COMMUNICATION FROM THERMAL POWER STATION SWITCHYARD TO LOAD

DISPATCH CENTER

Each subLDC collects data from various 'Remote Terminal Units' (RTUs), installed at
important sub-stations (400KV, 220KV and few 132KV) and powerhouses. So far in
UPPTCL, 72 RTUs have already been integrated with the system. Each RTU
automatically picks up required information (MW, MVAr, KV, Hz, Circuit breaker &
isolator status) of the sub-station/powerhouse and transmit it to its subLDC through
communication system. This information is processed in the data Server of subLDC.
Data in the form of binary stream of pulses are sent by RTU at the speed of 300, 600
or 1200 bits per second rate (baud). At subLDC, the information is updated within 10
sec.
For managing power system at load dispatch centers, communication plays a vital
role by providing path for transmitting of data & voice. Work of these control centers
is dependent upon SCADA (Supervisory Control and Data Acquisition) System and
various types of communication systems.
Transmission of Data
Below in Figure 2, main equipment from substation/power house to its subLDC has
been shown in a very simple form.

Figure 2: Transmission of Data from substation/Power house to subLDC

Current Transformers (CTs) and Potential Transformers (PTs), installed on
transmission lines, provide inputs to transducers of SIC (Supervisory Interface &
Control) & RTU (Remote Terminal Unit) panel. Circuit breakers & isolators' status are
extended up to SIC panel. If for such extension extra potential free contacts are not
available in the Control Panels, Contact Multiplying Relays (CMRs) are used to
provide potential free contacts. The output of RTU is connected to the communication
equipment, through Modem. In between substation & subLDC, a communication link
has been shown. Telephone exchanges are connected with the communication
equipment. Such communication links can be of any type. UPPTCL has got its own
three different type of communication systems, i.e. PLCC (Power Line Carrier
Communication), microwave and fibre-optic. PLCC system is more prevalent in
UPPTCL. Modem output at receive side is connected with the CFE (Communication
End Frame). Its output is connected with data takes over. Each RTU is automatically
polled by Server of subLDC to obtain each data of repeats at least once in 10 sec and
is stored in the database of subLDC. This data is processed in database formats and

is retrieved for different applications. These formats or graphics are displayed or

printed as per requirement. At subLDC, System Control Officers use this data to
monitor and analyze position of the grid.
Below in Figure 3, main equipment from subLDC to SLDC, Lucknow has been shown
in a very simple form.

A systematically combined/processed data of all RTUs, in server of subLDC, is

transmitted to SLDC Lucknow. This data in the form of 64Kb/s signal is sent through
multiple paths/channels. Presently four channels are used. For this purpose 'Routers'
are used. Routers basically work as modem but is has multiple paths for LAN, WAN
or internet, etc. In UPPTCL, for transmission of data, from subLDC to SLDC, only
wideband communication system (microwave or fibre-optic links) is being used. In
SLDC, data from all other subLDCs is also received simultaneously and are processed
for different purposes and applications. From Inter-Control Centre Communications
Protocol (ICCP) Servers of SLDC, complete data of all subLDCs is sent to NRLDC,
New Delhi through wideband communication system. This way communication plays
a major role in grid management.
Communication for 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.
C) EMS- Energy Management System
A) TELECOMMUNICATION
There are three different types of telecommunication systems in UPPTCL i.e.

i.
ii.
iii.

