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'1 v 'u . . , . . \ b ‘ . v-~ .’ n n . . ‘ l -1-’~ Mo __, ~ A " r*« u.— 3;. ~ “up-'3.)- “"33 .._,.. . .- Inteerepartment Corrésfiondence MEMORANDUM ' Date ' . . 7 To noun a the ma School , ~ ,. Frgfnn. s. Felts. hurt. at 3.3:. - ‘ sable“ Approval 0! MI tar 3.8- m 1! m. I ' : mac-norm. ng’nmc "a mu- .. . ' ammunumwmnA ‘ ._ n2"- 1‘0 tpprond. PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. - DATE DUE ‘ DATE DUE DATE DUE 6/01 cJCIRCIDateDue.p65-p.15 .‘LN I T WEST I Cf: T I (TN 2’3 F . If. IlTl-IDAI'FC ".3 OF AN AL’ITRI-IATING CUBIC??? ARC IN AIR A Thesis Submitted to the Faculty OF Michigan State College of Agriculture and Applied Science by Webster Lazell Bowler Candidate for the Degree Master of Science September 1934 Ca '1) (<3; L \ This Thesis is submitted to the Faculty of the Graduate School of Kichigan State College as partial fulfillment of the requirements for the Degree of Faster of Science in Electrical Engineering. ACE’CNOE’JLEDCTLCNT For their willing and helpful advice and assistance I wish to thank Professor Foltz and the other members of the Elec- trical Engineering Department. The solution of this problem was made possible through the kindness of the City of Lansing Board of Water and Light in the loan of the transformers and due to the cooperation of Mr. F. H. Kitchell, college electrician, in loaning to me the necessary switching equipment. W. B. TAB LE OF COT-WSI‘ETS Page Number Introduction ............................... 5 The Problem ................................ 7 History .................................... 8 Procedure .................................. 11 Photograph of Apparatus .................... 20 Schematic Diagram .......................... 21 Diagram of the Electrode Mechanism ......... 22 Test Data .................................. 23 Electrode Hardness ......................... 29 Computed Data .............................. 33 Oscillograms ................................42 Procedure of Plotting Characteristics ...... 49 Arc-Line Characteristics ................... 61 Discussion ................................. 68 Conclusions ................................ 75 Bibliography .0000...OOIOOOOOOOOIOOIOOOOOIOC '75 *** INTRODUCTION Dry air under ordinary conditions is said to be a di. electric. If the molecules of this same air be sufficiently excited, the air becomes ionized or conductive. Heat is the most common source of energy for ionization. Ionization of air may be produced by an electrostatic field, and the passing through it of X-rays or ultra-violet rays. If two conductors, having a difference of potential between them, are allowed to come in contact with each other, s.current will flow, tending to neutralize the difference of potential. If these conductors are separated, a shall spark may be visible at the point of separation. This spark pro- duces heat which, in turn, produces ionization of the surrounding air. If the spark continues as an arc, the electrodes may become heated to their fusing temperature. If the air alone were the source of ionized particles, the discharge between electrodes would be short lived since all of the particles (ionized sir) would be swept away rapidly by the electrostatic field. at the fusing temperature of a metal the mmlecules become agitated to such a degree that some of them.at the surface are removed from.their neighbors and away from the surface to such distances that they become more susceotible to the action of the electro— static field than to the force holding them in.the metal. The impelling field then causes the charged particles to form a part of the are stream. At a given condition of temperature and pressure the number of molecules in unit volume of the conducting vapor is fixed. Since the surrwndinp; air cools the arc plasma, the conducting; vapor is confined to a stream, the area of which is proportional to the current. It is assured that the 4 current density of an arc is constant. is the plasma of the arc is cooled, energ‘ is given up in the form of heat. If more heat is supplied, the arc will continue. If a sufficient amount of heat is not supplied to the arc plasma as it cools, recombination will telze place more rapidly than ionization and the arc till be extinguished (3). Consider nor-r a transmission line whose wires may be swinging to and fro. Suppose an are be struch between the swinging sires. As this are pulls out or decreases in length, the voltage across it may vary betweai wide limits. It has been determined that the effective current values do not vary a considerable amount under such conditions. since, in an arc, the impedance is wholly resistance, power is the product of the voltage and current of the arc. It is this power in which we are here interested. 