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Contents A. 220/132 KV & 400 KV SUB-STATION
1. Definition
2. Introduction
B. About the substation
B.1 Construction –Site Selection & Layout
C. Equipment in a 220KV & 4 0 0 K V Substation
1) Bus- bar 2) Insulators
a) Pin type insulators
b) Suspension type insulators
c) Strain type insulators
3) Isolating Switches 4) Circuit breaker
a) SF6 Circuit breaker
b) Air Circuit breaker
c) Oil Circuit breaker
5) Protective relay
6) Instrument Transformer
i. Current Transformer
ii. Voltage Transformer
7) Metering and Indicating Instrument
8) Miscellaneous equipment
9) Power Transformer
a) autotransformer
10) Lightening arrestors
11) Line isolator
12) Conductors
I. Bundled conductors
II. Ground wires
13) Wave trap
14)Communication in power system
A) Telecommunication
I. Microwave Communication System
II. Fibre Optic Communication System
III. Power Line Carrier Communication System
B) SCADA system
A.1) Definition of sub -station : -
“The assembly of apparatus used to change some
characteristics (e.g. Voltage ac t o d c freq. p.f.
etc) of electric supply is called sub-station”.
A .2 ) Introduction : -
The present day electrical power system is a.c. i.e.
electric
power is generated, transmitted and distributed in
the form of Alternating current. The electric power is
produce at the power station, which are located at
favorable places, generally quite away from the
consumers. It is delivered to the consumer through a
large network of transmission and distribution. At
many place in the line of power system, it may be
desirable and necessary to change some characteristic
(e.g. Voltage, ac to dc, frequency p.f. etc.) of electric
supply. This is accomplished by suitable apparatus
called sub-station for example, generation voltage
(11KVor 6.6 KV) at the power station is stepped up
to high voltage (Say220KVto 132 KV) for
transmission of electric power. Similarly near the
consumer’s localities, the voltage may have to be
stepped down to utilization level. This job is again
accomplished by suitable apparatus called sub-
station.
B) About the substat ion : -
Panki Thermal Power Station is located at Panki in Kanpur district
in the Indian state of Uttar pradesh , about 16 km from Kanpur . It
has an installed capicity of 220 Mega Watts.
The Central government has commissioned a 210 MW unit at Panki
Power Station.
At PTPS, 2x110 MW BHEL made coal fired turbo generating units
are presently in operation. These 110 MW machines were
manufactured, supplied and commissioned by M/s BHEL, during
1976-77 with features of reheating and regenerative feed heating.
The Steam Generator is balanced draft, radiant, dry bottom, single
drum, natural circulation, vertical water tube type construction with
skin casing and semi direct type of firing system. Apart from the
above 110 MW units, 2x32 MW Russia made turbo generating units
were also installed at PTPS in 1967-68, however these units have
become obsolete and permanently closed now after running for
about 30 years.
The most important of any substation is the grounding
(Earthing System) of the instruments, transformers etc.
used in
the substation for the safety of the operation personnel as
well as
for proper system operation and performance of the protective
devices.
An earthes system comprising of an earthing mat buried at a
suitable depth below ground and supplemented with ground
rods
at suitable points is provided in the substations. These
ground the
extra high voltage to the ground. As it is dangerous to us
to go
near the instrument without proper earth. If the
instruments are not ground properly they may give a huge
shock to anyone who would stay near it and also it is
dangerous for the costly
instrument as they may get damaged by this high voltage.
B.1) Site Select ion & Layout 220KV & 400 KV
Substat ion : -
220KV Sub -Station forms an important link
between
Transmission network and Distribution network. It
has a vital influence of reliability of service. Apart
from ensuring efficient transmission and
Distribution of power, the sub-station configuration
should be such that it enables easy maintenance of
equipment and minimum interruptions in power
supply. Sub-Station is constructed as near as possible
to the load center. The voltage level of power
transmission is decided on the quantum of power to
be transmitted to the load center.
