Which of the following are classified as instrument transformers?

Instrument transformers are devices used in electrical engineering to step down high voltages and currents to manageable levels for measurement and protection. The two primary types of instrument transformers are potential transformers and current transformers.

Potential transformers are specifically designed for voltage measurement, allowing for the accurate measurement of high voltages by stepping them down to a lower level that can be safely monitored by standard measuring instruments. Current transformers serve a similar purpose but for current measurement; they transform high currents into lower, measurable values.

By identifying potential transformers and current transformers as the two essential types, it becomes clear that the correct classification involves these two types of devices. The answer highlights that both potential and current are the key components of instrument transformers, aligning with the practical functions and roles these devices play in electrical systems.

Other options such as voltage and reactance, or potential and resistance, do not accurately represent the primary types of transformers used for measurement. Voltage, while relevant, does not specifically denote the class of transformer as it can refer to many components in electrical systems. Similarly, reactance and resistance are properties related to circuits rather than types of transformers, making them unsuitable choices for this classification.