of The South African Institute of Electrical Engineers van Die Suid-Afrikaanse Instituut van Elektriese Ingenieurs

Transcription

1 VOL 73 ^LT 2 FEBRUARY 1982 FEBRUARIE 1982 The Transactions of The South African Institute of Electrical Engineers Die Handelinge van Die Suid-Afrikaanse Instituut van Elektriese Ingenieurs Research Note No. 6: Reduction of energy losses in magnetic bearings due to imbalance signals by G L Bredenkamp Faraday-Henry 150th Anniversary Commemoration: Address by G R Bozzoli SYMPOSIUM ON TELEMETERING AND TELECONTROL SvnODSeSRegistered at the G.P.O. as a newspaper Determination of the apparent movement of the sungeregistreer by die h.p.k. as n nuusbiad

2 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 how do you n measure it? 22! 9 GENERAL PURPOSE SOUND LEVER METER TYPE Accuracy to IEC R123. "Fast" and "Slow" meter damping, range dB(A). Lightweight, approximately 350 gram, large easy to read meter scale PRECISION SOUND LEVER METER AND OCTAVE ANALYZER TYPE Accuracy to IEC R179, A & C weighting network and linear mode. 10 octave filters with centre frequencies from 31.5 Hz - 16 khz. Ability PRECISION INTEGRATING SOUND LEVEL METER TYPE Reads Lea to ISO R1996, R1999.Thd sound level meter complies with IEC 179 and 179A. PEAK HOLD and IMPULSE facilities. 50dB linearly graduated meter scale. q, LoX and elapsed time e indicated on large LCD splay. Uses: termination of Leq for sessment risk of hearing ss or noise annoyance. vestigation of noise dose stribution versus locality d time NEW! NOISE DOSE METER TYPE 4428 is designed to be worn by personnel throughout a working day. The instrument will measure true accumulated noise exposure. Concealed or visable 4 digit LCD display continuously provides readout directly in percentage of allowable daily noise dose i.e. 100% corresponds to 85dB(A) for 8 hours. Leg with the aid of conversioniables. Dynamic range 80 to 140dB(A). NOISE LEVEL ANALYZER AND STATISTICAL PROCESSOR TYPE 4426 will read Leq directly in accordance with ISO standards. The instrument is suitable for the assessment of risk of hearing loss, and the evaluation of risk of noise annoyance, outputs for level recorder and alphanumeric printer. Battery or mains operation in one compact portable unit. General statistical signal level analysis of AC and DC signals e.g. flow, Briiel & Kjaer Please mention our Journal when contacting the above Company Sole South African Agents Sole South African Agents: TELKOR (Pty) Ltd. (formerly D&D Electronics Ltd.) 7th Floor, 192 Hendrik Verwoerd Drive, P.O. Box 50856, Randburg Telephone Johannesburg (011) , Cape Town (021) GREY-PHILLIPS. BUNTON. MUNDEL& BLAKE65948

3 Die Handelinge van Die Suid-Afrikaanse Instituut van Elektriese Ingenieurs Vol73 Deel2 Februarie 1982 Posbus 61019, 21O7 Marshalltown, Transvaal TELEFONE /4TELEGRAFIESE ADRES 'FARAD' ELEKTRIESE EN ELEKTRONIESE INGENIEURSWESE NATUURWETENSKAP EN TEGNOLOGIE INHOUD Standpunt 21 Navorsingsnota No 6: Reducing of energy losses in magnetic bearings due to imbalance signals deur G L Bredenkamp 22 Faraday-Henry 150th Anniversary Commemoration: Toespraak deur Prof G R Bozzoli 24 SIMPOSIUM OOR TELEMETING EN TELEBEHEER: Sinopses 28 Item of Practical Interest: Determination of the apparent movement of the sun cfeur H TAspinall31 NuusuitTak 34 Advertensie-inhoudsopgawe xvi Produksie-redakteur A WATERS Advertensie Bestuurder J B CROYSDALE Die kopiereg ten opsigte van alle materiaal wat in hierdie tydskrif verskyn mag aan die Instituut behoort en geen materiaal wat aan hierdie kopiereg onderwerpe is mag in geheel of ten dele gepubliseer word sonder die toestemming van die Instituut nie. Waar sodanige toestemming gegee word, moet 'n geskikte erkenning gepubliseer word in n vorm en op 'n plek soos bepaal deur die Instituut. Desnieteenstaande word toestemming nie benodig om abstrakte te maak nie op voorwaarde dat volledige verwysing na die bron gegee word. Enkelkopiee van materiaal waarvan die In stituut die kopiereg hou mag gemaak word vir doeleindes van navorsing of privaatgebruik sonder verwysing na die Instituut. REDAKSIE GROEP Ereredakteur Grant A Park Ereassistent-Redakteurs E J Davison LH James Prof J P Reynders Prof JD van Wyk Eremederedakteurs D H Mills Prof JD van Wyk Prys per exemplaar: Lede R1.75. Nie-lede R2,00 Uitgegee deur L H James Prlng, BSc(lng) (Witwatersrand), FSAIEI Prlng, BSc (Lond ext) (Leicester) FSAIEI Prlng, BSc(Elek) (Natal), FSAIEI Prlng, BSc(Eleklng), PhD (Witwatersrand) MSAIEI Prlng, BSc(lng), MSc(lngMEIek) (Pretoria), DrScTechn (Eindhoven), MSAIEI (Pasuitgetrede President), Prlng, BSc(Elek Ing) (Witwatersrand) Prlng, MSc(lng) (Elek) (Pretoria), DrScTechn(Eindhoven),MSAIEI (Voorsitter Navorsingsreferate Komitee) Prlng, BSc(Elek) (Natal), FSAIEI (Voorsitter Tegniese Program Komitee) Kelvin Publications (Pty) Ltd DERTIENDE VLOER, LONDON HOUSE, LOVEDAYSTRAAT, JOHANNESBURG. Posbus 2988, 2000 Johannesburg Tel Telegrafiese Adres: 'KELVIC

4 The Transactions of The South African Institute of Electrical Engineers Vol 73 Part 2 February 1982 PO Box 61019, 21O7 Marshalltown, Transvaal TELEPHONES /4TELEGRAPHIC ADDRESS FARAD' ELECTRICAL & ELECTRONIC ENGINEERING SCIENCE & TECHNOLOGY CONTENTS Viewpoint 21 Research Note No 6: Reducing of energy losses in magnetic bearings due to imbalance signals by G L Bredenkamp 22 Faraday-Henry 150th Anniversary Commemoration: Address by ProfGR Bozzoli 24 SYMPOSIUM ON TELEMETERING AND TELECONTROL Synopses 28 Item of Practical Interest: Determination of the apparent movement of the sun by H TAspinall 31 Branch Notes 34 Advertising Index xvi Production Editor A WATERS Advertisement Manager J B CROYSDALE Copyright in all matter appearing in this jour nal may vest in the Institute and no material subject to such copyright may be published in whole or part without the permission of the Institute. Where such permission is granted a suitable acknowledgement shall be made in the form and place determined by the Institute. Notwithstanding the foregoing, permission is not required to make abstracts on condition that a full reference to the source is shown. Single copies of any material in which the In stitute holds copyright may be made for research or private purposes without reference to the Institute. EDITORIAL PANEL Honorary Editor Grant A Park Honorary Assistant Editors E J Davison L H James Prof J P Reynders Prof JD van Wyk Honorary Associate Editors DH Mills Prof JD van Wyk Price per copy: Members R1,75. Non-members R2,00 Published by LH James PrEng, BSc(Eng) (Witwatersrand), FSAIEE PrEng, BSc (Lond ext) (Leicester) FSAIEE PrEng, BSc(Elec) (Natal), FSAIEE PrEng, BSc(ElecEng), PhD (Witwatersrand) MSAIEE PrEng, BSc(lng), MSc(lng) (Elek) (Pretoria), DrScTechn (Eind hoven), MSAIEE (Immediate Past President), PrEng, BSc(ElecEng) (Witwatersrand) PrEng, MSc(lng) (Elek) (Pretoria), DrScTechn(Eindhoven), MSAIEE (Chairman Research Papers Committee) PrEng, BSc(Elec) (Natal), FSAIEE (Chairman Technical Pro gramme Committee) Kelvin Publications (Pty) Ltd THIRTEENTH FLOOR, LONDON HOUSE, LOVEDAY STREET, JOHANNESBURG. PO Box 2988, 2000 Johannesburg Tel Tel Add KELVIC

