NTPC National Thermal Power Corporation

Project: Study the Working Principles and Functioning of the Power plant

-Anurag Reddy Manda-Ankitha Miryala

Installed Capacity Stage 1 - 3*200MWStage 2 - 3*500MW Stage 3 - 1*500MWTotal = 2600MW

Location Ramagundam, Andhra Pradesh, India

Coal Source South Godavari Coal Fields of Singareni Collieries for Stage 1&2Kobra Coal Fields of SECL for Stage 3

Coal Consumption

10 million tones per annum

Coal Transportation

Merry go round system of 21 km

Water Source Sri Ram Sagar Dam on Godavari River from Pochampad Reservoir

Transmission System

2457km of 400kv line

SAILENT FEATURES OF RAMAGUNDAM SUPER THERMAL POWER STATION(RSTPS)

-Salient Features Continued

Total land allotted for RSTPS

~10000 acres

Total Investment 20592.2 million rupees for Stage 1&218184.6 million rupees for Stage 3

Length of Earthed Dam 8.5km

Height of Chimney Stage 1 – 225mStage 2 – 229mStage 3 – 275m

Beneficiary States Andhra PradeshKeralaKarnatakaGoaPondicherryTamil NaduPGCIL(for HVDC)

-Salient Features Continued

Stage Unit Generation in MW

Date of Installation

1 IIIIII

200200200

November 1983May 1984

December 1984

2 IVVVI

500500500

June 1988March 1989

October 1989

3 VII 500 August 2004

UNITS COMMISSIONING SCHEDULE

DISTRIBUTION OF ELECTRICITY

State Distribution (MW)

Percentage

Andhra Pradesh

754 29%

Tamilnadu 598 23%

Karnataka 442 17%

Kerala 312 12%

Goa 130 05%

Pondicherry 65 2.5%

Out of the many departments in the power plant we have studied a few of them in detail.We have learnt about the following in the Electrical field: The Switch Yard The Generator Transformers The HT(High Tension) motors The LT(Low Tension) motors The ESP(Electro Static

Precipitators)

The topics learnt related to Mechanical and Civil fields ate as follows:

Boiler ( Operation and Maintenance)

Coal conveyer belts Coals mills Furnaces Feeders Boiler drum Condensers Super heaters

Topics studied

SWITCHYARD EQUIPMENT: Circuit Breakers Isolators Earth switch Bus Bar Surge/Lightning Arresters Current Transformer Capacitive Voltage

Transformer Wave trap One And Half Breaker

Scheme

To perform switchyard

operation activities perfectly, operation staff should have good knowledge about the equipment provided in switchyard as well as in control room. They should be familiar with the control system adopted here and a good understanding about the procedures to be followed during the emergencies, outage requirements and charging. Brief description about switchyard equipment is given below. 

The Switch yard

CIRCUIT BREAKER:It is an automatic device capable of making and breaking an Electrical Circuit under normal and abnormal conditions such as short circuits. SF6 is the arc quenching media for all the 400 KV and 220 KV breakers installed in the switchyard. Pneumatic operating system is provided in AEG, ABB and NGEF make breakers and Hydraulic operating system is provided in BHEL make breakers. 132KV breakers provided in 132 KV lines are of Minimum oil type operating on spring charge mechanism. ISOLATORS:Isolator is an off load device provided in conjunction with circuit breaker to disconnect the equipment or the section, which is to be isolated from all other live parts. The isolators provided in the switchyard are of central break type. The operation of Isolators can be done from control room (remote) or local. Motorized operation for opening & closing of Isolator is provided, however Isolators can also be opened & closed manually in the even of non-availability of motorized operation. EARTH SWITCH:Earth switch is mounted on the isolator base on the line side or breaker side depending upon the position of the isolator. The earth switch usually comprises of a vertical break switch arm with the contact, which engages with the isolator contact on the line side. Earth switch is required to discharge the trapped charges on the line or equipment (under shut down) to earth for maintaining safety. Earth switch can be operated only from local either by electrical operation or manually. BUSBAR:Busbar is an Aluminum tube of 4” IPS having wall thickness of 0.4”, where all incoming and outgoing feeders are connected in a schematic way to enable smooth operation and Maintenance of equipment without any interruption to the system. At RSTPS one and half breaker scheme is provided for 200 MW generator feeders and 400 KV outgoing lines, Two-breaker scheme is provided for 500 MW generator feeders.

