, so generally both breakers will independently see it and trip. Both Zone 2's also saw it in their area, but have a time delay to prevent false tripping and let the Zone 1's handle it.

If a fault occurs right outside the station, let's say right outside the fence from East Substation, things are different. "B" Zone 1 picks it up and trips immediately, but "A" Zone 1 doesn't see it. "A" Zone 2 knows about it, though and trips "A" after perhaps 6 or 10 cycles (up to 0.15 seconds). The delay is important, because Zone 2 can see into and probably slightly beyond the next station. In this case, if a fault occurred just outside of East Substation on some other line, "A" Zone 2 probably sees it, but it would not be appropriate to knock off this line when the fault is somewhere else. The time delay allows the local Zone 1's for that other line to take care of business. If they don't, "A" Zone 2 trips after its delay.

From here, things get more complicated. For advanced protection arrangements, there is equipment to block or force tripping independently of what a relay is seeing for itself. Relays at different substations can communicate with each other in a variety of ways, such as fiber optic networking, microwave radio, or a carrier tone through the actual power line itself.

If false tripping is a problem or seriously needs to be avoided, is where Zone 3 comes into play with blocking schemes. Zone 3 generally looks backwards as far as the remote Zone 2 looks through it. In the previous case of an unrelated fault elsewhere right outside of East Substation, West "A" Zone 2 sees it, but so does East "B" Zone 3, and it knows that the fault is not on this line. It will communicate to West "A"s relay scheme that a trip would be bad, telling that relay to ignore any Zone 2 trip it might want to try (at least for a bit, it will eventually allow it if the fault persists). Thus, no false tripping and better stability of the grid.

Cool, huh? It gets better.

For lines where relay techs have determined that a potential Zone 2 clearing duration of up to 0.15 seconds is too long and the disturbance too great, the permissive transfer-trip scheme is used. Sensitive transmission lines and very high voltage lines at or above 230kV is where you'll see these. In these cases if either Zone 1 picks up, it automatically tells the other side to trip without waiting for the remote side to go through its Zone 2 time delay. This ensures that a fault on either end that falls outside of the dual Zone 1 coverage still gets cleared as if both relays saw it as Zone 1.

Think about that. A fault occurs. The PT/CT inputs are picked up by the relay. The relay concludes it is a Zone 1 fault and must trip. It sends a signal to its local circuit breaker to trip, and also sends a signal to the relay at the other end of the line. The local circuit breaker trips. The remote relay gets the "trip now!" message from the local relay that detected the fault, and tells its own circuit breaker to trip, and it does. From fault to cleared, with all that communication and mechanical response from the circuit breakers, probably no more than 4 cycles - 0.066 seconds - elapsed.

Once you have these fundamental ideas about zones of protection and calculating fault locations and intensities, you can imagine that some relay techs can dream up some amazingly elaborate protection schemes. When they work, it is pure beauty. Even when the special schemes fail for some reason, the fallback default Zone 1-2-3 systems still work.

What we learned: (1) Power lines act a lot like fire hoses in some ways, but we already sort of knew that. (2) Pressure and flow rates (volts and amps) measured at the right places can provide a lot of information about what's going on if analyzed the right way. (3) Protection zones back each other up, which we also sort of knew. (4) Special schemes that cost a lot of money to engineer and build can shave fractions of a second off a trip time, and that fast action can be very important to save the grid.

Whew. See what happens after such a long hiatus of tutorials? Blah blah blah blah... I talk too much. I see your coffee cup is empty again. Go fill it up and hide in a quiet place to absorb what you've learned today. Stay safe out there.

(Click this link to see all posts tagged "tutorial")

Checking in

This new boss gig is taking a lot of my time! But it is a good gig. This is evidenced by the dropoff in posts, as this blog was started for the same reason many are: to rant. I'm just not pressed to rant since starting the new job, because it is really agreeing with me and I am surrounded by good people and an intelligent leadership structure that more or less has a plan. It is AMAZING.

I am very lucky.

Also, not too many exciting fire or power grid stories to tell, but the rough season is approaching. Of course, there was the guy who complained when we fixed a streetlight in his area. He told the customer service rep that the light was damaging his DNA. We offered to shield his house from the light, and he insisted that he provide the shielding. I expected something wrapped in foil, but it turned out to be a flap of rubber from an inner-tube when they brought it to Dispatch so we could see it. OK, whatever floats your boat. Timo went out to install it, and we had a deputy along by request, just in case.

The blog got some pings from a discussion about wind power, leading me to realize that I have really dropped the ball on talking about future power grid trends as well as the tutorial series. Some new stuff is up with wind which I actually find encouraging. I still need to finish talking about circuit protection schemes and the relays that make them go. And the so-called "smart grid" you hear about from time to time? I'll fill you in on what it is supposed to look like, since no one in the media seems to have a clue except to use buzzwords like "demand management" and "smart supply", or some other useless catchphrase of the week.

And as my parting shot, check this out. While on the road this summer, putting a few thousand miles on the family transport to see the in-laws, I ran across this very creative way to recycle an old power pole. The Grumpy Dispatcher approves.

Knowing the Power Lines in your Fire District

Your house gong goes off, or your Minitor chirps. Traffic accident involving a power pole.

You arrive and find this.

You give your size-up, and you know you want the power company to be notified. Is it enough to give the power company - secondhand through your dispatchers - just a physical location?

How does this sound: Engine 9 arrived and is Broadway Command, semi truck head-on with a pickup truck, southbound lane blocked, power pole is broken but has not fallen, patients are still in the pickup truck which is under the power lines, start another medic, and law enforcement for traffic control, notify the power company.

It is possible to provide more information, and therefore provide for the improved safety of your crews, by knowing the line and feeder names, and knowing a little power company lingo, without seriously messing with your size-up.

