US Power Mains Frequency

[Reloadron]

This story off the AP ran yesterday in my local paper.

I don't see the sky falling.

Ron

 

[ben7]

Seems like the change in frequency won't be much though.

So how much money are they going to save by wasting money on this just to change the frequency by a teensy bit?

Sounds like the US government is doing it again...

-Ben

 

[Reloadron]

I really don't see it as an issue either. I have no clue either how much the cost is on a national basis of doing the corrections to the grid(s). Apparently a few interviewed in the article saw it as a problem? Beats the hell out of me.

Ron

 

[KeepItSimpleStupid]

14 seconds per day?

I hate articles like that. There is no explanation as to why.

 

[tcmtech]

I don't see how keeping track of the frequency slip is all that hard either.

If a simple high accuracy clock is ran against the mains frequency its easy to do a simple comparison of when the peak of each cycle should happen and from that just count how many cycles the mains frequency shifts forward or backward in any given time from where the ideal cycle timing point should be happening.

The uC guys here could easily design a mains cycle counter and clock reference device for very little. If they used the NIST or GPS time clock systems as a regular timing reference point I don't see why a simple uC device wouldn't be able to keep track of the timing shift of any period of time.

 

[Reloadron]

I was always aware the frequency was very accurate and time to time have monitored it just out of curiosity using lab counters synced to GPS. I was also aware that periodic corrections were made but not aware of how often, where or how exactly it was done. No idea either what the cost factor is in maintaining the grid with those corrections. I have read over the years a few articles on the subject and that is about it. While at some point years ago there was a need for accurate line frequency I doubt the line frequency really needs to be that accurate today. I can't think of many things that rely on line frequency being very, very accurate.

I wasn't even aware of a plan to change things till this article popped up one day in the local paper. I did find some of the comments between the US Naval Observatory and NIST to be what I thought foolish from my perspective.

Ron

 

[ericgibbs]

hi Ron,
There was a documentary on UK , TV about the history and development of the National Grid.

The way they try to maintain a constant 50Hz is amazing.

If the frequency drops a fraction, due to increased demand at the end of a popular TV show, [viewers switching on their electric kettles] they bring on line water storage generators within a few seconds.

This is all to keep my bedside clock accurate!
I must send them a note and tell I dont use the alarm any more as I am retired, so they can ease back a little on the frequency control.!
Eric

 

[aljamri]

Somtimes, I feel at night that my cyling fan is running faster (little bu noticable) than what i set it. When asked, sombody told me that it is related with this article subject.

 

[Nigel Goodwin]

Somtimes, I feel at night that my cyling fan is running faster (little bu noticable) than what i set it. When asked, sombody told me that it is related with this article subject.

It was always said that corrections are applied during the night, the water storage generators are probably to maintain voltage (during sudden demand) more than frequency. I remember seeing film of control rooms decades ago, with two big analogue clocks (one for real time, one from the electricity supply), and they speeded up (or slowed down) the generators until the clocks were back in sync.

 

[Reloadron]

Somtimes, I feel at night that my cyling fan is running faster (little bu noticable) than what i set it. When asked, sombody told me that it is related with this article subject.

Here in the US you would never see it. When I have looked at power line frequency what I typically see is 59.99 to 60.01 Hz. We are looking at hundredths of a Hz. Even synchronous AC motors that rely on frequency for their speed aren't really effected by these small fractional parts of a single cycle.

Anyway, in a few more years I'll be more like Eric. I won't really care what time it is or to quote Chicago "Does anyone really care what time it is". or .... Eric " Good enough is Perfect "

I guess what it comes down to is today how important (within reason) what the line frequency is as say compared to a few decades ago? That becomes the question, just how important is line frequency? Again within reason and what would be an acceptable error from what it is now?

Ron

 

[Birdman Adam]

Interesting!

Don't think it will be a problem for many though.

Only induction motors will be affected (in terms of speed), and only a tiny bit, as they rely on frequency.

I will check in with my DMM more often and see if I can notice the rise/falling of the frequency.

 

[nsaspook]

I think part of the problem is the control loops for frequency stabilization in most base-load generation plants are very damped and slow to react to rapid load variations and that's a good thing normally with massive power 'on one shaft'. My understanding is a very small changes in frequency against the grid is the method used with massive generators to increase torque and power delivered to the grid. So there is always a slight bias to run fast with unstable loads to keep the system synced on positive side. So it's the increasing percentage of unstable RE power that's causing the problem. I would think for inverter produced power from solar and wind it would be fairly easy to control the slight variations but with a large amount (above a few percent?) of Induction generator wind turbines needing to mechanically synchronize rapidly to the grid by frequency shifting several times a day or even per hour, that could create a fast bias unless corrected. Our local grid operators have been shutting down wind energy to stabilize the system here under low demand.
https://www.oregonlive.com/business/index.ssf/2011/06/wind_farm_owners_ask_federal_a.html

Grid Control:
https://www.electro-tech-online.com/custompdfs/2011/06/brozura_07_1009.pdf

 

[JimB]

I think that the problem is not so much the instantaneous frequency, which will be 60hz +/- a very small error, but the average frequency which must be 60hz exactly (in the USA) over a long period.

The problem comes from devices which use mains frequency for timing, such as many clocks.
When the average frequency is not 60hz, the clock will lose/gain.

Many clocks are controlled by a quartz crystal but only the best have accuracy appoaching that of the mains (in the UK at least, and I guess the USA as well).
Also many clocks take time from the various radio time code transmitters around the world.
However there must be many clock which still rely on good old mains frequency, and there lies the possible problem. These will drift if the average frequency is not maintained at 60 hz.

