Power frequency in USA (60 Hz)

Status
Not open for further replies.
M

mtnelectrical

Senior Member
Location
Essex, New Jersey
Is there are porcentage allow for POCO to the 60 HZ? I have a fire alarm installer complaining that he is getting this value changing from 40 to 110. Have you ever seen this before? Thanks for all your inputs in advance.
 
There is a tolerance on the power line frequency, but it is measured in milliHz. If you have a true measurement of 59.9 Hz, there is something major going wrong with the grid.

Variation of 40 to 110 indicates some other problem, such as an intermittent connection with arcing, power from a very bad local source, etc.

A _very_ common issue is that frequency is often detected by looking at the zero crossing of the AC wave rather than looking at the entire wave. A tiny amount of high frequency noise can cause extra zero crossings that confuse the frequency measurement. This sort of noise can cause power line referenced clocks to run fast, for example.

-Jon
 
mtnelectrical said:
Is there are porcentage allow for POCO to the 60 HZ? I have a fire alarm installer complaining that he is getting this value changing from 40 to 110. Have you ever seen this before? Thanks for all your inputs in advance.
Click to expand...
Where is he seeing that? Meter in switchgear? Meter in fire panel? Hand held Meter? I can't see that being correct at all. POCO controls hz.
They have a plus, minus range but it's a much smaller window that that.
I have seen generators "hunt" for the correct hz but that was usually because it had a UPS with very little load on it and the generator didn't like it at all....
 
winnie said:
There is a tolerance on the power line frequency, but it is measured in milliHz. If you have a true measurement of 59.9 Hz, there is something major going wrong with the grid.

Variation of 40 to 110 indicates some other problem, such as an intermittent connection with arcing, power from a very bad local source, etc.

-Jon
Click to expand...

Or maybe it it is intended to be used as DC rather than 40-110 Hz ??
 
qcroanoke said:
Surely as a fire alarm installer he knows that most all fire panels operate on DC? And is not trying to read HZ at the DC output.
Click to expand...
I would hope so, although if he's reading the ripple on the DC side I could see the 110, but not the 40. I'm inclined to think that winnie has the right idea.
 
gadfly56 said:
I would hope so, although if he's reading the ripple on the DC side I could see the 110, but not the 40. I'm inclined to think that winnie has the right idea.
Click to expand...
One would think that ripple would be a multiple of 60 hz. It could be that the peak to peak voltage of the ripple is not high enough to trigger the counting circuit on whatever meter he is using.
 
Adding to what Winnie said, the Pacific Northwest National Lab used to have a program that would display the real-time frequency at their test site; while it wandered a bit, the freq was never more maybe than 0.01 Hz away from 60.0.

(Part of the Texas grid almost-collapse a few years ago was that the load was so high it actually pulled the freq down by a couple of Hz. Some reports said that if it dropped below 57(?) Hz, power plants would start dropping offline and that would collapse the grid.)
 
In Europe they log the grid's moment to moment frequency. They can put a time-stamp on a digital audio recording.
But I'm sure that it's a lot more complicated than that.
 
zbang said:
Adding to what Winnie said, the Pacific Northwest National Lab used to have a program that would display the real-time frequency at their test site; while it wandered a bit, the freq was never more maybe than 0.01 Hz away from 60.0.

(Part of the Texas grid almost-collapse a few years ago was that the load was so high it actually pulled the freq down by a couple of Hz. Some reports said that if it dropped below 57(?) Hz, power plants would start dropping offline and that would collapse the grid.)
Click to expand...
I had that as a screen saver for a long time, but a few years ago, it stopped working.
 
In addition to regulating the instantaneous frequency within tight tolerances, the utility can also keep track of the total number of cycles over time and deliberately compensate for under-frequency time by raising the frequency long enough to ensure long term clock synchronization.
 
There is a probably apochryphal story about RCA pitching an early TV broadcast system to the Italian government.
The receivers would synchronize to the sync pulses in the transmitted signal, as long as it was within the design range.
But the transmitting equipment used line frequency as a readily available standard that did not require a precision oscillator.
When they set the demo system up for the government big wigs, the picture was rolling uncontrollably because the line frequency was out of the tolerance band of the receivers.
The engineer responsible for the demo thought quickly, grabbed a spare receiver system and took it to the city power plant and set it up in the control room.
"We are demonstrating this to the politicians, but we also want you to see it because of your importance to the city."
"Why is the picture rolling like that?"
"Oh, that. Just adjust this control until the rolling stops."
:)
 
230116-1757 EST

Just looked at my frequency.

In frequency mode I can only measure to 0.1 Hz and this requires 10 second averaging. Results 60.0 to 60.2 Hz at the present.

In time mode and 1 second averaging I was generally around 0.16669 mS, with most within +/- 0.00010 of the mean, but some jump out to 0.16673 and 0.16498 .

So 60.00 +/- 0.06 Hz was typical using 1 second averaging.

.
 
Thanks guys for those replies. I went there to check this weird reading. I just took my multimeter (Klein Tools CL 700) to measure this at the main entrance panel. It's a small building; office space at first floor and 2 apartments in 2nd and 3rd; 200 amps one phase service. I read 60.00 Hz for 10 seconds or so then changed to 59.99 for 20 seconds or so, then back to 60.00 Hz. I went to the box on the first floor feeding the fire panel with 120 volts and I read the same. Fire tech was there with his tester so we used his to measure again and we saw the hertz starting at 60.00 but then after a second started to change from 40 to 140, up and down . Conslusion: He needs a new meter. Sorry guys, but thank you, because your comments always teach some new points to some of us.
He had some code errors in this Honeywell addressable panel and thought that it was a power problem. He still has the codes but must be something else.
 
GoldDigger said:
In addition to regulating the instantaneous frequency within tight tolerances, the utility can also keep track of the total number of cycles over time and deliberately compensate for under-frequency time by raising the frequency long enough to ensure long term clock synchronization.
Click to expand...
IIRC, and that's asking a lot, in 1973-78, Duke Power (now Duke Energy) in its Charlotte system control center had 2 digital (others too, just these weren't analog only like many) showing present frequency and accumulated time error. Casual changes were ordered when time got outside the +/- 1 second range, more active measures when outside the +/- 2 second error.

Historical records were kept on those round paper charts. I don't think I've seen one in over 25 hears?
 
230117-1500 EST

Over the last day monitoring my frequency at random times using frequency measurement, and a 10 second averaging time ( 0.1 Hz resolution ), the frequency mostly reads 60.0 Hz with a very few fluctuations of +/- 0.1 Hz. And greater variations much less.

10, 20, or 30 years ago I saw much greater deviations. I don't check line frequency very often. Power interruptions cause much more timing variation of line synced clocks than does line frequency.

.
 
230119-1521 EST

Early this morning, about 4 AM, I looked at frequency using frequency mode for a short time. My 10 second average readings varied from 59.9 to 60.3 Hz. A little wider variation than earlier. Most readings were 60 Hz. Just now frequency is more stable. I am reading mostly 60.0 Hz with a few excursions to 59.9 Hz.

Why in the middle of the night did I see a slightly wide variation? I did not look at voltage during these measurements.

We have one of the world's most powerful lasers in town. I have no idea how much load this puts on the electrical system when the capacitors are being charged. Some time in the past I have commented on this laser. Its peak power output is huge. I don't remember its value, but it gets compared to the average power consumption in the world.

.
 
Status
Not open for further replies.
Top