互感器又称为仪用变压器，是电流互感器和电压互感器的统称。能将高电压变成低电压、大电流变成小电流，用于量测或保护系统。其功能主要是将高电压或大电流按比例变换成标准低电压（100V）或标准小电流（5A或1A，均指额定值），以便实现测量仪表、保护设备及自动控制设备的标准化、小型化。同时互感器还可用来隔开高电压系统，以保证人身和设备的安全。
Transformer, also known as instrument transformer, is the general name of current transformer and voltage transformer. It can turn high voltage into low voltage and high current into small current for measuring or protecting system. Its main function is to convert high voltage or large current into standard low voltage (100V) or standard small current (5A or 1A, all refer to rated value) in proportion, so as to realize standardization and miniaturization of measuring instruments, protective equipment and automatic control equipment. At the same time, transformers can also be used to isolate high-voltage systems to ensure the safety of personal and equipment.