Manual Hand Brake, Dynamic Braking and George Westinghouse’s Failsafe Railway Air Brake

Posted by PITHOCRATES - July 17th, 2013

Technology 101

Getting a Long and Heavy Train Moving was no good unless you could Stop It

Trains shrank countries.  Allowing people to travel greater distances faster than ever before.  And move more freight than ever before.  Freight so heavy that no horse could have ever pulled it.  The only limitation was the power of the locomotive.  Well, that.  And one other thing.  The ability to stop a long and heavy train.  For getting one moving was pretty easy.  Tracks were typically level.  And steel wheels on steel rails offered little resistance.  So once a train got moving it didn’t take much to keep it moving.  Especially when there was the slightest of inclines to roll down.

Getting a long and heavy train moving was no good unless you could stop it.  And stopping one was easier said than done.  As trains grew longer it proved impossible for the locomotive to stop it alone.  So each car in the consist (the rolling stock the locomotive pulls behind it) had a manual brake.  Operated by hand.  By brakemen.  Running along the tops of cars while the train was moving.  Turning wheels that applied the brakes on each car.  Not the safest of jobs.  One that couldn’t exist today.  Because of the number of brakemen that died on the job.  Due to the inherent danger of running along the top of a moving train.  Luckily, today, all brakemen have lost their jobs.  As we have safer ways to stop trains.

Of course, we don’t need to just stop trains.  A lot of the time we just need to slow them down a little.  Such as when approaching a curve.  Going through a reduced speed zone (bad track, wooden bridge, going through a city, etc.).  Or going down a slight incline.  In fact slowing down on an incline is crucial.  For if gravity is allowed to accelerate a train down an incline it can lead to a runaway.  That’s when a train gathers speed with no way of stopping it.  It can derail in a curve.  It can run into another train.  Or crash into a terminal building full of people.   All things that have happened.  The most recent disaster being the Montreal, Maine & Atlantic Railway disaster in Lac-Megantic, Quebec.  Where a parked oil train rolled away down an incline, derailed and exploded.  Killing some 38 people.  While many more are still missing and feared dead.

Dynamic Breaking can Slow a Train but to Stop a Train you need to Engage the Air Brakes

Trains basically have two braking systems today.  Air brakes.  And dynamic braking.  Dynamic braking involves changing the traction motors into generators.  The traction motors are underneath the locomotive.  The big diesel engine in the locomotive turns a generator making electric power.  This power creates powerful magnetic fields in the traction motors that rotate the axles.  The heavier the train the more power it takes to rotate these axles.  It takes a little skill to get a long and heavy train rolling.  Too much power and the steel wheels may slip on the steel rails.  Or the motors may require more power than the generator can provide.  As the torque required to move the train may be greater than traction motors can provide.  Thus ‘stalling’ the motor.  As it approaches stall torque it slows the rotation of the motor to zero while increasing the current from the generator to maximum.  As it struggles to rotate an axle it is not strong enough to rotate.  If this continues the maximum flow of current will cause excessive heat buildup in the motor windings.  Causing great damage.

Dynamic breaking reverses this process.  The traction motors become the generator.  Using the forward motion of the train to rotate the axles.  The electric power this produces feeds a resistive load that draws a heavy current form these traction motors.  Typically it’s the section of the locomotive directly behind the cab.  It draws more than the motors can provide.  Bringing them towards stall torque.  Thus slowing their rotation.  And slowing the train.  Converting the kinetic energy of the moving train into heat in the resistive load.  Which has a large cooling fan located above it to keep it from getting so hot that it starts melting.

Dynamic breaking can slow a train.  But it cannot stop it.  For as it slows the axles spin slower producing less electric power.  And as the electric current falls away it cannot ‘stall’ the generator (the traction motors operating as generators during dynamic braking).  Which is where the air brakes come in.  Which they can use in conjunction with dynamic braking on a steep incline.  To bring a train to a complete stop.  Or to a ‘quick’ stop (in a mile or so) in an emergency.  Either when the engineer activates the emergency brake.  Or something happens to break open the train line.  The air brake line that runs the length of the train.

When Parking a Train they Manually set the Hand Brakes BEFORE shutting down the Locomotive

The first air brake system used increasing air pressure to stop the train.  Think of the brake in a car.  When you press the brake pedal you force brake fluid to a cylinder at each wheel.  Forcing brake shoes or pads to come into contact with the rotating wheel.  The first train air brake worked similarly.  When the engineer wanted to stop the train he forced air to cylinders at each wheel.  Which moved linkages that forced brake shoes into contact with the rotating wheel.  It was a great improvement to having men run along the top of a moving train.  But it had one serious drawback.  If some cars separated from the train it would break open the train line.  So the air the engineer forced into it vented to the atmosphere without moving the brake linkages.  Which caused a runaway or two in its day.  George Westinghouse solved that problem.  By creating a failsafe railway air brake system.

The Westinghouse air brake system dates back to 1868.  And we still use his design today.  Which includes an air compressor at the engine.  Which provides air pressure to the train line.  Metal pipes below cars.  And rubber hoses between cars.  Running the full length of the train.  At each car is an air reservoir.  Or air tank.  And a triple valve.  Before a train moves it must charge the system (train line and reservoirs at each car) to, say, 90 pounds per square inch (PSI) of air pressure.  Once charged the train can move.  To apply the air brakes the engineer reduces the pressure by a few PSI in the train line.  The triple valve senses this and allows air to exit the air reservoir and enter the brake cylinder.  Pushing the linkages to bring the brake shoes into contact with the train wheels.  Providing a little resistance.  Slowing the train a little.  Once the pressure in the reservoir equals the pressure in the train line the triple valve stops the air from exiting the reservoir.  To slow the train more the engineer reduces the pressure by a few more PSI.  The triple valve senses this and lets more air out of the reservoir to again equalize the pressure in the reservoir and train line.  When the air leaves the reservoir it goes to the brake cylinder.  Moving the linkage more.  Increasing the pressure of the brake shoes on the wheels.  Further slowing the train.  The engineer continues this process until the train stops.  Or he is ready to increase speed (such as at the bottom of an incline).  To release the brakes the engineer increases the pressure in the train line.  Once the triple valve senses the pressure in the train line is greater than in the reservoir the air in the brake cylinders vents to the atmosphere.  Releasing the brakes.  While the train line brings the pressure in the reservoir back to 90 PSI.

This system is failsafe because the brakes apply with a loss of air pressure in the train line.  And if there is a rapid decline in air pressure the triple valve will sense that, too.  Say a coupler fails, separating two cars.  And the train line.  Causing the air pressure to fall from 90 PSI to zero very quickly.  When this happens the triple valve dumps the air in an emergency air reservoir along with the regular air reservoir into the brake cylinder.  Slamming the brake shoes onto the train wheels.  But as failsafe as the Westinghouse air brake system is it can still fail.  If an engineer applies the brakes and releases them a few times in a short period (something an experienced engineer wouldn’t do) the air pressure will slowly fall in both the train line and the reservoirs.  Because it takes time to recharge the air system (train line and reservoirs).  And if you don’t give it the time you will decrease your braking ability.  As there is less air in the reservoir available to go to the brake cylinder to move the linkages.  To the point the air pressure is so low that there isn’t enough pressure to push the brake shoes into the train wheels.  At this point you lose all braking.  With no ability to stop or slow the train.  Causing a runaway.

So, obviously, air pressure is key to a train’s air brake system.  Even if the train is just parked air will leak out of the train line.  If you’re standing near a locomotive (say at a passenger train station) and hear an air compressor start running it is most likely recharging the train line.  For it needs air pressure in the system to hold the brake shoes on the train wheels.  Which is why when they park a train they manually set the hand brakes (on a number of cars they determined will be sufficient to prevent the train from rolling) BEFORE shutting down the locomotive.  Once the ‘parking brake’ is set then and only then will they shut down the locomotive.  Letting the air bleed out of the air brake system.  Which appears to be what happened in Lac-Megantic, Quebec.  Preliminary reports suggest that the engineer may not have set enough hand brakes to prevent the train from rolling on the incline it was on when he parked the train for the night.  On a main line.  Because another train was on a siding.  And leaving the lead locomotive in a five locomotive lashup unmanned and running to maintain the air pressure.  Later that night there was a fire in that locomotive.  Before fighting that fire the fire department shut it down.  Which shut down the air compressor that was keeping the train line charged.  Later that night as the air pressure bled away the air brakes released and the hand brakes didn’t hold the train on the incline.  Resulting in the runaway (that may have reached a speed of 63 mph).  Derailment at a sharp curve.  And the explosion of some of its tank cars filled with crude oil.  Showing just how dangerous long, heavy trains can be when you can’t stop them.  Or keep them stopped.

