Number of the Month

March 2010

Pity the poor grid controller

The electricity grid is one of the great achievements of modern technology. It has been so well designed and developed that we take it for granted. Thanks to the dereliction of duty by ignorant and arrogant governments of the new political class, that will all come to an end when the power cuts start. The fact that the grid is so reliable is down to the skill of a relatively small number of engineers who have the responsibility to control it. That is also about to change as new uncontrollable devices are being attached to the grid for religious reasons. This is even more grotesquely in evidence with the encouragement of “microgeneration” by which consumers are encouraged to make their own input into the grid. Imagine the situation if people were encouraged to pump the untreated output of the wells in their back gardens into the water supply.

 The fundamental science behind the control of a mass distribution system is basic commonsense.

Here is a short quotation from Sorry, wrong number!

Consider, for example, what I call the Universal Law of Stuff, and I hope the lay reader will excuse a few simple equations. If we have a closed volume containing some stuff, as yet unspecified, there are only six things that could possibly happen to the stuff. Let us call the stuff Q and use subscripts to indicate each of those six possibilities. The stuff can:

Come into the volume, Qi
Go out of the volume, Qo
Be created within the volume, Qc
Be destroyed in the volume, Qd
Be stored in the volume, Qs
Be unstored in the volume, Qu

Now, as we have specified the only things that can change, it follows that if one of them increases by any amount, one or more of the others must decrease by the same total amount. Putting it mathematically:

Qi – Qo + Qc – Qd + Qu – Qs = constant

………

Now this law is absolutely immutable, besides being common sense. The stuff can be virtually any quantity you can identify and quantify. Examples are

Liquid
Gas
Electric flux
Heat
Information
Light
Electrons
People
Etc.

In a version of the law dealing with rates of change of these quantities (differentiation with respect to time) the algebraic sum must be equal to zero (always!).

In any particular application, some of these quantities will be identically zero. The gas grid has storage but not creation or destruction (unless, in the latter case, there are leaks, a potentially disastrous situation). Destruction in this context equates to losses. The water grid is similar, except that rather unsatisfactory levels of leakage are tolerated. Gas holders and water reservoirs ease the problem of control considerably, though their capacity is bounded and when the lower bound of an empty store occurs the results are rather catastrophic.

The electricity grid is bereft of a realistic storage system. Various mechanisms might be proposed (batteries, flywheels etc.) but they cannot economically be made of a practical capacity. The least preposterous idea is to use surplus energy to pump water up a hill and get it back as hydropower when it is needed.

To all intents and purposes the electric grid controller has to achieve a balance by controlling the input alone. This requires considerable skill and diverse knowledge. In England for example, extra standby capacity used to be switched in at half time during the televised football cup final, when half the nation put the kettle on. If an unexpected surge in load occurs, the voltage and frequency fall until a compensating input is engaged. In this light, adding intermittent power input from sources such as wind greatly exacerbates the control problem. It becomes necessary to vary the controllable supply to compensate for short term changes from the uncontrollable sources as well as the load. Such a system is potentially unstable if the changes of input are frequent and short-term. It is a useful demonstration for engineering students to present them with the problem of keeping a pointer (say of a voltmeter) at a given point with a varying input into a simple system. They quickly learn how to do this. Then you switch in a delay. They find that they are inevitably supplying a correction that is opposite to the one actually needed. An oscillation builds up until the pointer wraps itself round to the end-stop. This is a classical case of an attempt at simple control by negative feedback in a system with delay.

There are many forms of loss in the electricity distribution system – iron, eddy current, dielectric, corona and joule. They are relatively minor, though joule loss, which depends on the square of the current and the transmission distance, could be a major consideration in a badly conceived system (such as the proposal to transport solar power from the Sahara to Northern Europe).

Of course, if we had a d.c. distribution system, with all its concomitant disadvantages, apart from the storage problem, we could treat the electricity supply much the same as other utilities. With the a.c. system electricity suppliers have to deal with other considerations, namely:

·        Frequency

·        The purity of the waveform

·        The power factor

·         The balance of the three phases

·        The potential relative to ground of the neutral supply line

·        Maintaining a time reference for electric clocks, though this is now of diminishing importance owing to other technological developments.

With the rise of microgeneration all of these will become increasingly difficult to control. In particular, ill-maintained customer devices are likely to pump distorting harmonics into the network, which will interfere with some equipment and increase the problem of pick-up (inductively coupled interference). All of this is in addition to the enormous problems of the intermittency of wind-driven and solar devices. It cannot be over-emphasised that, as there is no effective energy storage, the suppliers will not only have to deal with sudden changes of load but also of supply. Any time-lag in responding to such changes will cause changes in the voltage and frequency of supply. The immutable universal law of stuff must be obeyed.

There is no economic or technological justification for the introduction of microgeneration, quite the reverse. It is a scheme to bribe people with their own money to display religious symbols on their roofs. The amount of power provided will always be a negligible proportion of the whole, but the potential for disruption is far from negligible. In order to maintain this farce, power from microgeneration is to be incongruously and inordinately subsidised by other customers (and the microgenerators themselves).

In these pages we coined the term “enginasters” for those who come up with half-baked proposals, originally for those promoting “flying generators”. Now the enginasters have turned to the concept of the “smart grid” (try Googling it). They produce elaborate flow diagrams of combined supply systems for all the utilities. In the centre is an empty box, which is the “controller”. This is the software that replaces the old fashioned human grid controller. You would think that the political class would have learned their lesson about the efficacy of large computer programs, but learning from experience is not in the nature of the beast. It is assumed that the system analysts will have thought of all the possible problems before they hand over to the programmers to produce the code. They never do. They are supposed to account for all types of natural catastrophe, criminal activity and terrorist attacks, as well as events that nobody has yet thought of. When the power cuts begin, they will have to choose which parts of the community are going to be cut off. Will the list be a state secret (until it leaks)? They will have to develop techniques for coping with cascading power failures and “brown-outs”. We will not know what they have failed to anticipate until it happens.

Meanwhile we have to rely on those poor human grid controllers, whose task will become increasingly impossible for no good reason at all.

As the old Chinese curse has it “May you live in interesting times”.

Meanwhile get yourself a generator set and a portable oil or gas heater.

28/03/10

Number of the month - 22,000

From the Daily Mail:

Smoking should be banned in all cars to save children from the health dangers caused by passive inhalation, says a report from the Royal College of Physicians.

Doctors are calling for urgent action after figures revealed passive smoking triggers 22,000 cases of asthma and wheezing in children every year.

Around 9,500 hospital admissions among children are linked to the effects of secondhand smoke inside and outside the family home, says the report, which analysed existing research etc etc

It is easy to demonstrate that this is a lie. In the 1950s we children did more passive smoking in one of our weekly visits to the cinema than most modern children do in their whole lives. Yet childhood asthma was almost unknown. It has steadily increased since then as smoke exposure has fallen. It is now a major health concern. You see children getting on the school bus clutching their Ventolin inhalers.

The crime of this particular bunch of zealots is that they have prevented research into the real cause of the implacable rise of juvenile asthma cases.

PS and don’t tell us that it is air pollution. In the early fifties we London children walked to school through thick, choking, sulphurous, smogs. Many people, mainly the elderly, died and the consequence was the first Clean Air Act.

19/04/10

PS apologies for the late posting. One of the usual frequent health incidents was followed by one of those trivial but agonising back muscle spasms.

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