Development of an On-Line Rotor Crack Detection and Monitoring System

Abstract

A very comprehensive technology of on-line rotor crack detection and monitoring has been developed. The technique, based on the vibration signature analysis (VSA) approach, can detect incipient transverse rotor cracks in an “on-line mode.” The technique is generic and is applicable to all machines whose rotors are subjected to some kind of bending load. These machines include turbines, generators, pumps and motors, etc. The technique is based on the analytical modeling of the dynamics of the system. The basic idea is that through the modeling approach, the crack symptoms can be determined in terms of characteristic vibration signatures. These signatures are then used to diagnose the flaw in real life situations. A 3-D finite element crack model and a nonlinear rotor dynamic code have also been developed to accurately model a cracked rotor system. This program has been used to develop a variety of unique vibration signatures indicating a rotor crack. Both the analytical crack model and the crack signature analysis techniques have been experimentally validated. A microprocessor-based on-line rotor crack detection and monitoring system has been developed. The system has successfully detected cracks of the order of 1 to 2 percent of shaft diameter deep in an “on-line” mode in a series of large-scale laboratory tests. The system has been installed on a turbine-generator set at a utility in the field in October 1986 and has since been operating continuously, both in on-line as well as in coast-down modes, essentially, flawlessly. The system has also been applied in a crack detection program for nuclear reactor vertical coolant pumps. This paper describes all aspects of the development, starting from the technical concept to the commercial field applications.