Uttar Pradesh Power Transmission Corporation Ltd. (UPPTCL) has a very large network of high voltage transmission lines in whole UP (about 24,000Km). Transmission lines transfer power from power houses to substations and from one substation to many other substations or vice versa. Power is generated at low Voltage (of the order of 3.3KV to 25KV) and is stepped-up to high voltage (765KV, 400KV, 220KV & 132KV) for evacuating power into the grid network through transmission lines.

33/11KV Substations of distribution companies (DISCOMs) draw power from transmission substations through 33KV lines and distribute that to consumers (at 0.04KV, 11KV or in few cases at 33KV). Distribution companies have industrial, rural and domestic load, which varies from time to time of the day and from season to season of the year. Sometimes, large variations in load cause over/under loading of lines, transformers or generators. Variations beyond limits and breakdowns cause fluctuations in voltages & grid frequency of the network. Control Centers, in hierarchical form, are set up for smooth functioning of the grid. Each generating unit or substation has its own Control Centre. These are also named as Unit Control Board (UCB)/Main Control Board (MCB)/Control Room. These Control Centres report to Area Load Dispatch Station (ALDS). ALDS report to Central Load Dispatch Station (CLDS at State Level), CLDS reports to Regional System Coordination & Control Centre (RSCC at regional level having a group of States and Central sector units of that region) & finally on top is National Load Dispatch Centre (NLDC) which is being set-up.

These control centers need real time information about generation, power flow, voltage, frequency, etc. of generators & substations. This information is exchanged in data or voice form. For exchange of such information, a reliable and dedicated communication system is required. Substations or power houses, situated at both ends of transmission line, need information in voice form. Trip commands (also called protection signal) are transmitted from one substation to the other substation, through transmission line. When 'earth' or 'over-current' fault is sensed by one end of the transmission line, a trip command is generated, which travels through communication system and opens circuit breaker (switchgear) of the other end. Dedicated communication system is required for transmission of protection signal.

Old Communication System

Most of the high voltage substations & power houses are located away from cities/towns or in outskirt area of the city. In mid sixties, in erstwhile U.P. State Electy. Board (UPSEB), even P & T lines were not available for communicating messages among substations and powerhouses. In some cases, telex messages were being sent through P & T department between few Control Centers situated in major cities. Later on, Power Line Carrier Communication (PLCC) systems were used for voice communication among substations, powerhouses, grid control centers and for sending protecting signals. In late seventies, sub-VF band of few PLCC links were used for transmitting tele-metering signal (containing data of power flow, voltage, frequency, circuit breaker/Isolator status, etc.) to Control Centers. Thereafter in eighties, microwave communication system was introduced and 38 nos. microwave stations were set up in Uttar Pradesh, starting from Rishikesh in the north-west to Rihand in the south-east. It was an analogue communication system and was partially successful. During this period, many 400KV substations and power houses came up but main dependency remained upon PLCC & P&T  communication systems.

