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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 protection system is used for bus bar?
Frame leakage
Circulating current
Both A and B
None of above
Both A and B
Quick Summary: Busbar protection schemes are essential to isolate faults within electrical substations. Both 'Frame leakage' (sensitive to leakage current to the structural frame) and 'Circulating current' (differential protection) are standard, well-established methods for protecting busbar sections against internal short circuits.
Busbar protection schemes are essential to isolate faults within electrical substations. Both 'Frame leakage' (sensitive to leakage current to the structural frame) and 'Circulating current' (differential protection) are standard, well-established methods for protecting busbar sections against internal short circuits.
∑Iin−∑Iout=Idiff — The fundamental principle for differential (circulating current) protection.
Ileakage=ZfaultVbus — Current flowing through the frame during a insulation failure.
The circulating current (Differential) scheme relies on Kirchhoff's Current Law, where the sum of currents entering and leaving the busbar must be zero under normal conditions; any deviation indicates a fault. The Frame leakage protection scheme detects current flow between the busbar conductors and the grounded metallic supporting frame, which occurs during insulation failure.
Differential protection is the most common method for high-voltage busbars.
Frame leakage protection is primarily used in small and medium voltage installations.
Busbar protection must be extremely fast to prevent equipment damage and system instability.
Stability and sensitivity are the two primary requirements for busbar relays.
High speed of operation for clearing faults
Provides selectivity by isolating only the faulty section
Comprehensive coverage for both internal and external faults
Requires high precision current transformers (CTs)
Can be sensitive to CT saturation during external faults
Complex installation requirements for high voltage systems
Power station substations
Grid interconnecting substations
Industrial distribution switchboards
| Feature | Circulating Current | Frame Leakage |
|---|---|---|
Protection Principle | KCL (Differential Current) | Insulation Breakdown to Earth |
For large high-voltage busbars, differential protection is the only practical solution.
Option A focuses on leakage to ground, while Option B focuses on the vector difference of currents.
C is correct — Both frame leakage and circulating current are standard protection methods employed to ensure the safety and reliability of busbar systems.
Always remember that differential protection requires the current transformers on all connected feeders to have identical characteristics to prevent false tripping during external faults.