My size-up would sound like this: Engine 9 arrived and is Broadway Command, semi truck head-on with a pickup truck, southbound lane blocked, power pole is broken but has not fallen, patients are still in the pickup truck which is under the power lines, start another medic, and law enforcement for traffic control, notify the power company to put Clarenceville Feeder 403 on non-auto and to not test.

I'll explain the jargon as we go on.

I'm not going to address the scene safety angle here regarding physical harm from falling hardware and/or snapping wire conductors, though. This here is a safety officer's nightmare to be sure (and there's enough in this pic for an entirely different post!), but I'm only going to talk about knowing the names of the lines and feeders in your area and how to talk to your dispatchers about it.

Every power line, be it a 500kV major transmission line or a single-phase 4kV distribution tap, is part of a named or numbered circuit. It is not impossible to keep track of these names, and there aren't as many as you might think.

If you have major transmission lines through your district, find out their names or numbers, and note them on your district maps. Major transmission is pretty much anything on a lattice steel tower or multi-pole wooden structure, or anything high up and with a lot of bell insulators.

Feeders are almost always numbered, and are usually associated with their source distribution substation. If you work for a city FD, there are probably five or less feeders in your entire first-due, with numerous taps branching off to reach everyone.

So, with a little research, a phone call at a minimum, a station visit by a power company field ops guy would be better, and a visit to the power company's control center if within reasonable geographic distance would be best, you get this info one way or another and know what the lines and feeders are called by the guys who operate them.

So what do you want of this stuff now that you know what to call it? What to do when you're attempting to mitigate the chaos?

Situation: It's energized, and you're working near it. There is a slight risk of contact or failure, but you do not feel that it needs to be de-energized. You want this circuit to be on non-auto, (or one-shot). This means you want the associated automatic circuit reclosers to be disabled, so that if the line trips, it will not automatically be re-energized.

Situation: It's not energized, but you've had no contact with the power company yet. If energized, it could create some undesired excitement. You want this circuit to stay out. This means the power company will verify that the reclosers are disabled, and they will not attempt to energize the circuit until they hear back from whoever asked for it to stay out, and even then they'll likely not try to put it back until they hear from their own personnel as well.

Situation: It's energized, you're near it, and there is a fairly significant risk of contact, and you'd be much happier to have it de-energized. You want this circuit to be on non-auto right away, and to be de-energized as soon as possible. This again means auto-reclosing will be disabled, and the power company will de-energize the line as soon as possible after ensuring no customers will be dropped. This could take anywhere from a few minutes if remote control is available, to an hour or more if it requires a crew response. It is not unreasonable to request an expected time frame before the circuit is dropped.

Situation: It's energized, and there is immediate danger to life. You want this circuit de-energized for life safety. The power company will do whatever it is capable of doing to drop that circuit without regard to who gets interrupted. Don't play this card unless you really need it. A couple of "cried wolf" events will slow their future reaction to this kind of request.  But when you do play it, make sure a scary phrase like "urgent life safety emergency" is used, to be very clear that all the stops should be pulled.

There is no nationwide standard for the jargon, but it is close enough from place to place that if you use these words and the 911 dispatcher repeats them verbatim to the power company dispatcher directly, your message should get across. Visiting with your local power company staff will ensure you have the locally correct jargon, too.

Anything you can do to reduce the number of go-betweens passing the message would be good. Ideally you want the 911 dispatcher talking directly to the power company dispatcher, and not having to go through the power company's customer service outage line. Even better, if they're willing, have the 911 operator pass along your cell number so the power dispatcher can talk right to you in the field.

I part for now with this: Power dispatchers are loathe to drop a circuit when it can be avoided, but they will (should!) do it immediately, no-questions-asked, if you clearly throw down the life-safety card and make sure that term reaches the power dispatcher's ears.

Not enough IC's use that card when it is truly needed, and there have been too many electrocution LODDs that would have been prevented if only the power dispatcher had been aware of the seriousness of the situation.

Stay safe out there.

Tutorial 9: System Protection, Part II

After a long layover, the tutorial is back.
I hope you enjoyed the break.

A quick total review of what we have learned so far:

In Tutorial 1 - DC vs. AC, we learned... well, the difference between Direct Current (DC) and Alternating Current (AC) and why AC is used for the grid.

In Tutorial 2 - AC Supply and Demand we learned that power on the AC grid is produced exactly at the rate it is consumed, and that it cannot be stored.

In Tutorial 3 - Generation Supply, Control and Scheduling we learned how power companies decide which power plants to run, and how they exchange power between companies.

In Tutorial 4: Basic ACE, and Reserve Sharing we learned how power companies determine if they are generating too much or not enough power, and how they quickly recover from the loss of a big power plant with help from their neighbors.

In Tutorial 5: Introduction to Power Lines we learned about the different types of lines and voltages are used to move power efficiently, and about transformers.

In Tutorial 6: Identifying the Wires and Tutorial 7: Identifying The Wires, Part II we learned how to... well, identify the wires.

And lastly, in Tutorial 8: Introduction to System Protection we learned why the system protects itself.

Wow, that rehash was long enough to be its own blog post. But it's been over a month since we did one of these, so I feared you might be rusty.

Well, I am, anyway.

Seriously, you might want to at least re-read Tutorial 8 to spin things up again before starting this one.

And you are hereby forwarned, this will be a LONG post. Go refill your coffee now and stop in the restroom on the way. We'll see you in a minute or two.

.....

OK, ready?

The electrical grid is protected at every point on its journey from the power plant's armature windings to the end terminals of the power cord inside of Firegeezer's coffee pot. For most of us, this power travels a pretty long distance, goes through several voltage changes up and down, passes through switches and circuit breakers, and does a few other exciting things before getting to you. It is not practical to dump the entire grid between you and the power plant if your coffee pot shorts out, so your household circuit breaker does the job. That action defines the first of many segments, or 'zones of protection' in power company parlance, the first (or last) of which is the zone between your breaker panel and your coffee pot, protected by your panel breaker.

