Page 33 - From Smart Grid to Internet of Energy

22 From smart grid to internet of energy

devices such as current transformers, power transformers, data processing
devices, sensors, transducers, breakers, switches, and actuators. All the field
devices are interfaced with Bay Level over ethernet switches that are separated
for feeder and transformer bays in Bay Level. Each bay is managed by two ded-
icated protection and control IEDs where one is used as active IED while the
other one is reserved as backup IED. The protection and control IEDs in Bay
and Station Levels are managed by computerized interfaces that are known
as human machine interface (HMI), station computers and supervisory com-
puters. The communication buses along the hierarchical architecture have been
separated as process bus and station bus where the process buses are responsible
to manage communication with latency between protection and control devices
and field devices while the station buses are dedicated for instant communica-
tion through separated bays and station controllers in addition to remote com-
munication and area networks [2, 13].
The preliminary protocols of early IEC 61850 versions were describing data
transmission methods over communication lines but they were lacking on data
management and data organizations. This caused manual configuration of
objects and system variables regarding to register definitions, input/output mod-
ules, and device configurations. However, recent versions of IEC 61850 have
brought exact definitions on data organization in addition to data transmission
methods over communication lines. In this definition, a physical field device is
connected to communication networks and it is addressed by network operator
with a unique identify. IEC 61850 allows logical devices to connect a physical
device to use it as a gateway or proxy server since each physical device includes
one or more logical devices. Thus, the data organization is organized in this
architecture. In this structure, each logical device includes one or more logical
nodes to organize one or more data element. The physical and logical device
interaction provides a communication structure transmitting SMVs as logical
data. The mapping process approach provides a standard method to describe
the power system devices regarding to abstract data and object models.
There are several communication services have been defined in IEC 61850
to describe priority and differences of applications in the power system. IEC
61850 functionalities and associated communication profiles are grouped into
five types as SMV multicast (SMV), Generic Object Oriented Substation Event
(GOOSE), Time Synchronization (TS), Generic Substation Status Event
(GSSE), and Abstract Communication Service Interface (ACSI). The SMV
and GOOSE applications are utilized to map into ethernet data frames and to
eliminate the middle layer processes. Manufacturing Message Specification
(MMS) protocols provide operation ability on TCP/IP layers and GSSE enables
communications on ISO architecture. The ACSI models are designed to bring a
set of services for IEDs to adopt to the network structure. This abstract model is
essential to provide interoperability between operation levels. Therefore, the
service sets require additional protocols to operate in practical systems and
to integrate to the power system network [2, 13].