5 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 21 Viewpoint ARBITRATION Arbitration as a means of settling disputes has a long history. It was provided for in Roman Law; is part of Roman-Dutch Law, and of English Common Law. It is also used in International Law. In South Africa it is today covered by the Arbitration Act (No. 42 of 1965). The main advantages of Arbitration as op posed to Litigation may be summarised as follows: (a)parties to the dispute can choose their own adjudi cators. (b)these adjudicators can be chosen for their exper tise in the area of dispute. (c)procedure can be informal and legal terminology avoided. (d)courts will not normally interfere with decisions which are final and subject to few statutory limi tations or constraints. (e)costs should be low and time should be saved. However, in recent years many arbitrations have been 'taken over' by the legal profession and have been held with Attorneys, Junior and Senior Counsel on both sides, under court procedure with verbatim records of proceedings transcribed and distributed to all parties. This has increased the cost to an extent that has led to criticism. In order to counter this tendency, interested parties have formed the Association of Arbitrators, one of whose principal objectives was to formulate a set of simple rules to enable parties to have arbitration without employing professional legal advice. This set of rules has now been published in both official lan guages under the English title 'Rules for the conduct of Arbitration'. Arbitrations held under these Rules should prove to be quick, low in cost, effective, and generally satisfac tory to all parties. It is suggested that contracts, where arbitration is specified as a means of solving differ ences, should in future, further specify that this be conducted in accordance with the abovementioned Rules. It is further suggested that where the Presidents of Institutes, or similar important persons are asked to appoint Arbitrators as is done in so many in stances they do so with the specific proviso that their appointees will conduct these arbitrations in accordance with these Rules. Such moves should remove the current criticism of Arbitrations and restore them as a rapid and effective means of solving disputes. N TroOSt, DSc(Eng), FSAIEE, FIEE (Past President) (The views expressed in this Editorial are those of the author, and do not necessarily reflect the views of the Council of the South African Institute of Electrical Engineers.)

6 22THE TRANSACTIONS OF THE S A INSTITUTE OF ELECTRICAL ENGINEERS February 1982 Research Note No 6 Reduction of energy losses in magnetic bearings due to imbalance signals G L Bredenkamp* MSc SYNOPSIS Cyclic displacement signals arising from rotor imbalance give rise to unnecessary losses in actively controlled magnetic bearings. A discrete notch filter that tracks the rotor rotation frequency may be used to eliminate these imbalance signals. Alternately the total displacement signal is sampled in such away that the imbalance signal component is aliased to appear as a dc component. In both cases the associated losses are eliminated. SINOPSIS In aktief beheerde magnetiese laers ontstaan daar tikliese verplasingseine agv wanbalans in die rotor. Hierdie seine gee aanleiding tot onnodige drywingsverliese in die laers. fn Diskrete keepfilter wat die rotasiefrekwensie van die rotor volg, kan gebruik word om hierdie wanbalansseine te elimineer. Alternatiewelik kan die verplasingseine op so 'n manier gemonster word dat die wanbaiansseine dmv aliasering as gelykspanningseine verskyn. In beide gevalle word die betrokke drywingsverliese uitgeskakel. Introduction It is virtually impossible to construct a high speed rotor system which is perfectly balanced I1). As a conse quence the rotor will tend to rotate about its centre of mass which does not normally coincide with the geo metric centre of that portion of the rotor from which the rotor position is sensed for the purpose of position con trol feedback. The position sensors would thus in turn give out a cyclic displacement signal which is synchronised with rotor rotation. The servo loop will thus constantly attempt to correct for this cyclic displacement giving rise to unnecessary losses in the system. This phenomenon is particularly eminent in the radial magnetic bearings. I Elimination of imbalance signals The frequency separation between the cut-off frequency required for the servo loop that will ensure a reasonable settling time and the lowest rotation frequency whereby the rotor is operated, is found to be rather small, typically about one half of a decade. This phenomenon makes a low pass filter impractical because a too steep cut-off will be required which will give rise to an associated ringing that will be quite unacceptable. The only practical solution seems to be the use of a sharp notch filter with centre frequency, coinciding with the rotation frequency. This centre frequency, however, will have to track the rotation frequency very closely. The latter requirement will be difficult to meet with any type of continuous time filter. A discrete time notch filter^2) which derives its sampling signal directly from the rotor will automatically track the rotor frequency. If at least two samples are taken per revolution the Nyquist criterion is automatically satisfied for the imbalance signals as well as the normal displacement signals which are normally assumed to be well below the rotation frequency. During run-up, whilst the rotation frequency traverses through the pass band of the servo loop, the sampling process may be disabled and the displacement signals allowed through continuously to prevent any aliasing. Since this run-up time will normally represent a very small proportion of the total operating time, the losses associated with imbalance during run-up will be negligible. 2 Discrete notch filter Assuming that two samples of the displacement signal are taken per revolution of the rotor, the sampling interval for the rotor frequency and consequently also the imbalance signal will be n radians per sampling inter val. A further assumption which is implied here is that the imbalance signal will be a pure sinusoid, which is not unreasonable provided that the rotor is machined circular at the sensors and the position transducers are fairly close to linear. Since the latter imbalance signal has to be eliminated a suitable notch filter is obtained by choosing a discrete transfer function H(z) which possesses a zero zx= \ and a pole px = a where a > 1 but close to 1 in the complex z plane. See Fig 1. COMPLEX -Z- PLANE ^Professor, Dept of Electrical and Electronic Engineering, Rand Afrikaans University, Johannesburg Fig I Notch filter pole-zero location.

7 February 1982 THE TRANSACTIONS OF THE S A INSTITUTE OF ELECTRICAL ENGINEERS 23 Thus H(z) = z + a (1) The corresponding difference equation for H(z) is Y(k) = X{k) + X(k -\)- ay{k- 1)(2) where Y(k) is the discrete time output of the filter and X(k) is the discrete time input to the filter. This filter is easily implemented by three sample and hold (zero order hold) circuits and one summing ampli fier as shown in block diagram form in Fig 2. The output of the notch filter for a discrete unity step input signal is given by Fig 4 Discrete notch filteifrequency response Y(k) ^ 1 + a + a Y(k) is plotted for various a in Fig 3. (3) interval where n = 0, 1, 2,... oo, and the rotation frequency corresponds to the case when n = 0, it is obvi ous that the fundamental component of the imbalance signal and all its odd harmonics will be eliminated. All the even harmonics corresponding to sampling intervals of 27r rad/sampling interval are abased and appear as a steady dc component. The nett effect of this dc signal will be to offset the rotor somewhat from its true neutral position. Most important however is that no cyclic displacement signal is generated and thus all losses associated with such cyclic signals are eliminated. YCk) l - Fig 2 Notch filter block diagram :,' \,- " -- _-.--^-..- ~.i ~< ~ ~ --.! parameter a Fig 3 Discrete notch filter step response 1520 sample no. (k) 3 Elimination of harmonics of the imbalance signal Since the above filter will totally eliminate all signals for which the sampling interval is (2n + 1)tt rad/sampling 10 4Alternate solution The above aliasing which causes the even harmonics to appear as dc signals suggests an alternate solution to the whole problem which is obtained by the simple expedient of sampling the displacement signal once per revolution instead of twice as above. This technique causes the Fourier components of the cyclic imbalance signal to appear as dc components simply because the sampling interval is now Inn rad/sampling interval. In other words the only addition required to be cascaded into the servo loop is a simple sample and hold circuit that is clocked once per revolution of the rotor. The price that has to be paid for this simpler solution is a factor 2 greater separation required between the maxi-^ mum frequency component of the true displacement signal and the rotation frequency, and the abovementioned steady (dc) displacement, which may be negligible in many applications, especially where the rotor is accu rately machined. 5References 1Bredenkamp, G L: 'Kinetic electric energy store for electric vehicles' (in Afrikaans). Electric Transport Symposium, SAIEE, CSIR, Pretoria, April 1979, pp S1-S17. 2Steiglitz, K: 'An introduction to discrete systems'. John Wiley & Sons, Inc, 1974.