An aside on circuit breakers. On this blog I pretty much always refer to the large breakers generally found in substations. These breakers have just one job: break the circuit. They cannot sense problems, so they only open when commanded to by other equipment. I might get into those big breakers later, but I want to differentiate the big breakers from the tiny breakers found on the breaker panel in your home. Your tiny breakers do both jobs; that is, they detect the problem AND break the circuit. Tiny breakers detect problems in two ways: The electromagnetic portion detects sudden surges, and the bi-metal portion detects high loads over time. Look it up if you want to know more about those, just so you know that aside from the size difference, there is also a functional difference between the big breakers and the tiny household ones.

Back to the zones.

The names I will use below I am more or less making up to keep things simple for the uninitiated, and may or may not be the terms used locally by your power company. In fact, they probably aren't. If you try to mention these specific zone names to linemen, other dispatchers or protection engineers, they will probably look at you with a raised eyebrow and try to tactfully change the subject.

So, the first zone we have identified. We'll call it the COMPONENT ZONE, referring to components that you plug into your outlets at home. The elements protected are, going backwards: Coffee pot, power cord, electrical outlet, wiring in your wall leading from your breaker panel to that outlet. If there is a problem here, as long as things are installed properly, your household circuit breaker should take care of it.

The next zone is relatively tiny, the PANEL ZONE, and pretty much just watches the stuff inside your breaker panel, between the main breaker and the individual circuit breakers. If something goes awry in the panel, the main breaker will dump the house. Also, if one of the circuits in your home in the COMPONENT ZONE has a serious problem and the assigned circuit breaker fails to clear it in a timely manner, and if things are configured properly, the main breaker should dump the panel to take care of business.

The next segment is the SERVICE DROP ZONE. This starts at your main breaker and goes upstream from there, to the source wires going through your wall and to the service drop or other point of entry, out via overhead or underground service wires to wherever your local service transformer is, be it a pad mount transformer or a poletop can transformer, and then up to the fused cutout serving the transformer. The fused cutout was touched on in the "Wires" tutorials, it is a switch where the opening part is also a large fuse. If something happens downstream from this cutout that draws enough load, the fuse will blow. It generally will blow for problems with the transformer, but if there is a problem downstream from that drawing a lot of fault current and not being cleared, it will eventually cook the transformer and cause the fuse to blow. Sadly, by the time the cutout blows for a problem at your panel or somewhere downstream that was not handled by the main breaker, your house is on fire already, causing me to drop what I'm doing and come see you in my Big Red Truck anyway. See, I'm involved either way.

The next segment is the FEEDER ZONE, which travels upstream from your cutout switch. That includes the jumper or other tap wire from the cutout to the primary distribution feeder conductor, and that feeder circuit back to the next breaking point. For most applications, that breaking point is a relatively small substation feeder breaker. Alternatively, there may be an in-line field recloser (basically a light-duty feeder breaker mounted on a pole) or other switch designed to sectionalize the feeder into pieces. Sectionalizing makes sense for long feeders or multi-branched feeders. If you can detect a problem and isolate just the troubled portion while still reaching the rest, it makes it unnecessary to dump the entire feeder. These breakers and reclosers cannot generally detect problems on their own, but rely on signals from other equipment, known as relays, which measure things like voltage, amps, flow magnitudes and such, for Bad Things. When Bad Things happen, the relay will then tell the appropriate device(s) to open. The relays at this point may take up to several seconds to decide there is a problem and clear the circuit. Also, the relays are often set up to attempt to reclose the breaker once or twice to see if the problem was transient (we talked about that in past posts), but will give up after enough failed attempts.

The FEEDER ZONE segment backs up the fused cutouts if they don't blow and draw enough fault current, but this backup is not very reliable. It is impractical to reliably get the relays to sense that kind of small fault that far away.

This picture placed here to give you some brief unrelated entertainment, because this post contains no other photos. Entertained adequately? Good.

The next segment is the DISTRIBUTION BUS ZONE, and is a small area running from the circuit breaker at your distribution station into the bus work at that station, which serves all of the other feeders. Typically this bus has a breaker on every component attached to it: Any and all feeder circuits, input sources from transformers, and voltage regulation devices. The relays watch the sum total of the electrical inputs and outputs of all of the things attached to the bus. They should sum to zero, as the bus does not keep any electricity for itself. If they don't sum to zero, the only plausible conclusion is a fault to ground, and all of the breakers attached to the bus are ordered by the relay to open, like breaking up the party and clearing all the uninvited teenagers out of the house. Bus faults are the worst thing that can happen to us dispatchers, particularly at large transmission stations. It just breaks the crap out of everything, often causing a serious disturbance when major transmission buses crater on us. Thankfully, bus faults and bus clearing events are rare.

The DISTRIBUTION BUS ZONE backs up the FEEDER ZONE. The relay that watches the feeder is responsible for telling that feeder's breaker to open. If that breaker fails to open for whatever mechanical odd reason, the feeder relay lets the bus relay know about the problem. The bus relay then rolls its eyes and clears the bus to handle the problem. Also, the bus relays watch the feeder and can detect the same faults that the feeder relays should operate for. If the feeder relay fails to open the circuit, and also fails to ask the bus relays to help out, the bus relay will eventually shove the unconscious feeder relay out of the way, grab the steering wheel and take over, again by dumping the bus to solve the problem. Relays on buses, as a rule, never attempt a reclose on a bus fault. One trip goes straight to lockout, and the station requires inspection before attempting to pick it up again.

