INDUSTRIAL TRAINING REPORT

ON2X500 MW POWER PLANT

UNDERTAKEN AT

BHARAT HEAVY ELECTRICALS LTD.

POWER SECTOR-EASTERN REGION, SITE- 2 x 500 MW PROJECT,

DSTPS, ANDAL, DURGAPUR, WEST BENGAL

CONTENTS

• Acknowledgement

• Introduction

• DSTPS: Andal 2x500 MW Power Plant

• Overview of the plant

• Main Structures of Plant

• Coal Handling Plant

• Boiler

• TG Section

• Balance of plant & Safety

• Electrical Package

• Switchyard

• Finance

• Conclusion

INTRODUCTIONBHARAT HEAVY ELECTRICALS LIMITED (BHEL) is one of the oldest and largest state owned engineering and manufacturing enterprise in India in the energy- related and infrastructure sector which includes Power, Railways Transmission and Distribution, Oil and Gas sectors and many more. It is the 12th largest Power equipment manufacturer in the world. BHEL was established more than 50 years ago, ushering in the indigenous Heavy Electrical Equipment industry in India. The company has been earning profits continuously since 1971-72 and paying dividends since 1976-77.74% total power generated in India is produced by equipment manufacture by BHEL.

It is one of the India's largest Public Sector Undertakings or PSUs , known as the Navratnas or “the nine jewels”.

Vision

A World Class Engineering Enterprise Committed to Enhancing Stakeholder Value.

Mission

To be an Indian multinational engineering enterprise providing total business solutions through quality products, systems and services in the field of energy, industry, transportation, infrastructure and other potential areas.

Values

• Zeal to Excel and zest for change.

• Integrity and Fairness in All Maters.

• Respect for Dignity and Potential for Individuals.

• Strict Adherence to Commitments.

• Ensure Speed of Response.

• Foster Learning, Creativity and Team Work.

• Loyalty and Pride for the Company.BHEL’s utility sets in India

DSTPS:ANDAL 2X500 MW POWER PLANT

This project report for “On Vocational Training” is submitted on the basis of self undergone first-hand training at Durgapur Steel Thermal Power Station (DSTPS), from 1st june ,2012 to 21st june,2012. Here 2(two) units, each of capacity 500MW, are under construction by M/s BHEL who has been awarded this contract on Turnkey basis by M/s Damodar Valley Corporation (DVC), the owner of this project, having head office at Kolkata.

• Name of Project:-

2x500 MW DURGAPUR STEEL THERMAL POWER STATION

• Location:

Andal, Durgapur, Dist.-Burdwan (West Bengal)

• Name of Customer:

Damodar Valley Corporation (DVC)

• Name of Contractor:

Bharat Heavy Electricals Limited

• Area:

The total area of the plant is 3.47sqkm.

• Seismological data: The area falls in Zone-3 of seismological zone.

• Communication: The site is located 0.5 km away from NH-2. The nearest railway station is Andal station which is about 3 km away from the site.

Vendor List:

• Prasad & Co. (Civil Works) – Unit – I

• M/s Power Mech. Pvt. Ltd. – Erection & Fabrication (Unit I)

• Bridge & Roof Co. (I) Ltd. – Unit II & UNIT I

• Bridge & Roof Co. (I) Ltd. - Erection & Fabrication (Unit II)

• NBCC- Chimney (RCC Shell including MS Twin Flue)

• Paharpur Cooling Towers Ltd. – Cooling Tower (Unit I & II) on EPC basis.

Layout of the Plant

FIG: LAYOUT OF 2 x 500 MW DSTPS, Andal

CLASSIFICATION OF POWER CYCLES

Vapour Power Cycles: Gas Power cycles:

Rankin cycle Otto cycleReheat cycle Diesel cycle Regenerative cycle Dual combustion cycle Binary vapor cycle Gas turbine cycle A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle.

A Rankine cycle with a two-stage steam turbine and a single feed water heater.

Typical diagram of a coal-fired thermal power station

1. Cooling tower 10. Steam Control valve 19. Superheater

2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan

3. transmission line (3-phase) 12. Deaerator 21. Reheater

4. Step-up transformer (3-phase) 13. Feedwater heater 22. Combustion air intake

5. Electrical generator (3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure steam turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan

9. Intermediate pressure steam turbine 18. Bottom ash hopper 27. Flue gas stack

The plant can be divided into four main circuits, namely:-

1. Fuel & Ash circuit.

2. Air & Gas circuit.

3. Feed water & Steam circuit.

4. Cooling Water circuit.

1.FUEL &ASH CIRCUIT:-

Fuel (coal ) is fed from storage at Coal Handling Plant (CHP )to the Boiler furnace using fuel feeding device. The ash produced, as a result of combustion of coal in the furnace to produce heat, collects at the back of the furnace & this ash is removed to ash storage using ash handling equipments initially & then to Ash Handling plant using other means of transport.

2. AIR & GAS CIRCUIT:-

Air for combustion is fed to the boiler furnace using Forced Draught fans (FD fans). This air is initially passed through the air-preheater where the air uses the heat of flue gases & gets heated up. The waste flue gases are then made to pass through chimney using Induced Draught fans (ID fans).

3. FEED WATER & STEAM CIRCUIT:-

The feed water & steam circuit consists of the Boiler,Condenser, Condensate Extraction Pump(CEP), LP Heater, HP Heater, Deaerator, Boiler Feed Pump(BFP).

4 . COOLING WATER CIRCUIT:-

Large amount of water is required to convert the steam utilized in Turbine back to water in the Condenser & to maintain a low pressure.

Hot water Cooling Tower CW Pumps

(cold water)

Condenser Condensing steam

COAL HANDLING PLANT (CHP):

Coal is the primary fuel of a thermal power plant. This coal, if fed to the boiler furnace in the form of large chunks, would result in inefficient, incomplete & smoky combustion. Hence this coal is pulverized (finely grinded into powdered form) in multiple stages in the coal handling plant to ensure complete & efficient combustion. Raw coal is carried out of the coal bed with the help of conveyor belt & sent to the CHP.

The following steps take place in a CHP:-

1. Coal receipt & unloading in the station.

2. Coal crushing and removal of impurities in the crusher house.

3. Manual sorting and storage of coal.

4. Transportation of the crushed coal to the coal bunker through conveyor belts.

Now it becomes ready to be used in the boiler furnace.