Selection of site :- Main points to be considered while selecting the site for
Grid
Su b-Station are as follows:
i) The site chosen should be as near to the load center as
possible.
ii) It should be easily approachable by road or rail for
transportation of equipments.
iii) Land should be fairly leveled to minimize development
cost.
iv) Source of water should be as near to the site as possible.
This is
because water is required for various construction activities
(especially civil works), earthing and for drinking purposes
etc.
v) T h e s u b -station site should be as near to the town / city
but
should be clear of public places, aerodromes, and Military /
police
installations.
vi) The land should be have sufficient ground area to
accommodate
substation equipments, buildings, staff quarters, space for
storage
of material, such as store yards and store sheds etc. with
roads
and space for future expansion.
vii) Set back distances from various roads such as National
Highways, State Highways should be observed as per the
regulations in force.
Viii While selecting the land for the Substation preference
to be
given to the Govt. land over private land.
ix) The land should not have water logging problem.
x) Far away from obstructions, to permit easy and safe
approach
/ termination of high voltage overhead transmission lines.
B . 2 ) Equipment in 220KV&400KV Sub - Station : -
The equipment required for a transformer Sub-
Station depends upon the type of Sub-Station,
Service requirement and the degree of protection
desired.
220KV EHV Sub-Station has the following major
equipments.
1 ) Bus - bar :-When a no. of lines operating at the same voltage have to
be directly connected electrically, bus-bar are used, it is made
up of
copper or aluminum bars (generally of rectangular X-Section)
and
operate at constant voltage.
The bus is a line in which the incoming feeders come into
and get into the instruments for furtherstep up or step
down. The first bus is used for putting the incoming feeders
inLAsingleline.There may be double line in the bus so that if
any fault occurs in the one the other can still havethe
current and the supply will not stop. The two lines in the
bus are separated by a little distanceby a Conductor having a
connector between them. This is so that one can work at a
time and theother works only if the first is having any fault.
Bus bars :-
b
2 ) I n s u l a t o r s : -The insulator serves two purpose. They support the
conductor (or bus bar) and confine the current to the
conductor.
The most commonly used material for the manufactures of
insulators is porcelain. There are several type of insulator
(i.e. pine type, suspension type etc.) and there used in Su b-
Station will depend upon the service requirement.
Ceramic insulators
Glass insulators
a) PIN INSULATOR:-
Offering an extensive range of 11KV, 22KV and 33 KV pin insulators that
are fabricated from high grade raw material as per the demand of various
electrical industries. Pin insulators it is supported on a pin and provide a
means to hold the insulator to the pin and provide a means to secure the
conductor to the insulator. We offer these pin insulators at varied
standard and customized specifications at cost efficient rates.
11 KV PIN INSULATORSOur range of 11KV pin insulators encompasses RR / PN / 1105, RR /
PN / 1103, RR / PN / 1104 and RR / PN / 1102 which are available in
different technical specifications. These highly efficient pin
insulators are less vulnerable to damage and can normally
withstand the line voltage for a considerable time with ease.
RR / PN / 1105 RR / PN / 1103
RR / PN / 1104 RR / PN / 1102
VOLTAGE CLASS 22 KV
AND 33 KVPin insulators in voltage class 22KV and 33KV have found application in
varied industries and are widely used in low cost distribution lines. Our
pin insulator is designed to secure the conductor to itself. Top quality pin
insulator includes RR / PN / 2201, RR / PN / 3301, RR / 004 / 22 PIN and
RR / 003 / 33 PIN.
RR / PN / 2201 RR / PN / 3301
RR / 004 / 22 PIN RR / 003 / 33 PIN
b) SUSPENSION INSULATORS:-
Suspension insulators are made of multiple units, with the number
of unit insulator disks increasing at higher voltages. The number of
disks is chosen based on line voltage, lightning withstand
requirement, altitude, and environmental factors such as fog,
pollution, or salt spray. Longer insulators, with longer creepage
distance for leakage current, are required in these cases.
