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Page1 Production of Electrical Energy（电能生产）English text From reference

Hydrogen can be recovered by fermentation of organic material rich in carbohydrates, but much of the organic matter remains in the form of acetate and butyrate.An alternative to methane production from this organic matter is the direct generation of electricity in a microbial fuel cell(MFC).Electricity generation using a single-chambered MFC was examined using acetate or butyrate.Power generated with acetate(800 mg/L)(506 mW/m2 or 12.7 mW/L)was up to 66% higher than that fed with butyrate(1000 mg/L)(305 mW/m2 or 7.6 mW/L), demonstrating that acetate is a preferred aqueous substrate for electricity generation in MFCs.Power output as a function of substrate concentration was well described by saturation kinetics, although maximum power densities varied with the circuit load.Maximum power densities and half-saturation constants were Pmax = 661 mW/m2 and Ks = 141 mg/L for acetate(218 Ω)and Pmax = 349 mW/m2 and Ks = 93 mg/L for butyrate(1000 Ω).Similar open circuit potentials were obtained in using acetate(798 mV)or butyrate(795 mV).Current densities measured for stable power output were higher for acetate(2.2 A/m2)than those measured in MFCs using butyrate(0.77 A/m2).Cyclic voltammograms suggested that the main mechanism of power production in these batch tests was by direct transfer of electrons to the electrode by bacteria growing on the electrode and not by bacteria-produced mediators.Coulombic efficiencies and overall energy recovery were 10?31 and 3?7% for acetate and 8?15 and 2?5% for butyrate, indicating substantial electron and energy loes to procees other than electricity generation.These results demonstrate that electricity generation is poible from soluble fermentation end products such as acetate and butyrate, but energy recoveries should be increased to improve the overall proce performance.Keywords：electricity generation，acetate，butyrate，energy

Page2

Electrical energy transmiion（电能输送）English text

From reference The economic theory of electricity transmiion pricing is now well-known.The first-best price of electricity at each point on a network(node)equals the marginal cost of providing electricity at that node.The electricity must not only be generated, but it must also be delivered to that node, taking account of transmiion constraints and electrical loes.If transmiion constraints are binding, so that the amount of power flowing through a line is at the limit which safety allows, then cheap but distant generation may have to be replaced with more expensive local generation, in order to reduce power flows.In the constrained area, the optimal price of electricity rises to the marginal cost of the local generation, or to the level needed to ration demand to the amount of electricity available.Even if there are no constraints, some power will be lost in the transmiion system(diipated as heat), and prices should reflect the fact that it is more expensive to provide electricity at the far end of a heavily loaded line than close to a power station.Transmiion Congestion Contracts(Hogan, 1992)could be used to hedge spatial price differentials, and to help coordinate investment.These principles are well-known, but few electricity systems have adopted them.New Zealand and a small number of US power pools have markets which are based upon nodal spot prices, but almost every other country in the world uses a simplified system of transmiion pricing.Nodes may be grouped together into zones, and the price differentials between zones are calculated from simplified models.Other systems still see transmiion as an “overhead” cost, and use simple “wheeling rates” to calculate payments if one company imports power from a second over the lines of a third.These payments are typically based upon the volume of the flow and the length of its contracted route(the MW-mile approach), and frequently ignore the fact that any transaction in an interconnected system will affect power flows on all the other networks in that system.A special iue of Utilities Policy(1997)discues the pricing rules adopted in eight electricity systems, aeing them against economic and political criteria.One common theme is that these rules tend to produce lower price differentials than would be aociated with optimal spot prices.How important are the differences between the relatively simple rules adopted in practice, and the prices which an optimal system would produce? One of the main economic functions of a price system is to signal the opportunity cost of alternative courses of action.On the demand side, an agent should buy something if it is valued at more than its price, while a supplier should produce it if this can be done for le than its price.If buyers and suppliers face the same prices, their independent decisions will ensure that the value of output at the margin is just equal to its marginal cost, which is optimal.If prices are above marginal costs, then too little of a good will be consumed and produced, while too much will be produced if prices are below marginal costs.1 The wrong prices can also lead to inefficient “bypa” as agents have an incentive to leave the market, and arrange deals at prices closer to their costs.2

This paper takes a simplified model of a transmiion system, calculates optimal prices and quantities, and compares the outcome with those that simpler rules would produce.The model has thirteen nodes, with demand at every node and generation at most of them.The amounts of generation and demand, and the links between nodes, are intended as a simplified version of the transmiion system in England and Wales.The profits earned by generators, and consumer surplus(the total amount consumers would be willing to pay for their consumption, le the amount which they do pay)can be calculated at each node for each pricing rule.Our main comparator is total welfare, equal to the sum of consumer surplus and profits.Keywords：electricity transmiion；The economic theory;differences;Node

