How should we view the issue of dual-UPS power supply for DCS system cabinets proposed by experts?

Technically, installing a dual-UPS setup can improve the reliability and stability of power supply for DCS system cabinets, especially in situations of unstable power or sudden outages. Furthermore, in fine chemical production, the stable operation of the DCS system is crucial for the success of the production process; therefore, it is recommended to use a dual-UPS setup to ensure a stable power supply for the DCS system. However, it should be noted that whether a dual-UPS setup is necessary depends on specific circumstances, including factors such as the layout of the site, power quality, and type of equipment. If the enterprise already has other reliable power protection measures, an additional dual-UPS system may not be necessary. Therefore, before making a decision, a comprehensive analysis of power supply protection solutions is necessary to find the most suitable option for one’s own enterprise. In summary, the issue of dual-UPS power supply for DCS system cabinets raised by experts is worth paying attention to; under other favorable conditions, having dual UPS units can enhance the stability and reliability of the DCS system, thereby reducing production risks. .

It is necessary; otherwise, the experts’ authority will be questioned, and future inspections will be troublesome. Although the regulations state that dual power supplies are \"preferred,\" it is not ruled out that this could soon be changed to \"required.\" To reduce the number of items that need to be corrected in the future, it’s advisable to use dual UPS units along with mains power if conditions permit.

SH/T3082 6.3 The dual-UPS dual-output circuit power supply scheme is suitable for powering instruments in the control rooms, field control rooms, or field cabinet rooms of combined units and similar installations.

HG/T 20509 5.3.5 For important chemical processing units, it is advisable to use a dual-UPS power supply for the measurement and control instruments.

Firstly, in accordance with the SHT 3082-2019 Standard for Power Supply Design of Petrochemical Instruments, the power supply for DCS systems is classified as an important load among primary loads. However, the design does not require dual UPS power supplies; it is sufficient to meet one of the following four power supply options: 1. Power supply via dual output circuits of UPS and GPS. 2. Dual UPS dual-output circuit power supply scheme. 3. Dual UPS multi-circuit output power supply scheme. 4. Power supply scheme with multiple UPS units and multiple output circuits

This post was last edited by cww9521 on 2023-6-2 at 21:04. Currently, in most fine chemical enterprises, the DCS systems are powered by one mains supply and one UPS, with each serving as a backup for the other. Nowadays, however, it seems that the DCS system “must” be equipped with two UPS units... which seems a bit excessive. Interpreting “it is advisable” as “it is required” undermines the original intent of those who drafted the standards; terms such as “can”, “it is advisable”, and “it is required” should have clear distinctions between them. This is an important aspect that experts need to consider carefully when interpreting standard provisions and ensuring that these provisions are applied appropriately. If it is identified as shown in the figure below, it must be rectified. If the wrong direction is not corrected in a timely manner, it will remain incorrect, and it is the companies that end up bearing the consequences. If the safety review recommends the use of a multiple UPS (3 or more) power supply scheme for the SIS and DCS systems, would this be interpreted as further enhancing the safety and reliability of the systems? If a chemical plant has dual power supply sources (two high-voltage mains supplies), and emergency generator sets are installed for primary loads as well as those that are particularly important among the primary loads, then the DCS system is powered by two sources: one mains supply and one UPS supply, with automatic switching between them. Additionally, regular charging and discharging tests of the UPS are carried out on a quarterly basis. In my opinion, such a configuration is undoubtedly safe and reliable. The above are merely personal opinions; currently, our SIS system is equipped with dual-UPS power supply based on the recommendations of experts.

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5.3 Uninterruptible Power Supply 5.3.1 UPS should be used for instrument power in the following situations: 1 Production facilities that utilize DCS, FCS, or SIS； 2 CCS ； 3 Online analyzers for interlock and process control ； 4 Flammable gas and toxic gas detection and alarm systems. 5.3.2 When a UPS is used as the power supply for instruments, it should be one with strong interference resistance and isolation devices at both the input and output ends. 5.3.3 The main power supply and bypass power supply of the UPS should be powered by different busbars to ensure reliable power supply. The switching device of the power supply system should be capable of achieving a disturbance-free switchover. 5.3.4 For measuring and control instruments equipped with dual power supplies, when powered by a UPS and another separate conventional power supply, an isolation transformer should be installed for the conventional power supply. 5.3.5 For important chemical processing units, the power supply for measurement and control instruments should preferably come from a dual-path UPS system. 5.3.6 For systems such as DCS, SIS, and FCS that require dual power supplies, the distribution cabinets (boxes) for the dual AC power supplies should be installed separately; air switches, terminal blocks, etc. should also be arranged separately 20509-2014

Experts who require dual UPS systems can also be a bit of a hassle

I would like to ask: the next standard specifies that DCS belongs to the category of particularly important loads among first-class loads, but the recommended wiring method suggests a power supply setup using UPS plus two circuits. Isn’t this contradictory?