Suspension type insulators:-
C) STRAIN INSULATORS :-A strain insulator is an insulator that provides both large electrical
insulation and a large load-bearing capacity. A typical strain
insulator is a piece of glass or porcelain that is shaped to
accommodate two cables or a cable shoe and the supporting
hardware on the support structure (hook eye, or eyelet on a steel
pole/tower). The shape of the insulator maximizes the distance
between the cables while also maximizing the load-bearing transfer
capacity of the insulator. When the line voltage requires more
insulation than a single insulator can supply, strain insulators are
used in series: A set of insulators are connected to each other using
special hardware. The series can support the same strain as a single
insulator, but the series provides a much higher effective insulation.
Strain type insulators:-
3) I s o l a t i n g S w i t c h e s : -
I n Sub -Station, it is often desired to disconnect a part of the
system for general maintenance and repairs. This is
accomplished by an isolating switchor isolator. An isolator is
essentially a kniff Switch and is design to often open a circuit
under no load, in other words, isolator Switches are operate
only when the line is which they are connected carry no load.
For example, consider that the isolator are connected on both
side of a cut breaker, if the isolators are to be opened, the C.B.
must be opened first .
3 pole switch :-
4 ) C i r c u i t b r e a k e r : -A circuit breaker is an equipment, which can open or close a
circuit under normal as well as fault condition. These circuit
breaker breaks for a fault which can damage other instrument
in the station.It is so designed that it can be operated
manually (or by remote control) under normal conditions and
automatically under fault condition.There are mainly two
types of circuit breakers used for any substations. They are
(a) SF6 circuit breakers;
(b) air circuit breakers;
(c) oil circuit breakers.
For the latter operation a relay wt. is used with a C.B.
generally bulk oil C.B. are used for voltage upto 66 KV while
for high voltage low oil & SF6 C.B. are used. For still higher
voltage, air blast vacuum or
SF6 cut breaker are used.
(a) SF6 CIRCUIT BREAKER :-
The use of SF6 circuit breaker is mainly in the substations
which are having high input kv input, say above 220kv and
more. The gas is put inside the circuit breaker by force i.e.
under high pressure.
When if the gas gets decreases there is a motor connected to
the
circuit breaker. The motor starts operating if the gas went
lower than 20.8 bar. There is a meter connected to the
breaker so that it can be manually seen if the gas goes low.
The circuit breaker uses the SF6 gas to reduce the torque
produce in it due to any fault in the line. The circuit
breaker has a direct link with the instruments in the
station, when any fault occur alarm bell rings.
SF6 ckt breaker diagram :-
(b) AIR CIRCUIT BREAKER :-
These type of breakers employ ‘air blast’ as the quenching
medium.The contacts are opened by air blast produced by the
opening of blast valve.The air blast cools the arc and sweeps away
the arcing products to the atmosphere.This rapidly increases the
dielectric strength of the medium between contacts and prevents
from re-establishing the arc.Consequently the arc is extinguished
and the flow of current is interrupted.
(c ) OIL CIRCUIT BREAKER :-
A high-voltage AC electrical switch whose main contacts are located
in a space filled with mineral (transformer) oil. Upon interruption of
the electric circuit, an electric arc forms between the contacts of
the circuit breaker. Because of the high temperature of the arc the
oil is evaporated rapidly and oil vapors are partially decomposed,
liberating ethylene, methane, and other gases. A gas bubble is
formed in the arcing zone; the pressure in the bubble may be as
high as several dozen mega newtons per sq m. The arc is then
extinguished, both because of its elongation upon parting of
contacts and because of intensive cooling by the gases and oil
vapor.
Low oil ckt breaker diagram :-
5) P r o t e c t i v e r e l a y :-A protect ive relay is a device that detects the fault and
initiates the operation of the C.B. to isolate the defective
element from the rest of the system”. The relay detects the
abnormal condition in the electrical circuit by constantly
measuring the electrical quantities, which are different under
normal and fault condition. The electrical quantities which
may change under fault condition are voltage, current,
frequency and phase angle. Having detect the fault, the relay
operate to close the trip circuit of C.B.
