This should be in Home Improvement - Heating and Air Conditioning
we use oil capacitor in horizontal way,This is correct or not?
In general, no. You need to use the correct capacitor as designed for the circuit.
to capacitate and correct
That is the correct spelling of the word "replacement."
A capacitor is placed across the supply of a fluorescent lamp circuit to correct the power factor
You might be able to but why you would want to is questionable. A capacitor could be used in air-con for two reasons. First to start the pump motor if it is a single-phase induction motor. Secondly, as a power-factor corrector. In both cases the two capacitors have probably been correctly selected and there is no point in using a different one. A replacement capacitor should have the correct voltage rating and the correct VAR rating (or the right capacitance in microfarads).
The electrolytic capacitor can only have voltage across it in one direction. Failure to comply will result in catastrophic destruction of the capacitor.
varactor diode is a correct answer
A capacitor is placed across the supply of a fluorescent lamp circuit to correct the power factor
Yes, that is correct.
Cable sizing is based on amperage of the load. The rating of the capacitor bank and the voltage at which it operated need to be stated to give an answer.
Is it the correct one for the motor being used? How often does it blow?