NORTH-WESTERN CENTRE: CHAIRMAN'S ADDRESSBy E. T. NORRIS, Member.*

"DESIGN"

(ABSTRACT of Address delivered at MANCHESTER, 1st October, 1946.)

I should like first to express my appreciation of the honour ofbeing elected Chairman of the North-Western Centre. I havebeen a member of the Centre for many years, so that my interestand concern in its welfare are of long standing.

In searching for a subject it seemed to me that it should haveas wide an appeal as possible and should be based on as muchpersonal expeiience and knowledge as possible. My choice was"Design"—an essential feature of all engineering production, rang-ing from the individual design of heavy engineering work to theoriginal design of mass-produced and standardized components.

I propose to discuss primarily, not the technical or intrinsicproblems of design, but the chief relations of design to otheraspects of production and operation, particularly specification,construction and application. My remarks are not addressedto designers as such. My chief aim is to discuss aspects of designwhich I think may be of interest and importance to purchasersand users of electrical apparatus. Although some of us may bedesigners in particular, we are all purchasers and users of someforms of electrical apparatus.

To simplify the discussion, I will take as a basis or referenceline, the academic type of design, i.e. a design based upon tech-nical, as distinct from practical, considerations. Such designis essentially theoretical. In application its principles are modi-fied and occasionally obscured by practical considerations, whichI shall consider. This line of approach is, I think, suitable,because many engineers on the supply and operating side ofengineering have in their minds such an academic picture ofdesign. For example, simple theory shows the cost of an articleto be the cost of the material. Practical influences frequentlyobscure this simple relation, so that a decrease in cost of materialmay increase the total cost and not decrease it, although thelabour cost is unchanged. The argument that it must be cheapersince there is less material in it is, I think, natural and plausibleenough to justify this study. It is certainly frequent enough.

For adequate treatment still further qualification is needed,and for that reason and also to avoid extra-mural complications,I shall bear in mind the fact that we are essentially engineers,and shall exclude political, financial and commercial aspectswhich do not have a direct relation to the engineering problem.Now engineering essentially includes consideration of cost, sinceit is the engineer's business to achieve the technical performancerequired as economically as possible. It is therefore necessaryto consider cost, but I hope to avoid the complications just

. referred to by distinguishing carefully between cost and price.This restriction will not affect the practical soundness and valueof the conclusions reached.

BASIC PRINCIPLESBasically the design determines the structure and composition

of the apparatus. In a manufacturing organization it is thedesigner's business to tell everyone concerned what to do: to tellthe commercial department what to offer to the customer; totell the production department what to make. It is not essentiallyhis business to tell them how to do it, or to see that they do it.That is the responsibility of the respective managers and foremen.

• Ferranti, Ltd.

The designer's work thus falls into two divisions: before theorder is received or manufacture is decided upon, to give technicaland estimating instructions to the sales department; and after theorder is received, to issue manufacturing instructions to the works.

The design itself may start at any stage. However, beforeeither of these objects can be achieved, the designer must acquiredetailed knowledge of the desired form and performance of theapparatus. For this purpose intimate contact is required, notnecessarily with the purchaser, but certainly with the user andoperating engineer. For apparatus sold direct to the public, thedesigner, as a member of the public, has his own individualexperience, but for the bulk of electrical engineering apparatusthis direct contact is not normally made. Now contact with thecustomer is essentially the business of the sales engineer. Infact, the intimacy and exclusiveness of this contact is commonlyregarded by him as a measure of his competence and is a prizedpersonal asset. Consequently, contact between the designer andthe user tends to be indirect via the sales department. This is,in general, inadequate.

Starting now from the academic basis, the theoretical part ofthe design will involve the application of fundamental laws—thermal, mechanical, electrical; for example, Ohm's law and thelaw of electromagnetic induction. A knowledge of theseprinciples and of the electrical and physical constants of thematerials is sufficient for the academic or theoretical design.It is from a mental picture based on this type of design that manyof the criticisms and arguments relating to industrial manu-facture and practical production are made. There are, however,many qualifications to this academic design, some of theminherent and some imposed by extraneous practical considera-tions. It is these I propose to consider.

