Turbine and Generator questions

[Already Gone]

I think that some of us are losing perspective here.
All IP wants to do is spin the turbine-generator set.  Assuming that the normal method (steam) is unavailable, several of us have suggested converting the generator into a motor.  Yes, excitation is necessary for this, with or without steam, because there is no permanent magnetism in the rotor.  The field must be generated by electrical current running through the windings in the rotor.  Once you have a magnetic field in the rotor, current through the stator bars will produce motion.
It does NOT take huge amounts of power to rotate this machine.  It is carrying absolutely no load.  As long as you have lift oil and lubricating oil to the bearings, you can spin the whole thing with very little force.  A few hundred kW will probably have the thing running with no problem.  The speed is determined by the number of poles in the generator and the frequency on the grid.
Reverse-powering a generator is commonly done.  Most of the larger gas turbines are started this way.  They take power off the grid to turn the generator until the turbine is fired up and then the process is reversed.  The difference is that nukes are not wired for this.  McGuyver-ing the wiring can easily overcome this defect.  As long as you have high enough voltage, and the field is flashed, you will have a motor.

[Fermi2]

It doesn't take anything from the excitation system. It merely takes a power source of sufficient voltage and current capacity to do it. I've seen a reverse power of catastrophic results.

For a large nuke generator it takes about 25MW Minimum off your grid in order to turn it via the generator.

That isn't an insignificant amount of power at all. Also consider at lower speeds it'll be drawing HUGE amounts of current.

Mike

[shayne]

The rotor would need some type of excitation to operate as a synchronous motor.  The other option is to short the field windings to make an induction motor. 

Most motors have a starting current of 6 to 10 times of normal current.  I would imagine this generator would have a starting current much larger than that.  Although there isn't really any load on the mechanical side, you would have to consider the system lineup, vacuum breakers open/closed, steam stops open/closed.  There will be more load on the turbine with no vacuum in the condenser. With this friction, how long until they heat up enough to cause rubbing on the casing?

[Already Gone]

Startup current for a motor with no load on it is not nearly that high.  To overcome the inertia of a 1300 MW turbine generator at rest, you need a motor about one quarter the size of the turning gear motor.  It can be done with an air-powered motor that is small enough to hold in your hands.
This brings me to another suggestion.
The heroine in this game could put a strap around the turbine shaft and a pulley attached to an electric motor.  This can spin the turbine.  The speed would depend on the ratio of the shaft size to the pulley on the motor.
This will not sustain enough torque to put any kind of electric load on either the generator or the exciter.  But the objective, as I understand it, is to spin the machine - not to generate power.
Still another scenario:  She puts the back tire of her Harley Davidson Fat Boy on the shaft and clamps the front wheel in place.  Fire up that baby and wind it out real good.  You won't even see the buckets.
 

[HydroDave63]

it would be helpful to know if she is trying to turn the thing slowly for whatever reason, or trying to move it at synchronous speed.
The power needed depends on that tidbit of data.

[IrradiatedPixel]

it would be helpful to know if she is trying to turn the thing slowly for whatever reason, or trying to move it at synchronous speed.

I was hoping I wouldn't have to say, ..   She needs it fast enough that a gun-wielding villain pushed towards the open blading might find their gun flung somewhere out of reach, and with a nasty injury to boot.  So I imagine we're talking a fair bit of power.  I know you could turn the thing with a hand crank if you had enough gears, but it's speed wouldn't subdue an ant. 

If it loses a lot of speed in the course of doing it's deed, she won't be too worried (although I should consider for animation purposes whether it would).

-Kevin

[Roll Tide]

Definitely a use for a "donkey boiler" with a jury-rigged steam flowpath.
Go from the 200# donkey boiler with 50,000 lbm/hr steam capacity backwards from aux steam (use the bypass valve) to main steam. Use the turbine throttle valve to admit steam to get it rolling, and use poetic justice for the cool effects of steam billowing up around the open LP turbine (the supply would be isolated, but the steam at very low pressure would flow back up from the condenser)
I think it would look good!

Some sites have onsite donkey boilers, others have them trucked in if needed.
http://www.wareinc.com/
I am not endorsing this company, but they do have pictures of their rental boilers.

[IrradiatedPixel]

Roll Tide, thank you for the donkey boiler suggestion, and the link.. that site will definitely be useful for figuring out the graphics.  And the steam coming up will be good for dramatic effect.

I'm wondering where the feedwater comes from for the aux boiler.  If from a tank, this would put a limit on how long it'll run, unless it's fed back from the main condenser.  Which also makes me wonder if you'd have to start condensate pumps, and also the circulating water to the condenser.   And as my handy-dandy PSAR here tells me, starting the CW pumps also depends on waterbox level, seal water minimum flow, and bearing lube.  Looks like my heroine might have a bit of running around to do.

Would we get a condenser loss of vacuum trip due to the one LP turbine that is open?

[Roll Tide]

I was speculating that you would not be able to have any condenser vacuum with the turbine open; McGyverette would have to go to bypass on that trip.

Circ Water is filled with a vacuum system (either vacuum pumps or ejectors) then started. The CW pumps are typically not in the turbine building / hall / deck; lot's of running around!

The donkey boiler is fed from the demin water system, or could be from a condensate connection.

[IrradiatedPixel]

Ideally, Deneisha should get the CW started so there can be a continuous supply of feedwater to the aux boiler.  However, more than likely the player will not figure on this the first time around, which leads to the question of how long you could expect this thing to run on stored condensate/makeup before the water dries up and the boiler shuts off from low water level...

[Roll Tide]

With a full DWST (or CST or whatever they call the thing at other plants), you should have enough water for at least a week on a donkey boiler.