Relay diagram :-
6 ) Instrument Trasformer : -
The line in Sub-Station operate at high voltage and
carry current of thousands of amperes. The measuring
instrument and protective devices are designed for low
voltage (generally 110V) and current (about 5A).
Therefore, they will not work satisfactory if mounted
directly on the power lines. This difficulty is overcome
by installing Instrument transformer, on the power
lines. There are two types o f instrument
transformer.
i ) Current Transformer : -
A current transformer is essentially a step-down
transformer which steps-down the current in a
known ratio, the primary of this transformer consist
of one or more turn of thick wire connected in series
with the line, the secondary consist of thick wire
connected in series with line having large number of
turn of fine wire and provides for measuring
instrument, and relay a current which is a constant
faction of the current in the l ine .
Current transformers are basically used to take the
readings of the currents entering the substation.
This transformer steps down the current from 800
amps to1amp. This is done because we have no
instrument for measuring of such a large current.
The main use of his transformer is
(a) distance protection;
(b) backup protection;
(c) measurement.
Current transformer(CT) diagram :-
i i ) V o l t a g e T r a n s f o r m e r : -It is essentially a step– down transformer and step down the
voltage in known ratio. The primary of these transformer
consist of a large number of turn of finewire connected
across the line. The secondary way consist of a few turns and
provides for measuring instruments and relay a voltage
which is known fraction of the line voltage.
Potential transformer(PT) diagram :-
7 ) Metering and Indicating Instrument
:-There are several metering and indicating Instrument (e.g.
Ammeters, Volt- meters, energy meter etc.) installed in a
Substation to maintain which over the circuit quantities. The
instrument transformer are invariably used with them for
satisfactory operation .
8) Miscellaneous equipme nt :-In addition to above, there may be following equipment in a
Substation :
i )Fuses
i i)Carrier -current equipment
i i i )Sub-Station auxiliary supplies
9) Power Transformer : - There are three transformers in the incoming feeders so
that the three lines are step down at the same time. In case
of a 220KV or more KV line station auto transformers are
used. While in case of lower KV line such as less than 132KV
line double winding transformers are used.
a) Autotransformer :
Transformer is static equipment which converts electrical
energy from one voltage to another. As the system voltage
goes up, the techniques to be used for the Design,
Construction, Installation, Operation and Maintenance also
become more and more critical. If propercare is exercised in
the installation, maintenance and condition monitoring of
the transformer, it can give the user trouble free service
throughout the expected life of equipment which of the order
of 25-35 years. Hence, it is very essential that the personnel
associated with the installation, operation or maintenance
of the transformer is through with the instructions
provided by the manufacture.
Autotransformer taping :-
10) Lightening arrestors :-Lightening arrestors with earth switch lightening arrestors
after the current transformer are used so as to protect it
from lightening i.e. from high voltage entering into it. This
lightening arrestor has an earth switch, which can directly
earth the lightening. The arrestor works at 30° to 45° angel
of
the lightening making a cone. The earth switch can be
operated manually, by pulling the switch towards ground.
This also helps in breaking the line entering the station. By
doing so maintenance and repair of any instrument can b
performed.
Different types of lighning arrestors :-
It is a device used on electrical power systems to protect the
insulation on the system from the damaging effet of
lightning. Metal oxide varistors (MOVs) have been used for
power system protection since the mid 1970s. The typical
lightning arrester also known as surge arrester has a high
voltage terminal and a ground terminal. When a lightning
surge or switching surge travels down the power system to
the arrester to the ground.
11) Line isolator :-
The line isolators are used to isolate the high voltage
Flow throughthe line into the bus. This isolator prevents
the instruments to get damaged. It also allows the only
needed voltage andrest is earthed by itself. In electrical
engineering, a disconnector or isolator switch is used to make sure
that an electrical circuit can be completely de-energised for service
or maintenance. Such switches are often found in electrical
distribution and industrial applications where machinery must have
its source of driving power removed for adjustment or repair. High-
voltage isolation switches are used in electrical substations to allow
isolation of apparatus such as circuit breakers and transformers,
and transmission lines, for maintenance.
