Question

The most frequently occurred fault in the power system is:

• A. L-L-G
• B. L-L
• C. L-L-L
• D. L-G

Hint:

Remember the fault hierarchy: - Most frequent: L-G Fault ($\approx 75%$) - Most severe/destructive: Three-Phase Balanced Fault (L-L-L)

Answer 1

The Correct Option is D

Concept: Faults in power networks are categorized into symmetrical faults (balanced faults affecting all three phases equally) and asymmetrical faults (unbalanced faults). Statistical analysis of power system failures shows that the frequency of occurrence varies significantly by fault type, largely due to environmental exposure and system design.

Step 1: Review the statistics of electrical fault types.
The general distribution of faults in overhead transmission and distribution systems is roughly as follows: 1. Single Line-to-Ground (L-G) Fault: Accounts for approximately 70% to 80% of all system faults. These are typically caused by lightning strikes, tree branches touching a single conductor, or insulator flashovers to the grounded tower structure. 2. Line-to-Line (L-L) Fault: Accounts for roughly 15% of occurrences, often caused by strong winds blowing conductors into contact with each other. 3. Double Line-to-Ground (L-L-G) Fault: Accounts for about 7% to 10% of occurrences. 4. Three-Phase Balanced (L-L-L or L-L-L-G) Fault: Accounts for less than 5% of occurrences. These are rare and usually result from severe mechanical failures or operator errors during maintenance.

Step 2: Conclude the most frequent fault type.
The single line-to-ground (L-G) fault is by far the most frequently occurring fault in power systems worldwide. Therefore, Option (D) is the correct answer.