Dealing first with the inherent qualifications, the theoreticalformulae can usually be analysed either by trial and error or bydifferentiation to indicate certain optimum proportions, such asthe armature dimension ratios in a motor or the copper/ironrelations in a transformer. These analyses are responsible forsuch statements as: the no-load losses should equal the loadlosses; or the cost of iron should equal the cost of copper. Itshould be realized that in practical engineering the importanceto be attached to mathematically optimum relations depends,not only upon the accuracy of the calculations, but inverselyupon the flatness of the curve connecting these relations. Inother words, the importance of zero value of the first derivativedepends directly upon the second derivative.

It is generally found that, although the mathematical optimumvalue may be as calculated, wide departures from this optimumhave little practical effect and are frequently justified by otherconsiderations. I would suggest that purchasers of apparatusshould refrain from insisting upon mathematically optimumrelations. An example is the specification of a particular ratioof losses in transformers and motors, or that maximum efficiencyshall occur at a particular load. Another instance is the specifi-cation of optimum total capitalized value of the first cost plusthe running or operating costs.

A comprehensive theoretical analysis frequently involves thehigher branches of mathematics and correspondingly complicated

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92 NORRIS: NORTH-WESTERN CENTRE: CHAIRMAN'S ADDRESS

formulae. This applies particularly to apparatus that is eithernew itself or intended for new applications. These generalformulae must be used until sufficient practical experience isobtained to set limits to the parameters involved. When this isdone comparatively simple formulae can be derived havinglimited application for a given range of parameters. Thesetheoretical analyses are also apt to lead to extreme conclusions,since their limits generally occur with parameter values of zeroor infinity. In fact, in order to simplify the problem sufficientlyfor mathematical expression, certain factors are frequentlyignored by assuming them to be zero or infinity, whichever is"on the safe side." Now in practical engineering zero andinfinity never occur. For example, no conductor has zeroresistance and no insulator has infinite resistance. Incidentally,the familiar square-paper graphs with arithmetic scales are oftenmisleading in this respect. The focus of this system—literally theorigin—is the zero point. This point is, from this aspect,imaginary, and the region all round it is distorted to give it theappearance of realism. Logarithmic charts are better in thatthey have no place for zero or infinity.

Hence, in practice, conditions are never either so good or sobad as the theoretical analyses would indicate. We are wellaccustomed to realizing that results will never be so good astheory expects, since this is an imperfect world and the ideal isgenerally unattainable. But T do not think we realize sufficientlyhow, fortunately, the converse applies. As a typical example,star-connected transformers and auto-transformers have been ingeneral satisfactory use for 40 years or more. The recent de-velopment of symmetrical-component mathematics has permitteda practical mathematical analysis of this problem and indicatesthe presence of alarming stresses under certain fault conditions.Now if this theoretical analysis had preceded the application,it is doubtful if star-connected transformers would ever have beenused, but fortunately, practical experience came first and has shownthat the extreme values indicated by theoretical analysis do notoccur in piactice, or at least only under exceptional conditions.

Assuming now that the technical information for design isavailable and that the desired form and performance of theapparatus are known, design calculations cannot be commenceduntil safe working stresses, electiical, mechanical and thermal,have been established. These will be derived from the ultimateor breakdown stresses, the connecting link being the factor ofsafety. It is surprising how frequently the actual or statisticalvalue of this factor is not definitely known, the design valuesbeing on a qualitative basis, depending upon whether the producthas proved sufficiently or insufficiently satisfactory in service.The factor of safety is, consciously or unconsciously, made up offour components:

(a) The incompleteness of the designer's technical knowledgeand experience.