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Primary Services, Power Redundancy, Double-Ended Primary Switchgear and Backup Generators

Posted by PITHOCRATES - July 3rd, 2013

Technology 101

The Higher the Currents the Thicker the Conductors and the Greater the Costs of Electrical Distribution

If you live by a hospital you’ve probably noticed something.  They never lose their power.  You could lose your power in a bad storm.  Leaving you sitting in your house on a hot and humid night with no air conditioning.  No lights.  No television.  No nothing.   And across the way you see that hospital lit up like a Christmas tree.  As if no storm just blew through your neighborhood.  Seemingly immune from the power outage afflicting you.  Why?  Because God loves hospitals.

Actually the reason why their lights never seem to go out has more to do with engineers than God.  And a little thing we call power redundancy.  Engineers know things happen.  And when things happen they often cause power outages.  Something we hate as we’ve become so accustomed to our electric-powered world.  But for us it is really more of an annoyance.  For a hospital, though, it’s not an annoyance.  It’s a life safety issue.  Because doctors and nurses need electric power to keep patients alive.  So engineers design ‘backup plans’ into a hospital’s design to handle interruptions in their electric service.  But first a brief word on power distribution.

Nikola Tesla created AC power transmission and put an end to Thomas Edison’s DC power dreams.  The key to AC power is that the alternating current (AC) allows the use of transformers.  Allowing us to step up and step down voltage.  This is very beneficial for the cost in electric power distribution is a factor of the size of the current carrying conductors.  The higher the currents the thicker the conductors and the greater the costs.  Because power is the product of voltage and current, though, we can reduce the size of the conductors by raising the voltage.  Power (P) equals voltage (E) times current (I).  Or P = I * E.  So for a given power you can have different voltages and currents.  And the higher the voltage the lower the current.  The smaller the conductors.  And the less costly the distribution system.

Neighborhoods typically get a Radial Feed so when we Lose our Power our Neighbors Lose their Power

Generators at power plants produce current at a relatively low voltage.  This power goes from the generators to a transformer.  Which steps this voltage up.  Way up.  To the highest voltages in our electric distribution system.  So relatively small conductors can distribute this power over great distances.  And then a series of substations filled with transformers steps the voltage down further and further until it arrives to our homes at 240 volts.  Delivered to us by the last transformer in the system.  Typically a pole-mounted transformer that steps it down from a 2,400 volt or a 4,800 volt set of cables on the other side of the transformer.  These cables go back to a substation.  Where they terminate to switchgear.  Which is terminated to the secondary side of a very large transformer.  Which steps down a higher voltage (say, 13,800 volt) to the lower 2,400 volt or a 4,800 volt.

We call the 240 volt service coming to our homes a secondary service.  Because it comes from the secondary side of those pole-mounted transformers.  And we can use the voltage coming from those transformers in our homes.  Once you get upstream from these last transformers we start getting into what we call primary services.  A much higher voltage that we can’t use in our homes until we step it down with a transformer.  Some large users of electric power have primary services because the size of conductors required at the lower voltages would be cost prohibited.  So they bring in these higher voltages on a less costly set of cables into what we call primary switchgear.  From that primary switchgear we distribute that primary power to unit substations located inside the building.  And these unit substations have built-in transformers to step down the voltage to a level we can use.

There are a few of these higher primary voltage substations in a geographic area.  They typically feed other substations in that geographic area that step it down further to the voltage on the wires on the poles we see in between our backyards.  That feed the transformers that feed our houses.  Which is why when we lose the power in our house all of our neighbors typically lose their power, too.  For if a storm blows down a tree and it takes down the wires at the top of the poles in between our back yards everyone getting their power from those wires will lose their power.  For neighborhoods typically get a ‘radial’ feed.  One set of feeder cables coming from a substation.  If that set of cables goes down, or if there is a fault on it anywhere in the grid it feeds (opening a breaker in the substation), everyone loses their power.  And they don’t get it back until they fix the fault (e.g., replace cables torn down by a fallen tree).

Hospitals typically have Redundant Primary Electrical Services coming from two Different Substations

Now this would be a problem for a hospital.  Which is why hospitals don’t get radial feeds.  They get redundant feeds.  Typically two primary services.  From two different substations.  You can see this if a hospital has an overhead service.  Look at the overhead wires that feed the hospital.  You will notice a gap between two poles.  There will be two poles where the wires end.  With no wires going between these two poles.  Why?  Because these two poles are the end of the line.  One pole has wires going back to one substation.  The other pole has wires going back to another substation.  These two different primary services feed the main primary switchgear that feeds all the electric loads inside the hospital.

This primary switchgear is double-ended.  Looking at it from left to right you will see a primary fusible switch (where a set of cables from one primary service terminates), a main primary circuit breaker, branch primary circuit breakers, a tie breaker, more branch primary circuit breakers, another main primary circuit breaker and another primary fusible switch (where a set of cables from the other primary service terminates).  The key to this switchgear is the two main breakers and the tie breaker.  During normal operation the two main breakers are closed and the tie breaker is open.  So you have one primary service (from one electrical substation) feeding one end (from the fusible switch up to the tie breaker).  And the other primary service (from the other electrical substation) feeding the other end (from the other fusible switch up to the tie breaker).  If one of the primary services is lost (because a storm blows through causing a tree to fall on and break the cables coming from one substation) the electric controls will sense that loss and open the main breaker on the end that lost its primary service and close the tie breaker.  Feeding the entire hospital off the one good remaining primary service.  This sensing and switching happens so fast that the hospital does not experience a power outage.

This is why a hospital doesn’t lose its power while you’re sitting in the dark suffering in heat and humidity.  Because you have a radial feed.  While the hospital has redundancy.  If they lose one primary service they have a backup primary service.  Unlike you.  And in the rare occasion where they lose BOTH primary services (such as the Northeast blackout of 2003) hospitals have further redundancy.  Backup generators.  That can feed all of their life safety loads until the utility company can restore at least one of their primary services.  These generators can run as long as they can get fuel deliveries to their big diesel storage tank.  That replenishes the ‘day tanks’ at the generators.  Allowing them to keep the lights on.  And their patients alive.  Even while you’re sitting in the dark across the street.  Sweating in the heat and humidity.  With no television to watch.  While people in the hospital say, “There was a power outage?  I did not notice that.”

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Even though Solar Panels and Natural Gas Home Generators allow us to Disconnect from the Grid we Shouldn’t

Posted by PITHOCRATES - April 21st, 2013

Week in Review

I remember losing power for a couple of hot and humid days.  The kind where you stick to everything because you’re just covered in sweat.  Making it almost impossible to sleep.  But I was able to borrow my father’s generator.  So I would not have to suffer through that insufferable heat and humidity.  While I was able to run my refrigerator, turn the lights on and even watch television I could not start my central air conditioner.  Even when I shut everything else off.  It was large enough to run the AC.  But it was just not big enough to start it.  I tried.  But as I did that inrush of current (about 40 amps) just stalled the generator.  Which could put out only 30 amps at 240 volts.  So even though I had a 30 amp generator to start an air conditioner that was on a 20 amp circuit breaker it wasn’t big enough.  Because of that momentary inrush of current.  So I suffered through that insufferable heat and humidity until the electric utility restored power.  And I never loved my electric utility more than when they did.