The next segment is the TRANSFORMER ZONE. Like the bus zone, it is small. Its only job is to protect the multi-million $$$ transformer. Or at the least clear it before it boils and blows up and takes the whole station out. Like the bus zone it measures the in and out flows, but can also be activated by other sensed problems such as gassing in the transformer, or a sudden pressure increase internal to the transformer. And like the bus zone relay, transformer relays do not reclose breakers into a problem seen on the transformer.

The TRANSFORMER ZONE backs up the DISTRIBUTION BUS ZONE in two ways. If the bus attempts to clear and is unable for whatever reason to do so, the bus relay will ask the transformer relay to dump the source into the bus (the transformer). Similarly, the transformer relay can detect high loads, particularly high fault current at the bus, and will unilaterally dump the bus if the bus relay doesn't take care of issues at home fast enough. And, if for whatever reason the FEEDER ZONE fails to trip, and the DISTRIBUTION BUS ZONE fails to help out, the transformer relay will usually still sense the crazy high current and low volts and eventually throw everyone out of the pool.

Do you see a pattern yet?

Upstream from the transformer there may be a "high side" bus (higher voltage than the other side of the transformer). If so, there will be a TRANSMISSION BUS ZONE. It works on the same principles of the distribution bus.

Leaving the station, on the other side of the breakers attached to the transmission bus, are the high voltage lines, making the TRANSMISSION LINE ZONE. They work similarly to feeders in regard to how problems are sensed, but they usually are cleared by high-speed relaying and high-speed breakers, and usually also include automatic reclosing. These transmission-clearing setups are really amazing. The problem occurs, the relays sense it, the relays decide where the problem is, the relays decide which breakers need to be opened to solve the problem, the relays tell the chosen breakers to open, the breakers get the signal to open, the breakers mechanically do their thing and break the circuit.... from fault to clearing, sometimes as fast as 1/10th of a second or less, TOTAL. FAST.

All along the way, transmission lines, transformers and buses are all protected by their respective zones and the neighboring zones poking their nose in the goings-on at each point, ready to take over as needed. Finally, at the power plant end, there are zones protecting the power plant's station components, which are more or less configured in reverse of distribution stations but rated for higher loads. And then a zone from the yard to the generator. The generator zone has a bunch of nifty things it watches for that I won't get into here right now, but there are just bunches of things that will excite one or another relay and trip a power plant, especially the steamers (coal/oil/gas/nuclear/etc). At pretty much all points above the feeder circuit breaker, there are multiple relays that can sense faults not just in their designated area, but for good distances through other zones as well. The relays with overlapping detection have built-in time delays to give the local equipment time to handle it, but will do what they can to solve the problem if too much time goes by (usually measured in just a few seconds). I think you get the idea without me spelling it all out. Your eyes glazed over five paragraphs ago anyway.

Goodness gracious, what a long post! But wait, there's more! Next time.

What we learned: (1) The path from power plant to power outlet at home is broken into many segments, each protected independently and usually backing each other up. (2) The clearing is designed to remove only the problem, to interrupt as few people as possible. (3) We remember now why I didn't get back to the tutorial series for a while. They are way too freaking long.

That's enough. Out.


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Your Thoughts and Opinions, Please

OK, I am humbly requesting feedback from my small pool of regular readers who aren't afraid to admit coming back here more than once to read my drivel.

The comments attached to the last few power grid tutorials are, well... they aren't. I am out of touch with how they are being received.

Are they working for you?

Are you learning anything?

Am I going too fast?

Are they too long?

Using too much jargon?

Do you care?

Is there something specific on the grid you want me to talk about?

Should I give up on it all and just make this another fire blog in blogosphere already getting crowded with better fire blogs than this one?

I just need to know what you want, so I can deliver.

Thanks for indulging me with your thoughts.....

Tutorial 8: Introduction to System Protection

What have we learned so far? We know the difference between AC and DC power, how energy is scheduled and accounted for, how it is decided which generators will run and how high, how interconnected power companies help each other out when they lose a unit, and quite a bit about power lines from big transmission to little distribution.
Has this been helpful so far?

Today's topic is in regard to why the system protects itself when bad things happen.

The system protects itself for two reasons: To prevent damage, and to maintain stability (ie. not collapse the whole house of cards). Although the correlation is not precise between fire hydraulics and electrical flows, nonetheless major system disturbances can have far-reaching and disruptive ripple effects that could be compared to the water hammer effect.

Extremely high or low amp flows and voltages pose a real threat of causing permanent damage to everything exposed to the swings, from multi-million dollar substation transformers all the way down to your DVD player. It is far better to instantly disconnect the world and drop the whole potato, because if you save the equipment, you have something to put back together. If you disconnect late, there isn't much point in trying to restore a system made up of fried parts.

When voltages and flows go to pre-programmed extreme limits (by line/equipment faults or simple overflows), protection systems activate to remove elements from the system in order to prevent damage to the transmission infrastructure, and also to prevent damage to customer equipment. It isn't unusual for a 'ripple' to occur when elements are removed, resulting in momentary spikes in flows and voltages, sometimes causing more elements to be removed, causing more ripples, causing.... yeah. There are well-paid transmission protection engineers who spend their careers trying to balance instant protection of the assets with not crashing things worse. Frankly, I find that stuff fascinating, but don't want their job.

It is a testament to those protection engineers that hundreds of major transmission lines and thousands of distribution circuits trip out as a matter of routine every day all across North America for all reasons imaginable, yet system protection isolates the problem so quickly that the vast majority of problems are cleared in seconds or a fraction of a second. Unless it is a distribution circuit that tripped and you're on it with several hundred other people, you don't generally notice that anything happened anywhere else.

The August 2003 Northeast blackout in the United States was a major comedy of errors and things going exactly wrong. How is it described by those dissecting airline disasters? An unfortunate sequential confluence of unforeseen events, or something like that. Super rare. It will happen again, but the 99.999999999% norm is that it doesn't, which is remarkable when you take in the scope and complexity of everything that goes into this machine.

