scada-networking protocol for data exchange

8/11/2019 SCADA-Networking Protocol for Data Exchange

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SCADA-Networking Protocol for

data exchangeByM K Ramesh

Manager(Grid Management),SRLDC, Bangalore.


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Presentation covers SCADA

Major Sub-Division SCADA Hardware

SCADA Software

Communication

Field Instrumentation

* RTU

* ADAPTATION WORK

Networking Protocol- IEC 870-5-101

- ICCP

- TCP/IP


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Supervisory Control And Data

Acquisition System


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THREE MAJOR SUB-DIVISION OF SCADA

COMMUNICATIONHARDWARE SOFTWARE


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BLOCK DIAGRAM OF A TYPICAL

SCADA SYSTEM

SCADA

H/W &S/W

MEDIA

C TX

O RX

M E

M Q

N P

T

C TX

O Rx

M E

M Q

N P

T

R

T

U

T P

R A

A N

N E

S L

D

U

C

ER

C & R

PANEL

CONTROL

CENTRE

SUBSTATION / GENERATNG

STATIONCOMMN

MEDIA


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SRLDC BANGALORE


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FUNCTIONS OF SCADA

DATA ACQUISITION.

PROCESSING OF ACQUIRED DATA.

DATA EXCHANGE.

LIMIT / STATUS MONITORING & ALARMING.

NETWORK STATUS PROCESSOR.

SEQUENCE OF EVENT RECORDING.

INFORMATION STORAGE & RETRIEVAL.

SUPERVISORY CONTROL.


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GUI FACILITIES

PAN, ZOOM, DECLUTTER, NAVIGATOR

ALARM FEATURES LISTING

SETTING

ACKNOWLEDGING

ENABLE/DISABLE AUDIO ON/OFF

EVENT LIST OPERATOR CONTROLS

CHANGE TO/FROM ALARM CONDITIONS

NON-ALARM CHANGE OF STATE

SOE ADD/REMOVE CONTROL/INFO TAG

ADD/REMOVE MANUAL OVERRIDE

APPLY/REMOVE ALARM DISABLE


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Data Acquisition Parameters

Circuit Breaker Status

Isolator Status

SOE data

Voltage Frequency

Current

Active Power

Reactive Power

OLTC tap position


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Weather Station data

( for EMS functions ) Temperature

Atmospheric Pressure

Wind direction Wind Speed

Humidity

Rainfall


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MAJOR ELEMENTS OF

SCADA SYSTEM

SCADA Hardware and Software.

Communication System. RTU

Adaptation Work

Auxilliary Power Supply Unit


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SCADA HARD WARE ELEMENTS IN CONTROL

CENTRE

MAIN SERVERS (Acquisition, Backup, EMS,DTS

Front End Processors (FEP)

Routers, Hubs, LAN Network.

Workstations for Man Machine Interface (MMI)Video Projection Displays (VPD)

Optical Disk, Cartridge Magnetic Tapes.

Loggers, Line Printers, Laser Printers (colour /b/w)

Time and Frequency system

Weather station Equipments.


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SERVERS

High End Computers with RISC capabilities

With ASCII Terminal

Data Acquisition Servers(FEP)

RT Data Server

AGC ServerNetwork Study Server

ICCP Server

Data Base Management Server

Historical Data Server

DTS Server


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CLIENTS

Display Computers with High Graphics capabilities

Machines used for Interface between Operators, Engineers,Managers with the Servers and have GUI facility.

The functions areReal Time Displays (Data, Graphs, Trends,SLDs, Grid ..)

Data Base Design Interface

Historical Data Analysis Interface

AGC Interface

PNA Interface

ICCP Interface

Programming Interface

DTS Interface

Playback Interface


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CONTROL CENTRE HARDWARE


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CONTROL CENTRE HARDWARE


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FRONT END PROCESSOR(FEP)

HDD 10GB

CD ROM

1

-8

9-

1617-

24

25-3233-

4041-

48

ESD BOND POINTM

V

M

E3600-1

PM

604

Dual

M

V

M

E

162

410

M

V

M

E

162

410

1 16


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FRONT PANEL INDICATOR

CHS(YELLOW)-C HECKSTOP-L ights when halt condition from

processor is detected. BFL(yellow)-B oard Failure-L ights when the board fail.

CPU(green)-C PU activity-Lights when data bus busy(DBB).

