Research on anti-interference requirements of DCS system

**Abstract:** The safe, stable, and reliable operation of a DCS (Distributed Control System) in power plants is significantly influenced by several critical factors, including power supply stability, signal classification, cable layout, and grounding system design. By analyzing the anti-interference requirements of DCS systems in terms of power, signals, and grounding, this paper discusses effective anti-jamming design strategies. It also highlights key considerations during construction and maintenance to ensure optimal performance. These insights are valuable for engineers working on small and medium-sized thermal power plants. **Keywords:** Small and medium thermal power plant; DCS; Anti-interference; Grounding **1. Introduction** The Distributed Control System (DCS) has become a standard in large-scale thermal power plants, offering improved control and operational efficiency. However, its application in smaller or regional thermal power plants is still evolving, with limited experience in design, installation, and maintenance. One of the main challenges in these systems is effectively managing electromagnetic interference (EMI), which can impact the reliability and accuracy of the control system. Due to the lack of technical expertise and operational experience, small and medium-sized thermal power plants must pay close attention to proper design and implementation. Ensuring a stable power supply, correctly classifying signals, laying cables appropriately, and implementing effective grounding are essential steps to reduce interference and enhance system reliability. This paper explores these aspects in detail, providing practical recommendations for project designers and maintenance teams. **2. DCS System Anti-Interference Requirements** To ensure the accurate measurement and control of a DCS system, it is crucial to address anti-interference measures during the design, installation, and maintenance phases. Interference can come from various sources, such as electrical noise, poor grounding, and improper signal routing. Therefore, careful planning and execution are necessary to maintain system integrity and safety. **2.1 Power Supply Requirements** Power supply stability is fundamental to the reliable operation of a DCS system. During the pre-design phase, it's important to select appropriate power supplies and switches that can handle the maximum current load, leaving sufficient margin for future expansion. The power lines should be chosen based on current capacity, mechanical strength, corrosion resistance, and flame retardancy. To ensure continuous and reliable power, the DCS power system should ideally be isolated from other systems. If this is not possible, an isolation device such as a UPS (Uninterruptible Power Supply) can be used. A dual-power supply setup is recommended, with one being an AC UPS and the other coming from the plant’s low-voltage section. An automatic transfer switch should be installed to minimize downtime and prevent any disruption to the control system. **2.2 Signal Requirements** Signal lines are a common pathway for interference to enter the DCS system. Signals are typically classified into four categories based on their sensitivity and potential to cause interference: - **Class I**: Low-level signals like thermocouples, RTDs, and millivolt signals. - **Class II**: Analog input/output signals (e.g., 0–5 V, 4–20 mA). - **Class III**: Switching signals with higher current (e.g., 24–48 V DC). - **Class IV**: High-voltage switching signals (e.g., 110 VAC or 220 VAC). Proper cable selection and routing are essential to minimize interference. Shielded cables should be used for sensitive signals, and different classes of signals should be separated to avoid cross-talk. Additionally, shielding should be grounded at a single point to prevent ground loops. It is also important to avoid mixing high-power and low-power signal lines in the same cable tray. **2.3 Grounding Requirements** Grounding plays a critical role in ensuring the safety and performance of a DCS system. It provides a common reference point, helps dissipate fault currents, and reduces electromagnetic interference. There are several types of grounding in a DCS system: - **Protective Grounding**: Prevents static charge buildup and protects personnel. - **System Grounding**: Establishes a reference voltage for signal transmission. - **Shield Grounding**: Reduces interference by shielding live signals. - **Intrinsically Safe Grounding**: Ensures safety in hazardous areas by limiting energy levels. A well-designed grounding system includes grounding connections and devices such as grounding plates, trunks, and electrodes. The grounding resistance must meet manufacturer specifications, typically less than 1Ω or 4–5Ω depending on the system. For systems requiring intrinsic safety, a separate grounding system may be necessary. **References** [1] Chen Bo, Ding Yongjun, Chen Xiaoqiang. Analysis and Suggestion on Grounding Status of DCS System in Zhejiang Thermal Power Plant [J]. Zhejiang Electric Power, 2008, (1): 51-54. [2] Zhang Wei, Niu Yugang. Overview of DCS and Fieldbus [J]. Electrical Automation, 2013, (01): 4-6+46.

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