Industrial Automatic Control Systems and Controllers Annotation << Back Improving the Fault Tolerance of GFU Air Cooler Control Systems: Transition from a Ring Topology to Isolated Segments Dyma I.S., Shevlyagina S.A. This article examines the low fault tolerance of air-cooled unit (ACU) control systems at gas fractionation units (GFUs), caused by the use of a serial ring topology. The causes of cluster failures of variable-frequency drives (VFDs) during single network equipment failures are analyzed. These failures lead to temperature disturbances during propane fraction condensation and pressure increases in the column equipment. A technical solution is proposed based on the transition to a star topology by implementing fi eld switches in each control cabinet. This approach ensures fault localization and eliminates the impact of a single port failure on the operation of the entire fan group. Additionally, the study substantiates the watchdog timer settings and drive behavior strategies in the event of communication loss, including fail-safe mode. This, combined with the proposed topological upgrade, ensures process continuity in the presence of industrial interference. Keywords: gas fractionation unit, air cooler, variable-frequency drive, network topology, fault tolerance. DOI: 10.25791/asu.6.2026.1664 Pp. 13-18.