STUDY OF ELECTRICAL SYSTEMS IN VIZAG STEEL PLANT

A PROJECT REPORT ON

Electrical Systems in Vizag Steel Plant UNDER THE GUIDANCE OF

SRI AJEET KUMAR SEN

ASSISTANT GENERAL MANAGER(ELECTRICAL)

THERMAL POWER PLANT

A Dissertation report submitted to the

TRAINING AND DEVELOPMENT CENTRE

RASHTRIYA ISPAT NIGAM LIMITED

In partial fulfillment of the degree of

PROJECT TRAINING IN ELECTRICAL ENGINEERING

SUBMITTED BY:-

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CONTENTS

S.No

TOPIC Page No.

1 CERTIFICATE 04

2 ACKNOWLEDGEMENT 05

3 DECLARATION 06

4 ABSTRACT 07

5 THERMAL POWER PLANT -AN INTRODUCTION 08

6 POWER REQUIREMENT 10

7 SOURCES OF POWER 13

8 MAIN EQUIPMENTS OF TPP. 20

9 BOILERS 21

10 TURBO-GENERATORS 25

11 TURBO-BLOWERS 36

12 AUXILIARIES OF TPP 37

13 POWER GENERATION AND DISTRIBUTION 45

14 ISLAND OPERATION SCHEME 48

15 BASIC KNOW-HOW OF ELECTRICAL ENGINEERING 49

16 CONCLUSION 52

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RASHTRIYA ISPAT NIGAM LIMITEDVISAKHAPATNAM STEEL PLANT

TRAINING AND DEVELOPMENT CENTRE

CERTIFICATE

This is to certify that the project work entitled “Study of

Electrical Systems in Vizag Steel Plant” is a original

record of study carried out by……, a bona fide students of

National Institute of Technology, Silchar under the guidance

and supervision of Mr. Ajeet Kumar Sen, Assistant General

Manager (Electrical).

Mr. Ajeet Kumar SenAssistant General ManagerElectrical DepartmentThermal Power PlantVizag Steel plant

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ACKNOWLEDGEMENT It is my privilege to have the working knowledge under the

guidance of Mr. Ajeet Kr. Sen who extended his support and

spared his valuable time to guide me through the course of

the project. He provided an insight into the functioning of the

thermal power plant along with delivering practical

knowledge.

I also extend my sincere thanks to Sri Abhay Kr., Sri M. C.

Mane of ERS, Sri Hanumant Rao of ECR and Sri Shailendra

Kumar, for sharing their valuable knowledge.

I also show my gratitude to Mr. Krishnasish Chanda for

availing me the opportunity for training in Vizag steel plant

With sincere regards,

VIKASH NAGAR MD. AFTAB ANSARI AJAY KUMAR CHANYAL NISHANT KUMAR GAURAV KHANDELWAL ANAND PRAKASH GAUTAM AMIT KUMAR MISHRA MEHUL MADHUKAR

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DECLARATION

We, Anand Prakash Gautam, Mehul Madhukar,

Gaurav Khandelwal, Vikas Nagar, Ajay Kumar

Chanyal, Nishant kumar,Md. Aftab ansari & Amit

Kr. Mishra, students of 4th year, Electrical Engineering of

National Institute of Technology, Silchar hereby declare that

the project entitled “Study of Electrical Power in Captive

Thermal Power Plant at Vizag Steel Plant” submitted in partial

fulfillment of the degree of Project Training in Electrical

Engineering is our own.

B.Tech ,

Electrical Engineering

N.I.T. Silchar

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ABSTRACT

This project entitled “Study of Electrical Systems in Captive Thermal

Power Plant at Vizag steel Plant” covers the complete operation of the

Thermal Power Plant and power distribution in Vizag Steel Plant.

The main objective of the project is to study the various equipments provided for

generation and distribution of power with their proper integration to meet the purpose.

Also some essential electrical ideas and facts which were learnt in due course are

incorporated at the end of this project report.

A generating station which converts heat energy obtained by the combustion of coal

into electrical energy is known as Thermal Power Station. A Thermal power plant

basically works on the principle as seen in Rankine cycle. Steam is produced in the boiler

by utilizing the heat obtained by combustion of coal. This steam is used to run the

prime movers where it gets expanded. This expanded steam is then condensed in a

condenser to be fed into the boiler again. The prime mover (here the steam turbine)

drives the alternator which converts the mechanical energy of the turbine into electrical

energy. Such types of power stations are generally commissioned where its main source

coal and water are available in abundance. As, this thermal power plant is annexure of

Vizag steel plant. Here we are also using Blast Furnace Gas, Coke Oven Gas, Fuel oil in

proper proportion for obtaining net heat for Rankine cycle.

Generated electrical power is distributed to various sections of steel plant and township

through different substations which are connected to generating unit. The total demand

is collectively meet by Captive TPP and Andhra Pradesh State Electricity Board.

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THERMAL POWER PLANT-AN INTRODUCTION

The fact that thermal energy is the major source of power generation itself shows

importance of Thermal power plants’ in India. More than 60% of electrical power is

produced by Thermal powered steam plants in India. The steep rise in the demand for

power demands a larger unit setup which requires the use of more fuel. These plants

are trying to keep the overall cost of power generation low using modern techniques

and devices.

In steam power plants the heat obtained by the combustion of fossil fuels (coal, oil or

gas) is utilized by the boilers to raise the steam to a high pressure and temperature. The

steam so produced is used in driving the steam turbines and sometimes steam engines

coupled to generators and thus in the generation of electrical energy. The steam

turbines or steam engines thus used not only act as prime movers but also as drives for

auxiliary equipments such as pumps, fans, turbo blowers etc.