3. For this and succeeding references see Bibliography TZ-TE PRO ELEM Since an arc may exist on a transmission line and may be pulled out into great lengths, it is evident that the poner starts from zero and varies with the current and the length. The absolute value of the power at any instant is a function of the voltage and current. he know that the voltage and current of any'system are functions of the circuit constants of that system. he know further that the arc impedance pulsates at twice the fre—- quency of the impressed voltage nave. . The object of this thesis is to determine the relation-- ship between the impedance of the arc and the impedance of the line over which it is fed. an expression for the are power can then be found: hots here Thevinin's theorem, which states that maximum power will be absorbed from a not when the impedance of the external circuit is the conjugate of the net impedance. If the external circuit be composed of pure resistance, maximum power will be absorbed from the net when the magnitude of the resistance is equal to the absolute value of the mt impedance. HISTORY Periodical history of the electric arc dates back as far as 1892, at which time we find articles dealing; with the back ebctronotive force of an electric arc. At that time it was the popular belief that the potential of an arc was composed of constant and variable components. The constant component was known as the counter electromotive force. It was believed that the constant component was due to the fact that the resistance, or a part of it, proportioned. itself to the current.- Sylvanius Thompson (60) reasoned that this phenomenon of voltage, which is independent of current strength and arc length, could exist only if there were at any om surface of an are a something; equivalent to a transition resistance which varied inversely with the area over which it takes place, and if the area over which it takes place is propor. tional to the current. These facts as set forth by lo‘erical deduction are. in crude form, facts which were later proved by lahoratory mthods. In The Electrician (66), 1897, an editorial states that for physical phenomenon have ever more successfully and per... sistently baffled experimental research than the secret of electric arc phenomenon. One party advanced the somewhat metaphysical idea of negative resistance as a basis of explanation. More recent experiments dealt with the are as a source of light, and it was in.this stage that an.immense amount of research was undertaken. mm the coming of the incandescent lamp the arc was to become a thing of the past as far as illumination was concerned. It became evident that the are was to continue as a factor in transmission and distribution of power. The pranks of arcs today offer to engineers and scien. tists problems which are overcome only with an expensive outlay of materials and comprehereive analysis. An interesting study of the effects of arcs upon reactance relays (€23) has shown that an arc, being mostly resistance, has a negligible effect. The distance measure- ment of a reactancé relay is based upon.the impedance of the line between the fault and the impedance of the fault. The effect Upon the relay, therefore, is to cases it to function as if the fault were more distant than it really is. This tendency, of course, depends upon.the arc impedance as a ratio or the line impedance to the fault location. In the same article it is pointed out that an impedance relay which should onerate in an intermediate time for a fault at the- end of a protected section may operate in less than inter- mediate time or may even fail to operate on faults involving long arcs, particularly on short lines or in the presence of wind. In general, reactance relays give the same indication for area at the end of long lines as they do for metallic faults at the same location. Engineers of today have contributed1much to the know- ledge or arcs. Er. J. Clepian* or the Westinghouse Electric * See Bibliography 10 a. manufacturing Company is probably our foremost scientist in this field. His articles on are extinction have aided much in the design of circuit breakers and other protective equip- ment. a most interesting study of arc imition characteristics (3) has been carried out by tiessrs Dow, Attwood, and Krausnic k, at the University of Isz'fichigan. In their analytical investi- gations they used the cathode ray oscillograph and applied the "probe measurement scheme as set forth by Langmuir. Actual conditions of are over were carried out on lines owned by Consurrzers Power Company (43}.- Results of them experiments show that the apparent power factor of an arc varies, with line constants, over wide limits. Values were found as low as '75 per cent in each type of circuit. It was found further that a high value of apparent power factor occurs at the start of the arc and decreases to a lower value near the point of extinction. PROCEDURE The nature of the problen of determining the true power of an arc is such that consideration must be given to the equipment procurable. When a transmission line arcs, an momens amount of power is apt to be consumed depending, of course, upon the Kr. 1:. available. It was considered advisable to attack the problem on a small scale and attempt to predict phenomena which might occur on a larger scale. Arc electrode that would be well insulated from ground and that would allow of drawing out the arc and adjustment of spacing required little material, and the construction was simple. Two fiber tubes 1 1/4 inches outside and 5/8 inch inside diameter and 4 3/16 inches