A plasmadyne relay was a component of a starship's warp drive systems, capable of improving quantum efficiency.

In 2370, upon examining a plasmadyne relay aboard the USS Enterprise constructed by Geordi La Forge, Cadet Wesley Crusher sardonically mentioned that a secondary phase inverter would be required, to protect the converter interface from failure due to excessive warp field stress, despite La Forge's insistence that the relay could withstand over 500 cochranes of stress. (TNG: "Journey's End")