The current drawn by the line due to corona losses is _______

Question

Examoogle · Accepted Answer

non-sinusoidal

Explanation: The current drawn due to corona loss is non-sinusoidal because the corona discharge occurs only when the peak voltage of the alternating supply exceeds the disruptive critical voltage. Since this discharge happens during a specific portion of the voltage cycle, the resulting current waveform is pulse-like and contains higher-order harmonics.

Working Principle: When the surface potential gradient of a conductor exceeds the dielectric strength of the surrounding air, the air undergoes ionization. This process is highly non-linear; it initiates when the instantaneous voltage is high and ceases when the voltage drops below the threshold. The discontinuity in current flow during the cycle introduces harmonics, rendering the overall line current non-sinusoidal.

Key Formulas: $P_c = \frac{244}{\delta}(f+25)\sqrt{\frac{r}{d}}(V_p - V_d)^2 	imes 10^{-5}$ — Peterson's formula for corona loss in kW/km/phase; $V_d = m_v g_0 \delta r \ln(\frac{d}{r})$ — Disruptive critical voltage

Key Points: Corona loss is non-linear and voltage-dependent.; The process generates ozone and nitric acid due to chemical reactions in ionized air.; Harmonic components caused by corona can interfere with communication lines.; Corona is more prominent in extra-high voltage (EHV) lines.

Disadvantages: Power loss; Radio interference; Ozone production; Inductive interference with nearby communication circuits

Applications: Design of transmission line conductors; Selection of spacing between conductors

Additional Info: The corona discharge is essentially a sequence of pulses recurring at twice the supply frequency.. Option B is correct because the non-linear relationship between voltage and ionization current creates a waveform rich in harmonics.

Answer: B is correct — The ionization process is non-linear, causing current to flow only during peak voltage portions of the cycle, which results in a non-sinusoidal current waveform.

Exam Tip: Always remember that any non-linear element in a power system circuit, such as corona discharge or saturated transformers, inherently distorts the sinusoidal nature of the current.

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