long: were tapped 5/4-16 at each end. They were then mounted perpendicularly on an asbestos board base with 15 inch spacing. A brass plug was screwed into the top of each tube and secured in place by a fiber lock nut. The plugasr;drilled to accomahte the electrode holders, which are 7/16 round, brass rods each 6 inches in length and tapped at one end to acconnmdate a fiber handle, at The holder threaded 52/1648. The opposite endAwas drilled along its center line to allow the electrode, which are .201 inches in diameter, to slip freely but without looseness into the holder. A connector was made to slip over the electrode holder. and a flexible wire connected the collar to a binding post pedestal placed 5 inches from the foot of each tube and 12 in line with them. a set screw was provided in the top of each plug to assure a good connection between plug and holder. Set screws were also provided for holding the electrodes accurately in place and for securing the connectors to the holders. The pedestals referred to are constructed.of 3/4 inch red fiber, each 4 3/16 inches long. They were bolted to the base, as were the tubes, and a binding post with a rubber top was secured to the top of the pedestal. The purpose of the rubber tOp is to prevent corona loss that might otherwise occur. The space between the base of the binding posts and. the bolt projecting up from the base was filled with sealim: wax. The entire apparatus*was placed upon a slab of the asbestos material to prevent any loss which might otherwise occur*through the reinforced concrete shelving. For adjustment of arc length a.taper scale was.made of tool steel and graduated in millimeters from.one to twenty. very accurate masurements were pee siblo since the ratio of length to thickness of the scale was about fifteen to one. The electrodes preper were nude from 351’ 4 D00 wire. The cotton was removed and the wire carefully straightened with a minimum of bonding to prevent altering the resistivity of the wire. Horn gaps, six and twelve inches in length, and strei ght electrodes were experimented with. It was evident that a curb steadier arc could be obtained between straight electrodes and the distance between than could be more accurately determined. The electrodes used finally were 2-1/2 inches in length, and the faces were very slightly curved. It was found that with slightly curved faces the arc length could be reassured just 13 as accurately and that the are tended to hold itself between the rounded tips of the electrodes with less fringing, and consequently less error in actual length of the arc stream. A 5 Kv-A, 4400-4433:)fi‘ansrormer was chosen for preliminary tests. The campus 440 volt power circuit was used as supply. It was found that an arc could be struck and dram out to a length of two to three inches before extinguishing it self due to air currents. At this point the transformer was found to be defective. ‘ 2300 In the first test two 250-115 volt potential transformers were connected in series across the arc to obtain oscillo- graph recordings. The wave form or voltage being so distorted the method seemed impractical. For volt meter readings, however, a potential transformer was connected across the primary (low voltage) side. This was carried out because in actual conditions the volt meter readings of voltage of that magnitude would be taken only through potential transformers. For oscillograph recording it was necessary to constmct a potential divider sh ich would consume negligible power and which nwld not break down under the strain of high potena- _ tials. It was possible to secure suitable wire wound resis- tors having 300,000 ohms when in series. The power consumed by this resistor at 4400, volts was approximately (stronga 3: 300,000 or E‘lR - 00.? watt. This power was consuzngdfg open circuit only. At the reduced vol- tage during arc discharge the power was reduced to a negli- gible value. a switch with a long insulated handle was . placed in the side of the resistor adjacent to the high p0... tential side of the are. This served as a protection to instruments as well as to the operator. The secondary was tapped from the end of the resistor nearest ground potential. The secondary of this potential divider must have a veryhigh resistance and must produce a minimum of 20 milli- aznperes for operation of a super-sensitive oscilloggraph element. The only possible way of ob taininf-g such conditions is to use the potential divider as a control circuit of an amplifier and the best type is that of a vacuum tube. Thus a 45 tube was connected with a grid bias suitable for class A amplification. A bypass condenser of 20 micro~forads is placed across the grid bias resistor to allow the desired voltage wave to pass through the grid filarent circuit of the vacuum tube. rl‘he grid circuit of this tube requires but micro amperes and thus no appreciable disturbance is set up. A key is wired across the filament grid circuit which pro... vides for short circuiting the amplifier except at the instant the oscillogram is taken. This is a needed protection against danage to the tube as the ratio of reduction of voltage is 143-1 across the potential divider. In operation