Hameedulla-Ekhlas
Senior Member
- Location
- AFG
Frequency:
I remember I had studied frequency limitation to 3%. Is it right?
I remember I had studied frequency limitation to 3%. Is it right?
frequency limitation
- Thread starter Hameedulla-Ekhlas
- Start date
- Status
In UK and probably EUland supply frequency tolerance is +/-1%.
- Location
- Illinois
- Occupation
- retired electrician
That sounds like a lot of deviation if you are talking about the utility supply. I seem to recall that the US grid operating system works with a normal deviation of +/1 0.05hz.
It is permitted deviation. Actual operating deviation is usually much less.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It seems grid inter-tie metering would be affected by such variations.
Why so?
Care to expand?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Because, from what I grasp, the grid-tied utilities buy and sell power based on metering the power flow, and vary this by adjusting the prime-mover torque, which seems would vary the relative frequency slightly.
In other words, they buy power by reducing their generation mechanical torque, letting their generators lag the grid slightly, and sell it by increasing the torque, causing their generators to lead the grid slightly.
mivey
Senior Member
You can lead the grid every hour and still buy power. It depends on what the sum of your loads is doing. Most utilities do not have all their customers and generators located all in one isolated box. This was the case years ago, but now all of the grids are tied together.
You meter the output from the generators and you meter all of the load meter points. Your buys & sells are the net of those two.
Suppose you had all the generating capacity needed to serve your loads. In any given hour, you try to estimate what your load will be for the next hour. You schedule the generation accordingly. The amount you miss the actual load will determine your buys & sells.
If you had a little excess generation and no one was there to use it, the transmission grid had a higher voltage in that hour. If someone else needed that exact amount because they scheduled too little, the grid voltage stayed the same and the other guy buys your excess. If everybody over-scheduled (say a storm took out a section of the grid), somebody is going to have to back a unit down or the voltage on the grid will get too high.
The guys in the control area already have procedures in place to tell who's units will come on or off if things don't go according to plan. they also have procedures in place to tell who gets cut off if there is not enough generation to go around to maintain system voltage.
It is a lot more complicated than that but that is a simple way to look at it.
I think it's lag and lead in terms for phase rather than frequency.
You can change the power factor of a grid tied alternator (or synchronous motor for that matter) by adjusting the excitation.
Synchronous motors were used, maybe still are, for power factor correction. Hence the term synchronous condenser.
skeshesh
Senior Member
- Location
- Los Angeles, Ca
Great discussion. Does anyone have experience with/knowledge about taking into account alternative energy being tied in at different points in case of distributed power generation? Would this just affect the overall scheme of lead/lag of the phase and result in the same system or are there more subtle differences?
mivey
Senior Member
One little distributed generation source is not going to change the system frequency. It is just pumping energy into the grid.
I skimmed an article a while back about a frequency/time adjustment on the grid but it was a coordinated effort. I'm sorry but I was not real interested at the time and don't recall the details. If anyone feels like Googling it, post a link.
skeshesh
Senior Member
- Location
- Los Angeles, Ca
I'll try digging it and posting in. I wasn't really speaking about one source but a large number spread throughout say a county, but I guess the result would be the same since the effect would be widespread and inconsistent.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
The short answer is that on a grid some regulatory power decides on the grid frequency tolerance, and it varies a lot by where you are.
The USA and the UK are really tight in their tolerances. Here in New Zealand (a 50Hz country) power stations are required to stay on the grid at 48Hz. This is because New Zealand is a small population, small load, physically quite big country, that is very thin for its height. So we have a fairly weak grid.
If one was to suggest that a UK or USA station stay on the grid with the frequency that far out one would be laughed at.
The USA and the UK are really tight in their tolerances. Here in New Zealand (a 50Hz country) power stations are required to stay on the grid at 48Hz. This is because New Zealand is a small population, small load, physically quite big country, that is very thin for its height. So we have a fairly weak grid.
If one was to suggest that a UK or USA station stay on the grid with the frequency that far out one would be laughed at.
rcwilson
Senior Member
- Location
- Redmond, WA
A few years ago I met with the Chief Protection Engineer for WAPDA in Pakistan to discuss our new power plant. (WAPDA is the Water and Power Authority, the government utility for all of Pakistan). He was responsible for keeping the country on line.
Taped to his office wall at eye level behind his desk was a little digital frequency meter plugged into the wall outlet. I was distracted during our discussions by watching the numbers float down to 49 Hz and up to 51.2 Hz as load and generation changed. My turbines were supposed to stay on line through all of that. Later, during plant testing we actually did ride through some <48 Hz excursions that slapped the equipment around pretty hard. Nothing broke, yet.
In US & Europe we are lucky to have a resonably solid frequency.
Taped to his office wall at eye level behind his desk was a little digital frequency meter plugged into the wall outlet. I was distracted during our discussions by watching the numbers float down to 49 Hz and up to 51.2 Hz as load and generation changed. My turbines were supposed to stay on line through all of that. Later, during plant testing we actually did ride through some <48 Hz excursions that slapped the equipment around pretty hard. Nothing broke, yet.
In US & Europe we are lucky to have a resonably solid frequency.
Great explanation. A lot to learn here. Do you know where I can find information to read up on this?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I was trying for slightly simpler.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Agreed. Otherwise, there'd be no synchronization.
mivey
Senior Member
There has to be some web info on power system operations. I have a decent library, but I'll see if I can hunt up some online resources.
- Status