Application of safety type combination switch in mine explosion-proof field
1 Introduction <br> The mine explosion-proof and intrinsically safe combination switch is mainly used to control the combined electrical equipment of coal mine underground coal mining, transportation and other complete sets of equipment. Its characteristics are conducive to the frequent relocation of equipment, speed up the advancement of the working surface, simplify cable connection, reduce cable usage and electrical equipment footprint. At the same time, it can reduce the voltage drop loss of the power supply line, reduce the workload of production installation and maintenance, greatly improve the production efficiency and power supply reliability, reduce the cost of coal mining, facilitate the user, and adapt to the various needs of the mining area. 2 Key issues addressed in the study 2.2 Protection and control system software design The protection and control of the switch is centralized by PLC. The software design is divided into main program, monitoring program and subroutine. In the PLC program design, a large number of sub-programs are used for structural design, which has the advantages of clear structure and convenient debugging. Each subroutine is a function module. They complete the initialization of the storage address, the processing of the sampling signal, the identification of the fault type, the setting of the flag bit, and the updating of the contents of the LCD screen. The monitoring program mainly completes the subroutine call, the start and stop of the motor and the fault judgment, and the LCD screen change function. The monitoring program uses the sequential job scheduling structure to perform leakage detection for 8 branches and minutes to determine whether there is a leakage accident in each circuit. After the motor is put into operation, the PLC stops the leakage detection of the circuit and starts sampling the current, phase failure and voltage signals to determine the working state of the motor. 2.3 Modular design of accessories  2.4 Design of explosion -proof housing The design of the explosion-proof housing is designed and manufactured in strict accordance with GB3836.1~2-2000 standard to ensure the explosion-proof performance of this product. The flameproof enclosure is designed as a square structure, which is more beautiful overall and is welded by high quality steel plates. The housing is divided into four chambers, a left and right wiring chamber, an isolating switch chamber and a main control chamber. Because there are many loops, there are many in and out lines. Therefore, two left and right wiring cavities are provided, and end caps are provided on one side of the binding posts, which is more convenient for cable connection and maintenance of each circuit. The isolation switch cavity is arranged above the main cavity, and the layout is more reasonable, and the locking between the isolating switches is convenient. The main control box adopts two quick opening door structures, which is convenient to open. The main control door is provided with a large-screen LCD display window and a touch-sensitive keyboard, which can visually display the running status of the device and can be parameterized. There is a reliable mechanical locking mechanism between the isolating switch handle and the front door of the main control chamber. The locking measures ensure that the product cannot be operated after the flameproof box opens the door, and all the conductive parts are not charged, and all the isolating switches are broken after opening the door. status. Conversely, the isolating switch and the contactor can only be closed after the door is properly closed. In addition, there is a reliable electrical lock between the disconnector handle and the electrical control system, and between the break button. The complete mechanical safety interlocking mechanism and electrical locking design ensure that this product has strong safety performance. 2.5 software anti-jamming design 3 protection function 4 Conclusion
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A combination switch can control 8 drives, each with multiple protections. Each drive unit adopts modular design and convenient plug-in technology to meet the requirements of rapid downhole troubleshooting and maintenance. The product realizes man-machine dialogue function through liquid crystal display and intrinsically safe keyboard, and has fault memory and fault inquiry function, which is suitable for the development of coal mine automation system at present and in the future.
2.1 Selection of control mode In order to adapt to the production process of coal mine underground, the combination switch design has single-loop control mode operation, single-machine single-speed control mode operation, multi-loop program control operation, dual-machine two-speed dual-loop control operation, and single-machine two-speed control operation. The two-machine low-speed operation control operation and other control functions, the intrinsically safe pilot circuit of the intermediate circuit under the program control is controlled by the foreground. This method satisfies the control requirements of the coal mine underground belt transportation system, “inverse coal flow start, and coal flow stopâ€. The design advantage is that in one mission, there may be non-programmable/single-machine control mode, and there may also be a program-controlled/multi-machine mode, that is, each loop can be independent of other loops, control other loops, and can be controlled. In other circuits or as a backup. The control method can be increased according to the user's requirements, and the free combination of the above control functions can be realized as needed.