For what it is worth, system disturbances do cause split-second bumps that go by faster than a blink of the eye in areas regional to the problem. Most dispatchers are attuned to that, and see it in a momentary hiccup in the lights several times a day at home and at work, often knowing a trip alarm is coming one or two seconds before it appears on the console, or wryly smirking when seen at home, knowing that some dispatcher is about to get interrupted. Sometimes we see it and the alarm doesn't come in, because it happened on a neighboring system. That said, these happen so fast that almost no one else notices them at all. Which is how we like it.

System protection is done in layers, in a way that breaks up the chain of transmission from the power plant to your breaker panel into many segments. Each segment has something protecting it, and each segment has at least one higher level of protection in place if the first one fails. And if the backup fails, the backup is backed up at the next level. And so on. Sometimes protection settings are not tight enough or sensitive enough (to wit: Must-See Video of Line Fault and Reclose) and issues happen, but the concept is generally very reliable.

I think that's enough for today. It's Saturday. You get the general idea, but no math or excessive technical jargon, nor homework.

What we learned: There's a ton of mysterious stuff set up out there designed to prevent blackouts, by removing faulted and overloaded parts of the grid faster than Barack Obama earns Nobel Peace Prizes. Oops, I said I wasn't gonna do that again. Sorry. And if you know a dispatcher and you see a minor nervous tic once in a while, don't worry about it, they just detected a line fault hundreds of miles away with their spidey sense, that's all.

Technical stuff next time. Don't worry though. It's pretty cool. Well, to some of us. Take it easy for the rest of the day.


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Why Tutorials 6 and 7 are Worthless

It's great and all that you can marginally identify stuff on the pole... as long as things are intact. But when things are intact - speaking mainly to my emergency services brethren - you are far less likely to be involved in the first place. It is when things are not intact that all bets are off. What good is it knowing what's what when it looks like this over the car wreck you're working?



Hands off. Call for backup from the power company. Keep everyone out. But, you knew that already.

Tutorial 7: Identifying The Wires, Part II

Welcome back. I have some old material that I wrote a ways back for another cause that I am bringing in here to recycle, in order to expand on the cause of identifying stuff on power poles. I took all of these pictures myself, so am more familiar with what's in them than the generic reference pics I used in the last tutorial.
This is going to be a VERY long post. Go refill your coffee now, get your potty break in, and then come back when you're ready to sit a spell. I am confident that, despite the length of this post, you'll be pleased with the information you pick up from it.

I think it is high time to put in a disclaimer, however.

I am a power dispatcher, but I have never been a lineman. I know enough about this subject to sound like I know what I am talking about, but any lineman knows enough to make me look clueless. If you are dealing with someone on site who should know what they are talking about (power company field employee), don't rate my info better than theirs.

Click on these pictures in order to open them up in a larger window to see better. If you 'right-click' the picture, you should be able to choose to open it in a new window, so you can have the picture up full size while also reading the text.

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In this picture, three conductors of this 14kv feeder are coming in from the upper left, and traveling towards the lower right, they are the wires at the very top of the front pole.

Under the top crossarm of the front pole there is a three-phase tap (all three conductors are tapped), and these travel downward in the photo to the pole across the street where they are then on the very top as they go off the left side of the photo. Also, on the right side of the lower crossarm is a single phase tap that travels off the right side of the photo.

So far, all of what has been described is 14kV, bare cable (not insulated).

Now, across the street you see the streetlight on the back pole. Just above where the light attaches is a triplex cable. Off the left side of the photo and out of view is a poletop transformer that steps down the 14kV to something the street light can handle, and the 120v insulated cable coming back from that transformer is wrapped around the neutral to form the triplex. The triplex then extends to the front pole and terminates. You can see on the right side of the front pole that the triplex at one time continued towards the right, but it is no longer in use, as the right side has been disconnected and is bundled back towards itself. The triplex on the left is hot, the triplex on the right is not (I only say this because I know what happens to the triplex off the right side of the photo, it dead-ends at nothing). Also, at the same point on the front pole, you can see the lone neutral wire coming in from the upper left and following the single phase tap off the right side.

Below the neutral is telecom stuff (cable TV and/or telephone) on both poles.

Remember that ANY wire can be hot: Neutral, cable TV, phone. Say for example a power pole is broken as a result of a traffic accident. The innocuous neutral or cable TV line may have whipped backwards and draped over a high voltage line before landing on the ground. Always visually trace the path of wires on the ground to their source regardless of the kind of line that is on the ground! Check for things contacting the guy wires, too!

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This is a different section of the same feeder. The 14kV uninsulated conductors are on the top crossarm.

Just below the crossarm is the poletop transformer, stepping the 14kV down to 120V. If you look very closely you can see that only the back of the three phases is tapped by the transformer. A solid rule is that a lone poletop transformer will only be connected to one phase of high voltage. As you go down a feeder you will see how transformers are tapped off of the different phases more or less sequentially (A B C A B C etc) to equalize loading on the three high voltage phases. That little gadget in the tap between the conductor and the transformer is the fused cutout, the fuse is a cylinder not quite 12" long in a spring clip or hinged apparatus. It can be opened/removed to de-energize the transformer and its taps.

Under the transformer the customer taps fan out. These transformers frequently may have only one tap, but there is no reason they can't have several, like this one. Starting with the first one that points almost straight left and going counter-clockwise, the first one goes to a house, the second one goes to the next pole (and thus is on the main neutral) to serve a street light, the third and fourth go to houses. The wire heading sharply down towards the right is just a guy wire. Heading from the transformer off the right are two more lines. One goes to another street light across the street, and then above that you can see the bare neutral going off the right but staying on this side of the street. Remember, all of these insulated cables are at the same potential as household current, so although a hazard exists it's not big time stuff.

Under all of that is telecom.

