ABB IEC61850 and Ethernet Redundancy Introduction and Applications

IEC 61850 and Ethernet redundancy

Communication services in the substation

- IEC 61850-8-1 part allows the elimination of copper wires between relays on a horizontal level, i.e. relay-to-relay communication - substation bus;

IEC 61850-9-2LE allows the sharing of digitised information from transformers or sensors with other relays in a standardised way - process bus.

These services are categorised as client-server services:

- The MMS traffic, defined in IEC 61850-8-1. allows MMS clients such as SCADA, OPC servers or gateways to access all IED objects "vertically".

This traffic flows on the station bus and the process bus.

Real-time services:

- The GOOSE flow, as defined in IEC 61850-8-1. which allows the IED to exchange data "horizontally" between machine rooms, or "vertically" between the process level and the machine room level.

In particular, status signals and trip signals are usually also used for interlocking. These information flows are usually transmitted via the station bus and/or the process bus.

- The SV (Sampled Value) flow is defined in IEC 61850-9-2 and is used to transmit voltage and current samples.

This flow is usually on the process bus, but can also flow via the station bus, e.g. for busbar protection, centralised protection and control, and phase measurement.

Generic Object-Oriented System Events (GOOSE)

- Standardised horizontal communication

- Replaces hard wiring between relays and controllers

- GOOSE is used to broadcast events between relays in a substation.

- The GOOSE communication link between relays is monitored and controlled by cyclically sending data.

- Ethernet technology provides a fast and reliable station bus for data transfer.

Sample-value-based merging unit/repeater

- Merge unit: The interface between the transformers (both conventional and non-conventional) and the relays is via a device called a merge unit (MU) or a relay with merge unit functionality.

The interface between transformers (both conventional and non-conventional) and relays is achieved by means of a device called a Merge Unit (MU) or a relay with MU functionality for centralised protection.

- The MU is defined in IEC 61850-9-1 as an interface unit that accepts current transformers (CTs)/voltage transformers (VTs) and binary inputs (BIs), and generates multiple time-synchronised serial single inputs.

and generates multiple time-synchronised serial unidirectional multipoint digital point-to-point outputs to provide data communication through the logical interface.

- IEC 61850-9-2LE or IEC 61869-9 defines 4 kHz (in a 50 Hz network) and 4.8 kHz (in a 60 Hz network) for the raw measurements.

4.8 kHz (in 60 Hz networks) sampling frequencies for the raw measurements to be sent to the user (the CPC unit or in some cases the relay protection device).

This simulates the signal from the transformer or sensor. In this way, the relay or CPC unit can run its protection and measurement functions without any adjustments.

Communication-specific mapping

- The abstract data and object model of IEC 61850 defines a standardised way of describing power system devices so that all relays can display data using the same structure that is directly related to their power system function.

- The Abstract Communication Service Interface (ACSI) model of IEC 61850 defines a set of services and responses to those services so that all IEDs operate in the same way from a network behaviour perspective.

- In addition to the mapping to the application layer, Section 8.1 defines profiles that depend on the "other" layers of the communication stack for the services provided.

Sampled values and GOOSE applications are mapped directly into Ethernet data frames, thus eliminating any intermediate layer processing;

The MMS Connection Oriented Layer can be run over TCP/IP or ISO; all data is mapped into Ethernet data frames of type "Ethernet Type" or "Ethernet Type".

ISO and GSSE messages are of data type "802.3".