mejia thermal power station(seminar)
TRANSCRIPT
Seminar on
Mejia Thermal power Station(DVC)
Introduction
Location and overview of the Plant
Power Plant Layout
Step wise procedure in generation of power
Topics to be discussed
What is a Power Station?
A power station or power plant is a facility for the generation of electrical power. Power plants basically convert other forms of energy, like chemical energy, gravitational potential energy or heat energy into electrical energy. At the center of nearly all power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor.
INTRODUCTION
Located at Durlavpur in Bankuradistrict in West Bengal.
Established in March 1996 Total
capacity=(4*210+2*250+2*500)MW, largest in West Bengal
16.2 Km long spiral welded MS water pipeline for transporting water from the right bank of Damodar river
220 m high RCC multi flue stack in Phase-I & 279 m in phase-II which helps in preventing air pollution. Its’ affluent water utilization plant has a dual purpose of water conservation & minimization of liquid affluent discharge.
Location and overview of the Plant
Thermal Power Station
A Thermal Power Plant converts the heat energy of coal into electrical energy. Coal is burnt in a boiler which converts water into steam. The expansion of steam in turbine produces mechanical power which drives the alternator coupled to the turbine.Thermal Power Plants contribute maximum to the generation of Power for any country . Thermal Power Plants constitute 75.43% of the total installed captive and non-captive power generation in India . In thermal generating stations coal, oil, natural gas etc. are employed as primary sources of energy.
Overall layout of the Plant
Coal Handling Plant
Coal transported from mines by railway
wagons
Unloaded to a moving
underground conveyor belt
Crusher house(20mm)
Dead storage(40 days)
Live storage(8 hrs)
(boiler House)
Coal MillPulverized
coal(200 mesh)
Boiler(hot air+coal dust)
Combustion
Conveyor System Live Storage(Boiler House)
Dead Storage
Pulverizing System
In modern thermal power plant , coal is pulverised i.e. ground to dust like size and carried to the furnace in a stream of hot air. Pulverising is a means of exposing a large surface area to the action of oxygen and consequently helping combustion. Pulverising mills are further classified as:1. Contact mill2. Ball mill3. Impact mill
Boiler is an enclosed vessel in which water is heated and circulated until the water is turned in to steam at the required pressure. Coal is burned inside the combustion chamber of boiler. The products of combustion are nothing but gases. These gases which are at high temperature vaporize the water inside the boiler to steam.
Types of Boiler:
1.Fire tube
2.Water Tube
Boiler and Auxillaries
Water tube Boiler
Schematic Representation Boiler Drum: Consists of steam
separators and dryers. Separate water and steam from the mixture generated in water wells. The drum internals reduce the dissolved solid contents of the steam.
Furnace is primary part of boiler where the combustion of oil and pulverized coal takes place.
The super heater are placed in the flue gas path to transfer heat by radiation and convection in such proportion that the outlet steam temperature can be maintained fairly constant at all loads
Reheater for reheating the low pressure steam (exhausted by HP turbine) again to 540°c are arranged in radiation zone
Economizer tubes recover some of the heat from the heat carried away in the flue gases up the stack and utilize for heating the feed water to the boiler
AIR PREHEATER, which increased the temperature of air supplied to the boiler. The purpose of air pre heater is to recover the heat from the boiler flue gases which increased the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas.
Schematic Representation
Boiler feed pump
De-aerator
Induced Draught Fan
Forced Draught Fan
Primary Air Fan
Seal Air Fan
Ignition air Fan
Scanner Fan
Several Boiler Auxillaries
A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft
Types:
1.High pressure(HP) 180Kg/cm sq. 540°c
(single flow cylinder)
2.Low pressure (LP)
(double flow cylinder)
3.Intermediate
Pressure(IP)(double flow cylinder)
TURBINE
A condenser is a device or a unit used to condense a substance from its gaseous it its liquid state, typically by cooling it. In so doing, the latent heat is given by the substance, and will transfer to the condenser coolant
Condenser
The condensate (water) formed in the condenser after condensation is initially at high temperature. This hot water is passed to cooling towers .Cooling tower is a device for reducing the temperature of the water by bringing it contact with an air steam where small portion of liquid is evaporated and major portion is cooled.