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This is a fused poletop switching point. Each of the three phases has an inline fuse (basically like the poletop fuse in the last post but with a higher rating). The fuses will pop as needed so that the entire feeder doesn't have to go dark for a fault on the far side of the fuses. Since it is a switch, the three fuses are attached to hinges so they can be collectively opened for work clearances on the far side of the switch.

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This one is a little more complicated.

You see the familiar three phases on the crossarm on top. On this pole, all three phases are tapped to inline fuses on the right side of the lower crossarm (at a right angle to the upper crossarm), then onto small insulators on the left crossarm and then into individual transformers. This is a large customer requiring three-phase service. The three phases and the neutral are individually tied to the pole instead of them being wrapped together, so you see four wires leading to the customer, but often they will be wrapped together and referred to as quadplex. You can also see that one of the low side lines is tapped for something else since it is running wrapped around the neutral to the far pole for something else.

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There is some increased danger here. The three phases are tapped into inline fuses before the lower crossarm, and then converted into insulated cable before heading into the riser tubing and going down the pole underground. Note that there are no transformers in sight on this pole. This means that the cables running down the pole behind a little flimsy sheet metal are a full 14kV. Smack a car into this pole hard enough and/or in the right place and you'll get a dandy light and sound effect show for a second or two until the fuses blow. Long enough to kill you for sure. Tread carefully here.

I think everyone can identify the neutral and cable TV/phone here, right?

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Another poletop switch, this one with bladed disconnects on the top of the crossarms, is on the right pole. A three phase customer is tapped off of the pole on the left. Linemen like this kind of switch a little more because it can be opened without a bucket truck. If you look close at the pole on the right you'll see a control rod going down the pole. This can be operated by hand with a hotstick while standing on the ground. Some control handles go all the way to the street level, and in these cases the control is locked in position with a power company padlock.

You might conclude that in an EXTREME emergency, you could theoretically open the switch, but this is a bad idea in every way. Linemen wear linemen's gloves for this kind of switching (for all switching, actually), because you never know when the switch is going to fall apart and something energized falls into the switchgear. Plus, you'd have to know without a doubt that there was no potential from the other side of the switch for it to be worth your trouble. And don't forget some dope might have an incorrectly installed generator on auto start on the dead side which would heat you up a few seconds later. Or... there might be an "auto flop" configuration installed by the power company to automatically energize from somewhere else down the dead line in an attempt to restore some customers after an equipment failure. You can see why there are far more chances of failure than success, plus major personal safety hazards in attempting it. Just put it out of your mind.

The picture on the left is a better angle on the this switch and control rod - that you won't be touching.

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Here we have the point that three phases are split into different directions, but they are still elevated distribution voltage.

The three phases come in from the upper right. The left phase can be seen as tapped to the upper wire going off the left. The middle phase dead-ends here. The right phase taps off to the upper wire going off the right. You have to look close to see it, but the second wire that looks like it is right next to the right phase is actually the neutral and goes to a point on the pole about 3' below the crossarm, and it also splits so a neutral is continued with each of the tapped single phases.

The three wires going downward on the left are guy wires. Since this pole is a dead end, there is a lot of tension pulling in one direction, the guy wires make up the difference so the pole is not yanked over.

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What you have here is some 34kV subtransmission on the right side tapped to underground. While it is underground and out of sight, it goes off the picture frame about 200' to a large pad-mount transformer where the voltage is reduced to (I think) 8kV. That's still 8,000 volts even on the 'low' side. Then it comes back through the underground and back up the pole on the left before being distributed by feeder to local customers. On both poles you have three phases of either 34kV or 8kV behind a relatively flimsy shield of sheet metal.

Even though there are not major differences in the size of the insulator bells on either the 34kV or 8kV to help you figure out which is which, the different sizes of the cutout fuses ('C'-clamp looking things) mounted below the crossarms gives the difference away. High side, low side, doesn't really matter, it'll all blow your arm off.

This is next to a two-lane 60 MPH highway. Can you imagine what would happen if a vehicle took out one (or both) of these poles and also careened into those propane tanks? Big Fun!

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Over here on the left, doesn't look like much, but this is 115kV, about 8 times higher voltage than most of what we've been looking at so far. Note the two shield wires above the three conductors.

This is outside a power plant.  The other wires crossing by are a distribution underbuild (meaning it runs under something larger), of the 14kV variety we've already been learning about .

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Over on the right, this is twice as much voltage as above, 230kV. Again, note the shield wires.

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On the left, this should keep some people honest... this angle shows that the wires some people are afraid of (because they are on lattice steel structures) can also be found on wooden pole structures that aren't as visually menacing. The voltage is the same on all of these, all 230kV stuff from the same substation. Note the quantity of insulators instead of judging by the structure. Better yet, stay away no matter what.

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This is 34kV subtransmission coming in from the upper right and being stepped down to (I think) 8kV distribution. This is a cheap way to get around building a proper substation behind a fence. The box on the second set of poles is a field recloser, the device which will open for a fault farther along the low side and then may attempt to reclose the line one or more times. If the fault self-clears, the customers see an outage of a second or two. If it doesn't clear, the recloser will give up and stay open.

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This tower on the left is one of the big dogs, a 500kV line, over twice again as big as the last big line picture earlier in the psot. If this is laying on your structure you better be a long, long way away from it.

As mentioned in the last tutorial, one clue to extremely high voltages is the presence of multiple conductors per phase. In this case, each phase is made up of three cables. You can see little triangular brackets holding them in place along the line. Then there's those really long insulator strings to clue you in.

Once again you can barely make out the shield wires way up on top.

On the right is a close up of the triple conductors on the 500kV line.

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The parting shot illustrates another exception to the rules. I kept going on about high voltage transmission lines always being present in threes, and here you can see there are only two conductors on what in every other way looks like high voltage.

