IEDs receive data from sensors and power equipment, and can issue control commands, such as tripping circuit breakers if they sense voltage, current, or frequency anomalies, or raise/lower voltage levels in order to maintain the desired level. Common types of IEDs include protective relaying devices, On Load Tap Changer controllers, circuit breaker controllers, capacitor bank switches, recloser controllers, voltage regulators, etc.
Digital protective relays
are primarily IEDs, using a microprocessor to perform several
protective, control, and similar functions. A typical IED can contain
around 5-12 protection functions, 5-8 control functions controlling
separate devices, an autoreclose function, self monitoring function,
communication functions etc. Hence, they are aptly named as Intelligent
Some recent IEDs are designed to support the IEC61850 standard for substation automation, which provides interoperability and advanced communications capabilities.