Specification of the coal used:

• Calorific value - 3500-4000 kcal/kg

• Grade - F

Coal consumption:

• On the basis of time: 150 tonnes/hour (approx.)

• On the basis of power produced: 0.6 tonnes/kW

N.B.- Sulphur content is an important aspect in choosing coal. It determines how fast it can catch fire.

BOILER

BOILER DESCRIPTION AT DSTPS,DURGAPUR

TYPE: - Top supported Fusion welded ww panels

Controlled circulation & Tangential firing

RATED: - 500 MW

Design Pressure: - 209 kg/cm2

Design Temperature: - 368 Degree-Centigrade

Superheater Outlet Pressure: - 191 kg/cm2

Superheater Outlet Temperature: - 540 Degree-Centigrade

Reheater Outlet Pressure: - 52.4 kg/cm2

Reheater Outlet Temperature: - 540 Degree-Centigrade

Design Code:- IBR

• HYDRAULIC TEST PRESSURE

1. For Boiler (including Eco & Super heater):- 313.5 kg/cm2

2. For Reheater: - 78.60 kg/cm2

Boiler operation

Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners

tangentially and it rapidly burns, forming a large fireball at the center. The thermal radiation

of the fireball heats the water that circulates through the boiler tubes near the boiler

perimeter. The water circulation rate in the boiler is three to four times the throughput and is

typically driven by pumps. As the water in the boiler circulates it absorbs heat and changes

into steam at 700 °F (370 °C) and 3,200 psi (22,000 kPa). It is separated from the water

inside a drum at the top of the furnace. The saturated steam is introduced into

superheat pendant tubes that hang in the hottest part of the combustion gases as they exit the

furnace. Here the steam is superheated to 1,000 °F (540 °C) to prepare it for the turbine.

Boiler description

• Water tube

• Top supported

• Fusion welded water wall panels

• Controlled circulation

• Tangential firing

Boiler steam capacity - 1625 tonnes/hour

Boiler installed in DSTPS is divided into two passes:

•Pass 1- It houses the furnace, divisional pendent super heater, platen super heater and re-heater front.

•Pass 2- it houses the economizer and low temperature super-heater.

BOILER FURNACE AND DRUM

Once water is inside the boiler or steam generator, the process of adding the latent heat of vaporization or enthalpy is underway. The boiler transfers energy to the water by burning of coal. The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum. Once the water enters the

steam drum it goes down the down comers to the lower inlet water wall headers. From the inlet headers the water rises through the water walls and is eventually turned into steam due to the heat being generated by the burners located on the front and rear water walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor once again enters the steam drum. The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum. The steam separators and dryers remove the water droplets from the steam and the cycle through the water walls is repeated. The boiler furnace auxiliary equipment includes coal feed nozzles.

WATER AND STEAM CIRCUIT OF 500 MW BOILER, DSTPS

RAW MATERIALS

The materials used for power generation are coal, LDO and water.

1.Primary Fuel

The primary fuel is coal. The coal consumption of the station is 200 ton/hr.

2.Secondary Fuel

The Secondary Fuel used in plant is Light Diesel Oil (LDO). Specific LDO Consumption of the division is 0.76ml/kwh.

Fuel Oil System

The main purpose of the fuel oil system is to facilitate start up the boiler, flame stabilization at low load/unstable flame condition with pulverized coal as the fuel. The fuel oil system, in addition to serving this purpose, is also capable of carrying about 20% of the boiler MCR load. The fuel oil system hence comprises of two subsystems namely-

• LDO SYSTEM- Light Diesel Oil is also provided for initial lighting up of the furnace during cold start up before firing with HFO.

• HFO SYSTEM- The Heavy Fuel Oil, which shall be used during normal operation, being quite viscous requires being preheated to attain requisite viscosity at the burner for proper atomization and combustion.

3.WATER

The plant gets its supply of water from Raw Water reservoir.

• BOILER ACCESSORIES:-

1. AIR PREHEATER:-

If the air entering the boiler furnace is pre-heated, better combustion is ensured. Pre-heating the air is done in an air preheater resulting in complete combustion of even low grade fuels like LIGNITE. The heat of the flue gases is utilized to preheat the air entering the boiler furnace. The thermal efficiency of the plant also increases as a result of this preheating.

2. ECONOMIZER:-

The economizer is a boiler accessory which is used to heat the Feed Water entering the Boiler Drum, the heat being taken from the flue gases. Commonly Green’s Economizer is used in Power Plants. Since the feed water is already heated to a high temperature, steam can be quickly produced from it in the furnace by using lower amount of heat thus increasing the boiler efficiency.

3. SUPERHEATERS:-

The steam vapor picks up more energy from hot flue gases outside the tubing and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high pressure turbine.

Superheater Tubes

Desuperheaters:

Provided in 1.superheater connecting links2.cold reheat line

• IMPORTANCE OF DE-SUPERHEATER:-

To permit reduction of steam temperature when necessary so as to save the high temperature superheater walls from being subjected to excessively high temperature.

The desuperheaters used in the reheater system is meant for emergency condition.The reheat steam temperature is controlled mainly by tilting burners.

4.REHEATERS:-

The reheater consists of a single stage having 2 Sections-

Front & rear pendant vertical spaced. The front section located between the rear water wall

hanger tubes and the superheater platen section. The rear section is located between water

wall screen and rear wall hanger tubes. Power plant furnaces may have a reheater section

containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high

pressure turbine is passed through these heated tubes to collect more energy before driving

the intermediate and then low pressure turbines.

Air circuit and the necessary equipments:1. PRIMARY AIR FAN(P.A Fan):-

Primary air fan supplies the air for sealing the bearing from coal powder in the coalmill ,drying and transporting the pulverized coal from the mill classifier to the boiler furnace. The PA fan is an axial type fan. There are 2 PA fans each having 2 stages and 20 blades in each stage.

Circuit: Atmospheric airPA fanAir Preheater inletAir Preheater outlethot air common duct mill inlet housingmill discharge valvecoal pipeburner

Blades of P.A fan at unit 2,DSTPS

2. FORCED DRAUGHT FAN:-

The FD Fans supply secondary air, which is heated by Air Pre-heater. Secondary air is required to provide excess air for combustion in the furnace. There are 2 FD Fans each having a single stage with 18 blades present in the stage.

