Turbine and Generator questions

[IrradiatedPixel]

I'm creating an interactive fiction (where the player has to figure out McGyver-type solutions), part of which is set in a PWR.  I'm trying to build in a certain amount of realism, which is why I signed up here so I could throw my off-the-wall questions to the experts.   I have too many for one post, so I'll go at these one at a time.  btw, I've already gone through nucleartourist.com and the like, so I hopefully won't ask anything too redundant.

Wonky question #1 (not really a nuke question) is set in the turbine hall.  The PWR is in an outage.  The heroine (who can more or less go/do where/whatever she wants) needs to make the turbines spin (I won't even get into why, ).  Getting the reactor running is complex and precluded, so I figured another way, but I don't know if it would really work.  The idea is to throw the generator onto the grid and use the off-site power to turn the generator into a motor.

Upon studying how these things work, my first observation is that it probably won't work, because there is no excitation current for the rotor field coils.  (Am I right?)  I came up with a strange way to possibly solve this.  I understand there is a motor, called a "barring" motor, that is used to rotate the turbines so that they cool down evenly after shutdown.  I figured that by turning this on, you could induce some limited current in the exciter, which would put some current into the field coils.

If all goes exactly right, the small current in the field coils might be enough, with the stator fully juiced, to produce a little torque that might be enough to speed the turbine up a little bit (the barring motor already has it turning very slowly).  Now that the turbine is running a little faster, the exciter will produce more current, which will increase the rotor field, which will in turn produce more torque, and so we have a positive feedback loop which should eventually see the generator turning full speed.

There are a lot of (at least for me) unknowns here, such as whether the initially very small current would be enough to make any impact, and whether the barring motor even can turn the 200 ton turbines at all from a stand-still (huge inertia).

Adventure games usually provide plenty of opportunities to **** up, and I invented one here, too.  If the player throws the generator on the grid before turning it with the barring motor, the following occurrs: Due to the lack of a rotor field, the generator doesn't turn, but instead the field in the stator induces a current in the field coils, much like what would happen in a transformer.  This in turn puts a current into the exciter, but since the exciter can't possibly (I assume) have enough torque to move the turbines, instead, it just burns out, causing a short which in turn heats the field coils, causing a fire in the generator.  Since the generator is hydrogen cooled, this causes the generator to go boom.

While nice and dramatic, I don't know how realistic the latter scenario is.  My guesses alternated between that and perhaps the generator would just start turning, since there's now a current in the rotor field coils.. but it's somewhat beyond my limited engineering knowledge whether the timing, phase, polarity, orientation, etc of this field would be suitable to turn the generator.. somehow I don't think it is.  Or... is there any practicable way the heroine could apply a current to the field coils other than by having the exciter turn?

Another issue is whether she could actually hook up the generator to the grid under shutdown condition, or whether there would be some safety system preventing this.  And if she could do it, where would she have to be to do it?  Would it just be a matter of her throwing a switch in the control room, or is there more to it than that?

Any info or comments would be greatly appreciated.  Naturally, mention in the credits goes to anyone who helps, if they want it.

- Kevin

[M1Ark]

LOL.....

Does this game have to be technically accurate?  If so, my response would be twice as long as your post.  We would bore everyone and is best done offline.  PM Broadzilla, he'll give you all of the technical details you need... he might even like this game once completed as long as you make the heroine look like Alyssa Milano.

[Already Gone]

By 'barring motor", I assume you mean the turning gear motor.  This not only doesn't have enough speed, but it doesn't produce enough mechanical torque to overcome the electrical torque you would create if you juiced up the exciter.
Once you get the generator rolling at speed though, it actually drives the generator which produces the excitation current.
I am not sure exactly how it is done, but large generators, like the ones in a nuke, can be made into motors.  This is the last useful purpose served by the Zion Plant in Illinois.  Its generators are used as motors to create a load on Chicago's very unstable grid.   When the grid is near full capacity, it can be difficult to put more generators onto it.  So, the Zion generators are used as motors to drag down the voltage, thereby allowing the oncoming generators to overcome the reactive load that happens when they are sync-ed.

I'm thinking that your heroine could just shut the main breakers, and the exciter breakers, and this would be a believable scenario for your game.

[shayne]

I too will be real brief...  The first thing that comes to my mind is that most generator breakers will not shut if the generator isn't excited.  Next is a relay race... The reverse power relay would trip the breaker.    Also, the torque it would take to move the generator from a standstill would most likely take out the breaker on overcurrent assuming that the generator has a type of squirrel cage rotor for frequency stability.  (Usually these windings are found on wind turbines.)  Loss of excitation and phase sequence relays would most likely trip also.