PCI(green)-P CI activity-T his indicates that the PCI mezzanine

is active. FUS(green)-F u se OK-Lights when =5Vdc,+12Vdc and12Vdc

power is available from base board to the transition moduleand remote devices.

SYS(green) System ControllerLights when the system ishealthy.


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CISCO ROUTER 7200

V.35 200PIN

V.35 200PIN

V.35 200PIN

V.35 200PIN

V.35 200PIN

LAN

FLASH MEMORY AUX MONITOR


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7200 SERIES ROUTER

CISSCO 7200 SERIES ROUTER MODEL 7206.

NPE 200 ( NETWORK PROCESSING ENGINE)

V.35 INTER FACE FOR WIDE BAND COMMUNICATION

10 BASE T ETHERNET INTERFACE WITH 4 PORTS FOR

LAN CONSOLE / MONITOR SERIAL 25 PIN PORT

FLASH CARD FOR IOS LOADING

IOS (INTER OPERATING SYSTEM) VER 11.


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ETHERNETSWITCH / HUB

SMART STACT MAKE INTELLIGENT SWITCH

WITH 24 PORTS.

HIGH SPEED PORTS 2 NOS

10-BASET PORTS ARE 20NOS

ALL PORTS ARE PROGRAMMABLE.


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SCADA SYSTEM S/W

1. OPERATING SYSTEM: -

Should be highly reliable because of ROUND the clockoperation on Real Time System-UNIX,MVS,NT

2. DATA BASE

Relational Data Base Management System (RDBMS)There will be multiple and independent DB ( Depends uponthe software design & operation)

SCADA Data Base

Historical Data Base

Real Time Data BasePSA Data Base


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3. APPLICATIONSData Acquisition and Displays

Data Recording for Historical Analysis

Picture EditorData Base Management ( All Modeling )

Automatic Generation Control

Power Network Analysis

Generation Scheduling

Load Fore Casting

5. Programming Languages

FORTRAN,C,C++,Sybase,Oracle,Visual C

6. communication protocols

Inter Control Centre Protocol


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COMMUNICATION SYSTEM


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COMMUNICATION SYSTEM

BASED ON MEDIA COMMUNICATION SYSTEM AS

FOLLOWS.

PLCC ( POWER LINE CARRIER COMMUNICATION)

BSNL LEASED LINE

RADIO COMMUNICATION - VHF / UHF COMMUNICATION

- MICROWAVE COMMUNICATION

SATELLITE COMMUNICATION

FIBER OPTIC COMMUNICATION


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VIJAYAWADATALLAPALLI

GAJUWAKA

VIDYUTH SOUDHA

GOOTY

SALEM400

UDUMALPETTRICHUR NORTH

MADURAI

TRICHY

SRIPERUMBUDUR

NEYVELI

CHINAKAMPALLYDAVANAGERE

RAMAGUNDAM

PONDY

SOMANAHALLI

P

N

PALLOM

KAYANKULAM

RSCC (1)

CPCC (1)

SLDC (4)

SUB-LDC / SCC (14)

FIBRE OPTIC LINK 110/132kv

FIBRE OPTIC LINK (220kv)

FIBRE OPTIC LINK (400kv)

FIBRE OPTIC LINK (SEB)

MICROWAVE LINK (35 links)

SATELLITE LINK (KEB)

RTU LOCATIONS 201

WARANGAL

PEDAPALLIDURSHED

JAMMIKUNTA

VTPS

VIZAG SWS

KAKINADA

BOMMUR

BHIMADOLE

NSAGARPH

SRISAILAM PH

SRISAILAM LBPHKURNOOL

SOMAYAJULAPALLI

MUDDANOOR RTPP

ANANTHAPUR

SHAPURNAGAR

GHANAPUR

CH.GUTTA

HYDERABAD 400

LEGENDLEGEND

CHALAKUDI

KALAMASSERY

VIAKKAM

KUNDRAPARIPALLI

TRIVANDRUM NORTH

VYDYUTHI BHAVANAM

KOZHIKODE

KANNUR-B

MADURAI400

CHENNAI

CHIDAMBARAM

MYLADUTURAI

SALEM230

ERODE

SIVAGANGA

KARAIKUDI

THIRUMAYAMPUDUKOTTAI

THIRUVARURORTHANADU

KOVILVENNI

ADANIKOTTAI

INGUR

PONGALORE

PANRUTI

VILLIANUR

SP.KOVIL

BANGALORE

KUMBALGODI

HUBLI

APSEB

RTUS

82

TNEB

RTUS

40

KSEB

RTUS

30

KEB

RTUS

22

PONDY

RTUS

05

CENTRAL

SECTOR RTUS

22


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Communication Channel for Information flow