The steam power plants may be installed either only to generate electrical energy or

electrical energy generation along with steam generation for industrial purposes such as

paper mills, sugar mills, chemical works, plastic manufacture, food manufacture etc.

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Generally Thermal power plants are categorized as

Utility Power Plant - Power is produced solely for the purpose of generation and

supplied to the various kinds of customers through grid.

Captive Power Plant - Power is produced for supplying quality power for the

effective functioning of the actual plant (say a case of a Thermal power plant

present in a steel plant). The import and export of power takes place in

accordance with the load.

The Thermal power plant seen in Vizag Steel Plant is a captive power plant. The power

requirement of VSP is met through captive generation as well as supply from APSEB

grid.

Captive capacity of TPP in VSP : 300.5 MW

3 units of 60 MW generation capacities.

1 unit of 67.5 MW generation capacity.

2 units of 7.5 MW capacities at Back Pressure Turbine Station (BPTS).

2 units of 12 MW capacities at Gas Expansion Turbine Station (GETS).

1 unit of 14 MW from new coke Oven battery.

The specialty of this power plant is that the energy from the flue gas is not wasted. It is

used in BPTS and GETS and some power is generated.

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POWER REQUIREMENT

Integrated Steel Plants are major consumers of electricity, with specific consumption of

power at around 600-650 kWh/Ton of liquid steel. The estimated annual power

requirement of Visakhapatnam Steel Plant, at full level of production in each shop

(corresponding to 3.0 MT of liquid steel), is 1932 million kWh. This corresponds to an

average demand of 221 MW. The demand is found to be 227 MW on an average and

260 MW peak value. The estimated energy consumption and average demand of major

shops is given below:

SHOP Annual Energy

(106 kW Hrs.)

Average

Demand (MW)

RMHP 35 4.0

CO & CCP 171 19.5

SINTER PLANT 254 29.0

BLAST FURNACE 210 24.0

SMS & CCS 126 14.5

LMMM 100 11.5

WRM 118 13.5

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SHOP Annual Energy

(106 kW Hrs.)

Average Demand

(MW)

MMSM 100 11.5

CRMP 35 4.0

TPP 310 35.0

ASP 258 29.5

COM. STATION & CWP 131 15.0

AUXILIARY SHOPS 20 2.5

WATER SUPPLY 15 2.0

TRAFFIC & OTHERS 7 1.0

TOWNSHIP 28 3.0

LOSSES 14 1.5

COAL CONVEYING SYSTEM OF TPP

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CC 58

ISBH

JUNCTION HOUSE 12

JUNCTION HOUSE 13

JUNCTION HOUSE 14

TPP BUNKER FLOOR

RMHP

CC 62

CC 63

CC 66

CC 67CC 68

CC 69

BUNKERS

SOURCES OF POWER

Power requirement of VSP is met through captive generation as well as supply from

APSEB grid. The captive capacity of 270 MW is sufficient to meet all the plant needs in

normal operation time. In case of partial outage of captive generation capacity due to

breakdown, shutdown or other reasons, the short fall of power is availed from APSEB

grid. Turbo Generators of VSP normally operate in parallel with state grid. Excess

generation over and above plant load is exported to APSEB.

The agreement with APSEB provides for a contract demand of 150 MVA and permit

export of power. Tariff for import, export; demand charges, penalties etc. are

stipulated. For purpose of billing, import and export energy is separately metered at

Main Receiving Station (MRS).

APSEB SUPPLY NETWORK

Power is supplied to VSP from APSEB switching station over two 220 kV lines on double

circuit towers. Power is received at the Main Receiving Station (MRS) located near Main

gate and further distributed to various units within the plant.

EXTRA HIGH VOLTAGE DISTRIBUTION (220 kV)

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Power from APSEB is received at Main Receiving Station (MRS). The entire plant is

configured as five electrical Load Blocks and Step down sub-stations are provided in

each block (designated as LBSS 1 to 5) with 220 kV transformers to step down power to

33/11/6.6 kV and for further distribution as indicated below:

STATION DESIGNATION AREAS COVERED

LBSS1 (220/11/6.6 kV) RMHP, CO & CCP, Sinter Plant, BF

LBSS2 (220/11/6.6 kV)

(220/33 kV)

BF, SMS, ASP, CRMP, Comp. House-1

Ladle furnace in SMS

LBSS3 (220/11/11 kV) MMSM

LBSS4 (220/11/11 kV) LMMM, WRM, Aux. Shops, Adm. Building

and Kanithi reservoir pump house.

LBSS5 (220/11&220/11/11 kV) TPP, Plant essential category loads, KBR &

Township pump houses & hospital.

MRS (220/33 kV) Plant, Township and construction network.

Power is distributed within VSP, between above major blocks and MRS over 220 kV

lines on double circuit towers. MRS and LBSS5 at TPP are interconnected by three tie

lines for bi-directional power flow. LBSS1 is connected to LBSS5 by two radial lines.

LBSS2, LBSS3 and LBSS4 are connected to MRS by two radial lines each.

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To ensure continuity of supply and also facilitate maintenance, the stations are connected by double circuit lines. MRS and LBSS5 are designed with double bus (Main Bus-1, Main Bus-2) and transfer bus arrangement. At LBSS1, 2, 3 and 4 provisions are made so that with only one 220 kV line and two transformers in service, all the loads can be catered to. The equipment installed is suitable for 15000 MVA fault level. The various equipment installed in these stations include 220 kV lighting arrestors, current transformers, potential transformers, isolators, SF6/MOCB circuit breakers, Transformers, Aluminum pipes, ACSR conductors, insulators structures, Relay and control panels, batteries etc.