Page 3 Protective relays(继电器)English text

From reference1

The function of protective relaying is to cause the prompt removal from service of any element of a power system when it suffers a short circuit, or when it starts to operate in any abnormal manner that might cause damage or otherwise interfere with the effective operation of the rest of the system.The relaying equipment is aided in this task by circuit breakers that are capable of disconnecting the faulty element when they are called upon to do so by the relaying equipment.Circuit breakers are generally located so that each generator, transformer, bus, transmiion line, etc., can be completely disconnected from the rest of the system.These circuit breakers must have sufficient capacity so that they can carry momentarily the maximum short-circuit current that can flow through them, and then interrupt this current;they must also withstand closing in on such a short circuit and then interrupting it according to certain prescribed standards.3 Fusing is employed where protective relays and circuit breakers are not economically justifiable.Although the principal function of protective relaying is to mitigate the effects of short circuits, other abnormal operating conditions arise that also require the services of protective relaying.This is particularly true of generators and motors.A secondary function of protective relaying is to provide indication of the location and type of failure.Such data not only aist in expediting repair but also, by comparison with human observation and automatic oscillograph records, they provide means for analyzing the effectivene of the fault-prevention and mitigation features including the protective relaying itself.Keywords：protective relaying；function；transformer；transmiion line；Circuit breakers

From reference 2

Some relays have adjustable time delay, and others are “instantaneous” or “high speed.” The term “instantaneous” means “having no intentional time delay” and is applied to relays that

operate in a minimum time of approximately 0.1 second.The term “high speed” connotes operation in le than approximately 0.1 second and usually in 0.05 second or le.The operating time of high-speed relays is usually expreed in cycles based on the power-system frequency;for example, “one cycle” would be /60 second in a 60-cycle 1 system.Originally, only the term “instantaneous” was used, but, as relay speed was increased, the term “high speed” was felt to be neceary in order to differentiate such relays from the earlier, slower types.This book will use the term “instantaneous” for general reference to either instantaneous or high-speed relays, reserving the term “high-speed” for use only when the terminology is significant.Occasionally, a supplementary auxiliary relay having fixed time delay may be used when a certain delay is required that is entirely independent of the magnitude of the actuating quantity in the protective relay.Time delay is obtained in induction-type relays by a “drag magnet,” which is a permanent magnet arranged so that the relay rotor cuts the flux between the poles of the magnet, as shown in Fig.4.This produces a retarding effect on motion of the rotor in either direction.In other relays, various mechanical devices have been used, including dash pots, bellows, and escapement mechanisms.The terminology for expreing the shape of the curve of operating time versus the actuating quantity has also been affected by developments throughout the years.Originally, only the terms “definite time” and “inverse time” were used.An inverse-time curve is one in which the operating time becomes le as the magnitude of the actuating quantity is increased, as shown in Fig.5.The more pronounced the effect is, the more inverse is the curve said to be.Actually, all time curves are inverse to a greater or leer degree.They are most inverse near the pickup value and become le inverse as the actuating quantity is increased.A definite-time curve would strictly be one in which the operating time was unaffected by the magnitude of the actuating quantity, but actually the terminology is applied to a curve that becomes substantially definite slightly above the pickup value of the relay, as shown in Fig.5.As a consequence of trying to give names to curves of different degrees of inversene, we now have “inverse,” “very inverse,” and “extremely inverse.” Although the terminology may be somewhat confusing, each curve has its field of usefulne, and one skilled in the use of these relays has only to compare the shapes of the curves to know which is best for a given application.This book will use the term “inverse” for general reference to

any of the inverse curves, reserving the other terms for use only when the terminology is significant.Thus far, we have gained a rough picture of protective relays in general and have learned some of the language of the profeion.References to complete standards pertaining to circuit elements and terminology are given in the bibliography at the end of this chapter.1 With this preparation, we shall now consider the fundamental relay types.Here we shall consider plunger-type and attracted-armature-type a-c or d-c relays that are actuated from either a single current or voltage source.Keywords：instantaneous；operating time；permanent maqnet;voltage source

