Which device is commonly used to measure high currents?

The correct choice is the current transformer, which is specifically designed to measure high currents. Current transformers operate by converting the high current flowing in a conductor into a proportional lower current that can be easily measured by standard metering equipment. This is achieved through electromagnetic induction, allowing for accurate measurement without directly connecting measuring instruments to high voltage systems, which would be dangerous and impractical.

Current transformers are widely used in electrical power systems for monitoring and protection purposes, enabling operators to keep track of the current flowing through high-voltage lines safely. They provide isolation between the high voltage system and the measuring instruments, minimizing the risk to personnel and equipment while ensuring accurate readings.

In contrast, a multimeter is a versatile device that can measure various electrical parameters including voltage, current, and resistance, but it is not ideal for directly measuring high currents due to its limitations in handling large electrical loads. An ammeter is specifically designed to measure current but is typically used for lower current values unless it is designed for high current ranges, which can lead to potential injuries or damage if used improperly in high-current applications. A voltage regulator serves a different purpose by managing voltage levels and is not used for measuring current at all.