Carrier communication apparatus is provided at MRS to contact any of the APSEB

stations.

HIGH VOLTAGE DISTRIBUTION (33/11/6.6 kV)

Two 220/33 kV Transformers installed at MRS feed power to Township step down

station (called as CPRS) through 33 kV cables. Here the voltage is further stepped down

to 11 kV by two nos. of 33/11 kV transformers. Outgoing feeders from this station

supply power at 11 kV through cables to township network. 11 kV overhead

construction power lines are connected to this sub-station.

The 33 kV supply form the transformer at LBSS2 feeds SMS ladle furnace transformer

and capacitor banks through cables. This is a highly fluctuating load and the voltage dips

on 220 kV systems can be felt when the furnace is in operation.

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Electric power at 11/6.6 kV stepped down at above LBSS station is distributed to smaller

Load Block Distribution Station (LBDS) located in each unit. Load Centre Sub-station

(LCSS) transformers which convert power form 11 kV to 415 V; converter, arc furnace,

11/6.6 kV High Voltage Load Centre (HVLC) transformers and 11 kV motors (above 200

kW rating generally) are connected to LBSS/LBDS, 11 kV switch boards through circuit

breakers. Power supply to essential category loads of various zones is extended form

TPP directly from Generator Switch Board (GSB) at 11 kV. Cross-linked Poly Ethylene

(ELPE) cables are used for 11 kV distributions.

6.6 KV supply is mostly used for motors (of rating >20KW and <200 kW generally). In

the zones fed by LBSS3, LBSS4 stations and also where 11 kV supply from TPP is

connected for motor drives, where ever required, step down 11/6.6 kV High Voltage

Load Centers (HVLC) are formed with suitable capacity transformers (20/10/6.3 MVA

capacity). High Voltage Motor Control Centers (HVMCC) are fed from 6.6 kV

LBSS/LBDS/HVLC stations. 6.6 kV motors are connected through breaker to

LBSS/LBDS/HVLC/HVMCC switch boards. Sometimes vacuum contactors are also used

for motor switching. Cross-linked poly ethylene cables are used for 6.6 kV distributions.

The 11 kV switch gear is of 1000/750/500 MVA rating. The 6.6 kV switch gear is of

450/350 MVA rating. All the equipment selected is suitable for use with ungrounded

system specifications. Zig-zag connected transformers are connected to Delta

connected secondary windings of 220/11/6.6 kV transformers to create neutral point.

The 11 and 6.6 kV system neutrals are grounded through resistance to limit the earth

fault current to 1000/600 Amps respectively. Appropriate protective relays provided to

quickly isolate faulty feeders/apparatus with suitable discrimination. All varieties of

breakers such as Bulk Oil/MOCB/VCB/SF6/Air Blast are used.

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MEDIUM VOLTAGE DISTRIBUTION (BELOW 650 V)

In each shop, to cater to Medium and Low voltage load, 11 kV/415 V LCSS are formed.

Power is fed from LCSS to motors, MCC, Power Distribution Boards (PDB), Lighting

Distribution Boards (LDB), ESP transformers etc. and for further distribution. The 3

phase 415 V distribution is solidly earthed neutral system. The transformers are of

standard rating 1600/1000/750/630/250 kVA in plant and township areas. PVC cables

are used for medium voltage distribution generally.

The secondary windings of converter transformers feed DC converters and other special

equipment for variable speed AC/DC drives. The secondary voltage of these

transformers suits to the particular application for which they are provided

LOW VOLTAGE DISTRIBUTION (250 V & BELOW)

Low voltage distribution consists of power supply on single phase to lighting equipment,

ceiling fans, portable hand tools and domestic appliances etc. For safety reasons, 24 V

distributions are also provided to cater to hand lamps etc. in some areas. PVC cables

are used.

SCADA

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The 220 kV, 11 kV and 6.6 kV distribution system is monitored by a centralized

Supervisory Control And Data Acquisition system. The plant

generation, import/export and consumption in each unit are monitored through SCADA.

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MAIN EQUIPMENTS IN TPP

The process of power generation takes place with the help of the following equipments

in chronological order:-

Boilers

Turbo-generators

Transformers

Turbo-blowers

Chemical water treatment plant

Coke Dry Cooling Plant (CDCP) boilers

Back Pressure Turbine Station(BPTS) and Cooling Water Plant (CWP) -1 and 2

Gas Expansion Turbine Station (GETS)

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BOILERS

No. of boilers : 5 (4 working+1 standby)

Steam capacity : 330Tons/Hr

Pressure : 101 ata

Temperature : 540oC

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Fuel : Pulverized coal, BF Gas, CO Gas,

Furnace oil/LSHS

Type : single drum, natural circulation,

suspended type, radiant,

multiple fuel, corner fired.

Coal for the plant is obtained from Talcher, Orissa. Lignite coal is obtained. Lignite is

porous, has 30-50% moisture, light weight. It is stored in coal bunkers (Immediate stock

bins) and then ground in coal mills i.e. pulverized to increase the surface area of

combustion. Then Primary Air (PA) fan sweeps the pulverized coal for combustion to

occur. The heat resulting due to this combustion is used to raise the steam in boiler to

the required temperature and pressure.

The water input given to the boiler is demineralized before sending into the boiler, to

prevent the corrosion and damage of boiler tubes and turbine blades.