8 24 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 Faraday-Henry 150th Anniversary Commemoration ADDRESS BY Professor G R Bozzoli* It is a very long time since I addressed a gathering of electrical engineers in this hall, and I must say that I experience pangs of nostalgia when thinking of the many memorable meetings that I attended here and the many enjoyable functions that my wife and I took part in. So when I was asked to speak to you this afternoon, I jumped at the opportunity of renewing old friendships and associations, always tinged with the sorrow that so many of them were with people who have now passed away. Although my address to you is by no means intended to be a service in memoriam, it is inevitable that if I am to talk about the growth of electrical engineering in South Africa I should be thinking about the men we knew who promoted and fostered its growth. However, the letter inviting me to speak at this function suggested an address 'of a lighthearted nature', and so I will content myself with re membering our many friends and associates of the past and believing that in spirit they are with us in this sig nificant year of the 150th anniversary of Michael Fara day and Joseph Henry. I puzzled a little about an address of a light nature. Could it mean a repeat of the things I said as first chairman of the Light Current Section in 1950 (now no longer current!)? Could it mean a talk about illumin ation in the twentieth century? or did it mean a kind of stag-party address with a few van der Merwe stories thrown in? Maybe, I thought, the answer lies in the reason why 1981 should represent the 150th anniver sary of Michael Faraday (1791 to 1867) and Joseph Henry (1797 to 1878). Let's try some arithmetic. If you take the average of their birthdates (which is 1794), and the average of the dates of their deaths (which is 1872), and then take the average of these two dates, you get 1833, and if you then subtract the number of people involved, which is two, you get 1831, which is exactly 150 years ago. Voila! The first electrical power installation in South Africa dates from 1881, when the Table Bay Harbour Board installed 22 arc lamps in the harbour, of candle power each, and this gives us another reason for choosing 1981 for celebration, the centenary of electric power lighting in South Africa. This is part of my 'light address', but I must still give pride of place to the light current chaps, because the first electric telegraph in the country began to operate in 1860 between Cape Town and Simonstown, and the first telephone ex change system in Port Elizabeth in If you now subtract the number of towns with telephone ex- * Past President, Honorary Fellow, Former Vice-Chancellor and Principal, University of the Witwatersrand. Presented at Kelvin House changes from this date, namely one, you come back to 1881, thereby firmly establishing 1981 as the year of years from three quite impeccable sources! Of course, electricity is somewhat older than any of these events, including Faraday and Henry and perhaps you will for give me if I do go back a little in history because there are some incidents in these early days of our science which are quite entertaining. I will skip over all the gruesome stories of Jove's thunderbolts because they were not recognised as elec tricity until Benjamin Franklin performed his experi ments some two hundred years ago, but it all began about two and a half thousand years ago, when the Greek philosopher Thales, who was born in the sea port town of Miletus in what is now Turkey, on the Aegean Sea, found that a yellow amber pebble, when rubbed, was able to attract small dry sticks and leaves to itself. The Greek name for amber is electron, and a thousand years later, in England, Dr William Gilbert gave the name electricity to the unknown force which seemed to collect on the amber pebble when it was rubbed. Dr Gilbert was a physician, and quite a famous one, because he was appointed 'Physician-inordinary' to Queen Elizabeth, whom we should now, of course, call Elizabeth the First. In this Shake spearian era, Dr Gilbert studied in Cambridge and Italy, and became the father of the science of magne tism. He did many experiments and wrote the first book ever, of the new science of electricity and magne tism. But he had no clear idea about electricity, and eventually came to the conclusion that it was an 'efflu vium'. Chemists say that an effluvium is something given off and usually detected by smelling. Presum ably, Gilbert had smelt the powerful odour of ozone, but I cannot believe that he really believed that elec tricity stinks! Enormous risks For the next hundred and fifty years many experi menters played around with electricity and magnetism, taking what we would now consider enormous risks in handling this power. During this time a certain Profes sor Muschenbroek of the University of Leyden de cided that electricity was not a smell, but a fluid, as many others had also come to believe. He was able to store it in a jar, the famous Leyden Jar, and one day tried to pour it from one jar into another, like water. In so doing, he grasped the charged surface of the jar and received a severe electric shock. He put it differ ently, however. He reported that 'the electricity in the jar had leapt out of the jar and struck him a fearful blow in the chest'! This might be described as the first electro-medical experiment, and the news got around quite quickly. When he heard of it, a certain Abbe

9 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 25 Nollet at the convent of the Carthusians in Paris de cided to try the experiment out on the troops as it were. What he did was to order all the inmates of the convent to come outside and hold hands in a line about a mile long. Then he connected his electric machine to the first monk... and made the intriguing obser vation that all the monks jumped half a metre into the air at the same instant. Through this experiment he es tablished two things, first that the electric effect trav elled at very high speed and second he established the first shock troops. At about the same time, Benjamin Franklin came on the scene, the first American to do so. He had re tired from his occupation as a printer (having been ap prenticed to his half brother) at the early age of 42 and began to experiment with electric shock. It seems that he enjoyed his little jokes by entertaining his friends by handing them a glass of wine which he had electri fied. He describes the effect as a shock to the lips but deplored the fact that the trick did not work very well if the drinker had a beard or moustache. His most famous experiment, however, was much more scien tific, and as we all know, it consisted of making a kite of silk and flying it during a thunderstorm. The wet string allowed the charge in the cloud to leak down to him and he was able to demonstrate that electric sparks jumped across the space from a key on the string onto his knuckle. No-one is quite sure how he got away with it, but his success in America inspired Professor Richman in Russia to try the same thing with Russian clouds. However, for once, it seems that Rus sian storms are bigger and better than American ones, because the unfortunate professor was struck dead. The next step was taken in 1780 by another doctor, Dr Galvani, who was also a teacher in the Medical School in the University of Bologna in Italy. While he and his wife were cutting up frogs for the usual repul sive experiments which the biologists love to carry out, he noticed that the frogs legs, when completely cut away from the animal, could be made to twitch when electrified. He concluded from this that electricity was not just a smell, nor even a fluid, but it was the very essence of life and he spent years of his life trying to prove this. He believed that the electricity came from the animal itself, and in fact he called it 'animal elec tricity'. This biological view did not go down at all with the physicists and Professor Alexander Volta, who taught physics in the neighbouring university in Pavia poohpoohed the theory, because he believed that the elec tricity came from the bits of metal connected to the frogs legs. Volta and Galvani spent years trying to prove the other wrong, and during these years, the French Revolution came and went, Napoleon came to power and finally conquered Italy. Galvani refused to submit to Napoleon and was dismissed from his post, eventually dying a poor man. Volta was completely disinterested in politics and simply went on trying to prove that Galvani was wrong. At last he succeeded by inventing the famous Voltaic pile, the first electric bat tery. The scientific world was thrilled by this invention and Volta was awarded every honour prizes, a title, a salary for life, and he retired to be a country gen tleman. It is interesting to speculate how things might have turned out if Volta had been the political animal and Galvani the one-track-minded scientist. Perhaps the most colourful figure in the story of electricity also lived at this time. He was Professor Ampere of the University of Paris, a mathematician who started life as a child prodigy. He was reputed to be able to do complicated sums before he could write and when he was thirteen he had read the twenty vol umes of the French encyclopaedia, and was able to re member most of it too. What a wonderful candidate he would have been for 'Flinkdink'! The Revolution hap pened when he was eighteen and he was so shocked when his father was guillotined that he never recov ered completely. He was the traditional absent-minded professor. He forgot to dress properly, his manners were, to put it mildly, forgetful, he used to wipe his face with the chalk-board duster, and everyone laughed at him. But he established the laws of electromagnetism and his name will be remembered for ever. So passed the eighteenth century and we arrive at the era of Faraday and Henry. Michael Faraday was born in London in His father was a blacksmith and young Michael went to work as an errand boy when he was thirteen. He afterwards became appren ticed to a bookbinder, but his interest lay in science. He read every book on chemistry and physics that he could lay his hands on, and conducted experiments in electricity at every spare moment. His ambition was to become a scientist and to join the Royal Institution. To try and get in, he used to attend the lectures and take careful notes of all that was said. Then he sent his beautifully written notes in to the lecturer, who was none other than Sir Humphry Davy, and at the same time applied for a job. He got it, and became a lab oratory assistant employed to assist the professors and lecturers by preparing the apparatus for a lecture. He was paid twenty-five shillings a week plus a room to live in. He studied and worked, and read and experi mented until, only twelve years later, he was ap pointed Director of the Royal Institution. His salary rose to 100 a year plus a free house, free coal and free candles, and his clear ideas and practical experiments really launched the era of electrical engineering. There is a little story told about Faraday, to the effect that one day the Prime Minister was talking to him about his work. 'What is the use of electricity?' asked the PM. 'Nothing now,' replied Faraday. 'It is just a baby, and what is the use of a baby? But like a baby, some day it will grow up, and then, Sir, you can tax it!' Joseph Henry, not to be confused with Edward, Frederick, Matthew, O, Patrick, William and all the kings of Europe of the same name, was an American scientist from Albany, New York, and I have no inti mate stories to tell you about him, except that apart from inventing induction, he applied the electric tele graph to meteorological research. One can imagine how frustrating it must have been to try to disseminate weather forecasts using a cleft stick runner. Perhaps the telegraph was the first application of electricity to spread around the world, but people in

