2018 18 Paper: Murray 1 U04 Turbine Bearing Failure Investigation

Murray 1 Power Station commenced a major refurbishment programme in late 2016 beginning with Unit 4, the first of ten units. Unit 4 was returned to commercial service on 29 May 2017, with a ‘first in last out’ preference placed to “run in” the unit and identify problems early.
In July 2017, following 773 hours service, a distinct temperature rise of both turbine bearing RTD’s occurred and the unit was taken out of service. The temperature rise pattern was consistent with a bearing wipe, prompting an investigation into the cause. The root cause of the event was not obvious.
The Murray 1 turbine bearings are a two piece shell design, and are the only ones in the Snowy scheme including both a cooling water jacket, and sump cooling (basic tube coolers). Initial investigation suggested possible disbonding as the likely cause, given previous bearing failures, however further NDT removed this theory. Following investigations into several other potential root causes, including a change in oil group, the failure mode of differential expansion between bearing journal and bearing was proposed. To investigate this root cause a creative use of 3D models, historian data, photos and measurements were used as evidence of the potential failure mode. This initial inhouse work provided the data to highlight the possibility of this previous unseen failure mode, which was then verified by an external consultant using thermal FEA analysis. This work validated the internal study that differential thermal expansion was the failure mode, caused by excessive cooling water flows.

• Author: Brian Hardwick
• Exchange: 2018 - Albury AGL
• Company: Snowy Hydro
• Topic: Alignment, Bearing, Francis, Operation & Maintenance, Runner, Thermal Expansion, Turbine
• Key Words: Bearing, Clearance, Cooling, Modeling, Oil Samples, RCA, Rehabilitation, Upgrade/Uprate