Physics of Power Generation

Answers:

	Picture taken 5/13/2007. You might find it interesting to hear that all of the gauges in a power station are standardized to a five-amp AC signal. In class I described how a voltmeter worked, indicating that in order to determine voltage across a region, one can take a sensitive ammeter (which works something like a compass) and place a high-resistance resistor in front of it. In this way, the tiny current that flows can be used alongside V=IR to map deflection on the ammeter to a voltage drop. The device you see here is designed so that if 1600 amps AC flow through the center of the loop, 5 amps AC will flow thorugh output nodes on ring. Question 1: How must the wires in the ring be wound? (Hint! Remember that the current of 1600 amps is AC. That is, it changes direction periodically. The AC in your wall changes direction and returns to its original state 60 times per second, or 60 Hz.) It seems odd, however, that in order to make this ring leech less power from the circuit that the designers wouldn't put a resistor in and lower the amperage coming out of the nodes on the ring. Question 2: Why haven't the designers included a resistor? (Hint! Consider the microscopic properties of a conductor).
Pictures taken 5/13/2007. Here you see the inside of the turbine housing, part of the turbine's final stage, then down into the coolers where the exhausted steam is condensed back into water and recycled into the generator. Note the wear on the metal due to the high-speed exhaust steam, which is surprisingly kept below atmospheric pressure for ease of boiling!
Pictures taken 5/13/2007. Here are the workers preparing the electromagnet from the center of the generator. By running a very large DC current through it, they produce a magnet of extreme power, more powerful than any permanent magnet could be. Question 3: Which way will the magnetic moment, e.g., the axis along with north-south lies, point? (Hint! Take a look at the windings and use the right-hand rule.)
Pictures taken 5/13/2007. Check out the size of the tools they use when they're working on this behemonth! The plant is constantly upgrading old parts; the picture on the right shows one of the new redundant Pentium plant control systems.
	Pictures taken 5/13/2007. This is the generator itself. The electromagnet you saw in the previous set of pictures is slid inside of this and rotated in order to produce an alternating current. The power produced is not the simple type of AC that comes out of your wall, but is rather a three-phase current, thus the name "Three-Phase Generator". Question 4: Based on your answer to question 3, which way must the windings on this generator go? (Hint! Consider the arrangement that would result in the largest change in flux in the windings per unit time.) Question 5: That center gray tube is made of very thin, lacquered plates of metal with holes periodically cut in it. What is the purpose of this construction?
	Pictures taken 5/13/2007. How creative--the conductors are hollow and full of water used to cool the system. Question 6: This is a very difficult question, and not one that we cover in this class. Does the fact that the conductors are hollow affect the resistance as seen by the AC current very much? (Hint: Have you ever heard of the "skin effect"?)
Pictures taken 5/13/2007. This is the water cooling system where river water is pumped into an array of pipes for the expended steam coming off of the turbine to condense on.
Pictures taken 5/13/2007. The furnace itself is enormous! The left picture gives an idea of just how much energy 300,000 homes consumes--this room is filled with a raging inferno of up to 400 tons of coal dust per hour (see the pictures from the last tour) 24 hours a day when the plant is in operation, on both sides of the center curtain and extending seven stories upward. The right picture is half the length of the furnace, with the equipment giving some idea of scale.
	Pictures taken 2/21/2006. These electrostatic precipitators are used to electronically remove fly ash from the exhaust. In essence, giant capacitor plates are charged up and then the exhaust gas is blown by it. The exhaust then is polarized and sticks to the capacitor plates, where hammers in these little tubes periodically hit them and knock the ash to collectors. Question 7: Why is some current observed to flow even though a capacitor is being charged with no closed connection in the circuit? If voltage was ramped up, would current increase? Why or why not? (Hint: What does it mean to be an ohmic conductor?)

Answer to Question 1: Considering the magnetic field of a long straight wire with time-varying current, I see that the loops should be perpendicular to the circular magnetic field of the wire to catch the maximum flux. Answer to Question 2: Remember that the resistance of resistors may change with temperature. The area of the surface defined by these coils encased in bakelite, however, will be the same at a much larger range of temperature for a much more stable reading. Answer to Question 3: By the right-hand rule, I have: Answer to Question 4: Since the north and south poles of the electromagnet are perpendicular to the axis of rotation, then the coils should be placed with their normal perpendicular to the axis of rotation, Answer to Question 5: Besides being shaped to enhance hydrogen flow for optimum cooling (the generator is under a hydrogen atmosphere), it is important that this tube does not produce a loops suitable for eddy currents to form in response to the rapidly changing magnetic field. In other words, its metal should not allow an amperian path to be drawn in its body with a large, changing magnetic flux. Answer to Question 6: The "skin effect", whereby AC currents tend to be confined to the surface of their conductor, ensures that hollowing out the conductor does not affect the resistance as seen by the AC current substantially. Answer to Question 7: The fly ash has a tendency to ionize and then get pushed over to the other plate, then de-ionize and such causing a "current" to flow between the plates! However, with the flow of fly ash held constant, increasing voltage will lead to a greater depletion of fly ash "charge carrier", and so the current will level out at the electric field times the number of fly ash particles entering the apparatus per second (the units work!). When I was there, typical amperages on the display looked to be about 1-2 amps.