Abstract: A method and apparatus for protecting switching elements, and, in particular, thyristor switching elements, which are used in a pulse generator to supply pulsed electrical voltage to a capacitive load, from damage resulting from a spark-over occurring in that load are described. Specifically, whenever the occurrence of a spark-over is detected, during, for example, the interval of time when a voltage pulse applied across the load is decaying, a trigger pulse is applied by a firing circuit to the thyristors to cause them to assume a substantially conductive state.

Abstract: A rotary kiln (1) having a plurality of cooler tubes (2) arranged in a planetary fashion therearound. The cooler tubes (2) rest in saddles in a ring-shaped member (3) surrounding the rotary kiln and are retained in the saddles by caps (4) with clearance so as to permit axial movement and radial heat expansion of the cooler tubes (2). The ring-shaped member (3) is attached to the kiln (1) by a plurality of ring support members having a first flange (6) attached to inner surface portions of the ring-shaped member, a second flange (5) attached to outer surface portions of the kiln (1) and an intermediate web member (7) having a substantially frusto-conical surface and connecting the first flange (6) and the second flange (5). Preferably, the first flange (6) and web member (7) have slots (8) extending axially of the kiln across their entire lengths. The slots (8) can extend axially of the kiln across the second flange (5) as well.