AND ECONOMIC

UNITED NATIONS

ECONOMIC AND

SOCIAL COUNCIL

Distr. |3 LIMITED = 11 October 1963

///5

Original: ENGLISH

ECONOMIC CGi&lISSICN FCK AFRICA African Electric Power iloeting Addis Ababa? 21-31 October 19-63

CHCICE OF THE TYPE AFD SIZE OF ELECTRIC POWER PLAFT

(by the secretariat)

1

63-3375

CONTENTS

Chapter I EXPLANATORY NOTE - . •

Importance'of preliminary analyses' Different cases for proceedings

Chapter II POWER PLANT FOR ELECTRICITY SUPPLY IN AREAS HITHERTO UNSERVED r

Obstacles in the preliminary work

Effect upon power plant design .. ■.■■..■

Chapter III THE CHOICE OP THE KIND OF POWER PLANT

... . .. Choice of the kind of power plant and its consequenoes Water power plant

Diesel power plant

Steam power plant . .. ' . :.. , ■ . ^

Gas turbine plant

Nuclear power plant . Special plants

Alternatives and their appraisal ..-.-. :.:.L'J

Chapter IV THE CHOICE OF SIZE.OF POWER PLANT

Repercussions of the plant size seleotion Influence by the dynamics of economy Definition of the size of power plant Peak-load for the plant under selection Problems of low load and minimum capacity Self consumption impact on plant capacity

3/CN.14/SP/5

11 -

Chapter V THE CHOICE OP THE TYPE OF POWER PLANT

Criteria for consideration of elements in the determination of type

Types of hydro-electric power plants Diesel power plants

Selection of type details on steam power plant project

Consideration of gas turbine power plant details

Nuclear power plants

Chapter VI ENLARGEMENT OP THE PRESENT POWER STATION

Increase of power production from an existing power plant

Erection of new equipment envisaged in previous design

Elaboration of a now design

Chapter VII ERECTION OF AN ENTIRELY NEW ADDITIONAL POWER PLANT

Advantages and disadvantages of an additional plant Parallel operation of the new power plant

Chapter VIII APPRAISALS AND PRIORITIES

Appraisal of the project definition

Appraisal of the project design .. . . Priorities ' -

CHAPTER I

EXPLANATORY KOI53

^rdj^.^ appropriate

decisions, on ne.v _~?cye?_jyXp-v.i. . . .

1. The increase of electric power consumption all over the world has accelerated to such a degree that it requires each year the provision of new supply facilities with Improved efficiency, reduced operation costs and greater reliability. The average world rate of increse proved over the pact 50 yc^o *- i .1 ^x' oont, and cue compound effect means that consumption is doubled evory ten years and thus in each subsequent decade as much new production capacity is necessary as.the existing total

available at the beginning of that decade. During the present decade the increased demand for electricity reached such a level that each year about 40,000,000 k; of new production capacity was required to meet it.

In other words, the establishment of adequate new investment projects requires now an annual outlay of abou1. US$6,000 million. These are only investments for r-ev potrer slants and. accordingly they do not comprise the investments for ticii&nis^ion lines, transformer stations and distribution

networks. "■-

2. In the ncrf develcroir.g countries the rate of increase is considerably higher than the world average dao to the lov starting point, therefore annual growth rat3E of 15 per cent are nothing peculiar, being rather often in the■ ran^e of 22-30 per osnt'b ■ In. some individual cases for; one year, and referring to retrain :imited areas onlyP even rates of 65*-72 per

cent have "been ocoasioiia,lly recci^cH^. ■ ..".■- ■ ■;:.■■,

3. Obviounlyj the t-jtal pnoun-: of investments for the creation of new electricity supply facilities in those countries is rather modest In comparison to the world total, "but they make a significant part of the

investment possibility in each particular country* Still, it can be expected

E/CH.14/EP/5

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that during the present decade the total investment in new electric power plants in Africa as a whole will "be over US$1>500 million since the demand on new capacity would he about 8-10 million kvr. Therefore new power projects must he studied thoroughly, as the outlay for each individual country ia great arxi imposes a heavy financial burden over years. A marginal difference of cnly a few per cent involved by the application of relevant factors

affecting the decision on individual projects means largs amounts either wasted or saved« It does not mean that a project involving the lowest investment cost ought to be recommended,for the cheapest project is not necessarily the best one and in fact seldom is. It does mean that the most efficient and most appropriate solution must be sought. Some of these

questions are considered in this paper.

Although the amount of the financial commitment is one of the most important items, the subject is much wider and besides the total investment cost a decision on the choice of new power plant projects can have a

considerable effeot upon the price of electricity, promoting or restricting the consumption and influencing accordingly the power-intensive industry, mechanization, electro-chemical and electro-metallurgical production, the supply of energy with regard to demand, imposing by certain solutions and limitations in unfavourable seasons, the effect upon the fuel consumption and the balance of payments of the country during the erection of the plant and its operation as well as on the whole policy of energy supply and develop

ment of the economy,,

4. All these points should be borne in mind when the approach to a power

project is made. Some of the points are discussed directly in the paper,

while the others could be considered by indirect application of elements

quoted in the corresponding paragraphs concerning the criteria for the

choice of project and the individual solutions. In addition, a lot of

valuable explanations, figures and advice can be found in other papers of

the Conference related to the same subject, whioh will certainly prove very

useful for the comprehensive consideration of futv-o per.;.:, projects.

Different cases for proceedings

5. pHi& choice of the type and size of a future electric power plant

depends on "the specific characteristics and requirements. It is impossible, therefore, to recommended any one method*

6, The following main categories could be considered as particular cases;

(a) Provision of a power supply in areas hitherto unservedj ,(b) Extension of energy supply in an isolated area with existing

individual plantj- ■■■.:■; . /

-■'■" (c) interconnected electric power system;

(d) Separate electric plant within an industrial enterprisej (e) Multi-purpose project,. . , .. ■ . . 7« As mentioned before, each of these categories is in many points

■different and, for "the sake of simple and clear consideration, they are given

separately one by one7 in this paper. Obviously,a'great many questions

which have to be answered would be" much the same or similar, but their

consideration, the criteria and consequently the replies will show for

each oase different' conclusions according to the characteristics of individ

ual cases, •

8, Before proceeding with the consideration of the substance of the paper,

it should be mentioned that the title "Choice of type and size of electric

power plant" includes both of the meanings of the word "type" as this

terni is used in various documents. Many experts use the expression "type of power plant" to distinguish the source of energy used for the plant's operation, e.g. water, diasel, steams, etc.

e/cn. 14/EP/5

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Others use it, on the contrary, as a technical term fcrr the "main

internal ..characteristic of a plant; for instance, the water power plant can "be of the run-in-river or of a storage-type, it could be of a high

head or of a load head type and the the like, while the steam power plant

can be of a blook or classical typej of a high pressure type, of a

condenser or back-pressure type, etc.

