The document discusses SCADA systems and Remote Terminal Units (RTUs). It defines SCADA as a system that allows operators at a remote location to monitor and control field equipment. The document outlines the major components of SCADA systems including the master station, RTUs, communication channels, and interfacing equipment. It provides details on RTU components, functions, configurations, and how they interface with field devices and communication systems to monitor and control equipment.

1. SCADA – RTU INTERFACE
BY
S . GANESH BABU

2. SCADA DEFINED
• A formal definition of SCADA system, as
recommended by IEEE, is:
• “A collection of equipment that will provide
an operator at a remote location with
sufficient information to determine the
status of a particular equipment or a
process and cause actions to take place
regarding that equipment or process
without being physically present”.
4/25/2014 2
s ganesh babu

3. Power System Automation
• A power system consists of devices that
generate, transmit, and distribute power.
• Power system automation is the act of
automatically controlling the power system via
automated processes within computers and
intelligent I&C devices.
• It consists of three major processes:
• data acquisition,
• power system supervision,
• and power system control, all, working in a
coordinated automatic fashion.
4/25/2014 3
s ganesh babu

4. Power System Automation (CONT’D)
• Data acquisition refers to;
• Collecting data in the form of measured analog
current or voltage values,
• The open or closed status of contact points.
• Control refers to sending command messages
to a device to operate the I&C (A collection of
devices that monitor, control and protect the
system is referred as instrumentation and
control
(I&C) system)and power system devices
4/25/2014 4
s ganesh babu

5. INSTRUMENTATION SUB SYSTEM:
 Measurement and feeding of various parameters such as :
 Voltage, Current, power, circuit breaker status, and alarms
needs a supporting sub system.
 The parameters are fed into the substation telemetry
equipment called RTU ( Remote telemetry unit or remote
terminal unit).
 Analogs:
 Bus voltage: source : bus potential transformer.
 and currents in all feeders and transformers: source –
current transformers.
4/25/2014 5
s ganesh babu

6. INSTRUMENTATION SUB SYSTEM (CONT’D)
 Power in MW, KVAR, Power factor from LV
breaker.
 Analogue measurements carried out by
Industrial standard transducers with an
output of 4 – 20mA and 1 to 5v D.C.
4/25/2014 6
s ganesh babu

7. STATUS INPUTS:
 Breaker “ON / OFF” status.
 Alarms for oil, buch’olz, oil and winding
temperature.
 OLTC positions for transformers.
 Capacitor banks.
 All status inputs calls for voltage free
contact terminals.

4/25/2014 7
s ganesh babu

8. SCAN RATE
 Central control room monitors a series of mixture
of analog and status inputs the frequency of which
is decided by the priorities and fleeting events.
 Scanning rate depends on nature of substation
parameters.
 Voltage rating and type of substation.
 Non fleeting status and analog would require a
scanning rate 0f 2 to 3 minutes.
 Fleeting and high priority inputs require a
scanning rate of 5 to 10 secs and is decided based
on the following factors.
4/25/2014 8
s ganesh babu

9. SCAN RATE CONT’D
 Importance of the substation to the grid.
 Voltage rating : Higher the voltage rating, the
more the importance,
 Cost factor, which decides the type of
communication and the choice of the scan rate.
 Ex: High Speed TDMA link between central
control center and the substation and its
exclusivity.

