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92February 2010Electrical India
Indian power grid is a geographically dispersed network of generators having capacity more
than 147,000 MW, and transmission lines of 265,000 or more circuit kilometers. The generating
capacity is a mix of thermal generation, hydro generation and nuclear generation and also some
non-conventional generation like wind power etc.
- P K Agarwal
Indian Power System
SCADAp r o j e c t
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Power System
The coal based thermal capacity is
concentrated in eastern part while
hydro capacity is concentrated in south
and extreme northern part of India. The
electricity is transported from these
concentrations to loads via transmission
systems comprising of 765 KV, 400 KV, 220KV, 132 KV AC network and HVDC system 500
KV. Operation of such complicated and vast
system requires a central coordination and
information system. For this a Supervisory
Control and Data Acquisition (SCADA) System
have been installed jointly by Powergrid, a
central transmission utility and state
electricity board, the agencies responsible
for electricity management in states.
For ease of operating whole Indian power
grid has been divided five regions namely -
NR (Northern Region), WR (Western region),SR (Southern Region), ER (Eastern Region)
and NER (North Eastern Region) as shown in
Fig. 1. Though these fives regions are
independent but electrically there are only
two grids one is central grid comprising of
NR, WR, ER and NER and other is Southern
grid of SR.
Each regional grid is managed by an
control center called Regional Load Dispatch
Center (RLDC) and each state power system
is controlled by a State Load Dispatch center
(SLDC). System under SLDC has further been
into Sub-Load Dispatch Centers (Sub-LDCs).National Load Dispatch Center (NLDC)
coordinates the activities of all RLDCs. NLDC,
RLDCs, SLDCs and Sub-LDCs have their own
SCADA systems, integrated in a hierarchical
structure. RLDC being at the top of hierarchy
at regional level, coordinates the day-to-day
operation of a region in consultation with
SLDCs.
Scada SystemHierarchical Structure
SCADA system is hierarchical in nature
having two distinct hierarchies - one at
national level other at regional level. At
national level, SCADA/EMS system of all five
RLDCs report to NLDC. Data from each RLDCis transmitted to NLDC in real time on
dedicated communication lines. The national
level hierarchical arrangement is shown in
Fig. 2.
Hierarchy at Regional Level
At regional level RLDC acts as apex body
and coordinates the all inter-state activities
of SCADA/EMS systems of SLDCs of a region.
SCADA systems of all Sub-LDCs of a state
reports to the SLDC of that state. The
hierarchy at regional level is shown in
Fig. 3 next page.
Functions implemented in SCADA/
EMS at RLDC and SLDC levels
Main components of the SCADA
system at RLDC and SLDC are SCADA/
EMS server and ICCP server. SCADA/EMS
or data server maintain all data acquired
from other SLDCs etc an make it available
to display and reporting. ICCP (Inter
Control-center Communication Protocol)
server acts as gateway for transfer of data
between SLDCs and between RLDC and
SLDCs. SCADA/EMS system at RLDC, SLDC
and Sub-LDC are based on distributed
architecture and open standards. Theirsalient features are:-
Operating system is POSIX compliant.
LAN and WAN uses OSI compliant
protocol.
Graphical User Interface is Motif.
ICCP (TASE 2) has been used for inter site
exchanges.
WAN communication is on X.25 with
S
SCADA system is
hierarchical innature having
two distinct
hierarchies -
one at national
level other at
regional level. At
national level,
SCADA/EMS
system of all five
RLDCs report to
NLDC.
Fig. 1: Electrical Division of India
Fig. 2: Hierarchy at National Level
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Multilink Bundled PPP
RTU communication is on IEC
65870.5 101 protocols.
RDBMS is used for historical data
archiving.The functions and responsibilities of
each control center (RLDC, SLDC and
Sub-LDC) are as follows:-
RLDC at top level coordinates all the
activities relating to transfer of
power from central sector/Interstate
generating stations to SEBs.
Scheduling, Metering and
settlement, open access etc are
some of the major activities comes
under the purview of RLDC. For
these activities RLDC is heavily
dependent on SCADA system. RLDC
also facilitate exchange of data
between SEBs .
SLDC & CPCC at lower level
coordinates and control the power
flow within the home sate. The SLDCcollects data directly from RTUs
connected to SLDC and indirectly
from its Sub-LDCs. The CPCC similar
to Sub-LDC is responsible for a
specific area of central sector power
system and reports to RLDC.
Sub-LDC at level three is responsible
for a specific area of its state-owned
power system. It acquires data from
RTUs connected to them and
provide the data to reporting SLDC.