The driver is designed as a separate unit, integrating contactors, current transformers, leakage units, moving contacts and other components in a box, and designed to be a highly interchangeable plug-in installation.
In order to realize the modularization of the combination switch device design, four main core frames are designed in the main control cavity. The core frame is bent and welded by 3 mm steel plate and bolted in the main control cavity at the rear of the core frame. A main circuit static plug is installed to accommodate the insertion of the drive.
In the whole design, the modularization of components and the interchangeability of main components are mainly highlighted, which is convenient for users to use and maintain.
Open the front door of the main control chamber, you can see that the drive unit is installed with the core frame, and the eight drive units are mounted on the pull-out spacer of the core frame. The driving device comprises a vacuum contactor, a current transformer, a resistance-capacitance absorption and a leakage protection unit. When the driving device is inserted into the core frame rail, the main power input and output plugs can be automatically connected, which is convenient for the user to use and maintain.
Because the underground coal mine environment is too harsh, in order to improve the reliability of the system, effective software and hardware anti-interference measures are adopted.
(1) Select the input filter for the digital input point and delay reading the input signal value to help filter out the input noise.
(2) The analog signal is sampled using an analog filter, and the effect of the instantaneous interference signal is reduced by multi-sampling and averaging.
(3) Reasonable shielding and routing, the control line and the measuring signal line are routed as far as possible and away from the main loop.
(4) Increase the self-test function of the system before and after power-on.
(5) Adopt software traps and instruction redundancy techniques.
3.1 Overvoltage and undervoltage protection voltage protection has transient overvoltage, steady state overvoltage and undervoltage protection. The transient over-voltage is completed by the RC absorption device. The steady-state over-voltage and under-voltage protection adopts the amplitude-correcting protection principle, which effectively prevents the long-term high voltage from damaging the motor insulation, and the voltage is too low to burn the motor. When the grid voltage is higher than 120% of the rated voltage, the overvoltage protection action; when the grid voltage is lower than 75% of the rated voltage, the undervoltage protection action.
3.2 Overload protection Overload and short circuit protection adopt the principle of amplitude correction. The current is sampled and sent to the PLC for processing, and compared with the setting current value stored by the CPU. The PLC issues an instruction to disconnect the corresponding fault circuit according to the comparison result, and displays and memorizes the type of the fault and the parameter at the time of the fault. . Combination switch overload protection.
3.3 Short-circuit protection The setting value of short-circuit current is set to 8~10 times of the rated current of the controlled motor. Once the circuit current is greater than the set value, the short-circuit protection action is 0.2~0.4 s.
3.4 Phase failure/unbalance protection combination switch phase failure and phase imbalance protection.
3.5 Main circuit leakage lock
The leakage blocking detection section still uses the principle of additional DC power. After the isolating switch is closed, the PLC detects the grounding insulation condition of the branch. If the branch-to-ground insulation resistance is less than the leakage blocking resistance setting value, the PLC blocks the fault circuit. At this time, the starting operation cannot be performed. Leakage lockout, showing the type of fault. When the insulation resistance of the branch to ground is greater than the set value of the leakage lockout resistance, the contactor can be closed for power transmission. At the same time as the contactor is closed, the leakage lock detection circuit is disconnected. The insulation resistance of the main circuit of the combination switch to the ground is in accordance with the provisions of Table 3. When the insulation resistance rises to 1.5 times the blocking value, the leakage lock is released.
(1) The combination switch integrates the control and protection of multiple motors, the components are modular, and the accessories adopt convenient plug-in technology. The drives are interchangeable to meet the requirements of rapid troubleshooting and maintenance in the underground.
(2) The working parameters of the motor are set by the intrinsically safe keyboard, and it is practical without the need for the professional to modify the parameters in the program.
(3) The use of the LCD screen makes the system intuitive. Through the fault memory, you can check the faults in the line during the operation to accurately grasp the operating conditions.
(4) The introduction and extraction of the main circuit cable can be carried out according to the specific requirements of the user, using cable connectors or traditional bell mouth wiring.
(5) The control method is flexible and can be changed according to user requirements.
The operation of industrial production shows that the combination switch has reliable performance and has good protection for each circuit motor, and has broad application prospects.
