Instrument transformers are devices that are used in electrical power systems to extend the range and isolate the measuring instruments. They play a crucial role in ensuring accurate measurement and protection of electrical equipment. Let's explore the reasons why option C is the correct answer.

Extending the Range
Instrument transformers are primarily used to extend the range of AC measuring instruments. AC measuring instruments such as ammeters, voltmeters, and wattmeters are designed to measure specific ranges of current, voltage, and power. However, in power systems, these values can vary significantly, and measuring instruments alone may not be able to handle the high currents and voltages present.

Instrument transformers, namely current transformers (CTs) and voltage transformers (VTs), are used to step down or step up the current and voltage levels, respectively. CTs are connected in series with the load or circuit being measured, and they step down the current to a level that can be accurately measured by the ammeter. Similarly, VTs are connected in parallel with the load or circuit being measured and step down the voltage to a level suitable for the voltmeter.

Isolating the Measuring Instruments
Another important function of instrument transformers is to isolate the measuring instruments from the high voltage and current levels present in power systems. This is crucial for the safety of the measuring instruments and the personnel operating them. By using instrument transformers, the measuring instruments can be located at a safe distance from the high voltage areas, reducing the risk of damage and ensuring the safety of the operators.

Applications in Generating Stations and Transformer Stations
Instrument transformers are extensively used in generating stations and transformer stations. Generating stations produce electrical power, and it is necessary to measure various parameters such as current, voltage, and power for monitoring and control purposes. Instrument transformers enable accurate and safe measurement of these parameters in generating stations.

Transformer stations, on the other hand, are responsible for stepping up or stepping down the voltage levels for efficient transmission and distribution of electrical power. Instrument transformers are used to measure the voltage and current levels at various points in the transformer station, allowing for proper monitoring and control of the power system.

Overall, instrument transformers play a vital role in extending the range of AC measuring instruments and isolating them from high voltage levels. They are widely used in generating stations, transformer stations, and other electrical power systems to ensure accurate measurement, protection, and safety.