A boiler channel on the whole is divided into 2 passes:

Combustion pass

Non-combustion pass

The boiler drum consists of steam at different temperatures. The one with higher

temperature is at top. On an average, the temperature of the boiler is 318oC .The boiler

seen in VSP undergoes natural circulation i.e. due to density difference the circulation

occurs. The heat is transferred by means of radiation.

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There are super-heaters which are used to increase the steam temperature to 540oC.

The heat from flue gas is used for the same. There are 3 types of super-heaters used,

namely,11100

Low temperature super-heater

Platen or Radiant super-heater

Final super-heater

A tubular air-heater is present which is used to preheat the primary air i.e. air from the

PA fan. This is done as low temperature air sticks dust and flue on to the pipes. Similarly

a Regenerative air-heater is used to preheat the combustion gas by using heat from flue

gas. Finally, an economizer is present to increase the feed water temperature, by using

heat from the flue gas.

A Forced Draft Fan is present to provide the required air for combustion. Also a negative

pressure is maintained in the furnace using the above.

As it is a multiple fuel and water tube- boiler, the temperature may change. A control on

the temperature of steam is highly essential. So a de-superheater is used.

It sprays a steam at lower temperature (300oC approx.) to cool down the temperature.

Also some tilting arrangements in the burner are provided in some places for the same.

FUEL COMPARISON :-

Fuel Calorific Value

• Coal 3200 – 4500 KCal / KG

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• Coke-Oven gas 4425 KCal / NM3

• Blast Furnace Gas 800 KCal / NM3

• Fuel Oil 10000 KCal / KG

0.223

30

46.8

Typical fuel Mix in Boilers

OilBFGCOGCOAL

To maintain a constant level in the boiler drum, a Feed Regulation System (FRS) is used.

Steam or water from FRS is sent to the boiler drum via economizer and platen water

tubes.

Ignition is done with the help of spark plugs. There are some igniter fans for cooling the

igniter guns if necessary. Also there are Flame Scanners to know if flames have occurred

or not. And for cooling the above, Scanner air fans are present.

Below the boiler, a Bottom Ash Hopper is present. About 15% of the ash is collected by

gravitational force. This is removed every 8 hours. Rest gets passed as flue gas,

precipitated in ESP (Electro Static Precipitator).

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An Induced Draft Fan is present at the far end of this system, to suck the gas thus

obtained and leave it out through the chimney high up in the atmosphere.

TURBO-GENERATORS

GENERATOR (60 MW)- TG#1,2,3

No. of units : 3

Make : BHEL

Type & description : TARI 930-36P

Rated power Active : 60000 kW

Rated power Apparent : 75000 kVA

Power factor : 0.8

Rated stator voltage : 11000 5% Volts

Rated stator current : 3936 Amp

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Rated rotor voltage : 300 Volts DC

Rated rotor current : 596 Amp

Rotational speed : 3000 RPM

Frequency cycles : 50 HZ

Critical speed : 1765 n1, >4500 n2

Class of insulation of winding : F

Air gap between stator and rotor : 55 mm

Type of cooling : Air cooling indirectly

Maximum temp. rise of stator winding : 120O C

Maximum temp. rise of rotor winding : 130O C

Winding type : double layer-with 36 slots

Turbine type : impulse-reaction (1:40)

EXCITATION SYSTEM:-

Type of excitation : Static

Rated output : 255 KVA

Rated voltage : 359 Volts

Rated current : 711 Amp

Exciter ceiling voltage : 575 Volts

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Nominal exciter response ratio : 2:4

GENERATOR COOLING SYSTEM

Make : BHEL

Type : Elements for tubes

Number (3 Operating & 1 standby) : 4 Elements

Material & construction details : Carbon steel

Quantity of cooing water required : 360 M3/hr

Max. temp of water inlet of cooler : 36O C

Max. temp cooling air at cooler : 40O C

GENERATOR AIR COOLER

Service unit : Air

Position : Horizontal

Heat duty : 1027 kW

Qty. circulation air : 108000 M3/hr

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Cool air temp. : 40O C

No of cooler elements : 4

No. of water paths : 2

Air design pressure : 6 kg/cm2

Test pressure : 9 Kg/cm2

Design temperature : 100O C

GENERATOR (67.5 MW) - TG#4

No. of units : 1

Make : BHEL

Type & description : TARI 930-36P

Rated power Active : 67500 kW

Rated power apparent : 84375 kVA

Power factor : 0.8

Rated stator voltage : 11000 5% Volts

Rated stator current : 4429 Amp

Rated rotor voltage : 300 Volts DC

Rated rotor current : 625 Amp

Rotational speed : 3000 RPM

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Frequency cycles : 50 HZ

Critical speed : 1765 n1, >4500 n2

Class of insulation of winding : F

Air gap between stator and rotor : 55 mm

Type of cooling : Air cooling indirectly

Maximum temperature rise of stator winding : 120O C

Maximum temperature rise of rotor winding : 130O C

EXCITATION SYSTEM

Type of excitation : Static

Type of excitation : Static

Rated output : 255 KVA

Rated voltage : 308 Volts

Rated current : 625 Amp

Exciter ceiling voltage : 461 Volts

Nominal exciter response ratio : 2:4

GENERATOR COOLING SYSTEM

Make : BHEL

Type : Elements for tubes

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Number (4 Operating & 1 Standby) : 5 Elements

Material & construction details : Carbon steel

Quantity of cooing water required : 420 M3/hr

Max. temp of water inlet of cooler : 36O C

Max. temp cooling air at cooler : 38.38O C

GENERATOR AIR COOLER

Service unit : Air

Position : Horizontal

Heat duty : 1161 kW

Qty. circulation air : 108000 M3/hr

Cool air temp. : 42O C

Hot Air Temperature : 74.34°C

No of cooler elements : 5

No. of water paths : 2

Air design pressure : 6 kg/cm2

Test pressure : 9 Kg/cm2

Design temperature : 100O C

There are 3 turbines which rotate and thus make the turbo generators to rotate.