4/25/2014 9
s ganesh babu

10. Applications of SCADA System
 Automatic Switching
 Emergency Load shedding
 Re-routing services for station maintenance
 Automatic transfer schemes
 Load sectionalizing
 Custom, automatic reclosing schemes
 Automatic service restoration
 Circuit breaker control and interlocking
 Feeder automation and fault recovery
4/25/2014 10
s ganesh babu

11. Applications of SCADA System
 Protection and Control
• Circuit breaker lockout
• Protective relay interface/interaction
• Dynamic protective relay setting for
dynamic station topology
 Voltage Regulation Management
• Load Tap Changer (LTC) control
• Voltage regulator control
• Capacitor control
4/25/2014 11
s ganesh babu

12. Applications of SCADA System
 Transformer Management
• Parameter monitoring and alarming
• Real-time modeling
• Interface to existing transformer monitors
 Automatic System Diagnostics
• Power apparatus health monitoring
• PLC and communications self monitoring
• Report and alarm on IED self diagnostics
4/25/2014 12
s ganesh babu

13. Applications of SCADA System
 Maintenance and Safety
 Kirk Key interlock management
 Maintenance ‘Lock-out/Tag-out
management
 Automatic circuit isolation
control
4/25/2014 13
s ganesh babu

14. Applications of SCADA System
 Station MMIs – Graphical User
Interface (GUI)
 Interface real-time single-line displays
 Interactive real-time breaker and switch
control display
 On-line operation and maintenance logs
 Sequence of events recording
 IED detail displays
 Parameter trending displays
4/25/2014 14
s ganesh babu

15. Advantages of SCADA system in power sector
 Increased reliability, lower costs.
 Forecasting accurate demand supply
management
 Faster restoration of power in case of a break
down
 Better active and reactive power
management
 Reduced maintenance cost, conditioning
monitoring
 Reduce human influence and errors
 Assists operator for faster decision making
 Automated meter reading
 Easy fault diagnosis
4/25/2014 15
s ganesh babu

16. Additional advantages of SCADA system in power
sector
 Availability of information
 Analysis of information
 Decision making
 Optimized system operation (competitive
environment)
 Equipment condition monitoring (ECM)
 Equipment parameters are automatically
tracked to detect abnormalities.
 Timely action, Extended life
 ECM IEDs available
 Sequence Of Events (SOE) recording
4/25/2014 16
s ganesh babu

17. SCADA System
 A SCADA system generally
consists of a master
station and a number of
geographically dispersed
Remote Terminal Units
(RTUs), all interconnected
to master station via a
variety of communication
channels.
4/25/2014 17
s ganesh babu

18. Supervisory Remote Terminal Units
 RTU is the eyes, ears and
hands of the Master
Station.
 In most applications the
RTU is the slave of the
Master Station, but in
some applications the RTU
is equipped with internal
computational and/or
optimizing capabilities.
4/25/2014 18
s ganesh babu

19. 4/25/2014 19
s ganesh babu

20. Remote Terminal Units
 AVAILABILITY:
 The availability of the RTU shall
be 0.999 over the 12 month
period of maintenance exclusive
of communication channel and
other purchaser caused down
time.
 Availability =
MTBF / ( MTBF + MTTR)
 MTBF = Mean Time between
failure
 MTTR = Mean Time to repair
4/25/2014 20
s ganesh babu

21. REMOTE TERMINAL UNITS (RTU)
 RTU consists of:
 The protocol processor module
 Communication module
 Data processing Module
 I/O modules for analog inputs
 Digital input and output
 RTU signals from transducers, relays, breaker
auxiliary switches, and TVMs.
 Data transmitted to DCC through
communication media (TDMA and MAR)
4/25/2014 21
s ganesh babu

22. REMOTE TERMINAL UNITS (RTU)
 Functions of RTU include
 Input scanning
 Alarm,
 And change of state detection.
 With high degree of reliability,
security and integrity.
4/25/2014 22
s ganesh babu

23. Transmission and coding system of RTU.
 The I/O channels are defined based on the need of each
substation, and the RTU is configured accordingly.
 These modules interface through memory mapping to the
micro processor.
 The RTU scans analogue and digital data non stop, and
stores the analogue information after converting it in its
memory.
 The RTU’s at each substation are accessed and addressed
independently.
 The electrical and communication format to the mail port
is usually RS 232.
4/25/2014 23
s ganesh babu