(b) The variability of the material and labour employed.—It isnot possible to predetermine with exactness the technical per-formance of most machinery and apparatus, owing to disturbingfactors over which the designer or the manufacturer has nocontrol, such as variations in the quality of the materials usedand irregularities in construction and assembly. Statisticalanalysis of component items of both material and labour in themanufacture of apparatus has been developed lately in the formof quality control. By reliable inspection and measurement themean or average value of any given characteristic can be deter-mined, but for the reasons just stated, these values will be subjectto variations more or less serious and governed by the vagariesof chance. The probability of these variations is indicated bythe standard deviation.

For apparatus in mass production, the probability distributioncould be determined by a direct analysis of performance fpr each

product. This direct method is not applicable to most engineer-ing machinery, since the quantitative production of identicalunits is too small. This difficulty can be overcome by expressingthe measured value in terms of some common reference or specificconstant or of deviations from a standard formula or curve. Ina recent paper* I discussed details of this process and describedpractical methods for deriving appropriate values of designinstructions and performance guarantees.

(c) The variability of operating conditions.—In certain casesoperating conditions can be closely defined within narrow limits;for example, an electric motor driving a refrigerator. But inmost applications the operating stresses aie not so closely knownand frequently involve degrees of severity depending upon theparticular service conditions; for example, transformers in trans-mission and distribution circuits are subjected to normal-loadoperating conditions, temporary overloads at times of peakdemand, emergency overloads due to failure of other apparatusand finally fault or short-circuit condition. There seems no wayof expressing this overall performance quantitatively or statisti-cally, and the general effect upon the factor of safety is a matterof judgment and discrimination.

id) The manufacturing standard or reputation of the makerconcerned.—This is, in effect, a margin for repute and standing.Here again, the effect on the factor of safety cannot be quantita-tively established, but is a matter for judgment and discrimination.

Before detailed design can be attempted, it is necessary toselect the general type of system or method, and there arefrequently several alternatives. In established applications,operating experience has determined the relative merits andparticular advantages of each alternative method; i.e. the decisioncan be made objectively. For new fields, however, this experi-ence is missing and the choice is frequently clouded by con-troversy largely subjective and influenced more by creed than byanalysis. Historical examples are the d.c./a.c. arguments of the1890's; the rival claims of core and shell construction for trans-formers, in which, for many years, manufacturers took sides.Even to-day a similar atmosphere surrounds problems such as elec-tronic versus electromagnetic operation and the various systemsof earthing or non-earthing. Time and experience will eliminatethis conflict and establish the respective fields of application.

The extraneous influences on design may be convenientlygrouped under the headings: production, commercial and opera-tion considerations.

PRODUCTION QUALIFICATIONSThe limits set by the characteristics of the materials available

are mostly obvious, and, in general, physical constants are wellknown. A further limitation is set by the standard sizes andqualities available from the suppliers. A still further limitationoccurs where a smaller variety of qualities or sizes is stockedby the manufacturer himself in the interests of quick delivery.Apart from the supply of comparatively raw materials, manu-facture may involve castings, mouldings or pressings requiringexpensive tools and therefore produced in relatively few sizes,each covering a considerable range. Moreover, the productionof a range of apparatus usually involves a series of frame sizesproportioned in geometrical progression. In general, there areusually abrupt increases in cost in changing from one frame sizeto the next higher, and, although these steps may be ignored andthe average considered in general production, cases may arise ofparticular orders for large quantities or standardization ofparticular sizes in which this is a consideration and affects thedesign. The restrictions involved are usually apparent.

The limitations due to labour considerations are more com-plicated and severe and, at the same time, less rational, since the

* "Performance Guarantees," Journal I.E.E., 1946, 93, Part II, p. 140.

