Publication: Western Electrician
Chicago, IL, United States
Experiments with High Tension Currents
The firm of Siemens & Halske, Berlin, Germany, has for a couple of years been experimenting with converters for high tension current, and also with conductors and insulators suitable for this system of electrical transmission. In opposition to similar experiments made
at the Oerlikon factory in Zurich, Switzerland, described in the WESTERN ELECTRICIAN, April 4, 1891, this concern has been working to abandon the use of oil insulation for converters. It has undertaken the task of finding a dry material that would be as effective as oil, hoping that whatever good results might be obtained would prove valuable in the construction of high insulation cables as well as in converters. A series of experiments in this line was recently made at the club rooms of the Electro-technical society in Berlin, by Dr. Koepsel, who read an interesting paper in explanation.
The apparatus employed in the lecture room consisted of three converters of different construction, but of an even capacity of 10,000 watts; a group of 200 incandescent lamps (10 candle power, 120 volt) connected in series, and another group of 200 lamps (16 candle power, 120 volt) connected in multiple. In addition to
this there was a complete set of instruments for indicating the current, electromotive force, etc. A 1,000 volt, 10 ampere, Siemens & Halske alternating dynamo supplied the current. This machine was located at the factory, whence the current was carried for a considerable distance to the club-room. Copper conductors of a carrying capacity equal to No. 12 B. and S. gauge, supported by oil insulators, Fig. 1, were used. The wires were joined to converter No. 1, Fig. 2, and the dynamo current of 1,000 volts and 10 amperes was transformed into 20,000 volts, also 0.5 ampere. Through converter No. 2 the tension was again reduced to 1,000 volt, and through converter No. 3 to 100 volts and 100 amperes. At this pressure, 100 volts, the current was fed to the second group of lamps, supplying the 200 16 candle power, 100 volt lamps in multiple. Volt and ampere meters indicated during the display the exact condition of the current, and also the loss of energy in converting. As one experiment the current was taken from the secondary coil of converter No. 1, with a tension of 20,000 volts, and was carried through a fine wire to the first group of 200 lamps (10 candle power, 120 volt) connected in series. The current consumed in these lamps proved to be only 0.3 ampere. During the experiment an interesting phenomenon was observed in the lamps. The carbon filaments in the outside lamps of the series were noticed to vibrate rapidly, the rate of vibration decreasing in the lamps toward the center of the group, where the filament remained quiet. The cause of this vibration was explained by means of an electroscope, Fig. 3. From five points of
the windings of the secondary coil in the converter and from corresponding points in the lamp group wires were connected to two sets of foil electroscopes supported by rods of hard rubber. The connections were such that the two terminal wires, both from converter and lamps, were joined to the two outside foils of each group, and the center wire from each side to the center foil of the electroscope, and so on. In sending a current through the converter and lamps it was found that the outside foils of both sets would diverge considerably, while the foils next to them would be less disturbed, and the foils in the center would remain uninfluenced. Dr. Koepsel explained this as a proof that there are two points in the circuit where the difference of potential between the circuit and the ea