Is power cut explained in simple term possible?

[Bbird]

I am not an electrical engineer but have worked in power industry all the time. Power cuts are fact of life and we have them all the time, except in recent years they seem to spread to a much wider area.

Without prejudging the outcome of the investigation into the American black out 14 August 2003 there seems to be ample evidence of poor management of the grid system by the owners, competition between regional and national regulatory agencies without a workable protection scheme in place and a antiquated transmission system.

The 28 August 2003 power cut to London was reported due to a part failure of a transmission grid. There were suggestions that the severe disruption to the London Underground could be linked to the company abandoning its own power gerating stations and in favour of relying solely on the national grid.

The 23 Sepytember 2003 black out in Danmark and especial at the capital was initaited by transmission line linked to Sweden.

The 28 September 2003 black out to the whole nation of Italy was blamed on the failure of the transmission line from Switzerland. Italy apparently imports up to 17% of its power from outside. If something goes wrong in the border transmission line the exporters cut the loss and keep the power for their own countries leaving the importer to suffer.

The above cases seem to suggest that individual power providers no longer have a reasonable spare of power output and have to depend on the interconnected system. The over-reliance of the "system" led to its partial failure and the wide spread power cut.

Is it no longer possibe to arrange for localised failures? Even for Italy surely it is possible to arrange the nation to have electricity at the expense by shutting down some areas in a pre-prgrammed manner. They are doing it anyway after the big black out when the power shortage became a reality. So this cannot be a technical but a political (regulatory) problem.

Can power cut be explained in simple term as above possible?

 

[rsherry]

This is an interesting post - the following info might be useful for the debate... apologies if this is all old hat to everyone..
Transmission networks (at least in Europe and the USA) are designed to survive specific permanent faults. For most faults the network can be recovered without losing any load - in a way the blackout 'problem' may lie in this security.
There are backup automatic protection schemes that will attempt to localise the effects of major faults or loss of import (load shedding schemes) and save as much of the network as possible. These schemes are designed to cater for huge outages or faults outside the designed security and can be effective (e.g. the 1987 hurrciane in the English Channel which did not black out the whole of England or France). Load shedding schemes are usually triggered by low frequency and/or low voltage on the grid - but by the time these systems respond they can be too late to halt the sort of cascade failure of generators that occurred in New York. In theory there is no reason why a network cannot shed load to match the loss of generation without a total shutdown but in practice the level of network disturbance that is being experienced during a major fault and the cascade tripping of generation can overtake these protective schemes.
This means (as the original post implies I think) that the design of these backup protection systems has been allowed to 'slip' by the Transmission companies.. and has not kept pace with the way the networks are now operated. The schemes are crude and haven't changed much over the years so this charge may be valid...

 

[allmend]

„...the design of these backup protection systems has been allowed to 'slip' by the Transmission companies...“

Hi rsherry,

I think that the transmission companies just do not have enough money to keep pace with the development of the market.

 

[lengould]

Are transmission operating company incentives still the same now as they were in "the good old days" before this type of massive blackout? Seems from what i'm hearing, there is an enormous, almost unreasoned, unwillingness to trip inter-regional ties under any circumastances in the North American system. Load shedding required that bad a PR move?

 

[pablo02]

I can't speak to the Italian scenario, but here in the States, there are a couple of underlying situations that have, in my opinion, laid the groundwork for what happened in the East (not to say that these were the causes -- just that these issues would eventually contribute to what happened sooner or later)

a) there has been no significant investment in the transmission system in over 10 years (although our load growth has continued onward and upward) -- this is a result of who's going to pay for it? the rate payers? the stockholders? and what return will it provide? the introduction of competition has resulted in the Rate Commissions not willing to have the rate payers carry this burden especially since FERC has mandated that the transmission lines are open to whoever needs them and the stockholders aren't going to see any return since RTO's and IPO's now want to control the lines... so, until there is a mandate of how these will be financed and the investors can see a rate of return, there will continue to be a reluctance to build, exacerbating our existing problem...

b) electricity has a natural thing of following the path of least resistance even though the marketers have purchased transmission rights along a specific path... now the regional dispatcher looks at his load flows and tells ABC utility to reduce load on a given line -- so how does he accomplish that? he cuts his own sales and cuts his own customers -- yeah, right -- you see more and more utilities disregard those instructions (they're not mandatory yet) so they can keep their revenue stream going... [ah, the great advantages of the marketing world controlling our utility reliability...] so, there are sections of the transmission system that are overloaded due to the massive flows of electricity through them -- and the utility is playing risk games to keep a purchase deal made somewhere else from reducing their own income....

I think we shall see more of what happened unless things change soon...

 

[Bbird]

I agree with Pablo02 that we are going to see the situation getting worse better it gets better.