Types:
1. Natural Draught
2. Forced Draught
Cooling Tower
The river water contains suspended matter with colloidal particles & inorganic impurities which make it necessary for chemical & mechanical treatment.
Before entering to the D.M. Plant, the raw water passes through another plant i.e. Pretreatment Plant as:
DE-MINERALIZED PLANT (DM PLANT)
AerationFluxmixture
(Alum)Stealing chember
Separation chember
ClarifloculatiorGravity filter
bedFeed water Reservoir
D.M. Plant
DE-MINERALIZED PLANT (DM PLANT)
ACF
• ACTIVATED CHARCOAL FILTER: It is the set of filters having activated charcoal dust. Free residual chlorine & colloidal particles are eliminated in this portion.
SAC
• STRONG ACID CATION EXCHENGER: It consists of resin beds. It eliminates organic molecules & functional group (strong cations like H+)
DGTANK
• DE-GASIFIED TANK: Water is sprayed & atomished H2CO3. Thus remove CO2 from the water.
WBA
• WEAK BASE ANION EXCHANGER: It eliminates Sulphates & Chlorides. But Silica passes through it.
SBA• STRONG BASE ANION EXCHANGER: It extracts Silica from the water.
MB
• MIX BED: If any element passes through the above filters, they are extracted well in this portion. & finally produce the DM Water.
Ash Handling Plant
The percentage of ash in coal
is 5% in good quality coal &
about 40% in poor quality coal.
Power plants generally use poor
quality of coal , thus amount of
ash produced by it is quite large.
A modern 1000MW plant
produces about 4800 tons of ash
daily.
The stations use some conveyor
arrangement to carry ash to
dump sites such as SILO for
cement manufacturing industry.
A particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge.
Used to remove fly ash and other colloidal particles, from the exhaust flue gas before entering Chimney.
Electrostatic Precipitator(ESP)
Simplified Diagram For The Operation Of ESP
2 sets of electrodes insulated from each other.
The first set is composed of rows of electrically grounded vertical parallel plates called the collecting electrodes, between which the dust-laden gas flows.
The second sets of electrodes consist of wires called discharge or emitting electrodes that are centrally located between each pair of parallel plates. The wire carries a unidirectional negatively charged high voltage (between 20-100 KV) from an external DC source (HVR).
Electrostatic Precipitator(ESP)
Collected particulate matter is removed from plates by a mechanical hammer scrapping system run by rapping motors.
The vibration knocks the particulates matter off the collecting plates and into a hopper at the bottom of the precipitator.
Electrostatic Precipitator(ESP)
Converts mechanical power into electrical form and feeds it into the power system network. The working principle behind the operation of Alternator is Faraday’s law of electromagnetic induction. The induced alternating voltage in a generator can be expressed as-E=4.44fTФ VoltsWhere,E=Voltage induced in volt.f=frequency of rotation in Hz.T=no. of turns.Ф=flux per pole in Wb.
Alternator
The purpose of excitation system is to continuously provide the appropriate amount of D.C field current to the generator field winding. The types of excitation system are
1. DC excitation
2. Static excitation
3. Brushless excitation.
Excitation System
Brushless Excitation System
Heart of excitation system of the generator.
Uses semiconductor elements to achieve high reliability with very fast response.
Has two independent channels, the auto channel with close loop voltage regulation and the manual channel with open loop regulation.
Automatic Voltage Regulator
Stator Cooling
Coolant is Water
2 full capacity single stage centrifugal pumps with change over facility 3Ph. 415V A.C motor drive the pump
The stator water is shell and tube type heat exchanger
through which DM water flows.
Generator Cooling & Sealing System
Rotor Cooling System
Hydrogen Gas is coolant
Cooling Fans
Propeller type cooling fans at both the ends of rotors are provided for forced circulation of H2 (H2 cooled machines) or air (air-cooled machines) inside the generator.