STEAM TURBINE:

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SPECIAL FEATURES

• Electro Hydraulic Turbine Governing System.

• Controlled extraction at 13 ata and 4 ata for process steam needs. (Only in TG

1,2 & 3)

• Central admission of steam to reduce axial thrust.

• Air cooled Generators.

Each Turbo-Generator has the following auxiliaries:

One condenser is designed to achieve the vacuum of 760 mm Hg.

Three condensate extraction pumps of 50% capacity each

2 steam ejectors- 1 standby

1 starting ejector to create vacuum within 30 minutes

Gland steam condenser

2 HP Heaters to condensate from 90oC to 140oC

2 LP Heaters to heat feed water from 140oC to 215oC.

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Electro-Hydraulic control system

Turning gears, main oil pump, auxiliary oil pump, emergency oil pump, and

jacking oil pump.

4 oil coolers (2 standby)

7 boiler feed pumps ( with multistage centrifugal pump and barrel type casing)

OPERATIONAL LIMITS:

For analyzing the operational problems and taking necessary steps, operational limits of

the generator should be known to the operator. If the generator operates within the

limits, the system will work without any disturbance. These are the possible occurrences

of disturbance due to some fault seen in generator.

Problems are studied to occur at the following conditions:

a. Generator field failure trip

b. Generator negative phase sequence trip

c. Over voltage and over current trips

d. Fault in static extension equipment and pole slipping trips

e. Fault in Automatic Voltage Regulator

f. Stator or rotor temperature high

VAR IATION OF TERMINAL VOLTAGE

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Generator can develop rated power factor when the terminal voltage changes within +/-

5% of the rated value i.e. 10.45 to 11.55 kV. The stator current should accordingly be

changed within corresponding values of the MVA outputs and stator currents are also to

be carefully observed. During operation of generator at 110% of the rated value of

continuous operation, stator current should not exceed 4130 A corresponding to 105%

of the rated value.

VARIATION IN FREQUENCY

The generator can be operated continuously at rated output with a frequency variation

of +3 to -5% over the rated value i.e. 47.5 to 51.5 Hz. However the performance of the

generator with frequency variation is limited by the turbine capacity. The variation in

frequency depends on the load and generation. Frequency detector is connected to

sense the frequency variation which gives command to governing system which control

the steam flow to turbine by opening or closing the valves.

Generation>demand : High frequency

Demand>generation : Low frequency

OVERLOADING

Under abnormal condition, generator can be overloaded for a short duration.

Permissible value of short time-overloads in terms of stator and rotor currents and

corresponding duration at rated power factor and rated voltage and rated parameters

of cold air and stator and rotor temperatures can be applied.

OPERATION UNDER UNBALANCED LOAD

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The turbo generator is capable of operating continuously.

When unbalanced system loading is provided, a continuous negative sequence current

during this period shall not exceed 5% of the rated stator current.

If unbalance exceeds permissible levels, measures are to be taken immediately to

eliminate or reduce the extent of unbalance within 3 to 5 minutes. If not, the machine

trips.

SYNCHRONISATION

A generator requires to be synchronised if it is to be run in parallel with others. Before

it is connected electrically to energised bus bar, the following conditions must be

satisfied.

(a) Equality of voltage

(b) Equality of frequency

(c) Synchronisation of phases

With these requirements fulfilled, there will be no voltage difference between any

corresponding pairs of terminals of machines and bus bars, so that points can be

electrically connected without disturbance.

ASYNCHRONOUS OPERATION

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Asynchronous operation of the generation on field failure is allowed depending upon

the permissible degree of the voltage dip and acceptability of the system from the

stability point of view. During field failure there are important points to be noted.

Field failure with under-voltage

Field failure without under-voltage

Field failure with under voltage will be sensed and the machine will get tripped without

any delay.

During field failure without under voltage, active load on the generator shall be

decreased to 40% of rated load immediately. The generator can operate at 40% of the

rated load asynchronously for a total period of 15 minutes from the instant of failure of

excitation. Within this period, steps should be taken to establish the reasons of field

failure to restore normalcy. If it cannot be restored then the set has to be switched off.

Then the set should be switched over to the reserve excitation.

SOME OBSERVATIONS

When excitation is removed from the turbo generator, it acts as induction generator. It

takes reactive power from the grid and gives active power to the grid. Note that the

reactive power in a generator is nothing but the power derived from the magnetisation

due to excitation of the generator.

On stopping the mechanical input to the generator, the machine starts working as a

synchronous motor. It takes active power from the grid and supplies reactive power to

the grid.

If both excitation and input to the generator are stopped, it acts as an induction motor.

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So these methods cannot be used to shut down a generator.

SHUTDOWN OF GENERATOR

Slowly bring down mechanical input to a minimum level. Then the machine is tripped

using breakers from the grid. Load is also reduced to avoid abnormality i.e. to prevent it

from affecting other systems.

TURBO BLOWERS

BLOWERS - 3 (2 Working + 1 Standby)

CAPACITY - 6067 m3 /min

SPECIAL FEATURES

Constant Speed with EHTC (Electro Hydraulic Turbine Governing system)

Inlet Guide Vane Control

Axial type largest blowers in India.