the amplifier was found not to give a proper recording of the voltage on both sides of the voltage zero. This trouble was remedied by altering; the bias of the tube so as to obtain an unattenuated wave on one side of the axis with an attenuated wave on the other. It was so adjusted, however, that the lowest portions of both curves were correctly reproduced, and it could thus be observed whether or not rectification was taking}; place. Note that the indies- 15 tion of rectification muld be a displacment of the waves to one side of the voltage zero. By reversing the polarity of the amplifier with respect to the oscillograph, the voltage wave can be made to fall on either side of the axis. In the second set of films this was done so that the 0301 llogtrams could be more easily analyzed, 1. 9., the voltage and current waves were made to record 180 degrees out of phase, which is not the normal respective position. The plate or oscillo- graph current was furnished by a power pack. Before taking data the oscillosgraph was calibrated by determining the millimeters deflection per volt applied to the are. This was done by insertim a slide wire resismr, capable of carrying the exciting current of the transformer, in series with the transformer primry and adjusting; the Open circuit voltage, as recorded by a potential transformer and calibrated meter. through a range of values from 20 to 6000 volts. The deflection was read by a scale from the ground glass plate of the revolving mirror attachment- The nave form of the arc current was determined by placing an oscillograph element across a 0.1 ohm shunt in the grounded side of the arc circuit. The oscillograph series resistance eleme nt in the current circuit was set at zero, and the corresponding element in the voltage circuit was adjusted to give 30 millianps plate current as read by the plate current millismeter. For the second set up there was obtained from the City of lensing Board of Water and Light two 0. .73. 5 Kv-AH 220.2200 volt transformers. It was necessary to lanes with 16 all accuracy practicable the constants of the circuits mployed. Ience, resort was made to a laboratory generator as a source of power. Open circuit and short circuit tests were made on the two transfomers'and the equivalent circuits computed in terms of the. high side. The leakage was small and could have been disregarded. However, it was carried through for sake of completeness. a saturation run and zero and unity power factor load tests were made upon the generator as! its synfrmnous impe- dance curve plotted for the zero power factor loading. To obtain as stable conditions as possible the fields or the generator and synchronous driving motor were excited by laboratory storage batteries. The line connecting the generator with the transformer consisted of two g?- 6 rubber covered, copper wires tightly taped together. From the data it was possible to estimate the total impedance of the line, transformers, and generator. For protection or the transformers and gmerator a current limiting reactance was inserted in the line. This reactance served also as the line impedance of the test conditions. W¢8 The generatorflrated at 7.5 Kv-A and the transformers at 5 was inserted Kv—A each, «giving enough reactamebto prevent the generator. current exceeding its normal, value with the trensi'omr pri- maries short circuited. In construction, the reactors were identical. Each consisted of 450 turns of if 8 D00 copper wire wound on a bobbin 2.75 4., oiwaside diameter, 12 inches wueide diameter, 17 and winding space 3.3 inches in width. The bobbins were secured together by eight brass bolts and were wrapped with unvarnisbed cambric.- Bach coil had an inside, a cater, and an outside terminal. The center terminal permitted either the outside or inside portion of the winding to be used. _ After some preliminary experimenting it was found that cer... tain combinations of these inside and outside coils gave a range of impedance values suitable for these tests. Single pole, single throw knife switches were attached to the coils, three to two of the units and two to the rsnaining. These switches were so arranged that they could be easily and rapidly manipulated. The connections made possible by means of switching were outside and center coil, center coil only, outside and center coils short circuited. In Operation the coils were so placed on the floor that their mutual effect was wall. As a safety precaution a magnetic switch was installed with the control buttons on the table directly before the operator. when the switch was closed, two 220 volt lamps (red) more in parallel line- across the live circuit. It may here be said that the lamps served their pumose well. As a further precaution a single pole mechanical circuit breaker in series with the high potential side of the line was so placed that it was easily opened before adjusting the apparatus. For safety and for the protection of material, it was necessary to place all raters in the side of the secondary nearest ground potential and to make certain by inspection 13 that the ground circuit could not be opened by Opening; oscillograph stitches. THIS CCHDITIOII tins