Abstract: Abstract:This paper addresses the issue of excessive temperature in the lower guide bearing of a pumped storage power station variable speed unit discovered during the commissioning period. Through careful analysis of the bearing structure and temperature trend data, the root cause of the problem was identified. After shutting down and disassembling, it was found that the seal ring of the lower guide bearing was not strictly sealed. Subsequent commissioning proceeded smoothly, providing practical experience for the design and selection of domestic pumped storage variable speed units, and possessing reference significance.