SCADA-Functions
Author, Vineeta Agarwal
Place PSTI, Bangalore
Date 29-4-2011
NLDC
1
Responsibilities of RLDCs
 Operation, monitoring and control of Regional Grids.
 Control of Central Sector Transmission System.
 Allocation of Central Sector Generation.
 Data Exchange with SLDCs.
 Data exchange with NLDC
NLDC
2
Responsibilities of SLDCs and Sub-LDCs
 SLDCs



Operation, monitoring and control of state owned power
system.
Data Exchange with Sub-LDCs.
Data exchange with RLDC
 Sub-LDCs


Responsible for Operation, monitoring and control of power
system data in its area
Data Exchange with SLDCs.
NLDC
3
ULDC Scheme
 Unified Schemes for all regions for compatibility
 Three level hierarchical SCADA along with EMS
 More than 2,100 km of Optic fibre network
 More than 3,000 km of microwave network
 More than 10 lakhs sq. km geographical area
NLDC
4
Scada
 Supervisory Control and Data Acquisition
SCADA is the system responsible for gathering,
processing, and displaying information about the
state of a monitored system. From a SCADA control
center, operators and application programs can
oversee and change the operating state of monitored
devices.
NLDC
5
SCADA FUNCTIONS
 TO SUPPORT REAL TIME MONITORING AND
CONTROL








Data Acquisition
Supervisory Control
Data exchange
Data Processing
Alarms, Flags
SOE, Generalized calculations
Disturbance Data Collection (HDR)
Historical Information Storage & Retrieval
NLDC
(ISR)
6
Data Acquisition
 Data Acquisition process samples real world physical
conditions and convert the samples into digital
numeric values for use by computer.

Components of Data Acquisition System




Sensors/transducers that convert physical parameters to
electrical signals.
Signal conditioning circuitry to convert sensor signals into a
form that can be converted to digital values.
Analog-to-digital converters
A Scada system to process this digital data.
NLDC
7
SCADA Host Functions
 Primary task is to maintain SCADA databases.
 Performs other functions:

Converts raw data to engineering units.

Performs limit checks.

Processes alarms.

Processes calculations.

Manages communication devices.
NLDC
8
Data Processing
 The major function of the data processing module is to
place data from RTUs into the database.
Status Points
Analog Values
Retrieved values
checked for any
status changes
Retrieved values
converted to
engineering units
and placed in
database.
Points then checked Engineering value
for a defined
checked against
“normal state”
operational limits
and rate of change
limits.
NLDC
Pulse Accumulators
Last retrieved value is
converted to floating
point and scaled.
Conditionally, difference
with respect to previous
value is computed, with
adjustment if value
negative (counter wraparound)
9
TELEMETRY FOR ULDC
P
P
Q
SS
P
DS
SS
V
F
V
DC
SS
SS
SS
F
DS
SS
P
Q
O
SS
MW
Q
MVAR
O
DS
Q
TAP POSITION
FREQUENCY
SS
SINGLE STATUS
ISOLATOR POSIITION, PROTECTION,
LOSS OF VOLTAGE
DC
SS
SS
DS
F
DS
SS
SS
SS
P
Q
DS
SS
SS
SS
SS
Q
DS
V
VOLTAGE
THE
PARAMETERS
ARE
FOLLOWING STATIONS :
FOR
•Substations 220 KV and above
•132/110KV AC Interstate Tie lines and in loop of 220
KV transmissions system
•Generating Station above 50MW capacity.
•Significant stations identified by constituents
DOUBLE STATUS
CIRCUIT BREAKER POSITION
DIGITALCONTROL
CIRCUIT BREAKER CONTROL
MONITORED
NLDC
10
Data types
 SCADA processes and stores three different types of
data:
 analog,
 status, and
 count data.
NLDC
11
Analog Data
 Analogs are numeric values representing the state of
variable-state devices, such as power lines,
transformers etc
 In the monitored system a physical variable is usually
measured by a transducer, and the output of the
transducer is passed through an analog-to-digital
(A/D) converter in the RTU .
NLDC
12
Transducer
 linear Conversion
NLDC
13
Status Data
 Status values represent the state of devices, such as
circuit breakers, tap changers, LOV,BPT
NLDC
14
Digital Data
Potential free contacts are used to transfer switch position to
control centre.
NLDC
15
Data flow from RTU  RLDC  NLDC
NLDC
16
Data polling method
 Analogs are defined as periodic/Cyclic data .
 The periodicity varies from 10 seconds to 15 seconds
depending upon the quantity of data and available
bandwidth .
 Digital input state changes are to be reported
spontaneously .
 The Digital input data have higher priority than
Analog values.
NLDC
17
Data Flow
NLDC
18
Supervisory Control
 In Scada systems control actions are performed by
RTU or PLC.
 operator of the control room can override or adjust
normal PLC (RTU) controls
NLDC
19
ALARMS
NLDC
20
ALARMS
 ANALOG
 DIGITAL
NLDC
21
Alarms-analogs
 Normal limit-Range of limits which device is considers
to be operating normally
 Reasonability Limit-range of values that SCADA uses
to determine whether the value retrieved for the
analog is realistic.
 Forbidden Limit-Range of values that SCADA
considers violated when the analog point fall within
that range
 Dead band Limits-On a pair of low or high limits if it is
violated the value must rise above the limit by at least
the dead band amount before the SCADA consider s
the analog to be back within normal limits .
NLDC
22
Normal Alarms-analogs
 MW/MVAR/MVA/FREQ/VOLTAGE
 ALARM LIMIT-OPERATIONAL
 ALARM LIMIT-ALARMING
 ALARM LIMIT-EMERGENCY
NLDC
23
Alarm Limit -Mw
 ALARM LIMIT-OPERATIONAL
+/- 1.05*(1.732*V*I*O.8)
 ALARM LIMIT-ALARMING
+/- 1.10*(1.732*V*I*O.8)
 ALARM LIMIT-EMERGENCY
+/- 1.15*(1.732*V*I*O.8)
V-NOMINALVOLTAGE I-NOMINAL CURRENT
NLDC
24
Exception Displays
 Abnormal digital status points and analogs displayed
in chronological order
 Abnormal digital status points and analogs displayed
as per category.
 Abnormal digital status points and analogs displayed
per location
 Failed (LDC) sites displayed in chronological order
 Failed substations and devices in chronologically
order.
NLDC
25
Exception Displays
NLDC
26
Priority Alarms
 Alarms are categorized in 8 category