ThII‘ITAl’iIL‘D. This was facilitated by grounding both primary and secondary windings of the transformer to a water pipe. The meters used are of the vane type and are described on the data sheets following. Each meter used was calibrated, simultaneous readings being taken of standard and of rater on test. The circuit diagram shows the locations of the various instruments. Starting; the are by fuse wire and by 51' 30 cepper was attempted but without satisfaction. It seemed that a more rapid means should be available. Due to the relatively short are lengths used it was possible to start the are by bridging the gap with the charred end of a bakelito rod. This method proved safe, simple, and rapid. In taking readings the preper line impedance was set, the mechanical circuit breaker closed, the generated voltage checked, the oscillogi‘aph shutter adjusted for automatic operation, the mgnetic switch closed, the are started, if necessary, by the red, the switch connecting the potential divider closed, and the oscillograph motor started. Imo- diately before taking; readings the short circuiting lover of the key was released am the key depressed, the slide camera shutter opened, the hey released, and the control switch of the oscillograph turned to the suitable stop determined by the condition of film speed. At the instant the shutter Opened, ahich was accompanied by the characteristic click, tar readings were taken. Again the key was closed, the 19 camera shutter closed, the magnetic snitch Opened, and the potential.divider also disconnected. In the first test are lengths from 1 to 10 nm. were used at intervals of one millimeter with the exception of the 9 millimeter length. Seven values of line impedance were used at each arc length.) Oscillograms were taken at the same value of line impedance for mch length of arc. In addition, so that the arc characteristics could be determined, a voltage reading, 33, was taken.as described above. The reading obviously does not give the correct value of r.m.s. voltage across the are due to the distorted wave form. These readian are referred to in the discussion as apparent vol- tags readings and the impedance thus computed as the apparent impedance. For obtaining the second set of data.a.higher film.speed was used so that the oscillograph records could be more accurately analyzed. This time the potential transformer was eliminated from the circuit to avoid any possibility of error from that unit. Three are lengths were used and five impe— dance values for each length. Oscillograms were taken at each reading, but it was found later that the oscillograph failed to record voltage after oscillcgram.# 11 had been taken. The reason for this was discovered later as‘being the fault of the element but not or a nature that previous_ pictures had been affected. 20 Safety D. C. Milliammeter Lamps Oscillograph Arc Apparatus Circuit Magnetic Start Horn Gape in Place Breaker Switch Button \‘L‘T/ My , am 1' _ M56 " -' WW Potential ggwer Oacillograph Electrodes Divider Pack Cameras Starting I Current Rod Amplifier Shunt Transforllfire (under lodge in rear of apparatus) and capacitor not visible in photograph. PHOTOGRAPH OF APPARATUS 2/ ink bbk VQ VQoxw KO § U ‘1 ~53: 6Q 00%» -83 x .. hwy + l 3‘ s g E \kd N 3 QQIWX T K 836? \Ruo r co» .3 >6 $ n muzwm oh 5 k ,6 w 0 \ Q m .68 Q m i QMQ§\ Wm, MKQDW W Ahfimao 0k Quw ‘ 1 L 22 UQT KO EQQOYRN QM\\.W>\\Q {$36 #3 fi‘ fls\\ MQVAqu $ N JV 1 W)“ L 2 31 To ill N. .m. T all F U W .MmMV .. . mm. _ e NT N? -L 3* m. * .3253 (mm\..\ .KmuQAK H + \\ KWQQQU ‘3} ”\Lml mSSSQ l .l . .9 - a- 4.4K)” flxlklfl \S oQ 2, «in / bmaoocomiw / .lllml . 0 o SE wk tokow§3o o a SQ mm aoQQool MQooRom ow Emmi w buwxxu>§ >\\ hkaxbzwsz 43‘ 23 TEST FATA 24: REGULATION DATA OF G-8 Field of 3-8 Excited by S. H. Storage battery Field of 3:1... Excited by LL. 3;. Storage battery Resistance Load Test Inductive Load 'Ibst Resistor-Heater Element. Bank Inductor - Banks A 8: B Series # Igen. ‘ Egan ¢ Igen. Seen. 1 o 220 o A 220 5.0 214 2.95 205 6.6 I 212 5.3 191 10-0 206 7.4 1'79 11-? 202 ‘ 9’25 169 14-2 196 t 12 .2 152 15.8. k 191 13.5 145 17.9 185 14.7 158 19.4 1'79 16 .6 125 20.8 P 1'75 19.2 110 22.1 _ 168 21.8 96 23.5 , 162 22.8 91 24.4 ’ 156 23.3 1 es Field Current (1!? 3-8, 2.0 Anperee Rating of 6.8, 5 Kv—A, 220 tn, 60 cycles 25 LINE PATA Data taken after three hours operation Anperes Volts ‘ Ohms IL EL ‘ RL 3 2.9 .967 9 8.4 .954 15 13.9 .926 Average resistance 0.942 ohm. 26 IEAKSFURKER DATA Low Side Parallel - High Side Series Ratio 20:1 O. 0. Data: EL Ice WL [Y‘I g; Jb 171 fi“.515 50* .00559 .00205 .00294 180 .57 65 .00572 .00200 .00513 200 .81 78 .00405 .00200 .00552 3 210 .895 86 .00425 .00195 .00579 220 1.05 05 .0047? .00198 .00454 250 1.85 104 .00712 .00197 .00890 S. c. Data: 1 ‘ 2' IL E” I, ‘9” [2”] T + J: 2.5 14.2 .3 5.5 47.4 58.9 27 11.0 28.2 .48 11.5 54.1 49.5 21.8 15.0 58.8 .82 25.5 45.4 36.6 28.4 20.0 52.0 1.09 45.2 47.7 58.1 27.7 1 25.0 85.0 1.28 85.0 50.8 40.4 80.8 Rating of Trans formers 5 Kr-A - 220.440 - 1100 -.2200 volts 60 cycles 90.18185 0011 140-11 2]..) L (n) b 7 if x I I .851 .0575 ‘ 1 + II .880 .0575 1.959 45.0 I III .858 .0572 I I , .418 1.0175fl&¢ 2 1 II 1; .850 .0575 1.758 55.25 5.97 111 .858 .0572 7 ' I .418 .0175 l t 5 II .415 .0171 ‘ 1.491 7 27.45' 7.49 III .558 .0572 ~ W WWI WV .418 .0175 7 1 4 II 0560 1’ 00375 10078 2100 ' 992 1 III 0 O I 7, .418 .0175 . . 