Studying Constant Fire Water Control System

There are many problems in traditional water supply system, such as the frequent start or stops in the frequency under the control of pressure nodes. This control system not only damages electric equipment, and consumes much more electricity, but also disables to achieve long-term low-speed motor running. With the development of power electronic technology, VVVF technology has been widely used in the various industries because of its superior performance and energy-saving advantages. But for the users, there are still many unknowns in some aspects, such as the principle of concrete realization, design ideas, technological transformation.This paper is to elaborate design ideas, design a train of thought, the proper use of automatic equipment by the fact of fire water control system under constant pressure.The thesis is to study how to supply fire-fighting water under constant pressure making use of the frequency transformer and PLC. The system is a closed cycle which is composed of the famous brand frequency transformer(Siemens company MicroMaster 430), intelligence controller (LOGO! Controller), pressure sensor and water pump. Its core is AC inverter technology and automatic control technology. This system can automatically adjust the water pump rotation rate and the number of pump operation to maintain the pressure set of pipe net, which can enhance the quality of supplying water and high-effect energy conservation. The system may substitute equipments such as high water level box, water tower and control valve, to improve the automation supplying water degree.This paper studies VVVF control programme, whice adopts a pump frequency of the control scheme. That is, when water consumption is low, the inverter controls 1#(or 2#) pump to realize a constant pressure water supply. When water consumption gradually increases, and the 1#(or 2#)pump frequency increases up to 50 Hz,its electric motor will be switched by the frequent power supply. At the same time, the converter will be switched to the 2#(or 1#) pump, to supply water. Instead,when water consumption gradually reduces, even if the 2#(or 1#)pump frequency has been reduced to 0 Hz, and the water pressure is still a bit high, then should be turn off the 1#(or 2#)pump. Mainwhile the frequency of the 2#(or 1#)pump should be increased rapidly, to control constant pressure.This control programme has obvious effects on energy conservation and the low investment.Compared to the traditional water cooling towers, the frequency constant pressure water supply system has the following advantages:1. Advanced technology:PLC and the frequency transformer realizes the intellectualized constant pressure according to water supply and fire-fighting control;2. Highefficiency and energy conservation:System can set up pressure according to demand, then it automatically adjusts the water pump rotation rate and the number of runing pump, to ensure that equipment operates high-efficiently in the best condition;3. The stability of water supply pressure:Closed-loop control system can automatically adjust the margin of settings pressure and system pressure, to maintain constant pressure.4. Prolong the life span of the electric motor and water pump:Every pump srarts circularly,so that the backup pump will not rust due to not using for long time or will not wear out due to the frequent running.5. Perfect protective function:The Circuit has various protective functions, for example short-circuit,over current, over-voltage, overheating, overload protection. If the water pump has a fault, it will stop working and give an alarm. The system has many functions, such as self-inspection, fault judgement, memory failure, failure display and automatically activation the standby pump.6. Easy-operation:The programing and setting of frequency converter and controlleris very simple and convenient, which can be mastered easily.7. Manual and automatic switching function: The backup manual switch control can ensure continuous and secure operation of the equipment.8. Implementation unattended.