Nthytronic Group iRTUe I/O Expansion Module

Nthytronic Group iRTUe I/O Expansion Module: A High Performance I/O Solution for Substation Automation

In contemporary substation automation systems, there is an increasing demand for real-time performance, reliability, and flexibility. Traditional serial communication protocols and fixed configuration I/O modules are no longer sufficient to meet advanced application requirements such as logic interlocking and load offloading. The iRTUe series I/O expansion module has emerged - it transforms any main control unit (RTU, gateway, or third-party IED) into a powerful I/O processing center through IEC 61850 GOOSE communication (processing time less than 3ms), while being compatible with traditional Modbus protocol, making it an ideal choice for new construction and renovation projects. This article provides a comprehensive technical guide for power system engineers by analyzing the hardware configuration, communication mechanism, I/O characteristics, installation selection, and typical application scenarios of iRTUe from an engineering application perspective.

Product positioning and core values

IRTUe is a modular and flexible I/O expansion unit designed specifically for substations and the energy industry. It is connected to the main station equipment (such as iRTU, iGW, or other third-party control units) through dual Ethernet (copper or fiber optic) or serial EXP422 interface, greatly expanding the data acquisition and control output capabilities of the main station. Its core values are reflected in:

Fast GOOSE communication: IEC 61850 GOOSE messages based on publish/subscribe mechanism, processing time ≤ 3ms (compliant with IEC 61850 performance level P2), meeting the strict requirements of real-time protection and automation.

Highly flexible I/O configuration: Each iRTUe can accommodate two I/O cards, providing various combinations such as digital input, relay output, DC analog input, AC voltage and current input, and supporting up to 48 DI, 16 DO, 16 AI, or 3 AC voltage+3 AC current.

Wide protocol compatibility: Supports both modern IEC 61850 GOOSE and Modbus with event buffering and timestamps, facilitating communication with outdated substation equipment or third-party master stations.

Robust electromagnetic compatibility: compliant with power industry standards such as IEC 61850-3, IEC 60870-2-1, IEC 60255-26, suitable for harsh electromagnetic environments.

Deep Analysis of IEC 61850 GOOSE Communication Mechanism

2.1 Working principle of GOOSE

GOOSE (Generic Object Oriented Substation Event) is a fast and reliable message transmission mechanism defined in the IEC 61850 standard. It adopts a publish/subscribe model: iRTUe acts as a subscriber (or publisher), receives GOOSE messages from intelligent electronic devices (IEDs) in real time, parses the state variables (such as circuit breaker position, fault signals), and updates the local I/O status. The enhanced retransmission mechanism ensures reliable delivery of messages even in network congestion.

Processing time<3ms means that the end-to-end delay from GOOSE message reaching the network port of iRTUe to message content being parsed and applied to output relays or internal logic is extremely low, which allows iRTUe to participate in interlocking and fast load unloading logic with extremely strict time requirements.

2.2 VLAN and Priority Tagging

GOOSE messages support IEEE 802.1Q virtual LAN and priority tagging. By allocating GOOSE traffic to independent VLANs and assigning high priority (such as 4 or 5), it can be ensured that critical GOOSE messages will not be blocked by regular data flows (such as file transfers and log uploads) even when the network load is high. In the complex network of substations, this characteristic is the foundation for achieving reliable GOOSE communication.

2.3 GOOSE Configuration and Address Setting

The GOOSE communication address of iRTUe can be easily configured through the side dip switch, and the default multicast group is set to 0 (which can be modified through the iConf tool). For more complex logical node configurations, iRTUe predefines GCIO logical nodes, and future firmware upgrades will support importing any SCL (Substation Configuration Language) file, seamlessly integrating it into the entire IEC 61850 model.

I/O board configuration and electrical characteristics

IRTUe adopts a modular design, with each unit supporting the installation of two I/O cards. The following predefined configuration models are provided (a total of 8 standard configurations, which can also be customized according to needs):

Model suffix: Digital input, Relay output, Analog input (DC), AC input

#DIDI 48 0 0 0

#RIRI 0 16 0 0

#AIAI 0 0 16（4-20mA） 0

#DIRI 24 8 0 0

#DIAI 24 0 8 0

#RIAI 0 8 8 0

#OOQI 0 0 0 3 voltage+3 current

3.1 Digital Input (DI)

Maximum quantity: 48 channels (divided into two groups, each with 24 channels)

Isolation voltage: 2.5 kVrms (shared common terminal for every 8 inputs)

Activation threshold: ON when>85% rated voltage, OFF when<60% rated voltage (other thresholds can be customized as needed)

Rated voltage options: 24 Vdc, 48 Vdc, 125 Vdc, 220 Vdc

Special feature: Each input can be configured as a counter and comes with an independently adjustable anti shake filter. The timestamp accuracy reaches 1 ms.

