IEEE Power & Energy Magazine - July/August 2019 - 52

CT inaccuracy and saturation. Because DITs can be linearly
accurate for all levels of current, the sloped differential
characteristic will be unnecessary for differential protection
when using DITs. DITs also eliminate the oil used as the
insulating medium in traditional standalone CTs and VTs.
This lack of oil reduces not only the possible environmental
impact but also the weight and size of the instrument transformer, and thereby decreasing installation time.
The PIUs will publish and subscribe to data from a communication network. The 61850 standard defines Ethernet as the
physical architecture of the process bus communication network. Ethernet's packet-switched architecture allows multiple
protocols to run across the same network, which maximizes
the use of the communication infrastructure. While point-topoint Ethernet is an allowed implementation of the 61850 standard, switched Ethernet process bus will be the physical architecture of larger substations in the future. The Ethernet switch
will be the backbone of these networks. These switches will be
configured devices in the process bus networks used to control and shape the flow of traffic in the network using virtual
local area networks, media-access-control address filtering,
and deterministic Ethernet solutions, such as time-sensitive
networking. The switches will also need to be configured to
maintain security and pass timing signals.
Clocks will become a critical protection component in
the substation of the future because of the need to synchronize published streams of data, as this is necessary
for all of the published streams of analog data. Otherwise,
elements, such as differential protection, may misoperate because of the wrongly calculated angular differences
associated with communication latency. Several clock
synchronizing methods exist today, but all signals that can
be communicated over the network will be sent that way
rather than through wired communications. Therefore,
future substations will use the precision time protocol signal defined in the IEEE 1588 standard.
IEDs will be the application containers of the substation
of the future. These containers will subscribe to data and then
use that data to make protection decisions, provide operation
data, or provide monitoring and diagnostic data. These containers will also control and operate the substation based on
the data that they subscribe to. In the substation of the future,
discrete IEDs will be replaced by a single IED that acts as
the centralized protection unit. The centralized protection
unit will make all protection decisions for the substation and
will act as a gateway to serve operational and maintenance
data. This centralized protection unit will likely be included
in the substation edge device. Because all digital substation
components are critical to the protection of the substation,
redundancy, for PIUs, IEDs, clocks, and communications
networks, will have to be addressed at each level.
Benefits of Process Bus

Process bus brings clear benefits to the substation of today, and
those benefits will drive the adoption of the substation of the
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future. Benefits include reduced expenditures, smaller substation footprints, and flexibility and adaptability of the substation.
Capital expense reduction is the most often-touted benefit. This
decrease does not come from a cutback of equipment, because
there will be more actual equipment in the substation. Rather,
it comes from reduction of labor to design and construct the
substation. This decrease of labor on the design side will be
realized through the tools that configure the substation. The
designer will configure the substation through software tools
rather than design the substation as is done today.
Because the substation will be a standard configuration,
it will be easier to duplicate than today's designs. With a
duplicated design, the designer can create standard modules for the substation. The design process would mean
connecting the modules together and minimally configuring each standard module. As information is contained
and transmitted in communication packets rather than in
discrete wires among equipment and IEDs, deduction of
installation expense in the process bus is realized because
of the decreased field wiring and the lower number of terminations of field wiring.
Because there will be fewer cables in the process bus
architecture, the substation can be smaller. Instead of many
copper cables among the control house and the primary
equipment, the same functions can be accomplished over a
single fiber-optic cable. This will allow the cable trench of the
substation to shrink. Because the IEDs will not be required
to house space-to-land analog and digital inputs and outputs,
the IED itself will be smaller, which will translate into a
smaller control house with fewer panels.
A requirement of the substation of the future is that the
substation design be flexible and adaptable. Process bus
allows designers to add bays or lines to the substation very
quickly because the design will consist of adding a substation module and modifying the configuration rather than
redesigning the substation. During construction, the outage
time to install new equipment will be reduced because the
work performed during the outage will be to install and save
the new configuration to the centralized protection unit.

Examples of Digitally Enabled
Substation Applications
Substations of the future will enable new use cases by providing critical data as well as a platform for new decentralized applications. New use cases are required by the higher
penetration of new DERs, the aging of the existing grid
assets, and the application-driven workforce. Every one of
the applications described here will be delivered as a software service into a substation edge device.

Asset Lifecycle Management
Helping to manage the lifecycle of the grid's assets will
continue to be an important role of the substation of the
future. Part of this strategy is APM, which integrates and
analyzes all data from the power system with the goal
july/august 2019

IEEE Power & Energy Magazine - July/August 2019

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