CABLE TESTING 703 



442. This is a test-room instrument intended for use on the 

 switchboard. 



When the instrument is operating, the peak voltage is pro- 

 portional to the length of the band of light on the screen. 



The necessary vertical and horizontal adjustments of the beam 

 of light can be made from the front of the switchboard by means 

 of two milled heads which actuate the two adjusting rods. To 

 compensate for changes in the amplitude of vibration due to 

 variations of temperature and other causes, an adjustable 

 rheostat is connected in series with the vibrator. By connecting 

 the vibrator circuit to a source of direct current by means of a 

 double-throw switch the calibration may be quickly and ac- 

 curately made. The magnets are operated at high saturation 

 so that fluctuations in exciting currents affect the instrument but 

 slightly. The instrument as used is connected to the secondary 

 of a potential transformer, whose primary is connected directly 

 to the high-tension circuit or to a voltage winding on the 

 transformer. 



In any case where a potential transformer is used for very 

 high voltages, one should be on guard against the effect of dis- 

 tribntod capacity in the transformer and satisfy himself by 

 independent tests that no error is thus introduced. 



References 



1. "Location of Broken Insulators and Other Transmission-line Troubles," 

 C. L. NICHOLSON, Trans. American Institute Electrical Engineers, vol. 

 26, part II, 1907, p. 1319. 



2. "Location of Faults in Underground High-tension Power 

 WILLIAM A. DURGIN, National Electric Light Association, Thirty-third 

 Convention, 1910, Proc., p. 498, vol. 1. See also "Location of Faults in 

 Underground Cables," WILLIAM A. DURGIN, Electrical World, vol. 54, 



Testing of Cables," W. I. MIDDLETON and C L. DAWES, 

 Tmns. American Institute Electrical Engineers, vol. 33, part II, 1< 14 p. 1185. 



4. "The Crest Voltmeter," L. W. CHUBB, Trans. American Institi 

 trical Engineers, vol. 35, 1916, p. 121. 



5. "Peak Voltmeter," C. H. SHARP and E. D. DOYLE, Trans. Amer* 

 //lite Electrical Engineers, vol. 35, 1916, p. 129. TTnRicKS 



B Voltmeter Coil in Testing Transformer, A B. H 

 JB., Trans. American Institute Electrical Engineers, vol. 35, 1 >16, p. 138. 



7. "Notes on the Measurement of High Voltage " WILLIAM R. WORK, 

 7V,,*. American Institute Electrical Engineers, vol. 35, 1916, p. 206. 