9» All these details are very important and they represent fundamental charaoteristios of a plant and its economy. Since in power production the economy and the engineering are extremely closely connected and inter dependent, they are also very important points in this paper. In order to avoid any confusion and to distinguish the two fundamental meanings, both of them widely discussed in these pages, two different terms are used.

10, Accordingly the term "kind" of power plant means the external economic

and technical characteristics of'a plant determined by the source of power

used for the production of electric energy like water power, steam and

others., The term "type",of power plant is retained for the main internal

characteristics, design.and lay-out of-linddviqlual plant in the.sense mentioned above. Consequently, tha paper's topic is in fact "Choice of kind, type and, size of ..electric power plant". The ^practical side of the point should be taken into account in spite of the ;fac.t that it sounds perhaps a little unusual.

PO'riER PLANT

FOR ELECTRICITY 'SUPPLY IK AREAS HITHERTO UNSEXVED

Obstacles in the prcP.iminar;/ wor'i

11. The establishment of ? power plant in Qn area hitherto without

electricity supply whatsoever is a case very often met with in the developing countries since there are a. great many provinces in African countries

unserved by electric power and the supply of electricity is the first step

to any ens3ntial development. Also places,with a very primitive electricity supply, with a few lamps, for a modest lighting, usually not only with very limited range but also with current available over a few hours in the., evening? should be considered practically as places hitherto unserved.

12, The preliminary study r-.:id pi1 -parstion of a project :"or a plant in a non^-supplied area in not eaey3 particularly as fa*? as the determination of

the-'Size of tho :::"utv.re plant is concerned, because it is affected by the lack of information concerning demand and the future development. The

calculation hat; only a,' few points to rely on, therefore much of the data has to be included in the study as a mere estimate and assessment.

13- ?::"-■■•' -.E therefore indispensable fo:/ each item of the preliminary stud;/" and design because of considerable ris^ in technical rating, in

investment costs, production coaic, profitability, timing; etc. Experience has shown' that in sucli caeeF often the p,dvioe and rule—of—thumb figures from

■the'professional literature:are surpassed. For instance, in one African place, a regior.rj. cer/^ro with z, popula t.'-o:: of 30,000- a primitive electric supply of-120 I ■ has "been reconstructed and 2 new diesel-generating sets of 250 lr"' eacL-put- in operations The increase has been so remarkable that the next year 2 additional genera tore had to be provided in a great hurry and a new power station of 5?000 kW had to be designed." The consumption lias

■increased'in 2 years from 32OSCOO kKb to 1,200 000 klfa. In another African

E/CN.U/EP/5.

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area the new capacity of 3,300 1 - expected to be sufficient had to "be increased after 3 years to 18,500 kW or 450 per cent. For the next 5 years a further increase of 520 per cent is now being estimated. In a third area, in Africa as well, besides existing facilities of 130 kW sufficient for many years, a new hydro-power plant of 6,000 ktf has been under construction; but during the building time of 3 years the demand has increased in such a way that a diesel plant of 700 ktf has been provisionally created in a desperate hurry to fill the gap pending the

operation of the hydro-power plant*

14», There are many similar examples. Still it does not mean that it must necessarily be the same development since its dependence on the over-all economic life is obvious, There are also examples, in spite of the much smaller number, where the expectations and forecast did not come true. Therefore, the uncertainty still remains.

Effect upon power plant

T5» The consequences of those circumstances must be taken fully into account, As a direct repercussion of the preparation of a preliminary project, the contingencies on all calculations either technical or

financial should be accordingly higher. But besides this, the selection of capacity and particularly the lay-out of the plant should be done in such a way as to allow operation at low power without difficulties if the load increase is slower than that forecast. On the other hand, the erec tion of additional equipment should be provided for in the initial lay out so that it can "be installed within a short time if urgently needed.

16; And in addition to this, there is the fact that the supply of the area

under consideraTioia depends entirely on this plantj the design must,

therefore, provide more stand-by generating sets as capacity reserve as

well as other adequate measures for uninterrupted operation. It is obvious

that the financial implications of these requirements result in higher

capital cost? longer pay-off time which could be offered to the supplier

of the funds, limited interest amount, impossibility of acceptance of any

tight financial terms vrhen negotiating the loan, etc. Consequently, the

entire policy-making considerations are affected not only very deeply but

differently frcm power projects which are part of an interconnected system.

CHAPTER III

THE CHOICE G? r:i"l KIITD OP P073R PLANT

Choice of the kind of T*nrer riant and its consequences

17. When erecting a new electric power plant,first of all the kind of plant must be selected. The kind of the future power plant is determined by the form of primary energy to be used for the Operation of generating sets aiid'the choice is most important, for its technical and financial

consequences and as well as its implications on the national economy, • :

Also the pattern, construction and operation of a power plant is fundamen

tally influenced by the source of energy to be used.

18, The possibility is limited very seldom to only one solution which

thus would determine the kind of plant and impose the proceeding to

find out the best size and type within this individual kind. The selection

of a power plant depends ::orr&l?.7 0- "'.hi k'.nd of generating power to be used,

i.e. water, high grade long haulage coal, low grade local coal, oil fuel,

diesel oil, natural gas, exhaust gas, waste heat, nuclear energy, wind, geothermal energy, solar or tidal energy*

19. The whole subject is very varied and is a matter of policy-making

because the decision on the choice of the kind will affect not only the

project itself but also the national economy., beneficially or otherwise,

short-range or in the lons-rur?.; whether or not it has been properly

considered and duly assessed by the exports and others in charge of the

project.

20, The choice determines predominatly the amount of the investment cost for a certain capacity rarige? i.e. the fund* required to be

available for the project^ it affects considerably the structure of invest

ments, particularly the ratio of equi^.vr.'; to uivil engineering cost, which

E/CN. 14/EP/5

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means also the ratio of foreign exchange and local currency and the participation of local manpower; it affects the future production costs and their structure, particularly the part of capital cost and depreciation and fuel costsj it affects the maintenance cost, the pay—off time, the demand upon the manpower skill and the need for foreign specialists, the dependence en clircctic circuni3tanoe«? particularly in regard to water-supply or the dependence on import of fuels7 *h,e reliability of, the generating operation as far as the number and susceptibility of potential "break—down, points and the danger of interruption in operation ?z-e..concerned; it affects predominantly the time needed for a stand-by set to be capable of "being on the line generating at full load from a complete shut-down conditipnj it r affects the demand on maintenance that means particularly, the time, betwee.n overhauls as well ae the. time for an ..individual overhaul b^th resulting in..

the periods Of non-availability as prodixction capacity* Since the various cases of the power plant selection are given more consideration in the following paragraphs, reference is also made to these points as far as individual bases are affectecU

Water+

21.' Establishment of new hydro-electric power plants Tiave for many African

countries an outstanding significance for two important reasons: firstly,

African :c6iintries'.a,re, with very few^exceptions, rich in:available water power y'whins* fuels,- coal^-natural gas or oil, are available in abundance in

some:6f them 'only5 secondly? the construction of hydfo—power plants offers the possibility of multi-purpose projects together with irrigation* which' is important for ma^y African countriesfl

22, The enormous importajice of -water power in Africa is obvious from the following table shewing !;he figures of the total water power potential in many regions according to the rough assessments made at low water rates of

flow (whether developed or not developed)» ::

TABLE 1

Region Total water power

potential at low rate

Africa

North America

Asia (USSR not incl.) Europe (USSR not incl.)

