Transmission Line in Power SystemPublished on 30/3/2016 and last updated on 9/11/2018
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What is Transmission Line?Transmission line is the long conductor with special design (bundled) to carry bulk amount of generated power at very high voltage from one station to another as per variation of the voltage level.
Type of Transmission LineIn transmission line determination of voltage drop, transmission efficiency, line loss etc. are important things to design. These values are affected by line parameter R, L and C of the transmission line. Length wise transmission lines are three types.
Short Transmission Line
- Length is about 50 km.
- Voltage level is up to 20 kV
- Capacitance effect is negligible
- Only resistance and inductance are taken in calculation capacitance is neglected.
Medium Transmission Line
- Length is about 50km to 150km
- Operational voltage level is from 20 kV to 100 kV
- Capacitance effect is present
- Distributed capacitance form is used for calculation purpose.
Long Transmission Line
- Length is more than 150 km
- Voltage level is above 100 kV
- Line constants are considered as distributed over the length of the line.
What is the Transmission Efficiency?Transmission efficiency is defined as the ration of receiving end power PR to the sending end power PS and it is expressed in percentage value. cosθs is the sending end power factor. cosθR is the receiving end power factor. Vs is the sending end voltage per phase. VR is the receiving end voltage per phase.
What is Transmission Line Voltage RegulationVoltage regulation of transmission line is defined as the ratio of difference between sending and receiving end voltage to receiving end voltage of a transmission line between conditions of no load and full load. It is also expressed in percentage. Where, Vs is the sending end voltage per phase and VR is the receiving end voltage per phase. XL is the reactance per phase. R is the resistance per phase. cosθR is the receiving end power factor. Effect of load power factor on regulation of transmission line:
- For lagging load
- For leading load
- Power factor is lagging or unity, and then VR is increased and goes to be positive.
- Power factor is leading, and then VR is decreased and goes to be negative.