Abstract : The air cooler fan's status in the DCS system only displays normal operation, without any indication of shutdown or fault. The restart time after the frequency converter protection shutdown causes fluctuations in system operating parameters, affecting product quality and normal production. To address this issue, frequency converter parameters were optimized and control circuitry improved. Now, when the air cooler fan's frequency converter protection shuts down, the DCS system displays the fan shutdown and issues an alarm signal. The restart time has been reduced from 3 minutes to less than 5 seconds, significantly shortening the fan startup time and resolving the impact of fan shutdown on the unit, ensuring continuous and stable production operation. Keywords : fan; frequency converter; control system; modification[b][align=center]Modifications to Frequency Transformer Control System of the Fan of Air Cooler in DCS System ZHANG Xue—feng, BIAN Lian—fang, LIU Feng, CHEN Feng (Natural Gas Processing Plant of Zhongyuan Oil&Gas High Technology Stock Co., Ltd., Henan Puyang 457162, China)[/align][/b] Abstract : In DCS system, although the state of air eooler on normal operation is well informed, no message is available when the fan of air cooler is in shutdown and/or breakdown and the longer restart time is one of main reasens for the unsteadiness of operational parameters and product quality． To solve this problem, we had opti-mized frequency transformer parameters and improved the control circuits, added the alarm message to DCS sys-tem once the air cooler fan is in breakdown. At the same time, we improved the restart time from 3 minutes to 5 seconds. Based on these effects, the negative influence of shutdown and/or breakdown on the production system is avoided effectively. Key words : fan; frequency converter; control system; modification 1 System status before modification (1) Normal startup process: After pressing the start button SB2, the circuit is formed by L11→FU→KA→SB1→SB2→→KM→KH→N. KM and KA1 are energized and engaged. After releasing SB2, due to the self-locking effect of the contacts of KM, KM and KA1 remain engaged. The frequency converter TD2000 is energized, FWD is the input terminal for the frequency converter operation control, KA1 is closed to make the frequency converter enter the running state, and the air cooler fan is energized and runs. At this time, the normally open contact of KM is closed, and the DCS system displays that the air cooler fan is running. [b][align=center]For details, please click: Modification of DCS status display control system for air cooler fan frequency converter[/align][/b]