[Already Gone]

Yeah, you're going to have to defeat some protective relays.  But a McGuyver type could probably find a way to do that with a few pairs of jumper cables and a coat hanger or two.
Of course the "barring motor", or turning gear, can roll the turbines from a dead stop.  You will need the oil to be flowing.  As long as the bearings are lubricated properly, and the lift oil is running, you can actually move the entire train with a very small motor.  You just can't move it very fast.  It will likely not be enough to generate enough current from the exciter to flash the field.
Synchronization is not a problem, since the generator is now going to be a motor.  There is nothing to sync.

Another thought is that the field current need not come from the exciter.  You could just apply it directly to the rotor through the brushes.  Again, you would need to "hotwire" this from somewhere.  Luckily, there is no shortage of wiring in a nuclear plant.  She could just rip some away from somewhere in the plant and hardwire the brushes from some live circuit.  Likewise, she could hotwire the generator.  Just hook up some live wires to the busses.  You don't need a lot of power to turn the machine.  You don't even need the high voltage.  I'd bet that you could "borrow" the wiring from a large pump motor and have enough power to spin the turbines.

I'll try to ask one of the generator specialists what it will take, but it may be a week or so before I see one.

[IrradiatedPixel]

Thank you for taking an interest in my post.. you guys are awesome!

I'll admit I can't make the game 100% accurate.  I wouldn't have much of a story if I did.  At the same time, I find that throwing in little details can make a big difference in making something more interesting.  The adventure game is a much different (and rare) breed than your usual "shoot-em-ups".  For instance, as the player goes through the plant, they can look at different things they see and get a little explanation of what it is, what it does, etcetera.. not so long as to bore, but a little something to get the mind going.  We usually throw in a little humour, too, while still being informative.  And we make the player think their way through problems, instead of pulling out a gun.

BeerCourt, that's quite interesting that they actually do this in the Zion plant.. I wouldn't have imagined my wacky idea had some practical use outside of my game's plot. 

Having to hotwire the field coils is a good idea, and interestingly, you'd still have to run the turning gear in order to get the oil flowing (hadn't even thought about that).. more steps the player has to go through.. I'm liking it <evil grin>.  I'll be interested to hear what the generator people say if you do get to ask.  No problem about the delay.. I appreciate the help, and I have a million other things to do to get this whole project done anyway, so it's no rush.

I don't recall where I ran across the term "barring motor" but I gather that's not what it's called.  Turning gear it is. 

Another thing that occurred to me, is that in my hypothetical plant, one of the LP turbines has the casing removed in preparation for inspection/repair.  If the heroine gets this thing going full speed, I wonder if that's going to have her hair up in the air and loose articles flying all over the place in the turbine hall! .  (Great.. more stuff to think about.  But it'll be worth it.)

- Kevin

[Roll Tide]

May I suggest an alternate approach for spinning the turbine? It actually spins quite simply with admission of steam. While starting up a reactor is complicated, the system is held in standby conditions with 1005# steam pressure available. You can't power the grid (you are actually a load on the grid with Reactor Coolant Pumps providing the heat source) without the reactor, but you could spin the turbine up to speed; this was done prior to initial fuel load during construction.

Just set your IC (Initial Conditions) as "Hot Standby" for realism. As an opportunity for mucking things up, if you try to carry load you will cool down the plant until there is no steam available.

[Roll Tide]

On second thought, you probably want something spectacular for the boo-boo. Close the generator breaker while out of phase with the grid. YEE-HAW!

[alphadude]

why not use the edg (emergency d. generators) to supply the power to motor.. they are easy to start you just have to find the circuit to feed it with..

typically duing outages links are opened in the switch yard to prevent getting to the grid. you have to back feed through the start up transformer to get juice. 

[Roll Tide]

BTW,
I find Turbine Halls to be rather dreary, but not creepy enough for a dungeon feel. Perhaps you would consider a plant without a Turbine Hall (or Building); Turkey Point does not have a ceiling or walls around the "Turbine Deck". It is also home to half the nesting North American Crocodiles (though they don't come into the plant without permission!)

[Already Gone]

It's actually the reverse, you have to have oil flow to start the turning gear, or any other rotation, or else you'll destroy the bearings and the thing won't turn - or at least won't turn very well.

[Fermi2]

You'd need:

Oil Pumps
Stator Water Pumps
Hydrogen Seal Pumps
About 70% of the generator output voltage available (this is about standard for motors

You probably wouldn't need to jumper out any relays, most likely you could lift a lead in the breaker trip circuitry.

You wouldn't be able to generate enough voltaage from the field to do anything with it.


AND Hey I SAW the post about Alyssa Milano!! Todd and Bubba are messed up.

