Optimized Operation Mode of UPS Power Supply in DCS Power Systems
Currently, the vast majority of petrochemical production plants utilize a Distributed Control System (DCS) to manage and operate their production processes. To enhance system reliability, DCS power supplies commonly employ Uninterruptible Power Supplies (UPS). UPS systems eliminate instantaneous power interruptions, mitigate harmonics, voltage and frequency fluctuations, and reduce noise, while providing backup power for a limited time, allowing operators to perform emergency shutdowns if necessary.
In recent years, the increased reliance on UPS systems has led to occasional unplanned shutdowns of production units due to UPS failures—sometimes causing greater disruption than actual power outages. Ensuring the reliability of UPS power supplies and maintaining the seamless operation of both the UPS and DCS during normal and abnormal grid conditions is crucial for petrochemical plants that require continuous operation.
1. DCS Power Supply Requirements
A typical DCS consists of three key components:
- Human-Machine Interface (HMI)
- Network Communication
- Control Station
Among these, the Control Station is the most critical, as it handles device control and data acquisition. As long as the Control Station functions correctly, brief power outages in other areas will not significantly impact production. Therefore, maintaining power supply to the Control Station is essential to ensure the overall reliability of the DCS.
Due to the importance of the Control Station, all vital components are designed with redundancy and fault tolerance. This includes the power supply, which is a critical element. Power supply units for important DCS system components use regulated switching power supplies in a dual or multi-supply mode. In other words, all key DCS control stations have at least 1:1 redundancy, meaning they are powered by two independent sources. These sources typically meet the following specifications:
- Voltage: 100-132V / 187-264V AC single-phase
- Frequency: 50Hz ± 3%
- Maximum allowable distortion (THD): 8%
- Maximum allowable power-down time: 10 milliseconds.
2. UPS Dual-Redundant Power Supply Scheme in DCS Power Systems
After analyzing the causes of UPS power failures, the benefits and limitations of UPS backup systems, and the power supply requirements for petrochemical plant DCS, it becomes evident that achieving 1:1 redundancy is crucial for ensuring reliable DCS power supply. This can be accomplished by using two independent UPS units, each powering a separate DCS power supply.
In this scheme, two independent UPS units power the two groups of power supply modules in the DCS control station, each drawing from a separate power grid. In the event of a grid failure, the DCS control station remains operational, ensuring network redundancy and uninterrupted system operation. A portion of the operator stations will always remain functional, enabling continuous monitoring and control. This configuration allows for flexibility in UPS brand selection and is well-suited for upgrading older systems.
3. Conclusion
Relying on a single UPS unit in a DCS power system presents risks during the switching process. Therefore, a multi-unit power supply approach is essential. The dual-redundant DC power supply scheme offers the benefits of backup redundancy while avoiding the drawbacks of AC synchronization, such as circulating current issues. This enhances the reliability of the power supply and increases the scheme’s applicability for modern and retrofitted systems.