Measurement of transients

The transient crest meter was developed to investigate several pressing problems in high-voltage transients. It consists of a gold leaf electroscope in series with a rectifying device, an electron tube, which enables the electroscope to charge, but prohibits discharge. The charge that is captured in this manner is proportional to the maximum impressed potential, and where adequate insulation is possible, will remain substantially undiminished for many seconds or even minutes after the transient has passed by. The instrument described is thus seen to be essentially a crest voltmeter. By the proper use of inductance, resistance, and capacitance it is possible to make the applied voltage dependent upon the maximum peak, maximum slope, or maximum area of current and voltage waves, thus giving information regarding the character as well as the size of the transient. The method of calibration, and the precautions that must be taken in measuring transients with this instrument are pointed out in detail in the paper. In particular, care must be taken to carefully insulate the gold leaf. The minute charge stored at several hundred volts makes it necessary to employ special vacuum bulbs with the filament and plate leads coming through opposite ends of the tube. The crest meter has already served successfully in several investigations. The first application was the measurement of the potential of the sphere electrode of a high-voltage oscillator. The method followed consisted in measuring the charging current to the sphere by means of a shielded electroscope resting within this electrode. When combined with a second gold leaf acting as relay contact to give an alarm at a given voltage, the instrument is admirably suited for the study of transmission system disturbances, for the observer need be tied no closer to the test than remain within hearing distance of an electric bell. Such an application was made during four months of the past summer on a 110 kv. line belonging to the Pacific Gas & Electric Company, in an effort to discover the cause of apparently unprovoked flashovers which this particular line experiened from time to time. Other similar applications become evident as their need arises.