SURGE / LIGHTING ARRESTERS:Surge Arresters are provided to ground the over voltage surges caused by switching and lighting surges. Surge Arresters provide leakage path to the ground whenever the system voltage rises above the specified value. They are equipped with surge monitors, which measures the leakage currents and a counter to record the number of surges taken place.CURRENT TRANSFORMER (CT): Current Transformers are provided to step down the current to low values suitable for measuring protection and control instruments. Current Transformers also isolate measuring and protective devices from high system voltage. CTs in the switchyard consist of five secondary cores. Core 1&2 are used for bus bar protection, 4 & 5 are for main 1&2 protection and core 3 is for measuring instruments.CAPACITIVE VOLTAGE TRANSFORMER (CVT):CVTs step-down the system voltage to sufficiently low value (110V) for measuring, protection and synchronizing circuits. CVT has a H.F. terminal point for receiving & transmitting the high frequency signals for carrier protection and communication. WAVE TRAP:Wave Trap is a parallel resonant circuit tuned to the carrier frequency connected in series with the line conductor at each end of the protected transmission line section. Wave trap offers high impedance path for high frequency signals and low impedance path for power frequency current. This keeps carrier signal confined to the protected line section and does not allow the carrier signals to flow into the neighboring sections. One and half breaker scheme : In Ramagundam we use one and half Breaker scheme with 3 current transformer method.

To interconnect generating station to the load centers different voltage transformations and power switching operations are necessary. The place where the voltage transformations and power switching operations takes place for evacuating power is called switchyard. 400KV Switchyard at Ramagundam super thermal power station

is the most vital switching station in the southern grid. A total of 2600MW of bulk power generated by three 200MW units and four 500MW units of NTPC Ramagundam is evacuated for supplying to the southern states.

Switchyard consist of two 400kv bus bar system fed by 7 numbers of generator feeders, 9 numbers of 400kv feeders, 3 numbers of 220kv feeders and two numbers of 132kv feeders as shown in the single line diagram of 400kv switchyard.

In addition to the above, three Tie Transformers, five Auto Transformers and two shunt reactors are provided as shown in the single line diagram of 400kv switchyard.

RSTPS 400KV SWITCHYARD

TRANSFORMER

Transformer is a static piece of apparatus by means of which electric power in one circuit is transformed to electric power of the same frequency of another circuit.Types of Transformers in a Power Plant Generator Transformer (GT) Unit Auxiliary Transformer (UAT) Station Transformer (ST) Tie Transformer Auto Transformer

The use of transformers has become inevitable in any thermal power plant rather in any industry today: For example: In 500MW generation at RSTPS stage-II, stage-III the

electricity is generated at 21KVand current is approximately 16000A. If we transmit the same electrical energy to the grid then to transmit a current of 16000A, we need very very heavy conductors, very strong transmission towers. Moreover, the lines loss shall be extremely high because current is very-very high and loss is proportional to the square of the current.

So, by using generator transformers (G.Ts) the voltage level is raised to the level of 400KV, hence the current level comes to 16000A to 800A. By doing so, the current is reduced approx. by 1/20 times.

Hence the losses are reduced by 1/400 times. The high voltage levels (i.e., 400kv) can be easily tackled by making high towers. The cost of such towers is quite low, comparatively and conductor size also will be very low for 800A current.

Properties: The efficiency of the transformer is very high, as there are no moving parts there are no mechanical losses.

Transformer Properties and Purpose

GENERATOR TRANSFORMER

The importance of Generator Transformer is that it is the prime component required for the transmission of energy(electricity produced) from the plant to the grid at a specific voltage. The GT’s are usually step-up transformers with where the Low-Voltage Delta windings energized by the generator voltage and the High-Voltage Star windings are connected to the transmission lines. The Generator is connected to this transformer by the bus duct. This transformer is used to step up the generating voltage of 18 & 21KV to grid voltage (400kV). This transformer is generally provided with OFAF cooling. It is also provided with off circuit/on load taps on the high voltage side. This transformer has elaborate cooling system consisting of number of oil pumps and cooling fans apart from various accessories.

