scadainindianpowersystem_pka

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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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Electrical IndiaFebruary 201093

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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Power System

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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Power System

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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Power System

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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Power System

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.

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