Mike

[shayne]

Considering that there is Maintenance going on the turbine generator, this complicates the scenerio.  Now you  have to consider the Lockout/Tagout requirements on systems such as the generator breaker disconnects, generator grounding disconnects (or similiar devices), exciter (field breaker, field flash, PT Fuses, excitation transformer, etc.), turning gear, lube oil & jacking oil, cooling water or cooling systems.

I would think that shorting out the rotor field at the sliprings would be an easy way to make an wound rotor induction motor vice exciting the rotor field to make a synchronous motor.  (I'm assuming that this large power generator probably doesn't have much of a squirrel cage rotor design.)

[IrradiatedPixel]

Roll Tide: That's an interesting idea, to run the turbines from standby steam.  Actually, adventure games often have multiple solutions available.  The only problem is, I suspect it can't be in hot standby, because the RX head has to be off for unrelated reasons.  Also, the casing is off of one of the LP turbines, so the steam would be lost from that one's moisture separator.  I assume it's possible to close off the input to one of the separators, though.  (That would be part of the puzzle.)

alphadude: Thanks for the tip about the switchyard.. yet another little detail I hadn't realized.   Actually, there is another unrelated puzzle involving the EDGs (there's more or less a puzzle for each major plant area).  I know the EDGs have to be fairly powerful to be able to run coolant pumps etc., but the whole turbine rig is an awfully big load.  Maybe Deneisha should go out and reconnect the grid.. gives me an excuse to get the switchyard involved.  Yay, more stuff for me to have to figure out, .

I stumbled upon NRC IN 84-76, and apparently breakers have two knife switches if you go in the "breaker cubicle" (let's see if I can find a pic of one), one of which can interrupt the breaker control circuit.  So, it shouldn't be too hard to prevent any sort of trip.. she just has to know what trips to prevent.   (I know, I know, she's awfully smart, .)

Shayne: Initially I didn't know enough about motors, but I did some reading last night.  I like the idea of shorting the slip rings to make a wound induction motor.. probably not the most efficient arrangement, but Deneisha's not too worried about efficiency.

And thanks for the tip about lockout/tagout.  I'm thinking there might be a lock on the turbine stop valve.  I know firsthand that picking a lock is surprisingly easy if not Abloy or Medeco (had to rescue my clothes from my building's laundry room one night - an internet search and a few pieces of metal later, and I had my clothes, ).  Deneisha has to pick a lock earlier in the game (prior to the power plant), so she's got the tools handy already.  I'm not sure if the breakers on the generator would be locked, too.  The generator isn't taken apart, but maybe they'd lock it on the logic that the grid could conceivably turn the turbine.

One issue is just how much it'd take to move the whole turbine rig.  I know the exciter wouldn't stand a chance.. the idea behind hotwiring it was only to get a field set up in the generator, not to turn the exciter.  It's a question of whether the generator could move the whole thing.  As BeerCourt pointed out, they do turn the generator from the grid at Zion.  But I gather this might be with most of the weight of the turbines removed.  The inertia would be a monster, but maybe the turning gear motor could help defeat that.

Here's a rendering of my LP turbine rotor.  I still have to dirty it up a bit, of course:

[Fermi2]

Knife switches are only used in load shedding or differential circuits. Usually they aren't used on reverse power circuits. You'd have to pull the relay, pull fuses, or lift leads.

EDGs don't run Coolant Pumps. I can't think of an EDG in the country that would have the capability of running a coolant pump in a large reactor.

Mike

[shayne]

.... You'd have to pull the relay, pull fuses, or lift leads.

or short CT's.

The Breakers may even have two trip coils off different power supplies for redundancy as well as a primary and backup protection relaying.  You may also have to consider that if the generator or grid protection asks for a trip and the breaker doesn't open, the system may be set up to trip the next breaker/(s) on the grid (Breaker and a half type setup).  This could complicate your scenerio if that or those breakers are offsite and miles away.

[Fermi2]

JUst about all SWitchyard Breakers have redundant DC Trip Coils. I can't think of any schematics I've seen that don't have them.

As for other breakers in the system tripping to isolate the generator, that wouldn't happen on a reverse power, reverse power technically isn't a fault, it's there to prevent the generator from a large inrush AND in case of turbines it's there to prevent the last stage LP Blades from overheating due to windage in event of a loss of vacuum trip with failure of the output breaker to open. In fact at Fermi they relied on the reverse power trip. My curent plant has a 30 second timer, after a turbine trip the output breakers will open 30 seconds later.

Fermi reverse powered for too long at least twice when I was there. The first time it did so for 12 minutes post reactor trip, an Operator noticed it then opened the output breaker. This was why the output breaker step was placed in the first few steps of the Reactor Scram procedure.

