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DISTRIBUTION AUTOMATION BASED ON IEC61850
Nirmal Thaliyil
nirmal@kalkitech.com
Kalki Communication Technologies Pvt Limited
Abstract: This paper illustrates an example of
an interoperable and decentralized
distribution automation system based on the
IEC61850 standard. Advanced distribution
automation controllers residing along with
primary equipment such as load break
switches, sectionalizers, autoreclosers and tie
switches have enough resources to make use
of IEC61850 ACSE services for information
exchanges between each other as well as with
the central location. Network information
from neighboring nodes can help field
controllers make decisions faster and more
accurately thereby making the distribution
network self- healing and reliable.
I. Distribution Automation
The challenges faced by Distribution utilities
have increased significantly recently, due to
increased demand, higher expectations of
reliability and power quality by customers and
integration of distributed resources into the
grid. Distribution Automation (DA) allows
utilities to operate power systems more
effectively. It improves reliability by using a
network that is self-healing with improved
power quality and efficiency (reduced losses),
better asset utilization, is immune to physical
and cyber breaches, and can incorporate
more energy generation and storage options.
The main distribution automation functions
which assist utilities to accomplish the above
requirements are
a)
b) Fault location isolation and service
restoration (FLISR)
c) Feeder Load balancing
d) Volt-VAR optimization
e) Conservative voltage reduction (CVR)
f) Condition monitoring
In this article, we choose one of the
elementary Distribution Automation use cases
called Volt-VAR optimization to try and find
the most suitable communication protocol,
media and data model, which may be best
suited for standardization.
II. Volt-VAR Optimization
The objectives for using Volt-VAR optimization
as a use case are:
a) Minimize kWh consumption at
voltages beyond given voltage quality
limits (i.e., ensure standard voltages
at customer terminals)
b) Minimize feeder segment(s) overload
c) Reduce load while respecting given
voltage tolerance
d) Conserve energy via voltage reduction
e) Reduce or eliminate overload in
transmission lines
f) Reduce or eliminate voltage violations
on transmission lines
g) Provide reactive power support for
distribution bus
h) Provide spinning reserve support
i) Minimize cost of energy
Capacitor banks are more widely used in
distribution systems for VAR (reactive power)
and regulators for voltage control. Controlling
the capacitor banks and regulators would

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require measurement from single or multiple
phases e.g. voltage level, power factor, VAR
flow and time of day. The VAR/voltage control
devices can be used to switch capacitor banks
on/off in order to minimize the reactive
power flows on the system and to maintain
the bus voltage.
III. IEC61850
The IEC61850 communication standard had
originally been conceived by TC57 group for
substation automation functions. It provides a
panoptic view of the power system domain
and is now making the object model more
comprehensive and more standardized the
communication structure. Some of the
application areas added are hydro power
plants, DER, substation to substation and
substation to control center communication
and wind power plants. There are also work
under progress for adapting the standard for
feeder automation, electrical storage,
transportation, transferring synchrophasor
data etc.. This trend opens up new opportunities
for the development of intelligent applications for
the power system.
IEC61850 has an inherent ability to support
more sophisticated automation systems with
larger numbers of smart devices. The
adoption of 61850 by vendors in their
products will provide a standardized
information model for each type of vendor
product, e.g., relay, capacitor bank,
switchgear, etc. The principal benefits of using
IEC 61850 for Distribution Automation
functions are
 Object oriented data model
 Adaptable data exchange rate as per
application
 Peer to peer communication topology
 Process bus integration
 Simplified engineering process
 Enhanced security features
IV. Modeling for Volt-VAR control
The Shunt capacitor can be modeled as
shown in Figure 1.
A capacitor bank normally consists of several
parallel capacitors per-phase. Therefore each
phase has more than one switch logical node
XSWI (Circuit Switch) associated with it to
engage and disengage capacitors into the
circuit. For measurement purposes, there are
three instrument transformers TCTR (Current
transformer) and TVTR (Voltage Transformer)
for each phase. ZCAP (Capacitor bank) logical
node represents capacitor bank status such as
health, device status, name plate, and
operation time. Automatic control logical
node AVCO (Automatic Voltage controller)
can either be based on local setpoints or
setpoints that are received remotely through
a communications link from a centralized or
peer capacitor controller. Scheduled or set
points for a certain range are available for
taking necessary actions. Ranges are normally
used for voltage, VAR, temperature and
current.
Voltage regulators with automatic tap
changing capabilities allow for controlling the
XSWI
AVCO CSWI
ZCAP
MMXU/
MMXN
XSWI
XSWI
XSWI
XSWI
XSWI
TCTR
XSWI
XSWI
TVTR
Figure 1: Modelling capacitor bank

