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Application Scenarios
In a chemical plant’s Emergency Shutdown System (ESD) or Safety Instrumented System (SIS), the SS822 is installed in the control cabinet. It takes inputs from two separate 24V DC power supplies (e.g., ABB SD821/SD822 series). If the primary supply fails due to a breaker trip, the SS822 detects the fault within milliseconds and seamlessly switches to the secondary supply, preventing a dangerous loss of power to the safety controllers and I/O modules.
Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | ABB SS822 (Ordering Code: 3BSC610042R1) |
| Manufacturer | ABB |
| Product Category | Redundant Power Voting Unit (PVU) |
| Input Channels | 2 independent 24 V DC (typically 20A max per channel) |
| Output | 1 combined 24 V DC (Max 20A continuous) |
| Switching Time | < 10 ms (seamless transfer, no interruption) |
| Mounting | DIN Rail (35mm) |
| Width | 50 mm (compact) |
| Safety Level | Suitable for SIL 2/3 safety systems |
| Operating Temp. | -20 °C to +70 °C (industrial grade) |
Technical Principles and Innovative Values
The SS822 is engineered for fault-tolerant systems where power loss is not an option.
- Innovation Point 1: True Redundancy with Voting Logic: Unlike simple diode ORing modules, the SS822 actively monitors both input sources for undervoltage, overvoltage, and failure. It uses a “voting” mechanism to decide which source is healthy, providing a level of intelligence and safety beyond basic power combining.
- Innovation Point 2: MOSFET-Based Switching: It utilizes MOSFET semiconductor switches instead of mechanical relays. This provides extremely fast (<10ms) and bounce-free switching between sources, eliminating the voltage drop associated with traditional diode solutions and ensuring clean power to sensitive electronics.
- Innovation Point 3: Integrated Diagnostics: The module provides visual LED status indicators and often a fault relay contact. This allows the DCS or PLC to be alerted immediately if a power supply has failed, enabling predictive maintenance before the redundancy is lost.
Application Cases and Industry Value
A nuclear power plant’s reactor protection system requires absolute power availability. The SS822 was deployed in the S800 I/O cabinets, fed by two independent UPS-backed 24V DC sources. During a simulated primary power failure test, the module switched to the backup source without causing any glitch or reset in the controllers. This validated the system’s SIL 3 compliance and demonstrated its value in protecting against single-point power failures in high-consequence environments.
