b'Partner News Summer 2022 35CorporateThe machine was now returned onshore and tested. The rotor end windings were split, and a volt drop test carried out on the now separated windings with the result below.It is possible to detect inter-turn faults on windings using Recurrent Surge Oscillograph testing (RSO). This technique looks at the reflected wave of an input rectangular pulse and is carried out offline,not generally on site. This test was carried out once the machine was returned to the onshore repair facility and the result presented below.Both tests clearly indicate a fault on the rotor winding and serve to authenticate the MVBI results.Corrosion of the copper on the windings is visibly breaking through the insulation which can be seen in the picture. This is not easily observed in location owing to the construction of the machine, frame, end covers and proximity to the air gap.Repair and re-installOnce the generator had been repaired and re-installed on the platform further tests were taken. These established that the fault seen before repair was no longer evident - confirming that the diagnostic interpretation of the signals had been correct, and that the repair was carried out satisfactorily.In addition, at this time, tests were repeated on the second generator, and the tests showed there were no indications of the same problem. The resulting certainty meant a decision not to overhaul the second machine could be made. This represented a direct cost saving of 500,000, reduced the risk of operating with no redundancy in the power system and decreased any chances of indirect costs which may have resulted from the loss of production. MVBI is becoming more widely recognised as a technique that caneasily be installed, on a permanent or temporary basis, to detect both electrical and mechanical anomalies. It is useful for inaccessible equipment such as submerged pumps where it is difficult to use techniques like vibration analysis. As this example shows, it can also give previously unavailable online condition indication of synchronous machine rotors.'