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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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In a 3 core cable, capacitance between two conductors with sheath earthed is 3 μF. The capacitance per phase will be
5 μF
3 μF
6 μF
12 μF
6 μF
C is correct because the capacitance per phase in a 3-core cable with the sheath earthed is twice the capacitance measured between any two conductors, resulting in 6 μF.
Capacitance between two conductors with sheath earthed (Ccc) = 3 μF.
Cph=2×Ccc
Identify given parameters
In a 3-core cable, the capacitance between two conductors when the sheath is earthed is given as Ccc=3 μF.
Ccc=3 μF
Relate phase capacitance to conductor-to-conductor capacitance
For a 3-core cable, the capacitance per phase (Cph) is calculated as the sum of the capacitance to neutral/earth. It is known that Cph=Cc+3Cs, which simplifies to Cph=2×Ccc in the configuration where the sheath is earthed and conductors are balanced.
Cph=2×Ccc
Calculate the value
Substitute the given value of Ccc into the formula: Cph=2×3 μF=6 μF.
Cph=2×3=6 μF
C is correct because the capacitance per phase in a 3-core cable with the sheath earthed is twice the capacitance measured between any two conductors, resulting in 6 μF.
In transmission lines, remember that capacitance increases with frequency and is a critical factor in determining the Ferranti effect in long cables/lines.