How do current transformers (CTs) function in a substation?

Current transformers (CTs) play a crucial role in substations by measuring and transforming high currents into lower, more manageable levels that can be easily monitored and used for protection and control purposes. This transformation is necessary because the primary currents flowing through the high-voltage systems are often too high to measure directly with standard metering equipment or protection relays.

By producing a secondary current that is proportional to the primary current, CTs enable the safe handling of these high currents. For instance, a typical CT might reduce a high primary current, such as 1000 amperes, to a much lower secondary current of 1 ampere. This allows engineers and operators to utilize standard instruments and devices for analysis and response without risking damage or inaccurate readings due to high current levels.

The other options do not accurately describe the main function of current transformers. For example, supplying power to control systems, acting as backups for low voltage equipment, and regulating temperature are not roles that CTs fulfill within a substation environment, as those functions are typically addressed by other equipment and systems. Thus, the emphasis on the measurement and transformation of currents is a fundamental aspect of the operational integrity and safety in electrical substations.