No. Copper-T which is placed in the uterus prevents pregnancy. It cannot prevent sexually-transmitted diseases.
Venereal diseases which are commonly known as sexually transmitted diseases (STDs) are infectious diseases transmitted through sexual contact. It is also referred by the name reproductive tract infections (RTI). Sexually transmitted diseases are the name given collectively to the diseases which spread sexually. However, every STD is not sexually transmitted; they can spread through non-sexual contact also. Non-contact modes include transfusion of contaminated blood and tissue, breastfeeding, sharing of syringes, etc.
Contraception is an artificial method or other methods mainly used to prevent or avoid pregnancy as a consequence of sexual intercourse. When a sperm reaches the ova in women, she may become pregnant.
Copper T is a contraceptive method. Copper-T are placed in the uterus to prevent pregnancy.
Hence, if a woman is using copper-T will not help in protecting her from sexually transmitted diseases.