Abstract: This article discusses the use of programmable PLC controller and inverter to regulate the motor speed, to achieve automatic control of fire water supply system pressure regulation. When the fire occurs when the fire pump automatically activated, so that the water pressure in a short period of time to meet the requirements, so as to maintain a relatively stable pressure to meet the actual fire water requirements, greatly improving the reliability of the fire system normal operation to avoid major accidents occur. Key words: fire pump, PLC automatic control, frequency control Introduction With the rapid development of China's power system, power plant fire water system is more and more important, safe, reliable and stable operation of automatic control of fire water system is also more and more The higher. The original manual control and simple electrical chain and other control methods, due to the lower degree of automation, poor reliability, has been unable to adapt to the power plant safe and reliable operation. With the programmable PLC automatic controller and inverter regulation principle widely used, it is suggested that the fire water system uses programmable PLC automatic controller and inverter to control the constant water pressure, effectively ensure the timely supply of water when the fire occurs, And can automatically switch back and forth to ensure the safe use of water supply system to achieve unattended to avoid errors due to human factors. 1. System Introduction As the original fire water supply system is completely controlled by hand, the fire pump can not automatically put into water supply when the fire happens. The water pressure can not meet the requirements in a short time. The pressure regulating pump can not effectively guarantee the pipe network pressure. And human error can also cause delays in water supply, easily lead to pipe burst, causing equipment damage. Therefore, the original fire pump control system with low degree of automation, poor reliability, there is a big flaw, and in the fire there is a great risk. 2, the design program The system equipment for a 250KW motor fire pump and a 15KW motor regulator pump, the use of PLC control, inverter control motor speed control, with unattended in the case, automatically meet Fire water requirements. The system uses a pressure sensor with analog output, a pressure range of 0 ~ 1.6Mpa pressure gauge P and a digital pressure gauge P1. The analog output as a given into the PLC, PI adjusted by the PLC output to the inverter, the inverter automatically adjusts the output frequency according to the size of the pressure to control the motor speed, so as to achieve the purpose of constant pressure water supply. At the same time, remove the required upper pressure limit 1.0Mpa and lower limit 0.8Mpa on the pressure display list, so that the inverter can automatically start the fire pump motor when the pressure in the pipe network is lower limit and stop the fire pump motor automatically when the pressure in the pipe network is upper limit. In addition, in order to ensure the safe and reliable operation of the stabilizing pump, when the upper limit signal of the pressure gauge P1 (ie, the pressure reaches 1.1Mpa), stop the stabilizing pump to avoid frequent starting of the stabilizing pump and affect the service life. Specific programs are as follows: 1) Hand / Auto Conversion: The system set up a hand / automatic transfer switch. Under normal conditions, the hand / auto switch is set to automatic and the fire pump motor is automatically controlled by the PLC. When the inverter fails or the pump body fails, the manual / automatic transfer switch to manual mode, then the inverter does not participate in the control, by manual button to start and stop the fire pump and booster pump. 2) fire water supply system in the absence of fire situation: In this state, the pressure loss in the pipe network is due to the check valve laxity, or leakage within the pipeline caused by the normal state, within the pipeline Water pressure 1.0Mpa, to ensure that when the fire water, fire hose access pipe can quickly water. In order to avoid wasting energy in the water supply system, the maximum pressure in the pipe (upper pressure limit) is set to 10 kg according to the specific working conditions. When the pressure in the pipe reaches the upper limit, no fire occurs as deemed necessary. The PLC stops the fire pump, Designed for 11 kg, the PLC stops the pump.