What is a current transformer?

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A current transformer is a device used in the measurement of electricity. Normally, electrical current is delivered at high voltage levels that are dangerous to humans. A current transformer allows current to be measured without diverting current to the measuring instrument, which can be risky for the device and the person holding it. This is usually achieved by measuring the magnetic field produced by the current, rather than the current itself.

There are two ways to supply regular electrical current to power a device: alternating current and direct current, sometimes abbreviated as AC and DC. Direct current is commonly used in battery-powered devices, including most automobiles. Power plants use alternating current to supply electricity to remote locations, as electricity in this form can be sent over long distances without significant energy loss. High voltage direct current lines achieve the same goal. Both forms are different from static electricity, which is electricity that occurs naturally and is too irregular to be used as a source of energy.

The high voltage used in the power supply is dangerous for anything that is not specially designed to carry that voltage. Measuring devices, even if insulated to protect users, can be easily damaged by fluctuations in high voltage electrical current. A current transformer eliminates these hazards by providing an accurate measurement without a direct connection to the current itself. The current transformer also allows for standard measurements of a wide range of different power devices. Current used in power supply systems can vary from device to device, so standard measurements are important for efficient management of complicated systems.

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Most power transformers are connected to the power distribution system, such as transformers that reduce the high voltage of power lines to safe levels for home use. The current transformer, however, does not require a physical connection to the line being measured. All devices with electrical current create a magnetic field. The current transformer uses this magnetic field to create a current directly proportional to the device or line being measured. A load of 400 amps, for example, can create a reading of 4 amps. The instrument user, knowing the ratio is 1:100, can deduce the actual device current.

The current transformer is an important tool in electrical engineering. Current levels should be monitored for safety and efficiency purposes. Measuring devices connected to current transformers allow this monitoring at various locations in the system. They can also be used to measure a building’s electricity usage for billing or inspection purposes.

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