I believe one of the by-products of the de-regulation/privatisation of the power industry is that nobody is now big enough or responsible to look after the stability of the transmission grid as a whole. Every power company or distributor has to look after its own interest. The consumer pays only the units he consumed and who cares how badly it is delivered. The power companies and distributors play the game as well because all they could be blamed for is the loss of their own systems and nobody can be fully responsible for the collpase of the common transmission system, especially it is in another country. It can be even conceived that the power companies are knowledgeable enough and have succeeded in ensuring a failure if occurs is out of the portion of their own faults, by leaning on each other like a set of dominos. I bet there is little in term of compensation anybody can claim from the whole saga, even though billions have been lost economically. Anyway if individual company does not look after the short term interest by maintaining the revenue stream and positive cash flow it may go under in no time at all. So long term investment and capital work programmes are bad news that no investor would want to hear.

Something radical has to happen before these big black outs can be stopped. I wouldn't be surprised that owners of the transmission lines are heavily fined in future and the consumers bear the increased cost.

 

[tomatge]

I agree that this is a thought provoking post.

I work in the electricity supply industry for a utility on a small island (peak demand 70MW). We have local generating plant, plus a cable link connection to Europe. We have similar problems to the symptoms described above in that failure of the interconnector results in severe inbalance between remaining generation and customer demand - fail to respond and the island suffers a blackout.

We have developed an automatic load shedding system that trips sectors of load in such an event. Actually, the system was developed before the interconnector, to shed in response to trips of on-island generation, but the basic principle is the same.

The system relies upon reciept of a trip mark from the interconnector or generator, then calculating the quantity of load to shed the restore balance between supply and demand. It then selectively trips blocks of load accordingly. It also has back up underfrequency shedding, but in reality the first method takes care of almost all trips.

The system works very well, but due to the size of our system we are better placed to do this sort of thing that most. We are able to load shed from only four sites, which are close together. It is simple to provide data communications between sites of adequate speed to respond fast enough. Most importantly, we are the only generator and distributor - therefore there are not difficult commercial issues with which bits get tripped, or what plant initiated the trip.

The only downside in that a single system effectively has "life or death" control over the total power network. Should that system malfunction, as happen recently due to a programming error, then its "lights out" for all ...

 

[johnd43]

I am outside the power industry, but reading the news recently I have noted a couple of interesting points:

Italy seems to import all its power (ie no domestic capacity worth mentioning) If it works most of the time, then transmission must be good.

London imports all its power (ie NO domestic capacity at all)..ergo, transmission must be good. It is good enough for us to get quite a lot of our power from France.

The same could probably be said about the other event-areas described by Bbird.

By contrast, in the 1940's, London was under aerial seige but the lights (broadly speaking) stayed on. Then there were apparently about 300 power generation sites in the Greater London area.

In the interests of efficiency and the competive market place we seem to have eliminated "redundancy" to such an extent that we have barely enough capacity on line to meet the average need. When there is an area fault, there is not the capacity online elsewhere to take up the load. How can this be when, in UK, we have experienced the 1980's "dash for gas" in which everybody who was anybody built gas fired power stations? Now they are all mothballed because owners can't afford to sell the power for less than the cost of generation.

Is this the golden age of the Global Market?

 

[rodar]

As a previous post said there is insuffecient reserve capacity in both transmission and gerneration. Utilities at one time only used 90% or so of their maximum. The remaining was a cushion to absorb load shed by other segments tripping out. Now these electric comanies are for profit and they would like to utilize 100% capacity to make share holders happy. When the lights go out they loose some sales but its worth it.

The solution is penalty for power outages that are not natural disater related, but equipment related, leavied on utilities that increase with the number and duration of customers inconvienenced being made progressively stiffer over a period of ten years.

This makes unreliable grid a profit problem for utilities.
We will all pay a little more in our electric bills but
the necessary upkeep of the utility infrastructure is worth
it.
what think?
rodar

 

[Bbird]

johnd43,

Just to correct a few points to prevent misunderstanding.

Italy, according to media reports, imports up to 17% power. Their Industry Minister wants to build 12,000MW, representing 1/4 of national current output, new power generation capacity. Thus Italy national domestic output is about 48,000MW. In UK our national total output is about 55,000MW.

I don't know the exact details of how London draws its power from but the people being asked to investigate confirmed the collapsed sector was supplied by two feeders and one of them went down prior to the back out (also reported in magazine). I mentioned the underground problem because that was the unacceptable face of the black out to the Mayor of London. I just wonder if London Underground could be better off if they had kept their own power stations.

My motive of writing the thread is to see the elimination of "redundancy" in the electricity system of your theory could be a major root cause of our problem today. In the past the Central Electricity Generating Board (CEGB) was responsible for the whole system in UK and we could look to them for having spinning reserve in the generation and spare capacity in the transmission lines. I just don't see anybody now in UK is shouldered with the same degree of obligation of looking after the security of electricity supply. American's regional and national agencies are not much better either.

Consumer pays for only he or her consumes. Generator does not generate unless he is paid. Transmission company do not have the money to invest for the future and will flog the horse until it is stone dead. Government cannot afford to cut back revenue, hand out subsidies or pass the burden through higher tax.

Tomatge also highlights an important point here when arranging load shedding. With one big national authority the cutting back of electricity can be carried out with little resistance. Now the system is common and used by a large number of small companies having an equal right to the system. Who can be chopped off when the supply cannot match the demand?