The other time was the infamous single phase open which ended up damaging the generator. I was on the root cause teams for both incidents which is why I know more than I care to about generator relaying and reverse powering!

Mike

[Roll Tide]

Nice LP turbine blading!

Perhaps the opposite unit (I am used to multiple unit sites) could supply steam via some obscure cross-connect piping? Or you could get really creative and use the auxiliary boiler (aka donkey boiler) to provide the steam. I am not saying you could put it on the grid, but you could get significant rpm.....

[Roll Tide]

BTW, don't get too carried away when you dirty up the blading; it basically looks like it is a rusty color in an operating unit.

[alphadude]

edg's run small pumps to provide cool down and power critical circuits-- but its a souce of power and dont take a lot to get them started. (designed that way for a reason)

[IrradiatedPixel]

Thanks to everyone's very helpful tips, I've come up with some preliminary flow charts of the logic for this scenario:

http://www.fantaplay.com/postpics/turbine-1.pdf
http://www.fantaplay.com/postpics/turbine-2.pdf

Let me know if these seem reasonable.   (I know box (21) might be a bit outlandish..)

Flow starts at (1) when player turns on/off generator breaker, (38) when they turn on the turning gear motor, or (44) when they open or close the connection to the grid in the switchyard.  I left out flows that have no immediate results.  The "Return" bubbles mean the puzzle isn't yet solved, but the player can take additional actions.

Nice LP turbine blading!

Thanks   I'll keep in mind not to make them too dirty.  In computer graphics, we usually add a bit of surface imperfections.  Otherwise, it has a sterile, fake look to it.  Fortunately, I have plenty of pictures to use as a guideline for how surfaces in an NPP should look.

Perhaps the opposite unit (I am used to multiple unit sites) could supply steam via some obscure cross-connect piping? Or you could get really creative and use the auxiliary boiler (aka donkey boiler) to provide the steam...

Using steam off the other unit is an interesting idea.  I don't know yet if there will be a second unit - that depends on how I end up modelling the plant (see other thread).  Since one of the turbines has the shell (for lack of the correct term) removed, Deneisha would have to make sure steam can't get to that one.  I assume there are valves to bypass a single LP turbine?

Donkey boiler.. now there's one my research hadn't uncovered at all!   Where might one find it, and how's it fired?  I might make this an alternative solution.  Not that I need to know for the game scenario, but I'm curious as to whether the aux boiler can provide enough power for the house loads (to effect a blackstart).

edg's run small pumps to provide cool down and power critical circuits-- but its a souce of power and dont take a lot to get them started. (designed that way for a reason)

Using an EDG could be another alternate solution, but that depends on whether it's reasonable to say it would have enough juice to move the turbines.  It's also involved in another puzzle, so whether I can use it for this one also depends on how the big picture develops.

-Kevin

[Fermi2]

There ain't no EDG in service at a nuke in the WORLD that has enough arse to backfeed a main unit transformer and turn a turbine. It'll go out on over curent LONG before the turbine turns.

Mike

[IrradiatedPixel]

There ain't no EDG in service at a nuke in the WORLD that has enough arse to backfeed a main unit transformer and turn a turbine. It'll go out on over curent LONG before the turbine turns.

I had a feeling that would be the case.. if they can't run the main coolant pumps, how can they move a 200+ ton turbine?  My guess is the diesel engine itself wouldn't have nearly the HP even hooked up mechanically, unless through a lot of gearing, and would then only turn slowly.  (But I'm no expert.)

I'm thinking the idea was to use it for the field excitation, which seems more reasonable... but you'd still need grid power.  And then you might have synchronization issues.  Just shorting the field coils to make an induction motor would probably be the simplest approach.  I'm just trying to twist their brains a bit, not make them give up, . 

[Fermi2]

I had a feeling that would be the case.. if they can't run the main coolant pumps, how can they move a 200+ ton turbine?  My guess is the diesel engine itself wouldn't have nearly the HP even hooked up mechanically, unless through a lot of gearing, and would then only turn slowly.  (But I'm no expert.)

I'm thinking the idea was to use it for the field excitation, which seems more reasonable... but you'd still need grid power.  And then you might have synchronization issues.  Just shorting the field coils to make an induction motor would probably be the simplest approach.  I'm just trying to twist their brains a bit, not make them give up, . 

It doesn't matter if it's excited. Because without steam excitation doesn't matter.

Mike

[IrradiatedPixel]

It doesn't matter if it's excited. Because without steam excitation doesn't matter.

Hm.  You mentioned situations you've seen where the generator was "reverse powered".. does that mean the turbine kept turning, using power off the grid, after the steam supply was removed?  (I realize keeping the turbines spinning and making them start spinning are two different things...)

-Kevin