Now suppose I wanted to go to solar power.  How large of a solar array would I need that would start my air conditioner?  If one square inch of solar panel provided 70 milliwatts and you do a little math that comes to approximately a 950 square-foot solar array.  Or an array approximately 20 FT X 50 FT.  Which is a lot of solar panel.  Costly to install.  And if you want to use any electricity at night you’re going to need some kind of battery system.  But you won’t be able to run your air conditioner.  For one start would probably drain down that battery system.  So it’s not feasible to disconnect from the electric grid.  For you’re going to need something else when the sun doesn’t shine.  And because there can be windless nights a windmill won’t be the answer.  Because you’re going to need at least one source of electric power you can rely on to be there for you.  Like your electric utility.  Or, perhaps, your gas utility (see Relentless And Disruptive Innovation Will Shortly Affect US Electric Utilities by Peter Kelly-Detwiler posted 4/18/2013 on Forbes).

NRG’s CEO David Crane is one of the few utility CEO’s in the US who appears to fully appreciate – and publicly articulate – the potential for this coming dynamic.  At recent Wall Street Journal ECO:nomics conference, he indicated that solar power and natural gas are coming on strong, and that some customers may soon decide they do not need the electric utility. “If you have gas into your house and say you want to be as green as possible, maybe you’re anti-fracking or something and you have solar panels on your roof, you don’t need to be connected to the grid at all.”  He predicted that within a short timeframe, we may see technologies that allow for conversion of gas into electricity at the residential level.

If you want carefree and reliable electric power you connect to the electric grid.  Have a natural gas backup generator sized to power the entire house (large enough to even start your central air conditioner).  And a whole-house uninterruptible power supply (UPS).  To provide all your power needs momentarily while you switch from your electric utility to your gas utility.  Well, all but your central air conditioner (and other heavy electrical loads).  Which would have to wait for the natural gas generator to start running.  Because if you connected these to your UPS it might drain the battery down before that generator was up and running.  No problem.  For we can all go a minute or two without air conditioning.

So this combination would work.  With solar panels and a natural gas generator you could disconnect from the electric grid.  But is this something we should really do?  Not everyone will be able to afford solar panels and natural gas generators.  They will have to rely on the electric utility.  Some may only be able to afford the solar panels.  Staying connected to the grid for their nighttime power needs.  But if our electric utilities cut their generation and take it offline permanently it could cause some serious problems.  For what happens when a day of thunderstorms blocks the sun from our solar panels and everyone is still running their air conditioners?  The solar panels can no longer provide the peak power demand that they took from the electric utility (causing the utilities to reduce their generation capacity).  But if they reduced their generation capacity how are they going to be able to take back this peak power demand?  They won’t be able to.  And if they can’t that means rolling brownouts and blackouts.  Not a problem for those with the resources to install a backup generator.  But a big problem for everyone else.

We should study any plans to mothball any baseload electric generation.  For renewable sources of energy may be green but they are not reliable.  And electric power is not just about comfort in our homes.  It’s also about national security.  Imagine the Boston Marathon bombing happening during a time of rolling blackouts.  Imagine all of the things we take for granted not being there.  Like power in our homes to charge our smartphones.  And to power the televisions we saw the two bombers identified on.  We would have been both literally and figuratively in the dark.  Making it a lot easier for the bombers to have made their escape.  There’s a reason why we’re trying to harden our electric grid from cyber attacks.  Because we are simply too dependent on electric power for both the comforts and necessities of life.  Which is why we should be building more coal-fired power plants.  Not fewer.  Because coal is reliable and we have domestic sources of coal.  Ditto for natural gas and nuclear.  The mainstay of baseload power.  Because there is nothing more reliable.  Which comes in handy for national security.

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Electric Power, Alternating Current, Transformers, Magnetic Flux, Turns Ratio, Electric Panel and Circuit Breakers

Posted by PITHOCRATES - February 6th, 2013

Technology 101

AC Power is Superior to DC Power because it can Travel Farther and it Works with Transformers

Thanks to Nikola Tesla and his alternating current electric power we live in the world we have today.  The first electric power was direct current.  The stuff that Thomas Edison gave us.  But it had some serious drawbacks.  You needed a generator for each voltage you used.  The low-voltage of telephone systems would need a generator.  The voltage we used in our homes would need another generator.  And the higher voltages we used in our factories and businesses would need another generator.  Requiring a lot of power cables to hang from power poles along our streets.  Almost enough to block out the sun.

Another drawback is that direct currents travel a long way.  And spend a lot of time moving through wires.  Generating heat.  And dropping some power along the way due to the resistance in the wires.  Greatly minimizing the area a power plant can provide power to.  Requiring many power plants in our cities and suburbs.  Just imagine having three coal-fired power plants around your neighborhood.  The logistics and costs were just prohibitive for a modern electric world.  Which is why Thomas Edison lost the War of Currents to Nikola Tesla.

So why is alternating current (AC) superior to direct current (DC) for electric power?  AC is more like a reciprocating motion in an internal combustion engine or a steam locomotive.  Where short up & down and back & forth motion is converted into rotation motion.  Alternating current travels short distances back and forth in the power cables.  Because they travel shorter distances in the wires they lose less power in power transmission.  In fact, AC power lines can travel great distances.  Allowing power plants tucked away in the middle of nowhere power large geographic areas.  But there is another thing that makes AC power superior to DC power.  Transformers.

The Voltage induced onto the Secondary Windings is the Primary Voltage multiplied by the Turns Ratio

When an alternating current flows through a coiled wire it produces an alternating magnetic flux.  Magnetic flux is a measure of the strength and concentration of the magnetic field created by that current.  When this flux passes through another coiled wire it induces a voltage on that coil.  This is a transformer.  A primary and secondary winding where an alternating current applied on the primary winding induces a voltage on the secondary winding.  Allowing you to step up or step down a voltage.  Allowing one generator to produce one voltage.  While transformers throughout the power distribution network can produce the many voltages needed for doorbells, electrical outlets in our homes and the equipment in our factories and businesses.  And any other voltage for any other need.

We accomplish this remarkable feat by varying the number of turns in the windings.  If the number of turns is equal in the primary and the secondary windings then so is the voltage.  If the number of turns in the primary windings is greater than the number of turns in the secondary windings the transformer steps down the voltage.  If the number of turns in the secondary windings is greater than the number of turns in the primary windings the transformer steps up the voltage.  To determine the voltage induced onto the secondary windings we divide the secondary turns by the primary turns.  Giving us the turns ratio.  Multiplying the turns ratio by the voltage applied to the primary windings gives us the voltage on the secondary windings.  (Approximately.  There are some losses.  But for the sake of discussion assume ideal conditions.)

If the turns ratio is 20:1 it means the number of turns on the primary windings is twenty times the turns on the secondary windings.  Which means the voltage on the primary windings will be twenty times the voltage on the secondary windings.  Making this a step-down transformer.  So if you connected 4800 volts to the primary windings the voltage across the secondary windings will be 240 volts (4800/20).  If you attached a wire to the center of the secondary coil you can get both a 20:1 turns ratio and a 40:1 turns ratio.  If you measure a voltage across the entire secondary windings you will get 240 volts.  If you measure from the center of the secondary and either end of the secondary windings you will get 120 volts.

The Power Lines running to your House are Two Insulated Phase Conductors and a Bare Neutral Conductor

This is a common transformer you’ll see atop a pole in your backyard.  Where it is common to have 4800-volt power lines running at the top of poles running between houses.  On some of these poles you will see a transformer mounted below these 4800-volt lines.  The primary windings of these transformers connect to the 4800-volt lines.  And three wires from the secondary windings connect to wires running across these poles below the transformers.  Two of these wires (phase conductors) connect to either end of the secondary windings.  Providing 240 volts.  The third wire attaches to the center of the secondary windings (the neutral conductor).  We get 120 volts between a phase conductor and the neutral conductor.

The power lines running to your house are three conductors twisted together in a triplex cable.  Two insulated phase conductors.  And a bare neutral conductor.  These enter your house and terminate in an electric panel.  The two phase conductors connect to two bus bars inside the panel.  The neutral conductor connects to a neutral bus inside the panel.  Each bus feeds circuit breaker positions on both sides of the panel.  The circuit breaker positions going down the left side of the panel alternate between the two buss bars.  Ditto for the circuit breaker positions on the right side.