10 26 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 those days were not sure how far, nor how fast elec tricity could travel. Certainly they knew that a line of monks one mile long could be made to jump two feet into the air at the same moment, but when the tele graph cable between England and America was first proposed, no-one was really sure whether it would work or not. The money for making and laying the cable was being put up by an American financier called Cyrus P Field and the consultant for the cable com pany was Professor William Thomson, later Lord Kel vin. Thomson went very carefully into the perform ance of such a long cable and came to the conclusion that the cable would work provided the telegraph was not operated too fast, on the grounds that the speed of propagation of the electrical signals was slower than might have been expected. This opinion came to Mr Field's ears and Mr Field was worried. He asked Pro fessor Thomson 'You say it will take some time for a signal to be sent from one end of the cable to the other. About how long will it take?' 'It will take about one second', was Thomson's reply. 'Ah well,' said Field, 'I guess I can wait that long'. The electric telegraph It was not an easy matter to persuade governments to make use of this new invention, the electric tele graph. An attempt was made to do this in 1816, and after many letters had been written and many officials interviewed, the reply came back in a large blue letter well tied up with red tape, which said, 'With reference to your communication, your attention is drawn to the fact that the war is now over, and that telegraphs of any kind are in future entirely unnecessary.' This was, of course, the Battle of Waterloo, and it was over the next 100 years that telegraph, telephone and radio was to transform the entire concept of communication, and it was ironically enough in England that Marconi was to find real support for his system of wireless tele graphy. The mystery that was electricity and radio is well il lustrated by the little story of Sambo and Rastus who had been talking about these new-fangled things. Ras tus was questioning Sambo, who had been to high school and the question was, 'Sambo, what is elec tricity?' 'Well,' answered Sambo, 'if there were a dog so long that when his tail was in Chicago and his head in New York, then that dog is like electricity, because if you tramp on his tail in Chicago, he would squeal in New York'. 'Yes,' said Rastus, 'I see that, but what is wireless?' 'That,' said Sambo, 'is exactly the same, ex cept that the dbg is imaginary'. This has brought us to the latter part of the 19th cen tury past 1881 and up to 1895 when the first steam gen erating installation of any size in South Africa was in augurated near Brakpan by the Rand Central Electric Works, which also supplied power to the Johannes burg mining area via 10 kv transmission lines, all cul minating in the birth of the VFP in 1906 and the ap pearance of Bernard Price and other pioneers in our colourful electrical history. There are people whom many of us knew as fellow engineers, in the VFP and ESCOM, in the Post Office and the Railways, in the mining industry and the municipalities, in the manu facturing and marketing industry, in the universities and the research bodies and the technical colleges and technikons, and it was Kelvin House that gave them a common meeting ground. One has only to look down the list of Past Presidents and Honorary Fellows to see the historical development of electrical engineering in South Africa, and even in Southern Africa, recorded in personalities since I was privileged to know such men as Dr Bernard Price, Col J H Dobson, Dr H J van der Bijl, and all the Past Presidents from Major E F Rendell to the present day, and to be a participant in the growth of the profession since What one remembers par ticularly about the twenties and thirties, is that every graduate who could make it, tried his utmost to be ac cepted into one of the graduate apprenticeships off ered by the electrical engineering companies in the UK, to become one of the brotherhood of MetVick, then later BTH (Better Than Home, they called it), and many others. This was, of course, an exercise in engineering salesmanship of the highest order on the part of these companies, because they knew that every successful graduate apprentice would remain for ever a staunch protagonist of their products, wherever he might end up. Unfortunately, the war interfered with the scheme, and certain subsequent large scale take overs have created a totally different climate. What I find interesting is that the kind of training that many, if not most, employers of electrical engin eering graduates were looking for in the twenties and thirties was almost what the technikons are offering their technician trainees today, and probably the pic ture has changed only in aspect, and not in quality, be cause the man in most demand in industry today is still the technician. What has changed, of course, is the de mand for the really highly skilled engineer, in numbers which are not being provided by the universities. In fact in my experience, the universities have never been able to satisfy their customers' needs. There was even a time when one of my own students toured the city looking, not for a job, but at the jobs available. One of the chiefs he had been to see phoned me in quite a state to say that this young man had asked him all about the job, the prospects, the pay and the con ditions of service, and then turned round and said, 'No thanks. I have had a much better offer from XYZ'... Chief in apoplexy! Since the war, of course, the growth has been phe nomenal, and this has not only been in the magnitude or quantity of engineering effort or in the number of engineers and the work they are required to do, but in the quality of the operations they become involved in. This has been due to a great increase in local manufac ture, which demands development and design, plus an enormous increase in sophistication of plant, plus all the new areas flowing from electronics and its solid state follow up. Today one cannot put one's face into a modern plant without being faced by a computer, and although I did introduce computers to Wits in 1960, my young and nimble successors and students soon

11 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 27 swept by with a flourish, and I retired into the security of an administrative job from the electric chair to the hot seat. I think that the SAIEE and Kelvin House in general can be very proud of the part they have played in the development of this vigorous and vital industry and there is no doubt at all that they will continue to play this part in the future. That is to say, provided they do not perform the kind of dangerous experiment that Professor Richman in Russia did in trying to repeat Franklin's experiment and receive a direct delivery of one of Jove's thunderbolts. And this gives me the opportunity, in concluding, of quoting a delightful little couplet by Hillaire Belloc, who must have had the Russian Professor in mind when he wrote: 'A smell of burning filled the startled air, The electrician was no longer there'.

12 28THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERSFebruary 1982 Symposium on Telemetering and Telecontrol This Symposium which was attended by 256 delegates was held at the University of the Witwatersrand on 11th September, The Symposium was opened by Dr R B An derson, President and the closing address was given by Prof J J du Plessis, Department of Electrical Engineering, University of Stellenbosch. Organising Sub-Committee A R Atkins (Chairman), L W Card, A E Day, E J Davison, O J van Zyl, T Y Poole (Secretary). Eleven papers were presented at the Symposium. The synopses of these papers, titled as follows, are shown below: Introductory paper Fundamental issues in Telemetering and Telecontrol by HE Hanrahan A question of telecontrol by EJ Davison Design objectives in the development of a telecontrol system by PJ Westwood Telecontrol of a petroleum products pipeline bylw Card Telemonitor van die SA UK FM-en TV Uitsaaistasies deurdc Conradie A unidirectional randomly-timed radio borne data acquisition system by P Chandler Radio frequency telemetry in South African gold mines byba Bowles A telemetering system used in South African mines by NJ van der Walt and BJ Bout Planning for computer-based control systems: A case for distributed computing by M M Kagan andrvanolst Desirable practical features of a telecontrol system by N van Wyk and G Smith Telecontrol in a distribution network by G Marloth Fundamental Issues in Telemetering and Telecontrol H E Hanrahan* BSc(Eng), PhD, PrEng, MSAIEE, FSAAI INTRODUCTION The notice announcing the Symposium indicated clearly that its principal objective is to provide an overview for the firm or organisation wishing to enter the telemetry and telecontrol field. It is directed equally to the firm wishing to design, manufacture and supply equipment as well as the customers wishing to avail themselves of telemetry and telecontrol tech nology. It is appropriate in this paper, coming before the others in this Symposium, to attempt to present an overview of the subject and to provide a background against which the more detailed papers can be read. In Section 2 the terms telemetry and telecontrol are defined and the salient properties of the industry are reviewed. Arising out of this is the idea that the telemetry and telecontrol field is indeed a vast one and requires inputs from many aspects of electrical engineering. The range of skills required is reviewed in Section 3. The manner in which telemetry and telecontrol systems are evolving is discussed in Section 4. INLEIDING Die kennisgewing wat die simposium aankondig, het duidelik aangedui dat die belangrikste objektief is om die firma of organisasie wat graag tot die telemeting en telebeheer gebied wil toetree te voorsien van 'n oorsig. Dit is ook direk van toepassing op die firma wat graag toerusting wil ontwerp, vervaardig en verskaf, sowel as kliente wat graag gebruik wil maak van telemeting en telebeheer tegnologie. In Afdeling 2 word die terme telemeting en telebeheer gedefinieer en die uitstaande eienskappe van die industrie beskryf. Na aanleiding hieruit, is die idee dat die telemeting en telebeheer veld inderdaad 'n ontsaglike een is en vereis toevoering van menige aspekte van die elektriese ingenieurswese. Die reeks bekwaamhede wat vereis word, is in Afdeling 3 omskryf. Die manier waarop telemeting en telebeheerstelsels ontstaan word bespreek in Afdeling 4. * Head, Department of Electrical Engineering, University of the Witwatersrand A unidirectional randomly-timed radio borne data acquisition system P A Chandler* PrEng, BSc (Eng) SYNOPSIS This paper discusses the design of a telemetry system which had to work without mains power. Primary batteries were chosen to power the sensing stations and solar cells were used at the radio re peater sites. The need to conserve power influenced the design of the communication philosophy, the message structure and the hardware. By making careful choices at each stage it was possible to make a system in which the sensing stations could operate for more than a year on a set of 14 'C size dry cells. SINOPSIS In hierdie artikel is die ontwerp bespreek van 'n telemetrie (afstand meting) stelsel wat moes funksioneer sonder hoof kragtoevoer. As hoofkragbron is batterye by die metingstasies en sonselle by die versterkerstasies gebruik. Die behoefte om krag te bespaar het die ontwerp van die kommunikasie filosofie, die boodskapstruktuur en die hardeware bei'nvloed. Met versigtige keuses tydens elke fase, was dit moontlik om 'n stelsel te ontwikkel waarin die metingstasies vir meer as 'n jaar met een stel van 14 'C grootte droe sel batterye kon funksioneer. * Formerly with SATI, Pretoria (now incorporated with Siemens Ltd)

