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A 3-phase, 50 Hz transmission line has a capacitance of line to neutral Cₙ = 0.01 μF/km. The voltage of the line is 100 kV. The charging current per kilometer of line is
181 A/km
181×10–³ A/km
51 A/km
73×10³ A/km
181×10–³ A/km
Given: System voltage VL = 100 kV = 10⁵ V, Frequency f = 50 Hz, Capacitance Cn = 0.01 μF/km = 0.01 ×10−6F/km.
System voltage VL = 100 kV = 10⁵ V, Frequency f = 50 Hz, Capacitance Cn = 0.01 μF/km = 0.01 ×10−6F/km.
Ich=3VL×2πfCn
Calculate phase voltage
Since the line voltage is given as 100 kV, the phase-to-neutral voltage is Vph=3VL=3105≈57735V.
Vph=3105
Determine angular frequency
The angular frequency ω for 50 Hz is calculated as ω=2πf.
ω=2×π×50=314.16 rad/s
Calculate charging current
Substitute the values into the charging current formula: Ich=Vph×ω×Cn.
Ich=3105×314.16×0.01×10−6
Final Result
Performing the arithmetic calculation: Ich≈57735×3.1416×10−6≈0.1814A/km.
Ich≈181×10−3 A/km
B is correct because the calculated charging current per kilometer is approximately 181 mA/km, which is equivalent to 181 × 10⁻³ A/km.
Understanding charging current is vital for calculating Ferranti effect and voltage regulation in long transmission lines where shunt capacitance becomes significant.