South America USSR

Oceania

275,000,000 HP 120,000,000 108,000,000 87,000,000 70,000,000 68,000,000 22,000,000

23» The importance of water power for Africa is even more outstanding -

if considered in per oaput figures, and if the. fact is "borne in mind, that the highly developed regions in the world have already made use of a greater part of their water potential and the "best sites have been

"built up while in Africa the waters are hardly touched.

24. There are some Afrioan countries particularly rich in water power

potential. Some examples shown here as illustration are rough assessments

at average flowy all of them being subject to correction when detailed

studies have been carried out.

E/CN.14/EP/5 ■

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TABLE 2

Country :. Assessed water

. . : : ■■. power potential

Congo - Leopoldville . "'■. . \ 130,000,000 HP

Congo - Brazzaville ". 50,000^000

Cameroon . 20,000s000". /

Nigeria . 13,000,0OO ■'■

Malagasy . •. 7,000 5 000

Angola . 6,000,000

Ethiopia / 6,000,000

Liberia ■- 6,000 ,000

Mozambique 6 ? 000,000

Tanganyika 4,000,000

25» When erecting a -water power plant, the main characteristics, of such .-:

a kind of power generation, must be talcen into accounta: namely: v ■ .,..-•

(a) .high ^n^ostmen't cost pea? .unit of■ capacity v-Mch is .variable

... ■:■.-■ zi -^depending on. ci^-conditions, sj.v-e imprpveiflentsj .-damsj storage , ., . .re.seryo,ir.3j 1rann,els ..and, o.-^hep dataller while the outlay for...,..,.,-

the part whioh is independent of the greater., part of the ; hydraulic installation is much:less variable and generally in

a range of 90-120 U3$/kW aocoi-dins to the size and type of

equipment^ the total cost can amount to US$ ?.^.Q ~ 400 per kW;

("b; dependence on water—flow and its considera'Dlo variations caused

"by hydro-raetoreological factors and climatic seasons;

(c) huge preparatory work with extensive and costly investigations,

often of a complex nature and taking a long timej for these

studies adequate hydrclogical documentation is required,otherwise preliminary observations over many years must precede the

"beginning of the working-out of the study itself \

numerous test drillings;

(e) -long construction times with extensive civil engineering work and complex building site organization;

(f) slow turn-ratio of capital, that ;means long pay-off time as a consequence of large investment in comparison with the

production value; . .... . . ..

(g) long depreciation time; -because of the considerable .influence of capital cost;and depreciation upon the price of electricity and very ;long physical life of the most expensive parts,.of the project,the tendency is to apply a low depreciation rate, resulting in slow accumulation of the amortization fund;

(h) low production cost, and consequently the price;of^electricity mainly consists of financial rather than technical components;

(i) favourable foreign exchange ratio on investment due to large share of civil engineering work, i.e, work locally carried out and locally paid; the ratio is even better during operation

with the exoeption if a foreign loan has been used for investment

"and has "to\^'repard"'ih'fbreign11"currenby5 (j) minimum maintenance requirements;

:.(k)-"-;low skill- demand in operation which is-relatively the-simplest

in comparison with all the other kinds of power generation;

(l) possibility of; combination with multi-purpose projeot and manifold benefits)

(m) no fuel import, hence no dependence on any foreign supply in

the operation;

(n) favourable implication for plant projects of any capacity,

because a properly designed water power plant-can be efficient

for any size of project capacity; ;

B/CN,14/EP/5

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(o) relative inflexibility as regard the site since the water

potential can "be used only in the place where, it exists;

(p) indispensable international co-operation if a river basin

stretches beyond the country1s frontiers.

26. While some of the above mentioned features of the water power plant

are obviously advantageous and others not so, there are points which may have different significance9 depending oh the case or on the policy pattern adopted by a particular country for a certain period. It is hardly possible to set a strict rule and it depends upon each individual oase whether or not to give the preference to water*

27 • Ime following table will give some idea of the great differences in the utilization of water power in electricity production in various

countriest . ■ . .

TABLE 3

Participation of wa.ter power in electricity supply of certain countries

Country Year Production of Percentage of

hydro-electric power the total electric in billions of kWh power production

in the country

Switzerland Norway Canada Italy France USSR USA

Great Britain Netherlands

,1960 1960 1954 1960 1960 1960 : 1960 1960 1960

• 19 -, TWh ■

31

63

46 40

51 149

3

0

99.5

99.0

85.5

82.0

56.4

22.9

17.8

2.4 0

TABLE 3 (Cont.)

Country Year Production1 of

hydro-electric power

in "billions of kWh

Percentage of the total electric power production in the country

AFRICA:

Cameroon

Congq (Leop»)

1959

1959

Morocco 1960

Algeria - : i960 Southern Rhodesia 1959

0,8 TWh

2,5 .:■

0,9 ""

0,4

97

93

26,5

0.1

28* Taking into consideration all the relevant factors and local situations, it seems advisable for African countries to pay, in the long run, special attention to the utilization and development of their water potential.

Diesel power plant

29. This kind of electric generation is of particular interest for smaller centres and remote areas of countries in development with not too extensive consumption. The considerations of eventual selection .of this kind of power plant have to take into account the following main characteristics of

diesel power plantss ;

(a) simple preliminary study, in fact the simplest of all possible

: kinds of power plant solutions;

(t>) relatively very small dependence on local conditions, therefore

only a brief investigation on the spot required for collection and checking of a few "basic l

Page 14

(c) very short time for preparation of the study and design, as well

as very short preparatory period for erection;

(d) quick delivery since the dlesel generating sets and corresponding

^ ■ equipment are mostly of current standard production at big

delivering firms (if not exceptionally large output rating

requested or a design not from the type list); as they are usually ordered as standard delivery, they are very often supplied directly from stock or from manufacturing in process or finishing;

(e) simple layout and design of plant where considerable part of the

details are also of standard design requiring only that the available drawings be inserted appropriately; in some cases, for smaller plants, practically the entire design may be supplied-from standard patterns or in a bigger plant may be made up from a few

basic units*

(f) small civil engineering work and simple shape of machine founda

tions,' relatively easy and scon prepared;

(g) transport of the equipment to the building site and assembling

on the spot are not very complicated? : . .