24. SYSTEM DIAGNOSTICS
 Typical diagnostics and indications provided in the RTU are :
 Power LED:
Indicates power applied to the base board when switched on.
 RUN LED:
Indicates healthy operating system.
 LPAT LED:
Indicates too low voltage on the input side.
 Watch Dog time out LED.
 Status LED:
Gives a binary coded output if the system fails a soft ware
confidence test.
4/25/2014 24
s ganesh babu

25. SYSTEM DIAGNOSTICS (cont’d)
 Diagnostic capability at the I/O module level.
 Hardware read back at telecom and output circuit
for verification of data at the field connection
point.
 Verification of memory and certain peripheral
chips in operating system.
 Communication diagnostics to indicate activity on
the receiver and transmitter lines for both main
and local ports.
4/25/2014 25
s ganesh babu

26. Communication Subsystem
 The communication subsystem is
the interface between the
communication network and the
RTU internal logic.
 This subsystem receives the
messages from the master,
interprets the message, initiates
action within the RTU, and sends an
appropriate response to the master.
4/25/2014 26
s ganesh babu

27. Communication Subsystem (cont’d)
 PRIMARY COMMUNICATION
 64 kbps TDM/TDMA (time division multiple
access operating in 2.3/2.5 GHZ band and
the out stations extend to EHV stations.
 SECONDARY COMMUNICATION:
 Is 9.6 KBPS MAR (multiple access
Radio) system operating in 849/943
MHZ band.
 Mar remotes are located in all 33/11
kv substations.
4/25/2014 27
s ganesh babu

28. 4/25/2014 28
s ganesh babu

29. Logic Subsystem
 The logic subsystem consists of the
main microprocessor and the database.
 It handles all major processing, time
keeping, and control sensing.
 It also handles analog-to digital
conversions and computation
/optimization, if required.
4/25/2014 29
s ganesh babu

30. Termination Subsystem
 The termination subsystem provides the
interface between the RTU logic and
external equipment such as the
communications lines, primary power
source and the substation devices.
 These assemblies must be designed to
protect the RTU logic from the harsh
environment of the station.
4/25/2014 30
s ganesh babu

31. Power Supply Subsystem
 The power supply, like the termination
subsystem, must meet the various voltage
surge standards.
 The power supply convenes primary power,
usually from the substation battery, to the
supply requirements of the other RTUs
subsystem.
 If a station battery is not available, the unit is
normally ordered for ac operation with built-
in battery back-up to cover several hours of
operation.
 Care should be exercised in selecting an ac
supply circuit to assure a reliable and stable,
noise-fee source.
4/25/2014 31
s ganesh babu

32. Communication
 In addition, occurrences of noise on the
communication channel seeks
reinforcements in the form of additional
master station and RTU hardware and
software design to ensure distortion free
signal transfer.
 Communication channels limit the speed
at which data acquisition and control can
be performed, thus affecting the master
station man-machine interface and
applications software design.
4/25/2014 32
s ganesh babu

33. Communication channels
4/25/2014 33
s ganesh babu

34. 4/25/2014 34
s ganesh babu

35. SCADA System Configurations
 The configurations of communication
systems are dictated by the following:
 Number of RTUs
 Number of points at RTUs and required
update rates
 Location of RTUs
 Communication facilities available
 Communication equipment and techniques
available
4/25/2014 35
s ganesh babu

36. SCADA System Configurations
 Block diagram for a
one-on-one SCADA
system configuration,
with a master unit
for each remote unit
M R 1
M R2
4/25/2014 36
s ganesh babu

37. SCADA System Configurations
 Block diagram for
a star or hub
SCADA system
configuration, with
one master unit
for several
remotes, but with
only one remote
on each
communication
channel.
M
4/25/2014 37
s ganesh babu

38. SCADA System Configurations
 Block diagram for a party-line SCADA system
configuration, with several remote units on a
single communication channel.
M
R1 R2 R3 R4
4/25/2014 38
s ganesh babu