SPECIFICATIONS OF THE TRANSFORMER:

Manufacturer Mitsubishi

No. of units 3

Rating HV&LV {MVA} 200MVA

Rated voltage, HV 420/3KV

Rated voltage, HV 21HV

Rated current, HV 825amps

Rated current, LV 9520amps

No. Of phases 1

Frequency 50Hz

Type of cooling OFAF(Oil Forced Air Fan)

The UAT draws its input from the main bus-duct connecting generator to the Generator Transformer.

The total KVA capacity of unit auxiliary transformer required can be determined by assuming 0.85 power factors and

0.9 efficiency for total auxiliary motor load.

It is safe and desirable to provide about 20% excess capacity than circulate so as to provide for miscellaneous auxiliaries and possible increase in auxiliary load.

UNIT AUXILIARY TRANSFORMER

The station transformer is required to feed power to the auxiliaries during start ups.

This transformer is normally rated for the initial auxiliary load requirements of unit. In typical cases, this load is of the order of 60% of the load at full generating capacity.

But in large stations where more than one units are

operating, the station transformers should have sufficient capacity to start two units at a time in addition to feeding the common auxiliaries.

It is also provided with on load tap changer to cater to the fluctuating voltage of the grid.

STATION TRANSFORMERS

The TIE Transformers are installed to tie (connect) between the GRID and the Station Auxiliaries through Station Transformers.

Generally it is used for two purposes one for it takes 400KV voltage from 400KV bus bar and step down to 33KV and it is used for station supply system having 33KV switch gear.

The capacity of TIE Transformer should be at least the sum of connecting station Transformers plus miscellaneous requirements.

The no of TIE Transformers more than one improves reliability.

 

TIE TRANSFORMERS

It is a single winding transformer this is used to increase or reduce the voltage at required level. Both primary and secondary are connected electrically, magnetically and mechanically. The portion of the winding works as primary and other as secondary.

The main purpose of autotransformer is to step down the high voltage to feed the load near by generating

station. The transformer used in NTPC {RAMAGUNDAM} having a tertiary, which is having a voltage of 33kv, but is not in use. To ensure security of supply, autotransformers are installed in two, three or four such that in case of one transformer being unavailable, the load is carried by remaining transformer.

AUTO TRANSFORMER

A Generator is an A.C/D.C machine that converts mechanical energy into electrical energy based on the principle faraday’s laws of electromagnetic induction. In an A.C generator, armature is stationary and field is rotatory. Whereas in a D.C generator the field system is stationary and armature is rotatory.

Operating principle: The magnetic poles are excited or magnetized from D.C supply by a D.C source i.e., D.C shunt generator, which is belted or mounted on the same shaft of alternator. Because the field magnet(s) is rotating this current is supplied through slip rings. When the rotor rotates the stator conductors are cut by the magnetic flux inducing EMF in them , because the magnetic poles are alternatively north and south . Due to the induced EMF, current is developed in armature conductors.

Generator

The Importance of Generator protection

The Generator is very complex and elaborative. Generator(s) is a large machine and is connected

to the bus bars. Unit transformer, Auxiliary transformer and bus system accompany it

It is also accompanied by excitation system, prime mover, voltage regulation system and cooling system etc., Hence it is not single equipment the protection of generators should be coordinated with the associated equipment.

It is a costly and an important equipment and therefore shut off would result in emergency power shortages.

Methods of protection

The Generator should be protected from several faults The present practice and other alternative protection from several other abnormal conditions are done using alarms and indications. A power plant whose installed capacity is >100MW should be properly protected from the faults below,

Excessive temperature in stator Differential protection Earth fault protection Stator inter turn protection Loss of field protection Uneven temperatures at bearings.

CRUSHERHOUSE: The coal from the track hopper is transferred to the

crusher house through conveyor belts. In this crusher house the coal is made into 20mm by crushing. The crushed coal is sent to the bunkers and some of the coal is sent to reserve called coal handling plant or stack yard.

BUNKERS:Bunkers are the coal storage tanks which will be near the boilers. The coal from the bunkers is sent to the mills. If the bunkers are filled up then the coal is sent to the coal handling plant to keep stock. In case of any interruption in the supply of coal, the coal is taken from the stack yard or coal handling plant and sent to the bunkers .we are using the special equipment called Reclaimers which consists of buckets so that the coal kept in the yard is taken through buckets and place on the conveyor belts.