: (h) limited need for cooling water or if water is not available, air

■ cooling can be used; ■ . . . ■

(i) Very flexible in operation, quick start from dead stop"till full

" load, excellent stand-by possibility, no'problems at low load

operationj

(j) low fuel consumption, therefore little fuel transport and ■ -

possibility of long-term stocks.if- necessary; economical operation

over full range of capacity;

(k) no big demand upon operating manpower skill and good possibility

for automation or remote contro'l;

(l) investment cost per unit of capacity is favourable, being roughly

about 140 - 170 $/fcWj

(m) maintenance cost is considerable and the plant requires a lot

of maintenance care and relatively frequent interruption of continuous operation for overhaul or attendance; spare parts supply essential;

(n) life-time of engines is considerably shorter than for other

kinds of power plants : ;

■:~- (o) -vsTy good flexibility as regards site'and it can "ba set up

practically in any place;

(p) the generating plant can be shifted to another site without

complications and in a short time; diesel plants are therefore suitable also for temporary power supply pending the erection of a bigger plant and after it takes over the production, the former diesel plant can be transferred to another place;

(q) top capacity of diesel power plants is limited according to the

technical possibilities of diesel engines; this kind of electric generating is particularly appropriate for small plants and for engine units ranging from 50 to 1,000 kW and still very good for generating sets with an output from 1,000 to 3>000 kW per unit;

while only exceptionally there are big diesel—generators up to 18,000 kW single output in practical operation or diesel power plants of 30,000 kW total output;

(r) possibility of mobile power plant units on tire-wheels and a

rated output up to 250 kW, which can be transported from place to place and put in operation in extremely short time.

Steam power plant . . ■ .

30. That is without doubt the most important kind of electric generating plant at the. present time, since about 69 per cent of world electricity is supplied by^ steam power plant* Steam power production varies in various individual countries; it is only in a very few cases that it is not the main source of supply.

The following table gives some illustrative figures for 1956s

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TABLE 4

Electxic power supplied

"by thermal plants in certain countries

Country Percentage of the steam power plants

of total installed of the total electric

capacity MW energy pro duo tion kWh Great Britain

German Federal Republic USSR

USA France Japan Sweden Canada Norway ■ ■ Switzerland

or per continents:

America

Europe inol. USSR Africa

Asia Oceania World total

84.3 80.4

80.8 52.8

38.7

12.0

72.5 68.4..

81.7

50.9 68.6

69.1

97.6

84.9 84.7 81.7 51.9 28.6 12.5 6.2

1.0

0.5

71.6

70.5 85-9

41.3

69.3 69.3

31. It is expected that during the present and coming decades 70 per cent of

all new electric power generating facilities to be established will b© steam

power plants; this means, according to the assessments, an average increase of

about 30,000,000 kW of new thermal power plants annually, probably more than

90 per cent of which will be conventional .steam power plants. ■>

32, Of course, it docs not necessarily mean that the same participation is to be expected on each continent and in each country. Cn the contrary, as

the examples of some countries in the table show, there are considerable divergencies as a result of existing circumstances.

33. ■ When contemplating the establishment of .a new electric generating unit and the possible use of a steam power plant, the following main points

should "be borne in mind:

(a) the equipment is complicated and comparable only to a nuclear plant;

(b) considerable engineering experience is required and consequently extensive consultations; it is very often essential to bring in many specialized and well known consulting firms, which con

sequently involves rather high expenditures;

(c) preparatory period is reasonably convenient, that means not too long if carried out properly, with adequate experience;

(d) considerable minimum capacity demand is a prerequisite, therefors a rated output of less than 2,000 kW per turbo-generator is not justified and it is more advisable at over 10,000 kW per unitj (e) decisive advantages correlative with the increase of capacity as

regards the investment and operation costs, therefore large plants are particularly appropriate;

(f) fuel supply is needed in large quantities and in addition also adequate transportation facilities as well as considerable fuel

stock on the spot; ' ■■

(g) water demand is high and this fact reduces the choice of situation since only the sites with an adequate water supply can come into consideration; still in most cases the cho.ioe of sites not involving exaggerated transmission costs will be sufficiently wide;

E/cur. h/ep/5

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(h) up-to-date machinery is a prerequisite for efficient operation

but delivery can be obtained only from countries with highly developed industries; consequently steam power plants imply high foreign exchange and dependence on foreign countries; *

(i) skilled, specialized and fully experienced workers-are essential

even if foreign specialists must be hired for temporary engagement;

(j) favourable total investment cost and rather accurate assessment

: are obtainable by project documentation, usually being i7O-25O$/kW;

(k) low production cost, determined more by fuel than by capital or

financial expenditure *tarns;

(l) supply to consumer is reliable because the operation is independent

of metereology, seasons *nd the like and fully under control of . ,management; ■ ■

(m) plant can "be expanded without difficulty "and erected by stages

according to required capacity;

(ri) considerable maintenance required but it can mainly be done on the

time schedule basis.

34- Steam power plant has progressed considerably during the past 10-15 years this has resulted in a remarkable increase of efficiency and output rates and a reduction in investment and operation costs; but at the same time it has

made very large units more advisable.

. ■'■■.■-.■■■ "" •

Gas turbine plant : :

35* The following are some of the ©ain:characteristics of a gas turbine plant:

(a) a gas turbine plant is very small as regards the space required and

involves little, mostly non-complicated, civil engineering work;

(b) the preparatory work is simple and needs only relatively little

study;

(c) the time necessary for erection is short even if the preliminary work and designing are taken into account;

(d) the investment costs are moderate, the price per unit of capacity

for smaller plants could "be estimated at 130-150$/kWj

(e) no water demand and extremely fa^urable flexibility as,regards the site selection;

■ •■■;■"' !.■ .■,■"■ ' ■ .-.■.. . - .

(f) quick start at any. time from complete shut-down in a matter,.of-, :. ■

minutes and ready for full load a few minutes later (for example the experience in Sweden, plant Varberg, shows the start time of

.2 minutes,and the full load in-an additional 5 minutes, while the

experience in France, plant Tours, has been 10 and 10 minutes respectively and in Switzerland, plant Beznau, 20 and 20 minutes

for the start and'full load respectively);

(g) it can operate with natural gag, available on the spot or supplied

by a pipe-line without prior.processing and with simple transport;

handling and storage; , .

(h) suitable for operation by direct utilization of most exhaust gases

from industrial processing; ■

(i) although the construction of gas turbines has been considerably

developed over the past decade and reached a remarkable level of quality, there is steill room for a lot of improvement;. , . . ■■

(3) the physical life is.somewhat shorter compared with, steam plant?

but the annual depreciation oost is low due to the low total .

investment amount; : - , , : ;: .