Circuit: Atmospheric airFD FanAir Preheater inletAir Preheater outletwindboxfurnace

N.B:- 1)The amount of air inducted by the PA fan and FD fan is controlled by hydraulic oil pressure which reciprocates the cylinder of the servo-motor controlling the blade pitch thus contolling the blade speed and affecting the amount of the air induced.

2) The different parts of the fans are as follows:

a)diffuser

b)housing

c)suction chamber

d)expansion joint

e)silencer

f)roof assembly

3. INDUCED DRAUGHT FAN:-

Two ID Fans are provided at the base of the chimney, which suck the flue gases produced due to combustion of Coal & discharge these gases through the chimney. ID fan is a radial type fan and its speed is controlled by variable frequency drive.

4. COAL MILL:-

Coal Mill is a very critical part of a power plant both from operation and maintenance point of view. It is a very important boiler auxiliary as it pulverizes the coal and feeds the pulverized coal to the boiler via the burner.

5. ELECTROSTATIC PRECIPITATOR:

The principle components of an electrostatic precipitator are two sets of electrodes insulated from each other. The first set is composed of rows of electrically grounded vertical parallel plates, called the collection electrodes, between which the dust-laden gas flows. The second set of electrodes consists of wires, called the emitting electrodes that are located between each pair of parallel plates. The wires carry a unidirectional negatively charged high- voltage current from an uniform electric field whose magnitude is greatest near the discharge electrodes. When that voltage is high enough, a blue luminous glow, called a corona, is produced around them. Electrical forces in the corona accelerate the free electrons present in the gas so that they ionise the gas molecules, thus forming more electrons and positive gas ions. The new electrons create again more free electrons and ions, which result in a chain reaction. The positive ions travel to the negatively charged wire electrodes. The electrons follow the electrical field towards the grounded electrodes, but their velocity decreases as they move away from the corona region around the wire electrodes towards the grounded plates. Gas molecules capture the low velocity electrons and become negative ions. As these ions move to the collecting electrode, they collide with the fly ash particles in the gas stream and give them negative charge. The negatively charged fly ash particles are driven to the collecting plate by the force of electric field. When the particles collect on the grounded plates, they lose their charge on the ground. Collected particulate matter must be removed from collecting plates on a regular schedule. Removal is usually accomplished by a mechanical hammer scrapping system.

Corona Formation

View Of ESP,DSTPS,Andal

ASH HANDLING PLANT

Fly ash generated is transferred to ESP Hopper and stored in the Silo. The ash stores is disposed via various processes, one of them is Wet disposal. the fine particles are carried away by water which takes it to the slurry sump. The mixture of ash and water is known as slurry. Slurry sump acts as suction tank for the slurry pump which delivers the slurry from the sump to ash pond. The ash is deposited in the pond and the overflowing water is recycled.

Structure based building in power plant

• Power house

• Mill & Bunker

• ESP controlled building

• T.P.(Transfer Point)

• Chimney

• Compressor House

• C.W. Pump House

• Air Washer Pump House

• Pipe & Cable Rack

Turbogenerator

The turbo-generator forms the heart of a power plant. A turbo-generator consists of a turbine generator and other auxiliaries like condenser, pipelines carrying superheated steam etc.

TurbineThere are three turbines installed in DSTPS- HP turbine, IP turbine and LP turbine. Steam via main steam line at 170-175 bar pressure and 540 ˚C temperature enters HP turbine. Steam after partial expansion in HP turbine goes to re-heater via Cold Reheat Line (CRH). From re-

heater, steam then enters IP turbine via Hot Reheat line (HRH). Steam after partial expansion in IP turbine directly enters into LP turbine through Cross Around pipe (CAP). Steam after expansion in LP turbine goes into condenser. Extraction of steam is done to feed the HP and LP heater.

TURBINE SPECIFICATIONSLoadRated Load 500 MWMaximum Load under valve wide open(VWO) condition

524.9 MW

SpeedRated 50 c/sMaximum Speed, no time limitation 51.5 c/sMinimum Speed 47.5 c/s

TG AUXILLIARIES

1. CONDENSER 2. VACCUM PUMP3. CONDESATE EXTRACTION PUMP 4. LP HEATER 5. HP HEATER 6. BOILER FEED PUMP 7. DEAERATOR

CondenserCondenser is basically a heat exchanger.The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases.

Diagram of a typical water-cooled surface condenser. 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 100 °C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented.

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.The cooling water used to condense the steam in the condenser returns to its source without having been changed other than having been warmed. If the water returns to a local water body (rather than a circulating cooling tower), it is tempered with cool 'raw' water to prevent thermal shock when discharged into that body of water.

VACUUM PUMPVacuum is created in the condenser by vacuum pump so that steam directly flows into the condenser. In absence of vacuum pump, the water will strike back the turbine blades. There are two vacuum pumps installed in each unit of DSTPS which are being procured from abroad.

CONDENSATE EXTRATION PUMP (CEP)

The condensate is extracted from the condenser with the help of condensate extraction pump. There are three CEPs installed in each unit of DSTPS namely CEP-A, CEP-B and CEP-C.Specification of CEP:

• BHRC 28T TYPE CONDENSATE EXTRACTION PUMPS (210 MW):• PUMP• 3 numbers per unit• Multistage, vertical turbine centrifugal pump• Low specific speed, medium head• Medium capacity• Discharge 281T/hr• Manometric 201m• Head • NPSH 3.5 m• RPM 1489• No. of stages 8• HP 256• MOTOR• Power 220kW (300 HP) Voltage 6.6kV

LP HEATER:The condensate is heated at low pressure in the LP Heater. This heating is done by bled steam via suitable point from the low pressure turbine.

DEAERATORIt is fitted in between the LP heater & HP heater to draw out the dissolved gases & air present in the feed water. The temperature of water rises after passing from LP heater. It uses hot steam for this purpose as high temperatures reduces the solubility of the dissolved gases in the feedwater, thus driving them away.

HP HEATER : Water coming out of the Deaerator is heated in the HP Heater at high pressure.

BOILER FEED PUMP:

Feed water is delivered to the boiler with the help of boiler feed pump. There are two types of BFP’s:

• MDBFP - Motor Drivebn boiler feed pumps. Here we have 2 such pumps. These pumps are used when the plant is not in full operation.

• TDBFP - Turbine Driven boiler feed pumps. Here we have a single such pump. It is used when the plant is in full running condition.