JimB

 

[Nigel Goodwin]

I think that the problem is not so much the instantaneous frequency, which will be 60hz +/- a very small error, but the average frequency which must be 60hz exactly (in the USA) over a long period.

Correct, there's nothing done about short time variations (there's no need or point), and certainly in the past corrections were done late at night to make sure all mains syncronous clocks were corrected.

 

[aljamri]

Sorry Reloadron if I diverted your thread, but I think here is the place for a question that I've long time in my mined, since your thread directed the attention of most ETO experts .

What is the constructional difference between the same two electrical equipment, one with 50 Hz and the other is 60 Hz.
and can I use the 50Hz device on a 60Hz mains and vice versa ?

 

[JimB]

What is the constructional difference between the same two electrical equipment, one with 50 Hz and the other is 60 Hz.

60hz equipment such as transformers and motors can be built smaller and lighter than their 50hz counterparts.
Because the frequency is higher, the same inductance can be made with less iron in the core, hence smaller and lighter.

and can I use the 50Hz device on a 60Hz mains and vice versa ?

Yes, but be aware of a few traps, a 60 hz transformer running on 50hz will run a bit hotter due to the higher magnetising current in the windings (less iron, lower inductance).

Induction motors motors will run at different speeds.
An induction motor which runs at 1450RPM (just under the synchronous speed of 1500rpm) on 50 hz will run at about 1750RPM (just under the synchronous speed of 1800RPM) on 60hz.

JimB

 

[Reloadron]

Sorry Reloadron if I diverted your thread, but I think here is the place for a question that I've long time in my mined, since your thread directed the attention of most ETO experts .

What is the constructional difference between the same two electrical equipment, one with 50 Hz and the other is 60 Hz.
and can I use the 50Hz device on a 60Hz mains and vice versa ?

No problem at all as it is just an open thread dealing with AC Mains Frequency.

Anymore most power type transformers are marketed as 50/60 Hz. Here is a basic example of what I am talking about. The merit here is that large transformer manufacturing companies (like in the link) can easily market their product globally using a single product. For example if the transformers in the link were 50 Hz. only or 60 Hz. only they would be manufacturing two each for each version. Seldom will you find a basic power transformer labeled 50 or 60 Hz. only.

Devices that use SMPS (Switch Mode Power Supplies) such as home computers really don't care if the mains frequency is 50 or 60 Hz. making them pretty universal devices.

Many years ago I spent 3 years living in Italy with 220 volt 50 Hz. mains (when the power grid actually worked )When I arrived I got a good deal on a US specification refrigerator. Designed for 120 VAC 60 Hz. operation. All I used was a big step down transformer to reduce the voltage. While I am sure the compressor motor was not happy running slower and hotter that unit worked fine for me over 3 years of service. Motors designed specifically for 60 Hz. do not like running at lower frequencies and tend to get hot.

Today it is not unusual to find motors (Synchronous AC Motors) that will run fine on 50 or 60 Hz. The difference being the shaft rotational speed. As Jim B points out.

The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation: RPM = 2 * F * 60/p where RPM = (Synchronous) Revolutions per minute F = AC power frequency p = Number of poles, usually an even number but always a multiple of the number of phases.

The above quote taken from here. Additionally this link shows how the nameplate data is derived between a motor unloaded or loaded. Check out the chart.

So in conclusion, the majority of appliances marketed today will run on either 50 or 60 Hz current without a problem. They are designed that way.

All of this with a focus n home appliances and not aircraft power systems which can be another can of worms. Most aircraft power systems (AC) are 400 Hz. for exactly the reasons Jim B mentioned as to size and weight.

Ron

 

[Menticol]

Awesome post, thank you Ron

 

[MrAl]

Hi there,


First we should get the numbers straight. Depending on the location, clocks can be off my as much as 85 minutes per year, not 20 minutes. Already they understate the side effects and we havent even gotten to the test yet. That means about 7 minutes per month for some people here on the East coast. Most people would have to reset their clocks every 2 weeks i would think. That means throwing out the clock and getting a new one that doesnt rely on the line frequency.

That's not nice at all, but the real question is how much better will the grid be once the line frequency is allowed to change within a larger error margin, and just what is this newer error margin going to be. We dont seem to be given enough information to make a good judgment call here. It does take power to keep the frequency in step, but we really have to know just what the limits are and how much this 'change' would make the grid better.

The other question is even worse to think about:
Given the freedom to change the grid frequency to within a larger error margin today, how much will they want to change it tomorrow? They will find cost benefits from changing the frequency here and there and complain that they really should be able to do this and then we're stuck with that even worse tolerance next.

I dont care as much about the clocks as that is just a side effect and most people can afford to buy a new 10 dollar clock if they need to, but i do worry about the future of the grid once they are allowed this new found freedom to screw up our electric supply. The rule of thumb is that given the freedom, they tend to do what is better for *them* than what is better for *us* (the consumers).

Another possible problem could be with traffic lights.

 

[Reloadron]

Thank you MrAl for an outstanding post that provides several things to think about. I admit I have no clue how many people are using clocks that rely on mains frequency. We use small battery powered alarm clocks at the bedside here. More interesting and what I can't find, is the numbers. Like what they will consider a "new" allowable deviation. I also like the political perspective which is quite true. I hear my father's words as they echo in my head "Ronald, I give you an inch and you take a mile". While initially I was sort of unsure, maybe this really needs more attention. You really made some good points.

Ron