(k) gas turbines are particularly suitable for stand-by duties because

■■-. of the short-time needed for:the start, as well as for peak-load coverage; the low depreciation financially allows operation at low load-factor; moreover.the simple start-up and shut-down, proceedings are favourable factors;

B/CH.14/EP/5

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(l) when a gas turbine is not in use for power generating, the

electric generator can "be employed as a synchronous compensator, of course, only in parallel run with other generators;

(m) possibility of combination with an inward-compressing free-piston,

thus obtaining moderate turbine inlet temperature despite improved

over-all thermal efficiency,

36. According to the stage of development,the advisable output rating is

limited nowadays at about 20 MW or exceptionally up to 30 MWj recently gas turbine makers have increased output up to 50 MW and programming up to 100 MW has made it feasible to increase economic efficiency up to 37 per cent with a drop in the cost per unit of installed capacity from actual 130-

150$ to expected 85$/kW. '

37- Still specialized experience is required, e.g. measures for avoiding ash-deposits on the turbine blades, particularly when running on bunker-oil;

for overtaking incomplete combustion, or preventing fire in the heat exchange units of regenerators etc. Under African conditions, if it is proposed to

site a gas turbine near the sea or a salt lake, there is a possible risk of salt deposits on- the compressor blades thus reducing the compressor's

efficiency because the air inducted by the compressor contains salt in addition to the usual impurities. There is also the,risk of an overcharge

of dust in areas affected by desert sand.

Buclear power plant

38. It seems that this kind of power production will hardly be suitable for African countries at least for the next ten years; but after that period perhaps for countries like the Republic of South Afrioa or the United Arab Republic, according to the expected pattern of energy production and demand. In view of the present'development stage of nuclear power it ie still too early to speak of its utilization for'the following reasons* :

(a) nuclear power generation is still in its preliminary stages but

great improvements are expected in the near future, particularly

as far as the reactor type is concerned;

(b) investment op.sts are extremely high; in :r:.,te of the fact that .the prices for nuclear stations have shown a steady decrease

with time, the price-of contemporary nuclear power plant is still

roughly about 4OO-45O$/kW in comparison with about 160-220 $/kW

for, a. conventional thermal pliant of the same size;

(o) unsatisfactory thermodynamic efficiency of nuclear power plant, : being about 2-22 per cent due'to the'low temperature of operation

of fuel elements;; it is expected that by 19-66 the new design of

graphite moderator and gas coating reactor operating it's fuel elements' at a higher teir;orature would allow a thermodyhamic efficiency tit"5?" t»or cent; f*'f*wr& -rhich cr?n be achieved by

conventional thermal plants even nowadays;

(d) very high cost of -the initial charge of fuel which is about 20

.per cent of the capital coat of the power station itself?

(e) nuclear plant oould come into consideration only for a.very high ." ' capacity limit of at least 200;000 ktf electrical output;.

-(f) . operation is ^possible, only in interc-onnepted power systems-working parallel with other non-nuclear plants, because of indispensable

high amotant of running hours a year and a. very high load factor,

preferably over 70 per .-oest; ;Ai ■■"■■■*'•'■' (g) operation icosts are unfavc'vvcble aad the price of electricity

-'exceeds the price from oon-vtontioaal"p'oire?: plants;

(h) fuel supply can be accomplished only "o.y v^r^ few .hi^Jy. developed

countries and in spite of ths tAc/b that a charge ehpuld.stay in reactor for several years it has to oo replaced afterwards, and

■that means considerable frro-lgn currency outlay and complete dependence on the delivering countries afi well; . '_.■.■.:

handling of the plant and of :the fuel replacement requires highly specialized an4 very- skilled personnel? as well as comprehensive safely measures./

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39* Taking all this into account it is obvious that nuclear power plants

are not yet suitable for African countries and that their power demand can

"be met more economically "by conventional power plants rather than by nuclear

stations*

Special plants .

40. Recently, attention has been focused on the utilization of additional kinds of generating power and harnessing new power resources. Most of the developed countries will exhaust the water power they dispose of during the next 10-15 years and they urgently need to prepare, besides conventional and nuclear plants, new kinds of energy resources like tidal or geothermal

energy. In developing countries the conventional sources of energy are

hardly touched and the utiliaable potentials are enormous, quite adequate to meet the largest programmes of development for a considerable time.

41. Accordingly, there is no urgent need to seek new kinds of energy or consider special plants for general electrification. Partner, special plants

using geothermal, solar, wind of other unconventional primary energy have very particular features, including some unfavourable characteristics,

speoially as far as the intensity factor is concerned. Besides they are more pr less in a developing stage. Therefore, they could, be taken into considera tion only in special cases and within a limited range* There are parts of African countries, particularly in remote and semi-desert areas, where such

special cases can be justified, as,for instance, the utilization of wind or solar energy for small plants for the supply of water for population, livestock and irrigation, or for energy supply for cooling purposes in refrigerators and the ike. The power of such special kinds is limited to

several hundred kilowatts only,

Alternatives and their appraisal

42. It is very seldom that only one kind of electric generation will be feasible and a correct decision is essential. The choice of the kind of electric power plant is closely connected with and depends on the size, i.e.

the estimated consumption demand as well as the fundamentals of the layout

of the plant,.although for practical reasons they are reviewed in the paper in separate chapters. The planning of a new power plant of any great

capacity involves decisions that affect the national economy, in many sectors although they may "be partly or entirely "beyond the control of the persons responsible for energy supply* This fact should "be stressed, the. more so as it is often ignored when new investment programming for electricity supply is "being drafted and new projects analysed and selected* The point is sometimes under-estimated or overlooked even in countries introducing s.

planned co-ordination in economy development; thus missing the opportunity of energy supply "balance on the basis of planned demand pro jection0

43. No attempt is "being made here to analyze the subject as a whole,

"because it is "beyond the scope of this paper. The aim is simply to emphasize the interdependence existing "between considerations of new power plant, en the one hand,and the energy development policy and the economy policy of the country, on the othor^ Accordingly, it ±3 advisable to include the . mutual effect; of these factors in any survey of new plant and to consider

the resultant effects.

44« When considering and deciding upon a power plant,the following factors

should be considered: .

(a) availability of primary energy resources, their quantity, kind

and situation? as wqll as eventual alternative priority allotment of a particular resource for another designation iii the economy: .

