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The maximum efficiency in the transmission of bulk AC power will be achieved when the power factor of the load is:
slightly less than unity leading
slightly less than unity lagging
considerably less than unity
unity
slightly less than unity leading
Maximum transmission efficiency occurs when the I┬▓с┤┐ losses are minimized relative to the power transferred. By operating at a slightly leading power factor, the voltage drop across the line inductance is compensated by the capacitive current, allowing the line to deliver power at higher efficiency.
Maximum transmission efficiency occurs when the I┬▓с┤┐ losses are minimized relative to the power transferred. By operating at a slightly leading power factor, the voltage drop across the line inductance is compensated by the capacitive current, allowing the line to deliver power at higher efficiency.
╬╖=PoutтАЛ+3I2RPoutтАЛтАЛ├Ч100% тАФ Efficiency of a three-phase transmission line
P=XVSтАЛVRтАЛтАЛsin╬┤ тАФ Power transfer capability formula
In a long transmission line, the voltage drop is given by VSтАЛтЙИVRтАЛ+I(Rcos╧Х+Xsin╧Х). When the load has a slightly leading power factor (╧Х<0), the term Xsin╧Х becomes negative, which helps in maintaining the sending end voltage closer to the receiving end voltage. This reduction in current magnitude for a given real power reduces the ohmic losses (I2R), thereby maximizing efficiency.
Efficiency is defined as the ratio of power delivered at the load to the power sent from the source.
Leading power factor loads act as a source of reactive power, reducing the burden on the transmission line to supply inductive VARs.
Transmission lines possess inherent series inductance and shunt capacitance.
Maintaining a slightly leading power factor helps optimize voltage regulation alongside transmission efficiency.
Reduced transmission line current for fixed real power.
Lower I2R power losses.
Improved voltage profile along the line.
Requires reactive power compensation (e.g., synchronous condensers or shunt capacitors).
May lead to overvoltage conditions at the receiving end during light loads (Ferranti effect).
High Voltage AC (HVAC) transmission networks.
Industrial power factor correction schemes.
Unity power factor minimizes current for a fixed voltage, but the transmission line impedance is inductive, making slightly leading power factor superior for efficiency in long lines.
Option D is often confused as the correct answer because unity power factor minimizes current in simple resistive circuits, but it neglects the reactive component of the transmission line impedance (XLтАЛ).
A is correct тАФ slightly less than unity leading power factor compensates for the line's inductive reactance, minimizing line losses and maximizing efficiency.
Remember that unity power factor is ideal for minimum current in the load, but for transmission systems with significant inductance, a slightly leading power factor is the optimal engineering compromise.
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