5 II .415 .0171 .855 15.19 15.88 III to _ 0 h 1 f I - .851 .0575 r |« . a II :0 0 .851 1 14.58 12.55 111 0 o , I .418 00173 1 1‘} ' 7 II 0 O 418 5053 ' 2003’? III 0 O 1 1- chance- h henries 28 CALIBRATION DATA of Westinghouse Portable Oscillograph. Supersensitive Element - Position He. II. Element series resistance 3000 ohms IODC Reading 5 .6 01-10 126DC Reading 8.0 Cm. Open Circuit Millimeters l Mm. deflection represents 43 volts. Arc Voltage Deflection Ema: D 368 8.5 566 13.0 850 19.0 1130 27.0 1414 32.0 1698 35.0 1980 37.0 2260 40.0 2540 42.0 2840 43.0 29 STANDARD MONOTROKB HARDNES OF ELECTRODES S BEF RE AND AFTER TLSTS Average hardness before tests 10.0 Monotrone average hardness after tests 7.5 Konotrone Data taken at tip of electrodes with Monotrone diamond point instrument Depth of impression 0.0006 inches EH... P at... .1".‘KI.‘\ In. 0...;I s ...D .1 \.. : 1".7. F .. I 5 .v I 1 . r . 30 DATA -‘VO A. CKARACTERISTICS, NO. 1 2 ‘ 5 fl 4* 1 5 T:5 I 9' I 217 210 196 179 , 184 142 6.0 7.45 9.60 13.4 12.1 19.4 397 u 369 ‘ 460 670 610 970 340 520 300 320 200 120 217 210 200 178 185 140 5.9 9.7 9.4 13.4 112.25 20.1 ’ 294 v 580 480 665 w 820 1200 380 t 440 440 180 f 150 ‘ 120 , 217 209 199 178 182 139 509 7.4 904 1304 12-5 3001 290 , 855 485 570 620 1100 I 520 284 240 180 200 150 Eg 225 1 2211r 182 209 182 186 145 4 Ig 5‘1 601 1306 907 1308 12.8 2096 In 250 300 , 680 480 f 680 y 630 1400 ' E8 1 320 280 ’ 208 844 204 ; 200 F 160 A ' E3 226 221 214 212 221 186 141 5 lg 1 501 600 7051 9050 600 1208 26 In 245 295 5'70 580 L 510 655 1400 # Be 200 368 320 334 480 840 160 E3 226 321 213 203 182 186 142 6 IS 5007 6.05 7050 907 1306 1207 2004 I: 253 302 370 475 690 640 1020 380 340 ' 320 280 220 ' 340 200 23 225 221 215 202 181 186 14.5 7 lg E5.05 L 5.90 7.50 9.70 * 15.40 12.7 20.5 * Is 250 J 287 l 551 480 680 64-0 1020 1.25 560 512.fl 340 300 250 250 1 220 7% g; 1“ fig 225 220 r 214 20 2 182 1% 142 5‘05 6900 7050 9070 1304 1306 2005 IS 250 300 368 480 670 530 1025 ES :ir500 440 400 340 500 292 r 216 #; ‘Eg F 226 221 215 203 182*‘ 138 142 Ia 245 295 383 , 455 660 620 1020 Be 600 L 680 560 500 360 360 348 Ln.“ on 5; at: Key to table on next page. * Reaotance value at which oscillograms 1 ..10, inc., were taken. ** Oscillogram|IO-b taken.at this point. 3 a voltage at transformer primary. g1 01 u 249 volts a generated e.m.f. Is - are current in milliamperes. Ig - ganerator current. f 8 60 cycles 32 DATAd-VOLT-AEPERE CHARACTEWISTICS Test No. II. Impedance Setting 2 3 4 6 Are Length Reading 08c. Nos. 1 2 3 4 4 E8 213 205 201 189 I8 600 7.35 8.2 10.27 I8 .296 .558 .402 .535 080. N08. 10 9 8 7 212 216 202 190 6 5.85 7.6 8.48 10.4 .290 .356 .408 .550 One. Nos. 11* 12* 13 14 E 244 256 201 190 8 6.9 8.5 8.18 10.3 .341 .423 .405 .550 Note: E03, generated e.m.f., 245 volts. E3, generator terminal voltage, volts. Ig, generator current, amperee. 12' are current, nulliamperee. r. frequency, 60 cycles . * E06 increased to 275 volts to hold are. 160 15.6 .780 15 161 15.5 .775 33 COHPUTED DATA 57 CUE? TED TRAI-ISFORIIER DATA Equivalent Circuit Data 1‘ n 60 11 Low Sides Parallel 111,311 Sides Series Open Circuit Data: E s 220v. I... . 1.1 amperes 13.1%; .415 g a 0.002 who 13 - 0.004 mo Short Circuit Data: E . 122 volts I a 45.4 amperes P.F.- .78 em - .625 z A 47 ohm a (36.7 + 129.4) Reduced to Low Side ‘2‘ 3 (0.003 .. 50.004] who 2. =- (0.091'7 4- 30.0734) ohms Reduced to Big: Side . Y '- (0.000005 .. 1.00001) 122110 23 '3 (3607 'U' 32964:) ohms GENERATOR SYNCHRONOUS AT CHOSEN CU} I Are Current“ Millianperee 300 Generator Current 6 . 2 Amperes Generator Synchronous 5 .32 Reactance Ohms Synchronous 2,128 Reactance Reduced to High Side Ohms 400 5.41 2,164 ‘59 60-0 12.2 5.56 2,224 £72.10le N CE 800 16.2 5.58 2,232 iEI-IT Il‘I'l‘ERVAIS 1000 20.2 5.62 2,248 . 1200 24.2 5.63 2,252 I‘ll! . . n x. I... . ‘ .n.1.\.l".t .l...... Y‘..,.Ilo. '..§p.v TOTAL EXTERNAL MEDLHCE AND WITTANCE m 0W1; :- *1 a: Total 2' Absolute 2] V 22‘ 56.? +1 29.4 N . 300 mm. ZL 576.8 0 23 220 2,128.0 i z. 660 15.520 1,296 +5 17,677 17.700185"? Zr 56.? +1 29.4 400 Ms. Z 376.8 0 ‘ 1 23 220 2164.0 “ Z0 520 # 9200.0 1,153 4»: 12,402 - “701%” 2: 36.7 .3 29.4 ' 600 338:. EL 37508 O 25 220 2224 2.6 340 _ 6000 976 {1 8,253.41 8,300 82PM 2.1- ' 36.7 29 .4 , 800222. EL r506.8 0 Zg 220 2262 , Zr 36e7**3 29.4 100° 11a! 21, I 3176.8 0 Zg 220 2248.0 4 ’ 2.0 168 , 2720.0 801.5 +1 4,997.4 5.060480"- Zr 36.? .3 29.4. 1 1300 166.. Z. 376.8 0 ¢ 23 , 220 2252.0 1‘ J z. 120 + 1840.0 753.5 +1 4,121.4 ~ 4.110499% flats: Zr - transfomer impedance ZL - line impedance 2g - generator synchronous impedance Zc :- reector coil impedance 1 "' 50¢' €301.08- 1.) n> 0.0% u 6.3 0 / .‘t “MOI“.‘(SN QWK oS>xlNkL$<§ 1 \ . ..Zi\.§ a 1 +3 .1 a...» .q \v 1.226611, < .//I\\. AoflIV .¥U°~U .Fuv. 1 e A T. QMkchmRLw .2 2.90% kbhk b6 625.600.2060 to... .0631 6330440.... 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Tom. 8% .81 38.. We». We». 3». ofipooua A . 833.8 conga 3.". «am. cod. you. and. bod... 83. Ana. ha. 3.1. smug: [ii 33:2 3.8 3 ca o o c a v a a a 5.33330 4949 Hanna» figs. 1. 