Parts of a BFP:• BOOSTER Pump• Hydraulic Coupling• Feed Pump

Specification of BFP:

• Number of stages 6• Suction pressure 12.3 atm.• Quantity of water for minimum take off 100 tons/hr • Discharge capacity / head 430 tons/hr/1830MWC • Quantity of water for warming up 8 tons/hr• Feed water temperature 164.20 C• Consumption of cooling water 280 LPM • Speed 4320 rpm • Lubrication Forced• Stuffing box Mech. Seal • Net weight of pump 5850 kg

COOLING WATER(CW) CYCLE:-

• VARIOUS PARTS OF A CW CYCLE:

• CW PUMP AND PUMPHOUSE

• HOTWELL

• NDCT(Natural Draught Cooling Towers)

• CW RESERVOIR

CW PMP & PUMP HOUSE - It comprises of 3 main parts :-

a) Sump area b) Feed pool c) Duct area

Eight chambers are constructed where CW pumps are placed. The water in the chambers will be pumped to condenser through C.W. conduits.The water from the cooling tower is conveyed into the feed pool through the CW duct. Water is stored in the feed pool and sump area.

Apart from the 8 CW Pumps, we have two AUXILLIARY COOLING WATER Pumps( ACW Pumps).

HOTWELL - The cooling water, after heat exchange with the condensate in the condenser, collects in the hot well.

NDCT - The cooling water used to condense steam is pumped to the cooling tower for its own cooling, and recirculation. The shape of the NDCT’s is so designed so as to ensure max. rate of cooling by natural air. The height of the NDCT’s at Andal site is 126m.

Cooling towers of DSTPS

BALANCE OF PLANT (BOP)

Balance of plant includes all those portions of the power plant other than those related to the Boiler & Boiler House and Turbines. These includes-

• Refrigeration including AC• Ventilation • Diesel Generation• Battery system• Compressed air system• DM Plant• Fire fighting• Cooling water system

1. Refrigeration - It is the process of removing heat, and the practical application is to produce or maintain temperatures below the ambient. Here the refrigerant used is R22 i.e. HCFC.

AIR HANDLING UNIT (AHU) - The main purpose of the air handling unit is to supply cool air to the various offices and control panel rooms, removing the hot air present within them. , but during the winter months when we require air at a temperature greater than the ambient for room heating, then in the air washer, air is cleaned only but no cooling. The air is then heated by means of heaters.

2. Ventilation System - is separate for each unit. It serves the TG hall, MCC, switch gear room, etc. Other offside plant and other buildings, which are not connected with main ventilation system, are provided with ventilation fans of adequate numbers.

3. DIESEL GENERATOR- In load shedding condition, the diesel generators (two running and one in standby condition) will keep the plant working by supplying power when plant power line and power line from the grid are tripped.

4. BATTERY SYSTEM- When diesel generator, power line from the grid and plant power line are all tripped charged batteries are kept in battery room from which power is used for only some important drives.

5. COMPRESSED AIR SYSTEM- In the compressor house, different compressors are present so as to provide compressed air to required parts of the power plant. There are two types of compressed air :

• Instrumentation air –Mainly required for valve operations (pneumatic valves)

• Secondary air – Mainly used for cooling purposes

6.DM PLANT - The water that is circulated in the boilers is essentially demineralised water (DM water). DM water is used because it is free from minerals which would have caused scale formation and corrosion in the different boiler parts.

N.B. – Pure DM water is deadly. It corrodes any surface in contact, very much. Hence DOSING OF NaOH is done. It is added to remove its acidic nature & make it alkaline in nature.

Dissolved oxygen (DO) of water is made less than 20 ppb. & pH is about 8.

7. FIRE FIGHTING SYSTEM - Some red coloured tanks are provided in the plant that stores water for extinguishing fire. Fire water pump house is present where pumps are installed to pump water to the fire affected zone.

8. COOLING WATER SYSTEM – This system includes cooling of the water,used to cool the condensate, which have already been discussed in TG section.

• Fire water pump house 2. Fire water tank & DM water tank

ELECTRICAL PACKAGE

MAJOR ELECTRICAL COMPONENTS :

• GENERATOR

• ISOLATED PHASE DUCT

• GENERATOR TRANSFORMER

• STATION START UP TRANSFORMER

• UNIT TRANSFORMER

• UNIT AUXILIARY TRANSFORMER

• SEGREGATED PHASE BUS DUCT

• DISTRIBUTION TRANSFORMERS

• AUXILIARY TRANSFORMERS

• MEDIUM VOLTAGE SWITCHGEARS

• SECONDARY UNIT SUBSTATIONS

• MOTOR CONTROL CENTERS

• MAIN GENERATOR [ 500 MW /21 KV /2 pole /50Hz ]

The generator produces electrical power from mechanical power. The three primary components of a generator are the rotor, exciter and the stator.

STATOR: it has two primary parts: the stator core and the armature windings.

The core is constructed out of a donut shaped laminated iron alloy sheets that have slots around the inner circumference. It has a dual purpose of supporting the armature windings and concentrating the magnetic flux around the conductors of the armature.

The armature windings are located in the stator slots. The induced voltage from the rotating field produces current in the conductors. The current being large in magnitude creates significant heating due to I2R losses. In order to remove this heat, the conductors are hollow and cooled with H2 gas.

The hydrogen is circulated in the generator in a closed circuit by a multi-stage axial fan located on the turbine end. The fan sucks hot gas from the air gap and delivers it to the cooler where it is cooled and re-circulated.

The generator generates 3-phase power with 3 voltages 120 degrees apart in phase.

The armature leads exit the generator at the bottom and passed through cubicles with pt and ct for metering and protective relays. Here the neutral grounding equipment is used for monitoring the current in the neutral with protective relays.

ROTOR: the rotor on the main generator is composed of a steel shaft to which a field winding has been added. The field winding is located is located in slots machined into the rotor. This shaft connects to the main turbine shaft and rotates at the same rotational speed as the turbine. When dc current is passed through the field winding the rotor forms an electromagnet with N-S poles. Here the rotor has two pole designs. It has a fan mounted on each end of the shaft. The fan is used to farce gas into the generator for cooling. Here the gas used is hydrogen due to its high heat transfer capacity.