A single-pole circuit breaker attaches to one of the bus bars.  Then a wire from the circuit breaker and a wire from the neutral bus leave the panel and terminate at an electrical load.  Providing 120 volts to things like wall receptacles where you plug things into.  And your lighting.  A 2-pole circuit breaker attaches to both bus bars.  Then two wires from the circuit breaker leave the panel and attach to an electrical load.  Providing 240 volts to things like an electric stove or an air conditioner.  Then a reciprocating (push-pull) alternating current runs through these electric loads.  Driven by the push-pull between the two bus bars.  And between a bus bar and the neutral bus.  Which is driven by the push-pull between the conductors of the triplex cable.  Driven by the push pull of secondary windings in the transformer.  Driven by the push-pull of the primary windings.  Driven by the push-pull in the primary cables connected to the primary windings.  And all the way back to the push-pull of the electric generator.  All made possible thanks to Nikola Tesla.  And his alternating current electric power.

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The Horse, Waterwheel, Steam Engine, Electricity, DC and AC Power, Power Transmission and Electric Motors

Posted by PITHOCRATES - December 26th, 2012

Technology 101

(Original published December 21st, 2011)

A Waterwheel, Shaft, Pulleys and Belts made Power Transmission Complex

The history of man is the story of man controlling and shaping our environment.  Prehistoric man did little to change his environment.  But he started the process.  By making tools for the first time.  Over time we made better tools.  Taking us into the Bronze Age.  Where we did greater things.  The Sumerians and the Egyptians led their civilization in mass farming.  Created some of the first food surpluses in history.  In time came the Iron Age.  Better tools.  And better plows.  Fewer people could do more.  Especially when we attached an iron plow to one horsepower.  Or better yet, when horses were teamed together to produce 2 horsepower.  3 horsepower.  Even 4 horsepower.  The more power man harnessed the more work he was able to do.

This was the key to controlling and shaping our environment.  Converting energy into power.  A horse’s physiology can produce energy.  By feeding, watering and resting a horse we can convert that energy into power.  And with that power we can do greater work than we can do with our own physiology.  Working with horse-power has been the standard for millennia.  Especially for motive power.  Moving things.  Like dragging a plow.  But man has harnessed other energy.  Such as moving water.  Using a waterwheel.  Go into an old working cider mill in the fall and you’ll see how man made power from water by turning a wheel and a series of belts and pulleys.  The waterwheel turned a main shaft that ran the length of the work area.  On the shaft were pulleys.  Around these pulleys were belts that could be engaged to transfer power to a work station.  Where it would turn another pulley attached to a shaft.  Depending on the nature of the work task the rotational motion of the main shaft could be increased or decreased with gears.  We could change it from rotational to reciprocating motion.  We could even change the axis of rotation with another type of gearing.

This was a great step forward in advancing civilization.  But the waterwheel, shaft, pulleys and belts made power transmission complex.  And somewhat limited by the energy available in the moving water.  A great step forward was the steam engine.  A large external combustion engine.  Where an external firebox heated water to steam.  And then that steam pushed a piston in a cylinder.  The energy in expanding steam was far greater than in moving water.  It produced far more power.  And could do far more work.  We could do so much work with the steam engine that it kicked off the Industrial Revolution.

Nikola Tesla created an Electrical Revolution using AC Power

The steam engine also gave us more freedom.  We could now build a factory anywhere we wanted to.  And did.  We could do something else with it, too.  We could put it on tracks.  And use it to pull heavy loads across the country.  The steam locomotive interconnected the factories to the raw materials they consumed.  And to the cities that bought their finished goods.  At a rate no amount of teamed horses could equal.  Yes, the iron horse ended man’s special relationship with the horse.  Even on the farm.  Where steam engines powered our first tractors.  Giving man the ability to do more work than ever.  And grow more food than ever.  Creating greater food surpluses than the Sumerians and Egyptians could ever grow.  No matter how much of their fertile river banks they cultivated.  Or how much land they irrigated.

Steam engines were incredibly powerful.  But they were big.  And very complex.  They were ideal for the farm and the factory.  The steam locomotive and the steamship.  But one thing they were not good at was transmitting power over distances.  A limitation the waterwheel shared.  To transmit power from a steam engine required a complicated series of belts and pulleys.  Or multiple steam engines.  A great advance in technology changed all that.  Something Benjamin Franklin experimented with.  Something Thomas Edison did, too.  Even gave us one of the greatest inventions of all time that used this new technology.  The light bulb.  Powered by, of course, electricity.

Electricity.  That thing we can’t see, touch or smell.  And it moves mysteriously through wires and does work.  Edison did much to advance this technology.  Created electrical generators.  And lit our cities with his electric light bulb.  Electrical power lines crisscrossed our early cities.  And there were a lot of them.  Far more than we see today.  Why?  Because Edison’s power was direct current.  DC.  Which had some serious drawbacks when it came to power transmission.  For one it didn’t travel very far before losing much of its power. So electrical loads couldn’t be far from a generator.  And you needed a generator for each voltage you used.  That adds up to a lot of generators.  Great if you’re in the business of selling electrical generators.  Which Edison was.  But it made DC power costly.  And complex.  Which explained that maze of power lines crisscrossing our cities.  A set of wires for each voltage.  Something you didn’t need with alternating current.  AC.  And a young engineer working for George Westinghouse was about to give Thomas Edison a run for his money.  By creating an electrical revolution using that AC power.  And that’s just what Nikola Tesla did.

Transformers Stepped-up Voltages for Power Transmission and Stepped-down Voltages for Electrical Motors

An alternating current went back and forth through a wire.  It did not have to return to the electrical generator after leaving it.  Unlike a direct current ultimately had to.  Think of a reciprocating engine.  Like on a steam locomotive.  This back and forth motion doesn’t do anything but go back and forth.  Not very useful on a train.  But when we convert it to rotational motion, why, that’s a whole other story.  Because rotational motion on a train is very useful.  Just as AC current in transmission lines turned out to be very useful.

There are two electrical formulas that explain a lot of these developments.  First, electrical power (P) is equal to the voltage (V) multiplied by the current (I).  Expressed mathematically, P = V x I.  Second, current (I) is equal to the voltage (V) divided by the electrical resistance (R).  Mathematically, I = V/R.  That’s the math.  Here it is in words.  The greater the voltage and current the greater the power.  And the more work you can do.  However, we transmit current on copper wires.  And copper is expensive.  So to increase current we need to lower the resistance of that expensive copper wire.  But there’s only one way to do that.  By using very thick and expensive wires.  See where we’re going here?  Increasing current is a costly way to increase power.  Because of all that copper.  It’s just not economical.  So what about increasing voltage instead?  Turns out that’s very economical.  Because you can transmit great power with small currents if you step up the voltage.  And Nikola Tesla’s AC power allowed just that.  By using transformers.  Which, unfortunately for Edison, don’t work with DC power.

This is why Nikola Tesla’s AC power put Thomas Edison’s DC power out of business.  By stepping up voltages a power plant could send power long distances.  And then that high voltage could be stepped down to a variety of voltages and connected to factories (and homes).  Electric power could do one more very important thing.  It could power new electric motors.  And convert this AC power into rotational motion.  These electric motors came in all different sizes and voltages to suit the task at hand.  So instead of a waterwheel or a steam engine driving a main shaft through a factory we simply connected factories to the electric grid.  Then they used step-down transformers within the factory where needed for the various work tasks.  Connecting to electric motors on a variety of machines.  Where a worker could turn them on or off with the flick of a switch.  Without endangering him or herself by engaging or disengaging belts from a main drive shaft.  Instead the worker could spend all of his or her time on the task at hand.  Increasing productivity like never before.

Free Market Capitalism gave us Electric Power, the Electric Motor and the Roaring Twenties

What electric power and the electric motor did was reduce the size and complexity of energy conversion to useable power.  Steam engines were massive, complex and dangerous.  Exploding boilers killed many a worker.  And innocent bystander.  Electric power was simpler and safer to use.  And it was more efficient.  Horses were stronger than man.  But increasing horsepower required a lot of big horses that we also had to feed and care for.  Electric motors are smaller and don’t need to be fed.  Or be cleaned up after, for that matter.

