Sphere-Gap and Point-Gap Arc-Over Voltage As Determined by Direct Measurement

This is a report of some of the work done at the Ryan High Voltage Laboratory, Stanford University, during the school year of 1927-28. A new method of measuring high voltages is described, in which the current through a water resistor is recorded on an oscillograph. Over a million volts to ground was measured with an accuracy believed to be better than 2 per cent. A calibration of the meter sphere gap was determined for voltages up to 1100 kv. and the arc-over voltages for point gaps were determined for distances up to 30 ft. Point to plane arc-over voltages were also measured. Included in the report are some tests made in connection with the shielding of the water resistor determining to what extent capacity currents were causing error. Sphere gaps were also used in connection with the determination of the arc-over voltages of the point gaps to determine whether there was any high frequency, set up by the heavy corona streamers from the point, that could not be recorded by the oscillograph. The procedure of taking an oscillogram of the corona current from a pointed electrode a million volts above ground is described. The practicability of the use of the meter sphere gap for voltage measurement is discussed.