Priority 1 -Emergency threshold overshoot and status point alarms
of controllable switching devices, ICCP links and other ICCP data
exchange related alarms)
• Priority 2 -Point alarms of non-controllable switching devices.
• Priority 3 -Protection trips and substation alarms
• Priority 4 -Alarms relevant to RTU’s, communication lines, and
alarms of “unreasonable” category
• Priority 5 - “configuration management” alarms, i.e. hardware
failures (mimic board, printer, etc.) and software failures
• Priority 6 –All Network alarms-state estimator , contingency
analysis) and the alarms detected by the generation applications
(AGC and LF)
• Priority 7 -Scada topology alarms
•Priority 8 -HDR, Tagging, Limit Replacement.
NLDC
27
Flags

Gives Source and Quality of data

Source of data






RTU -----------Telemetered
ENTERED-----Manually Entered
EXTERNAL----Always to be entered manually
INTERSITE-----Data from other site
CALCULATED—Calculation tag
Quality of data




GARBAGE-The data is unreliable. The flag appears when data
is uninitialized.
SUSPECT-Data is labelled suspect when there is one or more
of this flag (OLD, BAD, OVER and RESUSP)
REPLACED-Data is labelled replaced when MANREP,
ESTREPor REMPL)
GOOD-Data is labelled GOOD when it is not GARBAGE,
SUSPECT and REPLACED.
NLDC
28
Flags
NLDC
29
Flags








Unit: - uninitialized.
Old:-Could not be retrieved in the last scan
Telemetry failure:- communication with RTU failed
BAD: - when RTU returns one or more standard test values in the
RTU outside the allowed limits. Either Transducer is faulty or
there is an RTU malfunctioning.
Over Range: - Raw Value Received from RTU is outside the
expected Range.
Unreasonable:-The converted value has crossed the
reasonability limit.
Anomalous:-Basically not a data quality Flag .State Estimator
considers the above measurement not fit for the solution.
Manually replaced:-Replaced by operator
NLDC
30
Flags







