This paper described the check

analysis and process for a complete shutdown accident of air-cooling unit of a forced oil circulation air-cooled 220 kV transformer

and analyzed the reason why the air-cooling unit with complete shutdown status failed to alarm.Moreover

the control circuit for automatic restart of the air-cooling unit and the circuit of delay tripping and start when the complete shutdown happens were modified

leading to the elimination of maloperation and misoperation of the secondary circuit in the transformer’s air-cooling unit

and to the safe operation of the main transformer.