Today a 40 pound electric motor can do the work of one 1,500 pound draft horse.  Electric power and the electric motor allow us to do work no amount of teamed horses can do.  And it’s safer and simpler than using a steam engine.  Which is why the Roaring Twenties roared.  It was in the 1920s that this technology began to power American industry.  Giving us the power to control and shape our environment like never before.  Vaulting America to the number one economic power of the world.  Thanks to free market capitalism.  And a few great minds along the way.

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Internal Combustion Engine, Electric Motor, Fuel Economy, Emissions, Electric Range, Parallel Hybrid, Series Hybrid and Plug-In

Posted by PITHOCRATES - September 5th, 2012

Technology 101

We started the First Cars with a Hand Crank and Nearly Broke an Arm if the Hand Crank Kicked Back

The king of car engines is the internal combustion engine (ICE).  We tried other motors such as a steam engine.  But a steam engine is a heat engine.  Meaning it first has to get hot enough to boil water into steam.  Which meant any trip in a car took a little extra time to bring the boiler up to operating temperatures.  Boilers tend to be big and heavy.  And dangerous.  Should something happen and a dangerous level of steam pressure built up they could explode.  Despite those drawbacks, though, a steam engine-powered car took you places.  And as long as there was fuel for the firebox and water for the boiler you could keep driving.

Another engine we tried was the electric motor.  These didn’t have any of the drawbacks of a steam engine.  You didn’t have to wait for a boiler to get to operating temperatures before driving.  Nothing was in danger of exploding.  An electric motor was lighter than a cast-iron boiler.  And an electric motor could make a car zip along.  However, an electric motor requires continuous electricity to operate.  Provided by charged batteries.  Which didn’t last long.  And took hours to recharge.  Giving the electric car limited range.  And little convenience.  For the heavier it was and/or the faster you went the faster you drained those batteries.  Which could be a problem taking the family on vacation.  But they worked well in a forklift on a loading dock.  Because of the battery-power they produced no emissions so they’re safe to use indoors.  They had limited auxiliary systems to run (other than a horn and maybe a light).  And when they were running low on charge you rarely needed to drive more than 20 or 30 feet to a charging station.

The first ICE-powered cars took some manly strength to operate.  They didn’t have power brakes, power steering, automatic transmissions or starters.  We started the first ICE-powered cars with a hand crank.  That took a lot of strength to turn.  And if it backfired while starting the kick of the handle could easily break a wrist or an arm.  Putting a damper on any Sunday afternoon drive.  This limited the spread of the automobile.  They were complex machines that required some strength to operate.  And they could be very dangerous.  Then along came the electric starter.  Which was an electric motor that spun the ICE to life.  Making the car much safer to start.  Expanding the popularity of the automobile.  For there was no longer a good chance that you could break your arm trying to start it.  And through the years came all those accessories making it easier and more comfortable to drive.  Today automatic transmissions, power steering, power brakes, headlights, interior lights, power locks, power windows, powered seats, a fairly decent audio system, heat, air conditioning and more are standard on most cars.  All effortless powered by that internal combustion engine.

Current Battery Technology does not give the All-Electric Car a Great Range

The reason why an ICE can do all of this is because gasoline is a very concentrated energy source.  It doesn’t take a lot of it to go a long way.  And it can accelerate you up a hill.  It even has the energy to pass someone on a hill. It’s a fuel source we can take with us.  A small amount of it stores conveniently and safely in a gas tank slung underneath a car.  And when it’s empty it takes very little time to refill.  A ten minute stop at a gas station and you’re back on the road able to drive another 500 miles or so.  Even in the dark of night with headlights blazing.  While keeping toasty warm in the winter.  Or comfortably cool in the summer.  Things an electric battery just can’t do.  So why would we even want to trade one for the other?  In a word—emissions.

The internal combustion engine pollutes.  The more fuel a car burns the more it pollutes.  So to cut pollution you try to make cars burn less fuel.  You increase the fuel economy.  And you can do that in a couple of ways.  You can cut the weight of the vehicle.  And put in a smaller engine.  Because a smaller engine can power a lighter car.  But a smaller car carries fewer people comfortably.  And can carry less stuff.  A motor cycle gets very good fuel economy but you can’t take the family on a Sunday drive on one.  And you can’t pack up your things on a motorcycle when going off to college.  So the tradeoff between fuel economy and weight has consequences.

An electric car does not pollute.  At all.  (Though the power plant that charges its batteries does pollute.  A lot.)  But current battery technology does not give the all-electric car a great range.  Typically coming in at less than 75 miles per charge.  Which is great if you’re operating a forklift on a loading dock.  But it’s pretty bad if you’re actually driving on a road going someplace.  And hope to return.  The heavier the car is the shorter that driving range.  If you want to use your headlights, heater or air conditioner it’ll be shorter still.  On top of this short range recharging your battery isn’t like stopping at the gas station for 10 minutes.  No.  What one typically does is pray that he or she gets home.  Then plugs in.  And by morning the car would be fully charge for another 75 miles or so of driving.

To Maximize the Benefit of a Hybrid you’d want to Carry the Absolute Minimum of Batteries to Serve your Needs

So all-electric cars are clean but they won’t really take us places.  The ICE-powered car will take us places but it’s not really clean.  Enter the gas/electric hybrid.  Which combines the best of the all-electric car (clean) and the best of the ICE-powered car (range).  There are a few varieties.  The parallel hybrid has both an ICE and an electric motor connected to a transmission that powers the wheels.  The ICE also drives a small generator.  Batteries power the electric motor.  And a gas tank feeds the ICE.  The generator keeps the batteries charged.  The battery powers the electric motor to accelerate the car from a stop.  After a certain speed the small ICE takes over.  When the car needs to accelerate the electric motor assists the ICE.  The small ICE has excellent fuel economy thus reducing emissions.  The electric motor/battery provides the additional horsepower when needed to compensate for an undersized ICE.  And the gasoline-powered engine provides extended range.

In addition to the parallel hybrid there is the series hybrid.  It has the same parts but they are connected differently.  The series hybrid is more like a diesel-electric locomotive.  Gasoline feeds the ICE.  The ICE drives a generator.  The generator charges the batteries and/or drives the electric motor.  The electric motor drives a transmission that spins the wheels.  This car drives on batteries until the charge runs out and then switches over to the ICE.  For short commutes this provides excellent fuel economy.  For longer drives (well over 75 miles or so) it’s more like a standard ICE-powered car with a roundabout way of turning the wheels.

Then there’s the plug-in variety.  In addition to all of the above you can plug your car into a charger to further save on gasoline use and reduce emissions (produced by the car; not by the electric power plant).  Letting you recharge the battery overnight in a standard 120V outlet.  In a slightly shorter time with a 240 volt outlet.  And quicker still in a 480 volt outlet.  If your commute to and from work is 50 miles or less you can probably charge up at home and not have to carry a charger with you (to convert the AC power to the DC power of the batteries).  Saving even more weight.  But if you plan on charging on the road you’ll need to carry a charger with you.  Adding additional weight.  Which will, of course, reduce your battery range.  Also, you can adjust the number of batteries to match your typical daily commute.  The shorter your commute the less charge you need to store.  Which lets you get by on fewer batteries.  Greatly reducing the weight of the car (and extending your battery range).  A gallon of gas weighs about 7 pounds and can take a car 30 miles or more.  You would need about 1,000 pounds of batteries to provide a similar range.  So range doesn’t come cheap.  To maximize the benefit of a hybrid you’d want to carry the absolute minimum of batteries to serve your needs.  Knowing that if you got a new job with a longer commute you could rely on the ICE in your hybrid to get you to work and back home safe again.

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Inrush Current, Redundancy, Electric Grid, High Voltage Transmission Lines, Substations, Generators and Northeast Blackout of 2003

Posted by PITHOCRATES - August 22nd, 2012

Technology 101

In Electric Generators and Motors there is a Tradeoff between Voltage and Current

If you have central air conditioning you’ve probably noticed something when it turns on.  Especially at night.  The lights will momentarily dim.  Why?  Because a central air conditioner is probably the largest electric load in your house.  It draws a lot of current.  Even at 240V volts.  And when it switches on the inrush of current is so great that it sucks current away from everything else.  This momentary surge of current exceeds your electrical panel’s ability to keep up with it. Try as it might the panel cannot push out enough current.  It tries so hard that it loses its ‘pushing’ strength and its voltage fades.  But once the air conditioner runs the starting inrush of current settles down to a lower running current that the panel can easily provide.  And it recovers its strength.  Its voltage returns to normal.  And all the lights return to normal brightness.

