Ethernet in substation automation applications – Issues and requirements

Substation automation communications

This paper looks at the key issues and requirements for Ethernet in the substation environment and for substation automation applications requiring real-time performance. Trends in electric utility automation, specifically substation automation, have converged upon a common communications architecture with the goal of having interoperability between a variety of Intelligent Electronic Devices (IEDs) found in the substation.

This initiative was begun back in the late 1980s driven by the major North American utilities under the technical auspices of EPRI (Electric Power Research Institute).

The resulting standard that emerged is known as the Utility Communications Architecture 2.0 (UCA2.0) and is now an international standard as IEC 61850.

Specific topics addressed are:

1. EMI phenomena and atmospheric conditions in substations which can affect network performance,
2. New standards introduced by the IEC and IEEE that establish new EMI and environmental requirements specifically for communications networks (i.e. Ethernet) in substations,
3. Critical Layer-2 features of modern Ethernet switching hubs (i.e. switches) which enhance real-time deterministic performance as well as
4. Fault tolerant loop architectures and network redundancy.

EMI Immunity Requirements

The proliferation of Ethernet capable IEDs used for substation automation has increased markedly in the past several years. There are currently nine vendors of protective relaying devices alone offering Ethernet communications with their IEDs. Vendors of meters, RTUs and PLCs used for substation automation, also mirror this trend.

Standards such as IEEE C37.90.x and IEC 60255 define a variety of type withstands tests designed to simulate EMI phenomena such as:

1. Inductive load switching,
2. Lightening strikes,
3. Electrostatic discharges from human contact,
4. Radio frequency interference due to personnel using portable radio handsets,
5. Ground potential rise resulting from high current fault conditions within the substation and
6. A variety of other EMI phenomena commonly encountered in the substation.

This will also be true of the substation LAN equipment (i.e. the Ethernet switches).

Often the Ethernet switches will be installed in the same compartment or even on the same rack as protective relaying IEDs. Therefore, it has become necessary that the Ethernet equipment become “substation hardened”, from an EMI immunity perspective, to the same level as protective relaying IEDs.