VSP has 2 blast furnaces. To meet the blast air requirement, 3 turbo blowers, each of

6067 nm3/min capacity, are installed at TPP. These blowers are of axial type and are the

largest blowers installed in India.

These blowers are provided with suction filters, pre-coolers and inter-coolers.

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AUXILIARIES OF TPP

These include coal conveyors, cooling towers and pump house#4 for cooling water

system, pump house for ash water, ash slurry, fire water and fuel oil and emergency

diesel generators, electric switch gear for power distribution, ventilation and air

conditioning equipment etc. The entire power generated at Back Pressure Turbine

Station (BPTS) and Gas Expansion Turbine Station (GETS) is transmitted over 11 kV

cables to power plant, stepped up through a 220 kV transformer at LBSS5 and

transferred to plant grid.

TRANSFORMERS

TRANSFORMERS CONNECTED TO 60 MW GENERATORS (EXCITATION SYSTEM)

Make : May & Christ W.G.

Type : Dry type air cooled

Connection symbol : DYN5

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Class of insulation : F

Power rating : 650 KVA

Primary voltage : 11 kV volts

Secondary voltage : 480 Volts

TRANSFORMERS CONNECTED TO 67.5 MW GENERATORS (EXCITATION SYSTEM)

Make : BHEL, JHASI.

Type : Dry type air cooled

Connection symbol : DYN5

Class of insulation : F

Power rating : 500 KVA

Primary voltage : 11 kV volts

Secondary voltage : 380 Volts

There are 2 main types of transformers present in a Thermal Power

Plant :-

Generator transformer

Auxiliary transformer

A Generator Transformer is one which steps up the voltage to the grid for the purpose

of distribution.

An Auxiliary transformer is one which steps down the voltage for the plant purposes.

Page | 37

The transformer consists of a conservator tank, breather, buckholz relay, transformer

oil mainly. It also has on-load tap changers.

Conservator tank is used for conserving the transformer oil when it expands or

contracts due to change in temperature in insulation.

For the contact of air from inside to outside and vice-versa, a breather is present. It

consists of silica gel to trap moisture. When it changes from blue to pink, it has to be

replaced.

The transformer is generally surrounded by gravel, to avoid the growth of grass, and to

prevent insects, snakes and to isolate, restrict the area.

There is a Buckholz Relay which is used to show if there is any internal fault. When the

above occurs, bubbles get generated and float up, thus tripping the relay. There are 2

balls in this relay. The top one is for alarm and the bottom ball completely trips the

transformer.

The reading in the transformer is seen to be 50/63 MVA, which means it can withstand a

maximum of 50 MVA during natural cooling and 63 MVA during forced cooling.

SOME OBSERVATIONS

Transformer can have troubles in the following ways as observed.

Bus bar protection

Over flux protection

Over current

Earth fault

Page | 38

Under frequency

There are breakers and isolators in the switch yard along with CTs and PTs. Breakers are

on-load devices, while isolators are off-load devices since breakers have an arc-

quenching medium. The breaker in VSP is mainly made of SF6.

The speciality of this breaker is that the SF6 gets ionised and recombines as soon as the

arc is quenched.

CHEMICAL WATER TREATMENT PLANT

The Chemical Water Treatment Plant located in TPP produces high quality purified

Demineralised Water and soft water. There are 6 streams of de-mineralising units each

capable of producing 125 m3/hr. 2 softening units of 125 m3/hr each is present.

Demineralisation is done by the Cation and Anion Exchange process.

PROCESS

Water from the Kanithi reservoir is sent to a clariflocculator, where water is churned

and the suspended impurities settle down due to the centrifugal force and action of

gravity. Then this water is passed through anion exchanger beds where anions get

exchanged with Zeolite which combines with sulphuric acid and forms water. A similar

process takes place in cation exchanger beds also.

This DM water is supplied to TPP, Steel Melt Shop (SMS), CDCP Boilers at Coke Ovens

and Rolling mills. Soft water is supplied to Chilled Water Plant-I, II and SMS mould

cooling.

Page | 39

COKE DRY COOLING PLANT (CDCP) BOILERS

In VSP, hot coke produced in the coke oven batteries is cooled by circulating nitrogen in

CDCP. The hot circulating gas is passed through Waste Heat Boilers in which the steam is

produced at 40 kSCA pressure and 440oC temperature. There are 3 CDCPs and 4 Waste

Heat Boilers. These boilers are of 25T/Hr capacity.

EFFICIENT PRODUCTION

The heat of the flue gas is not wasted much in this plant. It is efficiently used for further

purposes in Back Pressure Turbine Station (BPTS) and Gas Expansion Turbine Station

(GETS). BACK PRESSURE TURBINE STATION (BPTS)

BPTS GENERATOR (7.5MW)

No. of units : 2

Make : BHEL

Type & description : TGN 218226/2

Rated power Active : 7500 kW

Rated power Apparent : 9375 kVA

Power factor : 0.8 lag

Rated stator voltage : 11000 5% Volts

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Rated stator current : 492 Amp

Rated rotor voltage : 140 Volts DC

Rated rotor current : 596 Amp

Rotational speed : 3000 RPM

Frequency cycles : 50 HZ

Critical speed : 1900 n1

Class of insulation of winding : B(Stator &Rotor)

Type of cooling : Closed Circuit Air cooling

Short Circuit Ratio : 0.610

Generator field Resistance : 0.334Ω at 20ºC

Moment of Inertia of Rotor : GD² = 101tm²

Max. Short Circuit Torque(for Coupling) : 15368 kg-m

No. of Generator Terminals : 6

Generator Phase Connection : Star

Generator Brushes : 4 for Ring (2 Rings)