EXCITER: The exciter provides the dc current to the field windings. Its output can be varied to control the armature voltage. This is done by varying the amount of dc current to the field winding. The exciter is typically a self-excited ac generator mounted on the same shaft as the rotor and turbine. Its output is rectified by a series of power diodes providing dc current for field winding. the exciter uses collector rings and brushes to pass the dc current to the rotor. The exciter used here is AVR (automatic voltage regulator).

The three phase pilot exciter is of revolving field type with permanent magnet poles. The three phase AC generated in the stator is fed to the field of the revolving armature main exciter via a stationary regulator and rectifier unit. The three-phase AC induced in the rotor of the main exciter is rectified in the rotating rectifier bridge and fed to the field winding of the generator rotor via the DC lead in the rotor shaft.

• ISOLATED PHASE BUS DUCT

It is used to connect the high voltage and the high current output of the generator to the step-up and step-down transformers.

It is comprised of large aluminium tubes approximately 18 inches in diameter. The tubes form a protective enclosure to house the actual energised bus bar which is mounted on the insulators. Each phase of the three phase system is isolated from the other two phases thereby minimising the possibility of short-circuit involving all three phases. The inner and outer tubes have field-welded connections with expansion joints that allow for the thermal expansion and contraction of both the conductors and housing tubes.

Large capacity bus ducts have cooling systems that circulates cooling air through the tubes to remove heat.

• GENERATOR TRANSFORMER[Three 1-phase delta-star / 200 MVA/ 21 KV/400KV]

The step-up transformer transforms the voltage from the generator to a higher voltage necessary for the transmission of the generator’s power over the grid. These large power transformers come in 2 basic configurations: single 3-phase transformer or 3 single phase individual transformers.

It is necessary to use 3 single phase transformers for step-up transformer application as the size of generators grow. An added benefit of this configuration is that a spare single phase transformer can be provided economically for back-up protection for a transformer failure.

• STATION START-UP TRANSFORMER[3 phase/ 90 MVA / 400 KV/ 11.5 KV]

The station transformer is a power transformer used to connect the power station to

the transmission system so that power available for the plant equipment when the plant is being started. This transformer provides the so called “Start up” power .The Start-up transformer is also used when the plant is being shut down to power the station equipment that operates regardless of whether the plant is producing power.

• UNIT TRANSFORMER[3 phase/25 MVA/21 KV//11.5 KV]

The Unit transformer is connected to the generator output by a tap off of the Isolated Phase Bus Duct. The high voltage winding of the transformer is designed to match the generator output voltage which is 21 KV here. This particular transformer is a three winding transformer. It has primary winding and two separate secondary windings at different voltages. This allows the station to have two different voltage levels one at 11 KV and the other at 3.3 KV. The higher voltage afforded by the 11 KV windings allows for the use of similar higher voltage motors for the large pumps or fans. The higher voltage motors offer several advantages over 3.3 KV motors such as higher starting torques and lower full load currents.

The Unit transformer is the normal power source for the station equipment when the plant is operating. Once the generator is brought on line and is connected to the transmission grid, the station loads can be transferred from the Start-up transformer. This would normally be done by closing the feed breakers from the auxiliary transformer while the feed breakers from the Start-up transformer are still closed. As soon as the auxiliary breakers are closed the plant operators open the feed breakers from the Start-up transformer.

6. UNIT AUXILIARY TRANSFORMER[3 phase/ 16 MVA/ 11.5 KV/ 3.3 KV]

The unit auxiliary transformer steps down the 11 KV output from the unit transformer to 3.3 KV and changes the switchboard to supply the various motors rated for the particular voltage. It is also protected by MV switchgear.

7. SEGREGATED PHASE BUS DUCT

Segregated phase bus duct is typically used to connect the station auxiliary transformers low voltage windings to the station switchgear. Some stations use parallel runs of cable or more isolated phase duct in lieu of Seg bus. Segregated bus duct is comprised of copper bus bars which are insulated and held in place with a support system made of fibre glass or some other non conducting material. All these bus bars are surrounded by a grounded metal enclosure.

Once installed and tested, segregated bus duct is a highly reliable component providing years of service with little maintenance required.

8. DISRIBUTION TRANSFORMER [3 phase/1000 KVA,1600 KVA,2000 KVA/11.5KV/415V]

These transformers ar used to provide 3 phase 415 V supply to low power rated motors and for general lighting of the area and household supply.

They can be of – 1) Dry type 2) Oil cooled

9. AUXILIARY TRANSFORMERS

a) Station service transformer

b) Ash handling transformers

c) DM and CW service transformer

d) Fuel-oil pump house transformers.

e) Vacuum pump house transformers.

f) Ash slurry transformers.

g) Service building or compressor house transformers.

h) Workshop or hydroplant service transformers.

i) Fire water transformers.

j) Ash water recirculation transformers.

k) Raw water transformers.

l) Make-up water transformers.

m) Water treatment plant transformers.

n) Coal handling plant track hopper transformer.

Transformers for ESP

10. MEDIUM VOLTAGE SWITCHGEAR

The 11KV and 3.3 KV buses shown in the one line diagram represent the palnt medium voltage switchgear. Switchgear refers to a line-up of equipment to house circuit breakers, protective relays and control wiring. The switchgear is completely enclosed in a metal structure that preventa individuals from coming in contact with the lethal voltages within this equipment.

Switchgear is made up of a series of cubicles which are bolted together in a row. Each

cubicle contains a rear section where the bus bars are located , a lower compartment where the circuit breaker resides , and an upper compartment where the protective relays and breaker control wiring is located. Typically, the incoming or feed breakers are located on the ends of the switchgear line up.

Each CB is mounted on a rack and the breaker is rolled or jacked into various positions such as all the way in which is the connected or in-service position, partially withdrawn which is the test position and fully withdrawn which is he disconnected position. While in the test position, the CB can be operated but it is not connected to the live bus bars. This allows functional tests to be performed on the breaker. Each cubicle contains protective relays in the top portion. This type of relay varies depending upon the breaker application. Typically , each breaker will have as a minimum some type of over current relay and ground fault relay. Vacuum CB are used in the plant for medium voltage.

11. SECONDARY UNIT SUBSTATIONS

Secondary Unit Substations (SUSs) are essentially a repeat of the configuration of the station auxiliary transformer and the Medium Voltage Switchgear but at a lower voltage. Breakers from one of the plant switchgear will feed a transformer that will reduce the voltage to 415 V. This transformer is an integral part of a line–up of 415 V switchgear. Sometimes the Unit Substations are designed with a transformer at each end of the switchgear. These are referred to as “double ended” secondary unit substations.

