ABB SS822

Technical Specifications

The specifications below define the electrical, physical, and operational limits of the standard SS822 configuration:

• Product Classification:
  • Type: Redundant Power Module / Voting Unit / Power Switch Module.
  • System Compatibility: ABB Symphony Plus, AC 800M DCS, and S800 I/O series.
• Electrical Parameters:
  • Input: 2 independent channels of 24 VDC.
  • Input Current: Each channel supports up to 20 A (typical for SD832/SD834 supplies).
  • Output: 1 channel of 24 VDC (regulated).
  • Output Current: Maximum continuous 20 A total load.
  • Voltage Trip Level: Factory set at 35 VDC ± 2% (adjustable in related models like SS823).
  • Isolation: High-voltage isolation between inputs and output to prevent ground loops.
• Performance Metrics:
  • Switching Technology: MOSFET ORing (eliminates the 0.7V drop associated with diodes).
  • Transfer Time: Ultra-fast switching of < 50 µs (microseconds), ensuring no voltage dip that could reset logic.
  • Efficiency: > 88% typical.
  • Ripple: < 100 mV peak-to-peak.
• Physical Characteristics:
  • Form Factor: Compact DIN-rail mounting module.
  • Dimensions: 90 mm (Width) x 50 mm (Depth) x 25 mm (Height).
  • Weight: Approximately 0.5 kg.
  • Cooling: Passive convection (fanless), low heat dissipation (approx. 10 W at full load).
• Environmental Parameters:
  • Operating Temperature: -25°C to +70°C (derating required above 55°C).
  • Storage Temperature: -40°C to +85°C.
  • Protection Class: IP20 (finger-safe) when installed in a cabinet.
  • Vibration/Shock: Designed to withstand mechanical stress typical in heavy industry and marine environments.
• Certifications:
  • CE, UL 508, IEC 61131-2, RoHS compliant.

Functional Features

• True Redundancy (Voting Logic):
  • The module continuously monitors both input power supplies. It only declares the output “healthy” if both inputs are within normal operating parameters. If one input fails or drifts out of spec, the module seamlessly switches to the healthy source without interrupting the output.
• MOSFET ORing Technology:
  • Unlike traditional diode modules, the SS822 uses MOSFETs for switching. This eliminates the voltage drop across the device, ensuring the connected controller or I/O receives the full 24 VDC even when running on a backup source. This is critical for maintaining the torque of fieldbus-powered devices and valve positioners.
• Advanced Monitoring and Diagnostics:
  • Visual Indicators: Dual green LEDs indicate the status of each input power supply.
  • Alarm Contacts: Equipped with a potential-free (dry) contact output that triggers a “Power Fault” alarm in the DCS/SCADA system if a power supply degradation is detected.
  • Pre-emptive Warning: Allows operators to schedule maintenance during planned shutdowns rather than reacting to an emergency failure.
• Robust Industrial Design:
  • Cold Start Capability: Designed to operate in extreme cold (down to -40°C), making it suitable for Siberian gas plants or arctic applications.
  • High MTBF: Expected Mean Time Between Failures (MTBF) exceeds 350 years at 25°C, ensuring extreme reliability.
  • Dense Packing: Can be mounted side-by-side with other DIN-rail devices (50mm width) without derating, saving cabinet space.
• Passive Operation:
  • The device is unpowered in the sense that it requires no software configuration, firmware updates, or system addressing. It operates purely on the electrical presence of the input supplies.

Application Scenarios

The ABB SS822 is deployed across a wide spectrum of critical infrastructure where power stability is non-negotiable:

• Power Generation:
  • Thermal & Hydro Plants: Protecting boiler control systems, turbine governors, and excitation systems.
  • Nuclear Power: Providing redundant power to safety-critical instrumentation and control racks.
  • Renewable Energy: Grid connection control for wind turbine pitch systems and solar inverter monitoring.
• Oil, Gas & Petrochemical:
  • Offshore Platforms (FPSO): Powering ballast control systems and safety shutdown valves (SSV) where maintenance access is difficult.
  • Refineries: Ensuring continuous operation of distillation column controls and pipeline monitoring.
• Water & Wastewater:
  • Pumping Stations: Preventing pump failures and flood risks by keeping SCADA systems online.
  • Desalination Plants: Protecting reverse osmosis membrane control systems.
• Marine & Transportation:
  • Shipboard Systems: Powering navigation systems, bridge control consoles, and engine monitoring units in environments with fluctuating voltage.
  • Railways: Signaling control and traction substation automation.
• Process Industry:
  • Pharmaceuticals: Protecting vaccine batch control systems where a power loss could spoil millions of dollars of product.
  • Pulp & Paper: Maintaining synchronization of high-speed paper machines.