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#226727 - 06/26/11 09:09 PM Electrical Grid Creaking at the Wrong Frequency
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3078

A sure sign that the electrical grid is reaching its load capacity, by letting the 60Hz frequency slip. frown

http://www.dailymail.co.uk/news/article-...ting-month.html

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#226730 - 06/26/11 09:50 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Am_Fear_Liath_Mor]
dougwalkabout Offline
Crazy Canuck
Carpal Tunnel

Registered: 02/03/07
Posts: 3219
Loc: Alberta, Canada
I wonder if you've misread the article. Keeping a perfect continent-wide 60 Hz. as a 'timing pulse' is very 1950s. Anything that relies on it now is bad technology. IIRC, it takes large base-load plants to manage frequency corrections. If we want a more flexible grid, with multiple inputs from solar/wind/tidal plus fire-on-demand natural gas plants, allowing a small range of deviation is practical and desirable.

My 2c.

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#226734 - 06/26/11 10:17 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: dougwalkabout]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3078
http://en.wikipedia.org/wiki/Utility_frequency

Quote:
Frequency and load

The primary reason for accurate frequency control is to allow the flow of alternating current power from multiple generators through the network to be controlled. The trend in system frequency is a measure of mismatch between demand and generation, and so is a necessary parameter for load control in interconnected systems.

Frequency of the system will vary as load and generation change. Increasing the mechanical input power to a synchronous generator will not greatly affect the system frequency but will produce more electric power from that unit. During a severe overload caused by tripping or failure of generators or transmission lines the power system frequency will decline, due to an imbalance of load versus generation. Loss of an interconnection, while exporting power (relative to system total generation) will cause system frequency to rise. AGC (automatic generation control) is used to maintain scheduled frequency and interchange power flows. Control systems in power plants detect changes in the network-wide frequency and adjust mechanical power input to generators back to their target frequency. This counteracting usually takes a few tens of seconds due to the large rotating masses involved. Temporary frequency changes are an unavoidable consequence of changing demand. Exceptional or rapidly changing mains frequency is often a sign that an electricity distribution network is operating near its capacity limits, dramatic examples of which can sometimes be observed shortly before major outages.

Frequency protective relays on the power system network sense the decline of frequency and automatically initiate load shedding or tripping of interconnection lines, to preserve the operation of at least part of the network. Small frequency deviations (i.e.- 0.5 Hz on a 50 Hz or 60 Hz network) will result in automatic load shedding or other control actions to restore system frequency.

Smaller power systems, not extensively interconnected with many generators and loads, will not maintain frequency with the same degree of accuracy. Where system frequency is not tightly regulated during heavy load periods, the system operators may allow system frequency to rise during periods of light load, to maintain a daily average frequency of acceptable accuracy.


Wider variations in the grid frequency also affect the grid stability criterion. Allowing a wider frequency tolerance in a grid doesn't only affect devices using the AC frequency as a measurement of time but will allow greater grid instability. Its really just an admission that generator load capacity isn't keep apace with the load demand especially for transient increases in load demand.



Thats why in the UK the huge power station built here at Ben Cruachan was built, to maintain the Grid Frequency.


Edited by Am_Fear_Liath_Mor (06/26/11 10:33 PM)

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#226737 - 06/26/11 10:44 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Am_Fear_Liath_Mor]
dougwalkabout Offline
Crazy Canuck
Carpal Tunnel

Registered: 02/03/07
Posts: 3219
Loc: Alberta, Canada
Hmm, but aren't we talking about a small range of frequency shift that is designed and deliberate? I don't find it credible that professional engineers would even consider a range of deviation that would destabilize the grid. That would be the mother of all career-limiting moves.

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#226739 - 06/26/11 11:07 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: dougwalkabout]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3078
Quote:
I don't find it credible that professional engineers would even consider a range of deviation that would destabilize the grid. That would be the mother of all career-limiting moves.


The bean counter would probably just move into a career in banking once the lights come back on after a few months vacation in the Caribbean. wink

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#226745 - 06/27/11 12:26 AM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Am_Fear_Liath_Mor]
dougwalkabout Offline
Crazy Canuck
Carpal Tunnel

Registered: 02/03/07
Posts: 3219
Loc: Alberta, Canada
Originally Posted By: Am_Fear_Liath_Mor
[quote]The bean counter would probably just move into a career in banking once the lights come back on after a few months vacation in the Caribbean. wink


Dear me, A_F_L_M, don't you have any faith left in humanity at all? grin

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#226758 - 06/27/11 03:20 AM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Am_Fear_Liath_Mor]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
Originally Posted By: Am_Fear_Liath_Mor

A sure sign that the electrical grid is reaching its load capacity, by letting the 60Hz frequency slip. frown


Funny, the article doesn't mention failing power systems, load capacity limits, or allowing frequency excursions (term of art in the power industry) saving power or making it go farther. I think you read far too much into it.

