Plugging Of Stator Cooling Water System: Root-Cause Analysis And Chemical Cleaning

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Dr Thomas Bauer
SvoBa Tech, Inc

Large electric generators are directly cooled with high purity water to remove the heat from the coil efficiently. This stator cooling water system (SCWS) can operate without issues for years, but when problems arise, it can go quickly. Reduced heat transfer results in power downgrades, reduced insulation lifetime, forced outages and/or irreversible damage to the generator. The most common problem is reduced heat transfer due to plugging of the copper hollow conductors with copper oxides.

The current publication is focusing on 3 different case studies, its root cause analysis and restoring cooling efficiency.

All three cases exhibit in a different root-cause for the plugging mechanism: Case A first indicated plugging of the filter, case B within the strainer and case C in both, the strainer and the filter. Thorough analyses revealed that also the stator was already plugging up in all three cases. Root causes were found to be improper layup, hardware malfunction, improper chemistry regime and/or hardware design issues.

Chemical cleanings during operation (online) or during outage (offline) removed all copper oxides within the systems and restored full cooling capacity in all three cases, preventing forced outages of the Power Plants.

Thomas Bauer (Ph.D., Material Science, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland) worked for Siemens Transformers Austria in Weiz, Austria during his master studies in the field of chemistry-related issues with transformer oils. After his Ph.D. he joined Alstom Thermal Power in Baden, Switzerland in 2012 where he worked in the field of water-cooled generators and especially on chemical cleaning of stator and rotor coils. Additionally, he was project manager of R&D projects related to water-cooled generators. In September 2014 he co-founded SvoBaTech, Inc. an independent service provider for stator cooling water systems (SCWS). His key competence is on an all-in-one solution for SCWS, ranging from designing and commissioning of alkalization systems and support in troubleshooting and data analyses to chemical cleaning of stator and rotor coils as well as updating SCWS instrumentation.

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