Someone who is hiv positive and takes his/her arvs in time which led him to test when results shows negative. can he transmit the virus to a partner who is negative?

I believe the answer is No.

Explanation:

HIV is a virus which lacks the mechanism to reproduce since it is just an enclosed bunch of genetic material. With that in mind, it requires a mechanism to survive and reproduce and for that it targets the T-lymphocytes since the cells have receptors for the virus. It starts its cycle by attachment, penetration, biosynthesis, maturation and lastly budding. It adds it's genetic material to the DNA chains in the nucleus which the human cells replicate unknowingly. Most of the anti-retrovirals target to prevent this replication through targeting enzymes such as protease inhibitors. Taking of the drugs only reduces the replication of the virus lowering the viral count to less than 200 where we cannot count them anymore because they are widely distributed. Having a viral count <200 does not mean you are free of the virus but only that it is very low to be counted or cause significant health problems but the small number can still be transmitted if protection is not used.