Generator Cooling & Sealing System
KW 500Mw
PF 0.85 lag
KVA 588000
Stator Voltage 21kv
Stator Current 16200A
Rotor Voltage 340Volt
Rotor Current 4040A
rpm 3000
Frequency 50Hz
Connection YY
Coolant Water & Hydrogen
Gas Pressure 3.5bar(g)
Insulation Class F
Specification of Alternator
KW 39
KVA 65
Volts 220
Amps 195
rpm 3000
Phase 3
Coolant Air
Insulation Class F
Connection YYYY
YYYY
Specification of PM generator
KW 3780
Volts dc 600
Amps dc 6300
Excitation Volts dc 107
Excitation Amps dc 142
rpm 3000
Coolant Air
Insulation Class F
Specification of Exciter
Generator protection concerns especially the electrical protection of machines and associated circuits. The purpose of generator protection is to provide protection against abnormal operating condition and during fault condition.
Generator Protection
Generator Protection
Abnormal Running Condition
Over current protection
Over load protection
Over voltage protection
High flux density
Unbalance loading protection
Loss of excitation protection
Loss of prime mover protection
Pole slip protection
Fault Condition
SC current protection
1. Pole slip protection
2. Inter turn fault protection
3. Back up impedance protection
Stator Earth fault protection
1. 95% stator earth fault protection
2. 100% stator earth fault protection
Rotor earth fault protection
The process of interconnection of the generator with the grid which a number of generators are already connected is known as synchronization. For successful synchronization and parallel operation of the generator the voltage, frequency and phase sequence of the incoming generator must be same as that of the grid(running system).
Synchronization
Transfers electric energy from 1 AC circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage
in MTPS Phase-II there are 2 sets of Generating Transformers(GT) (each set for each Alternator unit). Each set comprises of 3-single phase transformers connected as star in output and delta at input.
Each 1-phase 200MVA transforms 21KV to 400KV known as Generating Transformer(GT)
Each Station Transformer(ST) transforms incoming 400kv from switchyard to 11kv
Further stepped down to 3.3KV by SATand 415V by SST
Transformers
1-Single Phase GT 1 Three-Phase ST
Transformers
Interconnections of Various Transformers
Transformer Cooling
Types of Cooling:
1. Oil Natural Air Natural
2. Oil Natural Air Forced
3. Oil Forced Air Natural
4. Oil Forced Water Forced
5. Oil directed Air Forced
6. Oil directed Water forced
Transformer Cooling
1. Oil Natural Air Natural : Here natural convectional flow of hot oil is utilized for cooling. In convectional circulation of oil, the hot oil flows to the upper portion of the transformer tank and the vacant place is occupied by cold oil. This hot oil which comes to upper side, will dissipate heat in the atmosphere by natural conduction, convection & radiation in air and will become cold.
Transformer Cooling
2. Oil Natural Air forced: Heat dissipation can obviously be increased, if dissipating surface is increased but it can be make further faster by applying forced air flow on that dissipating surface. Fans blowing air on cooling surface is employed. Forced air takes away the heat from the surface of radiator and provides better cooling than natural air.
Transformer Protection
Common Transformer faults:
i. Open Circuits
ii. Overheating
iii. Winding short-circuits (eg.-earth-faults, phase-phase faults and inter-turn faults)
Transformer Protection
The principal relays and systems used for transformer protection are :
(i) Buchholz devices providing protection against all kinds of incipient faults i.e. slow-developing faults such as insulation failure of windings, core heating, fall of oil level due to leaky joints etc.
(ii) Earth-fault relays providing protection against earth-faults only.
(iii) Overcurrent relays providing protection mainly against phase-to-phase faults and overloading.
(iv) Differential system (or circulating-current system) providing protection against both earth and phase faults.
Transformer Protection
Buchholz Relay Earth Fault Relay
Overcurrent Relay
Switchyard
Definition: Switchyard is basically a yard or an open area where many different kinds of equipment are located (isolator, circuit breaker etc.), responsible for connecting and disconnecting the transmission line as per requirement (e.g. any fault condition).
