Seal oil ingress in large turbo generators: A South African utility perspective

South African utility is examined. Hydrogen cooling offers high thermal efficiency, but it relies on a pressurised seal oil system to maintain hydrogen purity and prevent air or moisture from entering the generator casing. When operational deviations or equipment issues occur, seal oil can migrate into the generator interior, where it is dispersed by rotor airflow and deposits on stator and rotor components. Over time, this contamination degrades insulation, disrupts slip planes, restricts hydrogen dryer performance, and reduces generator reliability.

Although comprehensive Original Equipment Manufacturer (OEM) procedures exist for gasup, degas, and steady state operation, inconsistent adherence to these requirements has contributed to recurring ingress events. The most common causes include incorrect seal oil activation during pressure transitions, malfunctioning detraining equipment, seal assembly defects, and failures in differential pressure control. Limited operator awareness and incomplete reporting further obscure the scale of the problem.

Two case studies illustrate the severity of ingress. In one event, a generator tripped when a leakage detector alarm triggered, and significant oil contamination developed within an hour.

In another case, repeated minor ingress incidents accumulated over time, resulting in sludge formation and slot insulation wear that contributed to a stator bar failure. These examples show how both acute and gradual ingress can create long term mechanical and electrical degradation. Laboratory testing of seal oil samples highlighted elevated particulate contamination at several sites, with ISO 4406 particle counts exceeding acceptable limits. Some samples also contained high copper levels, indicating bearing wear, and elevated silicon, signalling dust ingress. Water content was within acceptable limits across all oil samples. These findings confirm that contamination and wear metal presence significantly influence ingress severity.