Define symmetrical and asymmetrical faults in a three-phase system.

• A. Symmetrical faults affect all three phases equally (rare); asymmetrical faults involve one or two phases (e.g., L-G, L-L, L-L-G).
• B. Symmetrical faults involve only one phase.
• C. Asymmetrical faults involve all three phases.
• D. Symmetrical faults are common.

Answer: (A)

In a three-phase system, faults are described by how many conductors are affected. A symmetrical fault involves all three phases equally, such as a three-phase short circuit, where each phase carries the same current magnitude and sequence. This kind of fault is rare because it requires a fault path that connects all three phases together at once.

Asymmetrical faults involve one or two phases, which is more typical in practice. Examples include line-to-ground faults (one phase to earth), line-to-line faults (two phases shorted), and double line-to-ground faults (two phases shorted to ground). These faults produce unbalanced currents and voltages, which is why sequence network analysis is often used to study them.

So the statement that symmetrical faults affect all three phases equally and that asymmetrical faults involve one or two phases (with examples like L-G, L-L, L-L-G) correctly captures the distinction. The other propositions conflict with these definitions or with how common each type is.