The functions provided at RLDC and
SLDC levels are similar except minor
differences. Like Dispatcher Training
Simulator (DTS) exists only for RLDC
system. Functions provided at Sub-LDC
level are for data concentrator only and
have limited control facility.
The list of major functions of the
SCADA/EMS system are summarizedbelow:-
SCADA Functions
Data acquisition from RTUs and
storage of data in online database.
Processing of data for converting
the raw values to engineering
values, checking quality, assigning
quality flag and checking limit.
Supervisory control of power
system element (not being used at
present).
Historical data storage and retrieval. Reconstruction and replay of events.
Protective and informative tagging
of power system device.
Load Management.
Sequence of events recording.
Generalized calculation for adding
and removing operators defined
calculations.
Providing user interface to
operators.
Inter control center communication.
Real time and historical trends.
State Estimation.
EMS Functions
Real time generation function
allows the operator to monitor,
analyze and control real time
generation.
Automatic generation control
(AGC).
Economic dispatch - helps the
dispatcher to determine economic
base points for a selected set of
units.
Reserve monitor for calculatingspinning reserve, operating reserve
and regulating reserve.
Production costing calculates the
current cost of generating power of
online units.
Transaction scheduling.
Real time network analysis.
Real time contingency analysis.
Fig. 3: Hierarchy at RLDC Level
Fig. 4: Typical Configuration of a RLDC and SLDC (Showing only main servers)
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Load Forecasting.
MIS Reporting.
Study mode functions
Power flow analysis.
Optimal power flow.
Study security enhancement
Study contingency analysis. Study state estimation.
Resource Scheduling and
Optimization.
Ensuring 24X7 hrsAvailabilityGeneral
To ensure the 24x7 availability, the
backup of every device, software
functionality, communication path etc
has been built in the SCADA/EMS
system. Fig. 4 shows a typicalconfiguration of SCADA system at
RLDC and SLDC. Configuration of
SCADA system at Sub-LDC is shown in
Fig. 5. The layout arrangement of the
devices etc in the diagram has been
rearranged for clear visibility of
redundancy of the systems. It can be
seen that the redundancy exist at each
device level as well as communication
level etc.
Backup at RLDC and SLDC level
The hardware configuration atRLDC level (refer fig. 4) is fully
duplicated. Each and every hardware
device has its backup device in active
and hot standby state. In the event of
failure of operational hardware the
back will take up the functionality.
Intra control center communication
has been implemented on Ethernet
LANs with two different speeds. One is
100Mbps on 100base-T for connecting
SCADA/EMS servers and other is 10
Mbps on 10base-T for the remainingdevices. Both LANs are in dual mode i.e.
two separate LANs called LAN A and
LAN B exists for intra control center
communication. Each LAN has separate
network cards, switches and cabling
and works independent from the other.
During normal operation, data flow
takes place on both the LANs
simultaneously. In normal situation,
data is read/written on LAN A. In case of
failure of LAN A, nodes automatically
started reading/writing the data from
LAN B.HUB chassis are used as back plane
for housing the switches and routers.
Two HUBs are installed acting as back
up to each other. One chassis houses
the switches and routers pertaining to
Fig. 6: Control Room of RLDC
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LAN A and other houses for LAN B. The
power supply modules within the HUBs
are also is in backup configuration.Each HUB has N+1 power supply
modules i.e. in normal situation one
module act as backup to the remaining
modules. Hence failing of any of the
power sully module will not hamper
the operation of the HUB in turn LAN.
This N+1 configuration of power supply
modules also facilitates hot swapping
of the failed module.
Terminal servers are used for
connecting the serial devices like
loggers, processor terminals, hard copy
printer and line printer to the LAN. Two
terminal servers have been provided
one on LAN A and other on LAN B. Each
terminal server connects the loggers/
line printer for logging of events.
Logger are also backed by other logger
or line printer on each terminal server.
Other devices like processor terminal,
hard copy printer are not essentially
required in online mode hence been
provide on only one LAN either on LAN
A or LAN B.
Data servers provide the most of thefunctionalities of SCADA/EMS system.
The real time database resides on these
servers. Data servers are responsible for
acquiring data from RTUs and providing
the same to all other subsystems like
HMI for displays, ICCP server for inter
control center data transfer, ISR server
for storage and retrieval of old data.
Two SCADA/EMS server have been
provided in the main and hot standby
mode. Both connected to both theLANs. One SCADA/EMS servers acts as
main server and other remains in hot
standby mode and in synchronism to
the main server Standby server keeps
monitoring the health of other server
and take over the responsibility in case
failure of main server. Further to this,
both the data servers are in clustered
mode, hence provided the redundancy
of software module also. It means that
if only a software module fails on the
main server module on other server will
provide the functionality.
