GRID T&D iRTUe-D1R1-W.125 Distributed I/O Expansion Unit

The GRID T&D iRTUe-D1R1-W.125 is a remote I/O expansion module from the iRTUe series, designed for electrical substation automation and SCADA systems. This unit provides 24 digital inputs and 8 relay outputs, housed in a compact industrial enclosure. It supports both serial Modbus RTU (via RS‑422) and IEC 61850 GOOSE (Generic Object Oriented Substation Events) communication over Ethernet. The iRTUe-D1R1 is intended for use with iGrid T&D gateways (iGW) or any third‑party RTU/PLC that supports the appropriate protocols. Its main application is extending the I/O capability of a central controller to remote points in a medium‑voltage network.

Technical Specifications

• Model: iRTUe-D1R1-W.125

• Type: Distributed I/O expansion unit (Remote Terminal Unit)

• Digital Inputs: 24 (dry contact or 24/48/125/220 Vdc selectable)

• Relay Outputs: 8 (Form C, 5A at 250V AC)

• Communication Ports: 1 × RS‑422 (Modbus RTU), 2 × 10/100BaseTX Ethernet (RJ45 or fiber ST/SC optional)

• Protocols: IEC 61850 GOOSE (publisher/subscriber), Modbus RTU

• Time Synchronization: NTP, IEEE 1588 (PTP client)

• Redundancy Support: PRP, HSR, RSTP

• GOOSE Processing Time: < 3 ms (type 1A class P2)

• Operating Voltage: 125 Vdc (nominal, range 88–140 Vdc) as indicated by "-W.125" suffix

• Operating Temperature: -25°C to +70°C

• Protection Rating: IP40 (when installed)

• Mounting: DIN rail (EN 60715)

I/O Configuration

The iRTUe-D1R1 contains two I/O cards: one card providing 24 digital inputs (optically isolated, with selectable voltage thresholds), and a second card providing 8 relay outputs (each with common terminations). The digital inputs support wet contacts (external voltage) or dry contacts with the module providing a test voltage. Each input has an LED status indicator. The relay outputs are rated for 5A at 250V AC (resistive) and are suitable for controlling circuit breakers, motor contactors, and alarm signalling. The "-W.125" suffix specifies a 125 Vdc power supply input for the module logic.

Communication and Protocols

The iRTUe-D1R1 can communicate with a host RTU or gateway via two methods: serial Modbus RTU over the RS‑422 port (typically used for connection to iGW devices) or Ethernet using IEC 61850 GOOSE messaging. When using GOOSE, the unit operates as a publisher (sending input status) and a subscriber (receiving output commands). GOOSE messages are transmitted on a substation Ethernet network with a processing time under 3 milliseconds, enabling fast interlocking and load shedding schemes. The module also supports time synchronization via NTP or PTP (IEEE 1588) to align events across the substation.

Physical and Environmental

The iRTUe-D1R1 is housed in a metal/plastic enclosure rated for industrial substation environments. It operates from -25°C to +70°C and can withstand high humidity and temperature cycling. The unit is designed for pollution degree 3 and is CE and RoHS compliant. It includes surge protection on power inputs and communication ports. Vibration resistance: 2g (10–150Hz), shock resistance: 15g.

Applications

This I/O module is used to monitor and control switchgear, circuit breakers, transformer tap changers, and auxiliary contacts in medium and low‑voltage substations. It is also used in railway power supply substations and renewable energy plants (solar/wind) where remote I/O expansion is required.

Configuration and Diagnostics

The module is configured using iGrid T&D’s proprietary software (iRTU Configurator) or via GOOSE subscription files. Configuration includes assigning IEC 61850 data models (GGIO), setting input debounce times, output hold times, and communication parameters. The unit logs events and provides diagnostic data via Modbus or GOOSE reports.

Conclusion

The GRID T&D iRTUe-D1R1-W.125 provides a rugged, high‑performance distributed I/O solution for substation automation, combining traditional digital inputs/relays with modern IEC 61850 GOOSE communication.