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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Which is Unsymmetrical type fault?
LG
LL
LLG
Any of above
Any of above
Quick Summary: Unsymmetrical faults occur when the balanced three-phase system is disturbed, causing unequal currents in the phases. These include Line-to-Ground (LG), Line-to-Line (LL), and Double Line-to-Ground (LLG) faults, which lead to the flow of negative and zero sequence current components.
Unsymmetrical faults occur when the balanced three-phase system is disturbed, causing unequal currents in the phases. These include Line-to-Ground (LG), Line-to-Line (LL), and Double Line-to-Ground (LLG) faults, which lead to the flow of negative and zero sequence current components.
Iphase=Ibalanced — Characterization of current imbalance
Ia+Ib+Ic=3I0 — Fundamental relation for zero sequence current
In a balanced power system, currents are equal in magnitude and displaced by 120°. An unsymmetrical fault creates an impedance imbalance between phases or between phase and ground, causing asymmetrical current distribution. These faults are analyzed using symmetrical components (positive, negative, and zero sequence networks) linked at the point of the fault according to the fault type.
Unsymmetrical faults are characterized by the presence of negative and zero sequence currents.
The LG fault (Line-to-Ground) is the most frequent type of fault occurring in power systems.
Balanced faults (Three-phase faults) are symmetrical, whereas LG, LL, and LLG are unsymmetrical.
Symmetrical components analysis is essential for calculating fault currents in unsymmetrical conditions.
Allows engineers to model complex system behaviors
Essential for setting relay protection parameters
Creates mechanical stress on electrical machines
Leads to voltage unbalance and phase angle deviation
Circuit breaker rating selection
Relay coordination studies
Approximately 70-80% of all faults in a transmission system are of the LG type.
Three-phase faults (LLL or LLLG) are the only type of symmetrical faults.
D is correct — All listed fault types (LG, LL, and LLG) result in asymmetrical currents in the power system network.
Remember that only the three-phase fault is considered a symmetrical fault; all other faults (LG, LL, LLG) are inherently unsymmetrical and require symmetrical component theory for calculation.