DCS power supply issue
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The SH/T 3082-2019 Standard for Design of Power Supply for Petrochemical Instruments specifies four simple methods for powering instruments, with all mains power supplies being dual-circuit. However, the HG/T 20509-2014 Standard for Instrument Power Supply Design specifies that instrument power loads are classified as particularly important loads within Class I loads and as Class III loads. For first-class loads, a dual-power supply is required; therefore, it is necessary to determine whether the mains supply for the DCS should be based on a dual-power supply or dual-circuit system.
The mains power supply for DCS should be designed with dual power sources, as per the HG/T 20509-2014 Code for Design of Instrument Power Supply, DCS is classified as a particularly important load among category one loads. Considering the importance of the DCS system and the need for continuous and stable operation, dual-power supply can better ensure its operational stability. .
In the power supply design for petrochemical instruments, the mains power supply for the DCS (Distributed Control System) should be designed as a dual-power-source system. HG/T 20509-2014 \"Code for Design of Instrument Power Supply\" stipulates that instrument power loads fall into the category of particularly important loads within Class I loads, as well as Class III loads; for Class I loads, dual power supplies are required. Although SH/T 3082-2019 \"Code for Design of Power Supply for Petrochemical Instruments\" specifies four simple methods for powering instruments and requires that all mains power supplies be dual-circuit, this does not mean that the mains power supply for DCS systems can also be arranged as a dual-circuit system. Although both dual power supplies and dual circuits feature two power supply paths, their meanings and requirements are different. A dual power supply refers to two separate power sources; when one of them fails, the other can continue to provide power, thereby ensuring the uninterrupted operation of critical loads. A dual-circuit system refers to two circuits connected to the same power source; when one circuit fails, the other can take over, but this does not guarantee a continuous power supply in the event of a failure of the power source. Therefore, to meet the requirements for Class I loads specified in HG/T 20509-2014, the DCS should be powered by a dual-power supply system in order to enhance the reliability and stability of power supply. In actual design, comprehensive consideration must also be given to specific circumstances, including factors such as the capacity and reliability of the power supply as well as the switching time, in order to ensure the proper operation of the DCS system. At the same time, relevant standards and specifications should also be followed to ensure the rationality and safety of the design.
However, the specifications for 3082 specify an AC power supply system for the instruments and control systems, and the control systems certainly include DCS. From what I’ve seen in many factories (in the pharmaceutical and chemical industries), a dual-circuit + UPS setup is used; it’s rare to see DCS systems powered by two separate power sources. This raises some doubts – some smaller factories may not even be able to meet the requirements for primary load coverage
. This matter depends on the power supply method of the device. If the production facility has only one power supply circuit, it is neither necessary nor possible to implement a dual-power supply with a UPS. .
The specifications require dual power supply, but many industrial parks do not have such a setup; as a result, many companies opt for a dual-circuit system, using diesel generators as a backup source for secondary loads. UPS systems are also installed, so that in the event of a power outage in the park, the diesel generators can continue to supply power to the UPS.