3.2 Relay Output (DO)

Maximum quantity: 16 channels (2 outputs per group, shared isolation)

Contact type: dry contact (passive)

Isolation voltage: 6 kVrms between coil and contact

Breaking ability:

250 Vac: 8 A (resistive)

30 Vdc：8 A

110 Vdc：0.3 A

220 Vdc：0.12 A

3.3 DC Analog Input (AI)

Maximum quantity: 16 channels (2 inputs per group)

Range options: 4-20 mA (± 20% adjustable), ± 10 Vdc

Accuracy: better than 0.15% after calibration

Isolation: 2.5 kVrms

3.4 Communication Analog Input (AC)

Configuration: 3 voltage channels+3 current channels

Voltage range: 110 Vac (other ranges can be customized)

Current range: 1-5 A

Measurement parameters: voltage, current, phase, frequency, harmonics

Connection method and time synchronization

4.1 Communication Interface

IRTUe provides two ways to connect to the main station:

Dual Ethernet ports (RJ45 or ST/SC fiber 100Base FX): Supports IEC 61850 GOOSE or Modbus TCP. Two ports can be configured for independent communication or redundant mode.

Serial EXP422 port: used to connect iRTU or iGW series devices, using Modbus RTU protocol.

4.2 Time synchronization

To ensure the accuracy of event timestamps and the coordination of GOOSE messages, iRTUe supports the following synchronization methods:

NTP (Network Time Protocol): Obtaining time through Ethernet

EXP422 client: Retrieve time from main station device

The accuracy of time synchronization directly affects the quality of fault recording and SOE (sequence of events recording). In applications that use GOOSE for interlocking, the time difference between each I/O module needs to be controlled within 1ms, and iRTUe can meet this requirement.

Engineering application scenarios

5.1 Load Shedding

In case of power system failure or insufficient power supply, it is necessary to quickly cut off secondary loads to protect critical loads. Traditional solutions rely on hard wiring and PLC scanning cycles, which often result in longer response times. By utilizing iRTUe's GOOSE communication (<3ms), the main station RTU can subscribe in real-time to overload or low-frequency signals from various feeder IEDs and immediately trip the corresponding circuit breaker through iRTUe's output relay. This flexible wiring method is not only fast, but also easy to modify strategies.

5.2 Circuit breaker interlock

In double busbar or bridge type wiring, complex electrical interlocking needs to be established to prevent misoperation of isolation switches. Through GOOSE, the state sharing between IEDs in each interval is achieved. iRTUe collects the position signal of this interval and publishes it, while subscribing to the state of adjacent intervals. After logical judgment, it locks or allows the operation. Compared to traditional hard wiring, GOOSE interlocking greatly reduces the amount of cable laying and maintenance costs.

5.3 Renovation of old substations

Many old stations' main control units (RTUs) do not support IEC 61850, but their I/O points are insufficient. IRTUe can be connected to the old RTU through Modbus serial port or Ethernet, and the newly added I/O signals can be provided to the master station in the form of Modbus registers. At the same time, the master station can also control the output of iRTUe through Modbus. This' plug and play 'approach avoids the high cost of replacing the main station.

5.4 Distributed I/O Expansion

When the monitored devices (such as switchgear and transformers) are scattered in a large area, an iRTUe can be installed locally at each location, forming a ring or star network through fiber optic Ethernet. The central station realizes centralized monitoring of all I/O through GOOSE. Fiber optic communication solves the problems of long-distance electrical signal attenuation and electromagnetic interference.

Mechanical specifications and environmental adaptability

Dimensions: 173 mm (height) x 78.4 mm (width) x 137 mm (depth)

Protection level: IP30 (suitable for indoor switchgear installed on DIN rails)

Working temperature: -25 ℃ to+70 ℃, meeting standards such as IEC 60068-2-1/2/14/30

Vibration and Shock: Complies with IEC 60068-2-6 and IEC 60068-2-7

MTBF：177, 000 hours (approximately 20 years)

Power selection

Wide range type (W): 32-250 Vdc, isolated 2.5 kVrms

Low voltage type (24): 19.5-60 Vdc, isolated 2.5 kVrms

In substations, 110 Vdc or 220 Vdc operating power supplies are typically used to directly supply power to iRTUe without the need for additional power conversion.