NORRIS: NORTH-WESTERN CENTRE: CHAIRMAN'S ADDRESS 93

human element is involved. Although wage rates and labourcosts may be accurately known, they are the result of labour andtrade union discussions involving a compromise of many interestsand many points of view, so that the resulting agreed rate maybe, and usually is, a considerable distortion of the originalrational intentions. For a range of apparatus where the type oflabour changes from boys or girls for the smaller sizes to skilledmen for the larger, there are sudden jumps in cost. These maybe averaged for normal production, but a particular design formass- or large-quantity production or for standardization maywell be affected by this factor. For example, it may be arrangedthat armatures using round wire up to a certain size are woundby girl labour and the larger sizes by men. Tn particular ordersfor large quantities on the border line the design may be corre-spondingly affected.

The last item to consider under the heading of production isoverhead cost. This is the amount to be added to the directmaterial and labour costs to give the total cost, and is usuallyexpressed as a factor of either material or labour or both. It isa matter usually of surprise and frequently of suspicion to usersand purchasers of apparatus to find how large these costs are, forthey are generally much larger than the direct labour cost. Theydepend among other things upon the ratio of mechanical to humanlabour, so that large values may well be justified or even desirable.

This is not the time for a study of overhead allocations—acomplicated subject not free from controversy. So far as designis concerned, the elements of arbitrariness in the allocation andthe necessarily broad spread over a range of products frequentlyaffect individual design considerations, particularly where theratio of material to labour can be controlled by the designer.

COMMERCIAL QUALIFICATIONSThe most obvious effect of commercial considerations is to

set a standard for most attributes of the apparatus concerned,including technical performance. These values are, in general,well known. It frequently happens that particular attributes ofthe products of individual competitors, whether of performanceor of application, may necessitate modification of the design inthis particular respect. Alternatively, the competition may bemet by attractive features in other directions or the general levelof performance may be regarded as sufficient. The first two ofthese solutions will of course affect the design.

Where standard price values and performance data have beenestablished, the information is usually recorded in tables coveringranges of characteristics such as rating, voltage, current, etc.These will have been derived originally from technical considera-tions, but before publication it is usually felt that they shouldprogress in sequence or "line up" for every combination ofvariables. This 1 elation must obtain vertically and horizontally andpossibly diagonally in every table, and also through correspondingpositions of a series of tables. The adjustments resulting fromthis rationalization will usually affect the original design values.

Commercial pressure will influence the values to be guaranteedfor the technical performance. The purpose of guarantees is toemphasize the performance of the apparatus and to ensure theresponsibility of the manufacturer for the relation betweenpromise and fulfilment. From a manufacturer's point of viewthe guarantee should be as good as possible in order to make theoffer technically attractive. It must be moderate enough tolimit the risk of rejection on test. In addition, the proportionof test results coming outside the guarantee must be reasonablysmall, or else the customer will feel that he is not getting value forhis money. On the other hand, a large proportion of lesultswell within the guarantee, whilst satisfactory to the purchaser,will be expensive to the manufacturer, and the guarantee willthen not do justice to the actual product.

It is usual to give guarantees subject to tolerances. Thesehave always been, and still are, a vexed question between manu-facturers and purchasers—partly because the purchaser naturallyprefers a definite guarantee, and partly because tolerances areoften associated with commercial astuteness or incompetence inmanufacture. Since the tolerances are primarily due to statisticalvariations in production, the ideal solution would be a statementof the mean expected value together with the standard deviation.No method, however, has yet been suggested of achieving thisend in a satisfactory manner. A guarantee together withsuitable tolerances gives the user a better indication of the actualperformance, a result in many ways fairer to the manufacturerand of more value to the customer. The effect of these con-siderations upon design is obvious, since technical performanceis one of the major factors.

The last item in the list of commercial limitations covers thequalifications introduced by the individual customer. This itemobviously does not apply to mass-produced articles sold direct tothe public. The qualifications are usually due to the purchaser'sendeavour either to improve the standard product or to avoidwhat he regards as undesirable details of design or construction.

