Abstract: Main cells that constitute a semiconductor element having a trench gate structure include first cells, and second cells having a structure in which gate insulating films are more easily broken by energization than those in the first cells, and the number of which is smaller than that of the first cells. At a time of driving the semiconductor element, a common gate drive voltage is applied to gate electrodes of the first cells and the second cells. An electrical characteristic is measured to detect failure of the second cells due to energization at the time of driving. The gate electrodes of the failed second cells are electrically isolated from the gate electrodes of the first cells so that the gate drive voltage is not applied to the failed second cells. The failure of the first cells is predicted based on the failure of the second cells.

Abstract: A solids-liquid separator comprises a basin in which liquid containing solids is introduced from an inlet port of the basin in a direction tangential to the side wall of the basin so as to produce a swirling flow of the liquid. The swirling flow also generates a secondary flow, and both flows promote the floating of floatable solids on the surface and the settling of settlable solids on the bottom. The solids floating on the surface are discharged by the overflowing liquid and the settled solids are discharged through a discharge pipe opening at the bottom of the basin. The liquid from which solids are separated is discharged outwardly from an outflow opening of the basin independent from the discharge of solids. The inlet port and outflow opening are separated circumferentially with respect to the flowing direction so that the circumferential separation thereof subtends at least 180 degrees about the center of the basin.