Content abstract: By using programmable controller to design and transform heating and drying furnace, this system replaces the application of traditional thyristor intelligent module, phase shifting regulator and other components, and realizes the whole process of automatic, safe and accurate drying temperature control of electrical equipment by using program control, sampling, feedback and other links. After repairing and replacing windings, electrical equipment such as motor and transformer should be dipped and dried. The temperature and time of preheating, low-temperature drying and high-temperature drying should be strictly required according to different insulation grade equipment in the drying process. The quality of drying is related to the quality of equipment maintenance and operation cycle. Therefore, a safe and reliable drying process must be guaranteed.
The original drying furnace of instrument factory of Liaoyang Petrochemical Company is DFH10 electric heating blast constant temperature drying box, which is the form of manual control contact thermometer. The heating temperature and time of heating furnace are often controlled manually over time or out of control, which destroys the drying process and even burns down electrical equipment. In addition, due to the imperfect control and protection system of the drying furnace, faults often occur, and the resistance and control system of the electric furnace are burned down, resulting in waste of labor and energy, which seriously affects the production. The heating and drying furnace is designed and reformed by using programmable logic controller. The main and auxiliary heating actuators (furnace resistance) are controlled by program, and the solid state relay is controlled by temperature controller in intermittent mode of operation.
The application of solid-state relay has replaced the use of thyristor intelligent module, phase shifting regulator and other components. After several years of application, it can safely, accurately and automatically complete the temperature control of electric equipment dipping and drying. The main circuit utilizes the resistance of the existing electric heating furnace. Firstly, the resistance of the electric furnace in the heating furnace is divided into two groups, one is the main actuator with a power of 14 KW, the other is the auxiliary actuator with a power of 5 KW. The working state of the main executive element heating tube is controlled by programmable controller, which plays a heating role in the system. The auxiliary executive element heating tube controls the conduction and disconnection of the solid-state relay by the temperature controller to work intermittently, which plays a role of insulation in the system. And the operation of the whole system. The closing button SB1, the opening button SB2, the upper and lower limit contacts of the electric contact thermometer and the high temperature alarm of the temperature controller are used as the input points of I1, I2 and I3 of the PLC respectively, and the contactors KM1, KM2 and KM3 are used as the output points of the main actuator, the auxiliary actuator and the agitator fan respectively. The PXW-9 temperature controller sets the temperature and time, and controls the intermittent operation of solid-state relay. The feedback temperature in the heating furnace is sent to the temperature controller and PLC. It replaces the traditional electromagnetic relay with fast switching speed, low price and long service life. Voltage 380V, current 25A.
According to the program, the 0-10VDC signal sent by the temperature controller is intermittently connected or disconnected, and the system is insulated. It replaces the functions of thyristor intelligent module and phase shifting regulator, and makes the circuit simple and applicable. And temperature controller, as the circuit contact switch of temperature regulation in this system.
When the power supply switch is closed, the power supply of the programmable logic controller (PLC) and the thermostat gets power, the system has no fault and the drying time does not meet the requirements, after setting the drying temperature of the thermostat and the ultra-high temperature alarm temperature of the electric contact thermometer, the start button SB1 is pressed. According to the program operation, the output point Q1 of the PLC has output, and the contactor KM1 is sucked. The main executive component (resistance of 14KW electric furnace) works, and the temperature in the furnace begins to rise. According to the different drying temperature and time set by the material temperature controller with different insulation grade, the electric contact thermometer in the furnace feeds back the temperature in the furnace. Before the temperature in the drying furnace does not reach the set temperature, the main actuator works all the time, and the temperature in the furnace keeps increasing until it reaches the set drying temperature. When the temperature in the furnace reaches the set temperature requirement, thermostatic element the output point Q1 of the PLC is controlled according to the program, and the main actuator (resistance of 14KW electric furnace) stops working. The temperature in the furnace is kept at the set temperature. After the main actuator (resistance of 14KW electric furnace) stops working, the temperature in the heating furnace remains at the set working temperature. If the temperature in the furnace drops, then the auxiliary actuator starts to work intermittently with the cooperation of programmable logic controller (PLC) and solid state relay (SSR).
(The purpose of the auxiliary actuator is to work when the temperature in the outside environment changes or the temperature in the furnace is too low. ) If the temperature in the furnace is lower than the set value, the temperature signal in the thermocouple feedback furnace is given to the temperature controller. The temperature controller outputs 0-10VDC signal to the 3 and 4 terminals of the solid state relay. The 1 and 2 terminals in the main circuit are turned on, the solid state relay is turned on, the output point Q2 of the programmable logic controller (PLC) is output, the contactor KM2 is sucked in, and the auxiliary actuator starts to heat.
The temperature in the reduced furnace is raised again. When the temperature in the furnace reaches the set value again, the temperature signal in the furnace is fed back by the thermocouple to the temperature controller.
The temperature controller output 0-10VDC signal is turned off, the solid state relay is not turned on, and the output point Q2 of the programmable logic controller (PLC) has no output. At this time, the auxiliary component (5KW furnace resistance) stops working. The temperature controller sends out 0-10VDC to control the solid state relay to regulate the temperature, which guarantees the technological requirements, and can change the working state of the main and auxiliary components through the program. The application of this method saves the application of three-phase AC module and phase shifter, and greatly saves the capital. This system has perfect protection function. The original electric contact thermometer has lower and upper contact points. The lower limit contact is the temperature at which the main actuator begins to heat, and the upper limit contact is the alarm temperature at ultra-high temperature, which is used as the backup protection for the damage of the temperature controller.
When the temperature in the heating furnace reaches the set high temperature alarm upper limit (generally higher than the normal set working temperature upper limit of 10 C), the temperature controller will input the high temperature alarm 7 and 8 terminals of the thermocouple to the programmable logic controller (PLC) according to the feedback signal of the thermocouple. At this time, the output points Q1 and Q2 of the programmable logic controller (PLC) are turned off and the output is maintained. When the thermocouple is burned out or the temperature control instrument is out of order, the system fault is set according to the PLC program, and the heating furnace stops working completely. This double-insurance protection system ensures the safe operation of the electric furnace. A three-phase motor with a power of 0.75KW is used as a stirring motor to stir the hot air temperature in the furnace.
When the main executing element works, the output point Q3 of the PLC is controlled according to the PLC program. The contactor KM3 is sucked in. The motor works, and the hot air in the stirring furnace makes the furnace temperature even up and down. The working condition of the motor is controlled by programmable logic controller (PLC) program to intermittent work. Solid state relay is easy to heat when it works. When the auxiliary actuator works, the cooling fan in the program control box of PLC starts to work, which ensures the working environment of solid state relay.
When in use, all the programs in the programmable logic controller (PLC) have been input and completed. It only needs to start with the start button, set the required drying temperature on the temperature control instrument, and set the lower threshold starting temperature and the upper limit ultra-high temperature alarm temperature on the electric contact thermometer respectively. The operation is simple and clear. The intermittent working nature of two groups of heating elements saves electric energy; the programmable logic controller (PLC) program automatic control saves the application of thyristor intelligent module and other elements, and improves the efficiency and ensures the quality of drying. After many years of application, the reformed electric heating furnace has no faults and is still used in the electric repair workshop.