Power Generation question

quique

Hi guys,

Im reading a document at Academia.edu about Power Systems. Its pretty good but I just ran into a paragraph that confuses me:

Figure 2-10 shows the layout of a typical steam power plant. Notice the steam line used to transfer superheated steam from the boiler to the turbine and then through the condenser where it is returned to a water state and re- cycled. Notice the steam turbine connected to the generator. The turbine speed is controlled by the amount of steam applied in order to control frequency. When load picks up on the electrical system, the turbine shaft speed slows down and more steam is then placed on the turbine blades to maintain frequency.

What confuses me is, when load picks up (im assuming this means when more electricity is demanded by the city), the turbine slows down. Why slow down and not speed up?

I did also read this somewhere else but Im not sure how its related:

changing rotor's speed = changes frequency
increasing coils = increases voltage

Cariboocoot

Re: Power Generation question

quique wrote: »

Hi guys,

Im reading a document at Academia.edu about Power Systems. Its pretty good but I just ran into a paragraph that confuses me:



What confuses me is, when load picks up (im assuming this means when more electricity is demanded by the city), the turbine slows down. Why slow down and not speed up?

I did also read this somewhere else but Im not sure how its related:

?

If you increase the demand on any generator it requires more HP input to maintain speed. Thus the 'load picks up' (increases - badly worded on their part) will slow the turbine down requiring more steam to be applied to increase speed and keep the frequency where it belongs.

Very simply if you need 'X' amount of power electrically you have to supply 'X' amount of power mechanically (plus loss allowance).

BB.

Re: Power Generation question

Does not slow down on because they want it. the turbine slows a tiny bit and they add more stream to bring it back to 60Hz.

-Bill

quique

Re: Power Generation question

Oh ok BB, I get it, it slows down and so they add steam to compensate...

BB.

Re: Power Generation question

With PID controls (Proportional, Integral, Derivative based controller)--They can do things like measure the output current on the generator and "compensate" when there is a step change in current (power) and adjust the steam (water, etc.) based on the instantanious change vs "waiting" for the turbine to slow down a bit.

Of course, a modern power plant is immensely complex--And the monitored/controlled parameters are probably in the dozens or more. And when you are talking about "networked" power plants, they have to respond to the entire "universe" of the power network.

I.e., the turbines are all "synchronized" or "locked" together--With AC, you cannot have a turbine turning at 61 Hz and another running at 59 Hz sharing the same AC connection--"Slipping a cycle" is a big deal for a large power plant. At one point the alternators are "adding" current together (in phase) and at another point they would be 180 degrees out of phase (the out of phase alternator looks like "worse" than a dead short on the network).

So, short term regulation looks more like the "harder" (more torque) you supply, the more current that alternator supplies to the network.

If you want to increase the frequency (from 59.9999 to 60.0001 Hz), the entire network has to "agree" to what frequency the grid needs to operate at and how much power/current each individual alternator needs to "dispatch" to the grid.

Anyway--That is about as deep as I can go (and probably a bit over my head anyway). The math behind the PID controller/control theory is quite interesting and what made "calculus" real for me (as opposed to all of those word problems in grade school).

-Bill

quique

Re: Power Generation question

Wow, you really went out there!

Too heavy for May 1st!

But who doesn't love calculus!? I'd love to know more about the calculus part!

techntrek

Re: Power Generation question

quique wrote: »

But who doesn't love calculus!?

Me. Evil stuff.