A Programmable Logic Controller Based Design And Implementation Of A Fully-mechanized Simulated Working Face Load Control Center

With the rapid development of national economy, large and medium-sized coal mines have realized fully-mechanized mining production. At the same time, protection to underground power supply units has also been improved as the traditional relay protection being replaced gradually by microcomputer control along with the booming computer technology. Programmable logic controller(PLC hereafter) gains a great success in controlling fully-mechanized coal mining equipment with its robust function, reliable and safe operation and strong anti-interference. Switchgear is the abbreviation form of exPLCsion-proof and intrinsically safe switchgear, also named as load control center. It is a multi-functional switch consisting of an exPLCsion-proof enclosure and a certain amount of vacuum contactors and the driving part in it. The control equipment for fully-mechanized coal mining has evolved from a single independent control switch into a comprehensive control load center. Taking PLC as the control core, this comprehensive control load center is to have the driving part drive related motors and enable a sequential control and linkage control of several motors, which can realize the completion of several control modes while providing protection to the motors. The equipment it controlled mainly includes shearers, AFC’s, loaders, breakers, belt conveyors and other exPLCsion-proof electrical devices. The control equipment for fully-mechanized coal mining stimulated working face built by Yankuang Technical School in the early 1990 s has fallen far behind and out-dated, leading to the disconnection between teaching activity and production reality. Therefore, it is of great practical significance to develop a suit of load control center to be used on the fully-mechanized coal miningstimulated working face.The main characteristics embodied in the study are as follows: in view of the controlling features of the fully-mechanized mining stimulated working face, it takes advantage of Mitsubishi’s PLC, HMI and fieldbus control to achieve various protections for power supply lines and the machine itself. The load control center consists of main circuit, control protection system, driving part and display elements. Based on sampling and processing of parameters like the voltage or current protection values, the control center shall be capable of enforcing the functions in conformity with the requirements of Coal Mines Safety Regulation on electrical protection against short circuit, overload, phase-loss, leakage and three phase imbalance. It uses peak-removed average filtering to address the false actions in the process of analogue signal data collecting due to the large fluctuations created by instantaneous interference on site. For the over-voltage in operation, resistance capacitance snubbers are applied. Software and HMI design are involved in this design. The HMI with a touch screen is one of the MT8000 series products supplied by Taiwan WEINVIEW.What is more, commissioning is conducted to individual function and the system respectively. The result shows good electrical protection and performances and HMI is proved to be friendly, which can meet the demands of student training and practicing. Furthermore, it will definitely provide a strong support for teaching and training of the fully-mechanized mining electrical equipment.