Which of the following is not classified as a reactive resource?

A transformer is not classified as a reactive resource because its primary function is to transfer electrical energy between two or more circuits through electromagnetic induction. While transformers can influence voltage levels and provide certain reactive power characteristics, they do not inherently supply or consume reactive power like the other options listed.

In contrast, a reactor bank, capacitor bank, and synchronous condenser are all components explicitly designed to manage reactive power within an electrical system. Reactor banks are used to absorb reactive power, while capacitor banks store and supply reactive power. A synchronous condenser operates similarly to a generator, providing reactive power support to the grid as needed.

Understanding the role of these components helps clarify why the transformer stands apart as it serves a different primary purpose, focusing on voltage regulation and energy transfer rather than direct reactive power management.