If you have ever been stopped by a train at a railroad crossing you’ve seen another example of this voltage-current tradeoff.  As a diesel-electric locomotive starts moving you’ll see plumes of diesel exhaust puffing out of the engine.  Why?  The diesel engine drives a generator.  The generator drives electric traction motors that turn the engine’s wheels.  These traction motors are like turning on a very large air conditioner.  The inrush of current sucks current out of the generator and makes the voltage fall.  The load on the engine is so great that it slows down while it struggles to supply that current.

To prevent the engine from stalling more fuel is pumped into the engine to increase engine RPMs.  Like stomping on the accelerator in a car.  Causing those plumes of diesel exhaust.  As the wheels start turning the current in the motor windings creates a counter electromotive force (the electric field collapses on the windings inducing a current in the opposite direction).  Which resists the current flow.  Current falls.  And the voltage goes back up.  If the engine is pushed beyond its operating limits, though, it will shut down to protect itself.  Bring the locomotive to a standstill wherever it is.  Even if it’s blocking all traffic at a railroad crossing.

Generators have to be Synchronized First before Connecting to the Electric Grid

The key to reliable electric power is redundancy.  To understand electrical redundancy think about driving your car.  Your normal route to work is under construction.  And the road is closed.  What do you do?  You take a different road.  You can do this because there is road redundancy.  In fact there are probably many different ways you can drive to work.  The electric grid provides the roads for electric power to travel.  Bringing together power plants.  Substations.  And conductors.  Interconnecting you to the various power plants connected to the grid.

Electric power leaves power plants on high voltage overhead transmission lines.  These lines can travel great distances with minimal losses.  But the power is useless to you and me.  The voltage is too high.  So these high voltage lines connect to substations.  Typically two of these high voltage feeders (two cable sets of three conductors each) connect to a substation.  Coming out of these substations are more conductors (cable sets of three conductors each) that feed loads at lower voltages.  In between the incoming feeders and the outgoing feeders are a bunch of switches and transformers.  To step down the voltage.  And to allow an outbound set of conductors to be switched to either of the two incoming feeders.  So if one of the incoming feeders goes down (for maintenance, cable failure, etc.) the load can switch over to the other inbound cable set.

Redundant power feeds to these substations can come from larger substations upstream.  Even from different power plants.  And all of these power plants can connect to the grid.  Which ultimately connects the output of different generators together.  This is easier said than done.  Current flows between different voltages.  The greater the voltage difference the greater the current flow.  Our power is an alternating current.  It is a reciprocating motion of electrons in the conductors.  Which makes connecting two AC sources together tricky.  Because they have to move identically.  They have to be in phase and move back and forth in the conductors at the same time.  Currents have to leave the generator at the same time.  And return at the same time.  If they do then the voltage differences between the phases will be zero.  And no current will flow between the power plants.  Instead it will all go into the grid.  If they are not synchronized when connected there will be voltage difference between the phases causing current to flow between the power stations.  With the chance of causing great damage.

The Northeast Blackout of 2003 started from one 345 kV Transmission Line Failing

August 14, 2003 was a hot day across the Midwest and the Northeast.  People were running their air conditioners.  Consuming a lot of electric power.  A 345 kV overhead transmission line in Northeast Ohio was drawing a lot of current to feed that electric power demand.  The feeder carried so much current that it heated up on that hot day.  And began to sag.  It came into contact with a tree.  The current jumped from the conductor to the tree.  And the 345 kV transmission line failed.  Power then switched over automatically to other lines.  Causing them to heat up, sag and fail.  As more load was switched onto fewer lines a cascade of failures followed.

As lines overloaded and failed power surged through the grid to rebalance the system.  Currents soared and voltages fell.  Power raced one way.  Then reversed and raced the other way when other lines failed.  Voltages fell with these current surges.  Generators struggled to provide the demanded power.  Some generators sped up when some loads disconnected from the grid.  Taking them out of synch with other generators.  Generators began to disconnect from the grid to protect themselves from these wild fluctuations.  And as they went off-line others tried to pick up their load and soon exceeded their operating limits.  Then they disconnected from the grid.  And on and on it went.  Until the last failure of the Northeast blackout of 2003 left a huge chunk of North America without any electric power.  From Ontario to New Jersey.  From Michigan to Massachusetts.  All started from one 345 kV transmission line failing.

In all about 256 power plants went off-line.  As they were designed to do.  Just like a diesel locomotive engine shutting down to protect itself.  Generators are expensive.  And they take a lot of time to build.  To transport.  To install.  And to test, start up and put on line.  So the generators have many built-in safeguards to prevent any damage.  Which was part of the delay in restoring power.  Especially the nuclear power plants.  Restoring power, though, wasn’t just as easy as getting the power plants up and running again.  All the outgoing switches at all those substations had to be opened first before reenergizing those incoming feeders.  Then they carefully closed the outgoing switches to restore power while keeping the grid balanced.  And to prevent any surges that may have pulled a generator out of synch.  It’s a complicated system.  But it works.  When it’s maintained properly.  And there is sufficient power generation feeding the grid.

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Electric Grid, Voltage, Current, Power, Phase Conductor, Neutral Conductor, 3-Phase Power, Transmission Towers and Corona Discharge

Posted by PITHOCRATES - August 15th, 2012

Technology 101

The Electric Grid is the Highways and Byways for Electric Power from the Power Plant to our Homes

Even our gasoline-powered cars operate on electricity.  The very thing that ignites the air-fuel mixture is an electric spark.  Pushed across an air-gap by a high voltage.  Because that’s something that high voltages do.  Push electrons with such great force that they can actually leave a conductor and travel through the air to another conductor.  Something we don’t want to happen most of the time.  Unless it’s in a spark plug in our gasoline engine.  Or in some movie prop in a cheap science fiction movie.

No.  When we use high voltage to push electrons through a conductor the last thing we want to happen is for the electrons to leave that conductor.  Because we spend a pretty penny to push those electrons out of a power plant.  And if we push the electrons out of the conductor they won’t do much work for us.  Which is the whole point of putting electricity into the electric grid.  To do work for us.

The electric grid.  What exactly is it?  The highways and byways for electric power.  Power plants produce electric power.  And send it to our homes.  As well as our businesses.  Power is the product of voltage and current.  In our homes something we plug into a 120V outlet that draws 8 amps of current consumes 960 watts.  Which is pretty big for a house.  But negligible for a power plant generator producing current at 20,000 volts.  For at 20,000 volts a generator only has to produce 0.48 amps (20,000 X 0.48 = 960).  Or about 6% of the current at 120V.

Between our Homes and the Power Plant we can Change that Current by Changing the Voltage

Current is money.  Just as time is money.  In fact current used over time helps to determine your electric bill.  Where the utility charges you for kilowatt hours (voltage X current X time).  (This would actually give you watt-hours.  You need to divide by 1000 to get kilowatt hours.)  The electric service to your house is a constant voltage.  So it’s the amount of current you use that determines your electric bill.  The more current you use the greater the power you use.  Because in the power equation (voltage X current) voltage is constant while current increases.

Current travels in conductors.  The size of the conductor determines a lot of costs.  Think of automobile traffic.  Areas that have high traffic volumes between them may have a very expensive 8-lane Interstate expressway interconnecting them.  Whereas a lone farmer living in the ‘middle of nowhere’ may only have a much less expensive dirt road leading to his or her home.  And so it is with the electric grid.  Large consumers of electric power need an Interstate expressway.  To move a lot of current.  Which is what actually spins our electrical meters.  Current.  However, between our homes and the power plant we can change that current.  By changing the voltage.  Thereby reducing the cost of that electric power Interstate expressway.

The current flowing through our electric grid is an alternating current.  It leaves the power plant.  Travels in the conductors for about 1/120 of a second.  Then reverses direction and heads back to the power plant.  And reverses again in another 1/120 of a second.  One complete cycle (travel in both directions) takes 1/60 of a second.  And there are 60 of these complete cycles per second.  Hence the alternating current.  If you’re wondering how this back and forth motion in a wire can do any work just think of a steam locomotive.  Or a gasoline engine.  Where a reciprocating (back and forth) motion is converted into rotational motion that can drive a steam locomotive.  Or an automobile.