Standard Compliance and Certification

IRTUe follows multiple international standards to ensure safety and performance in the power environment:

EMC standards: IEC 61000-6-4 (emission), IEC 61000-6-5 (immunity), and IEC 61000-4-2 to -4-29 sub tests

Product safety: IEC 60950-1

Protection relay standards: IEC 60255-5, IEC 60255-22

Environmental classification: IEC 61850-3 (Environmental requirements for substation communication networks and systems)

Telecommunications port: EN 55022

These certifications mean that iRTUe can be installed in harsh electromagnetic environments near primary equipment such as switchgear and CT/PT rooms without the need for additional shielding.

Configuration and Debugging Tools

The configuration of iRTUe is completed through the iConf tool. This tool runs on a Windows PC and can be connected to the device via Ethernet or serial port to achieve:

Set IP address and GOOSE subscription/publishing parameters

Configure the debounce time and counter mode for digital input

Calibrate the zero and full scale of analog inputs

Define Modbus register mapping (function code, address, data type)

Import/export SCL files (future firmware support)

Online monitoring of I/O status and GOOSE communication quality

For rapid on-site deployment, the Modbus address and GOOSE multicast group can be set using the side dip switch, and basic communication parameter configuration can be completed without the need for a computer.

Selection and Ordering Guide

During the project design phase, the iRTUe model should be determined according to the following steps:

Determine the required type and quantity of I/O

For example: 32 DIs, 12 DOs, and 4 AIs are required → optional # DIRI (24DI+8DO) plus one # DIDI (24DI) or # AIAI (8AI)? Note that each iRTUe can only accommodate two I/O cards, so it needs to be combined reasonably. If there are many points, multiple iRTUes can be cascaded.

Select power supply voltage range

The DC control voltage inside the station is usually 110V or 220V, and a wide range type (W) should be selected. If it is a 24V system, choose the 24 type.

Select Ethernet interface type

Copper cable (RJ45): suitable for short distances (≤ 100 m) inside cabinets

Fiber optic (ST/SC): suitable for cross spacing, anti electromagnetic interference, or long-distance (≥ 2 km) connections

Confirm if it is necessary to communicate analog quantities (OOQI)

If it is necessary to measure bus voltage, line current, frequency, harmonics, etc., the # OOQI configuration must be selected.

Confirm if timestamp and SOE are required

All numerical inputs come with a 1ms timestamp, no additional options are required.

Ordering example: iRTUe # DIRI-W-RJ45 represents 24DI+8DO, wide range power supply, dual RJ45 Ethernet ports.

Key points for installation and debugging

10.1 Mechanical Installation

Install using standard DIN rails (35 mm) to ensure adequate heat dissipation space (at least 50 mm above and below).

When connecting I/O cables, use the accompanying MVSTBR 2.5 series plug-in terminals for easy maintenance. Each group of 8 digital inputs shares a common terminal (COM), and relay outputs are grouped every 2 channels. Before wiring, the polarity of the common terminal needs to be checked.

10.2 Communication Wiring

Ethernet: Use shielded CAT5e or higher grade Ethernet cables, and clean the fiber optic end face.

EXP422 serial port: Use shielded twisted pair cables, with a maximum distance of no more than 1200 meters. It is recommended to add terminal resistors at the end.

10.3 Configuration Process

Connect the device through iConf and set the IP address (if using Ethernet) or Modbus serial port parameters.

Configure digital input debounce time (e.g. 2 ms for fast signals and 20 ms for mechanical contacts).

Calibrate analog input: Apply 4.00 mA and 20.00 mA standard currents to the 4-20 mA circuit and record the calibration values.

Configure GOOSE subscription: Specify the GOOSE control block reference (GoCBRef), dataset members, and data type to listen on.

Create Modbus mapping table: Map internal I/O points to Modbus register addresses (supports 0x/1x/3x/4x).

Save the configuration and restart the device, monitor the GOOSE communication status indicator light.

10.4 Troubleshooting

GOOSE cannot receive data: check VLAN settings, multicast group address, switch IGMP listening configuration.

Digital input signal jitter: increase the time of the debounce filter; Check if the input voltage is close to the threshold area.

Relay output unable to operate: Measure coil power supply (24V from autonomous station or external), check if the output is logically locked.

Inaccurate timestamp: Confirm whether the NTP server is reachable and check the time difference between iRTUe and the main station.