Answer / sidharth

The pf is maintained at 0.8 because generator has to supply reactive power to the connected transmission line if pf is maintained at 1 then the distribution transformers would not be energized as it requires some reactive power for its core to produce magnetic flux.Also the due to line capacitance the receiving end voltages will get higher than the sending end voltages. For more reference consult reactive power control topic.

Answer / lokeshraj

We use the capacitor bank to maintain the power factor at .8 when it goes below this value, capacitor compensate the reactive power needed, and improves the power factor. Why don't we use this much value of capacitor that the pf becomes unity. Because if we use the capacitor at the load end and makes the pf unity the losses in the line will be decreased and the load capacity of the line will be increased.
Only in unloaded or lightly loaded condition the receiving end voltage of the line becomes higher than the sending end voltage.

Answer / mintuk1@gmail.com

For transmitting power with low value of ferrenty effect .power generating station pf should kept 0.85 -0.80

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