Surge impedance of 400 Ω means

Question

Examoogle · Accepted Answer

Option A: Line can be theoretically loaded upto 400 Ω

Explanation & Concepts:
The surge impedance of a transmission line, denoted as $Z_c$ or $Z_0$, is the characteristic impedance at which a line is theoretically 'surge impedance loaded' (SIL). When a lossless transmission line is terminated with a load equal to its surge impedance, the line operates at a state where the reactive power generated by its shunt capacitance is exactly balanced by the reactive power absorbed by its series inductance.

Working Principle: The surge impedance is derived from the distributed line parameters as $Z_c = \sqrt{\frac{L}{C}}$. At this specific loading condition, the line voltage and current are in phase, resulting in a unity power factor and a flat voltage profile along the line. Since this condition represents the equilibrium of the line's inherent reactive characteristics, it is often used as a benchmark for determining the power-carrying capacity of transmission lines without requiring additional compensation.

Key Formulas: $Z_c = \sqrt{\frac{L}{C}}$ — Surge impedance definition in terms of line inductance and capacitance.; $SIL = \frac{V^2}{Z_c}$ — Power capacity of the line at surge impedance loading.

Key Points: Surge impedance represents the load at which a line draws zero net reactive power.; For overhead lines, the surge impedance typically ranges between 350 Ω and 450 Ω.; At SIL, the voltage profile along the transmission line is flat (voltage magnitude is constant).; Underground cables have a much lower surge impedance due to high shunt capacitance.

Advantages: Minimizes voltage fluctuations along the line.; Simplifies reactive power management.; Provides a reference point for line compensation studies.

Disadvantages: SIL is often significantly lower than the thermal capacity of the line.; Maintaining SIL at all times is not always economical or possible.

Applications: Power system planning and stability analysis.; Designing voltage compensation schemes using reactors or capacitors.; Transmission line performance evaluation.

Additional Info: The term 'theoretically loaded' implies the specific condition where reactive power balance occurs, ignoring resistive losses in practical cables.. Options C and D are incorrect as surge impedance is a property of the transmission line parameters $L$ and $C$ and is independent of terminal conditions like open or short circuits.

Answer: A is correct — Surge impedance of 400 Ω represents the characteristic impedance of the line at which it can be theoretically loaded to maintain a balanced reactive power profile.

Exam Tip: Always remember that SIL is a function of the line geometry ($L$ and $C$); doubling the voltage increases the loadability limit by a factor of 4.

Examoogle · Answer

Option B: Line can be practically loaded upto 400 Ω

Examoogle · Answer

Option C: Open circuit impedance of 400 Ω

Examoogle · Answer

Option D: Short circuit impedance of 400 Ω

Correct Answer

Discussion (0)

Correct Answer

Related Questions

Discussion (0)