A common instance is the prohibition of particular materialsdue to the purchaser's experience of an individual failure ordefect. Manufacturers know how widespread is this practiceand how restrictive in design it is for the heavier machinery whichis made largely individually. The design of every apparatusinvolves a compromise of several variables, usually intei dependentand frequently mutually contradictory. As a general practice, itis therefoie desirable for the customer to specify no more ofthese vatiables than is essential for the particular application.

For example, the stipulation of a particular value for thereactance of a transformer may complicate the design and isfrequently at variance with the desired efficiency and loss ratios.The purchaser's modification may consist in calling for moreonerous tests, usually in the belief that this will result in moreleliable apparatus. Until non-destructive testing has becomegeneral—and it is now in its infancy and very limited in scope—this piactice of abnormally increasing the severity of tests maywell fail in providing the assurance expected, even if it is notactually harmful. Cases have occurred where ihe design becomesa matter of providing sufficient strength to pass the test and yetleaving enough remaining strength for normal working condi-tions. I considered this aspect of the matter in detail in myAddress before the Transmission Section.* I might summarizethis Section by saying that the specification should essentiallystipulate what the customer wants, but not how it should be done,and should leave design and constructional details, as far aspossible, to the«manufacturer.

Apart from the general construction and performance of theapparatus, the designer may be confronted by demands for parti-cular features in appearance. This is especially so in attemptingan entry to a new market, whether at home or abroad. As anexample, many years ago, a line of distribution transformers wasintroduced into a foreign country where the engineers had beenused to octagonal tanks. The home production was standardizedin square tanks, but it was felt essential to make the change solelyin order that the apparatus would not present a strange appear-ance to the operating engineer. A similar case occurred morerecently where a change from square to circular shape was con-sidered advisable. One cannot generalize on such matters, sincein some branches of engineering a manufacturer would actuallyprefer his product to look different and thus possibly distinctive.

This hesitation over difference from the general product mayapply not only to external appearance. A constructional feature

* "Relations between the Manufacturer and the Purchaser of Electrical Equipment,"JournalI.E.E., 1946, 93, Part I, p. 37.

94 NORRIS: NORTH-WESTERN CENTRE: CHAIRMAN'S ADDRESS

obviously different from the accepted standard may be unwelcomeon the grounds—not often openly expressed—that if it were adesirable feature it would not be peculiar to one manufacturer.This criticism does not apply, of course, to features which canbe patented. As an example, a method of on-load tap-changingin power transformers was developed many years ago, usingparallel windings. This method is very much simpler, is cheaperand, in my view, is much more reliable than the usual methods,and 20 years' experience has established it clearly as beingthoroughly satisfactory. However it failed to receive approval,on the grounds that there must be some snags in it or othermakers would also use it. There is some logic in this argument,and it should be met, the answer in this case being that theparallel-winding method essentially required a high-voltagetapping switch and it so happened that the switch, which hadbeen developed for other classes of work, was of this type.

All these direct influences of the customer vitally affect designand manufacture and interfere with purely technical and academicconstruction.

OPERATION QUALIFICATIONSConsiderations under this heading include installation and

maintenance as well as normal operating routine.Many of the requirements for installation will have been taken

care of in the original specification or even in the appropriateBritish Standard Specification. These chiefly refer to the inter-changeability or replacement of either the complete apparatus orof fittings or parts. A common problem is the compromisebetween ease of installation and cost or other characteristics.To the installation engineer the former is, of course, paramount,but since, in general, installation occurs only once, it may well bethat some sacrifice in convenience is justified here by, say, lowercost or more compact assembly. It should, of course, always bepossible to make the installation safe and reliable. As anexample, compactness apart from cost is a very desirable featurein feeder pillar or joint boxes, and may justify extra time requiredfor initial installation.

The importance of accessibility for maintenance depends uponthe life or reliability of the component concerned. To pointout the attractiveness of accessibility is frequently to make avirtue of necessity. For example, if the gear box of a motor carwere an unreliable component giving continual trouble and need-ing continual attention, we should probably find manufacturersmounting it on the running-board. As it is, the gear box isan established component of highly reliable performance and cansafely be installed in an extremely inaccessible position.

