Did current weirdness make BGE meters run fast?

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BryanMD

BryanMD

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Maryland "the land of pleasant living"
Local business writer is perplexed by a spike in recent electric bills. A reader of his has a theory: grid frequency fluctuation.


"Something happened and I suspect it might be technical in nature. As an engineer with a degree in electronics and electrical technology, I suspect that perhaps the electrical characteristics of the alternating current supplied our homes was abnormal, causing meters to spin faster than normal."

"The frequency of alternating current should be 60 cycles per second, or 60 Hertz. What if the power generating stations were erroneously making electricity at 65, 70, or 75 Hertz? Just as the frequency of the alternating current will affect the speed of a motor, it will affect the speed of electric meters."

"There should be records of the alternating current frequency from the monitoring equipment at the power plants made available to the PSC for review."

So... this is way over my head. What say you guys?
 
Bryan

On a small electrical grid, one machine is usually operated in Isochronous Speed Control mode, and any other (usually smaller) generators which are connected to the grid are operated in Droop Speed Control mode. If two prime movers operating in Isochronous Speed Control mode are connected to the same electrical grid, they will usually "fight" to control the frequency, and wild oscillations of the grid frequency usually result. Only one machine can have its governor operating in Isochronous Speed Control mode for stable grid frequency control when multiple units are being operated in parallel. (There are Isochronous Load Sharing schemes in use in various places around the world, but they aren't very common.)

On very large electrical grids--commonly referred to as "infinite" electrical grids--there is no single machine operating in Isochronous Speed Control Mode which is capable of controlling the grid frequency; all the prime movers are being operated in Droop Speed Control mode. But there are so many of them and the electrical grid is so large that no single unit can cause the grid frequency to increase or decrease by more than a few hundredths of a percent as it is loaded or unloaded.

Very large electrical grids require system operators to quickly respond to changes in load in order to control grid frequency properly since there is no Isochronous machine doing so. Usually, when things are operating normally, changes in load can be anticipated and additional generation can be added or subtracted in order to maintain tight frequency control.
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Got that from the following link if you need a more complete discussion.
http://www.control.com/1026221805/index_html
 
The US electrical grid is so interconnected that is is all but impossible for the grid frequency to fluctuate by more than tenths of a frequency. If you ever saw 70Hz, the reading would immediately be followed by 0Hz as the grid shuts down causing a multi-state power outage.
 
BryanMD said:
Local business writer is perplexed by a spike in recent electric bills. A reader of his has a theory: grid frequency fluctuation.


"Something happened and I suspect it might be technical in nature. As an engineer with a degree in electronics and electrical technology, I suspect that perhaps the electrical characteristics of the alternating current supplied our homes was abnormal, causing meters to spin faster than normal."

"The frequency of alternating current should be 60 cycles per second, or 60 Hertz. What if the power generating stations were erroneously making electricity at 65, 70, or 75 Hertz? Just as the frequency of the alternating current will affect the speed of a motor, it will affect the speed of electric meters."

"There should be records of the alternating current frequency from the monitoring equipment at the power plants made available to the PSC for review."

So... this is way over my head. What say you guys?
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NERC Regulates the grid to 60Hz +/- 5%, so the highest you could see is 63Hz. But local regulations are more restrictive and the most you typically see is 60.1 Hz for sustained periods. Over/Under frequesncy relays would prevent any large distortion as Jim said.
 
Just think of all the electric clocks that would run fast!
Most devices that use large amounts of electricity for heating or lighting are rather frequency insensitive.
 
A major hamburger chain noticed their employees were leaving early(10-15 minutes) but all their time cards and punch clock said they had worked the 8 hours.Electrical Equipment interference(voltage zero crossings) within the chain were speeding up all the time clocks.:)
 
Aside from all that, if I'm not mistaken a kWH meter speed is based on power, not frequency. In other words, it is not directly frequency dependent. If a higher frequency was applied everything with a coil would have overheated and died. It would be the same as having a bunch of European appliances designed for 50Hz plugged in to 60Hz in the US. Faster motors, hotter transformers etc. There would have been a LOT more negative affects than just a higher bill.
 
Additionally customers on the grid with equipment sensitive to frequency would be screaming. Such as UPS users and the area you are talking about is loaded with UPS systems NSA for one.
 
Speedskater said:
Just think of all the electric clocks that would run fast!
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I have been told that each grid interconnect has a master clock that tracks the cumulative effects of the grid frequency. If they have been running below 60 Hz and the clock gets behind, they will run over 60 Hz to bring the clock back into sync with real time. Over time a clock based on the grid frequency is very accurate.
 
don_resqcapt19 said:
I have been told that each grid interconnect has a master clock that tracks the cumulative effects of the grid frequency. If they have been running below 60 Hz and the clock gets behind, they will run over 60 Hz to bring the clock back into sync with real time. Over time a clock based on the grid frequency is very accurate.
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Even small grids watch this. One place I worked, the city had 36MW, we had 27MW with a 5MW tie between us - no connedction to any other grid. We ran mostly with the tie closed drawing our 5MW.

We had two clocks on the wall, one set to WWV, the other a high grade 120VAC plugged into the wall. We were rarely off more than 30 seconds. Interestingly, the frequency is rarely 60hz dead on. One is either behind, running fast, and creeping up on the time - or ahead and ... As don said, over time, the total cycles is very accurate.

cf
 
Power generating plant is damaged during under or over frequency excursions, so it will go offline at the drop of a frequency excursioning hat.

Where I live in New Zealand we have one of the hardest requirements in the world for generators. We are a 50Hz country with a requirement that frequncy must be in the bounds of 49.75 to 50.25 Hz, but if it all goes wrong, plant is required to remain online down to 47Hz. 3Hz is a massive excursion, and a tough specification for generators to achieve.
 
090217-1623 EST

Put an accurate frequency meter on line and monitor frequency. Add filtering to keep noise from the meter if necessary. In the following I just switched in the built in low pass filter.

Here are 6 consecuctive 10 second averages from the present time:
16665.4 MS = 60.005 Hz
16663.9 MS = 60.010 Hz
16661.8 MS = 60.018 Hz
16660.1 MS = 60.024 Hz
16660.9 MS = 60.021 HZ
16661.2 MS = 60.020 HZ
a number of minuters later
16669.2 MS = 59.991 Hz

These measurements are based on time interval because it takes too long to get high accuracy by counting cycles.

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