This is one of the small handful of high voltage DC transmission lines in North America. Six DC lines tie the Eastern and Western electrical interconnections across the Rockies, two DC lines tie Texas to the rest of the U.S., two DC lines tie Quebec to the world, and there are probably no more than 10 or so major DC lines anywhere else in North America. Other than the interconnection tie points, they always go a long long way (many hundreds of miles) when they are built.

All major AC lines, the stuff that makes up 99.9% of the grid, are three phase and require three conductors to be in service. DC lines are singular, thus you can run either one of these individually, but normally both are in service. So, despite the 'rule of threes', here is a way you can get one or two cables of high voltage, and these run at around 250kV. The long insulator strings should give away the high voltage present, anyway.

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What we learned: (1) You can now impress your friends and coworkers by identifying the clutter on poles. Impress them further by showing that you know enough to stay away from all of it no matter what. (2) The Grumpy Dispatcher's posts are waaay too long, except for those nifty FAIL pics he puts up once in a while.

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Tutorial 6: Identifying the Wires

Last time we learned, at a very high level, about the different voltages of power lines used to get electricity from the generation station to your power outlet. Along with that we touched on the concept of voltage as pressure, how it is raised at the generation station so that the electricity can be efficiently moved closer to where it will be consumed, and as it gets closer to the end user, it is gradually dropped in steps, depending on where it is going, until it is stepped down to household current right before it goes into your home.

Please understand that there is so much more, and I mean a lot more, stuff to be learned about this if you're technically minded and interested. I am intentionally only glossing over a lot of this stuff, as my intent is to make you, my patient and suffering readers, merely aware of what is going on, and not trying to make any of you experts. If I am successful in imparting this basic awareness of how stuff works, then it theoretically will make you understand my rants and grumblings. Isn't that pathetic of me? Deliberately teaching you guys so that I can rant, in order that you can nod in empathy and agree, yeah Grumpy, that sure is lame. Manufactured sympathy!

OK, enough reflection. What a buzz kill.

Today, we take a first look at what is on the transmission towers and power poles.

The overriding rule of always is: EVERYTHING IS DANGEROUS AND SHOULD BE CONSIDERED ENERGIZED. Even if you know what it is, don't touch it, EVER. I'll get into that more later.

First up: High voltage transmission. It's easier to sort out.

Pictures 1 and 2 you'll probably want to click on to view full size at some point. Both illustrate the same thing, though. High voltage transmission is always three-phase, meaning each circuit consists literally of three sets of conductor. In Picture 1, there are two circuits on the tower. In Picture 2, each tower has two circuits, for a total of four circuits in this power line corridor.

You'll note that in Picture 1, each phase consists of a bundle of four individual wires, while in Picture 2, each phase consists of two wires. Added wires is like a larger hose, less resistance, better efficiency. Typically, you'll see single wire phases up to 230kV. Two wires per phase starts to appear at 345kV. Three wires at 500kV and up. But there are exceptions. The number of insulator bells also is a good indication of how high the voltage is, but there are different manufacturers, ratings, and sizes of the bells, so the actual number doesn't mean as much as the overall distance. None of this really matters much from our point of view though, as all of these will pretty much flash-roast you if you touch them.

In both Picture 1 and Picture 2, if you look close, you'll see a couple of faint, thin wires at the very top of the structures. These are called static wires or shield wires, and they are grounded at every structure. They are not energized, per se, but you can frequently detect voltage on them due to induction from being so close to the actual power lines. Literally, the invisible magnetic field around the power lines passes close enough to induce voltage in them. Their real purpose is to provide a preferred target for lightning strikes, by being grounded, they draw the lightning bolt away from the power lines themselves. They are not used to carry a current, but they are still entirely unsafe to touch. Sometimes power companies also run fiber optic cables along side or attached to the static wires, because the existing power grid infrastructure provides a ready-made grid useful for laying down an information/data grid. The power company uses a tiny, negligible portion of this bandwidth for data transfer between stations, and can lease the remaining bandwidth to cable, telephone and data providers.

That's basic transmission. Not too complicated. Subtransmission lines, say at voltages down around 34kV-69kV, will be similar in concept if not design. Smaller towers or more often wooden poles, three phases of single-wire, a single static line sometimes but not always. The main thing is that subtransmission usually remains uncomplicated, unlike the distribution stuff we're about to get into.

Picture 3 is a distribution pole. As a rule, the most dangerous stuff is at the top of the pole, and decreases in its danger score as you go down.

From the top down, then....

Three-phase primary, I am guessing somewhere between 8kV-14kV. The wires coming from either direction are installed as dead-ends, and are attached to the ends of the insulator strings. The dead ends from either direction are then connected with "jumpers" that are attached to the wire on each side and are held in place by an insulator on top. Although not preferred compared to an actual line switch, these jumpers can be detached from either side to "open" the circuit.

The sharply angled wires leading down to the right are guy wires, used to brace or hold the pole in place, entirely expected on poles where the circuit takes a turn, and as you can see the three phase is turning slightly to the left at this pole. Without the guy wires, this pole would want to be pulled to the left by the weight and tension of the primary.

The next single wire down is the neutral. It is grounded at frequent intervals along the circuit (ideally at every pole), and leads back to the big transformer neutral at whatever substation(s) this circuit travels to. The neutral is also extended to each customer service drop and ultimately grounded through the grounding rod at every customer site.

When you see the "braided" service drop at your house, there are usually two "hot" wires, with black insulation, wrapped around an un-insulated cable that carries the tension from the pole to your home. This bare cable is also the neutral. Since there are typically three wires total, we call this "triplex".  You can see some of the triplex here, the hot insulated wires coming from a nearby poletop transformer and apparently provided to power the streetlight.

The last wires on the bottom are nondescript telecommunication stuff: Phone, cable TV, etc.

