When planning the installation of permanent probes, the following advance planning subjects should be addressed
Permanently Mounted Probe Installations
When planning the installation of permanent probes, the following advance planning subjects should be addressed.
- Magnetic wedges in the rotor coil slots reduce the air-gap slot leakage flux signal. Thus, shorted turn detection sensitivity is reduced in these slots. (Note the #1 coil slot data in Figures 3-9). If plans are being made to assemble an air-gap probe, extra effort and possibly cost should be expended to ensure that all wedges in the leading slots at the axial position of the flux probe are non-magnetic. On some fields, this may require purchasing 2 to 4 non-magnetic wedges from the Original Equipment Manufacturer. The wedges would be used to replace the magnetic wedges near the turbine end in the slots leading the pole. Discussions with Generatortech, Inc. should be made early in the planning stages.
- Critical machine dimensions such as rotor outer diameter (O.D.), retaining ring O.D., and stator core I.D. will have to be supplied to Generatortech, Inc. so that the flux probe can be manufactured before assembly. Generatortech, Inc. will provide a drawing showing which dimensions must be supplied. If desired, Generatortech, Inc. personnel will take the dimensions. An extra trip to the plant will be required for that purpose.
In this online brochure, we have described a simple air-gap flux probe assembly, testing, and analysis program which will significantly improve your ability to understand your generator performance variations. The probe described must be assembled while the rotor is removed from the stator core. There may be cases where critical shorted-turn conditions are experienced before a planned outage. On many generators, it is possible to assemble a temporary probe as shown in the figure below. The data from this probe will provide the same definitive test results, thus allowing you to determine whether corrective action should be performed at the next outage. Generatortech, Inc. can help you evaluate the feasibility of installing the temporary test set-up.
Generatortech, Inc., 31 Sutherland Drive, Scotia, NY 12302. Tel: 518-399-4646; Fax: 518-399-4646.