Clocks in town mysteriously changing by 10 minutes

  • #26
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geometer said:
If you're connected to the grid, you can't fudge frequency - it will be rock solid at the grid frequency no matter what you try. All you can really affect is the amount of reactive power you generate and its sign (in or out as they say in the utility biz).
That is exactly right. The amount of power out on the grid is so enormous that once you connect to the grid, the grid determines the frequency of your turbine/generator. In order to connect to the grid, you have to make sure that you are synchronized to it meaning that you are at the same speed, that is a really complicated issue which I believe goes farther than just speed. Electric utility companies have what are called "power system supervisors." They continuously watch the flow of power through the grid in their service territory and monitoring frequency is how they do this. If they notice that the frequency is slowing down because of an increase in demand, they will bring more generation "online." That is right though, that the amount of power produced by one plant is so small compared with the amount of power on the grid, that the loss of one plant will not make a huge difference in frequency on the grid. But if you have in the case of the blackout last year, a transmission line drops out, suddenly you have a huge loss of load, the generators have over/under frequency protection which trips a generator offline at 57 or 63 hz, so you will have all these plants tripping offline.
As for being connected to NIST to maintain frequency...I know 60 hz is a standard frequency, so the power system supervisors might use that as a reference point for maintaining grid frequency and use the time signal of WWV for keeping accurate records. Not sure.
Reactive power has to do with the inductance of your loads, and that's all you can compensate for in generation. That is a complicated matter.
 
  • #27
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The exciter adjusts the phase of the generator. The phase is the angular difference between your voltage and your current waveforms. If your load is purely resistive (i.e. no motors or any other form of inductance), you will produce only watts. But when you have huge motors connected to your generator, you start to take your voltage and current out of sync with each other and then you will introduce a power factor and you will also be producing VARS or reactive power. A few posts back it was mentioned that customers pay more for the higher reactive load they have. They can make up for this by setting up capacitor yards to try and cancel out the inductive reactance by using capacitive reactance.
 
  • #28
Averagesupernova
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striker said:
A few posts back it was mentioned that customers pay more for the higher reactive load they have. They can make up for this by setting up capacitor yards to try and cancel out the inductive reactance by using capacitive reactance.
If you are attempting to quote me you are MISquoting. The customer does NOT pay for volt-amperes. They pay for TRUE watts. If the subscribers load becomes excessively reactive the power company may raise the rate until the subscriber agrees to compensate.
 
  • #29
Ivan Seeking
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Industry does pay for VARS.

In our area, IIRC, the customer pays according a sliding scale based on the power factor.
 
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  • #30
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The customer can then reduce the amount they are charged by lowering the amount of reactive power they consume by installing capacitors.
I may be way off; tis a very confusing subject... and VARS is way off from the original point of this thread.
 
  • #31
russ_watters
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Billing is pretty complicated. Commercially, they bill for peak demand (kW), consumption (kWh) and power factor if you are outside of a certain range (.85 maybe...?). There are a host of complexities such as time of use, demand ratcheting (if you set a high peak in August you get charged for part of that in Sept.), price bands for different usages, etc. Its so complicated my dad makes a living by finding billing and rate errors and saving clients money.
 
  • #32
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Averagesupernova said:
I've never worked for the power company but I know a little bit about something called tracebility. Tracebility deals with how an end product or service is tied back to the National Bureau of Standards. Most likely a number of power plants, if not all of them, are tuned into WWV out of Ft. Collins CO in order to obtain a frequency standard. They then use this timebase to measure the frequency of or RPM of the generators. However, it probably doesn't do much good for error correction since if one generator measures a frequency error, all the plant can do is report it to the rest of the grid. I believe they also count the TOTAL number of cycles in a given period of time (possibly a day or more) and actually simultaneously correct for it. Probably over a period of a couple of minutes or something, maybe more I am not sure. This was told to me by an electrical engineer who had power distribution classes in college.
I've been away from this thread for a while, so I apologize if I'm beating a dead horse, but I think it needs to be made clear here that utilities do not regulate their frequency by checking with some central standard. The generators in utility plants are built with so many poles in them and given that number of poles, you can calculate the RPM your turbine has to turn to give you a 60 Hz (or any other frequency) output. The turbines then have governors on them that keep them at that RPM. Once connected to the grid, if your turbine RPM drops a little, you get some complicated feedback from the grid that will drag your turbine back up to the appropriate RPM and frequency.
 

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