Final answer:
The equivalent sequence network for a line-to-line fault consists of positive and negative sequence networks connected in parallel. The zero sequence network is not used as the fault does not involve the earth. This network model is essential for fault analysis in electrical power systems.
Step-by-step explanation:
Equivalent Sequence Network for a Line-to-Line Fault
A line-to-line fault (LL) is one of the types of short circuits that can occur in an electrical power system. This type of fault involves a connection between two of the three phases, without involving the earth. To analyze the effects of an LL fault, an equivalent sequence network is used, which comprises three separate networks: the positive, negative, and zero sequence networks.
During a line-to-line fault, the positive and negative sequence networks are connected in parallel with each other because the fault only involves two phases and there is no ground connection. The zero sequence network is not included in the analysis of a line-to-line fault, as this network is only relevant when the earth is part of the fault.
The current in the faulted lines will have components from both the positive and negative sequence networks. As these networks are parallel, the voltage across the fault is the same in both sequences. The use of equivalent sequence networks is crucial for correct fault analysis and subsequent protective relay coordination and system design.