These are used to feed the large majority of components in a power plant by further distributing power to load centres, motor control centres and battery chargers. In addition, medium range motors 200 to 300 horsepower are fed by individual 415 V SUS circuit breakers.

12. MOTOR CONTROL CENTRES

Based upon sheer numbers of components fed, Motor Control Centres feed to most components in the power plant. These include motor operators for valves, small to medium motors, lighting panels, receptacle power panels to name a few. Motor control centres are composed of vertical sections of cubicles or buckets. Each bucket contains a moulded case CB. , motor starter, control transformer, control fuses and wiring. In the rear of the MCC buckets, vertical bus bars distribute power to the different buckets. The vertical sections of buckets are bolted together to form the MCC. Below is a picture of an outdoor Motor Control Centre.

Motor Control Centres are located throughout the power plant and are placed near groups of loads for convenience. Outdoor MCCs are located in an additional enclosure for weather protection. A door opens to reveal each vertical section.

11 KV MOTORS: Are connected with:

• PA fan

• ID fan

• CW Pump

• MDBFP (Motor Driven Boiler Feed Pump)

• FD fan

3.3 KV MOTORS: Are connected with:

• Condensate Extraction Pump (CEP)

• Bowl Mills

• Boiler Cooling Water

• Service Air Compressor

• IA Compressor

• Auxiliary Cooling Water

• De-mineralised cooling water turbogenerator.

• Demineralised cooling water service generator.

• HP water pump

• Conveying water pump

• Slurry disposal pump

• DIESEL GENERATORS - In load shedding condition, the diesel generator will keep the plant working by supplying power. These generators are operated on diesel. There are three diesel generators, with two running and one in standby condition.

Specifications:

• Phase- 3 Phase

• Rating- 1500 KVA

• Power factor- 0.8

• Output voltage- 415 V

• Power- 1200 KW

• Frequency- 50 Hz

• VARIABLE FREQUENCY DRIVE

VFD’s are used in ID fans to control the speed of rotation of the fan blades, and hence the speed and amount of the discharge through the chimney.

Various areas of application:

• Fans

• Pumps

• Compressors

• Static stators

COOLING: Indirect Cooling:

Definition: Indirectly cooled machines dissipate their losses to a cooling medium, which is entirely outside the coil insulation. All air-cooled machines, with rare exceptions, are cooled in the manner, as well as most hydrogen-cooled machines under 100mm VA. Turbo-generators rated above 100mVA usually employ direct cooling.

Cooling Media: Air is the most commonly used medium. Hydrogen provides better heat transfer with much less wind age loss, which is nearly proportional to density. Frequently hydrogen is used at higher than atmospheric pressure, which further improves its heat transfer capabilities but with greater wind age loss. Other advantages of hydrogen are the reduction of insulation oxidation and fire hazards. The hydrogen is circulated in the generator in a closed circuit by a multi stag axial fan located on the turbine end. The fan sucks hot gas from the air gap and delivers it to the coolers ,where it is cooled and re-circulated.The hydrogen at the outlet of the coolers is divided into three flows-the first portion is admitted into the rotor at the turbine end below the fan hub for cooling of the turbine.the second portion is passed from the cooler section to the individual frame compartments for cooling the stator core.the third portion is passed to the stator in winding space and the excitor end through guide ducts in the frame for cooling of the excitor end half of the rotor and the core end portion.after taking away the heat generator at various parts in their paths,these parts flows or discharge into the air gap where they are mixed and returned to the fan and finally to the cooler.

Direct Cooling:

Definition: Direct cooling is the process of dissipating the armature and field coil losses to a cooling medium within the main conductor insulation wall. Machines cooled in this manner medium is in either direct contact with the conductor copper or is separated only by thin materials having little thermal resistance. Direct cooling eliminates the temperature differential resulting from heat flow through the coil insulation, providing greater current-carrying capability for the same hot-spot temperature rise.

Cooling Media: Hydrogen, water and oil are normally used. Most directly cooled turbine generators operate in a hydrogen atmosphere, which provides cooling for all the machines except, in some instances, the armature coils. These may be cooled from the common hydrogen stream or by a separate oil, water or high-pressure hydrogen steam. Because of the limited cross section available within the coils for cooling medium flow the temperature raise of the cooling medium in absorbing the heat loss is usually the most important factor determining the hot-spot temperature raise. Direct water-cooling of the rotor windings of very large turbine generators are also employed. Direct cooling is also applied to salient pole synchronous capacitors and hydro generators of the largest rating. The direct cooling medium is usually water. Electrical insulation with hydrogen direct cooling must also allow for adequate creep age distances at the coil hydrogen inlets and outlets. Oil and hydrogen system require in addition, insulated piping. Water is de ionized to maintain electrical conductivity. In rotating machinery the heat is dissipated principally by convention. For small machines, either by natural cooling or by a fan mounted on the shaft, heat can be dissipated. For bigger machines the core masses becomes too large to be adequately cooled by either outer surface. Radial and axial ducts must be used together with proper means of supplying cooling air to the new surface exposed. As one of the most difficult case, the turbo generator with its exceptionally massive core requires a highly elaborate gaze duct cooling system, in order that all parts of the core may be kept at temperatures within the limits imposed by the insulation.

SWITCHYARD

• What is a Switchyard?

The switchyard is a junction connecting the Transmission & Distribution system to the power plant.

• What is a Substation?

An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers.

• What is the difference between Switchyard and Substation?

The function of substation is to stepping up or down the voltage as per requirements. It receives electrical power via incoming transmission lines and delivers electrical power via the outgoing transmission lines.

The function of Switchyards is to deliver the generated power from power plant at desired voltage level to the nearest grid.

• ELEMENTS OF A SUBSTATION :

1. Incoming Lines.

2. Outgoing Lines.

3. Substation Equipments.

• Galvanized steel structures for towers, gantries and equipment support

• Bus Bar

• Insulators

• Lightning Arrestor

• Circuit Breaker

• Isolator

• Earthing Switch

• Current Transformer

• Voltage Transformer / Capacitor voltage transformer

• Power transformer

• Shunt reactor/Capacitor

• Power Cables

• Control Cables for protection and control

• Control and Protection Panel

• PLCC Equipments

• LV AC Switchgear

• DC Battery and Charging Equipment

4. Station Earthing Systems.

5. Station Lighting System.

6. Fire Fighting System.

7. Air Conditioning System.

Description of the main equipments-

Bus-bars – There are two types of busbars – Strain busbars and Rigid busbars. String busbars consists of ASCR conductors strung with sag compensating spring. Rigid busbars are tubular

conductors. Such busbars have high rigidity and reduced corona.