(b) estimated demand of electric energy- maximum load, variation in

load demand and form of load curves expected;, tentative size of the plant, load, plant, utilisation and power factors? etc.;

(c) investment cost and the ratic of foreign currency to local

expenditures;

(d) additional cost for transmission and transformation In respect of

the potential plant situation;

(e) availability of funds; foreign as well as local;

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Page 24

(f) cost of money, ±^ee interest rate, depreciation and loan

repayment and their share as fixed charges in the price of . :

. electricity; ■

(g) expected energy cost and the ratio of operating cost to fixed

chargesj

(h) maintenance requirements and physical lifetime of equipment;

(i) consulting, engineering, design and supervision and circumstances.

in whioh the work is to be carried outj

(j) degree to which the operation depends on the importation of

investments or on the fuel supply from another independent firm and consequently reliability of supply as well as the risk of

price fluctuation^ .-.-■_

(k) seasonal fluctuations and availability of resources, particularly

as far ac water is concerned; ■

(l) time needed for preliminary work and for the construction and,

commissioning of the project;

(m) possibility of extension of capacity at a later stage;

(n) skill of labour force, particularly for operation and maintenance

as well as technical supervision;

(o) interdependence with some other investment projects in view*

45» ^e evaluation of any contemplated variants of a future power supply should take these points into consideration. It is obvious that each kind of power plant would meet local needs in different ways, advantageously in some oases and adversely in others. It is seldom that any individual■

solution would offer the ideal answer to all the pointsj in most cases, the answer would be a positive and negative combination and it would be a matter of appraisal which compound of adverse influences to recommend as the most appropriate.

46. *»*> choice »urt toto iato aoooxmt ttf circumstances of the individual country and its economic policy, also the assumed rated output of the

plant. Priorities can to selected only in accordance with the evaluation of the most appropriate plant, particularly as far as its main characteristics

«.. concerned in regard to the economic policy and to the expected efficiency

of each individual case*

47. Investment prio* and operation; cost are factors of the utmost importance, therefore a special paper has been prepared on that topic as one of the

valuable contribution by the Economic Commission for Europej thus it is not necessary here to go into further considerations of the price and cost which

havevfceen fully dealt with-in a. separate paper, .

48. In conclusion, a few brief illustrative considerations are submitted not as exclusive guidance but more as suggestions likely to be acceptable.

49. Water power plant could,be advisable for any size of output, from the smallest to the largest, provided that natural circumstances are favourable, that there is sufficient time for preliminaries and construction and that considerable investment funds are available, It is advantagtous for a *ount*y which is anxious to employ unskilled people and thus increase the local

purchasing powerj it is advantageous as well for the policy directing

expenditures towards local currency, because in that case equipment makes up only 20-30 per cent of the cost, and operation of the plant is simple.

Hydro-energy is particularly useful in cases of multi-purpose application and if time is the only negative point it can be overcome by another provisional plant of limited size to fill the gap temporarily,

50. Diesel power plants are only appropriate for output, below 5*000 kW but in special cases they might be the best solution for plants of 10,000 -

15,000 kW if there is a critical shortage of wate* or if very urgently required or if after a few years a change to another area is envisaged, Diesels can also be recommended if a very low load for a few hours daily is expected. In the case where the country depends on the importation of oil, the balance of payment would not be essentially affected due to low fuel

consumption *

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Page,26"

51. Gas turbine would be advisable only in exceptional cases like, e^.

establishment in natural gas fields, in pipe line stations, oil refineriec, eventual iron works or" certain chemical factories, mostly if .the plant is in the range of'3,000 to 20,000 kW, obtaining thus a good..peak^ coverage ar.d

stand—by characteristics*. ■ : , .

52. Steam power plant is appropriate if the country tends to invest

considerably over and above its capital formation ueih'g:extensively foreign '■■-■■ - financial sources-;against the risk, of making local currency a bottleneck.

T^his method" oan .increase remarkably the rate of growth but requires projects

■:. ; with prevailing foreign exchange ratio. Steam power plant is just

* -appropriate sinoe, roughly 75r8O^eri cent of the investment is equipment cost, i.e. foreign deliverpr:.; If..that is not the cane, the 'steam-

. , , . plant.may be a good choice where local fuel is available, a possibility for cooling water"exists and a relffle pLower supply is required, particularly if the plant output^is in the range of 50,000 KW of ffiore-: with expected ' 'extension at abater stage. Tte erection of ■ a., ateam plant is a ^suitable :'J JVi policy also'if1 water-1 power'is available, but.it requires, a, number of years

' and ;should therefore be considered only as. an additional second electric

"plant o'ri'e 'decade later-. - ■ ■■■ - ...

~ *',■ ' . ■ ■..;*!

CHAPTER IV ■ '

■ ^ THE CHOICE OF SIZE OF POWER PLANT

Effects of the sige of the plant

53. The decision concerning the size of a power plant, or at least the selection of the capacity range, affects not only the considerations of

a kind and type selection, but is also of considerable consequence

regarding the operation efficiency and the influence on the economic life of the country. A forecast of the electric power demand and an estimate of demand are essential, of course accepting any reasonable

margin of error.

54. Both.the over-estimating and the under-estimating of demand have

unfavourable, repercussions, the important difference "being that the over

estimated error will be automatically lessened each year by an increase in demand, while the under-estimated will grow worse year by year due to the same reason. Therefore there is a good reason to believe that the average error cost of an under-estimate is higher than that of an over-estimate, particularly as regards the economy as a whole. According ly a value higher than the average would be the most advisable target for capacity selection, particularly in the case of a developing country.

55. Consequences of over-rated capacity are higher total investment cost,.

i.e. waste of money and a greater commitment of a country's financial

potential or foreign loans - thus influencing unfavourably the financing of other projects - higher production cost and smaller profitability due to the lower load factor and higher depreciation, consequently longer

pay-off time.because of smaller instalments and larger total sum. On the other hand the over-rated capacity can contribute to the quicker development of the economy in the supply area, offering the advantage of.

abundance of energy, reliable supply, ample stand-by capacity and reserve which can meet a large increase in demand as well as some measures.for stimulating the consumption of electricity particularly by favourable tariffs.

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56. The under-estimated demand results in inadequate capacity. That leads to insufficient production, interruption of supply because of overload, prevention of peak-load by the application of measures to .;.

refuse a part of load? use of a scheduled svi-tch-off of selected areas thus depriving certain consumers of electricity^ administrative

circular order, for limitation of consumption, refusal of application submitted by potential consumers for new supply or extension, deterio ration in quality of electricity supply by disturbing variations in . voltage and frequency, etc. The general consequence of all that is the drop in industrial output by forced reduction of capacity utilization and the restriction of overall development due to the shortage in

energy.

57 • Therefore, assuming that the electricity demand forecast reveals considerable uncertainty as to its future trend, it is recommended justifiably to prefer investment projects with a greater flexibility and designed to provide a relatively easy extension of capacity. Not only the tota^. electricity demand per year should be kept in view, but also the peculiar characteristic of electricity that it can not be stocked; it is therefore indispensable to follow exactly the daily load diagram and particularly to meet its critical parameters, i.e. the maximum load, the minimum load, a load pick-uu characteristic, and the area of the load diagram. It is advisable to exercise the greatest care in making a proper estimate of the parameter because of possible repercussions.

