Additional texts. Transformers

Power transformers convert power-level voltages from one level or phase configuration to another. They can include features for electrical isolation, power distribution, and control and instrumentation applications. Transformers typically rely on the principle of magnetic induction between coils to convert voltage and/or current levels.

Current transformers measure power flow and provide electrical inputs to power transformers and instruments. Current transformers produce either an alternating current or alternating voltage that is proportional to the measured current. There are two basic types of current transformers: wound and toroidal. Wound current transformers consist of an integral primary winding that is inserted in series with the conductor that carries the measured current. Toroidal or donut-shaped current transformers do not contain a primary winding. Instead, the wire that carries the current is threaded through a window in the toroidal transformer.
Current transformers have many performance specifications, including primary current, secondary current, insulation voltage, accuracy, and burden. Primary current, the load of the current transformer, is the measured current. Secondary current is the range of current outputs. Insulation voltage represents the maximum insulation that current transformers provide when connected to a power source. Accuracy is the degree of certainty with which the measured current agrees with the ideal value. Burden is the maximum load that devices can support while operating within their accuracy ratings. Typically, burden is expressed in volt-ampheres (VA), the product of the voltage applied to a circuit and the current.
There are a variety of applications for current transformers. Some devices are used to measure current in electronics equipment or motors. Others are used in street lighting. Current transformers with small footprints mount on printed circuit boards (PCBs) and are used to sense current overloads, detect ground faults, and isolate current feedback signals. Larger devices are used in many three-phase systems to measure current or voltage. Commercial class current transformers that monitor low-power currents are also available. Some current transformers are weatherproof or are rated for outdoor use. Others meet MIL-SPEC, ANSI C-12, or IEC 1036 standards. Generally, ANSI class devices are intended for power monitoring applications where high accuracy and minimum phase angle are required.

Voltage Transformers are devices used to measure voltage in electric circuits. Their main role is to condition (step down) the voltage to be measured to levels suitable to the measuring instrument.