Intelligent electronic device

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 Electronic Devices.
Some recent IEDs are designed to support the IEC61850 standard for substation automation, which provides interoperability and advanced communications capabilities.

Generic Substation State Events (GSSE)

Generic Substation State Events (GSSE) is an extension of event transfer mechanism in UCA2.0. Only Status data can be exchanged through GSSE and it uses a status list (string of bits) rather than a dataset as is used in GOOSE. GSSE messages are transmitted directly over IEC/ISO 8802-2 and 8802-3 using a similar mechanism to GOOSE messages (refer IEC 61850-7-1 Clause 12.2, IEC 61850-8-1 Clause 6.4). As the GSSE format is simpler than GOOSE it is handled faster in some devices. GSSE is being progressively superseded by the use of GOOSE and support for it may eventually disappear.

Generic Object Oriented Substation Events (GOOSE)

Generic Object Oriented Substation Events (GOOSE) is a control model mechanism in which any format of data (status, value) is grouped into a data set and transmitted within a time period of 4 millisecond. The following mechanisms are used to ensure specified transmission speed and reliability.

• GOOSE data is directly embedded into Ethernet data packets and works on publisher-subscriber mechanism on multicast or broadcast MAC addresses.

• GOOSE uses VLAN and priority tagging as per IEEE 802.1Q to have separate virtual network within the same physical network and sets appropriate message priority level.

• Enhanced retransmission mechanisms - The same GOOSE message is retransmitted with varying and increasing re-transmission intervals. A new event occurring within any GOOSE dataset element will result in the existing GOOSE retransmission message being stopped. A state number within the GOOSE protocol identifies whether a GOOSE message is a new message or a retransmitted message.

• GOOSE messages are designed to be brand independent. Some vendors offer intelligent electronic devices (IED) that fully support IEC61850 for a truly interoperable approach within the substation network without requiring vendor specific cables or algorithms.