2o 5. 4. 5e 6e 7e 8. 9. 10 0‘ 12. 13. 49 PROCEDURE F ’R PLOTTIIIG CHARACTERISTICS Plot volt ampere characteristics from data of Test $10. 1. From curves of (1) determine voltage at equal incremnts of arc current. Prom data of (2) compute impedance at chosen current intervals. From (2) and (5) plot: A. are impedance ?" arc length. F3. are impedance - arc current. C. Arc voltage .- arc length. D. Arc voltage «- reciprocal of arc current. From (Ii-D) obtain EO and C' for each arc length. From (5). plot ED - arc length to obtain 3 and d . From (5) plot 0' - arc length to obtain r and 5 - . From (5; 6, and '7) write the equation for the arc charac- teristics. From generator and transformer data compute equivalent circuits reduced to the high side or the system. From the coil data determine resistance and reactance at various positions or test. From (10) plot reactence and resistance of coils against corresponding line currents. Plot line current «- arc current. From (11) and (12) plot are current against values of reactor impedance (XL and R) as in (ll). 14- 1| 14c 15; 16; 1'7; 18.". 19. 20. 21. 22; 23. 50 From (13) determine 1: and KL of coils at values of arc current corresponding to those chosen in (2). From data on line determine line constants. From (9, l4, and 15) determine the resultant line impedance at chosen values or are current. From (4.23 and 16} record and plot are impedance values against corresponding; line impedance values. Compute power consumed by are from (2) and plot against max external impedance. Plot power consumed by are against the resistance component of the external line impedance. _ From the oscillogram data of Test No. 2, plot the volt- ampere characteristics et'the 4 mm. arc length... on same sheet plot volts - reciprocal of arc current. Plot arc resistance against corresponiing circuit impedance at the 4 mm. arc length. The plot of power against absolute line impedance is made on the same sheet. 52 «on «no coma com; emm mod was «on novel one a ooH.e «ma «on as” one «on one one ooa .uano one a coma one. an! 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I I.» .... . o 1m. o N.- N... I. v . . 68 I'JISCUSSIOI‘;~IT By graphical methods (49)" it is shown that in general the voltage - current characteristics of an Alternating Current Arc in air between capper electrodes have the following equation”: E - E0 0% - (g Mil) + Lozéllp volts where I; s 104 volts, is the voltage required to maintain an are at the theoretical infinitely short length. 0(a- 5.4, is a constant and represents the rate of change of 30 with a change of arc length, 1. 13° is the voltage across the are which is independent or currmt but a function of length. Y = 12, is a constant which represents the power in watts dissipated at me electrodes. 6 a 9.6, is a constant and represents the rate of change of C with a change of arc length. C is the power consumed by the arc in watts. I is the current through the arc in amperes. Characteristics of are impedance show that the impedance increases with an increase in arc length at a given current value. It increases more rapidly as current decreases. (See page 58) '3 The method followed has been used by other experimenters in determining characteristicivarcs between carbon elec- trodes. °f ** The values here presented are based upon the apparent voltage as recorded with a vane type voltmeter, using a potential transformer. (See procedure, page 16) 69 Are impedance decreases with an increase of current at a given arc length. For a constant lmgth of path and increasing; current the area or the are stream increases with currmt, thereby increasing the area of the conducting path and decreasing the resistance. For a periodic current wave, then, it is reasonable to assume that fine resistance or the path pulsates at twice the frequency or the current wave. a decrease in external impedance allows the current to increase in the are circuit, and ccnsequently the voltage across the arc will fall. Thus a falling are impedance exists with a corresponding decrease of circuit impedance. The rate at which are impedance decreases is greater for longer arcs since the impedance in general or a long are is greater than that of a shorter one at similar current values, and for any arc length the limiting impedance is a constant. The product E x I or an arc decreases as line impedance increases. That is, since arc impedance increases with line impedance, the current squared of the arc decreases faster than the impedance increases and the power conseqmntly must decrease, giving a falling characteristic. For any given arc length, within the limits examined, the falling impedance .