D. Exciter

A transformer installation typically includes the following components:

• Conservator: A device that separates the oil in the transformer from the air outside, and allows the oil to expand and contract as the temperature changes, without allowing air to enter the transformer.
• Breather: A device that allows air to flow in and out of the transformer as the temperature changes, preventing the build-up of pressure or vacuum inside the transformer.
• Buchholz relay: A device that is used to detect and indicate internal faults, such as arcing or a broken core, in the transformer.

An Exciter is not a part of transformer installation, it is a device that generates a small voltage to excite the field windings of a generator so that it can produce power.

The correct answer is D. Excite