Sub-LDC

SLDC

RLDC

SLDC

Sub-LDC

RTU RTU

Wide Band /

PLCC Commn

Wide Band

Commn

Wide Band

Commn

(MW / FO)

RTU


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Sub-LDC

Sub-LDC

Sub-LDC

Sub-LDC

Info. From RTUs

SLDC

Info. From RTUs

Info. From RTUs

Info. From RTUs

Nodal centre for despatch operation in the State - SLDC

(Intermediate in the Hierarchy)

Wide band network

Data from Sub-LDCs under its control is gathered through Digital Microwave

/ Fibre optic network and processed by the SLDC for effective monitoring andcontrol. Data is further processed to the next level viz., the Regional level

Regional Load Despatch Centre at Bangalore


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Wide Band Network

Data from the SLDCs is passed on to the Regional Load Despatch Centre(RLDC) through Digital Microwave / Fibre optic system

APTRANSCO-SLDC

TNEB-SLDC

KPTCL-SLDCRLDC

KSEB-SLDC

PONDY-SCC

CS-RTUs

Regional Load Despatch Centre at Bangalore

(The Highest in Hierarchy)


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SCADA HARDWARE CONNECTIVITY WITH COMMUNICATION SYSTEM(PLCC) AT

SUB-STN/GEN ST

RTU

N

S

K

5

PLCC T x / R x

SPEECH / DATA

PANEL

RS 232 CONNECTIVITY

PLCC

INDOOR EQUIMENT


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SCADA HARDWARE CONNECTIVITY WITH COMMUNICATION SYSTEM(WIDE BAND)

RTU

MUX

RADIO

TX / RX

OLTEOLTE

RADIO

TX / RX

MUX

MUXMUX

FEP

FEP

RTU

DIGITAL MICROWAVE

FIBER OPTIC SYSTEM

SUBSTATION/ GEN STN SIDECONTROL CENTRE


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Auxiliary Power Supply System

Uninterruptible power supply ( UPS ) systems for allSCADA/EMS computers and support equipment atcontrol centres

Emergency standby diesel electric generator sets tosupplement the normal power sources at controlcentres

Redundant 48V DC power supply systems for RTUs,communication equipment, PABX, emergencylighting, miscellaneous support equipment at controlcentres and field sites


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FIELD INSTRUMENTATION


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MAJOR COMPONENTS OF FIELD

INSTRUMENTATION

OUT DOOR EQUIPMENTS

- CVTs / PTs

- CTs

LIGHTING ARRESTORS

CIRCUIT BREAKERS

ISOLATORS

INDOOR EQUIPMENTS

- CONTROL & RELAY PANELS

-TRANSDUCERS

- RTUs

AUXILLIARY POWER SUPPLY

OUT DOOR EQUIPMENTS


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OUT DOOR EQUIPMENTS

CURRENT TRANSFORMER

CT CONSIST OF TOROIDAL AND HAVE SINGLE PRIMARY TURN, THE POWERR

CONDUCTOR WHICH PASSES THROUGH THE CENTRE.CT RATIO RESULTS FROM NO OF TURNS WOUND ON THE CORE TO MAKE UP

THE SECONDARY WINDING.

PERFORMANCE OF CT BASED ON FOLLOWING:

1) CORE CROSS SECTIONAL AREA

2) DIAMETER

3) MAGNETIC PROPERTIES.MAIN FUNCTIONS OF CT:

1)TO MEASURE THE CURRENT(METERING)

2)FOR PROTECTION

3) IT PROVIDES CURRENT REPLICA FOR METERING, CONTROL & PROTECTIVE

RELAY.CT PERFORMANCE CHARACTERISED BY RATIO CORRECTION FACTORS,

SATURATION VOLTAGE, PHASE ANGLE ERROR AND RATED BURDENS.


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TYPES OF CTs

METERING CT:IT WILL HAVE SMALL CORE CROSS SECTION TOMINIMIZE EXCITING CURRENT EFFECTS. It ALLOW TOSATURATE AT FAULT CURRENT LEVEL.

