Ethernet Switch: Enabling Communication Between IEDs and RTU
An Ethernet switch is a networking device used to establish communication between various
devices, such as Intelligent Electronic Devices (IEDs) and Remote Terminal Units (RTUs), in a
substation's Ethernet-based Local Area Network (LAN). The switch facilitates the exchange of data by
directing Ethernet packets between devices connected to it.
How an Ethernet Switch Works
1. Packet Switching:
o The switch receives Ethernet frames (data packets) from a connected device (e.g., an
IED).
o It uses a MAC address table to determine the destination port and forwards the
packet accordingly.
2. Full Duplex Communication:
o Each connected device can send and receive data simultaneously, enabling efficient
data transfer.
3. Traffic Segmentation:
o The switch prevents data collisions and ensures that communication between two
devices doesn’t interfere with others.
4. Prioritization:
o Advanced switches can prioritize critical traffic, such as SCADA commands, using
Quality of Service (QoS) features.
Example Substation Setup
Scenario:
A modern substation integrates multiple IEDs (protection relays, measurement devices) and an RTU
for data aggregation and control. These devices communicate over Ethernet.
Setup Components:
1. IEDs:
o Communicate using protocols like IEC 61850 GOOSE or Modbus TCP/IP.
2. Ethernet Switch:
o Serves as the central hub for Ethernet communication.
3. RTU:
o Collects data from IEDs and communicates with the control center via a Wide Area
Network (WAN).
Workflow in Ethernet Communication
1. Data Exchange:
o IEDs measure parameters (e.g., voltage, current) and send this data to the RTU
through the Ethernet switch.
o The RTU processes the data for monitoring or control purposes.
2. GOOSE Messaging:
o IEDs use Generic Object-Oriented Substation Event (GOOSE) messaging for real-
time peer-to-peer communication during fault scenarios. The Ethernet switch
ensures that these critical messages are delivered with low latency.
3. Remote Access:
o Engineers can remotely access IEDs via the RTU for maintenance or configuration
tasks, with the Ethernet switch enabling this connectivity.
Example Devices and Features
Managed Ethernet Switches:
o Examples: Siemens SCALANCE, Cisco Catalyst, or Moxa EDS Series.
o Features include VLAN support, QoS, port mirroring, and redundancy protocols like
RSTP or HSR.
Unmanaged Ethernet Switches:
o Simple plug-and-play devices without advanced management features.
o Examples: Netgear ProSAFE or TP-Link Switches.
Example in Action
System Setup:
IEDs: Protection relays (Schneider P632 and ABB REF615).
RTU: Siemens SICAM AK RTU.
Ethernet Switch: Managed switch supporting VLANs and QoS (e.g., Moxa EDS-508A).
Scenario:
Normal Operation: IEDs continuously send measurement data to the RTU for monitoring.
The Ethernet switch directs the data to the RTU based on the destination MAC address.
Fault Event: During a fault, one IED sends a GOOSE message to another IED (e.g., circuit
breaker) for tripping. The switch ensures the GOOSE message is prioritized and delivered in
real time.
Benefits of Ethernet Switches in Substations
1. Scalability:
o Easily add more devices to the network.
2. Efficiency:
o Enables high-speed data transfer with minimal latency.
3. Redundancy:
o Advanced switches support protocols like PRP and HSR for fault tolerance.
4. Security:
o Managed switches can implement VLANs, port security, and access control for
enhanced cybersecurity.
Conclusion
Ethernet switches play a crucial role in modern substations, enabling robust and efficient
communication between IEDs and RTUs. By supporting advanced protocols and features, they
ensure the reliability, scalability, and security of the substation's communication network.