The Voltages of our Electric Grid balance the Cost Savings (Smaller Wires) with the Higher Costs (Larger Towers)

An electric circuit needs two conductors.  When current is flowing away from the power plant in one it is flowing back to the power plant in the other.  As the current changes direction is has to stop first.  And when it stops flowing the current is zero.  Using the power formula this means there are zero watts twice a cycle.  Or 120 times a second.  Which isn’t very efficient.  However, if you bring two other sets of conductors to the work load and time the current in them properly you can remove these zero-power moments.  You send the first current out in one set of conductors and wait 1/3 of a cycle.  Then you send the second current out in the second set of conductors and wait another 1/3 cycle.  Then you send the third current out in the third set of conductors.  Which guarantees that when a current is slowing to stop to reverse direction there are other currents moving faster towards their peak currents in the other conductors.  Making 3-phase power more efficient than single-phase power.  And the choice for all large consumers of electric power.

Anyone who has ever done any electrical wiring in their home knows you can share neutral conductors.  Meaning more than one circuit coming from your electrical panel can share the return path back to the panel.  If you’ve ever been shocked while working on a circuit you switched off in your panel you have a shared neutral conductor.  Even though you switched off the circuit you were working on another circuit sharing that neutral was still switched on and placing a current on that shared neutral.  Which is what shocked you.  So if we can share neutral conductors we don’t need a total of 6 conductors as noted above.  We only need 4.  Because each circuit leaving the power plant (i.e., phase conductor) can share a common neutral conductor on its way back to the power plant.  But the interesting thing about 3-phase power is that you don’t even need this neutral conductor.  Because in a balanced 3-phase circuit (equal current per phase) there is no current in this neutral conductor.  So it’s not needed as all the back and forth current movement happens in the phase conductors.

Electric power travels in feeders that include three conductors per feeder.  If you look at overhead power lines you will notice they all come in sets of threes when they get upstream of the final transformer that feeds your house.  The lines running along your backyard will have three conductors across the top of the poles.  As they move back to the power plant they pass through additional transformers that increase their voltage (and reduce their current).  And the electric transmission towers get bigger.  With some having two sets of 3-conductor feeders.  The higher the voltage the higher off the ground they have to be.  And the farther apart the phase conductors have to be so the high voltage doesn’t cause an arc to jump the ‘air gap’ between phase conductors.  As you move further away from your home back towards the power plant the voltage will step up to values like 2.4kV (or 2,400 volts), 4.8kV and13.2kV that will typically take you back to a substation.  And then from these substations the big power lines head back towards the power plant.  On even bigger towers.  At voltages of 115kV, 138kV, 230kV, 345kv, 500kV and as high as 765kV.  When they approach the power plant they step down the voltage to match the voltage produced by its generators.

They select the voltages of our electric grid to balance the cost savings (smaller wires) with the higher costs (larger towers taking up more land).  If they increase the voltage so high that they can use very thin and inexpensive conductors the towers required to transmit that voltage safely may be so costly that they exceed the cost savings of the thinner conductors.  So there is an economic limit on voltage levels  As well as other considerations of very high voltages (such as corona discharge where high voltages create such a power magnetic field around the conductors that it may ionize the air around it causing a sizzling sound and a fuzzy blue glow around the cable.  Not to mention causing radio interference.  As well as creating some smog-causing pollutants like ozone and nitrogen oxides.)

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Conservation of Energy, Potential Energy, Kinetic Energy, Waterwheels, Water Turbine, Niagara Falls, Dams, and Hydroelectric Power

Posted by PITHOCRATES - July 25th, 2012

Technology 101

Roller Coasters use Gravity to Convert Energy back and forth between Potential Energy and Kinetic Energy

We cannot destroy energy.  All we can do is convert it.  It’s a law of physics.  The law of conservation of energy.  A roller coaster shows this.  Where roller coasters move by converting potential energy into kinetic energy.  And then by converting kinetic energy back into potential energy.

The best roller coasters race down tall inclines gaining incredible speed.  The taller the coaster the faster the speed.  That’s because of potential energy (stated in units of joules).  Which is equal to the mass times the force of gravity times the height.  The last component is what makes tall roller coasters fast.  Height.  As the cars inch over the summit gravity begins pulling them down.  And the longer gravity can pull them down the more speed they can gain.  At the bottom of the hill the height is zero so the potential energy is zero.  All energy having been converted into kinetic energy (also stated in units of joules).

Roller coasters travel the fastest at the lowest points in the track.  Where potential energy equals zero.  While kinetic energy is at its highest.  Which is equal to one half times the mass times the velocity squared.  So the higher the track the more time gravity has to accelerate these cars.  At their fastest speed they start up the next incline.  Where the force of gravity begins to pull on them.  Slowing them down as they climb up the next hill.  Converting that kinetic energy back into potential energy.  When they crest the hill for a moment their speed is zero so their kinetic energy is zero.  All energy having been converted back into potential energy.  Where gravity tugs those cars down the next incline.  And so on up and down each successive hill.  Where at all times the sum of potential energy and kinetic energy equals the same amount of joules.  Maximum potential energy is at the top.  Maximum kinetic energy is at the bottom.  And somewhere in the middle they each equal half of their maximum amounts.

(This is a simplified explanation.  Additional forces are ignored for simplicity to illustrate the relation between potential energy and kinetic energy.)

We build Dams on Rivers  to do what Niagara Falls does Naturally

So once over the first hill roller coasters run only on gravity.  And the conversion of energy from potential to kinetic energy and back again.  Except for that first incline.  Where man-made power pulls the cars up.  Electric power.  Produced by generators.  Spun by kinetic energy.  Produced from the expanding gases of combustion in a natural gas-powered plant.  Or from high-pressure steam produced in a coal-fired power plant or nuclear power plant.  Or in another type of power plant that converts potential energy into kinetic energy.  In a hydroelectric dam.

Using water power dates back to our first civilizations.  Then we just used the kinetic energy of a moving stream to turn a waterwheel.  These waterwheels turned shafts and pulleys to transfer this power to work stations.  So they couldn’t spin too fast.  Which wasn’t a problem because people only used rivers and streams with moderate currents.  So these wheels didn’t spin fast.  But they could turn a mill stone.  Or run a sawmill.  With far more efficiency than people working with hand tools.  But there isn’t enough energy in a slow moving river or stream to produce electricity.  Which is why we built some of our first hydroelectric power plants at Niagara Falls.  Where there was a lot of water at a high elevation that fell to a lower elevation.  And if you stick a water turbine in the path of that water you can generate electricity.

Of course, there aren’t Niagara Falls all around the country.  Where nature made water fall from a high elevation to a low elevation.  So we had to step in to shape nature to do what Niagara Falls does naturally.  By building dams on rivers.  As we blocked the flow of water the water backed up behind the dam.  And the water level climbed up the river banks to from a large reservoir.  Or lake.  Raising the water level on one side of the dam much higher than the other side.  Creating a huge pool of potential energy (mass times gravity times height).  Just waiting to be converted into kinetic energy.  To drive a water turbine.  The higher the height of the water behind the dam (or the higher the head) the greater the potential energy.  And the greater the kinetic energy of the water flow.  When it flows.

Hydroelectric Power is the Cleanest and Most Reliable Source of Renewable Energy-Generated Power

Near the water level behind the dam are water inlets into channels through the dam or external penstocks (large pipes) that channels the water from the high elevation to the low elevation and into the vanes of the water turbine.  The water flows into these curved vanes which redirects this water flow down through the turbine.  Creating rotational motion that drives a generator.  After exiting the turbine the water discharges back into the river below the dam.

