This is technical requirements for electrical wiring and power distribution for DCS control system. The distributed control system (DCS) is a computer-based system used in industrial processes to control a variety of inputs and outputs. DCS is a key component of the automation and control system for industrial processes. To ensure that the system works properly and safely, the electrical wiring and power distribution must be designed and installed correctly. This article provides an overview of the electrical wiring and power distribution requirements for DCS systems.
Electrical Wiring Requirements
Electrical wiring up to but excluding vendors’ standard cabinets must be designed in accordance with Saudi Aramco Engineering Standard SAES-J-902. This standard covers the design, installation, and testing of electrical wiring and power supplies used in industrial processes.
Power Supply to DCS Cabinets
DCS cabinets with active electronic components must be fed from parallel redundant UPS systems or dual stand-alone UPS systems as per SAES-P-103. For sites utilizing parallel redundant UPS systems, separate output power circuit breakers feeding redundant UPS power distribution panels are required.
Two separate UPS circuits must be used to supply UPS power to DCS cabinets. Each circuit must be connected to separate UPS power distribution panels. Redundant UPS power feeders must be terminated to individual circuit breakers within the DCS cabinet.
Power Distribution within DCS Cabinets
Cabinets must be equipped with power distribution panels for distribution of power to equipment located within the cabinet. Terminal blocks in the power distribution panel must be segregated by voltage level. Power distribution terminal block wiring must not be daisy-chained using wires or crimp connectors. Jumper bars or preformed jumper combs designed for the specific terminal blocks being used must be used for distribution of power to multiple terminal blocks.
Each power supply circuit must be individually fused or protected by a circuit breaker. Wiring, terminal blocks, wire tagging and terminal block coding within the power distribution panel must be as per the requirements defined in the relevant sections of 34-SAMSS-820. Power supply circuits must be clearly labeled. Branch circuits or power cords to redundant modules must be clearly labeled identifying the circuit to which they are connected.
Redundant power supply circuits must be provided for process controllers, input and output modules, and communication modules. Equipment which accepts redundant AC power supply input circuits must be fed from separate, redundant power circuits within the cabinet. Each circuit must be fed from separate, redundant UPS power sources within the cabinet power distribution panel.
Equipment which accepts redundant DC power supply input circuits must be fed from separate, redundant DC power supply modules. Each DC power supply module must be sized to accommodate 110% of the maximum expected load. Redundant 24 VDC power supplies must be provided in cabinets containing instrument circuits which require an external 24 VDC power source (e.g. not powered from the DCS I/O card). Both power supplies must be used to feed a single DC power bus through the use of DC diode auctioning to ensure bumpless transfer in the event of a single power supply failure.
Power Supply and Distribution to DCS Consoles, Servers and Workstations
DCS servers and workstations must be fed from UPS power sources. This requirement applies to the processor, monitor, and other peripheral devices associated with the workstation.
For redundant workstations within an operator console, it is acceptable to supply power to the workstations using either of the configurations described in option a & b below. Sites which have redundant UPS power distribution panels are required to utilize the configuration described in (a) below. Sites which do not have redundant UPS power distribution panels shall utilize the configuration described in (b) below.
Commercially available multiple outlet power strips may be used to distribute power to multiple components of a workstation (i.e. processor, monitor, and associated peripheral devices) provided that each power strip feeds equipment associated with a single workstation. The power strip must provide integral short circuit protection, have an integral circuit breaker and must carry either UL listing, CSA certification, or CE marking.
Utility Power
Duplex-type convenience outlets, rated at 120 VAC, 15 amp must be provided to provide utility power within PCS System, Network, Server and FTA cabinets. One convenience outlet must be provided per bank of three cabinets, as a minimum. The selection of the cabinet containing the outlet must be made to minimize the distance between the cabinet and the other cabinets for which the outlet may be utilized. The distance between the cabinet containing the outlet and any other cabinet in the bank of three cabinets must not exceed 20 feet.
Two, duplex-type convenience outlets, rated at 120 VAC, 15 amp must be provided within each console for utility power. The outlets must be placed on opposite sides of the console to enhance availability. Convenience outlets must be wired to a separate terminal strip which in turn is sourced from a non-UPS AC source.
Grounding
Grounding design must be per vendor standard recommendations and per the applicable sections of SAES-J-902; whichever is more stringent. Grounding philosophy must be consistent with Saudi Aramco standard drawing number DC-950150 unless specifically prohibited by the PCS vendor.
Conclusion
The electrical wiring and power distribution requirements for distributed control systems must be designed and installed correctly to ensure the system works properly and safely. This article has provided an overview of the electrical wiring and power distribution requirements for DCS systems.
- International Codes and Standards Used in Process Control System.
- Process Control System Segregation in Terms of Risk Areas.
- Spare and Expansion Capabilities of Process Control System.
- Process Control and Equipment Protection.
- Control Console Technical Specification for Industrial Control Projects.
- Operator Graphical Displays for Process Control System.
- Guidelines for Process Alarm Systems: Alarm System Management.
- Distributed Control System (DCS) Historization and Trending.
- Process Control System Access and Security.
- Process Control System Integration and Interface with other Disciplines.
- Technical Requirements for System, Network and Server Cabinets – PCS.
- Process Control Network Cabling Requirements | PDFBAG