If you are coming by taxi from Chennai, it will take approximately 3.30 hours from Chennai Central railway station, or about 3 hours from Chennai airport.
If you want to travel by bus from Chennai, you should first go to Koyambedu Bus Stand, which is about an hour-long drive by auto-rickshaw from the Chennai Central Station.
From Koyambedu Bus Stand, you can take a bus to Pondicherry, which will take around 3.30 hours.
When you arrive at the Pondicherry bus stand, you will need to take an auto-rickshaw to reach SACAR. Please ask the driver to bring you to Vaithikuppam, near Padmini Nagar Post-office, Masimagham road (as it is locally known).