Phase angle/frequency correction is an ongoing, quite time consuming and expensive, housekeeping duty with any power system. Failure to keep the frequency within the previously tight standards saves the cost of constant adjustment but it doesn't make the existing power go any farther.

The down side is that cheap and non-critical devices are the only ones which use the line-power frequency for timing. All the critical systems have timing devices independent of the line power. Typically a quartz crystal. Fact being that their example, a coffeemaker, and cheap clock radios, are pretty much the only pieces of equipment which immediately come to mind as being line frequency based.

In the industrial sector motor RPM is dependent on line frequency but the industrial sector has a lot of experience in handling this. Critical systems, and a whole lot of systems which aren't critical, have shifted to steppers and VFDs in the last twenty years simply because they offer finer process and power control, and higher efficiencies. Every year more motors are shifted from 'dumb', line frequency limited, to variable frequency.

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#226780 - 06/27/11 04:23 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Am_Fear_Liath_Mor]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
Our electrical grid IS from the 1950s, isn't it?

Sue

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#226796 - 06/27/11 10:33 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Susan]
Art_in_FL Offline
Pooh-Bah

Registered: 09/01/07
Posts: 2432
Originally Posted By: Susan
Our electrical grid IS from the 1950s, isn't it?


Little of the electrical generation and distribution system is still around from the 50s. Much of it listed as being from the 50s has been renovated and upgraded, often a bit at a time, over the following 30 years. Some things just don't need to be changed because electricity, and the basics of generation and distribution, haven't changed much since the 20s.

A few years ago I worked on an industrial plant which was wired in the early 30s. Electrically it was still sound and was still humming along without any major electrical issues. That said, it was totally obsolete and inadequate from a safety standpoint. It had bare, exposed buss bars (3P/480v), unenclosed knife switches, substandard space to work, knob and tube branch circuits and few equipment grounds. In some ways it was really easy to troubleshoot because everything was right out in the open and all the switch gear and buss bars ran nice and cool because it was all well ventilated because it was suspended in free air or bolted to a piece of slate.

That system kept chugging along because once you get a system that works, as long as it isn't overloaded or allowed to deteriorate, it will tend to keep working.

The majority of electrical generation and distribution dates back to the 70s. In and of itself this isn't a bad thing. It does mean that these systems don't use the advances made since then. The US, for the most part, doesn't have a 'smart grid' that can automatically compensate for shifting loads, and automatic monitoring, that would link in with a smart grid, is pretty rare but the systems keep working.

The biggest problem is not the dated nature of the system, even as we might benefit from it being modernized. The big problem is that we haven't, as a nation or through the power industry, invested on our electrical infrastructure. The government used to make investments but since the 80s the political dogma is that it is better to allow private industry to take the lead. Unfortunately private industry cannot justify major investments in infrastructure because they can use bottlenecks and unimproved distribution systems as a way to drive up prices and increase profits. These profits far exceed those which might be made selling the use of the infrastructure they might build.

ENRON made its profits, in part, by creating local shortages and bottlenecks, and profiting from the increased 'fair market' price shortages justified. Until ENRON self-destructed, after people asked uncomfortable questions, they were celebrated as market makers and innovators.

We presently have, for the most part, adequate generation capacity. The distribution system is adequate but a lot of it is in the wrong place, and very little of it fully benefits from advances made in the last thirty years.

Some of the variation is regional. In much of the southeast power is smaller scale and run by local or municipal power companies. This avoids much of market perversity seen in larger systems. If power is generated locally, and distributed as a municipal amenity there is no reason to put off updating the system and now easy way to deliver less and profit more.

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#226799 - 06/27/11 11:27 PM Re: Electrical Grid Creaking at the Wrong Frequency [Re: Art_in_FL]
Am_Fear_Liath_Mor Offline
Carpal Tunnel

Registered: 08/03/07
Posts: 3078

Considering the noises made by the authorities regarding the substantial threat due to cybersecurity issues and the so called 'terrorist and cyber-warfare' threats, perhaps someone should point out that computers and communications network infrastructures still rely on the technology from the turn of the 20th century for their successful operation. i.e. The electrical grid power generation and transmission network.

Bootstrapping a black start power transmission network would be a ugly business. As has been seen at Fukushima, a batch of boiling water nuclear reactors melted down because essentially grid power was lost to keep the cooling systems working and the on site backups failed i.e. Battery and Diesel Generators failed.

All it takes for example in the UK is for the the 50Hz Frequency to deviate either way by 1.5 Hz (48.5Hz or 51.5Hz) and the a wide area Blackout in the UK will occur. The frequency changes are due to a mismatch between the capacity of the generation supply and the load.

Relaxing the frequency standards of the power transmission network just makes the chances of an external disturbance i.e. a repeat of the 1858 Carrington event, have a greater probability of knocking the network down (risking complete network blackout requiring black start and critical nuclear accidents) due to its less resilience capacity to external influences.

Its the classic safety versus cost situation once again.

http://www.youtube.com/watch?v=D_8h_twNP_0

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