Influence by the dynamics of economy : ■

58. The size of a power plant., although an individual project, is not a separate matter but closely connected with the activity of the

economy in the supply area. The interdependence is particularly emphasized as far as all types of industry are concerned. The fact should be borne in mind that the demand for electric energy is not a

Tage 29

fixed value "but a function of a number of variable relevant factors.

Therefore it should not "be forgotten that the situation will be changing year by year, and that the difference should be taken into consideration, 59. Consequently the size of the contemplated power plant must be in accordance with the expected increase in demand, taking into account

that the availability of volume, conditions and price of power supply

can have considerable influence on the demand, accelerating the increase

in consumption if they are favourable. As it has been stressed before,

the trend in developing countries can be much over the usual average.

60. The choice of the size for a future plant requires a careful

analysis of the forecast for the next 10-15 years, on the basis of which

not only the size can be adequately assessed but also the point at which the chosen capacity will cover the curve of consumption increase.

If the capacity meets the consumption curve before.the selected point,

that means that a shortage in power supply will arise after the break

even of the selected former capacity or change in timing, when the next capacity will.be available in addition.

61. The latter is in a sense limited, because the timing could be shortened only to a reasonable extent since the preparatory work and construction take time and it is therefore important to start the planning and execution of the work a few years in advance, so as to

provide new capacity to cover the demand beyond this break-even point.

In the countries with an overall economic planning the appropriate points should necessarily be included in the plan.

Definition of the size of power plant

62. Plant capacity can be assessed on the basis of the assumed level

of production and of the expected load curve pattern for a certain

selected year in the future. The plant must be able to carry out

smoothly and without interruption the full assumed peak-load, which includes also the total losses at peak-load in production, transmission

'Page. 3*)

and distribution s.s well as the energy consumption of all auxiliary

equipment, ' ■■.■•■ .

63f To meet that demand satisfactorily, i.e. the accomplishment of electricity generation, at 'the full ]>v.dT. isi': rrlv.nt shuuld h:\ve1 in opera tion'generating sets --a"■.]-.■ "?. tot-^i constant r ■-■-'.■.-... output equivalent to the peak-load, retaining the short-tame overload capability to meet any

unexpected requirement by the consumers, to admit the engines governor full sensibility to keep up and the exciter to affect the.generators to sustain any -disturbance cj::d thv.3 the 71 --tV J-r r.+-M$ in f ul fl running with adequate steady and transient stability*

64. The total- size of -the plant can be determined on the basis of the output of running generating sets Tor the peak-load and the rated

■capacity of the additional generators out of operation either as stand by capacity or for the purpose of maintenanceP Hie ratio is indicated by the "utilisation factor" of the plant which measures the use made of the total installed capacity at the peak-load shown as follows:-

,.,'.■ ,. j, ' , peak-load utilization 1 actor »

plant capacity

65* The utilization factor for a plant depends upon the kind and the type of system- accepted for the plant in considerations .and particularly upon the plant lay-out, since a stand-by set .capacity depends definitely upon the division of the total capacity, That problem is discussed in the paragraphs 104.and 145• Generally the utilization factor will be better in the case of a water power plant or the plants envisaged as a part of an inter-connected system, with the exception if the plant is used only for stand-by purposes in a system or if uhat capacity has been installed well in advance of need. In the case of isolated plants a high-value means the likelihood of good detii^ .,1 Lli j-eu. reserve-capacity allowance.- The high value mea^ifj the. over-rated capacity or some extre mity in-plan? lay-out;, which is no t. necessarily a mistake by itself,

Page 31

since it depends vary much upon the consideration of specific relevant factors and perhaps the adopted evaluation of one of them as the

prevailing one, . , ,

66, For a new isolated plant a well balanced utilization factor is advisable within limits 0,75-0,66 or in the worst case 0,60. In an inter-connected system it can be 0,80 or even better, particularly for base load plant and if water power is used for generating,

,, .. ..^

67.• The total power plant size would accordingly be fixed by the following equation:

j. -, -, 3 -4. peak-load

installed, capacity - wtili£ation faotor

68, In African countries there are considerable variations in the

utilization factors as a result of operation experiences. The following

table gives a few' figures for the year i960.

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Table 5,

Utilization factor in selected African power plants

Plant Kind of

plant

Peak load kW

Installed oapacity kW

Utiliaation .factor

Francqui (Katanga) Bia-Koni (Katanga)

Tangier

Salisbury :„.

Tananarive

Benghazi Capetown Johannesburg Accra

Lagos Or an

Sekondi (Ghana)

Lusaka Alexandria

Bloemfontein (South Africa)

Khartoum

Lourenco Marques

Brazzaville Bangui

Tema (Ghana)

water water diesel steam .diesel + .water

diesel steam steam diesel steam steam diesel steam steam

steam steam + diesel steam + diesel water water diesel

62.500 36.000 9.280 113.800 9.600 4-500 232.400 420.000 11.700 27.000

49-674

4.820 12.100 50.200

40.800 17.450 9.500

2.500 950 1.200

70.000 44*000 12.000 150.000 12.780 6.150 325.000 590.000 16.800 40.000 102.750 7.200 19.000 85.OOO

82.500 36.000

25.800

7.500 4.000 5-270

0,89

0*82

0,77 0,76 0,75

0V73

0,71

0,71

0,70

0,67

0,66 0,66

0,64

0,59

0,50 0,48

0,37

0,33 0,24 0,23

69. Naturally the utilization factor changes in day-by-day operation according to the change of peak-load. If the change of peak-load over a year shows distinct seasonal or other periodical variations, it is advisable to check accordingly the expected operation of the plant as well as the plant feature for that case. It is also advisable to re- examine the size of the plant and the utilization factor in the light of a plant lay-out selected later. Also consideration of plant

operation at the minimum load should not be omitted.

Peak-load for the plant under selection

70. It is obvious that the peak-load is a prevailing factor when deciding upon the size of a new power plant. The peak-load depends on the capacity of all individual consumers connected at that moment, i.e.

of the total absorption power of all devices of each particular consumer which run at the same time and consequently to thsir load. Since all the connected units never run at full load at the'same time the ratio of maximum demand and connected load is characterized by equation:

, , _ , maximum load demand factor = connected loadt—t—77—r

71. The demand factor for utmost of industrial plants is in the range.' of 0,50-0,75, for few as high as 0,80; yet. for the non-industrial con sumer mostly between 0,40 and 0,60. In addition there is the advantageous influence of the peak diversity factor, due to the fact that the peak demand of various consumers does not occur just at the time of peak- load of the plant. The larger the supply area and the greater the number of consumers, the better the influence of the peak diversity

factor in a sense of moderating the peak-load of the plant. The analyses can" be done more accurately on the basis of particular load curves of the most Important individual consumers, while for rough assessment the effect of the peak -diversity factor can "be assumed at 2—30 per cent

of the system full load. ' ■ ■

72. Of considerable^advantage for/ a .study of a future power plant is the diagram of the load-duration curve, which in fact is a simple

E/CU.14/EP/5

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re-arrangement'of all the load elements of a chronological' curve to the time a particular load lasts in one day and in the order of descending

magnitude. The criterion of plotting for the construction of the load-

duration curve from the chronological load curve, makes the abscissa at

any load ordinate on the chronological curve, and the beginning of the graph is at 0 hour with the peak load of the actual load curve. The areas under the load-duration and the corresponding chronological curves are equal, representing on an adequate scale the total production of energy in 24 hours. In practice the procedure is usually simplified and

the often violent fluctuations or at least considerable variations are

made smoothly by half of an hour average approximation, therefore the area will generally be two or three per cent different from the measured energy production.

