400 KV sub

400 KV sub-station at Sriperumbudur’ It would also ease the burden of the lone 400 KV sub-station at Sriperumbudur which was at present supplying power to Chennai and its suburban areas. The new sub-station would supply power generated from North Chennai Thermal Power Station to Sunguvarchatram and its nearby areas and facilitate smooth power supply to nearby industries and residences. The sub-station has two in-built 400/230 KV transformers and two 200 KV transformers. It would also be linked to 2 x 600 MW North Chennai Thermal Power Staion-2, 400 KV Alamdai sub-station, 400 KV Sriperumbudur station and the 400 KV sub-station at Puducherry. It said Multi Circuit Transmission Lines were being laid to carry power. An important function performed by a substation is switching, which is the connecting and disconnecting of transmission lines or other components to and from the system. Switching events may be "planned" or "unplanned". A transmission line or other component may need to be deenergized for maintenance or for new construction, for example, adding or removing a transmission line or a transformer. To maintain reliability of supply, no company ever brings down its whole system for maintenance. All work to be performed, from routine testing to adding entirely new substations, must be done while keeping the whole system running. Perhaps more important, a fault may develop in a transmission line or any other component. Some examples of this: a line is hit by lightning and develops an arc, or a tower is blown down by high wind. The function of the substation is to isolate the faulted portion of the system in the shortest possible time. There are two main reasons: a fault tends to cause equipment damage; and it tends to destabilize the whole system. For example, a transmission line left in a faulted condition will eventually burn down; similarly, a transformer left in a faulted condition will eventually blow upWhile these are happening, the power drain makes the system more unstable. Disconnecting the faulted component, quickly, tends to minimize both of these problems. Design The main issues facing a power engineer are reliability and cost. A good design attempts to strike a balance between these two, to achieve sufficient reliability without excessive cost. The design should also allow easy expansion of the station, if required.

Selection of the location of a substation must consider many factors. Sufficient land area is required for installation of equipment with necessary clearances for electrical safety, and for access to maintain large apparatus such as transformers. Where land is costly, such as in urban areas, gas insulated switchgear may save money overall. The site must have room for expansion due to load growth or planned transmission additions. Environmental effects of the substation must be considered, such as drainage, noise and road traffic effects. Grounding (earthing) and ground potential rise must be calculated to protect passers-by during a short-circuit in the transmission system. Of course, the substation site must be reasonably central to the distribution area to be served. Distribution substation A distribution substation in Scarborough, Ontario disguised as a house, complete with a driveway, front walk and a mown lawn and shrubs in the front yard. A warning notice can be clearly seen on the "front door". A distribution substation transfers power from the transmission system to the distribution system of an area. It is uneconomical to directly connect electricity consumers to the main transmission network, unless they use large amounts of power, so the distribution station reduces voltage to a value suitable for local distribution. The input for a distribution substation is typically at least two transmission or subtransmission lines. Input voltage may be, for example, 115 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility. The feeders run along streets overhead (or underground, in some cases) and power the distribution transformers at or near the customer premises. In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. Distribution substations are typically the points of voltage regulation, although on long distribution circuits (of several miles/kilometers), voltage regulation equipment may also be installed along the line.