PROTECTION CT:EXCITING CURRENT AT LOW LOAD IS NOTCONSIDERED IMPORTANT.

RELAYING CTS:IT IS DESIGNED TO FAITHFULLY REPRODUCETHE CURRENT AT MANY TIME. THEIR THERMAL RATING TOALLOW ACCURATE SENSING OF FAULTS.


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POTENTIAL SOURCE

POTENTIAL SOURCE ARE

1) Potential Transformers : It is wound Transformer which provide the best performance with ratio &

phase angle suitable for billing.

2) Capacitive Voltage Transformer: It Use capacitor stack diver to obtain a primary voltage replica and itis not much accurate.

-Metering grade CVTs are Less stable and Less Accurate than PTs.

It is affected by Load & Ambient Temp.

In the field these can be calibrated indiviually to bring ratio error with in 1% and it can be recalibratedwhen the load has changed.

Older CVTs can be expected to change ratio upto +/- 5% with Ambient Temp variation.

SCADA system metering have to consider all criteria.

Periodic calibration program for CVTs can also help to maintain their performance at satisefactorly.


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INDOOR EQUIPMENTS


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TRANSDUCERS


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TRANSDUCERS

TRANSDUCER IS A DEVICE WHICH CAN CONVERT ONE FORM OF ENERGYTO ANOTHER FORM OF ENERGY WITHOUT ANY CHANGE IN PHYSICALQUANTITY.

TYPES OF TRANSDUCERS:

- VOLTAGE TRANSDUCER - CURRENT TRANSDUCER

- FREQUENCY TRANSDUCER

- ACTIVE / REACTIVE POWER TRANSDUCER.

RESPONSE TIME:


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TRANSDUCERS

CLASSIFICATION

SELF POWERED/AUXILARY POWERED

INPUT

VOLTAGE/CURRENT/POWER/POSITION

OUTPUT

0-10mA, 420mA, 0--5mA 0-5v,0-10v

OUTPUT IMPEDANCE

500,1000,2000 ACCURACY

0.2 CLASS, 0.5 CLASS, CLASS 2 AND ABOVE


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Voltage Transducers

Measures any phase to phase voltage providing an output tothe RTU analog input point.

Rated Quantities

- Rated Voltage 110V phase to phase or 115v phase to phase

- Measured range 0 to 120 % of the rated voltage

- Frequency 50 Hz, Range 45 to 55 Hz

- 4-20 ma dc output signal, +/- 0.5 % accuracy class, IEC 688

- 48 volts external DC Power supply


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Frequency Transducers

Measures the line frequency providing an output to the RTUanalog input point.

Rated input Quantities

- Rated Voltage 110V phase to phase or 115v phase to phase

- Measuring range 4555 Hz- 4-20 ma dc output signal, +/- 0.5 % accuracy class, IEC 688

- External 48 volts DC power supply


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Current Transducers

Measures the single phase current providing an output to theRTU analog input point.

Rated Quantities

- Rated Current 1A or 5A

- Measured range 0 to 120 % of the rated current- Frequency 50 Hz, Range 45 to 55 Hz




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Active Power Transducers

Measures 3 phase active power either balanced or unbalanced

2 wattmeter method measuring bi-directional power flow

Rated Quantities

- Voltage 110V phase to phase or 115V phase to phase

- Current 1A or 5A

- Frequency 50 Hz, range 45-55 Hz




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TYPES OF RTU


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TYPES OF RTU

SINGLE BOARD RTU

MODULAR RTU

SINGLE BOARD RTU


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SINGLE BOARD RTU

COMPACT,

CONTAINS ALL I/O ON A SINGLE BOARD.

NORMALLY HAS FIXED I/O

16 DIGITAL INPUTS, 8 DIGITAL OUTPUTS

8 ANALOGUE INPUTS, AND 4 ANALOGUE OUTPUTS.

NORMALLY NOT POSSIBLE TO EXPAND.


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d f i li i


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Hardware functionality in an RTU

CPU

VOLATILE MEMORY NON VOLATILE MEMORY FOR STORING PROGRAMS AND DATA.

COMMUNICATIONS CAPABILITY

EITHER THROUGH SERIAL PORT(S)

SOMETIMES WITH AN ON BOARD MODEM.

SECURE POWER SUPPLY (WITH BATTERY BACKUP).

