126 



THE WORLD'S ADVANCE 





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FlG.4. 



Diagrammatic Plan of the 

 New Type of Spark Gap. 



times as long as one of these gaps. On 

 the other hand, the voltage required to 

 produce a spark through such a series 



of n short gaps 

 is practically the 

 same (in some 

 cases less than) 

 that required to 

 bridge a single 

 gap n times as 

 long. Thus, 

 subdivisions of 

 the total dis- 

 :harge favors 

 the suppression 

 :>f an arc, yet 

 requires no ad- 

 ditional poten- 

 tial to produce 

 sparking. 



The present gap, shown in the illustra- 

 tions Figs. 3 and 3a, was arranged for 

 non-synchronous operation on 7o-cycle 

 supply. The disk is constructed of y%" 

 Bakelite and is 12" in diameter. It car- 

 ries 24 studs, which are threaded into 

 the Bakelite and clamped by lock nuts 

 on each side of the disk. Bakelite is far 

 superior to either fibre or hard rubber 

 in the construction of a disk of this kind, 

 as it can be obtained in sheets of very 

 uniform thickness and does not warp nor 

 absorb moisture. 



Some attention was given to procuring 

 a suitable metal to be used for the spark 

 gaps proper. Copper electrodes tend to 

 "bead" in the electric spark; that is, the 

 exposed surfaces become covered with 

 small globules of copper. Zinc, on the 

 other hand, tends to "pit." It has been 

 found that an alloy of copper and zinc, 

 copper predominating, wears down quite 

 evenly, the pitting tendency of the zinc 

 apparently counterbalancing the beading 

 tendency of the copper. 



The gap is shown diagrammatically in 

 Fig. 4. It is seen here that eight spark 

 gaps are bridged in passing through the 

 disk. The stationary gaps are arranged 

 as shown in Fig. 5. The electrodes are 

 beveled and set at an angle with the disk, 

 pointing in the direction of rotation. 

 This method effectually prevents me- 

 chanical destruction of the gap should 

 stationary and revolving electrodes come 

 into contact. Radiating flanges are pro- 



vided as shown to aid in dissipating the 

 heat. The electrodes are mounted in 

 Bakelite and those on one side of the disk 

 can be moved as a unit for the purpose 

 of rough adjustments in gap length. For 

 this purpose the disk is also moved along 

 the shaft. The closer adjustments are 

 made by swinging the individual side 

 electrodes themselves in their supports. 

 Considerable care had to be exercised in 

 construction so that all of the eight gaps 

 were in their proper positions for spark- 

 ing at the same instant. The disk was 

 balanced by mounting on the shaft which 

 was then supported on knife edges. A 

 small 10-24 machine screw was used to 

 obtain exact balance ; it was placed about 

 four inches from the center of the disk. 

 The bearings are bronze and no trouble 

 has been experienced from heating. 



Experiments to study the behavior of 

 this gap were carried out on a 2 kw. 70- 

 cycle transmitter. The transformer volt- 

 age was approximately 20,000 volts (ef- 

 fective), and the spark- frequency used 

 was 700 per second. The gap was found 

 to exhibit properties of pseudo-impact 



DIRECTION OF ROTATIOM 



n n n 



LJ LJ LJ 



FlG.5. 



Arrangement of Stationary Electrodes of the Spark 

 Gap. 



excitation, provided the individual gaps 

 were kept very short. There was also 

 a decided improvement in the power fac- 

 tor measured on the primary of the trans- 

 former, readings of 75 per cent, being 

 obtained with eight gaps, as compared 

 with 62 per cent, when only two gaps 

 were used. This is probably due to the 

 decrease in arcing at the gap when the 

 eight gaps were used. An arc at the 

 transformer terminals constitutes a more 

 or less severe condition of short circuit, 

 and a short-circuited secondary is equiv- 

 alent to an inductive load on the trans- 