13

14 1 I Telemecanique

15 MULON Micro Switches Micro Switch push buttons rel6 finder n_ Single phase, three phase kilowatt hour meters Peterrein* Schaltgerflte On load isolators Switch fuse units 8 pin and 11 pin plug in relays 8 pin and 11 pin plug in bases Power factor correction capacitors for 400V, 525 V, 3.3KV, 6.6KV, 11KV Power factor control relays, seven step, for above VAAL ELECTRONICS DIN Limit switches Clip on terminals Electronic timers Electronic level controllers Electronic phase fail relays Electronic current limiting relays frapil TERASAKI Moulded case circuit breakers Air circuit breakers Industrial panel metering in four sizes 48mm, 72mm, 96mm and 144mm, consisting of: Volt Amp maximum demand Watt, VAR power factor indicators Frequency indicators Running hour meters Current transformers Shunts Push button and illuminated pilot devices Rotary switches Push button control stations SPRECHER AND SCHUH - Contactors, overload and control devices STROMBERG - Switch fuse units, Isolating switches CRADY - BS88 Fuse Carriers and fuse links - DIN fuse carriers and fuse links SUNX - Photoelectric components GHISALBA - Contactors and overloads ATW PRODUCTS - Electric timers and control devices

16 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 Polyester enclos^res-] for all season \ "VV A Johannesburg September Kindon Road Robertsham 2091 P.O. Box Southdale 2135 L-"^(Pty) Ltd Telex SA Tel. (011) Nat^l S CONSOLE K (Pty) Ltd Tel DBN. (031)

17 February 1982THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS29 A question of telecontrol E J Davison,* PrEng, BSc, MSAIEE SYNOPSIS As this decade draws to an end and the computer-based telecontrol industry is surveyed, those mistakes prevalent at the beginning of the decade are still being perpetrated today. This paper should encourage a searching approach by those involved with the purchase or manufacture of telecontrol systems such that properly armed with answers to appropriate questions raised during every stage up to the signing of a contract, they will more often satisfy the real needs, on time and within the budget. SINOPSIS 'n Oorsig van die Rekenaar-tipe afstandsbeheer vervaardigings industrie aan die einde van die huidige dekade, toon dat die foute so kenmerkend aan die begin van die dekade nog steeds met ons is. Die mikpunt van hierdie referaat is om 'n ondersoekende benadering optewek by diegene wat gemoeid is met die aankoop van rekenaartipe afstandsbeheerstelsel. So 'n benadering lei tot 'n aantal vrae watnodig is om, algemeen gesproke, die ware noodsaaklike aspekte te bevrediggedurende elke stadium vanafdie ondertekening van die kontrak binne die perke van tyd en begroting. * Formerly Senior Engineer (Telecontrol) ESCOM Design objectives in telecontrol outstation development P J Westwood* MSAIEE, MIEE SYNOPSIS The design of telecontrol outstations can be a critical factor in the success of a telecontrol system, in which the conflicting requirements of low cost, ruggedness, versatility, availability and ease of main tenance have to be taken into account. This paper describes the design problems taken into consideration and some of the solutions that resulted in the development of a telecontrol outstation. SINOPSIS Die ontwerp van telebeheerde buitestasies lean as 'n kritiese faktor beskou word sover dit die sukses van 'n telebeheerde stelsel aangaan waarin die teenstrydige vereistes van lae koste, stugheid, veelsydigheid, beskikbaarheid en die gemak van onderhoud in ag geneem moet word. Hierdie referaat beskryf die ontwerp-probleme, inagnemende sommige van die oplossings wat gevind is in die ontwikkeling van 'n telebeheerde buitestasie. * Dowson and Dobson Electronics Telecontrol of a petroleum products pipeline LW Card* PrEng FSAIEE SYNOPSIS Operation of a petroleum multi-products pipeline poses similar problems to any other business undertaking; how to cut costs, how to exploit capitalised equipment, how to increase the efficiency of the operation and how to eliminate expensive manual processes. Telecontrol provides the solution to some of these problems but, in turn, raises some problems of its own. This paper describes some of the steps taken to exploit redundant equipment provided for the purpose of increasing the availability of the control system. It also describes some novel approaches to maintaining the outstation equipment and also feedback from the control system to aid management. SINOPSIS Soortgelyke probleme ontstaan vir meerprodukte-pypleidingbedryf as in enige sake-onderneming; hoe om koste te besnoei, hoe om gekapitaliseerde toerusting uit te buit, hoe om werkverrjgting van die bedryf te verbeter en hoe om duur menslike hanteering uit te skakel. Telekontroletoepassing los party van die probleme op maar dit gee aanleiding tot ander probleme. Hierdie referaat beskryf stappe wat gedoen word om staatmakertoerusting ten voile te benuttig benewens die daarstelling om die beskikbaarheid te versterk. Dit beskryf ook sekere benaderinge tot die instandhouding van buitestasietoerusting en terugvoering van informasie uit die kontrolestelsel vir die bystand van bestuur. * Formerly with South African Railways and Harbours Telemonitor van SAUK FM- en TV-uitsaaistasies D G Conradie*Hons -Blng (Stell) SINOPSIS Dit word onder andere van die SAUK verwag om 'n diens met so min as moontlik onderbrekings te lewer. Om hieraan te voldoen, het die SAUK sy FM- en TV- uitsaaistasies, wat onbeman is, in instandhoudinggroepe ingedeel, elk met sy ete instandhoudingsentrum. Die personeel by so 'n sentrum benodig inligting oor stasietoestande op die verskillende stasies sodat hulle onmiddellik kan optree indien daar iewers 'n fout opduik. Met die koms van TV het die SAUK reeds oor 'n telemonitorstelsel vir FM-stasies beskik, en daar is besluit om n nuwe TV-monitorstelsel te ontwikkel sodat meer stasietoes tande, asook videokwaliteit, gemonitor kan word. Hierdie nuwe stelsel vervang ook die ou FM-monitorstelsel waar dit geinstalleer word, maar gebruik nog dieselfde transmissiekanale. Hierdie nuwe TVtelemonitorstelsel word hier beskryf, met spesiale verwysing na die metodes en beginsels van die monitor van videokwaliteit tydens uitsendings. SYNOPSIS One of the responsibilities of the SABC is to maintain an uninterrupted service to the public. The Corporation runs its FM and TV transmitter stations on an unattended basis. Groups of stations are serviced from maintenance centres. One of the techniques used to avoid programme interruptions is the continuous relaying of the status of station equipment to the maintenance centres. The advent of television required a very large increase in the capacity of the existing remote monitoring system. Unlike sound broadcasting, television broadcasting permits the continuous monitoring of the technical quality of a programme during the programme. An increase in the sophistication of the monitoring system was required to handle this additional information. It was decided to replace the original monitor ing system at transmitter stations used for FM and TV broadcasts while retaining the existing data transmission system. This paper describes the development of the new monitoring system with particular reference to measuring of video quality during programme broadcasts. *Ingenieur: Senders, SAUK, Johannesburg A telemetering system used in South African mines N T van der Walt,* MSc, (Elee Eng) PrEng and B J Bout,* PrEng SYNOPSIS Telemetering of both analogue and/or ON/OFF electrical information from remotely situated underground locations to surface and vice versa is becoming increasingly useful in South African mines. This paper describes a low frequency multiplex telemetering system which is successfully being used in gold mines for a variety of applications. SINOPSIS Die telemeting van beide analoog en/of AAN/AF elektriese inligting van afgelee ondergrondse plekke na die oppervlakte en omgekeerd word al hoe meer nuttig in Suid-Afrikaanse myne. Hierdie refer aat beskrywe 'n lae frekwensie multipleks telemeting sisteem wat suksesvol vir 'n verskeidenheid van toepassings in goudmyne aangewend word. ' Electronics Laboratory of the Anglo American Corporation of South Africa