- power characteristic seams to approach a limiting value which must be in the minimum power necessary to sustain an are under these conditions. That is, if the external line impedance be increased mouggi, the arc current will fall and the voltage will rise, but the power will also fall until a point is reached at which the power '70 given up by the arc (in the nature of recombination in the arc plasma) is equal to the poser consumed by it, and the arc extinguishes. It may be noted here that as the length of an arc increases, the power consumed also increases as p::“actically a straight line function of length. (See page 64) Also, the recombination and cooling increase since the area of the plasma has been increased in the Operation. In this manner also, a point of equilibrium is approached beyond which stability is impossible. Below a certain length an arc may be blown out and it will re-ignite by itself due to the breakdown of the air. This phenomenon sakes possible the are which travels up the horns of a stationary horn gap of suitable spacing and again strikes itself, repeating this process continually. The oscillograms of Test 130. 2 were analyzed for average and effective values of both voltage and current by drawing 25 ordinates per half cycle and analyzing the representative half cycle of each oscillogram. By representative half cycle is meant the curve which most nearly fits all of the eaves recorded during an exposure. 1. pencil tracing was made of each wave, and the average of these tracings was inked. For comparison and check, planime tar average values were also computed. The fact that these averages disc}: is proof that the selected ordirmtes are representative of the complete half cycle and are satisfactory for the computation of effective values. It is suggested that this method may be used more in 71 the future for determining effective values of this type of wave since e.very close check is noted. From computations it was determined that the current was very near sinusoidal since the form factor is close to 1.11. The voltage save, it is interesting to note, gives an average form.factor of 1.38 for the waves photographed after discarding two unreasonable figures. It may‘be pointed out that a value of .75 to 1.0 for the ratio of effective power to apparent power has been observed (43f under actual field.t¢et conditions. This reciprocal ratio would be from 1.33 to 1.0. The effective volt - ampere characteristic of these computations is similar to that of the previous set of data. From the volts - reciprocal of current curve (See page 63) there is obtained an intercept of E0 a 140 volts for the 4 m. length. The corresponding value from the other test is 125 volts. This result is valid since computations have shown that actual effective values are higher than apparent values (meter readings). To explain.mathematically the relationship between are power or arc impedance and line impedance from the standpoint of per cent of maximum values is a difficult task due to the discontinuous nature of the voltage characteristics, and can be undertaken only through the medium of complex mathematics. This fact has been brought out by Dr. C. P. Steinmetz (E71 and is presented in his work entitled, Alternating Current Phenomenon. Further, it has been pointed out by him.that a Fourier's analysis does not apply. '72 It has been shown in the paper by Liessrs nttsood, Dow, and Timoshenko (3) that, except for the first few microseconds after current zero, the voltage builds up according; to the law volts . e . 992 - 1,1318'0’0147t + 642'1‘64t . an. equation applies, as pointed out by the authors, only during, the re-igmition period, that is, while the vol... tags is building up to its maximum value. For the particu- lar circuit under cmsideration the equation applied after about five microseconds after current zero, and resignition lasted for about 3'7 microseconds. After this a glow took place during which period the voltage rose slightly and at a slower rate for about 24 microseconds. This period was followed by the arc discharge and the accompanying; fall of voltage. It seems reasonable to assume that after the arc is struck, the current will build up according to a law governed by the impedance and resistance of the external circuit, and further by the resistance of the ionized and conducting column of ionized vapor which is a differential function of the current fleeim and the potential impressed at any in.- stant o '73 C OE CLUS IONS In conclusion, within the limits examined, a. power consumed by an.alternating current are increases linearly with an increase of arc length rift-h git-on circuit values of r and 1. At a given arc length the power consumed by the arc diminishes as the impedance of the external circuit is ' increased. Power is not a linear function of the external impedance, but the characteristic becomes more nearly linear as the arc length is increased. The poser consumed by the are appears to approach a constant maimed value for each arc length as the circuit impedance is increamd. This minimum value is probably the minimum power required to sustain an arc of the corresponding length. Arc impedance increases as a straight line function of line impedance for large line impedance values. At smaller values of line impedance the rate of increase of arc impedance becomes less. 74 BIBLIOGRAPHY l. 2. 3. 4. ‘75 BIBLIOGRAPHY Compiled from Science nbstnacts, Sections a B, 1905 to 1932, inc. Engineering Index. American Institute of Electrical Engineers Journal and Transactions. Electrical World. *¥**¥¥*$¥$ Section I. Transmission Line Arcs and Other Power Arcs. Section II. 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