Thyristor rectifiers are supplying arround 44 KA to our CLO2 Electrolysers at 120 Volts DC. The power factor of the rectifier transformer (12 KV HT) is very poor ranging 0.78 to 0.8. Can I use Capacitor in LT/HT side .How it will effect the performance of rectifiers

Hello abc

There are two types of power factor, displacement power factor and distortion power factor.
You can correct displacement power factor using capacitors, but you can not correct distortion power factor.
In you case, I suspect that you have a combination of both displacement power factor and distortion power factor, but the distortion power factor could be most prominent under loaded conditions.
If you install capacitors in an environment where there is a high distortion power factor, there can be issues with excess harmonic currents flowing through the capacitors and causing them to fail. You need to install detuning reactors with the capacitors if this is the case.

You need to determine firstly if there is significant displacement power factor problems when the transformer is under load. If there is, then consider correction capacitors.

Best regards,