18 30THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERSFebruary 1982 Planning for computer-based control systems: a case for distributed computing M M Kagan* BSc (Eng), MBA, AMCSSA and R van Olst** Pr Eng, MCSSA SYNOPSIS A set of design objectives is proposed for the planning of computer-based control systems. These design objectives cater for the three functional areas which these control systems most often serve; viz on-line processing, supervisory management functions and system enhancement functions. In addition the design objectives of availability, reliability and maintainability are discussed. Two system architec tures are proposed, which serve to meet the design objectives mentioned above, namely the so-called centralised and distributed computing philosophies. The advantages of each approach are highlighted. Two real-life case studies are used to further demonstrate the particular advantages of the distributed computing philosophy. The first case study demonstrates that greater system availability may be pro vided by designing suitable levels of autonomy into the distributed network elements. The second case study shows how distributed processing reduces the response time within a telecontrol system to changes of state at the outstations and improves communications channel utilisation within the network. These benefits are of great economic importance in telecontrol applications, where incremental increases in communicators' channel capacity may be costly. SINOPSIS 'n Reeks ontwerpdoelwitte word voorgestel vir die beplanning van beheerstelsels wat op rekenaars gebasseer is. Die doelwitte maak voorsiening vir die drie funksionele gebiede waar die beheerstelsels gewoonlik aangetref word. Dit is gekoppelde verwerking, toesighoudende bestuursfunksies en verheffende stelselfunksies. Die ontwerpdoelwitte van beskikbaarheid, betroubaarheid en herstelbaarheid word ook bespreek. Die argitektuur van twee stelselsoorte word voorgestel om bogenoemde ontwerpdoelwitte na te kom. Die twee soorte is die sogenoemde sentraal- en verspreide rekenaar benaderings. Klem word gele op die voordele van elk. Om die voordele van die verspreide rekenaar benadering verder uit te wys, word daar verwys na twee stelsels wat in die praktyk gebruik word. Die eerste geval maak dit duidelik dat verhoogde stelselbeskikbaarheid moontlik is, wanneer daar aan die elemente van die verspreide netwerk gepaste outonomie toegeken word. Die tweede geval wys hoe verspreide verwerking die reaksietyd van 'n telebeheerstelsel verminder. 'n Verandering by die vergeiee toerusting word vinniger verwerfc, terwyl die kommunikasiebaan van die network ook beter benut word. Hierdie voordele is utters belangrik vir die ekonomie van 'n telebeheerstelsel, want toenemende kommunikasiebaankapasiteit kan duur wees. * Software Engineer, Perseus Computing and Automation (Pty) Ltd ** Senior Manager, Perseus Computing and Automation (Pty) Ltd Radio frequency telemetry in South African gold mines B A Bowles* MSc(Eng)(Manchester) SYNOPSIS The poor reliability of cables underground in mines as direct carriers of telemetry signals requires that other transmission methods be used for transmitting data to surface. Radio would be an ideal choice were it not for its limited propagation distance underground. However, useful ranges can be achieved by inductively coupling the radio frequency carrier into a power line. By this means ranges of up to three kilometres have been achieved but are limited by mining installations such as induction motors which are connected to the line and act as shunt loads. These loads also introduce noise due to their significant harmonic content at high frequencies. Noise is also caused by bells and buzzers and on surface by radio stations, navigational beacons and lightning activity. A telemetry system has been developed to transmit data from underground to surface. However, some form of noise detection and error correction is required if inductive coupling into power cables is to be used effectively. A radio telemetry system is also described which has been developed to monitor parameters from the reamer of a raise borer. The mechanical problems of the system are discussed and a narrowband PCM-FM system has been built and is undergoing field trials. SINOPSIS Die onbetroubaarheid van kabels ondergronds in myne as regstreekse draers van telemetrieseine vereis dat ander transmissiemetodes gebruik word om data na die oppervlak oor te send. Radio sou die ideale keuse wees as dit nie vir die beperkte ondergrondse voortplantingsafstand daarvan was nie. Bruikbare afstand kan egter verkry word deur die radiofrekwensiedraer induktief aan 'n kraglyn te koppel. Op hierdie wyse is afstande van tot drie kilometer bereik, maar dit word beperk deur mynbou-installasies soos induksiemotors wat met die lyn verbind is en wat as omtaklaste dien. Hierdie laste veroorsaak ook geruis weens hulle beduidende bofrekwensie-inhoud by hoe frekwensies. Geruis word ook deur klokke en gonsers en aan die oppervlak deur radiostasies, navigasiebakens en weerlig veroorsaak. 'n Telemetriestelsel is ontwikkel om data van ondergrondse plekke na die oppervlak oor te send. Een of ander vorm van geruisopsporing en foutkorreksie is egter nodig om induktiewe koppel ing aan kragkabels doeltreffend te gebruik. 'n Radiotelemetriestelsel, wat ontwikkel is om parameters vanaf die ruimer van 'n styggangboor te moniteer, word ook beskryf. Die meganiese probleme van die stelsel word bespreek, en 'n smatband-pkm-fm-stelsel is gebou en ondergaan veldproewe. * Electrical Engineering Division, Mining Technology Laboratory. Chamber of Mines Research Organisation Desirable practical features of a telecontrol system N Van Wyk, and R G M Smith SYNOPSIS Centralised control afforded by modern telecontrol can pose unexpected problems to the uninitiated. The basic requirements of a telecontrol system are established based on the experience gained with two generations of computer-based telecontrol systems operated on the ESCOM National Power Grid. The criteria for accurately presenting essential information to the operator in an acceptable form are considered. The ability of a telecontrol system to adapt to a continuously changing power system is determined by the data base management facilities available. Reliability and security against malfunctioning due to external or internal failures are enhanced by special built-in hardware checks. Continued successful operation of the system can be assured only by staff of the required skill having the necessary tools and equipment at their disposal. SINOPSIS Gesentraliseerde beheer, moontlik gemaak deur moderne afstandsbeheer, skep onverwagte probleme vir die nuweling tot di6 gebied. Die basiese vereistes van 'n afstandsbeheerstelsel word gefundeer uit ondervinding met die gebruik van twee geslagte van rekenaargebaseerde afstandsbeheerstelsels op die EVKOM-Nasional Kragnet. Die kenmerke van akkurate voorstelling van noodsaaklike inligting aan die operateur word bespreek. Die vermoe van 'n beheerstelsel om aan te pas by die gedurig veranderende kragstelsel word bepaal deur die beskikbare databasis verwerkingsfasiliteite. Ingeboude elektroniese eienskappe verhoog betroubaarheid en voorkom foutiewe werking as gevolg van interne of eksterne foute. Volgehoue suksesvolle bedryf van so 'n stelsel kan slegs verseker word deur personeel van die nodige bekwaamheid gerugsteun deur voldoende toerusting. Telecontrol in an electricity distribution network G R Marloth*, BSc (Eng), MSc (Eng), MIEE SYNOPSIS An electricity distribution network requires a telecontrol system capable of controlling and acquiring data from a large number of individual devices. Existing applications include the replacement of time switches, automatic meter reading, the control of interruptable loads and the control of distribution equipment. The load control facility can constitute an integral part of the generation control for the main power system. Several communication media are discussed and the features of the commonly used power line carrier systems including the need for advanced signal processing techniques are dis cussed in detail. SINOPSIS Die distribusie vlak van 'n elektrisiteitsvoorsieningstelsel benodig 'n afstandbeheerstelsel wat in staat is om 'n groot aantal individuele toestelle te beheer en om data van di6 toestelle te verkry. Bestaande toepassings sluit in die vervanging van tydskakelaars, outomatiese meterleesstelsels, die beheer van onderbreekbare laste en die beheer van distribusie-apparaat. Die lasbeheervermoe kan 'n integrale deel van die beheerstelsel vir kragontwikkeling in die hoofstelsel uitmaak. Verskeie kommunikasiemiddelle word bespreek en in besonder, die eienskappe van kraglyndraerstelsels en die behoefte aan gevorderde seinprosesseringstegnieke. * System Engineer, Electricity Department, City of Johannesburg

19 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 31 Item of Practical Interest Determination of the apparent movement of the sun H T Aspinall BSc(Hons) (Viet), MSc(Eng) (Witwatersrand), FSAIEE, FIEE Introduction As a preliminary to the description of a simple piece of apparatus, possibly novel in character, for determin ing the apparent paths of the sun at the summer and winter solstices leading to the development of a new type of solar heater, reference is made to generally well-known facts relating to the daily and annual motion of the earth as depicted respectively in Fig 1, Fig 2 and Fig 3. As an example, Pretoria is taken as the place of observation of the sun's apparent motion. In Fig 1 is shown the earth which rotates round its axis once daily with its axis inclined at an angle of 23 with the perpendicular to the plane of the ecliptic which includes the centre of the earth and that of the sun and serves as a plane of reference. Fig 2 illustrates the maintenance of the angle of 23 with the result that in any one position, the earth's axis is parallel to that in any other position. Fig 3 depicts diagrammatically the apparent motion of the sun to an observer at the Tropic of Capricorn on the assumption that the earth has stopped rotating. To the observer the sun reverses its motion, that is, north ward to southward and vice versa every six months at about June 21 and December 22 respectively. The re spective times of apparent reversal of motion are termed the winter and summer or the June and De cember solstices in the Southern Hemisphere. An experimental method The principle of the experimental method to deter mine the apparent paths of the sun at Pretoria at the December and June solstices is illustrated in Fig 4. In the figure is shown a sun's ray xps striking the surface of the transparent hemisphere or dome D at the point p and the centre of the base at s. In the rightangled triangle pvs, 0 is the angle of elevation of the sun at s regarded as the place of observation, namely, Pretoria. perpe plane Tropic of Cancer Latitude - 23^ JSdge of plane^ of ecliptic pricorn 23^S March equinox NORTH March SOUTH December solstice December ice solstice of Earth September equinox horizontal plane O Observer at Tropic of Capricorn Fig 2 Fig 3

