Issues related to the shared use of UPS systems in DCS, SIS, and GDS systems

1. The UPSes for DCS, SIS, and GDS systems can be shared. There are no standard specifications requiring the UPSes of DCS, SIS, and GDS systems to be independent of each other.

The source of the requirement for an independent system power supply is as follows: 1. Article 1 of Document No. An Jian Zong Guan San 116, issued by the State Administration for Work Safety, which provides guidelines on strengthening the management of chemical process safety instrument systems, explicitly states: “It is necessary to fully recognize the importance of improving the management of chemical process safety instrument systems. Such systems include safety interlock systems, emergency shutdown systems, as well as systems for detecting and protecting against toxic and harmful gases, flammable gases, and fires.” The safety instrumented system is independent of the process control system (such as distributed control systems, etc.). 2. In GB/T50770 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\", the following provision exists: 5.0.8 The safety instrumented system shall be independent of the basic process control system, and shall perform its safety-related functions independently ； 5.0.9 The safety instrumented system shall not interfere with or replace the operation of the basic process control system ； 5.0.10 The basic process control system shall not interfere with the operation or logical operations of the safety instrumented system ； 5.0.11 The safety instrumented system shall be designed to be fail-safe. When a fault occurs within the safety instrumented system, it should be able to bring the process into a safe state in accordance with the design specifications ； 5.0.16 The AC power supply for safety instrumented systems should preferably be provided by a dual uninterruptible power supply system ； In the provisions: 5.0.16 For the safety instrument systems of large-scale petrochemical production units, dual independent uninterruptible power supplies shall be used.

SH/T-3082 \"Code for Design of Power Supply for Petrochemical Instruments\" specifies the scope of power supply for instruments and control systems, including process control systems (DCS, PLC, FCS, SCADA, etc.), safety instrument systems (SIS), compressor control systems (CCS), machine set monitoring systems (MNS), combustible and toxic gas detection and alarm systems (GDS), online analyzer systems (PAS), electronic instruments installed in cabinet rooms and control areas, as well as field detection, alarm instruments, and actuator devices. The regulations stipulate that, based on the importance of electrical loads in the production process and the requirements regarding the reliability and continuity of the power supply, the electrical loads of production facilities should be classified into Class I loads, particularly important loads within Class I, Class II loads, and Class III loads ； Each level of load has specific requirements regarding the power supply. Level 1 loads should be powered by two sources; in the event that one source fails, the other should not be damaged as well ； For particularly important loads among first-class loads, in addition to being powered by two power sources, an emergency power source must also be provided, and it is strictly prohibited for other loads to be connected to the emergency power supply system ； The text states that the power supply for instruments and control systems belongs to the particularly important category of primary loads, and UPS should be used for power supply. The two power supplies here can find a clear answer in the configuration scheme for AC power supply to instruments specified in SHT-3082 \"Design Specifications for Power Supply of Petrochemical Instruments\". A dual-power supply system refers to two power input sources connected to different bus sections of the power distribution device.

It is generally not recommended to share UPS units for DCS, SIS, and GDS systems. These three systems have different functions, as well as varying requirements in terms of security level and power supply reliability. Sharing a UPS may affect the stability and security of the system. Therefore, to ensure that each system can operate independently and stably, it is generally recommended to use a dedicated UPS for each one. .

The power supply for Distributed Control Systems (DCS), Safety Instrumented Systems (SIS), and Gas Detection and Alarm Systems (GDS) constitutes particularly important loads among the first-class loads, and should be supplied by Uninterruptible Power Supplies (UPS). The UPS shared for powering the SIS, DCS, and GDS systems meets current standard requirements, adheres to safety and reliability principles, and satisfies the needs of safe production.

For reference: “Examples of UPS Power Supply System Design and Engineering Applications”.

The specifications state that independent installation means that the SIS and DCS should be installed separately; nothing is mentioned regarding power supplies and UPS. If one has the money and the means, it’s of course possible to configure a UPS specifically for SIS.

The purpose of having an independently installed SIS is to prevent operators from interfering with the SIS while using the plant control system; a separate safety interlock system is provided outside the control system, and this has no direct relation to whether the UPS is independent or not. Power supplies are particularly important loads among primary loads, and SIS is fail-safe, ensuring safety even in the event of a power outage.

The boss said to do as he tells us to do. Your thinking is very dangerous

For the projects I’m in charge of, the UPS systems for the DCS, SIS, and GDS systems are installed separately and independently. With increasingly strict safety requirements and larger project investments, the proportion of investment allocated to separate UPS systems is smaller; it is therefore recommended to have them set up independently, as this arrangement will satisfy inspections by experts at any level.