WATCHDOG TIMER (TO ENSURE THE RTU RESTARTS IF SOMETHING FAILS).

ELECTRICAL PROTECTION AGAINST "SPIKES".FOR INPUT OUTPUT CARDS

REAL TIME CLOCK.


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Software functionality in an RTU.

Real time operating system.

scanning the inputs,

monitoring the communications ports.

Driver for the communications system

Device drivers for the I/O system (field devices)

SCADA application

scanning of inputs

processing and storing of data responding to requests from the SCADA master

S ft f ti lit i RTU


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Software functionality in an RTU.

CONTD..

Some RTU's may have a file system with

support for file downloads. This supports user

programs, and configuration files. All RTU's

require the above functionality. In many RTU'sthese may be intermingled and may not be

identifiable as separate modules


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INPUT


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A/D CONVERSION AT RTU LEVEL(16 BIT ADC).

FOR MW / MVAR TRANSDUCER:INPUT:PT SEC PHASE TO PHASE : 110VAC

CT SEC TWO PHASE CURRENT (R & B): 1 AMPS.

OUTPUT :420mA(TRANSDUCER OUTPUT)

IN ADC:

AT 4mA = 6553 Count

AT 20mA = 32767 Count

12mA IS THE CENTRE POINT.

(+/- 0.1% IS THE ACCEPTABLE RANGE OF ERROR ON FULL SCALE)

( Ref Calculation Sheet for all type of Measurand)

Basic operation


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Basic operation

THE RTU WILL OPERATE SCANNING ITS INPUTS,NORMALLY AT A FAIRLY FAST RATE.

SOME PROCESSING SUCH AS

CHANGE OF STATE

TIME STAMPING OF CHANGES,

STORAGE OF THE DATA AWAITING POLLING FROM THE SCADAMASTER.

REPORTING TO THE SCADA MASTER

SOME ALARM PROCESSING

GENERALLY SCADA MASTER POLLS THE RTU'S ASKINGFOR CHANGES.

RESPOND TO MASTER WHEN POLLED MASTER, THE RTU

HARDWARE CONNECTIVITY DIAGRAM FOR SCADA AT SUBSTATION / GEN.STATION


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MAINCPU

BOARD

PSUCOMMNBOARD

A

N

A

L

O

G

I / P

D

I

G

T

A

L

I / P

C

O

N

T

R

O

LO/P

TERMINAL

BLOCK

TERMINAL

BLOCK

TERMINAL

BLOCK

REMOTE TERMINAL UNIT

TRANSDUCER O/P TERMINAL

MVAR VOLTMW

TRANSDUCER I/P TERMINAL P T

SEC

110VAC

CT SEC

1 AMPS

FR

O

M

S

W

I

TC

H

Y

A

R

D

-F

I

E

L

D

EVENT LOGGER

PANEL

D

R

I

V

E

R

R

E

L

A

Y

TRANSDUCER PANEL

RS232 PORT


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Principles for data acquisition

Busbar Section A) Voltage

- 400, 230-220 and 132-110 Kv; one value per bus bar

- 66-78 Kv; one value per station

- 33 Kv; no value

B) Frequency- 400 Kv; one value per busbar

- 230-220 Kv; one value per station except for stations where power units areconnected to or having inter state feeders

- 132-110, 78-66 KV; one value per station where power units are connected to

- 33 KV; no value

C) SS

- 1 SS for loss of voltage per bus bar ( bus bar disconnectors are countedseparately )

Principles for data acquisition Contd


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Principles for data acquisitionContd..

Busbar Couplers

- 2 DS per Circuit breaker

- 1 SS for only one out of the 2 disconnectors

Bus Transfers- 1 DS per circuit breaker

- 1 SS for each disconnector on both sides of the CB

Busbar Disconnectors

- 1 SS for each busbar disconnector

Capacitor

- 1 SS for each bus selector disconnector

- DS per circuit breaker


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Bus Reactor- Reactive Power1 value

- 1 DS per circuit breaker

- 1 SS for each bus selector disconnector

Gas/Hydro/Thermal Generators

- Active Power1 value

- Reactive Power1 value

- DS per Circuit breaker

- 1 SS for each bus selector disconnector in case of single breakerarrangement.