MILLS

The most efficient way of utilizing coal for steam generation is to burn it into pulverized form. Coal can be pulverized in any of the following: Slow speed mills(15 to 25rpm) Medium speed mills(50 to 100rpm) High speed mills(750 to 1000rpm)Selection of the type of the mill depends on many factors but mainly on capital, operation, maintenance, cost and quality of end-product required. The milling system is considered as the heart of a power plant as it decides the overall performance of the power plant. The coal to be ground is fed into the center of the mill through a vertical

pipe connecting coal feeder & mill from the end of the center pipe the coal is dropped onto a revolving bowl. Centrifugal force causes the coal to travel it towards the perimeter of the bowl. During its travel the coal passes between the bull ring segments the grinding rolls. The springs which load the rolls impart the pressure necessary for grinding. The partially pulverized coal continues to flow outwards and over the edge of the bowl. Hot primary air enters the mill side housing below the bowl and is directed upwards through the annulus formed by separator body and bowl. This upward movement is through a fixed or rotating vane wheel. The pulverized coal is directly sent to boiler and heavier particles lose their momentum and return back to mills.

PA FANS:Primary air fan is used to discharge air to carry the fuel(Coal) from the mills to the boiler furnace. It is an axial type fan. These are present before the air preheaters where the ambient air gets heated up in the air heaters and then is passed to the pulverized. The pulverized coal in smooth powder form is lifted off by primary air discharged from the PA fan, then pass through the classifier to the coal nozzles at the burner section. There are two PA fans for each unit. FD FANS:The main purpose of this fan is to supply adequate amount of air to the furnace for complete combustion. It is an axial type fan. The air supplied by the PAF is not sufficient for combustion process. The additional air required is supplied using FD fans (2 per unit -50% capacities each). This sucks air from atmosphere pressurizes it and sends it into the furnace. Prior to sending pressurized air is heated in secondary air pre heater (SAPH). The source of heating in SAPH is the hot steam from low pressure turbine. FD fan maintains the pressure inside the furnace.

ID FANS: The main purpose of this fan is to suck the flue gases from

the furnace and send it to the atmosphere through chimney and maintain furnace draft. The ash particles in the flue gases are precipitated in the ESP (Electro Static Precipitator) before entering the ID fan. It is an axial entry and radial discharge type. It also maintains the pressure inside the furnace.

The flue gases pass through the ID fans enters the bus duct and then to the chimney. The provision of the bus ducts avoids the problem of air to be accumulated when one of the equipment fails. Example: If one of the ID fans does not work, another ID fan sucks the inlet air of the other ID fan through the common bus duct.

These fans have a lower speed and are less susceptible to wear and tear due to the abrasive flue gases. The control of the I.D. fans is achieved through a variable speed Hydraulic coupling and motorized inlet damper. By introducing variable speed control through a hydraulic coupling the losses in the fan at various load has been minimized and efficiency of the fan has remained high at all operating conditions.

Fire-Tube Boilers:Fire-tube boilers rely on hot gases circulating through the boiler inside tubes that are submerged in water. These gases usually make several passes through the tubes, thereby transferring their heat through the tube walls and causing the water to boil on the other side. Fire-tube boilers are generally available in the range of 20 through 800 boiler horsepower and in pressures up to 150 psi. Electric Boilers:Electric boilers are very efficient sources of hot water or steam, which are available in ratings from 5 to over 50,000 kW. They can provide sufficient heat for any HVAC requirement in applications ranging from humidification to primary heat sources. Water Tube Boiler:Here the heat source is outside the tubes and the water to be heated is inside. Most high-pressure and large boilers are of this type. In the water-tube boiler, gases flow over water-filled tubes. These water-filled tubes are in turn connected to large containers called drums.

BOILERS

Combustion of coal: Carbon, hydrogen, sulphur

are sources of heat on combustion.

Surface moisture removed on heating during pulverization.

