# Question about balance of el. energy production and consumption

1. Jul 2, 2006

### Micko

Hello to all,
I have one question and hope you'll help me to answer it.
Recently I have visited one power plant. There I learned basics of el. energy production and also fact that in every moment production = consumption because el. energy cannot be conserved.
I also learn that by allowing more steam to turbine, more power of turbine and generator will be. So basicaly operator control valves and flow of steam to turbine so he controls power. However I know that in one simple circuit power is determined by consumer, if if reciver needs more current for same voltage, there will be more power. So basically my question is how is possible to control how much power is producted with just allowing more or less steam to turbine when real need is determined by consumer. Whr if more steam is sent to turbine that will enable more power on turbine, but system (consumers) does not need more power?
I hope there are some guys here who will know to answer my question.
Thanks

2. Jul 5, 2006

### Staff: Mentor

I'm not entirely sure of the details, but I'd expect that the variations in voltage on the AC mains are due to differences in the production and consumption of energy. As the local demand for power rises, the AC mains voltage will drop some until the production plant sees that droop in voltage and increases its power output.

But given the long transmission lines and multiple production sources, I honestly don't know how they manage the feedback function. Anybody know? Interesting question.

3. Jul 5, 2006

### Ramvich

Hello all, this is my first post and I should tell you I am not an engineer. I have been working in the electrical industry for 20+ years. I have studied electrical theory and do a great deal with local power generation.

Micko's question:
So basically my question is how is possible to control how much power is producted with just allowing more or less steam to turbine when real need is determined by consumer. Whr if more steam is sent to turbine that will enable more power on turbine, but system (consumers) does not need more power?

You give it enough steam to keep the turbine and generator turning at a constant speed. AC Generators need to turn at a predetermined speed to maintain the 60Hz that the US system runs at. The RPM of the generator and number of poles determines the frequency of the power produced. A six pole generator need to turn at 30 RPS or 1800 RPM to create 3 phase AC at 60Hz. The demand is determined by the consumer. Lets say the demanded load is .25MW, and the generator has a 1MW rating. It will take only enough steam to overcome the drag put on the generator to generate the wattage required by the consumer. If that load increases the drag on the generator will increase and the generator will slow down and the frequency will change. If you provide more steam to the generator until which point it gets back up to the proper speed to maintain the correct frequency. Electromotive force travels at near the speed of light the so long transmissions lines are more a mental obstacle then a physical one. The millisecond demand goes up the voltage drops across the system and more drag is introduced to every generating station on that grid. So in short you monitor the speed of the generator and apply enough steam or whatever energy source your using to maintain that speed. Hopes this answers your question.

Berkeman's Question:
But given the long transmission lines and multiple production sources, I honestly don't know how they manage the feedback function. Anybody know? Interesting question.

Electromotive force travels at near the speed of light the so long transmissions lines are more a mental obstacle then a physical one. The millisecond demand goes up the voltage drops across the system and more drag is introduced to every generating station on that grid. A generator never produces more power than is consumed. If the demand is low it will just require less "steam".

4. Jul 5, 2006

### Averagesupernova

I think Berkemans question concerns voltage loss at the far end of a line that changes with the load. The generating plant cannot compensate for that because the close to the generator end of the line will then be overvoltaged. The answer is:
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Voltage regulators. I'm not sure how they work, but I believe they are a mechanical device. A substation likely has several voltage regulators for the different lines that branch off of it. It most likely is magnetic and moves a wiper across an autotransformer. I'm not sure. I do recall calling the power company to report a line voltage of only 100 volts one time. The power company came and measured it at the transformer and then left. A few minutes later the line voltage went up to nominal and a few minutes after that the workers returned to meause the voltage. When I asked them what the trouble was the reply was: "A stuck regulator."

5. Jul 6, 2006

### WFO

The voltage at the generator is controlled by the excitation winding. As noted, the steam resources respond to speed, which is affected by the current draw in the line from the load. If the voltage drops, the feild of the excitation winding is increased to maintain voltage.

A voltage regulator is a multitapped autotransformer with a reversing switch. Typically they have 16 steps in each direction (i.e., raise or lower the voltage) in 5/8% increments for a total raise or lower capability of 10% either way. The voltage is sensed and, when it is out of tolerance, a motor operates to change the taps to a higher or lower step as necessary.