20 32 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 Fig 5 Fig 4 Apparatus and experimental procedure A general view of the apparatus is shown in Fig 5. The apparatus comprises a terrestrial globe with its axis inclined at an angle of 23 with the vertical. The hemispherical transparent dome is mounted concentri cally on a circular base graduated in degrees at inter vals and fixed tangentially to the surface of the globe. A small sphere is attached to the centre of the base for observation purposes immediately above Pretoria marked on the globe and a meridian is drawn through this point. A curved arm is fixed to the frame support ing the globe and lies in its plane; the arm carries a sec tor graduated in degrees lying along the equator. The adjustable stand supports the sighting tube which can be moved in three directions mutually at right angles to enable the sighting of the small sphere and the marking of the corresponding point on the dome for each observation for the construction of the relevant curve. Fig 6 illustrates in diagrammatic form only the con ditions for the first of the observations, namely, that corresponding to sunrise at the December solstice. The globe is rotated from the initial position until the spot representing Pretoria lies in the W-E vertical plane passing through the centre of the globe. The short ax ial pin projecting from the sighting tube is brought into contact with the globe and the point of contact is marked on the dome corresponding to zero elevation of the sun at sunrise following the necessary adjust ments. The angle of rotation of the globe from zero to the new position is found to be 90 a,, that is or, in terms of time, 06h00-44 min or 05hl6 for sunrise. Similarly, for sunset the corresponding angle of rotation is a2 where a2 = 11 and the time of sunset is 18h44 for the December solstice. In general, for (a) the December solstice and (b) the June solstice the respective sunrise and sunset times are (a) 6 OOh T 44 min and 6 OOh 44 min. It is convenient to mention at this stage that the length of day is greater than that determined from Fig 6 purely geometric considerations. Due to atmospheric refraction the sun is seen before it rises above the hor izon and it can actually be seen after it has set under favourable conditions. To determine points on the curve between sunrise and sunset for the December solstice the globe is ro tated in steps of 30 and the basic procedure previously described for the marking of the first point is followed. For the June solstice the axis of the globe is tilted forward through an angle of 47 from the existing pos ition and the experimental procedure is a repetition of that for the December solstice. The corresponding curves u and v are shown for convenience in Fig 7(b). Apart from the use of the apparatus for educational purposes the experimental results have proved useful in the design of a new type of solar heater. A new development One design of solar heater recently devised com prises a single Perspex shell carrying double convex

21 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 33 to storage tank ^^"^ i ^y^ i "^^v absorber shell /\ S. ^^, \ i \ f k- co.t.d coll^ct lens Vl E k fit SINGLE LENS TAKEN Fig7(a) Fig7(b) normal & oblique radiation /,\ * III It ///// / ax Y <'// ^ w/ /\ i nsulating base AS ILLUSTRATIVE diffuse radiation lenses, for example, mounted on a heat-insulating col lector base as shown diagrammatically in section in Fig 7(a). The absorber in this case is shown as a tank al though it could take the form of a coiled pipe with its axis horizontal for water boiling at atmospheric press ure and steam raising. The heater shown in the figure is designed to meet water-heating requirements on a fairly large scale. In a further development the individual lenses of Perspex fit into a shell of fibreglass; the radius of curvature of the outer surfaces of the lenses is the same as that of the shell itself resulting in a smooth exterior surface. A certain proportion of the total radiation is always focused at the base of the heater absorber and the re mainder of the direct plus the diffuse radiation is also absorbed by the solar heater. Fig 7(b), a diagrammatic view of the solar heater, shows the location of the lenses arranged for maximum utilisation in a belt across the hemisphere between the boundaries based conveniently on the results of the ex perimental method previously described. Although "the collector base is not maintained at right angles to the sun's rays, the 'follow-the-sun' ef fect enables the concentration of the available solar radiation in the absorber independent of the daily and seasonal variations in the direction of the radiation. The construction is designed with a view to obviating the use of narrow tubing involving numerous bends with the associated friction and heat losses, possible air / / locks, etc, and the relatively slow heating process nor mally associated with water heating by the panel-type solar heater invented many years ago. Apart from water heating on a fairly large scale with the appropriate thermal capacity of absorber and the possible use of acrylic Fresnel lenses the solar heater lends itself to high temperature applications such as steam raising, although to a limited degree in view of the very low density of incidence of solar energy on the earth's surface. For low-pressure steam raising the ef fective lens area would be increased by mounting the lenses required on an open steel framework of rela tively large base diameter forming a standard unit re sulting, however, in a loss of diffuse radiation. The ab sorbers of the various units would be connected in series. A power plant on the lines described should prove a more economical proposition than a 'tower power' station, for example. With this arrangement banks of remotely controlled heliostats or focused mirrors re flect the sun's rays into a boiler which is mounted at the top of a tall tower and drives a conventional steam turbine and generator. The heliostats are motor driven and a microprocessor ensures that they continuously follow the sun's rays. However, it is convenient to mention at this stage that substantive claims for the proposed solar heater cannot be made in the absence of research on a prototype preferably carried out by a responsible research body. Incidentally, it would appear that the limitations in the operation of solar heaters due to cloudy days and periods of darkness will be minimised by the use for heat storage of a recently discovered synthetic com pound which is a combination of a liquid unsaturated hydrocarbon, norbordiene, and chemicals in the methyl and cyano groups. It is claimed that solar en ergy can be stored for many years in this way and re leased on the application of a catalyst. A small solar heater of the type previously described should prove useful for distillation purposes in hot climates, namely, desalination or water purification particularly in desert areas. For example in desalina tion the salt water would be fed into a partially open absorber and the water vapour condensed on the in side of the upper part of the shell could run down into an annular channel at the base of the shell. Other applications could include the conversion of heat energy into electrical energy with the use of photo-voltaic cells, and small scale furnace work. In the latter case the lenses would be of glass of high opti cal precision to produce a sharp focus. A fibreglass shell of relatively small dimensions would support the not unduly heavy glass lenses. In conclusion it may be stated that the apparent path of the sun can, of course, be determined by a series of calculations with a high degree of accuracy. However, for everyday purposes, the experimental method appli cable to the solstices has the merit of simplicity. For further information application should be made to Mr H L T Jeffery, Business Manager, Journal for Vocational and Technical Education in South Africa, P O Box 3659, Johannesburg 2000.

