Abstract : This paper introduces the application of frequency converters in the Canglian fire protection system. Unlike the traditional method of using frequency converters in conjunction with PLCs to achieve constant pressure water supply, this system uses two frequency converters to drive two motors respectively, with each motor serving as a backup for the other, to achieve constant pressure water supply. Keywords : Frequency converter; Constant pressure water supply; Fire protection system 0 Introduction Our factory carried out a fire water system renovation. The entire fire water line is supplied by two 160kW motors (controlled by frequency converters) and two 250kW motors (reduced voltage start). In the original design, one of the two frequency converter motors was in operation, providing constant pressure water supply, while the other frequency converter motor and the two 250kW motors were in standby. The parameters of the two motors controlled by the frequency converters are as follows: Model: Y315L1-2 Power: 160kW Rated voltage: 380V Rated speed: 2890r/min The frequency converter used is the ABB ACS600 model. During trial operation, we found that once a fire occurs and the fire protection system is activated, the fire water pressure drops rapidly in a short period of time. A single 160kW motor may not be able to meet the requirements. Therefore, it is necessary to have two variable frequency drive (VFD) motors that can serve as backups for each other, automatically starting the other when one fails to meet the fire water pressure requirements. This ensures that fire water needs are met quickly while also allowing time to start the other two 250kW fire pump motors. Currently, domestic fire water systems generally consist of one VFD pump and several fixed frequency pumps, controlled by a dedicated control device (such as a PLC) for pump operation and automatic start-up. The VFD pump automatically adjusts its speed based on pressure signals to maintain constant pipeline pressure. In the event of a fire, the pipeline pressure drops sharply, automatically starting the fixed frequency pumps to maintain constant pressure; when water use stops, the pressure rises, automatically stopping the fixed frequency pumps. However, our factory's fire water supply system does not meet these requirements and requires hardware and software modifications. 1. Design Objectives and Countermeasures When a fire occurs and the fire protection system is activated, the fire pumps should be able to operate automatically as required, ensuring sufficient fire water pressure and ensuring the timely operation of the fire protection system. [b][align=center]For details, please click: Application of Variable Frequency Drive (VFD) Constant Pressure Water Supply in Cangzhou Refinery Fire Water System[/align][/b]