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NORTH CHENNAI THERMAL POWER STATION. North Chennai Thermal Power Station is situated about 25 KMs from Chennai on Northern side. NCTPS has a total installed capacity of 630 M.W comprising 3 units of 210 M.W each. All the three units are coal based.Coal for NCTPS is received from Mahanadhi coal fields Limited (Talchar & IB Valley), Orissa, Eastern coal fields Limited, Ranikanj, West Bengal.Plant load factor(PLF) for the year 2008-09 is 86.52 % The coal required for the Four Thermal Power Stations of TNEB viz. Ennore (450 MW), North Chennai (630 MW), Mettur (840 MW) and Tuticorin (1050 MW) Thermal Stations is supplied by M/s. Coal India Ltd (CIL) through its subsidiary companies of M/s. Mahanadhi Coalfields (MCL) in Orissa and M/s. Eastern Coalfiels Ltd., (ECL) in West Bengal through Railcum-Sea-cum-Rail route. The coal from the mines Talcher and Ib Valley of MCL and Raniganj and Mugma of ECL is transported to the load ports of Paradip (Orissa), Vizag (Andhra Pradesh) and Haldia (West Bengal) respectively through rail. Thereafter the coal is transported to the discharge ports of Ennore and Tuticorin by ships. From Ennore Port the coal is transported again through rail to Ennore Thermal Power Station and Mettur Thermal Power Station. For North Chennai Thermal Power Station the coal is transported by belt conveyor from the ship directly. At Tuticorin the coal received is fed to TTPS directly through belt conveyor system available at Port. Handling contractors are being engaged for handling of coal at load ports (Haldia, paradip and Vizag) and discharge Ports (Ennore and Tuticorin). The annual coal requirement for TNEB thermal stations is of the order of 14.5 million tonnes. The maximum daily requirement when all the units in all 4 stations work to the full capacity will be around 50,000 MTs. Heat into mechanical energy The second law of thermodynamics states that any closed-loop cycle can only convert a fraction of the heat produced during combustion into mechanical work. The rest of the heat, called waste heat, must be released into a cooler environment during the return portion of the cycle. The fraction of heat released into a cooler medium must be equal or larger than the ratio of absolute temperatures of the cooling system (environment) and the heat source (combustion furnace). Raising the furnace temperature improves the efficiency but complicates the design, primarily by the selection of alloys used for construction, making the furnace more expensive. The waste heat cannot be converted into mechanical energy without an even cooler cooling system. However, it

may be used in cogeneration plants to heat buildings, produce hot water, or to heat materials on an industrial scale, such as in some oil refineries, plants, and chemical synthesis plants. Typical thermal efficiency for electrical generators in the industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants. Plants designed to achieve peak efficiency while operating at capacity will be less efficient when operating off-design (i.e. temperatures too low.) The Carnot cycle is the theoretically most efficient closed thermodynamic cycle for conversion of heat energy into useful work, and practical fossil-fuel stations cannot exceed this limit. In principle, fuel cells do not have the same thermodynamic limits as they are not heat engines. Generator cooling While small generators may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the generator enclosure first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air. The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere. The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV, an insulating barrier such as Teflon is used to interconnect the water line and the generator high voltage windings. Demineralized water of low conductivity is used. [Generator high voltage system The generator voltage for modern utility-connected generators ranges from 11 kV in smaller units to 22 kV in larger units. The generator high voltage leads are normally large aluminum channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator high voltage leads are connected to step-up transformers for connecting to a high

voltage electrical substation (usually in the range of 115 kV to 765 kV) for further transmission by the local power grid. The necessary protection and metering devices are included for the high voltage leads. Thus, the steam turbine generator and the transformer form one unit. Smaller units, may share a common generator step-up transformer with individual circuit breakers to connect the generators to a common bus. Monitoring and alarm system Most of the power plant operational controls are automatic. However, at times, manual intervention may be required. Thus, the plant is provided with monitors and alarm systems that alert the plant operators when certain operating parameters are seriously deviating from their normal range. Battery supplied emergency lighting and communication A central battery system consisting of lead acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power plant's control systems, communication systems, turbine lube oil pumps, and emergency lighting. This is essential for a safe, damage-free shutdown of the units in an emergency situation. Transport of coal fuel to site and to storage Most thermal stations use coal as the main fuel. Raw coal is transported from coal mines to a power station site by trucks, barges, bulk cargo ships or railway cars. Generally, when shipped by railways, the coal cars are sent as a full train of cars. The coal received at site may be of different sizes. The railway cars are unloaded at site by rotary dumpers or side tilt dumpers to tip over onto conveyor belts below. The coal is generally conveyed to crushers which crush the coal to about ¾ inch (6 mm) size. The crushed coal is then sent by belt conveyors to a storage pile. Normally, the crushed coal is compacted by bulldozers, as compacting of highly volatile coal avoids spontaneous ignition.