Reference, Questions and Help > Nuke Q&A
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, lol). 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.
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