Microwave Communication System,

Fibre-optic Communication System,
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:
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 northwest, 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. Erstwhile UPSEB
had an analogue microwave system which was converted to digital microwave
system in 2001. Previous analogue microwave equipment was being used with
'frequency diversity' system where frequencies of Transmitters & Receivers of
'Normal' and 'Standby' equipment were different. In Frequency Diversity system both
Transmitters & Receivers are connected with antenna simultaneously. In present
digital microwave system, Transmitters & Receivers of 'Normal' and 'Standby'
equipment has got same frequency and is called 'hot standby' system. Only one
column is equipment has got same frequency and is called 'hot standby' system.
Only one column is connected with the antenna. Microwaves are susceptible to
'fading phenomenon' due to change in atmospheric medium above the earth, during
day & night and from season to season. Some links, which are suspected for
excessive fading during propagation of signal, have been provided with additional
antennas for 'space diversity'. In space diversity system, Transmitters & Receivers
have additional antennas, located at different heights. Each system has got its own
advantages. New digital microwave system has got many useful features for easy
maintenance. Its 'Network Management System' (NMS) helps in remote diagnosis
operation and maintenance. As an example, microwave NMS equipment at Lucknow
detects defective circuits between Obra-Pipri and diagnoses its problem. In some
cases, the maintenance personnel at Lucknow implements remedial actions and
reallocate channels, if required. This way immediate site visits for minor faults, in
many cases, are not required. Microwave equipment is of 'Nokia' Finland make.
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:

1. 400KV line between 400KV S/S Muradnagar - 400KV S/S Moradabad;

2. 220KV line between 400KV S/S Moradabad - 220KV S/S C.B. Ganj;

3. 400KV line between 400KV S/S Unnao - 400 KV S/S Panki;

4. 220KV line between 220KV S/S Sahupuri - 400KV S/S Sarnath and
5. 400KV line between 400KV S/S Sarnath - 400KV S/S Azamgarh.
'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.
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.
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 substations 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

2.

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.
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").
C) ENERGY MANAGEMENT SYSTEM (EMS)
For energy management of the power system, control personnel and application
software engineers use SCADA data available in the database by using EMS software.
The software functions are based on the Energy Management Platform (EMP). All
servers have 'Open VMS' operating system. All Personal Computers (PCs) have
'Window NT' operating system. Important features are as below:

1. The Data Base Compiler provides a consistent source of data usable for the

2.

applications in an efficient form. The Data Base Compiler does final checking
for completeness and consistency of the entries for a specific application and
prepares those special tables which are needed for the efficiency of specific
application programmes.
Recording of 'Sequence of Events' (SOEs) is the most innovative feature
provided in this system. A RTU has the ability to accurately time tag status
change and report this information to sub-LDC. All RTUs in the system are
'time synchronised' with the master station. Global Positioning System (GPS)
system has been used at all subLDCs & SLDC. In the event of any tripping,
sequence of events can be well established on time scale with a resolution of
10 milliseconds.

3. Normally, 'Automatic Generation Control' (AGC) function issues control

commands to generating plants using the concept of Area Control Error
(ARE). It is base on deviations in 'standard frequency (50 Hz)' and 'scheduled
area interchanges' from that of the 'actual frequency' and 'actual area
interchanges'. The scope of AGC function for UPPTCL has been limited to open
loop operation i.e. the software provides the desired corrective actions for
each plant, but the actual command are not issued. It is left to 'System
Control Officer' to take necessary action as divided by AGC Controller. In the
event of unavailability of sufficient generation to satisfy the AGC requirement,
the System Control Officer can enforce required quantum of load shedding.

4. For 'Operation Scheduling' the application software has 'short-term' and 'longterm' 'System Load Forecasting' functions to assist dispatching
Engineer/control Officer in estimating the loads that are expected to exist for
one to several days in advance. This function provides a scientific and logical
way of scheduling of resources in a very effective manner.

Under 'Short-term Load Forecasting' function, application software engineers

are able to forecast weekly peak demands and load duration curves for
several months into the future.

Under 'Long-Term Load Forecasting' function, forecasting of monthly peak

demands and load duration curves for several years into the future can done
for the use of 'Power System Planner'.

5. The other functions like economic dispatch, reserve monitoring, production

costing, inter system transactions scheduling, etc. are available to guide
System Control Officer to optimally use available resources.

6. Power System Control Officer/Analyst would be able to use contingency

analysis function to assess the impact of specified contingencies that would

cause line (s) overloads, abnormal voltages, and reactive limit violations.

7. The EMS software system may have many other applications for use, which

include network topology, performing of state estimation, optimal power flow

(OPW) programme, stability programme, power flow displays, help and
instructional displays, tabular displays, single line diagram displays, etc.