Lightning Arrestor/ Surge Diverter – In switchyard, the first and the last equipment is lightning arrestor, also called surge arrestor, as it protects the switchyard from any surges. Temporary over-voltages may be caused by a number of system events such as line to ground fault , circuit back feeding , load rejection, ferro-resonance. There may be also other internal surges known to be switching surges. A lightning arrestor resembling a safety valve of the system diverts these over voltages to ground by lowering its resistance.

Bus Post Insulator (BPI) – It is an insulator meant for only providing mechanical strength to the cables and maintaining a safe clearance distance.

The cylindrical structure with the three stack Porcelain insulator is called the CVT.

Capacitor Voltage Transformer (CVT) - It is combination of capacitive voltage divider and conventional EMVT measuring a reduced proportional voltage. As CVT consists of inductance in iron core and of capacitance, it would be subjected to ferro-resonance oscillations and transient phenomenon. Hence ferro resonance suppressor device is used. CVTs are used in EHV substation both as voltage transformer as well as coupling capacitor for power line carrier application.

• OUTDOOR COMMUNICATION EQUIPMENT:

• Line or Wave trap : It is an air cored inductance in series with the line at the entry point of the switchyard and offer a high impedence block to carrier frequency (15 Hz to 40,000 kHz) preventing it from entering switchyard equipments. Thus the carrier frequency is led to the electronic equipment through coupling capacitor, which offers low impedence to high frequency but high impedence to power frequency. Tuned LC filter is used here.

Reactors – As transmission lines generate capacitive VAR, compensation of the same by shunt reactor is necessary for control of increasing voltage. This capacitive VAR increases with increasing order of system voltage used, length of line and depends on spacing and configuration of conductors and becomes predominant.

.

. The central structure is CT.

Current Transformer (CT) – CT is a series connected transformer having single bar primary, several protection cores and one metering core of respective accuracy classes.The entire transformer element is kept in porcelain case with transformer oil in sealed condition and is pressurized by nitrogen for reducing corona.

Isolators – It is used for no load opening or closing of circuits. They can be operated remotely by motorized , hydraulic, pneumatic mechanisms or manually.Isolators have their positional switches at their mechanism boxes for development of a set of contacts according to ‘ON’ or ‘OFF’ status of the isolators.

Circuit Breaker (CB) - CBs are designed to oprate in faulty condition of circuit and have rated making and breaking capacities in MVA. Calculation of fault MVA by network analysis is essential for selection of CB to be of adequate capacity. Breakers are operated by either spring or hydraulic or pneumatic energy. There are different types of CB. The type of circuit breaker used here is SF6 type circuit breaker. SF6 being a strong electronegative gas, it is de-ionized and recovers breakdown voltage rapidly and arc extinguishes at natural current zero.

Earthing – There are two types of earthing – System earthing and Equipment earthing.The neutral point of a str connected system is earthed to avoid floating neutral condition and consequent over stressing of equipment by over voltage during unbalanced loading.

• System Earthing – When the system neutral is directly grounded without any impedence, the system is said to be effectively grounded. If current limiting device such as reactor is used in grounding circuit, then the system is said to be non-effectively earthed.

• Equipment Earthing – Under fault condition, the non current carrying metal parts attains a high potential at the fault location, and a potential gradient is developed along the path of the fault current which includes metallic part of the equipment and earth return path through soil. To limit the touch voltage along the metallic surface of the equipment and step voltage along the soil surface around the equipment, the non-current carrying metallic parts are connected to the general mass of earth by multiple electrodes.

Lightning mast – Switchyard is protected from lightening by installation of lightening masts having suitable height and distance between them so that the highest point of any equipment or conductor remains within the calculated protective zone under the masts.

BUS BAR SYSTEM :

Bus bar is that conductor where feeders from generating station & feeders for different load centre are connected. The type of arrangement adopted depends on various factors viz. to ensure uninterrupted and reliable power supply distribution, should be economically viable , should be easy for operation and maintenance , should be more flexible.

There are several bus bar systems. The advanced circuit breaker scheme is One and Half Breaker Scheme represented by the following picture.

CONTROL AND INSTRUMENTATION

The instrumentation system of a thermal power plant has two parts --- Measurement & Control.

Measurement part deals with the measurement of different parameters of the process by

deploying different sensor which is mainly known as primary instrument and brings it (measured value) in the notice of operating personnel by displaying it on indicator or recording it on recorder or storing it in Data Acquisition System (DAS) or in some cases, by generating audiovisual alarm signal & protective signal. Indicator, Recorder & DAS are mainly known as secondary instrument.

Sometimes, primary instrument i.e. primary sensing device is termed as Transmitter or Transducer. Transduction means the conversion of energy. So Transducer is the device, which converts energy from one form to another form.

Control part takes care for automatic/manual control of different parameters of the process. Error generator, controller (mainly PI controller) . In some cases it may be PID controller), auto/manual station, amplifier, electrical to pneumatic converter, actuator, etc. are the main component of control part.

Pressure Measurement

Pressure & Vacuum are the most common & important process parameter of a thermal power plant. Depending upon the importance of the parameter, which is to be measured, either Pressure Gauge or Electronics Transmitter is used for measurement of that particular parameter.

The Electronics Pressure Transmitters, which are normally used in thermal power station, are mainly either (i) Reluctance Type or (ii) Capacitance Type.

Temperature Measurement

Temperature may be defined as Degree of Heat, where as heat is usually taken to mean Quantity of Heat. Depending upon the importance of the parameters, which is to be measured, either Expansion thermometer or Change of state thermometer or Radiation and Optical Pyrometer or Electrical method of temperature detection system is normally used in thermal plant. Out of above said thermometers, only Expansion thermometer and Electrical type thermometer are widely used.

