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