Unified Scheme

In nineties, it had been felt that facilities for operation and management of power system were grossly inadequate. The erstwhile UPSEB was finding it difficult to properly manage its grid, as it was running in conjunction with other Constituents of Northern Region, comprising of electricity boards/departments of States - Rajasthan, Punjab, Haryana, HP, J&K, DESU and Central Sector Corporations (NTPS, NHPC, and PGCIL). After every grid failure or isolation, restoration time used to be very long. During post-mortem analysis of grid failures, it was difficult to pinpoint, confidently, the main culpri9t sub-station/State. At that time, only UPSEB had an analogue microwave communication system, but it was operative in few sections, while other States were totally dependent upon PLCC & P&T lines. Side-by-side there was a plan for formation of National Grid. To manage in inter-State & power drawal (export/import of power) and maintain a discipline, come rules/procedures (Grid Code) were being framed. In order to manage regional grid, need of 'online information', in the form of data, was felt. This online data, of grid substations & power houses, required a reliable and dedicated communication system. Thus, adoption upon that situation, Central Electricity Authority (CEA) & Northern Region Electricity Board (NREB) asked all its Constituents (UPSEB was also a Constituent of NREB) to make a combined effort in this direction. This gave birth to a 'Unified Scheme', a 'combined' project with other Constituents of NREB (NREB has now been named as Northern Regional Power Committee-NRPC). This project was formulated for establishment of modern computerized Load Dispatch Centres (LDCs), for having SCADA (Supervisory Control and Data Acquisition) and Energy Management System (EMS) along with strengthening of telecommunication facilities of  each State. Uttar Pradesh (included area which is now in Uttaranchal) was a major Constituent of NREB. Since, Power Grid Corporation of India (PGCIL) had presence in every State, the responsibility for implementation of 'Unified Scheme' was given to it by NREB, PGCIL got the equipment, installed & commissioned in the whole northern region. A Memorandum of Understanding (MoU) was signed between PGCIL and all other Constituents of NREB in 1994. Thereafter, it took four years for PGCIL to gather requirement of each Constituent and finalize orders with their Vendors/Contractors under Global offers. Later on, same scheme was implemented in other Regional Electricity Boards of India (such as Eastern, Western, North-east & Southern). By mid of 2002, major works of commissioning of 'Unified Scheme' were over in northern region.

Load Dispatch Centres

Before implementation of 'Unified Scheme' U.P. State had a 'Central Load Dispatch Station' (CLDS), at 5th floor of Shakti Bhawan, Lucknow. It was being assisted by its four 'Area Load Dispatch Stations' (ALDSs), situated at Sahupuri, Panki, Moradabad and Roorkee. After modernization & computerization of control centers, the nomenclatures of these control centers have been changed. A hierarchy of Control centers has been formed.

• The basic control centre, ALDS of every State has been named as sub-Load Dispatch Centre (subLDC)

• CLDS has been named as State Load Dispatch Centre (SLDC).

• Regional System Coordination & Control Centres (RSCC) of northern region at New Delhi has been named as Northern Regional Load Dispatch Centre (NRLDC).

In the above Figure 1 National Load Dispatch Centre (NLDC) has been shown at the top. Its Control Centre has been setup at New Delhi and will be operational in month of May/June 2008. Below this, five nos. regional level Load Dispatch Centers have been shown. Presently, except for Southern Region, grids of all other regions are interconnected and are running in combined form. This way, Northern Regional Load Dispatch Centre (NRLDC) is now part of all India Grid or say 'National Grid'. The role of the NRLDC is to monitor and supervise the grid and power generation of the region. It focuses attention on the regional interconnected network. By using 'Energy Management System' (EMS) and advanced application programmes, NRLDC coordinates with all inter-region and inter-state power exchange.

Below NRLDC, State level SLDCs and Central Project Coordination & Control Centre (CPCC) have been shown. The primary role of SLDCs is to monitor, control and coordinate the generation, transmission and distribution of power within the State while ensuring safety and continuity of its transmission and sub-transmission power networks. CPCC (North) coordinates with all Central sector projects of northern region such as those of NTPC, NHPC, Power Grid, Tehri, etc. CPCC gets data from Central Sector projects and that data is added at regional level. Each RLDC has the ability to exchange data with other RLDCs as well as with NLDC, but direct data transmission does not take place between SLDC of one State with SLDC of another State.

SLDC of Uttar Pradesh is situated at 5th Floor of Shakti Bhawan, Lucknow. This SLDC has the ability to exchange data with NRLDC, New Delhi and its sub-LDCs. Under it, there are five sub-LDCs. SLDC of UP & each subLDC is manned 24 hours of the day by shift engineers (except for subLDC Sultanpur, which is being managed from subLDC Panki). 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.

1. Microwave Communication System,

2. Fibre-optic Communication System,

3. 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 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. 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 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").

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 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.

2. 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 'long-term' '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.

LIST OF MICROWAVE STATIONS OF UPPTCL

 

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