The accountants have convinced the politicians that the privatisation/global market can bring down the electricity price in the short term but the people have not been told that the service is not the same quality as before.

In an era where everything is driven by economics and there is no mechanism or incentive to improve the overall electricity supply materially nothing will be done until the pain level has reached the unbearable limit for the majority. It is just funny to watch the politicians saying the situation is unacceptable but they could not pin anybody down to improve it.

 

[johnd43]

Bbird,

Thanks for your better details.

I think we all seem to share a similar philosophy.

I started to declare a political view at this stage, but that is not what this website is for. What it does serve, though, is to point out yet again that particular engineering is only part of the issue. That has been true of most of the threads that have caught my attention since I signed up.

Regards,

 

[rsherry]

Just to clarify a few points about the arrangements in the UK :

>> quote >>
In the past the Central Electricity Generating Board (CEGB) was responsible for the whole system in UK and we could look to them for having spinning reserve in the generation and spare capacity in the transmission lines. I just don't see anybody now in UK is shouldered with the same degree of obligation of looking after the security of electricity supply.
>>>>
This still exists and falls on the National Grid Company
which designs the network to have spare transmission capacity and to contract with the generators to hold reserve. The continuous reserve held on the UK system is 1000MW presently.

>> quote >>
Transmission company do not have the money to invest for the future and will flog the horse until it is stone dead.
>>>>
In the UK more money has been spent on the Transmission system recently (than in the period immediately prior to privatisation). The distribution systems (132kV and below) are less fortunate. Both recent UK blackouts (London and Birmingham) have been blamed on incorrect installation of new equipment (

http://www.ofgem.gov.uk)

and are not as worrying as the Italian one.

>> quote >>
With one big national authority the cutting back of electricity can be carried out with little resistance. Now the system is common and used by a large number of small companies having an equal right to the system. Who can be chopped off when the supply cannot match the demand?
>>>>
If load is disconnected deliberately (rather than by accident as happened in the recent UK blackouts), the local distribution companies are normally the ones who disconnect the load. They have both automatic systems and manual systems (e.g. when instructed by NGC). A very few loads are treated as un-interruptible (e.g hospitals without backup generators), below this the distribution companies prioritise which loads they disconnect but they usually do it on a circuit by circuit basis.

hth

 

[jbartos]

Suggestion: The overhead lines will always be depended on whether conditions and some blackouts will always materialize. Intent is to minimize the blackout to as small area as possible without any cascading or domino effects. This part is dependent on the power grid stability and protection design so that the malfunctioned part of grid is safely isolated. A great deal of the grid behavior may be found over the proper simulation of the power distribution and its protection. It is not unusual to see retrofits including additions of VAR compensators, additional transmission lines or local power generating stations, which may be a result of the power grid computer simulation.

 

[Bbird]

rsherry,

Thanks for the update. I was addressing the problem as general covering a national system between being owned by one big outfit before but is now divided into multiple entities. Due to my limited knowledge I could only quote UK examples.

Many UK engineers believe (me included) that our current system with only one transmission authority (NGC) should be more robust than the American system but I see the situation can degenerate with time due to the economic pressure. The recent London and Copenhagen black outs are nowhere near the scale in the America and Italy but the close proximity of the events will do doubt sharpen the decision makers a bit.

The extent of a black out is a good indication of robustness of a national system. It appears to a layman that every one of the above developed countries used to have a reasonable system before. Could these big black outs be a result of the management squeezing the longer term safety margin out of the system in favour of short term efficiency drive?

Would be it correct for people outside the power industry to suggest that the electrical transients and stability of the power system is the root cause of these black outs? The generation capacity appears adequate but the system is now known to have difficulty to change from one steady state (with no loss of transmission line) to another steady state after losing just a small number of transmission lines. Although the system has been designed to isolate the problem area quickly, both automatically and manually, yet an out-of-portion disruption of power supply still ensures. Also the technology to prevent or at least to control black outs is available now but mitigating measures not always fully implemented. Can this situation be changed by better management or some political action is required to shake up the system? Have the consumers asked for it by relentlessly driving down the price of electricity through the floor of security to end up in the basement of black outs?

Is it true that every problem can be solved by the engineer it is only a matter of “who pays”?.

 

[SidiropoulosM]

Bbird, you bring up many interesting issues but these have been discussed in the two "Big Blackout" threads I and II. There are many good comments, references and links in those threads on the subject of blackouts in general and the August 14 blackout in particular.

 

[Bbird]

Thanks SidiropoulosM. I have kept an interest in the 14 August blackout mainly in the news but will follow your advice.

I joined Eng-tips only recently and much later into this Forum as an outsider. The Italy blackout happened only a few days ago on 28 September and the end of "Big Blackout II" started to have some posters mentioning it. The problem seems to across the power industry of the world and not just confined to USA. Also it would be nice to know if the cause is similar in all four affected countries. The Italian case is unusal ( for managing a maximum of 17% power short fall nationally). It it would be nice to hear from what our Italian friends here could tell us.