Page 4

Motor（电动机）English text

From reference1

We do get asked for some strange things sometimes: Vauxhall Vectra fans may recall the original launch TV advert which for a few seconds featured on-screen, a large multi-dialled clock, which was supposed to show time speeding forward to catch up with the leap into the future made by the new Vectra.Others might have suggested it was simply counting down the hours towards a cambelt failure....The clock was a stage prop designed and built for the advert by a London model-making company.It now resides in a North London flat as a rather unusual coffee table.Unfortunately the expensive variable speed-regulated motors used to drive the three dials on the clock face were reclaimed by the production company and so despite the complex gearing system installed, it did not run.A rather odd telephone call from the owner revealed that he was looking for some way to get it going again at minimum cost.He had seen an advert in a hobby magazine for C167 starter kits and wondered if there were some examples around of how to control the speed of a DC motor.Being helpful types and major fans of the Vectra(no chance), we came up with a solution based on a recycled Phytec miniMODULE167, a 12v DC motor, a fan, an infra-red LED, a photodiode and some simple C code.The objective was to make the clock run in “real time”, accurate enough to keep good time for the duration of the average dinner party but be able to run at high speed(as in the advert)on demand to impre the guests, just after the traditional serving of peppermint Rennies.The result was a simple Proportional-Integral-Derivative(PID)controller for a 12v permanent magnet DC motor.PID is very widely used in industrial control systems and something we get asked for examples of very frequently.Strangely, a trawl of the Web revealed no C-coded examples of any sort so we decided to do it from scratch.To make the clock run at a constant speed, here 600rpm, some form of accurate speed regulator mechanism was required.This would ensure that over time, the average motor speed would be constant.The nature of the clock mechanism was that the load on the motor varies.For example, as the various hands move, small load peaks occur which tend to disturb the running

speed.The drag and motor efficiency were also subject to change, particularly as a result of temperature.A more appropriate motor drive mechanism to have used in this type of application would have been a stepper motor but most requests we get are for the control of conventional motors plus a reasonable DC motor just happened to be in the parts bin at the time....Keywords：Speed regulating motor；Photodiode；fan；PID;

From reference 2

The closed-loop controller is a very common means of keeping motor speed at the required “setpoint” under varying load conditions.It is also able to keep the speed at the setpoint value where for example, the setpoint is ramping up or down at a defined rate.The eential addition to the previous system is a means for the current speed to be measured.In the example, a three bladed vane was attached to the motor shaft.An infra-red LED was obscured from the view of a photodiode by the vane blades so that a series of pulses with a frequency proportional to motor speed is now available.In this “closed loop” speed controller, a signal proportional to the motor speed is fed back into the input where it is subtracted from the setpoint to produce an error signal.This error signal is then used to work out what the magnitude of controller output should be to make the motor run at the required setpoint speed.For example, if the error speed is positive, the motor is running too fast so that the controller output should be reduced and vice-versa.The clever part is how the output drive is worked out....At first sight it might be imagined that something simple like “if the error speed is negative, multiply it by some scale factor(usually known as ”gain“)and set the output drive to this level”, i.e.the voltage applied to the motor is proportional to the error speed.In practice, this approach is only partially succeful for the following reason: if the motor is at the setpoint speed under no load there is no error speed so the motor free runs.If a load is applied, the motor slows down so that a positive error speed is produced.The output increases by a proportional amount to try and restore the speed.However, as the motor speed recovers, the

error reduces and so therefore does the drive level.The result is that the motor speed will stabilise at some speed below the setpoint at which the load is balanced by the error speed x the gain.If the gain is very high so that even the smallest change in motor speed causes a significant change in drive level, the motor speed may oscillate or “hunt” slightly.This basic strategy is known as “proportional control” and on its own has only limited use as it can never force the motor to run exactly at the setpoint speed.The next improvement is to introduce a correction to the output which will keep adding or subtracting a small amount to the output until the motor reaches the setpoint, at which point no further changes are made.In fact a similar effect can be had by keeping a running total of the error speed speeds observed for instance, every 25ms and multiplying this by another gain before adding the result the proportional correction found above.This new term is based on what is effectively the integral of the error speed.Thus far we have a scheme where there are two mechanisms trying to correct the motor speed which constitutes a PI(proportional-integral)controller.The proportional term is a fast-acting correction which will make a change in the output as quickly as the error arises.The integral takes a finite time to act but has the ability to remove all the steady-state speed error.A further refinement uses the rate of change of error speed to apply an additional correction to the output drive.This means that a rapid motor deceleration would be counteracted by an increase in drive level for as long as the fall in speed continues.This final component is the “derivative” term and it is a useful means of increasing the short-term stability of the motor speed.A controller incorporating all three strategies is the well-known Proportional-Integral-Derivative, or “PID” controller.For best performance, the proportional and integral gains need careful tuning.For example, too much integral gain and the control will tend to over-correct for any speed error resulting in oscillation about the setpoint speed.Several well-known mathematical techniques are available to calculate optimal gain values, given knowledge of the combined characteristics of the motor and load, i.e.the “transfer function”.However, some simple rules of thumb and a little experimentation can yield satisfactory results in practical applications.9