12) Conductors:-
Aluminium conductors reinforced with steel (known as ACSR) are
primarily used for medium and high voltage lines and may also be
used for overhead services to individual customers. Aluminium
conductors are used as it has the advantage of lower
resistivity/weight than copper, as well as being cheaper.
While larger conductors may lose less energy due to lower electrical
resistance, they are more costly than smaller conductors. An
optimization rule called Kelvin's Law states that the optimum size of
conductor for a line is found when the cost of the energy wasted in
the conductor is equal to the annual interest paid on that portion of
the line construction cost due to the size of the conductors. The
optimization problem is made more complex due to additional
factors such as varying annual load, varying cost of installation, and
by the fact that only definite discrete sizes of cable are commonly
made.
I. Bundle conductors :-
Bundle conductors are used to reduce corona losses and audible
noise. Bundle conductors consist of several conductor cables
connected by non-conducting spacers. For 220 kV lines, two-
conductor bundles are usually used, for 380 kV lines usually three
or even four.
Bundle conductors are used to increase the amount of current that
may be carried in a line. Due to the skin effect, ampacity of
conductors is not proportional to cross section, for the larger sizes.
Therefore, bundle conductors may carry more current for a given
weight.
A bundle conductor results in lower reactance, compared to a single
conductor. It reduces corona discharge loss at extra high voltage
(EHV) and interference with communication systems. It also
reduces voltage gradient in that range of voltage.
Double conductors four
conductors
II. Ground wires :-
Overhead power lines are often equipped with a ground conductor
(shield wire or overhead earth wire). A ground conductor is a
conductor that is usually grounded (earthed) at the top of the
supporting structure to minimise the likelihood of direct lightning
strikes to the phase conductors. Shield wires on transmission lines
may include optical fibers (OPGW), used for communication and
control of the power system.
13) wave trap :-It is also called "Wave trap". It is connected in series with the power
(transmission) line.It blocks the high frequency carrier waves
(24 KHz to 500 KHz) and let power waves (50 Hz - 60 Hz) to pass
through. It is basically an inductor of rating in Milli henry (approx 1
milli Henry for 220 KV 1250 Amp.).
Wave trap diagram:-
14) Communication in Power System
Following are mainly three inter-related areas of functions in
UPPTCL for management of power system:
A) Telecommunication
B) SCADA- Supervisory Control and Data Acquisition System.
A) TELECOMMUNICATION
There are three different types of telecommunication systems in
UPPTCL i.e.
i. Microwave Communication System,
ii. Fibre-optic Communication System,
iii. PLCC-Power Line Carrier Communication.
Voice Frequency (VF) channels of all these systems have been
integrated/interconnected to make a hybrid communication system.
Microwave & Fibre Optic are multi-channels communication
systems and are also called 'Wideband communication system'.
PLCC is single channel communication system. A brief overview of
these three types of telecommunication system of UPPTCL is as
below:
I. Microwave Communication System
Microwaves travel in 'Space' and any object in the path can obstruct
communication system. Microwave is called 'line-of-sight'
communication system. As such, its antennas are mounted on high
towers so that even trees should not obstruct path of microwaves.
UPPTCL is using frequency band between 2.3 GHz to 2.5 GHz. The
height for antenna are calculated by taking into account many
factors, such as, distance between two locations, path clearance,
height from sea level of these locations, tropical area, reflection
points, and so on. As such, height of towers varies from location to
location. Tower heights at our microwave stations range from 30 to
110 meters. Starting from Muzaffarnagar (220KV substation Nara),
in the north-west, to Rihand (Pipri), in south-east of UP, 33
microwave stations have been established. A list of microwave
stations with height of towers has been given at the end of this
write-up. This covers a route length of over 1000 Km.
