Design of power supply and power supply system in DCS system

Power supply selection: including 220V AC power distribution board and 220V→24V (or 12V, 5V) power supply. For the control system, the AC/DC conversion power supply redundancy should be ensured, and the redundant power supply output should be connected in parallel through Schottky diodes (unless the source indicates that it can be directly output and connected in parallel), and avoid the redundant power supply being powered by one AC power distribution board. Generally speaking, the configuration of this type of power supply is provided by the DCS system supplier, but at this time, it should be noted that the design layout with poor heat dissipation efficiency caused by the close arrangement of multiple AC power supplies should be avoided. At the same time, the same type of backup power supply required from the supplier should be no less than 20% of the actual configuration (each type should have at least 1 spare part). In addition, the selection of 24VDC power supply should consider the function of fault alarm output, and input DCS through DI card for real-time detection and alarm; if there is indeed no fault output alarm, it should be considered to use the parallel relay to indirectly connect to DCS.
⑶ Selection of ventilation and cooling equipment: The ventilation capacity of all equipment in the entire system should be guaranteed. Especially AC/DC power supply equipment, control equipment and high-power diodes. The front and rear doors of the cabinet should be determined based on the actual heat dissipation of the internal equipment to determine whether to add fans and other cooling equipment. Due to the condensation problem, the top direct exhaust method should be avoided as much as possible (especially the DCS system cabinet), and it is best to provide a temperature detection alarm inside the cabinet.
⑷ Filtering equipment: On the basis of ensuring the ventilation and cooling of the heating equipment, dust and corrosive gases should be reduced from entering the cabinet or equipment. Therefore, the use of filters must be taken seriously.
⑸ System wiring: It should include dedicated communication, power supply, signal wires and cables and grounding wires provided by the DCS supplier and power supply (including 220V AC power supply cables and 24V DC distribution cables), signal and grounding system cables provided by the design department:
System supporting communication, power supply, signal and grounding cables: The connection quality should be checked.
220V AC power cables: Mainly for power supply to various subsystems, monitors, printers and other peripherals. Determine the cross-sectional area of ​​the power supply core according to the actual power consumption. Generally, a three-core hard copper wire of not less than 2.5mm2 should be selected. When the power supply distance is short (such as inside the cabinet or adjacent cabinets), two or three single-core hard wires can be used. When the power supply distance is far, armored shielded cables should be considered. To avoid interference with other signals, all AC cables should be routed in trough boxes or pipes (shielded insulated cables can be laid flexibly according to actual conditions), and the protective metal box or pipe should be reliably grounded.
24V DC wire: The external power supply of the monitoring equipment of the DCS system is generally the 24V DC provided inside the system. The 24V power supply required for integrated installation is generally the external power supply for I/O devices such as drive relay input and output, field transmitters , or certain terminal boards of the DCS system. Generally, ordinary wires or copper mesh shielded cables of not less than 1mm2 can be selected. When the load current of the equipment is large, the cross-sectional area can be appropriately expanded to 2.5mm2.
I/O input and output signals: It is better to choose shielded cables for ordinary signal lines, such as K series or J series special computer control cables. When funds are tight, consider using BVV or RVV series unshielded cables and try to avoid using wires; the choice of thermocouple wires or cables can be determined according to the funding situation.
Ground wire: It should be configured according to system requirements.
Terminal selection: AC power distribution, grounding, and 24VD power supply for multi-channel equipment should use O-type connection to improve the connection quality. I/O wiring and single-channel power supply for field transmitters should use Y-type or type I power supply to facilitate disassembly and maintenance. In addition, the crimping quality of the terminal should be guaranteed. When not using tubular (such as Weidmuller), special attention should be paid. The stripping length and crimping pliers should be selected according to the terminal that is suitable for use. When crimping, special attention should be paid to avoid pressing the insulation part, and the excess bare wire should be cut off to avoid overlapping other metals.
(6) Configuration configuration: The number of I/O configuration definitions of the device loop should not exceed 80% of the maximum I/O capacity of the same type of card provided by the system. The number of system I/O card configurations is determined accordingly, which will facilitate future configuration adjustments. In addition, in order to facilitate the inconvenience of increasing I/O configuration during system operation, it is possible to consider configuring some spare channels as temporary loops, which can be used at any time when needed.
⑺ Subsystem or node configuration: The system configuration should be no more than 60% of the maximum configuration allowed by the system. The control system redundancy design should use redundant configuration between card boxes or redundant configuration within the cabinet as much as possible, and the cables between cabinets should be reduced as much as possible. The number of spare cards or equipment should be no less than 20% (including the special equipment such as power supplies and fans that are not easy to purchase mentioned above).
⑻ Selection and layout of cabinets: Generally, standard cabinets 800X800X2200 are selected, but under the premise of considering the safety requirements of different systems, the corresponding side panels should be selected according to the requirements of the adjacent cabinet wiring (the width of the cabinet after the side panels should be reduced). The cabinet layout should be convenient for construction and maintenance, and the status indication or alarm indication should be easy to monitor. The cabinet should avoid direct sunlight.
⑼ Layout of the operating table and auxiliary operating table: The operating table and the skirting of the baffle under the table should be protected to prevent debris from entering the operating table. The layout should be based on beauty and convenience for operators. In particular, the location of the auxiliary operating table should be adjacent to the corresponding operating position. The operating table should avoid direct sunlight and CRT reflections that affect operation, which should be combined with the design of the machine room.