Evolution of Substation Communication

The Legacy Substation

Inter-IED communications (i.e. signaling and exchanging information) was typically done via a combination of rigid wiring between devices and low speed serial communications. Signaling was often accomplished by having outputs from one IED connected to the inputs of another. This system was by its very nature inflexible and limited in its scope of control. Most sophisticated inter-IED control schemes could require a large number of wiring interconnections between multiple IEDs and thus were not practical. Low-speed serial communications were often limited to master/slave half-duplex arrangements and thus true peer-to-peer communications between IEDs was not feasible.

The Substation LAN

The emergence of the Ethernet based Substation LAN (Local Area Network) has been steadily gaining momentum world wide. The main benefits of the substation LAN are:

• High-speed peer-to-peer communications between IEDs
• Reduced inter-IED wiring
• Coexisting multiple protocols (e.g. DNP, Modbus, IEC61850) on the same physical network
• Enables “Data over IP” for easy access to substation data

RuggedSwitch^® family of Utility Grade Ethernet Switches was specifically designed for implementing Substation Communications. Specifically, they were designed to the same standards as mission critical protective relaying devices (i.e. to meet the same EMI immunity, performance and reliability requirements).

The IEC 61850 Substation

The IEC 61850 standard view of substation communications can have two application domains: Station Bus and Process Bus. Station Bus refers to an application domain where relays and RTUs would attach to the LAN. Process Bus refers to devices such as CT/VT Merging Units (MU) providing sampled measured values of current and voltage via the LAN.

The RuggedSwitch^® family of Utility Grade ethernet switches have been specifically designed to meet the requirements of IEC 61850 and implement Station Bus or Process Bus LANs. Specifically, the RuggedSwitch^® family exceeds the the IEC 61850-3 EMI Immunity requirements and the fiber optical network interfaces help provide Zero Packet Loss™ (ZPL) performance under EMI stress. This is a must if the Station Bus LAN is to be used for tripping, blocking breakers or if sampled measured values of current and voltage are to be distributed over the Process Bus LAN.