Similar to data server, ICCP (Inter
Control Center Protocol) servers, ISR
(Information Storage and Retrieval)
server have back at the machine level
with connection to both the LANs
Communication between SCADA
and RTUs takes palace through
Communication Front End (CFE).
Directly connected RTUs connected to
the both the CFEs. RTUs critical to the
grid operation are connected with two
separate communication channels onefor each CFE. Other RTUs, have one
communication channel but are
connected to both the CFEs through
splitters. This concept ensures that data
from the RTUs will be available to the
control center in case of failure of any
communication channel or CFE.
Backup at Sub-LDC/CPCC Level
At Sub-LDC/CPCC, functionalities of
Data server and ICCP servers have been
implemented on the same server
machine. Two such machines have
been provided. One server acts as main
while other acts as standby ready to
takeover the operation in the event offailure of main server. The Typical
configuration of Sub-LDC and CPCC is
shown in fig. 5.
Like RLDC and SLDC LAN and WAN
equipment are also provided with back
up system. LANs are in dual
configuration as LAN A and LAN B and
operates similar to LANs at RLDC and
SLDCs.
Similar to RLDC/SLDCs, here also,
communication with RTUs takes palace
through Communications Front End(CFE). One CFE is on LAN A and other
on LAN B. Critical RTUs have two
separate communication channels one
for each CFE. Other RTUs, have single
communication channel but are
connected to both the CFEs through
splitters. Thus ensuring uninterrupted
availability of data in case of failure of
any of the equipment or communication
link.
Backup of Communication System
Sufficient redundancy has also been
provided for inter control center
communication so as to have 24x7 hrs
availability. All communication links,
devices like router for WAN required for
inter control center communication
have duplicate configuration. During
normal operation, flow of data takes
place on both the links in shared mode.
However, in the event of failure of any
of the link other link will take full data
flow.
Implementation of communication
system uses four communicationchannels for each data link between
Sub-LDC and SLDC, between RLDC and
SLDC and between CPCC and RLDC.
These four communication channels
have been connected two separate
routers with two channels on each
router of LAN A and LAN B. Thus, each
router has main and stand by
Fig. 5: Typical Configuration of Sub-LDC & CPCC
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P K Agarwal, DGM, NRLDC/Powergrid, electrical engineer fromMNIT, Bhopal Joined NTPC Ltd andWorked in area of construction ofEHV transmission lines andsubstations; in HVDC system inarea of control systems andmodification and testing of controlsoftware of ABB. He was posted atNorthern Regional Load DispatchCenter. He implemented SCADA/EMS system of Northern Regionand Open Access Managementsystem as online submission. He is
Member of AIMA, Institution ofEngineers and published papers onSCADA system and commercialmechanism in International Seminarorganized by BHUIT. He is projectmanager for Indias first pilot project
on Phasor Measurments.
P K Agarwal
communication channel. In case of
failure of main channel, router switches
the communication of standby channel.
Further to this, main and standby
channels have been chosen from
different routes of MW/FO circuits
ensuring the availability of at least onechannel in case of any eventuality.
To enhance further availability the
main and stand by channel of a router
have been bundled through PPP
Multilink bundled protocol stack thus
forming a single virtual channel by
combining capacity of both the
channels. In this configuration, two
separate physical channels act in a
single virtual channel adding the
bandwidth capacity of both the
channels. As the requirement ofbandwidth is less than or equal to the
capacity of a single channel flow of
data remains uninterrupted in case of
outage of a one of the channel from the
bundled channel.
ConclusionAs described above though the
backup concept have been
implemented at each and every point
of possible failure even the system may
not free form the situations were a
failure of some devices may lead tointerruption of operation. However,
possibilities of such situation are
remote. To provide absolute
redundancy is nearly impossible. One
has to optimize between the project
cost and cost of outages. For example,
in this system CFEs are connected to
either LAN A or LAN B. One CFE may
communicate to one SCADA/EMS
server only i.e. CFE1 works with SCADA/
EMS server 1 and CFE2 is tied up with
SCADA/EMS Server 2. In this scenariooutage of crossed device, i.e. outage on
CFE1 and SCADA/EMS2 or outage of
CFE2 and SCADA/EMS server 1 may
result in the outage of data from all the
RTUs of that control center.
Nevertheless, probability of such failure
is very low. Such optimizations have to
be done to achieve balance between
cost and performance of the project.