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voltage according to predefined automatic
logic or by remote access through the
operator command. Regulators can be
modeled as shown in Figure 2.
To regulate the voltage of a three-phase
three-wire system, banks of single phase
regulators can be created. The common
schemes are two single-phase voltage
regulators connected in an open delta
connection, or three single-phase voltage
regulators connected in a closed delta. Open-
delta configuration requires fewer devices at
the cost of a smaller regulation range. Typical
regulation range for open delta configuration
is ±10% for phases with regulators and ±5%
for phase without the regulator. In case of
closed delta configuration the range is about
±15% for all phases.
ATCC or Automatic Tap Changer Control
logical node will control the tap changers.
ATCC will have status indication for local
operation, operation counter, tap position,
parallel/independent operations and block
automatic control in addition to controlling
operation data and settings and other status
information. There may be three or two YLTC
(Transformer tap changer) logical nodes in the
system as per the scheme explained above.
V. Communication Protocols
Abstract data models defined in IEC 61850 can
be mapped to a number of protocols.
Currently, mappings are available for MMS
(Manufacturing Message Specification),
GOOSE (Generic object oriented substation
events) , SMV (Sampled Measured Values) and
Web Services. These protocols are usually run
over Ethernet links. Mission critical messages
that need to be transferred between devices
are transferred as GOOSE messages. GOOSE
messages are connection less packets that are
sent to the network as a multicast message on
layer 2 in the OSI model. The router is
designed to prevent broadcast and multicast
packets from leaving the LAN and only passes
IP packets on layer 3. However, this is
achieved by attaching a VLAN tag that can be
recognized by the router, with each GOOSE
message. The router converts GOOSE
messages with a VLAN tag into a routable IP
packet and sends it to the destination IP.
Decentralized automation methods are
chosen over centralized methods for higher
scalability, better performance and for
enabling micro-grid operations. Adoption of
IEC61850 for distribution automation
application requires transferring GOOSE
packets over IP for peer-to-peer
communication. Decentralized distribution
automation use cases FLISR, VVO (volt-var
optimization), CVR require sending
measurement and status information
between intelligent electronic controllers
residing in the field. Protocol Independent
Multicast (PIM) used for intra-domain
multicast is a bandwidth-conserving
technology that reduces traffic by
simultaneously delivering a single stream of
information to potentially thousands of
nodes. Bidirectional PIM variant can be
adopted for efficient many-to-many
communications within an individual PIM
distribution network domain. Although PIM is
said to be suitable because of less overhead,
MMXU/
MMXN
ATCC
XSWI
XSWI
TVTR
XSWI
XSWI
YLTC
XSWI
XSWI
TCTR
Figure 2: Modelling Voltage Regulators

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there are also other mechanisms to transfer
GOOSE packets over IP using layer 2 tunneling
protocol, GRE tunneling, MPLS encapsulation
and virtual private LAN service encapsulation
methods.
VI. Communication Technologies
As per the IEC61850 standard, the protection
class of a distribution network is P1 which
means it transfers trip signals in the order of
half a cycle i.e. 10ms. For other fast messages,
total transmission time shall be less than or
equal to 100ms. So it is critical to select the
communication technologies which will be
able to meet the above specified performance
criteria.
The assets of distribution utilities are spread
across their service territory. In urban areas,
the length of the 11kV feeder is typically 3 km
and in rural areas, the feeder length may go
up to 20km.
Wireless solutions have shown the greatest
potential for automating distribution
networks because they communicate virtually
anywhere at a comparatively less investment
cost.
VII. Conclusion
Communication latency, coverage/reach,
availability, security, installation, operating
and maintenance costs are critical parameters
that unremarkably drive the decision-making
behind the technology to be used for DA
applications. More over out of the above
listed communication technologies, only some
have the option for peer-to-peer
communication using meshing technologies
like 802.15.4 and 802.11 mesh. There are
standard guideline work in progress like
IEEEP1777 to develop the functional,
performance, security, and on-site testing
requirements for wireless data
802.15.4 Mesh WLAN
(802.11s)
WLAN (802.11b/g) Cellular/3G/LTE Wimax (802.16
d/e/m)
Usage Low data rate Last mile, broadband
for rural area
LAN & indoor
wireless,
Backhaul
connectivity, internet
Broadband internet/
VoIP/ IPTV
Frequency
range
ISM: 868 MHz ,
2.4GHz (unlicensed)
DSSS
900 MHz, 2.4 GHz,
5.8 GHz (unlicensed)
Both ISM and U-NII
frequency
bands
Unlicensed: 2.4 and 5
GHz; DSSS, OFDM
GSM 900 MHz, UMTS
1900/2100MHz,
GSM 1800 MHz,
PCS1900MHz,
Cellular 850 MHz
2.3, 2.5, 3.5 GHz
licensed bands;
450 MHz, 700 MHz
also used
Channel
Bandwidth
200kHz to 1.2MHz 20/40 MHz for
802.11n
20 MHz for 802.11
a/g
200kHz to 20MHz 20 or 25
MHz (United States)
or 28 MHz (Europe)
Coverage 50 to 1000 meters as
per line of sight
Varies with frequency
line of sight : 0-15
miles
non-line of sight :0-3
miles
Indoor: up to 100 m;
Outdoor: up to 250 m
3-5 miles (to base
station)
3-4 miles
Single user
data rate
20 to 250 kbps,
depending on
frequency band
As high as 300 Mbps 802.11b: up to 11
Mbps
802.11g/h/j: up to 54
Mbps
HSPA+: Up to 28
Mbps,
cdma2000/EVDO rev
B: Up to 14.7 Mbps
Typical 4-16 Mbps
Cost Low Moderate Low High Moderate

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communication technologies that are to be
used in different aspects (types, classes) of
power system operations. Whole success of
distribution automation depends on
communication technology which would be
able to cater to above mentioned network
constraints which can transfer data over
futuristic communication protocol also
meeting advanced distribution automation
use-cases.