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摘 要
随着现代工业的发展，锅炉由原始的燃煤炉向电热和燃气炉的方向发展。电热作为高效清洁的能源，越来越受到企事业的青睐，污染严重的燃煤锅炉亦加快了向电热炉转变的步伐，从而使电热锅炉得到了很大发展。工业电热锅炉实现自动控制可以将锅炉的水位、温度、压力等参数控制在规定的范围内，并能自动适应负荷的变化，从而使锅炉安全可靠经济的运行。
本论文通过对工业电热锅炉电气系统主回路进行详细的分析，计算出电动机、断路器、交流接触器、继电器、变送器、电缆线等主要电器的参数后，再选择了相应电器的型号、等级等具体数据。然后根据这些数据设计出电热锅炉电气控制系统、压力自动控制系统、水位自动控制系统。在综合考虑系统的精度、效率以及经济性等方面的因素之后，最终确定以PLC为控制核心。整个系统控制过程为先起动总电路开关让电热预热，接着依次自动运行引风机和鼓风机，然后自动点火，再喷油，使锅炉正常工作。本设计中的水位和压力自动控制系统工作过程为当水位或者压力超出锅炉要求的范围时，PLC分别控制水泵电机的运行和伺服电机的转动，从而控制水位和压力在正常工作的范围。
本毕业设计过程还包括了工业电热锅炉电气系统模拟样机的制作，电热锅炉电气控制系统程序清单的编制，用计算机绘制电气主电路图和PLC外围接线图等。
在本系统中，主要电机选择三相异步电动机并且采用Y-D起动控制，设计其过流保护,并完成了电源欠压保护及过压保护的设计。其中电机过流保护和电源欠压保护及过压保护的设计都没有用传统的继电器控制，而是采用了变送器和PLC的AD模块来完成，这样就能使控制更加精确，保护更加及时，电机运行得更加可靠。
关键字：水位控制；压力控制；三相异步电动机；伺服电机；PLC；A/D模块；变送器
Abstract
With the development of modern industry, the boiler is developed in the direction of from the original coal-fired boiler to the Oil-fired boiler. As a fuel efficient and clean source of energy, more and more enterprises and institutions in favor, cause serious pollution of coal-fired boilers also speed up the furnace to fuel the pace of change so that oil-fired boiler has been great development. Realize industrial boiler fuel can control the boiler water level, temperature, pressure, and other parameters in control within the provisions of, and can automatically adapt to changes in load, so that the economic boiler safe and reliable operation.
In this paper, through the industrial boiler fuel main circuit electrical system to conduct detailed analysis, calculate the motor, circuit breakers, exchanges and contacts, relays, transmitters, cables and other major electrical parameters, and then selected the corresponding electrical models , Grading, and other specific data. Based on these data, I design a boiler fuel electric control system, pressure control systems, and the water level control system. In the integrated system to consider the accuracy, efficiency and economy of such factors, I choose PLC for the control of the core. The entire process control system for the first start of circuit switching to fuel preheating, followed by automatic operation Fan and Blower, then automatically the ignition, and fuel injection so that the boiler work properly. The design of the water level and pressure control systems for the process when the water level or pressure exceeded the boiler, to the extent required, PLC respectively control the operation of motor pumps and servo motor of the rotation and thus control the water level and pressure in the normal scope of work. The graduate design process also includes the industrial boiler fuel electrical system simulation prototype production, oil-fired boiler electrical control system procedures for the preparation of the list, to use the computer mapping the main electrical circuit and PLC external wiring diagram, and so on.
In this system, the choice of the main motor and a three-phase asynchronous motor control Y/D starter, the design of their over-current protection, and completed the over-voltage protection and the protection of under-voltage power supply design. One motor over current protection and power under-voltage protection and over-voltage protection of the design did not use the traditional control relay, but using the transmitter and the A/D module to complete them; this will enable more precise control, the protection of more timely, motor running more reliable.
Keyword : Water Level Control；Pressure Control；Three-phase asynchronous motor；
Servo motor；PLC；A / D module； Transmitter