GB1173685A - Spark Gap and Discharge Control Apparatus. - Google Patents

Abstract

1,173,685. Surge diverters. OHIO BRASS CO. 31 March, 1967 [11 Oct., 1966], No. 14738/67. Heading H2H. A multi-stage surge diverter selectively responsive to surges having respectively slowly rising and fast rising wavefronts (e.g. switching surges and lighting surges) comprises the arrangement shown in Fig. 2 in which main spark gaps 21-24 are respectively shunted by pre-ionizer gaps 32, 36, 42 and by a capacitor 40, and also by grading resistors 35, 39, 41, 45. The value of resistor 41 is small relative to that of the resistors 35, 39, 45 which are of equal value, whilst the resistors in series with each pre-ionizer gap are chosen so that their value per stage progressively decreases from a maximum in stage S1 to a minimum in stage S4, the gaps 32, 36, 42 being designed to spark-over at substantially the same voltage. When a surge with slowly-rising wave front appears on the line 28, gaps 32, 36, 42 spark-over and alter the voltage distribution across the stages S1, S2, S4, so that the main gaps 21, 22, 24 fire in that order followed finally by the gap 23. During initial discharge of the gaps 21-24, the gaps 30, 31 spark-over until their arcs are extinguished by a magnetic blow-out coil 25 which thereafter serves to extinguish the arcs across the gaps 21-24. When the surge on line 28 is one with a rapidly-rising wave front, the voltage distribution across the stages is determined by the distributed capacitance of which the capacitor 40 is chosen so that the greater part of the impressed voltage is divided across the stages S1, S2, S4. These then fire in an indeterminate order determined primarily by the voltage variation between the stages caused by the impressed wave front, the stage S3 again being the last to fire. The arrangement of Fig. 2 may be made symmetrical by replacing members 36, 37, 38 by a capacitor (75), Fig. 5 (not shown), the values of the grading resistors and capacitors being chosen to obtain desired firing orders which may or may not be similar to those already described. In a modification of the symmetrical arrangement the grading resistors of the first and last stages are omitted. In both the described embodiments, it is preferred that the total resistance of the switching gap branch, when the gap is fired, should be less than the resistance of the associated grading resistor. The various stages of the arrester are constructed and arranged in the manner disclosed in Specification 1,173,686.