- 3 SS per bus bar connection for one and half breaker scheme


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Overhead line- Active & Reactive Power1 value

- 400, 230-220 and 132-110KV; one value for each outgoing line

- 78-62 Kv; one value of P&Q only for outgoing inter systems tie-line

- 33kv; no value

Current- 78-62 KV; one value for each outgoing line ( if it is not an outgoing inter system tie-line )

- 33 KV ; one value for each outgoing line

DS

- 1 DS per substation circuit breaker

SS

- 1 SS for each bus selector disconnector in case of single breaker arrangement- 3 SS for 3 disconnectors for each out going line in case of one and half scheme

- 1 SS for each by pass disconnector in case of single breaker + by pass arrangements

- 1 DC for each 78-66 and 132-110 KV out going line ( for quick switching operation requirements under loadshedding and emergency actions )


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TransformersActive & Reactive Power

- One value for P and one value for Q measured on the secondary level for the 400/220 KV or 220/132 KVtransformers or on the primary level for the 132/66, 132/33 or 132/11 KV transformers.( if thesecondary level does not belong to the same constituent as the primary level, P & Q are measured onthe primary level.

Current

- One current value measured on the primary level for the 66/33 KV, 66/22 KV, 66/11 KV or 33/11 KVtransformers

OLTC

- 1 value per transformer for 400/220 Kv, 400/110 Kv, 230-220/110 Kv transformers ( if on load tap changer isavailable )

DS

- 1 DS per CB. If the secondary level does not belong to the same network ( in case of central sector), one DS

shall also be collected for the secondary circuit breakerSS

- 1 SS for each bus selector disconnector in case of single breaker arrangement

- 3 SS for 3 disconnectors for one and half breaker scheme

- 1 SS for each by pass disconnector in case of single breaker + by pass arrangements


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IMPORTANT FEATURES OF ULDC RTU

Distributed Intelligent Technology ,Main processor is 32-Bit 16Mhz,submodules are 8-bit.

View Data and Communications specific to each peripheral board.

Troubleshooting Aid

S/W downloaded to and stored on each peripheral.

Access via PC-Based Configuration.

Password Protected.

32 Analog inputs per module ,14bit resolution.

Synchronous VFC provides conversion rate 660ns for all 32 inputs.

64 status inputs per module,1ms scan time for 64inputs,1ms SOEresolution.

32 control output per module. Display Local Real-Time Data.


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Networking Protocol

Transmission Methods


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Based on Sequence in Time

Serial vs Parallel

Based on Synchronization

Asynchronous

Synchronous

Based on Direction

Simplex, Duplex: Half and Full

S h i i P bl Si l Ill i


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Synchronization ProblemSimple Illustration

Transmitted data stream

Transmitter side clock

Receiver Side

1 12 1 23 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Receiver side clock

1 12 1 23 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18


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Error Detection and Control


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Error Control involves

Error Detection

Error Correction

Forward Error Correction

Automatic Repeat Request

Error Detection

Parity

Cyclic Redundancy Code

For a CRC of length N the rate of undetected errors isnearly 2

-N

Flow Control


75/83

The Need for Flow Control

Flow Control under Error Free Conditions Stop and Wait Flow Control

Sliding Window Flow Control

Flow Control in the Presence of Error Automatic Repeat Request (ACK & NAK)

Go-Back N ARQ


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ACK

DATA FRAME


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Interfacing


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Interfacing


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A Complete Protocol (HDLC)


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Introducing the protocol architecture

Physical Layerinvolves the medium specificationsand interfacing considerations including

synchronization

Data Link Layerprovides the protocol

specifications for controlling point to point,multipoint and local networks

A comprehensive data link protocol is the HDLC

(High Level Data Link Control) that provides

Flow Control

Error Control

Addressing schemes to accommodate multiple devices



82/83

FlagUsed for Synchronization

Address: Needed for multidrop lines and is

extendable to 16 bits

Control: Purpose and functions of the frame are

specified in this field, eg. Supervisory frame, dataframe, flow control bits

FCS: Frame Check Sequence (16 or 32 bit CRC)



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Three phases:

Initialization: Transmitting device initiatesoperation by sending out a message, agrees

who is primary control or peer, number of flow

control bits

Transfer of Data: Exchanges Data Frames,

Control frames for Flow or error control

Disconnect: Sends a disconnect frame and the

other side accepts the disconnect by sendingan Acknowledgement

scada-networking protocol for data exchange

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