Currently, electricity in the
sense is one of the basic necessity for the smooth functioning of day to day life
of the world. Thus, continuity supply of electrical energy to the consumers
is a must and it is irrespective of the operating conditions of the power
system to which the consumers are connected. Power systems, being the largest
and the most complex dynamic systems [1] are often exposed to numerous
physical disturbances and resulted in the conditions of instability.
Stability of a power system
The ability of a power system
to retain in its state of operation in equilibrium after being subjected to physical
disturbances is known as the stability of a power system. [1]
- Rotor angle stability; defines the ability of
maintaining synchronism through torque balance of a synchronous
machine. [1]
- Frequency stability; defines the ability of
maintaining the frequency in a specified range according to the demand and
generated active power balance. [1]
- Voltage stability; defines the ability of
maintaining steady acceptable voltage through reactive power balance. [1]
Reliability of a power system
To ensure the continuity of
supply, the power system must be designed so as to resist any disturbance. (E.g.;
short circuit followed by a line tripping, tripping of any element without
a fault etc.) [1]
The reliability of a power
system is, its potentiality of delivering an uninterrupted power supply to any
consumer maintaining the quality standards, and according to the demanded
amount, during normal conditions as well as the disturbed conditions. The
degree of Reliability is measured by the frequency, duration and magnitude of
adverse effect on consumer service. [1]
Security of a power
system
The power system security can
be defined as the ability to resist any kind of disturbance without
interruption to the power supply service. [1]
A power system is said to be
fully reliable if it is secure all the time. [1]
Security of a power system has
two aspects.
- Physical security; refers to the operation
at normal parameters of the primary and secondary circuits of an
electrical network on one side and generator and loads on the other side.
[1]
- Cyber security; refers to the precise
operation of the cyber system. (Cyber system includes, all the computer
communication and digital control devices installed in control centers,
power plants and in substations.) [1],[2]
 |
Figure 1:
SCADA in distribution network. (Picture courtesy: www.electricaltechnology.org)
|
SCADA- Supervisory Control and
Data Acquisition
SCADA, is a large scale
control system utilized in automated industrial processes. (E.g.: Power
systems, steel manufacturing, municipal water supplies and etc.) Such a system
is heavily capable of monitoring and controlling those processes, in real time by acquiring data from
sensors at a remote station and then transferring it to a central computer
system or the host that manages the operations using that information. [3]
Components of a typical SCADA system; [4]
- Remote Terminal Units
(RTUs)- Real time PLCs (Programmable logic controls ),
- Master Terminal Units
(MTUs)- Central Host/ SCADA center
- Communication System- Cable,
radio, satellite, telephone (PABX)
- Computer Workstations-HMI, Human Machine Interface.
 |
Figure 2:
Components of a SCADA system. (Picture courtesy: www.electricaltechnology.org)
|
 |
| Figure 3: Automation of a power system at a glance. (Picture courtesy: www.electricaltechnology.org ) |
Role of the SCADA in
automation of a power system is outstanding. At generating stations, it does a
major role to control the input flow rate to the turbine and at every time it
monitors the speed and the frequency. Also it detects the current flow and line
voltages and monitors the circuit breakers. [5]
SCADA system is the foundation
of the concept of Smart grid. The SCADA upgrades the performance and
efficiency of the entire power system by providing the special features like
real time monitoring, coordinating, controlling and operating, data trending &
logging, maintaining desired voltages, current and power factor, generating
alarms and etc. This eliminates the need for site visit for personnel
inspection at many cases. Remote Terminal Units (RTUs) are used to perform the
automatic monitoring task, protecting and controlling of various equipment. [4]
The
major functions of SCADA can be categorized into following types. [4]
- Substation Control
- Feeder Control
- End User Load Control
Substation Automation Systems
(SAS) using SCADA
Operations performed; [4]
●
Bus voltage
control
●
Bus load balancing
●
Circulating current control
●
Over current protection
●
Transformer thermal, earth leakage and differential protection
●
Bus earth leakage and differential protection
●
Line earth leakage, distance and differential protection
●
Gas Insulated Substation (GIS) distance control and monitoring
●
Continuous monitoring of the status of equipment
●
Collection of historical data of the substation
●
Alarm generation during electrical accidents and faults.
