Charging Current in Transmission Line

In a transmission line, air acts as a dielectric medium between the conductors. When the voltage is applied across the sending end of the transmission line, current starts flowing between the conductors (due to imperfections of the dielectric medium). This current is called the charging current in the transmission line.current-compressorIn other words, we can say, the current associated with the capacitance of a line is known as the charging current.The strength of the charging current depends on the voltage, frequency, and capacitance of the line. It is given by the equations shown below.

For a single-phase line, the charging current

first-equ-compressorWhere, C= line-to-line in farads
Xc= capacitive reactance in ohms
V= line voltage in volts

charging-currentAlso, reactive volt-ampere generated by the line = charging volt-amperes of the lines

third-equ-compressorFor a three phase line, the charging current phase

four-equ-compressorwhere Vn =voltage to neutral in volts = phase voltages in volts
Cn = capacitance to neutral in farads

five-equ-compressorsix-equ-compressorReactive volt-ampere generated by the line = charging volt-amperes of the lines

seven-equ-compressorwhere Vt = line-to-line voltage in volts.

Significance of charging current

  1. It reduces the load current, due to which line losses decreases, and hence the efficiency of the line is increased.
  2. It improves the power factor of the transmission line.
  3. Charging current improves the load capacity of the line.
  4. It improves the voltage regulation of the line because the voltage drop is quite small.

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