Unit-6 Industrial Electrical System Automation

Topic- SCADA Systems for Electrical Distribution

Nowadays, computer control is one of the most cost effective solutions for improving
reliability, optimum operation, intelligent control and protection of a power
system network. Having advanced data collection capabilities, SCADA system plays a
significant role in power system operation.
Typically, at distribution side SCADA does more than simply collecting data by
automating entire distribution network and facilitating remote monitoring, coordinate,
control and operating distribution components just like in Smart Grid System. Before
knowing distribution automation using SCADA, let us look at what exactly SCADA
is and its functioning and what they do in the distribution system.
SCADA (Supervisory Control and Data Acquisition)
Supervisory Control and Data Acquisition or simply SCADA is one of the solutions
available for data acquisition, monitor and control systems covering large geographical
areas. It refers to the combination of data acquisition and telemetry.

SCADA systems are mainly used for the implementation of monitoring and control
system of an equipment or a plant in several industries like power plants, oil and gas
refining, water and waste control, telecommunications, etc.
In this system, measurements are made under field or process level in a plant by
number of remote terminal units and then data are transferred to the SCADA central
host computer so that more complete process or manufacturing information can be
provided remotely.
This system displays the received data on number of operator screens and conveys back
the necessary control actions to the remote terminal units in process plant.
Components of Typical SCADA System
The major components in SCADA system are
Remote Terminal Units (RTUs)
RTU is the main component in SCADA system that has a direct connection with various
sensors, meters and actuators associated with a control environment.
These RTUs are nothing but real-time programmable logic controllers (PLCs) which
are responsible for properly converting remote station information to digital form for
modem to transmit the data and also converts the received signals from master unit in
order to control the process equipment through actuators and switchboxes.
Master Terminal Units (MTUs)
A central host servers or server is called Master Terminal Unit, sometimes it is also
called as SCADA center. It communicates with several RTUs by performing reading and
writing operations during scheduled scanning. In addition, it performs control,
alarming, networking with other nodes, etc.
Communications System
The communication network transfers data among central host computer servers and
the field data interface devices & control units. The medium of transfer can be cable,
radio, telephone, satellite, etc. or any combination of these.
Operator Workstations
These are the computer terminals consisting of standard HMI (Human Machine
Interface) software and are networked with a central host computer. These
workstations are operator terminals that request and send the information to host
client computer in order to monitor and control the remote field parameters.
Automation of Electrical Distribution System
Modern SCADA systems replace the manual labor to perform electrical distribution
tasks and manual processes in distribution systems with automated equipments. SCADA
maximizes the efficiency of power distribution system by providing the features like
real-time view into the operations, data trending and logging, maintaining desired
voltages, currents and power factors, generating alarms, etc.

SCADA performs automatic monitoring, protecting and controlling of various

equipments in distribution systems with the use of Intelligent Electronic Devices (or
RTUs). It restores the power service during fault condition and also maintains the
desired operating conditions.
SCADA improves the reliability of supply by reducing duration of outages and also gives
the cost-effective operation of distribution system. Therefore, distribution SCADA
supervises the entire electrical distribution system. The major functions of SCADA can
be categorized into following types.
 Substation Control
 Feeder Control
 End User Load Control
Substation Control using SCADA
In substation automation system, SCADA performs the operations like bus voltage
control, bus load balancing, circulating current control, overload control, transformer
fault protection, bus fault protection, etc.
SCADA system continuously monitors the status of various equipments in substation
and accordingly sends control signals to the remote control equipments. Also, it collects
the historical data of the substation and generates the alarms in the event of electrical
accidents or faults.

SCADA base sub station control system

The above figure shows the typical SCADA based substation control system. Various
input/output (I/O) modules connected to the substation equipment gathers the field
parameters data, including status of switches, circuit breakers, transformers, capacitors
and batteries, voltage and current magnitudes, etc. RTUs collect I/O data and transfers
to remote master unit via network interface modules.
The central control or master unit receives and logs the information, displays on HMI
and generate the control actions based on received data. This central controller also
responsible for generating trend analysis, centralized alarming, and reporting.
The data historian, workstations, master terminal unit and communications servers are
connected by LAN at the control center. A Wide Area Network (WAN) connection with
standard protocol communication is used to transfer the information between field sites
and central controller.
Thus, by implementing SCADA for substation control eventually improves the reliability
of the network and minimizes the downtime with high speed transfer of measurements
and control commands.
Feeder Control using SCADA
This automation includes feeder voltage or VAR control and feeder automatic switching.
Feeder voltage control performs voltage regulation and capacitor placement operations
while feeder switching deals with remote switching of various feeders, detection of
faults, identifying fault location, isolating operation and restoration of service.
In this system, SCADA architecture continuously checks the faults and their location by
using wireless fault detector units deployed at various feeding stations. In addition, it
facilitates the remote circuit switching and historical data collection of feeder
parameters and their status. The figure below illustrates feeder automation using
SCADA.

In the above typical SCADA network, different feeders (underground as well as

overhead networks) are automated with modular and integrated devices in order to
decrease the number and duration of outages. Underground and overhead fault
detection devices provide accurate information about transient and permanent faults so
that at the remote side preventive and corrective measures can be performed in order
to reduce the fault repeatability.
Ring main units and Remote Control Units (RTUs) of underground and overhead
network responsible for maintenance and operational duties such as remote load
switching, capacitor bank insertion and voltage regulation. The entire network is
connected with a communication medium in order to facilitate remote energy
management at the central monitoring station.
End User Load Control Automation by SCADA
This type of automation at user end side implements functions like remote load control,
automatic meter reading and billing generation, etc. It provides the energy consumption
by the large consumers and appropriate pricing on demand or time slots wise. Also
detects energy meter tampering and theft and accordingly disconnects the remote
service. Once the problem is resolved, it reconnects the service.

The above figure shows a centralized meter data-management system using SCADA. It is
an easy and cost-effective solution for automating the energy meter data for billing
purpose.
In this, smart meters with a communication unit extract the energy consumption
information and made it available to a central control room as well as local data storage
unit. At the central control room, AMR control unit automatically retrieves, stores and
converts all meter data.
Modems or communication devices at each meter provide secure two-
way communication between central control and monitoring room and remote sites.
Advantages of Implementing SCADA systems for Electrical Distribution
 Due to timely recognition of faults, equipment damage can be avoided
 Continuous monitoring and control of distribution network is performed from
remote locations
 Saves labor cost by eliminating manual operation of distribution equipment
 Reduce the outage time by a system-wide monitoring and generating alarms so
as to address problems quickly
 Improves the continuity of service by restoring service after the occurrence of
faults (temporary)
 Automatically improves the voltage profile by power factor correction and VAR
control
 Facilitates the view of historian data in various ways
 Reduces the labor cost by reducing the staff required for meter reading