Correct Answer - Option 4 : Ferranti effect
Ferranti Effect: At no load (or) at light load, the voltage at the receiving end of the transmission line is more than the sending voltage. It is known as the Ferranti effect. It is due to the charging current of the line.
How to reduce Ferranti effect:
- This effect can be controlled by placing the shunt reactors at the receiving end of the lines.
- A shunt reactor is an inductive current element connected between line and neutral to compensate for the capacitive current from transmission lines.
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Synchronous phase modifier(SPM) is used as under excitation it works similarly to shunt reactor which absorbs lagging reactive power and delivers leading reactive power.
The value of the shunt reactor is given by
\({X_{sh}} = \frac{B}{{1 - A}}\)
where A and B are T-parameter of the transmission line
Corona Effect:
When an alternating potential difference is applied across two conductors whose spacing is large as compared to their diameters, there is no apparent change in the condition of atmospheric air surrounding the wires if the applied voltage is low.
When the applied voltage exceeds a certain value (critical disruptive voltage), the conductors are surrounded by a faint violet glow called corona.