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The Intelligent Electronic Device (II) – The New on Automation – Power Engineering

This Post Refer the New uses and tech on Electrical , Electronical and Communications on The Power Systems Administrations and Controls

called  IED, the first post was make on Spanish and the second on English.

Go Ahead…  😉

The Intelligent Electronic Device (II)


The term ‘intelligent electronic device’ (IED) is not a clear-cut definition, as for example the term ‘protection relay’ is. Broadly speaking, any electronic device that possesses some kind of local intelligence can be called an IED. However, concerning specifically the protection and power system automation industry, the term really came into existence to describe a device that has versatile electrical protection functions, advanced local control intelligence, monitoring abilities and the capability of extensive communications directly to a SCADA system. This is the definition of an IED that will be applied throughout this book.

A multitude of relays from different manufacturers can perform the functions of protection, control, and monitoring (including measurement), but need the assistance of

an RTU or communications processor, to which they are hardwired, to communicate with the SCADA supervisor. These devices may be called intelligent relays but are not included in the definition of an IED.

Similarly, some relays can communicate directly to a SCADA, but lack the control functionality. These relays are often used in conjunction with bay controllers, which  provide the required control functions, to form a power system automation system. Again, these relays cannot be classified as IEDs.

The ability of an IED to perform all the functions of protection, control, monitoring, and upper level communications independently and without the aid of other devices like an RTU or communications processor (not including interface modules) is the identifying feature of an IED.

 Note: The above definition refers to ability, and not to a specific application, where an

IED may well communicate to an RTU, for example.


Functions of an IED:

The functions of a typical IED can be classified into five main areas, namely protection, control, monitoring, metering and communications. Some IEDs may be more advanced than others, and some may emphasize certain functional aspects over others, but these

main functionalities should be incorporated to a greater or lesser degree.



The protection functions of the IED evolved from the basic over current and earth fault protection functions of the feeder protection relay (hence certain manufacturers named their IEDs ‘feeder terminals’). This is because a feeder protection relay is used on almost all cubicles of a typical distribution switchboard, and the fact that more demanding protection functions are not required enable the relay’s microprocessor to be used for control functions. The IED is also meant to be as versatile as possible, and is not intended to be a specialized protection relay, for example generator protection. This also makes the IED affordable.

The following is a guideline of protection related functions that may be expected from the most advanced IEDs (the list is not all-inclusive, and some IEDs may not have all the functions).

The protection functions are typically provided in discrete function blocks, which are activated and programmed independently.

  • Non-directional three-phase over current (low-set, high-set and instantaneous function blocks, with low-set selectable as long time-, normal-, very-, or extremely inverse, or definite time)
  •  Non-directional earth fault protection (low-set, high-set and instantaneous function blocks)
  • Directional three-phase over current (low-set, high-set and instantaneous function blocks, with low-set selectable as long time-, normal-, very-, or extremely inverse, or definite time)
  • Directional earth fault protection (low-set, high-set and instantaneous function blocks)
  • Phase discontinuity protection
  • Three-phase over-voltage protection
  • Residual over-voltage protection
  • Three-phase under-voltage protection
  • Three-phase transformer inrush/motor startup current detector


Control functions include local and remote control, and are fully programmable.

  • Local and remote control of up to twelve switching objects (open/close commands for circuit-breakers, isolators, etc)
  • Control sequencing
  • Bay level interlocking 1 (one?) of the controlled devices 
    1. Status information
    2. Information of alarm channels
  •  HMI panel on device


      Monitoring includes the following functions:

  • Circuit-breaker condition monitoring, including operation time counter, electric wear, breaker travel time, scheduled maintenance
  • Trip circuit supervision
  • Internal self-supervision
  • Gas density monitoring (for SF6 switchgear)
  • Event recording
  • Other monitoring functions, like auxiliary power, relay temperature, etc.


   Metering functions include:

  • Three-phase currents
  • Neutral current
  • Three-phase voltages
  • Residual voltage
  • Frequency
  • Active Power
  • Reactive Power
  • Power Factor
  • Energy
  • Harmonics
  • Transient disturbance recorder (up to 16 analog channels)
  • Up to 12 analog channels



Communication capability of an IED is one of the most important aspects of power system automation and is also the one aspect that clearly separates the different Manufacturer`s devices from one another regarding their level of functionality.

By definition, IEDs are able to communicate directly to a SCADA system, i.e. upper level communications. Different manufacturers use different communication protocols, which will be discussed in detail in the next section.

An IED will, in addition to upper level communications, also have a serial port or optical interface to communicate directly to substation PC or laptop for configuration and data downloading purposes, should the SCADA link not be available or desirable in that instance.


Una respuesta

  1. I’m not sure why but this weblog is loading extremely slow for me. Is anyone else having this problem or is it a issue on my end? I’ll check back later on and see if the
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    22 febrero, 2013 en 12:22 AM


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