II. Fibre Optic Communication System
It is new communication system and has been introduced in
UPPTCL since 2001. Optical fibre cable, in the form of 'Optical Fibre
Composite Ground Wire' (OPGW), has been installed on
transmission towers by replacement of earth wire. Earth wires of
following five transmission lines, total route length of 408 Km., have
been replaced:
'Optical Line Terminal Equipment' (OLTE) have been manufactured
by Fujitsu, Japan and have been installed at eight sub-stations
(Muradnagar, Moradabad, C.B.Ganj, Unnao, Panki, Sahupuri,
Sarnath & Azamgarh). The electrical signal of 2Mb/s or 34Mb/s, as
the case may be, from OLTE is connected with Primary Multiplexing
equipment supplied by 'Nokia' Finland. Its NMS provides
operational support for the 'Fibre Optic Transmission System'
(FOTS). For testing, commissioning & maintenance 'FLEXR' and
'FLEXR Plus' computer software programmes have been provided.
'FLEXR' is used for initial settings of OLTEs of fibre optic network.
Similar to microwave NMS, 'FLEXR Plus' helps in remote diagnosis,
operation and maintenance of fibre optic network. For complete
communication control system, a NMS100 system has installed at
NRLDC, New Delhi, which is in position to diagnose faults of whole
northern region.
OPGW has been manufactured by Farukawa, Japan. They have done
replacement work, on live (hot) lines, by using a unique installation
technology. The OPGW in our system has got twelve (12) 'Dual
Window Single Mode' (DWSM) type fibres in it. Optical signals of
1310 or 1550 nanometer (nm) wavelength are being used. Only two
fibres are required for a multi-channel link between two stations.
One fibre is used for transmitting optical signal and second for
receiving from other end. In our system two fibres have been used
for 'Normal' communication path and two fibres for 'protection'
path. Fibre optic communication system has got a wide bandwidth
transmission capability. Two fibres are sufficient for providing more
than one lakh telephone channels on both sides. As such, a high-
speed data, containing large volumes of information can be
transmitted at low cost.
III. Power Line Carrier Communication
System
Power Line Carrier Communication (PLCC) is a single channel
communication system in which its channel (300 to 3400 Hz) is
divided into two parts i.e. speech band is generally kept 300 to
2400Hz or 300 to 2000Hz and rest is used as data band. Due to
narrow speech band in PLCC, voice of poor quality is available in
comparison to wideband communication system. In this system,
signal travels on the transmission line from one end to other end.
Transmitter output (Radio Frequency signal) is fed to the
transmission line through a Coupling Capacitor or CVT. RF power
output is in frequency band from 70 KHz to 500 KHz. Inductors,
called 'Wave Traps' are used at the ends of the signals. PLCC is also
used for line protection signal. Protection signals are transmitted
through PLCC system for tripping circuit breaker of other end of
transmission line. UPPTCL has a wide network of PLCC links.
Presently, its number of PLCC links are about 550.
Plc block diagram:-
B) SCADA SYSTEM
In SCADA system measured values, i.e. analogue (measured value)
data (MW, MVAR, V, Hz Transformer tap position), and Open/Closed
status information, i.e. digital data (Circuit Breakers/Isolators
position i.e. on/off status), are transmitted through
telecommunication channels to respective sub-LDCs. For this
purpose Remote Terminal Units (RTUs) at 400KV, 220KV and few
important 132KV sub-stations have been installed. System values &
status information below 132 KV have not been picked up for data
transmission, except for 33KV Bus isolator position and LV side of
generators. Secondary side of Current Transformers (CT) and
Potential Transformer (PT) are connected with 'Transducers'. The
output of transducers is available in dc current form (in the range
of 4mA to 20mA). Analogue to digital converter converts this
current into binary pulses. Different inputs are interleaved in a
sequential form and are fed into the CPU of the RTU. The output of
RTU, containing information in the form of digital pulses, is sent to
subLDC through communication links. Depending upon the type of
communication link, the output of RTU is connected, directly or
through Modem, with the communication equipment. At subLDC
end, data received from RTU is fed into the data servers. In general,
a SCADA system consists of a database, displays and supporting
programmes. In UPPTCL, subLDCs use all major functional areas of
SCADA except the 'Supervisory Control/Command' function. The
brief overview of major 'functional areas' of SCADA system is as
below:
1. Communications - Sub-LDC's computer communicates with all RTU
stations under its control, through a communication system. RTU
polling, message formatting, polynomial checking and message
retransmission on failure are the activities of 'Communications'
functional area.