Switchyard
Bay: It is a basically a way for the incoming power from generator as well as outgoing power for distribution. Power transmission is done at a higher vol. Therefore, the power generated by the turbo generator are stepped up to 400 kV are transmitted thereafter
Switchyard
Components:1. Bus Bars2. Circuit Breakers3. Pre-Insertion Resistors4. Grading Capacitor5. Isolator6. Earth Switch7. Current Transformer (CT)8. Capacitive Voltage Transformer (CVT)9. Lightning Arrester10. Wave Trap11. Battery Room12. Control Panel
Bus Bars
Bus bars are conductor to which no. of circuits are connected. The selection of any bus bar system depends on the amount of flexibility required in operation, immunity from total shut down, initial cost of the installation and load handled by the bus bar. Different bus bars schemes are as follows –
Single bus bar
Sectionalized single bus bar
Main & transfer bus.
Double bus double breaker.
Sectionalized double bus.
One &half breaker bus.
Circuit breaker is a device that makes and breaks the electrical contact between its input and output terminal. The circuit breaker is capable of clearing fault currents (tripping) as well as load currents. Circuit breakers are usually able to terminate all current flow very quickly, typically between 30ms and 150 msdepending upon the age and construction of the device.
Types:
1. Air-Blast Circuit breaker
2. Oil Circuit Breaker
3. Vacuum Circuit Breaker
4. Gas Circuit Breaker(SF6)
Circuit Breakers
The maximum switching over voltage occurs during closing of unloaded charge line. The function of Pre-insertion resistor is to reduce such over voltage during energization of charged or un-charged line and during auto-reclosure. These are fitted with arc extinguishing chamber of circuit breaker. Below 400KV system voltages, Pre-insertion resistors are not generally provided.
Pre-insertion Resistor
This is a high rating capacitor which is connected across the breaker contact. This capacitor maintain an equal potential at both the fix & moving contact to overcome heavy sparking and also decreasing the time period of arc extinguishing.
Grading Capacitor
Types:
1. Three post, center post rotating, double break type
2. Two post single break type
3. Pantograph type
Isolator
Disconnecting switches used for disconnecting a circuit under no current condition. Generally installed along with the circuit breaker. An insulator can be opened after the circuit breaker. After opening the isolator, the earth switch can be closed to discharge the trapped electrical charges to the ground. Isolator can operate only under no
load condition.
Double break type
Single break type
Pantograph type
Connected between the line conductor and earth. Normally it is open. When the line is disconnected, the earth switch is closed so as to discharge the charge trapped in the line.
Sequence of operation while opening or closing a circuit—
While opening-
Open circuit breaker
Open isolator
Close earth switch
While closing-
Open earth switch
Close isolator
Closed circuit breaker.
Earth Switch
Used for metering and relay purposes. The protective purposes include over current protection, overload earth fault protection, bus bar protection, and bus differential protection. Metering implies current measurement. The CTs used as MTPS phase –II are hermetically sealed units.
Current Transformer
Potential Transformer
Used in high voltage transmission networks, where it becomes increasingly economical.
It enables measurement of line to earth voltage by stepping down the voltage(110V) to relevant measuring devices rating.
A device designed to protect electrical equipment from transient high voltage, to limit the duration and amplitude of the follow current.
Connected between line and earth.
Consists of resistor elements in series with gap elements. Resistor element consists of blocks of non-collinear resistors and gap units consist of two conductor strips separated by gap.
Lightning Arrester
Traps the high frequency communication signals sent on line from the remote substation and diverts them to the telecom/teleprotection panel in the substation control room (through coupling capacitor and LMU).
This is relevant in power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleprotection signals and in addition, voice and data communication signals
Wave Trap
o Storage batteries are installed in rooms specially set apart and laid out for the purposes like Relay trip circuit, operating software’s & Hardware’s
o There are 220V & 24 V DC battery chargers installed and these are work in both BOOST & FLOAT mode.
Battery Room
The control and relaying equipment is installed in control rooms in the form of panels called control panels.
Control of generators, transformer circuits, etc. is provided on separate control desk.
The relays, meters and control units are mounted in or on control panels. Relays are mounted on separate panel call relay panels. Measuring instruments are placed on metering panels.
Control Panel
Single Flow Diagram of Unit-II
Seminar presented by:
I. Swadesh Banerjee
II. Jorseph Mahato
III. Shubham Kundu
IV. Bholanath Mondal
V. Koushik Giri
VI. Debanjan Kishore Roy