The iGrid T&D iRTU is a modular Remote Terminal Unit (RTU), bay controller and substation gateway, purpose-built to handle the most challenging communication and automation requirements in medium- and high-voltage substation environments. It is engineered for the retrofit challenge: consolidating serial Modbus RTU-connected IEDs and other legacy devices into a modern IEC 61850 MMS/GOOSE-published networked control center architecture without requiring a separate protocol converter, gateway, or PLC. The result is a dramatic reduction in panel space, wiring complexity, and equipment cost while providing an open, future-proof migration path. With 4 software-configurable serial ports, 2 Ethernet ports and 2 fiber optic ports with PRP/HSR/RSTP redundancy, optional integrated 4G/3G/GPRS wireless modem, and an IEC 61131-3 internal PLC, the iRTU simultaneously functions as a remote terminal unit, a bay-level automation controller, a protocol converter, and a redundant network switch within a single compact DIN-rail mountable package.

Hardware Redundancy and High-Precision Time Synchronization for Mission-Critical Grid Operations

• Redundant Communication Architecture: The iRTU integrates 2 independent Ethernet ports and 2 fiber optic ports into a single embedded Ethernet switch with RSTP, PRP (Parallel Redundancy Protocol), and HSR (High-availability Seamless Redundancy). This enables seamless failover between copper and fiber connections without a single point of failure in the communication path to the SCADA master. Dual Ethernet MAC addresses allow the iRTU to connect to two physically separate networks simultaneously—a control center LAN and a station bus, for example—without requiring an external network switch.
• 1 Millisecond SOE Timestamping with Fault-Tolerant Time Sync: The iRTU supports NTP, IEEE1588/PTP, and IEC 60870-5-101/DNP3.0 time synchronization with fault-tolerant priority schemes, ensuring that all event timestamps are accurate to within 1 millisecond. In the event of a time server failure, the iRTU relies on its high-accuracy real-time clock (1.5 ppm drift) as a backup. This precision is critical for post-fault analysis and sequence-of-events recording in utility substations, where accurate temporal relationships between protective relay operations and circuit breaker actions are essential for determining root cause.
• Optional Integrated Cellular Modem: For substations where wired Ethernet or fiber connectivity is not available, the iRTU-M series replaces one serial port with an internal cellular modem supporting 4G LTE, 3G, and GPRS. This provides wireless connectivity for remote substations, distributed generation sites, and feeder automation points, enabling SCADA communication over cellular networks without requiring an external router or additional power supply.

Comprehensive Protocol Support and IEC 61850 Interoperability

• DNV-KEMA Certified IEC 61850: The iRTU has achieved A Level certification from DNV-KEMA for both IEC 61850 MMS Client/Server and GOOSE Publisher/Subscriber functionality. This independent certification ensures seamless interoperability with all major manufacturers' IEC 61850-compliant equipment, including ABB, Siemens, Schneider Electric, and GE, eliminating the integration risks associated with uncertified or partially compliant implementations.
• Full Protocol Suite for Legacy and Modern Networks: The iRTU supports DNP3.0 (serial, UDP, TCP as both master and slave), IEC 60870-5-101/102/103/104, Modbus RTU/TCP, Profibus DP, DLMS, SNMP Agent/Manager, IEC 62056-21, Spabus, Mlink, and Procome. This breadth of protocol support enables the iRTU to interface with virtually any substation IED—from decades-old electromechanical relays with serial Modbus interfaces to modern digital relays with IEC 61850 MMS—and present all acquired data to the SCADA master through a unified protocol. The iRTU can function as a master on serial networks while simultaneously serving as an IEC 61850 server to the control center, effectively bridging legacy and modern communication domains without additional hardware.
• Transparent Serial-to-Ethernet Tunneling: The built-in transparent TCP bridging and configurable IP routing enables any serial protocol—including proprietary or non-standard protocols—to be tunneled over TCP/IP connections. This is an important capability for sites running proprietary or non-standard protocols where protocol conversion is not possible, allowing the iRTU to extend the reach of serial communication across Ethernet backbones without modifying existing device configurations.

Modular Design and I/O Expansion for Scalable Substation Automation

• Internal I/O Configurations: The iRTU is available with multiple internal I/O board configurations: up to 48 digital inputs with 1 ms timestamp accuracy (configurable as counters with individually programmable debounce and decluttering filters), up to 16 dry-contact electromechanical relay outputs, and up to 16 analog inputs with ±20 mA current range and 0.15% accuracy. All digital inputs feature 2.5 kV isolation, while relay outputs provide 6 kV isolation—essential for the electrically noisy environment of MV/HV switchgear.
• iRTUe Distributed I/O Expansion: The iRTUe remote expansion units connect to the iRTU via the EXP422 RS-422 serial port or Ethernet, supporting flexible I/O board configurations including 48 DI, 16 relays, 16 AI, 24 DI + 8 relays, 24 DI + 8 AI, or 8 relays + 8 AI. iRTUe units communicate via Modbus TCP/RTU and IEC 61850 GOOSE messaging with sub-3ms processing time, enabling advanced automation functions such as load shedding, interlocking, and distributed protection schemes. IEEE 1588 PTP synchronization ensures time accuracy across all distributed I/O modules.

High-Voltage Isolation and Robust Design for Harsh Substation Environments

• 2.5 kV and 6 kV Galvanic Isolation: All internal digital input modules are galvanically isolated to 2.5 kV, while relay output modules are isolated to 6 kV. These isolation levels exceed the typical requirements of most industrial RTUs, providing reliable protection against ground potential rise, switching-induced voltage transients, and electromagnetic interference that are common in high-voltage substation environments.
• Compliance with International Standards: The iRTU meets the requirements of IEC 61850-3 (general requirements for substation automation equipment), IEC 60870-2-1 (environmental conditions), and IEC 60255-26 (electromagnetic compatibility for measuring relays and protection equipment). This compliance ensures the iRTU can be deployed in the most demanding substation environments without additional protective enclosures or environmental conditioning.

Remote Configuration Web Server — On-Site Engineering That Does Not Require a Site Visit

• Browser-Based Live Configuration: Every iRTU includes a built-in web server accessible from any commercial browser on the station network. Engineers can configure protocol parameters, I/O channel properties, PLC programs, and communication port settings entirely through the web interface, without installing proprietary engineering software. Live configuration changes are applied immediately without requiring a cold restart—a critical feature for substation retrofits where extended downtime is not acceptable. The web interface also provides real-time diagnostic monitoring of communication link status, I/O states, and PLC program execution, enabling remote troubleshooting and commissioning without requiring an engineer to be physically present at the RTU.
• Removable SD Card for Local Data Storage and Firmware Updates: The iRTU is equipped with a removable SD card slot for local data storage, logs backup, and firmware updates. This allows commissioning engineers to prepare firmware and configuration files in the office, transport them to the site on an SD card, and apply them in a single operation—significantly reducing on-site configuration time and eliminating dependencies on network connectivity during commissioning.

Applications

• Substation RTU and bay controller for MV/HV substation automation
• Feeder remote terminal unit (FRTU) for overhead line and underground cable automation
• Generation plant gateway and protocol converter for PV, wind, and thermal power plants
• Integration of legacy serial Modbus RTU IEDs into IEC 61850-based substation SCADA architectures
• Distribution automation and load shedding schemes using the internal IEC 61131-3 PLC
• Redundant communication network topologies in mission-critical substation environments