Picture 4 is a single-phase distribution pole with a "fused cutout" and poletop transformer.

Again, from the top down....

Single phase primary.

Hard to make out is where the jumper is attached to the primary, but you can see just to the right of the top insulator, the clamp where the jumper is attached before it runs down to the fused cutout. In plain terms, a 'fused cutout' is a device that can be used to open the circuit leading down to the poletop transformer, and the part that can be opened also serves as a fuse which will blow and cut off power to the transformer if it were to fail.

Poletop transformer.

Neutral and service drop wires.

Clear as a bell or clear as mud?

What I want to leave you with, particularly regarding distribution poles, is this: There are no guarantees of safety about anything. You never know when a high voltage primary is damaged and has dropped down into some of the other stuff. Usually when this happens, if things are grounded properly, the resulting fault will cause a fuse or substation circuit breaker to open. Usually. On the other hand, what if you're touching something "safe" at the moment something "unsafe" falls into it? Depending on the sensitivity of the protection on that circuit, it could take up to several seconds to clear the fault, and in that delay your body would bear the brunt of it: You're dead.

A traffic accident involving a pole can tweak/whiplash all of the lines for blocks in all directions. So let's say you stumble upon a "benign" telecom cable hanging low, and you "know" it is safe, so you grab it to move it out of the way. Little did you know about the car that smacked a pole two blocks away, causing the primary at the wreck to fall onto the telecom, and the recoil/whiplash simultaneously causing the telecom in front of you to break loose from a mount and hang low. You reach out and... hey, where'd all these angels come from?

Until a power company guy is on the scene and says it is safe to touch, keep your hands off of EVERYTHING. Even when he says it is safe, he won't be offended if you ask him to touch stuff first.

Wow... long post. And I'm really only getting started!

What we learned: Forget what you just learned about what is what, all of that stuff can potentially kill you, even when all you see is telecom and no actual electrical power lines are in sight. Leave it all alone, keep people away, and wait for the power company guy.

So... it's time to ask again. Are these generic tutorials helping? Anything you want me to elaborate on? Too much? Not enough? Any requests for a particular topic?

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Tutorial 5: Introduction to Power Lines

It's been getting boring talking about math and meters, and about the ethereal nature of megawatts, which you cannot hold, observe, or really grasp in any physical sense. The wonders of Reserve Sharing Groups only turn the crank for dispatcher geeks, accountants and penalty-fearing compliance people. Let's move on to something tangible and different, to freshen the air.

Power lines. They're everywhere, above and blow the ground, so much a part of your life that you usually don't notice them. They come in all shapes and sizes, and to the untrained eye they are not always differentiated from other cables and wires strung around for various purposes.

To make sense of the different sizes and types of power lines, though, we have to delve ever so slightly into the technical aspects of power transformers.

And to get into power transformers, we have to poke at the terms 'voltage', 'amperes' (amps), 'watts' and 'ohms'. Dang, here we go with the boring/technical again. I'll try to be brief.

Let's convert those four things into the fire service world, applying what we know about the physics of moving water.

Volts = Water pressure
Amps = GPM flow rate
Watts = Gallons of water moved
Ohms = Friction loss

To move water efficiently and get the desired volume of water on the fire, you like good pressure and low friction loss in order to achieve a good flow rate. The same is true for electricity. The best efficiency to provide the desired amps and deliver the watts comes at high voltages with low ohms.

OK, we're past that boring definition part. That was quick, right?

Power generators typically produce electricity at anywhere from 6,000 to 14,000 volts depending on each station. Converted to industry terms, that's 6-14kV, and is about the same voltage used for residential distribution circuits running through neighborhoods. Voltages that low are not efficient at long distances greater than several miles, any more than trying to pump 1,000' of 1.75" attack line. You need to step up the pressure and put that water into some LDH (large-diameter hose), and bring it back down again near where it is to be used.

Bring in the transformer.

Without getting into its technical aspects right now, suffice to say that a transformer is what increases or decreases the voltage. Unlike the adjustable fire pump, they have a fixed ratio of conversion. For example, a 115/14kV transformer can only convert at that ratio. If its incoming high-side voltage, nominally 115kV, is reduced by 10% (to ~103kV), the outgoing voltage which would normally be 14kV will also be reduced by 10% (to ~12.5kV).

The concept of pressure regarding voltage also has to do with how far the electricity can potentially flash or arc to ground. Thus, the higher the voltage, the more clearance around the wires is provided and the longer the strings of insulators. Don't let the presence of only one or two insulator bells on a little distribution circuit make you think it is safe and small, though, as even the low end 6kV circuits can blow your arm off.

So, generators create power at relatively low voltages. The power stations have transformers that step up the voltage to efficient levels for long distance transmission, say anywhere from 115kV to 500kV, in some cases higher. High voltage = LDH. The network of high voltage transmission lines of various voltages generally comprises the "grid".

Attached to the grid are transmission substations. This is where the high transmission voltages are stepped down to levels suitable for delivering power to the distribution substations that actually serve the customers, bringing the big voltages through more transformers down to perhaps 34-69kV (subtransmission). Then, attached to these subtransmission circuits are the distribution substations with yet more transformers that step it down again for localized service, back down to the 6-14kV (distribution) last seen at the power plant.

Finally, in those gray 'cans' attached to the power poles, or under green metal boxes on small concrete pads on neighborhood street corners, are still more transformers, which drop the distribution voltage down to something Firegeezer's coffee pot and all your other household stuff can handle, converting whatever is on the power line down to a reasonable 120 volts (which of course can still kill you).

What we learned: (1) Moving electricity isn't quite so mysterious once we apply the moving water analogy to it. (2) Transformers are magic, but not very flexible about how they do their magic. (3) Volts, Watts, Amps and Ohms used to be totally mysterious, but now makes total sense because the water physics analogy helps us make sense of them.

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