Inherent moisture and volatiles are released at higher temperature, making coal porous and leading to char/ coke formation. (Thermal preparation stage)

Steaming Capacity:Large boiler capacities are often given in ton’s of steam evaporated per hour under specified steam conditions

A STEAM GENERATOR IS A COMPLEX INTEGRATION OF THE FOLLOWING ACCESSORIES:* ECONOMISER * LTSH* BOILER DRUM * DIV PANEL* DOWN COMERS * PLATEN SH* CCW PUMPS * REHEATER* BOTTOM RING HEADER * BURNERS* WATER WALLS * APHs

Steam Flows from Boiler to turbineSteam turbines are one of the oldest prime mover technologies still in use. Steam turbines extract heat from and transform it into mechanical work by expanding the steam from high pressure to low pressures

TURBINESTurbine is a shaft coupled to the generator and is divided in to three categories having same shaft coupling. 1. High Pressure Turbine (HPT) 2. Intermediate Pressure Turbine (IPT) 3. Low Pressure Turbine (LPT)Some quantity of steam is tapped from IPT, LPT and used to heat feed water in Low Pressure and High Pressure Heaters.

Characteristics Run from <1MW to >1300MW High pressure steam flows through the turbine blades and

turns the turbines shaft Steam turbine shaft is connected to and electric

generator for producing electricity. Power output is proportional to the steam pressure drop of

the steam - the larger the steam, the larger the output capacity of the turbine generator.

No emissions from a steam turbine

Classification of Turbines:Impulse and reaction TurbineThus the steam is generated and further action to struck the turbine then the turbines are two types i.e. impulse and reaction turbine. The diagrams are shown below

Impulse TurbinesAn impulse turbine uses the impact force of the steam jet on the blades to turn the shaft. Steam expands as it passes through the nozzles, where its pressure drops and its velocity increases. As the steam flows through the moving blades, its pressure remains the same, but its velocity decreases. The steam does not expand as it flows through the moving blades.

Reaction TurbinesIn the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor.

CONDENSERAfter expansion steam enters the condenser. The use of condenser improves the efficiency of the power plant by decreasing the exhaust steam pressure below atmosphere. Condensed steam can be recovered and provides a source of good and pure feed water to the boiler. Non-condensable gases are removed from the steam in the condenser.  CONDENSATE EXTRACTION PUMP (CEP)It is used to pressurize the water and to lift the water to de-aerator level.  LOW PRESSURE HEATER (LPH)It is a three stage heater to increase the feed water temperature to 130degrees. It is placed in between the CEP and de-aerator. The steam tapped from IPT and LPT is used to heat the coils in the LPH chamber containing pressurized water from CEP.

DEAERATOR:It is used to separate atmospheric air which may get mixed with steam as there is vacuum in the condenser and can damage the turbine blades. Water is sprinkled from the top to separate the dissolved gases and atmospheric air and pure feed water is collected. BOILER FEED PUMP (BFP): It pressurizes the feed water from De-aerator to about 200kg/cm2 and sends it to the boiler through the High Pressure Heater (HPH). HIGH PRESSURE HEATER: It is a two stage pressure heater to heat the feed water in HPH coils by using the tapped steam from turbine. In the coils, steam and feed water are sent in opposite directions for heat exchange. Feed Water Regulating System (FRS) regulates the quality of water to be fed in to the boiler.

Condensation Process

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100oC where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensable air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning. The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

ELECTROSTATIC PRECIPITATOR

It is a device which captures the dust particles from the flue gas thereby reducing the chimney emissionPrecipitators function by electrostatically charging the dust particles in the gas stream. The charged particles are then attracted to and deposited on plates or other collection devices.When enough dust has accumulated, the collectors are shaken to dislodge the dust, causing it to fall with the force of gravity to hoppers below. The dust is then removed by a conveyor system for disposal or recyclingElectrostatic precipitation removes particles from the exhaust gas stream of Boiler combustion process.

Six activities typically take

place

Ionization - Charging of particles Migration - Transporting the

charged particles to the collecting surfaces

Collection - Precipitation of the charged particles onto the collecting surfaces

Charge Dissipation - Neutralizing the charged particles on the collecting surfaces

Particle Dislodging - Removing the particles from the collecting surface to the hopper

Particle Removal - Conveying the particles from the hopper to a disposal point

ASH HANDLING PLANT

Fly Ash CollectionFly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks or railroad cars.

Bottom Ash Collection and Disposal At the bottom of every boiler, a hopper has been provided for collection of the bottom ash from the bottom of the furnace. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace. Some arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom ash to a storage site.

Familiarization of the Power Plant     

Submitted by

Anurag Reddy MandaAnkitha Miryala

 Department of Electrical Engineering

The Pennsylvania State UniversityUniversity Park, PA 16802

 May 31st, 2013

Thank You

-Ankitha Miryala-Anurag Reddy Manda