Process;
[4]
- Input/output (I/O)
modules gather field parameters data.
- Status of switches,
circuit breakers, transformers, capacitors and batteries
- Voltage and current
magnitudes
- RTUs collect I/O data and
transfer to the master unit (central computer system) via network
interface module.
- The master unit receives
and logs the data.
- The master unit displays
data on HMI, Human Machine Interface and generate control actions.
 |
| Figure 4: Substation control using SCADA (Picture courtesy: www.electricaltechnology.org) |
Advantage:
●
Enhance the reliability of the network and minimizes the failures
with high speed transfer of data and control commands. [4]
Feeder Control using SCADA
Operations performed; [4]
● Feeder voltage
(VAR) control: - voltage regulation and capacitor placement operations.
● Feeder automatic switching:
-
o
remote switching
of feeders
o
detection of
faults
o
identifying fault location
o
isolating
operation
o
restoration of
service
 |
| Figure 5: Feeder automation using SCADA (Picture Courtesy: www.electricaltechnology.org) |
Feeders
(underground and overhead networks) are automated through modular and
integrated equipment to reduce the duration of the failures and number of
failures as well. Measures can be taken to reduce the repeatability of the
fault.
Ring main units and Remote Control Units (RTUs) of
underground and overhead network are responsible for maintenance and operation
tasks, such as remote load switching, capacitor bank insertion and voltage
regulation. The entire network is connected to the communication medium to
facilitate remote energy management at the central monitoring station. [4]
End User Load Control using
SCADA
Operations performed; (User
end side) [4]
●
Remote load
control
●
Automatic meter
reading and billing
 |
| Figure 6: Centralized meter data-management system using SCADA (Picture courtesy: www.electicaltechnology.org) |
Process; [4]
- Smart meters extract the
energy consumption data and store those in a local storage unit as well as
transfer to central control.
- At the central control
room, AMR (Automated Meter Reading) control unit automatically fetches,
stores and converts all meter data.
Modems
at each meter ensure the secure two-way communication between the central
control room and remote sites. [4]
Advantage of the Centralized
data management system using SCADA;
● Easy and cost
effective method for automating the energy meter data and billing. [4]
Advantages of implementing
SCADA for power systems as a whole
● SCADA systems are equipped to make immediate corrections in the
operational system, so they can increase the life-period of the equipment and
save on the need for costly repairs. [4]
● Equipment damages can be avoided as timely fault identification is
done.
● Minimization of labor cost due to less human introversion as the
system is automated.
● The auto-generated reporting system ensures compliance with
regulatory principles. [4]
● Automatically improvement of the voltage profile by power factor
correction through VAR control. [4]
● Improves the reliability, security so the continuity of
supply. [4]
References
[1]
|
Venkata, S.s and Eremia,
Mircea and Toma, Lucian, "Background of Power System Stability," Handbook of Electrical Power System
Dynamics: Modeling, Stability, and Control, pp. 453-475, 2013.
|
[2]
|
E. G.N, "Cyber Security
and Power System Communication," Essential
Parts of a Smart Grid Infrastructure, IEEE Trans. on Power Delivery, vol.
25, no. 3, p. 1501–1507, 2010.
|
[3]
|
V. Beal, "SCADA -
supervisory control and data acquisition," webopedia, 2020. [Online].
Available: https://www.webopedia.com/TERM/S/SCADA.html. [Accessed 03 May
2020].
|
[4]
|
E. Technology, "SCADA
Systems for Electrical Distribution," ELECTRICAL TECHNOLOGY, 2018.
[Online]. Available: https://www.electricaltechnology.org/2015/09/scada-systems-for-electrical-distribution.html.
[Accessed 3 May 2020].
|
[5]
|
Introduction to SCADA System | Supervisory Control and
Data Acquisition System. [Film]. USA:
Automation design and development, 2017.
|
Nipuni Anuththara Herath
Department of Electrical and Electronic Engineering
Faculty of Engineering
University of Sri Jayewardenepura
Interesting.... keep it up
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