Size : 32 x 32 mm

Grade : HM6R

Minimum Permissible diameter of Slip Ring : 370mm

Page | 41

Max. output with one cooler out of service: 6562 kVA

Volume of cooling Air : 28800m³/hr

Designed for : Tropical Climates

GETS GENERATOR (12MW)

TG-1 TG-2

Make : RUSSIA RUSSIA

Type & description : TΠ-122-У3 TΠ-12-2T3

Rated power Active : 12000 KW 12000KW

Rated power : 15000 KVA 15000KVA

Power factor : 0.8 lag 0.8 lag

Rated stator voltage : 6300/10500 Volts 11000 Volts

Rated stator current : 1375/825 Amp 787Amps

Rated rotor voltage : 230/232 Volts DC 232 Volts DC

Rated rotor current : 268/270 Amps 270Amps

Rotational speed : 3000 RPM 3000 RPM

Frequency cycles : 50 Hz 50Hz

Critical speeds : 1720 n1, 4720 n2 1700n1, 4800n2

Efficiency : 97.6 97.6

Page | 42

Type of cooling : Closed Circuit Air cooling

Mass of Rotor : 6980kg 7500kg

Stator Mass : 14500/15300kg 15300kg

Rotor fly wheel Moment : 1.42 tm² 1.42tm

Page | 43

~ ~ ~ ~

4 Ata Process Steam13 Ata Process Steam

TG 1 TG 2 TG 3 TG 4TB 2 TB 1TB 3

Blast Air to BF

PH 4

CEPLPH

HPH BFP

DM Plant

Gen. Transformers63 MVA

90 MVA

Tie LinesMRS LBSS 5

Tub. Air

Heater

Economoiser

Boiler 5

101 Ata Main Steam Header

GSB-1 Co

ndenser

De-aerat

or

Ash Pond

Chimney

Ash Slurry Pump Hse

Ash Water Pump Hse

ID Fan

FD FanPA Fan

ESP

PROCESS FLOW CHART OF TPP &

BHRMHS

ISBs

POWER GENERATION AND DISTRIBUTION

Each generator of group 1, 2 and 3 is connected to one section of Generator Switch

Board (GSB). Each section of GSB-1 is in turn connected with each other by a bus coupler

with reactor and without reactor scheme.

The TG#4 which was added later on to augment power position of the plant and to

utilize full capacities of 4 running boilers, is connected through a power transformer to

220 kV side of the Load Block Sub-Station (LBSS)-5.

Page | 44

POWER NETWORKEASTERN BUS 400 Kv

DC BACK TO BACK

SOUTHERN BUS 400 Kv

TO JAIPUR

(ORISSA)

TO VIJAYAWADA (NUNNA)

315MVA400/220 KvAUTO X’MER

220 Kv

TO BOMMUR

U

TO PENDURT

HI

TOGAJUWAKA

MRS 220 Kv BUS 1BUS 2

BUS 1

BUS 2

TPP 220 Kv

LBSS 1

LBSS 3 LBSS 4

LBSS 212.5 MVA220/33 Kv X’MER

TO CPRS

AL1 AL2

ML1 ML2 ML3

BC

BC

T150/63 MVA

T250/6

3MVA

T350/63MVA

T590

MVA

T431.5/40/5

0MVA

11 Kv

TG 160 MW

TG 260 MW

TG 360 MW

TG 467.5 MW GETG

112

MW

BPTG 2

7.5 MW

MRS

LBSS 5

GSB 1 GSB 2

POWER GRID SUB STATION

APSEB SWITCHING STATION

- BREAKER

In addition, the plant has got total of 4 small generator sets (2 at coke ovens [CO] and 2

at blast furnaces) which utilize the waste heat and blast furnace top pressure

respectively to produce power.

Sets operating at CO area have a capacity of 7.5 MW each and at BF area have a capacity

of 12 MW each. One set each from CO and BF areas are connected to GSB-2 and GSB-3

respectively. New coke oven battery recently set up which treats upon the heat of waste

water has a capacity of 14MW.

GSB-1 is connected to the plant’s 220 kV circuit at LBSS-5 with 3- 11/220 kV, 50/63 MVA

transformers. GSB-2 and GSB-3 are connected to plant’s 220 kV circuit at LBSS-5 via a 3

winding 11/11/220 kV transformer. Power requirement of power plant is met by 2

switch boards namely 5LBDS7 and 05HVLC-1 connected to 3 section of GSB-1.

5LBDS-7is mainly a 11 kV switch-board with 3 sections and caters to the need of various

load centres throughout TPP. 05HVLC1 is a 6.6 kV load centre which meets the

requirement of HT drives.

ESSENTIAL CATEGORY LOADS

Some of the technological process/equipment requires all time availability of electricity.

Such loads are approx. 70 MW and spread over various plant units. These include

exhausters in CO & CCP, Cooling water pump houses in BF, SMS, Rolling mills, Intake

pump house, Kanithi Balancing Reservoir pump house, TPP auxiliaries, Township pump

house, Hospital etc. Disruption of supply to these loads may cause wide spread

dislocation to the process, involve dangerous situation to equipment etc. These are

classified as special/essential category-I loads. Power supply to them is envisaged from

two sources i.e. from Thermal Power Plant generator 11 kV switch board through cables

Page | 45

and also from 220 kV sub-station in that area. Depending upon level of captive

generation, the 220 kV system is so configured that in the event of isolation of captive

generators form APSEB grid, the load throw off at TPP and disturbance to plant units is

minimized.

