The reduction of voltages and amps in primary circuits of substations is achieved by what device?

The correct choice is the instrument transformer. This device is specifically designed to reduce high voltages and currents to manageable levels for measurement and monitoring purposes in power systems. Instrument transformers include types such as current transformers (CTs) and voltage transformers (VTs) which enable the safe measurement of high voltage and current systems without directly exposing instruments to potentially dangerous levels.

This reduction is crucial in substations, where high voltages may need to be monitored and controlled. By stepping down the voltage and current, instrument transformers allow for accurate readings and safe operation of various equipment without risking damage to measuring instruments or harm to personnel working in the proximity of high-voltage environments.

While transformers in general do step up or step down voltage and current levels in electrical circuits, instrument transformers are specifically tailored for metering and relay systems, thereby differentiating them from utility transformers that serve a broader function in power distribution. Synchronous motors and circuit breakers have different primary functions related to motor operation and circuit protection, respectively, and do not contribute to voltage and current reduction for monitoring and measurement purposes.