73. The load curve area, i.e. the total energy production of the day (the same method can obviously be applied for a period of a week, a month or a year), if transfigured in a form of rectangle would represent in its height (ordinate of' -the graph) the average load for the day,

respectively week, month or year. If the plant were to operate on this load continuously without variations over .the time, in that case the total energy production would be the same .as represented by the area of the actual chronological load curve,

74* It is possible by means of the average load for a selected period to calculate two factors that are useful for analyses of a plant

operation or for comparison of efficiency between individual plants or power systems. These factors are the "plant factor" and the "load factor".

75» The plant factor which is also termed "capacity factor", or "use

factor" shows the extent of use of the generating plant, i.e. the use of its total installed capacity. This factor is defined as

plant factor = averse load

plant rated capacity

76. If during the period under consideration the plant operates'on full load, i.e, it is used to the maximum extent technically possible, the plant factor will be 1.0 which means'100 per cent. If the plant is out of operation, for example as stand-by or due to maintenance work, the plant factor, would be zero per cent, .

77. The-load factor indicates the .degree of variation of the load over . a period of time in consideration. In a sense that is a measurement of the fullness of an actual chronological load curve, since the load factor measures variation only and does not give any indication of the precise shape neither of the chronological nor of the load duration

curve.

78. The load factor is defined as

average load load factor = peak_load

The load factor can follow the variations between one as the best and zero as the worst possibility. As the load factor approaches zero, that indicates a peak-load of very short duration with very low or no load during the major part of the operation time. As the load factor approaches one, it indicates a high sustained load, i.e. very good

utilization of capacity. If it reaches unity that means that the maximum and average loads are equal and that the plant runs the whole time at full load, a case that happens very seldom and only in interconnected power systems. Plant factor and load factor would become identical if the peak-load of the plant is equal to the capacity or the plant and the

operation is completely without any reserve.

79. There is another factor which can offer additional help in plant operation analyses or comparisons. That is the "average time of use" or the "utilization time" indicating the number of hours needed for the plant to produce the same energy covered by the load curve if the plant

were to operate continuously at peak-load.

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80, Accordingly the utilization time is defined a^

x-i- j.- x- ^o^al energy generated utilization time = - . °* "

peak-load

The utilization time is ciphered out in numbers of hours per year* In the following table a few examples of African power plants are available as illustrations referring to the operation records of the year l°60;

Table 6

The 1 for

Tema (Ghana Freetown

Blantyre-Zomba

Ibadan (Nigeria) Sekondi (Ghana)

Tangier

Lourenco Marques Lusaka

Luanda Khartoum Accra

Mombasa (-Kenya)

Lagos

Dar es Salam

Bia-Koni (Katanga)

Nairobi

Francqui (Katanga)

oad factor and a few selected

Total production fcWh in I960

4,800.00,0 20,883.110 25,871.686 ■

27,513.837

28,345*000 20,407.600 40,665,500 50,000*000 60,000.000 73,622.000 76,417.000 79,674*620 125?219.91O 154,836.676 158,600.000"

258,372.360 326,650.000

Bulawayo (S.Rhodesia) 334,197.900 Owen Falls (Uganda)

Salisbury

396,500.000 502,982.000

Port Elisabeth (South Africa)

Capetown Marinel-Zilo

(Katanga)

Johannesburg

507,690.111

836,496.434

1,114,000.000 1,615,654.272

the utilization time African power plants

Average load kW

550 2.380 2.960 3.140 • 3.230 3.460

4.58O'

5.700 6,850 8.400 . 8.7OO 9,100 14.300 17.550 18,10*0 29-500 37.300 38.100

45.200 57.300 58.OOO 95.7OO

127,000 I84.OOO

Peak load kW

1*

4.6.

6.

4- 9.

9.

12.

9.

17.

14.

14.

27.

32.

36.

52.

62.

72.

62.

113.

115- 232.

205.

420, 200 570 500 520

820

280

500 100 800 450 950

803

000 033 000 560 500 600 800 800 ,900 ,400

,000 ,000

Load factor

0,46 0,52 0,46 0,48

0,67 0,37 0,48

0,47 0,70

0,48 0,58 0,67

0,53 0,55 0,50 0,560,60 0,53 0,72 0,50

0,50 0,41 0,62 0,44

Utili zation time hours

4.

4.

4.

4.

5-

3.

4- 4«6,

4-

5.

5- 4.

4.

4.

4- 4.

5.

6.

4.

4.

3

5

3

000 570 000 210 ,880

— (•"i <-.

2oO ,210 ,120 ,110 .230 ,110 .340 ,650 ,840 ,410 .920 .240 .600 .300

.400' .390 .

.590 .420 .840

81. In the above mentioned table, to make the illustration as clear as

possible, the examples have been selected from very small up to very

large plants. The plants are listed according to the size of total

Page 38

production.

Problems of low load and minimum capacity

82. Since a part of a daily load curve shows usually very .low power

demand, the analyses of. a contemplated future- power plant should take into consideration also the run at low load. It goes without saying

that the overall efficiency at low load"operation will be less favourable, the percentage of losses and the percentage of internal power consumption for the plant auxiliaries considerably higher.

83. Apart from that rather economical aspect created by the impossibility

of electric power'storage so that such machines do not provide the most "

convenient operating conditions, there are purely technical aspects which have to be overcome, such as extensive cooling of individual parts,

problems of governor sensibility, the maintaining of stability in

continuous low load operation and unexpected transient changes, unfavour able power factors and inconvenient reactive components, particularly unpleasant at quick fault clearing, excitation system response and oscil lations of voltage regulation, overspoed out-of-step operation, etc.

84. Some of the points are more apparent mainly in water power plants

and some in thermal plants, yet anyway they have to be taken into consi deration seriously and if necessary certain measures should be taken in plant design to meet the problems imposed by low load.

Reserve capacity

85. Since the sustained and uninterrupted electricity supply is the top ■

priority requirement, each isolated power plant and each power system' must have 'reserve 'in capacity, for it is proved by experience that no.

machine is s0 dependable that it can-at all times be relied upon to ■"be- in operating condition, and particularly for the rated output, when it is wanted to be available for service, which in the case of electric power

plant is 100 per cent of the time. . ,