POWER DISTRIBUTION OF THERMAL POWER PLANT

To meet power requirement of its auxiliaries any power plant relies on station auxiliary

transformer in case of outage of its generation. But in the case of TPP whenever such

situation occurs, power requirement of its auxiliaries are met by the same power

transformer (which are used for power evacuation in case of normal generation)

through Generator switch board.

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ISLAND OPERATION SCHEME

A scheme has been envisaged at TPP to get isolated from the grid in case of system

disturbance or low frequency condition with ABB make relay type FCX 103b relay for

some conditions. Frequency is considered as the main parameter for this operation as it

is highly reliable compared to voltage and current.

The conditions are

When a frequency of 47.5 Hz or goes above 51.5 Hz is sustained for 0.5 seconds,

the mainline breaker will trip, isolating the plant’s 220 kV from grid. This is called

first stage of isolation.

When the frequency further drops down to 46.9 Hz and is sustained for 1 second,

the 11 kV section is cut off from the grid. This is called second stage of isolation.

If the rate of change of frequency is 2 Hz/second, sustained for 100 ms, isolation

occurs. Process is conventionally termed as Island operation Scheme.

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BASIC KNOW-HOW OF ELECTRICAL ENGINEERING

The basic principle of electrical safety is how to avoid electric shocks and fire hazards. At

the outset we will discuss about electric shocks.

The seriousness of the electric shock depends upon the following factors:

i) CURRENT STRENGTH: It has been experienced that in alternating current of low

frequency the current between 1mA and 8mA are just bearable, but currents between

8mA and 15mA give painful shock.

Thus it is seen that it is the current which gives shock although it depends on voltage.

The leakage current is given by I=V/R, where V=supply voltage and R=body resistance.

The body resistance is different under different conditions. When the body is dry, its

resistance varies between 70,000 - 1,00,000 /cm2, but when the body is wet, its

resistance reduces to 700-1000 ohm/ cm2. The average effective resistance of the body

may be taken as 50 k- when dry and 1-2k when wet. The high voltage causes burns.

Hence it is concluded that when body is wet, 100V supply is as dangerous as 10,000V

when body is dry.

ii) FREQUENCY OF CURRENT: The lower the frequency, more dangerous is the shock

and direct current shock is the most severe.

iii) PATH OF CURRENT: If the path of leakage current is without involving the chest

or heart, survival is possible but there will be severe burns on the parts of the body,

involved in the shock depending upon the value of the current.

WHY A FUSE IS NOT USED IN NEUTRAL:

Suppose a fuse be inserted in neutral path and let the metallic body of the electric

appliance be earthed to avoid electric shock. If the insulation value of the appliance

Page | 48

deteriorates and there is leakage current and which makes the fuse in the neutral to

melt first. But as soon as the operator touches the appliance in order to know what has

happened, he will complete the circuit through his body to earth and he will get a

severe shock since it is still connected from live lines.

ELECTRICAL SHOCK:

Electricity is an ideal form of energy which is efficient, economical, clean and quick,

available at the touch of finger. However, it is quicker and more efficient in causing

damage if safety aspects are not properly followed. To those who are unskilled and

inexperienced in electrical work, electricity is a serious source of potential danger.

Electrical hazards are not usually obvious. For instance, a live conductor does not differ

in appearance from a dead conductor, or the lack of grounding of a metal casing may

pass unnoticed until it is too late when it is touched and found to be dangerously live.

An electrical shock causing 10mA of current to pass through the heart will stop many

human heart beats. Voltage as low as 25V DC/ AC RMS should be considered

dangerous and hazardous since it can produce a fatal current under certain conditions.

Higher voltages are even dangerous.

We experience an electric shock when the body's nervous system is suddenly and

accidentally stimulated by electric current that will flow due to difference in voltage.

Shocks occur when the body becomes part of an electric circuit. The current enters the

body at one point and leaves at other. It may occur in one of the following three ways:

With both wires of an electric circuit

With one wire of an energised circuit and the ground.

With a metallic part that is in contact with an energised wire.

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SKIN EFFECT :- It is the tendency of a alternating electric current to distribute within the cross Section of the conductor such that current density is largest near the surface of the conductor and decreases with greater depths in the conductor. This causes increase in resistances of the conductor at higher frequencies where the skin depth is smaller thus reducing the effective cross section of the conductor.

Why area of cross section of neutral of 3-phase 4 wire system is half of that of phase wire?

The current carrying by the neutral of 3 phase 4 wire system is the unbalanced current. If the three phase system is completely balanced on all the three phases there could be no need for a neutral eg. 3 phase motor. This neutral current will be less than the phase current so, the reduction in neutral side is allowed.

Difference between a Switch and an isolator ?

A switch is a simple device to connect or disconnect power supply in one equipment or service. An isolator can have multiple areas of power distribution and these are can be isolated from power supply and taken for maintenance without functionally affecting the other areas. Hence, isolators are largely used in industries in power distribution panels. Isolator gives us a physical confirmation of whether the circuit has been closed or not.

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CONCLUSION

The detailed discussion over the generation and distribution of electrical power in the captive thermal power plant has been made in this report. An overview of the thermal power plant has been presented based on the study conducted in the period of the project training. In the due course we also learnt some basics of electrical engineering under the guidance of our project guide. An effort has been made in this project to bring out the complete idea behind the functioning of the thermal power plant and distribution scheme in Vizag steel Plant under Rashtriya Nigam Limited.

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A unit of absolute pressure in the metric.ATA(s): Abbreviation for "Atmospheres Absolute", defines as the total pressure exerted on an object, by a gas or mixture of gases, at a specific depth or elevation, including normal atmospheric pressure.

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