22 34 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 Branch Notes CAPE WESTERN CENTRE Energy saving The 296th general meeting was held on 10th Sep tember 1981 and attended by 35, persons. In opening the meeting the Chairman, Mr J M Carl son, welcomed those present and apologised for the absence of Mr R S Mann who, as had been circular ised, was to have presented a paper on 25 kv ac elec trification at that meeting but due to a snowstorm which closed Jan Smuts airport was unable to depart for Cape Town. The Chairman then introduced Dr M J Case, a Committee member, as the speaker for the evening who had agreed at very short notice to persent a lec ture under the title of These energy savers are they any good?' Reference was made in the lecture to a new class of electronic gadget which when connected be tween the supply and a fractional horsepower induc tion motor is claimed to improve power factor and save energy. The principle of operation is based on the fact that a small induction motor may, at reduced load, be oper ated quite successfully at a reduced voltage. The volt age may be reduced by means of a triac, controlled by an electronic current sensor. The disadvantage is the distortion which is inherent in any phase-controlled system. Power factor at the motor terminals is im proved but the overall power factor is always less than that of the motor itself. There are many unanswered questions about meter ing for the supply authorities which need further inves tigation. The Vote of Thanks was proposed by Mr W Penberthy followed by an interesting discussion, the Chair man adding his thanks when closing the meeting. Visit to AECI factory at Somerset West On 23rd September 1981 a visit was made by mem bers of the Institute to the AECI. Although attended by only eight persons the visit was most interesting. After a well organised tour of the works and the serv ing of excellent refreshments, the Vice-Chairman Mr C Bryant thanked the hosts for the hospitality and the trouble taken. It is hoped to repeat the visit. Bernard Price Memorial Lecture 1981 The 297th general meeting was held on 25th Oc tober 1981 and attended by 65 persons when the 30th Bernard Price Memorial Lecture was presented to this Centre at the University of Cape Town by Mr L M Muntzing, a member of the partnership Doub and Muntzing, chartered attorneys-at-law in Washington DC and Vice President/President-Elect of the American Nuclear Society. The title of the address which was also presented at meetings held at other centres of the Institute and which will be published in the Transactions in due course was 'Nuclear Power: An Emerging Answer to Energy and Economic Prob lems'. The Vote of Thanks was proposed by the Chairman Mr J M Carlson and seconded by Mr Cockbain, fol lowed by an interesting discussion. Annual Dinner The Centre's annual dinner was held at the Newlands Hotel on 29th October 1981 and attended by 52 persons which included the President of the Institute, Mr G Park and the 1981 Bernard Price Memorial lec turer Mr L M Muntzing, who proposed the Toast to the Cape Western Centre. The Chairman, Mr J M Carlson, who earlier in the evening had proposed the Toast to the State President, responded to Mr Muntz ing. The Toast to the Guests was proposed by Mr C Bryant, the Vice-Chairman, and the response by Mr A WLukens, Consul-General, USA. The attendance was considerably lower than that of last year, but this may be partly attributable to the fail ure of the GPO to deliver the initial batch of notices. Institute Visits In conjunction with its Cape Western Centre the In stitute organised a series of visits in the Western Cape for all its members. The first of these visits took place on the morning of 19th November 1981 when by kind permission of Cape Town's City Electrical Engineer members and their guests were shown round the Steenbras pumped stor age power station at Gordon's Bay. Although not the first visit to this power station, this occasion provided an opportunity for other members who were not able to take part in the previous visits. Details of this power station have already been published. After lunching at Lanzerac hotel, Stellenbosch, the party travelled along the wine route to Faure, where they were joined by other members of the Institute and their guests on a conducted tour of the National Accelerator Centre. About 70 persons comprised the afternoon party. The main building will contain a 200 MeV separated sector cyclotron and two solid pole injector cyclotrons for light and medium ions respectively and will be used for nuclear research, isotope production and medical applications/the present total installed transformer capacity is 8,5 MVA and is to increase to about 10 MVA later. The special and interesting laboratories and workshops were inspected and their functions ex plained by the relevant experts. This visit concluded with a cocktail party arranged jointly by the consulting engineers and the main con tractor. During the morning of 10th November 1981 mem bers were shown around ESCOM's Koeberg nuclear power station which is still under construction. The de-

23 February 1982 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS 35 sign and particulars of this power station have already been published in the Transactions. Noise pollution A recent visitor to Cape Town was Mr John Manuel, supervisor of the noise pollution control section, Pol lution Control Branch of the Ontario Ministry of En vironment, Toronto. Mr Manuel presented a lecture to a fairly well attended meeting held at the lecture theatre in Cape Town's Civic Centre on 10th Novem ber The subject was eminently topical at a time when South Africa is seriously concerned about the growing problems of environmental noise pollution, measures of control and the drafting of appropriate legislation. The lecture was arranged by the South African Acoustics Institute and the Cape Town City Council. The Vote of Thanks was proposed by Dr A Semmelink, a member of the SAIEE. Sonar applications The 298th general meeting was held on 12th Novem ber 1981 and attended by 27 persons. Prof Denbeigh of the central acoustics laboratory, Department of Electrical Engineering, University of Cape Town presented a lecture entitled 'Seeing with sound overview with sonar'. The principles of sonar which is an acronym formed from the words 'sound navigation and ranging' and asdic, an acronym of uncertain composition probably 'anti-submarine division' or possibly 'allied scientific division' or more probably 'Allied Submarine Detec tion Investigating Committee', were outlined. The superior propagation of sonic frequencies over electromagnetic waves in water was referred to. The principles involved and various applications including detection of submerged objects, depth surveys and fish detection were clearly illustrated by the screening of numerous interesting slides. The Vote of Thanks was proposed by Mr R R Gilmour, a Past Chairman who referred to some of his own experiences, experiments and tests which he had carried out in connection with the applications of sonic and ultrasonic frequencies in water, particularly in the biological field, and also to characteristics of piezo electric and electromagnetic transducers. An inter esting discussion followed after which the Chairman Mr J M Carlson added his thanks and closed the meeting. Annual Joint Cocktail Party The joint annual party for members including their ladies of the following institutions was held at the Athenaeum on 4th December The Cape Town Branch, SA Institution of Civil En gineers which was the host Institution and responsible for the arrangements on this occasion. The Western Cape Branch, SA Institution of Me chanical Engineers; The Cape Western Centre, SA In stitute of Electrical Engineers. Obituary Mr C R J Pilcher, a past member of the Committee for some years, and a member of the Institute for many years, passed away suddenly while on holiday with his wife in England recently. He was connected with the firm Reyrolle and Co for a long time before his retirement.

24 36 THE TRANSACTIONS OF THE SA INSTITUTE OF ELECTRICAL ENGINEERS February 1982 The South African Institute of Electrical Engineers Amendments to the By-laws (a)it is brought to the attention of members that Council, at its meeting on 5 June 1981, approved the following amendments to the By-laws. Amend By-law B8.4.3 to read: B8.4.3 The Chairman and the Vice-Chairman shall be corporate members of the Institute. For the first year of the formation of the Centre or Section, the Chairman and Vice-Chair man shall be appointed by Council. In addi tion, Council shall appoint one corporate member of the Institute to act in the posi tion of Immediate Past Chairman. These appointments shall be made prior to the calling for nominations for the Committee of the Centre or Section concerned. Amend By-law B8.4.3.I to read: B8.4.3.I For the years subsequent to the first year of the inception of the Centre or Section, the Chairman and Vice-Chairman shall be elected for the ensuing year by the outgoing Committee from those of its members who are eligible for election to these offices and who shall have served for at least one (1) year on the Committee prior to their ap pointment to these positions. They shall hold office for one (1) year unless otherwise approved by special resolution of Council. B8.4.5 amend margin caption to read: 'Ordinary Committee Members' Amend By-law B8.4.5 to read: B8.4.5 Committee members as indicated in B8.4.I.5 shall be elected to serve on the Committee for a period of two years. However, in the ballot held at the commencement of the first year of the inception of the Centre or Section, the scrutineers shall determine by lot which three (3) of the six (6) Committee members elected shall be required to retire at the end of the first year. Retiring mem bers of the Committee, whether at the end of a one or a two year period of service, shall be eligible for re-election. (b)the following amendment was agreed to by Coun cil at its meeting held on 5 September, 1980: Deletion of the following words from By-law B8.4.2: 'subject to prior consent of Council'. Die Suid-Afrikaanse Instituut van Elektriese Ingenieurs Wysigings tot die Verordeninge (a)lede se aandag word daarop gevestig dat die Raad tydens sy vergadering op 5 Junie 1981 die volgende wysigings tot die Verordeninge goedgekeur het. Wysig Verordening B8.4.3 SOdat dit lui: B8.4.3 Die voorsitter en vise-voorsitter moet korporaatlede van die Instituut wees. Die voorsitter en vise-voorsitter van die sentrum of seksie sal deur die Raad aangestel word vir die eerste jaar na stigting. Daarbenewens sal die Raad een korporaatlid van die Instituut aanstel om op te tree as naaste gewese voorsitter. Die aanstellings sal gedoen word voordat daar vir nominasies gevra word vir die komitee van 'die betrokke sentrum of seksie. Wysig Verordening B SOdat dit lui: B8.4.3.lVir die jare wat volg op die stigtingsjaar van die sentrum of seksie sal die voorsitter en vise-voorsitter vir die volgende jaar verkies word deur die uittredende komitee uit sy geledere van die lede wat verkiesbaar is vir die poste en wat minstens een (1) jaar op die komitee gedien het voordat hulle in die poste aangestel is. Hulle sal dan vir een (1) jaar die poste beklee tensy anders goed gekeur deur 'n spesiale Raadsbesluit. B8.4.5 wysig kantlynbyskrif sodat dit lui: 'Gewone komiteelede' Wysig Verordening B8.4.5 SOdat dit lui: B8.4.5 Komiteelede, soos omskryf in B8.4.I.5, sal verkies word om op die Komitee te dien vir 'n tydperk van twee jaar. Maar, tydens die verkiesing wat gehou word aan die begin van die stigtingsjaar van die sentrum of sek sie, sal die toesighouers die lot werp om te bepaal watter drie (3) van die ses (6) komi teelede wat verkies word, verplig sal wees om aan die einde van die eerste jaar uit te tree. Uittredende lede van die komitee, het sy na een of twee jaar diens, sal verkiesbaar wees. (b)die volgende wysiging is deur die Raad goedge keur tydens sy vergadering op 5 September 1980: Skraping van die volgende woorde van Verordening B8.4.2: 'onderworpe aan die goedkeuring van die Raad wat vooraf gekry moet word'.

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