1 C Protection of Transmission Lines Against Lightning Electrical Engineeiing Da t?» T/VIV.OF : UUNOX6 r rtt > « Digitized by the Internet Archive in 2014 http://archive.org/details/protectionoftranOOotis THE PROTECTION OF TRANSMISSION LINES AGAINST LIGHTNING BY HAROLD ANTHONY OTIS THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN ELECTRICAL ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS 1912 4 CM OH UNIVERSITY OF ILLINOIS Hay. 28, 19&2 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY HAROLD ANTHONY OTIS ENTITLED TBS PRQTOOTTQH OP. TB AIToMT S 5 I ON LINES AOAIBSLS L I6H.TH IB G IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE T DEGREE OF BACHELOR OF SCIENCE IT EL ECTPICAL ENCTNET'HTO y^y/ ^^Hnstructor in Charge Approved: HEAD OF DEPARTMENT OF filOTRICAL EN0INEEP.I1TG . 1219616 UIUC 1 THE PROTECTION OF THAU SKIS SI ON LIKES AGAIHST LIGHT-KING. Even in the earliest days of the transmission of electrical power, the engineers realized that the wires would have to be protect ed against what they called lightning. At that time lightning denot- ed electrical discharges between clouds or between clouds and ground, and when applied to electrical circuits, meant the results of such a discharge striking the wires. It was with this idea in mind that the earliest engineers started out to find some apparatus that would pro- tect their transmission lines and power plants against lightning. The Historical development of the lightning arrester is a very interest- ing subject, but due to the lack of time, only a brief outline will be given in this paper. Two engineers that gave most of their efforts to the devel- opment of the lightning arrester in its earliest forms were T.7urst and V.insor. The very first form of lightning arrester that was ever made consisted of a large glass bottle with a small neck. The bottle was supported on an insulated standard with the neck pointing down. Just below the opening in the neck was placed two carbon balls with a g r p between them of ab:)ut half an inch. One of these balls was con- nected by a short wire to the transmission line to be protected, and the other ball to the ground. Y.hen the line was discharged thru the ground wire, an arc was formed between the carbon balls. The heat from the arc expanded the air in the bottle. The only escape for this expanding air was thru the neck just above the carbon balls. This re- sulted in a rush of air from the bottle across the carbons which blew the arc out. This same general principle was followed by the experi- ment engineers for several years and several arresters of this type j were put in use. Another arrester of this type had a magnetic blow out coil instead of the air. The two carbon balls were placed in a gap in a rectangular iron core. The wire from the line was wound a- round the iron core before it terminated at one of the carbon balls. When the arrester discharged, an arc was formed between the two car- bon balls. But as the current flowed thru the arrester a strong mag- netic field was established acrossed the balls, due to the magnetic field, and this blew out the arc. About 1890 an engineer named Siemens became interested in the protection of transmission lines and started a series of experiments on different types of arresters. He did most of his experimenting on what he called the horn gap arrester, which consisted of two heavy copper wires bent in the shape of diverging horns, ue found that the arc, which was established at a discharge thru the arrester, would travel out the horns and break, lie also found that by shunting the horn gap by a high resistance the arc tended to be extinguished very rapidly, and the discharging ability of the arrester was increased, bo, in 1891 he put on the market an arrester which consisted of two of these horn gaps connected in series with an air gap of one-half inch. One side of one gap was connected to the line, and the other side of the other gap was connected to the ground. The gap on the ground wire side was shunted with a high resistance. This type of arrester let too much power current flow to ground, so he placed a fuse in series with one gap instead of the shunted gap of his original type of arrester. This was a good arrester and is used today on low voltages. The one serious objection to it is that it has to be placed where it can be watched, for as soon as the fuse is burned out the arrester is open circuited. About 1893 Wurst discovered that certain metals would not < 3. hold an arc after it was established. This lead him to experiment with those metals which resulted in what is now the modern non-arcing metal gap lightning arrester. He discovered that such metals as zinc, cadmium, antimony* and bismuth would not hold an arc after it was es- tablished. V/urst placed several cylinders made of zinc in a row along a piece of marble witl a gap of one-sixteenth of an inch between each cylinder. To the first cylinder he attached the line wire, and to the last the ground wire. He found that by increasing the line voltage to a certain amount he could make a spark jump across the gaps between the cylinders, and the line would discharge to ground. But the arc was immediately put out, and he could not maintain the arc except by holding the line voltage up above the discharging value of the arrest- er. While .Vurst was experimenting on a transmission line with his non-arcing metal arrester he discovered that some of the lightning discharges that come in on the v/ire were of very high frequency. These high frequency waves sometimes would rush past his arrester and enter the station. which resulted in some kind of damage. Between the arrest- er and the station apparatus he placed in the transmission line a , small coil of wire of a few turns. He found that this coil would hold back these high frequency waves long enough for them to be discharged thru the arrester. So in 1893 Wurst put on the market the modern multi - ple gap arrester and choke coil. From 1895 tOvl900 there v/as very little done on transmission line protection as the multiple gap arrester was considered perfect for all linsa ftt that time. But in the last ten years, big strides have been taken in the transmission of power. The voltage has been increased from a few hundred to above 100,000 and the power transmitt- ed has increased a large amount. It was found that the multiple gap 4. arrester was not very good for this voltage and high power transmiss- ion lines so a new form of arrester had to be invented. After careful experiments on numerous typos of arresters and protective apparatus, several types of electrolytic cell arresters were placed on the mark- et. These consisted, in main, of some electrolyte that tended to re- sist the flow of current up to a certain voltage but above this volt- age discharges current at a rapid rate. These arresters are taken up in detail farther along in this paper. This then brings the develop- ment of the lightning arrester up to the present day of high voltage high power transmission. It has been found within the last ten years that during at- mospheric disturbances, such as passing thunder storms, disturbances occurred in the electric circuits even without the discharge strik- ing the line. These disturbances, caused by induction, were also class ified as "lightning", and applied to electric circuits, lightning then came to mean all the effects of atmospheric electricity. Also, in the last ten years, with the introduction of electric circuits of higher voltage and larger electrostatic capacity, phenomena were observed in such circuits of the same characteristics and effects, requiring the same protective devices as disturbances of atmospheric electricty. Those internal surges may be caused by sudden loads on the line, switching, grounding, or numerous other similar causes. So the term lightning today has extended to include all the abnormal phenomena of the flow of generated power of the system, which results from any atmospheric or other disturbances, ^o in its most general meaning, when dealing with electric circuits and their protection, lightning ienotes all phenomena of abnormal voltage and abnormal frequency. Prom the above it is seen that the duties of a lightning ar- * 5. raster is three fold — first, to guard against the entrance or origin of disturbances, secondly, to guard against a disturbance leading to another disturbance, and thirdly, to discharge or suppress a distur- bance harmlessly. Lightning phenomena in electric circuits then consists of ex- ternal lightning due to atmospheric disturbances, internal lightning due to defects of the circuit or operation, and surges which are dis- turbances brough about by the flow of generated power which are start- ed by external or internal disturbances. The three principle forms in which these disturbances may occur in a circuit are— steady stresses or gradual electric charge; second, impulses or traveling waves; third standing waves or oscillations and surges. These steady stresses and gradual static charges may be built up on a transmission line in several ways. Whenever a thunder storm passes over a line the line has a potential of some value a little be- low that of the clouds induced on it and of the opposite kind as the earth.