State Estimator replaced:-Value for an analog is
overridden, or replaced, by state Estimator on operator
request.
Generalized Calculation: - Value replaced through
generalised calculation.
Maintenance mode: - The Device has been placed in
maintenance mode.
NIS:-device not in service. It will not allow scanning or
calculation to update the record which is marked NIS
Alarm Inhibit: - Alarms for this device inhibited.
Remote Suspect:-The value is suspect at source control
centre.
Remote Replaced:-The value has been replaced by
source control centre
NLDC
31
Sequence Of Events
 Sequence of events provides milli secs accurate
time of status changes for devices monitored by
Remote Terminal Units .
 The RTU clock is synchronized periodically by the
control center clock .
 Reading its internal clock when a SOE status
point changes state .
 Time stamped digital data stored in RTU buffer
and transferred as file or Digital data with time
stamped is transferred for SOE
NLDC
32
Historical DATA Recording
 Historical Data Recording (HDR) function allows you
to preserve a time series of any set of analog, status,
and accumulator measurements .

HDR functions




Saves the SCADA measurements in disk files called Historical
files.
Keeps track of the Historical files that have been created and
allows you to delete them.
The Database Reconstruction functions allow you to reconstruct
or create a Data History listing from the data in the Historical
files.
The reconstructed database can be moved to the network
database for use by other applications.
NLDC
33
Trend Displays
 Real Time Trend Display


Digital, analog or counter value can be viewed
simultaneously in different displays.
The information is usually sampled cyclically, stored in
memory on a circular buffer and plotted on a window against
time.
 Historical Trend Displays

To trend the value (digital, analog counter) with archived data
NLDC
34
Trend Displays
DISPLAY OBJECT
TRACK
NLDC
35
MODIFYING TRACK ATTRIBUTES
 AXIS DIRECTION Whether the X axis is horizontal (the
default) or vertical
 Grid lines Whether grid lines are visible or not (the default) in
the display area
 SCALE TO OBJECT All display objects are scaled to the
currently selected display object's scale
 AUTO
SCALE set automatically
maximum and historical minimum
based
the
historical
 FULL DATE STRING Whether the date and time is displayed
or just the time.
SCADA-EMS GROUP NRLDC
NLDC
36
36
Tagging





Tags are free formatted text, which provide critical
information to next shift operator .
Tags can be provided over digital, analog and counters datapoints.
Operators can insert, edit or delete any number of tags, if
they have privileges to do so.
Some operators may only be allowed to view tags.
These operations can be done from graphic displays by
selecting a dynamic object or from a system list of entities.
NLDC
37
Types of Data Outages
 All data became suspected.
 All the data pertaining to your organisation is out.
 All the data pertaining to other organisation is out.
 Data only from a one or some of the substation is out.
NLDC
38
Trouble Shooting
All the data on display
have become
suspected
1. Both Data server of this control
center are out.
OR
2. Master Data Server failed and
standby data server
has not taken over.
NLDC
39
Trouble Shooting
All the data pertaining
to your organisation
is not updating.
1.
All the data pertaining
to other organisation
is not updating.
Both ICCP server of this control
center are out.
OR
2.
Master ICCP Server failed and
standby ICCP server has not
taken over.
NLDC
40
Trouble Shooting (contd.)
Some Data is not
updating on display
or it is marked as
suspect
Find out from which
RTU it was coming.
Yes
Yes
Is this RTU
belongs to
your
organization.
Is RTU reporting
to this control
center.
No
No
Check
ICCP
Route
Check
CFE
Route
NLDC
41
Checking ICCP Route
Yes
Does the bad data belong
to your organisation.
Are both servers OK.
Communication
link between
Sub-LDC and
SLDC is out.
No
Data is interrupted
due to outages of
servers at Sub-LDC
Are the
ICCP
Servers
of RSCC
OK.
Yes
Find to which Sub-LDC
this RTU reports.
Yes
No
Yes
Are the
Data
Server
s of
RSCC
OK.
Data is interrupted
due to outages of
Data servers at
RSCC.
NLDC
No
No
Communication
between RSCC &
this SLADC not OK.
Data is interrupted
due to outages of
ICCP servers at
RSCC.
42
DATA BASE
 SCADAMDL
for the SCADA database
 NETMODEL
for the Network database
 GENMODEL
for the Generation database
 DTSMODEL
for the DTS database
 COMMUNICATION database
NLDC
43
Network Database
 Network Modeling
 NETMODEL
 How Network Components are electrically connected?

The Parameters used to model them.
NLDC
44
Network Database
 THE NETWORK DATA
 The topology of power network
 A description of every component in the system
 An equivalent model
 Schedules
 Tables
 A load model
 Operating limits
NLDC
45
Thank you !!
NLDC
46