A group is a set of components that is bounded by protection devices and/or open switches. Failure of a component in the group leads to an outage covering the whole group.
The network below has the following groups:
•150kV network with source
•150/10kV-transformer
•10kV node at the secondary side of the 150/10kV transformer
•both 10kV feeders from the secondary side of the 150/10kV transformer up to the 0.4kV fuses
•all 0.4kV feeders starting at the secondary side of the 10/0.4kV transformers
Example of a network with 9 groups