Abstract: An ultrasonic search system comprises a hollow nozzle block including a plurality of radial nozzle openings, and a probe holder disposed in coaxial relation to the nozzle block and cooperating with the nozzle block to define an annular passage therebetween. A plurality of probes are mounted within the probe holder in radial alignment with the nozzle openings and extend radially from the inner surface of the probe holder toward the nozzle openings, respectively. Water is supplied to the annular passage and injected from the nozzle openings to a test piece of a circular section such as a steel pipe. The test piece passes through the hollow nozzle block while the nozzle block and the probe holder are rotated by an electric motor. Ultrasonic waves are transmitted from the probes through the nozzle openings into the test piece so as to detect flaws in the test piece by reflections.

Abstract: A commutation circuit for an inverter using an auxiliary source to accumulate the energy for commutation is simplified by assigning to the main diodes mounted in series with the main thyristor of the inverter the role of preventing partial discharge of the storage devices during the commutation process.