2. Data Processing - After receipt of data through communication
system it is processed. Data process function has three sub-
functions i.e. (i) Measurements, (ii) Counters and (iii) Indications.
'Measurements' retrieved from a RTU are converted to engineering
units and linearised, if necessary. The measurement are then placed
in database and are checked against various limits which if
exceeded generate high or low limit alarms.
The system has been set-up to collect 'Counters' at regular
intervals: typically 5 or 10 minutes. At the end of the hour the units
is transferred into appropriate hour slot in a 24-hour
archive/history.
'Indications' are associated with status changes and protection. For
those statuses that are not classified as 'alarms', logs the change on
the appropriate printer and also enter it into a cyclic event list. For
those statuses, which are defined as an 'alarms' and the indication
goes into alarm, an entry is made into the appropriate alarm list, as
well as in the event list and an audible alarm is generated in the
sub-LDC.
3. Alarm/Event Logging - The alarm and event logging facilities are
used by SCADA data processing system. Alarms are grouped into
different categories and are given different priorities. Quality codes
are assigned to the recently received data for any 'limit violation'
and 'status changes'. Alarms are acknowledged from single line
diagram (or alarm lists) on display terminal in LDCs.
4. Manual Entry - There is a provision of manual entry of measured
values, counters and indications for the important
sub-station/powerhouse, which are uncovered by an RTU or some
problem is going on in its RTU, equipment, communication path,
etc.
5. Averaging of Measured Values - As an option, the SCADA system
supports averaging of all analogue measurements. Typically, the
averaging of measured values over a period of 15 minutes is stored
to provide 24 hours trend.
6. Historical Data Recording (HDR) - The HDR, i.e. 'archive',
subsystem maintains a history of selected system parameters over a
period of time. These are sampled at a pre-selected interval and are
placed in historical database. At the end of the day, the data is
saved for later analysis and for report generation.
7. Interactive Database Generation - Facilities have been provided in
such a way that an off-line copy of the SCADA database can be
modified allowing the addition of new RTUs, pickup points and
communication channels.
8. Supervisory Control/Remote Command - This function enables the
issue of 'remote control' commands to the sub-station/powerhouse
equipment e.g. circuit breaker trip command. Though, there is
provision of this function in this system, yet it is not used in U.P. As
such, related/associated equipment have not been ordered.
9. Fail-over - A 'Fail-over' subsystem is also provided to secure and
maintain a database of devices and their backups. The state of the
device is maintained indicating whether it is 'on-line' or 'failed'.
There is a 'backup' system, which maintains database on a backup
computer and the system is duplicated.
SLDC Lucknow has a large and active 'Mimic Board' in its Control
room. This mimic board displays single line diagram of intra State
transmission system i.e. grid network of 400KV, 220KV and
important 132KV sub-stations, transmission lines, thermal & hydro
powerhouses. Outgoing feeders, shown in the mimic board, have
'achieve' (LED display) colored indications, of three different colors,
to show the range of power flow at any moment i.e. 'Normal',
'Nominal' or 'Maximum' of its line capacity. UPPTCL's transmission
network is expanding rapidly and thereby number of RTUs is also
increasing. For new substations and lines, displays in active and
passive forms are required to be made in the Mimic diagram. But,
Mimic Board has a limitation that it cannot incorporate/add large
volume of displays for substations/power houses/transmission lines
in 'active' form due to space constraint and congestion. Due to this
Mimic Board is going to be supplemented with a Video Projection
System (VPS) at SLDC, Lucknow in near future. Also in SLDC &
subLDCs, displays of single line diagrams of RTU sub-stations/power
house are viewed on VDUs of large size (21").
Transmission & reciver block diagram :-
Scada system diagam :-