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The voltage drop, for constant voltage transmission, is compensated by installing
Capacitors
Synchronous motors
Inductors
All of the above
Synchronous motors
A synchronous motor, when operating in an overexcited mode, acts as a synchronous condenser (capacitor), drawing leading reactive power from the supply. By adjusting the excitation, the motor can supply reactive power to the transmission line to compensate for voltage drops caused by inductive loads, thereby maintaining a constant voltage profile.
A synchronous motor, when operating in an overexcited mode, acts as a synchronous condenser (capacitor), drawing leading reactive power from the supply. By adjusting the excitation, the motor can supply reactive power to the transmission line to compensate for voltage drops caused by inductive loads, thereby maintaining a constant voltage profile.
QcompтАЛ=V2╧ЙC тАФ Reactive power compensation principle
IleadingтАЛтИЭIfтАЛ тАФ Leading current dependency on field excitation
When the field excitation of a synchronous motor is increased beyond the normal level (overexcited), the induced back EMF EbтАЛ becomes greater than the terminal voltage V. This causes the motor to draw leading current, effectively behaving like a variable capacitor. The reactive power Q injected into the line effectively reduces the voltage drop across the line reactance XLтАЛ, which is given by ╬ФVтЙИIRтАЛR+IXтАЛXLтАЛ.
Overexcited synchronous motors operate at leading power factor.
They are often referred to as 'Synchronous Condensers' when used for power factor correction and voltage regulation.
Unlike static capacitors, the reactive power output is continuously variable by controlling field current (IfтАЛ).
Smooth and stepless voltage control
Provides both leading and lagging reactive power (if excitation is varied)
Improves system stability
Higher initial cost compared to static capacitors
Requires maintenance due to rotating parts
Higher operational losses
Large sub-stations
Industrial power systems requiring dynamic voltage support
Power factor correction at distribution ends
While static capacitors are cheaper, synchronous motors are preferred in large systems where dynamic, adjustable compensation is required.
Option A is partially correct for fixed compensation, but Synchronous Motors (Option B) are superior for 'constant voltage transmission' due to their ability to provide adjustable reactive power.
B is correct тАФ Synchronous motors, when overexcited, act as synchronous condensers to provide controllable reactive power for maintaining constant transmission line voltage.
Always remember that overexcited synchronous machines act as capacitors (leading pf), while underexcited machines act as inductors (lagging pf).