Our electricity is an alternating current at 60 hertz (or cycles per second).  These turbines, though, don’t spin at 60 revolutions per second.  So to create 60 hertz they have to use different generators than they use with steam turbines.  Steam turbines spin a generator with only one rotating magnetic field to induce a current in the stator (i.e., stationary) windings of the generator.  They can produce an alternating current at 60 hertz because the high pressure steam can spin these generators at 60 revolutions per second.  The water flowing through a turbine can’t.  So they add additional rotational magnetic fields in the generator.  Twelve rotational magnetic fields can produce 60 hertz of alternating current while the generator only spins at 5 revolutions per second.  Adjustable gates open and close to let more or less water to flow through the turbine to maintain a constant rotation.

The hydroelectric power plant is one of the simplest of power generating plants.  There is no fuel needed to generate heat to make steam.  No steam pressure to monitor closely to prevent explosions.  No fires to worry about in the mountains of coal stored at a plant.  No nuclear meltdown to worry about.  And no emissions.  All you need is water.  From snow in the winter that melts in the spring.  And rain.  Not to mention a good river to dam.  If the water comes the necessary head behind the dam will be there to spin those turbines.  But sometimes the water isn’t there.  And the dams have to shut down generators because there isn’t enough water.  But hydroelectric power is still the cleanest and most reliable source of electric power generated from renewable energy we have.  But it does have one serious drawback.  You need a river to dam.  And the best spots already have a dam on them.  Leaving little room for expansion of hydroelectric power.  Which is why we generate about half of our electric power from coal.  Because we can build a coal-fired power plant pretty much anywhere we want to.  And they will run whether or not we have snow or rain.  Because they are that reliable.

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Neutrons, Electrons, Electric Current, Nuclear Power, Nuclear Chain Reaction, Residual Decay Heat and Pressurized Water Reactor

Posted by PITHOCRATES - July 18th, 2012

Technology 101

We create about Half of our Electric Power by Burning Coal to Boil Water into Steam

An atom consists of a nucleus made up of protons and neutrons.  And electrons orbiting around the nucleus.  Protons have a positive charge.  Electrons have a negative charge.  Neutrons have a neutral charge.  In chemistry and electricity the electrons are key.  When different atoms come together they form chemical bonds.  By sharing some of those electrons orbiting their nuclei.  In metals free electrons roam around the metal lattice of the crystalline solid they’re in.  If we apply a voltage across this metal these free electrons begin to flow.  Creating an electric current.  The greater the voltage the greater the current.  And the greater the work it can do.  It can power a television set.  Keep your food from spoiling in a refrigerator.  Even make your summers comfortable by running your air conditioner. 

We use electric power to do work for us.  Power is the product of voltage and current.  The higher each is the more work this power can do for us.  In a direct current (DC) system the free electrons have to make a complete path from the power source (an electric generator) through the wiring to the work load and back again to the power source.  But generating the power at the voltage of the workload required high currents.  Thick wires.  And a lot of power plants because you could only make wires so thick before they were too heavy to work with.  Alternating current (AC) solved this problem.  By using transformers at each end of the distribution path to step up and then step down the voltage.  Allowing us to transmit lower currents at higher voltages which required thinner wires.  And AC didn’t need to return to the power plant.  It was more like a steam locomotive that converted the back and forth motion of the steam engine into rotational power.  AC power plants generated a back and forth current in the wires.  And electrical loads are able to take this back and forth motion and convert it into useful electrical power.

Even though AC power allows us to transmit lower currents we still need to move a lot of these free electrons.  And we do this with massive electric generators.  Where another power source spins these generators.  This generator spins an electric field through another set of windings to induce an electrical current.  Sort of how transformers work.  This electrical current goes out to the switchyard.  And on to our homes.  Simple, really.  The difficult part is creating that rotational motion to spin the generator.  We create about half of our electric power by burning coal to boil water into steam.  This steam expands against the vanes of a steam turbine causing it to spin.  But that’s not the only heat engine we use to make steam.

To Shut Down a Nuclear Reactor takes the Full Insertion of the Control Rods and Continuously Pumping Cooling Water through the Core

We use another part of the atom to generate heat.  Which boils water into steam.  That we use to spin a steam turbine.  The neutron.  Nuclear power plants use uranium for fuel.  It is the heaviest naturally occurring element.  The density of its nucleus determines an element’s weight.  The more protons and neutrons in it the heavier it is.  Without getting into too much physics we basically get heat when we bombard these heavy nuclei with neutrons.  When a nucleus splits apart it throws off a few spare neutrons which can split other nuclei.  And so on.  Creating a nuclear chain reaction.  It’s the actual splitting of these nuclei that generates heat.  And from there it’s just boiling water into steam to spin a steam turbine coupled to a generator.

Continuous atom splitting creates a lot of heat.  So much heat that it can melt down the core.  Which would be a bad thing.  So we move an array of neutron absorbers into and out of the core to control this chain reaction.  So in the core of a nuclear reactor we have uranium fuel pellets loaded into vertical fuel rods.  There are spaces in between these fuel rods for control rods (made out of carbon or boron) to move in and out of the core.  When we fully insert the control rods they will shut down the nuclear chain reaction by absorbing those free neutrons.  However there is a lot of residual heat (i.e., decay heat) that can cause the core to melt if we don’t remove it with continuous cooling water pumped through the core. 

So to shut down a nuclear reactor it takes both the full insertion of the control rods.  And continuously pumping cooling water through the core for days after shutting down the reactor.  Even spent fuel rods have to spend a decade or two in a spent fuel pool.  To dissipate this residual decay heat.  (This residual decay heat caused the trouble at Fukushima in Japan after their earthquake/tsunami.  The reactor survived the earthquake.  But the tsunami submerged the electrical gear that powered the cooling pumps.  Preventing them from cooling the core to remove this residual decay heat.  Leading to the partial core meltdowns.)

Nuclear Power is one of the most Reliable and Cleanest Sources of Power that leaves no Carbon Footprint

There is more than one nuclear reactor design.  But more than half in the U.S. are the Pressurized Water Reactor (PWR) type.  It’s also the kind they had at Three Mile Island.  Which saw America’s worst nuclear accident.  The PWR is the classic nuclear power plant that all people fear.  The tall hyperboloid cooling towers.  And the short cylindrical containment buildings with a dome on top housing the reactor.  The reactor itself is inside a humongous steel pressure vessel.  For pressure is key in a PWR.  The cooling water of the reactor is under very high pressure.  Keeping the water from boiling even though it reaches temperatures as high as 600 degrees Fahrenheit (water boils into steam at 212 degrees Fahrenheit under normal atmospheric pressure).  This is the primary loop.

The superheated water in the primary loop then flows through a heat exchanger.  Where it heats water in another loop of pumped water.  The secondary loop.  The hot water in the primary loop boils the water in the secondary loop into steam.  As it boils the water in the secondary loop it loses some of its own heat.  So it can return to the reactor core to remove more of its heat.  To prevent it from overheating.  The steam in the secondary loop drives the steam turbine.  The steam then flows from the turbine to a condenser and changes back into water.  The cooling water for the condenser is what goes to the cooling tower.  Making those scary looking cooling towers the least dangerous part of the power plant.

The PWR is one of the safest nuclear reactors.  The primary cooling loop is the only loop exposed to radiation.  The problem at Three Mile Island resulted from a stuck pressure relief valve.  That opened to vent high pressure during an event that caused the control rods to drop in and shut down the nuclear chain reaction.  So while they stopped the chain reaction the residual decay heat continued to cook the core.  But there was no feedback from the valve to the control room showing that it was still open after everyone thought it was closed.  So as cooling water entered the core it just boiled away.  Uncovering the core.  And causing part of it to melt.  Other problems with valves and gages did not identify this problem.  As some of the fuel melted it reacted with the steam producing hydrogen gas.  Fearing an explosion they vented some of this radioactive gas into the atmosphere.  But not much.  But it was enough to effectively shut down the U.S. nuclear power industry. 

A pity, really.  For if we had pursued nuclear power these past decades we may have found ways to make it safer.  Neither wind power nor solar power is a practical substitution for fossil-fuel generated electricity.  Yet we pour billions into these industries in hopes that we can advance them to a point when they can be more than a novelty.  But we have turned away from one of the most reliable and cleanest sources of power (when things work properly).  Using neutrons to move electrons.  Taking complete control of the atom to our make our lives better.  And to keep our environment clean.  And cool.  For there is no carbon footprint with nuclear power.

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