Facilities for maintenance must, of course, be provided toenable the apparatus to be kept in working condition, but thedegree of this will depend upon its nature. Dynamic apparatus,for example, needs more attention than static apparatus. Incertain cases, maintenance or servicing may become an overridingconsideration, an extreme instance being the maintenance byreplacement of the blades in a safety razor.

Perhaps the most important factor in operation affecting thedesigner is the cost of running or operating as distinct from theinitial or first cost. The total cost of operation, which should bea vital factor in the choice of apparatus such as motors, generatorsor transformers, includes the first cost and the capitalized costof the losses. It should be realized that maintenance is also arunning or operating cost. If it is possible to assess this costquantitatively it should be included in the capitalization.

From a choice of designs having different proportions of firstcost and performance, the design giving the lowest total capi-talized cost is chosen. This is essentially a problem for thedesigner. The correct balance of cost should be worked out

individually for particular cases, but for the normal standardproduction the design should be such that the best average com-promise is attained throughout the range.

The principles of capitalization are well established in theoryand are set forth in textbooks. But capitalization essentiallyinvolves expression of the future in terms of the present, so thatthe results can never be expressed with certainty nor even withmuch assurance. Thus, it is not the present running cost (unitcharge, maximum demand charge, etc.) nor the present loadingconditions (load factor, diversity, power factor, etc.) which shouldbe considered, but their respective averages over the life of theapparatus.

This criticism is one of degree and not of principle, since,although the future costs of generation and distribution may notbe known, they will certainly not be zero. Transformer losses,for example, will always be an important charge. The problemcalls for shrewd judgment and even political anticipation in thefinal choice, on the grounds that small relative deviations fromthe imagined future costs are justified by appreciable reductionin the first cost, which is not imagined.

If the technical and economical data concerned in capitaliza-tion were all accurately known and the capital resources wereunlimited, the optimum conditions of minimum total capitalizedcost could justifiably be chosen. But neither of these conditionsholds, and that part of the process which involves forecasting thefuture operating costs and loading conditions is fraught withdoubt. There is, however, no doubt about the initial cost. Onthe principle that a bird in the hand is worth more than one inthe bush, a certain saving of £1 in initial cost will be consideredworth more than an uncertain saving of £1 in capitalized cost.For example, a transformer costing only 70 % of the optimumvalue may involve a total capitalized cost only 2-5% more. Ingeneral, then, a transformer giving the minimum total capitalizedcost should not be chosen, but some alternative of lower first cost,the actual amount being a matter of individual judgment. Thisjudgment is expressed quantitatively as a "sagacity constant,"which may be defined as the amount to be saved in the initialcost of the apparatus to justify risking an increase of £1in the final nebulous capitalized cost. I have discussed thisaspect in detail in a recent paper.*

CONCLUSIONI have endeavoured to set forth some of the complications and

obstructions which are superimposed upon the purely technicaland theoretical considerations and result in a practical designwhich may be considerably distorted from the academic ideal.These disturbing factors are so many and so serious that it is notsurprising that the cost and performance of the apparatus con-cerned frequently seem to have little logical or rational relation-ship with the simple principles of design and manufacture.

As a broad generalization, assuming that modern methods ofproduction are employed, one should expect that any modifica-tion which interferes with the standardized construction is liableto cost more, even though the amounts of material and labourconcerned are less. This result, though not generally appre-ciated, follows naturally and logically from its inverse form—oneof the chief arguments for standardization—that cost per unit ofproduction varies inversely as quantity.

In conclusion, I should like to emphasize that throughout thisAddress I have been talking in broad generalized terms. WhilstI believe that the conclusions drawn are justified, there will, ofcourse, be numerous instances where some of them are discountedby particular individual circumstances.

• "Capitalization of Technical Performance," Journal I.E.E., 1946, 93, Part II,p. 137.