Shunt Resistors for Reactors

The object of this paper is to present the results of an investigation to determine the effect of resistors shunting current limiting reactors, on the impulse behavior of the typical system employing them. The typical system is reduced, without loss of essential generality, to a comparatively simple analytic network; and the impulse behavior of this network is then calculated mathematically. These calculations are adequately supported by test results with impulse generator and cathode ray oscillograph, both in the field and in the laboratory, and accurate agreement established. Methods are developed and illustrated for taking into account incident waves, such as those due to lightning, of arbitrary shape. Under the most unfavorable condition of wave shape and circuit conditions, voltages approaching four times that of the incident wave may be built up at the bus by reflections and oscillations. In general, through the use of a shunting resistor, of proper value, three beneficial results are obtained: (a) Oscillations are completely eliminated, thereby limiting the maximum voltage which can occur on the bus to never more than twice that of the incident wave. (b) The initial rise in voltage on the line side of the reactor, due to positive reflections, is reduced and can be held down to the final value corresponding to the tail of an infinite rectangular incident wave. (c) The internal oscillations in the reactor itself can be eliminated, and the voltage distribution improved.