Portal Spawners, also known as Portal Doors are test mechanics that appear in both games. When activated, it creates a portal which is linked with Portal Gun. Usually, the created portal is orange. They appear at the beginning of both games, when you dont have, or have only one-colored portal gun. They are usually activated by a timer, a button or by entering the test chamber.
Bugs
In both games, if you cheat yourself a portal gun where you dont own it and create a portal before Portal Spawner creates its own, you portal will be linked with the one made by Spawner, creating one unlinked portal with the same color.