39. SCADA System Configurations
 Block diagram for
a SCADA system
configuration,
combining the
characteristics of
the star and part-
line configurations,
with one master
and several
remotes on each of
various
communication
channels
M
R2
R1
R3
R4
R7
R8
R6
R5
4/25/2014 39
s ganesh babu

40. 4/25/2014 40
s ganesh babu

41. SUBSTATION SYSTEM
 Consists of two marshalling boxes accommodating:
 One, Interfaces the substation equipments with the
RTU.
 Accommodates transducers, TVM’s, contactors etc.,
 The other panel holds all other radio and
communication accessories along with RTU.
 The interfacing work at the substation
includes:
 Erection of SCADA marshalling panel, either
designed and custom made, or fabricated.
 Fixing of components and accessories,
 Wiring and dressing of the wires to be connected to
the components.
4/25/2014 41
s ganesh babu

42. Transducer
Input 5 A/1A
Output 4-20 mA
4/25/2014 42
s ganesh babu

43. Digital data (on/off) may have alarms attached
to one state or the other.
4/25/2014 43
s ganesh babu

44. Pulse data (e.g counting revolutions of a meter)
is normally accumulated or counted.
4/25/2014 44
s ganesh babu

45. 4/25/2014 45
s ganesh babu

46. 4/25/2014 46
s ganesh babu

47. 4/25/2014 47
s ganesh babu

48. 4/25/2014 48
s ganesh babu

49. 4/25/2014 49
s ganesh babu

50. 4/25/2014 50
s ganesh babu

51. 4/25/2014 51
s ganesh babu

52. SUBSTATION SYSTEM (CONT’D)
 Laying of 4 core and 10 core cables
from the field/ control room to the
panel including formation of cable duct
where ever required.
 Termination of the leads at appropriate
points including crimping of lugs and
provision of ferrules.
 Providing of Earth connection to the
marshalling box from the equi-potential
bar.
4/25/2014 52
s ganesh babu

53. SUBSTATION SYSTEM (CONT’D)
 Ensuring vermin proof cable entry points in
the marshalling box with the provision of
suitable cable glands.
 The components that are housed in the
SCADA marshalling box are:
 AC current transducer to every feeder to
measure Y phase current.
 Secure make electronic trivector meter for
measurement of TVM parameters at power
transformer LV breakers.
 Voltage transducers to measure HV and LV
voltages.
4/25/2014 53
s ganesh babu

54. SUBSTATION SYSTEM (CONT’D)
 Position transducers to indicate the tap
position.
 DC voltage transducers to measure D .C.
voltage.
 48V DC contactors to initiate close and
trip pulse to the breaker.
 48V contactors to raise and lower taps on
the OLTC.
 220/24 V contactors for annunciating
buch’olz and temperature alarms for each
transformer.
4/25/2014 54
s ganesh babu

55. 4/25/2014 55
s ganesh babu

56. CABLES
 Signal cables shall be of a type and installed in
a manner so to reduce common-mode and
induced noise to a minimum.
 Metallic shields shall be employed on all
cables. All grounding of shields and signal
circuits shall be at one point only to prevent
ground loops, except where double shielded
cable is used, in which case the outer shield
may be grounded at both ends.
4/25/2014 s ganesh babu 56

57. CABLES
 All terminals and terminal blocks shall
be clearly identified.
 All connectors, cable harnesses and
inter – rack wiring shall be clearly
identified so that no ambiguity can occur.
 Connector pin numbering shall be
identical at each and of the cable.
4/25/2014 s ganesh babu 57

58. 48V DC battery with Float cum boost charger
 Supplies DC voltage to RTU
and the contactors which
activates the operation of
OLTC and breaker
operations.
4/25/2014 58
s ganesh babu

59. Thank you all for
a patient
listening!
4/25/2014 59
s ganesh babu