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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The Army is looking to use Unreliable Renewable Energy to provide Reliable Energy Security on their Installations

Posted by PITHOCRATES - August 12th, 2012

Week in Review

The Army Corps of Engineers is following orders and going green.  Putting their installations at greater risk of electric power interruptions.  Even though the reason to go green was the complete opposite.  To minimize power interruptions.  As well as to lower costs (see Army’s Logic for Developing Wind and Solar Energy Makes No Sense by Daniel Kish posted 8/10/2012 on U.S. News & World Report).

The Army Corps of Engineers recently put out a request for proposal for renewable energy developers to build energy facilities on Army bases. The Army says building renewables such as wind and solar on Army bases will promote “energy security,” however this claim fails to acknowledge the inherent problem of reliability with intermittent sources of energy like wind and solar…

It is important to remember that under our system of civilian control of the military, political appointees direct the branches of the military to carry out administration policy, and the military salutes and carries out the orders. It would appear that politicians working to promote renewables is the reason the Army is making this move, because its proposal would essentially accomplish the opposite of what it says it intends to do…

The mission of the military is to kill people and break things.  And to deter others from killing Americans and breaking American things.  Two assets that have been very good at meeting these objects in the military’s arsenal are the B-52 bomber and the nuclear-powered sub.

Have you ever seen a B-52 take off?  A whole wing of B-52s in a Minimum Interval Take-Off (MITO)?  Their engines leave behind a thick black fossil-fuel-made cloud.  Yeah, that’s right.  Air pollution.  And those subs?  They use nuclear power because it lets those subs stay under water forever. The only thing that brings them up is the fuel the sailors need.  Food.  The B-52 pollutes.  And the nuclear sub uses the fuel the Left hates over all other fuels.  Radioactive fuel.  So given the choice the military will pollute and risk The China Syndrome in their subs.  Why?  Because the B-52 and the nuclear sub are the best assets for the mission.  And they will keep using them until their civilian commanders order them not to.  Just like they have ordered these Army installations NOT to use the best power source available but one that matches the current administration’s green agenda.  Unreliable renewable energy.  To help fight global warming.  A battle outside the mission of the military.  And will only weaken the military in their ability to fulfill their mission.

Wind or solar would make power production on military bases more secure if disruptions to the grid only happened when the wind was blowing or the sun was shining, and that will obviously not be the case…

Despite the fact that wind and solar are not reliable sources of energy, the Army’s request for proposal explicitly calls for proposals for wind and solar (see pages 6, 7 among others). Hammack’s [Assistant Secretary for Installations, Energy, and the Environment] argument that producing wind and solar on Army bases with increased “energy security” does not hold water, since the obvious alternatives, coal, and natural gas, are abundant in the United States: The United States has over 450 years of coal at the current rate of consumption, for example…

The Army also claims that the purpose of the renewable energy projects is to shield Army bases from electricity price hikes. But like the energy security argument, the Army’s assertion that its proposal will save money is rooted in fallacy. One of the reasons electricity prices are rising is because of regulations imposed by the Obama administration, and the Army could simply ask Congress to waive them for the military if high prices were the only issue at hand.

If you’re worried about cost you can make the electricity a coal-fired power plants produce less expensive by ending their war on coal.  But they won’t do that.  So it’s not about cost.  Besides, wind and solar power are some of the most expensive sources of power out there.  Yes, the fuel is free (wind and sunshine), but the infrastructure to capture it and use it is vast.  And costly.  Because each unit that captures these fuels is small.  So you need a lot of them to equal a fraction of what a coal-fired power plant can produce.

Electricity powers a hospital.  Without it their emergency rooms and intensive care units would go dark.  And people would die.  Because it is so crucial they have redundancies.  They will have a row of primary switchgear (4,800 volts or higher) fed by two different feeders going back to two different substations.  There will be an equal number of circuit breakers on each side separated by an open ‘tie breaker’ in the middle.  They will evenly (approximately) split the electrical load of the hospital on either side of the tie breaker.  Dividing the load evenly across the two primary feeds.  However, if one feed goes down (tree falls on wire, substation explodes, etc.) the breaker going to the down line will open and the tie breaker will close.  Putting the entire hospital on the one good primary feed.  It can do this because they size both primary feeds large enough to carry the full load of the hospital.

But redundancy doesn’t end there.  If an electrical event is great enough to take out both primary feeds the hospital will have backup generator power available as well.  Powered in most cases by on-site diesel fuel.  Some may use natural gas but they have to prove the reliability of their gas service.  As the last line of defense in a power outage, they want backup generator power self-contained and independent of all other municipal power sources.

This is redundancy.  And wind and solar simply do not provide this.  They are unreliable.  And they cannot carry the full electrical load of a hospital.  Or other large consumers of electricity.  At most these supplement baseload power.  They can’t replace it.  If these installations want true energy security, true power redundancy, they would be better off installing a diesel-powered turbine with onsite diesel storage for when their electric grid goes down.  Or a natural gas-powered turbine with a reliable (not connected to the local gas supply but a high pressure main) and secured gas feed to the base.  In other words, if they want true energy security they’d better be willing to pollute the air like a wing of B-52s taking off in a MITO exercise.  Because if you want true energy security you are going to have to pollute.


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