For measurement of temperature at those points / parts of the process, which are remote & critical from location point of view and / or which demands accuracy, precision and remote transmission, are normally measured by deploying Electrical method of temperature detection system. Normally, K – type Thermocouple (TC), Copper Resistance thermometers (CRT) and Platinum Resistance thermometers (PRT) are widely used in a thermal power plant. We know, by means of a suitable apparatus, a change of temperature can be converted into a variable electrical quantity i.e. voltage, current or resistance. TC, CRT & PRT operates on the basis of this phenomenon.

Resistance Temperature Detector (RTD): The resistance of pure metallic conductors

increases with temperature and this change can be detected electrically. RTD operates on the basis of this principle. It is a highly accurate method of temperature measurement and particularly useful for measurement of lower temperature scales down to – 400 OF and can be used up to 1300 OF.

In practice, Copper, Nickel and Platinum wire are used for RTD because they can be manufactured to a high degree of purity and they have high temperature co-efficient and are able to resist corrosion and oxidation. Normally, CRT is used for lower temperature scales. Nickel is a cheap substitute of Platinum up to 600 OF and Platinum can be used up to 1300 OF.

Measurement of Level:

In thermal power plant, measurement of level is essential for the purpose of safe and efficient operation of the plant. For the purpose of co-ordination and control, level measurement is also required. When liquid level is monitored for the purpose of guidance for operating personnel, level is measured by sight glass method. These are normally known as Direct Gauge Glass. Local gauges of Deaerator water level, Condenser Hot well level, Boiler Drum water level, HP heaters & LP heaters shell water level (HPH’s & LPH’s drip level), Lube oil tank level, etc falls under this category. In some cases, level is measured for remote indication and for control. For this type of level measurement differential pressure transmitters (dp transmitter) are normally used. The dp transmitter may be of LVDT type, Reluctance type or Capacitance type

Now a day, resistance method of liquid or water level measurement is widely used for measurement water level of pressurized vessel i.e. for measurement of boiler drum water level, Deaerator water level, HPH’s shell water level, etc.

CONTROL OF PROCESS PARAMETERS:

We know that in a thermal power station, controlling of some process parameters are essential for safe and economic operation of the unit or station.

The controls in a thermal power station may be Pneumatic or Electronic.

The control system of a process industry consists of the followings:

Measurement of Flow:

Like pressure, temperature and level, flow is also most important process parameter, which is monitored continuously for purpose of Control, Co-ordination and Safe Operation of the process.

In a thermal power plant, flow of liquid as well as flow of solid is also measured for periodic as well as for on line efficiency calculation, which plays an important role in the modern concept of power plant operation, of the process.

Normally, rate flow instruments are widely used for measurement of flow of Steam, Feed Water, Spray Water, Fuel Oil, Air, D. M. Water etc and integrators are used for measurement of flow of Coal.

Normally, in a Thermal Power Plant, Orifice Plate, Flow Nozzle, Piezomatric Ring etc are used as restriction. Flow Nozzle is used for Steam Flow (M.S. Flow) and Feed Water Flow measurement. Orifice Plate is used for measurement of Condensate Flow, BFP & CEP re-circulation Flow, SH & RH attemparation Flow etc. Piezomatric Ring is used for measurement of Air Flow.

Analytical Instruments or Analyser:

Unlike the aforesaid instruments, where measurement is done by displacement and mechanical means – based on physical properties, some instruments are used to analyse the sample – based on chemical heating or paramagnetic effects. Such instruments are normally termed as ‘Analytical Instruments or Analyser’.

In a modern thermal power plant, analytical instruments are essential to measure ‘Oxygen in Flue Gas’, ‘Dissolved Oxygen in Feed Water’, ‘Conductivity of Feed Water’ at different points of the process or circuit, ‘PH of Feed Water’ at different points of the process or circuit, ‘Silica content of Feed Water’ and ‘Purity of Hydrogen’ in generator casing.

The indicating instruments are provided to monitor the process for safe and efficient operation

The recording instruments (Recorder, data Acquisition system) are provided to study the performance of the unit and to suggest the operating personnel regarding the correct way of operation. The recording instruments are essential to build up the history of the unit and play an important role in modification work for further improvement of performance .

The signaling or annunciating instruments alerts the operating personnel at right time to take corrective action for safe and efficient operation.The controlling instruments regulate the process to maintain the designed operating parameters.The instruments are, therefore, designed and provided at suitable locations of the power station for safe, efficient and economic operation.

SAFETY

“Out of this nettle, danger, we pluck this flower, safety.” ~William Shakespeare Industrial safety can generally be divided into two parts .The first of them being: ELECTRICAL SAFETY ELECTRIC SHOCK AND ITS AFTERMATH:

• When the body becomes a part of the electric circuit which is closed (contact with wires, wires and ground).

• Electric shock is affected by the current, its path and length of time it is in the body.

• Voltage, presence of moisture in the body and phase of the heart cycle also affects the severity of electric shock.

• Slight current such as 1mA may cause tingling sensations whereas 6mA- 30 mA can be quite painful for the muscles. Muscular contraction and resulting death is very likely for a current of about 1A-4.3 A.

• Low and high voltages are equally dangerous for the human body. Lower voltages for longer periods of time(100 mA) can cause muscular fibrillation whereas higher voltages break down human skin .

• Electric shock can cause electric burns, internal injuries and involuntary muscle contractions.

• Injuries are less severe if the current does not pass through vital organs or major nerve centres.

• Electric shock results from

• Contact with live parts.

• Lack of ground fault protection.

• Path to ground missing or discontinuous.

• Equipment not used properly.

• Improper use of extension cables.

INSPECTION & QUALITY

Quality means a totality of characteristics of an entity that bear on its ability to satisfy stated and implied needs. Quality is referred to as,- “fitness for use”, “fitness for purpose”, “customer satisfaction” or “conformance to the requirements”. To achieve satisfactory quality we must concern all stages of the product or service cycle. In the first stage quality is due to a definition of needs. In the second stage it is due to product design and conformance. In the last stage quality is due to product support throughout its lifetime.

There are basically 4 main quality system documents used in BHEL which are:

1. QUALITY MANUAL

2. STANDARD PROCEDURE

3. DEPARTMENTAL PROCEDURE

4. WORK INSTRUCTION

There are various other documents maintained by us and those are the guidelines for keeping Quality as our supreme motto which covers every aspects of power plant such as Welding Manual ,Heat Treatment Manual ,NDE Manual, Welding Procedure Specification, Recommended Hydrostatic Test Procedure ,etc.

THANK YOU