Modern Impulse Generators for Testing Lightning Arresters

1. Thorough testing of lightning arresters requires a wide variety of impulse-current waves. 2. The strictly mathematical calculation of circuit constants to produce such waves is limited to the few cases where the circuit resistance is constant. 3. Valve-type lightning arresters have a resistance that is intentionally a function of voltage or current and the determination of the constants of circuits containing valve elements must be done experimentally. 4. Impulse-current waves of the same shape but various durations and magnitudes have circuit constants where R_T/√4L/C is fixed. 5. Once the circuit constants are determined for a particular wave, the constants for similar waves of other magnitudes and durations are easily calculated. 6. The curves of Figure 5 facilitate such calculations for the wide range of wave shapes shown in Figure 4. 7. The testing of various types and ratings of arresters with a number of different waves, requires extremely flexible impulse-generator circuits. 8. Ordinarily the impulse-generator capacitance is the most difficult circuit constant to adjust, but four special impulse generators are described having capacitance values easily adjustable over a wide range. Several years of experience with these generators, and the previously mentioned calculating methods, show that constants for any desired wave, within the capabilities of the equipment, can be computed and set up easily and quickly.