1

ADITYA INSTITUE OF TECHNOLOGY AND MANAGEMENT, TEKKALI

(AN AUTONOMOUS INSTITUTION) (Affiliated to JNTU, Kakinada, NBA Accredited, Approved by A.I.C.T.E)

STUDY OF GENERATION AND DISTRIBUTION AT THERMAL POWER PLANT

A project report submitted in partial fulfilment of

Requirements of the award of the degree

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted by

ABHISHEK KUMAR Y.DILEEP KUMAR (13A51A02E9) (14A55A0229)

Under the esteemed guidance ofSri SURESH KUMAR

Asst. General Manager (Elect)Thermal Power Plant

Visakhapatnam Steel PlantVisakhapatnam

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGAITAM, TEKKALI

2

ACKNOWLEDGEMENT

We express our profound gratitude to our external guide Sri SURESH KUMAR,

Asst. General Manager (Electrical), Thermal Power Plant of Visakhapatnam steel

plant for his valuable guidance rendered by his throughout the project.

3

ABSTRACTThis project titled “Study of Generation and distribution of electrical power

in thermal power at Visakhapatnam steel plant” covers the complete operation

of the Thermal Power Plant and power distribution in Visakhapatnam Steel plant. The

main objective of the project is to study the various equipment’s provided for power

and the process underneath it. Also some essential electrical ideas and facts which were

learnt in due course are added 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 Rankin cycle. Steam is

produced in the boiler by utilizing the heat obtained by combustion of coal. This steam

is used to run the prime mover 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.

4

INDEX

1. THERMAL POWER PLANT 4-19

2. BOILERS 19-25

3. TURBO GENERATORS &BLOWERS

4. LOAD MANAGEMENT 26-29

5. POWER SYSTEM IN VSP 30-32

6. CONCLUSION 33

5

1. THERMAL POWER PLANT

Introduction:

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

shows Thermal power plants importance 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 technique 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

equipment’s such as pumps, fans 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, and food

manufacture etc.

Generally Thermal power plants are categorized as:

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

various kinds of customers through grid.

Captive Power Plants- 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). Import and export of power takes place in accordance with the load.

6

The Thermal power plant seen in Visakhapatnam 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 : 286.5 MW

3 units of 60 MW generation capacity.

2 unit of 67.5 MW generation capacity.

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

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

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

used in BPTS and GETS power is generated.

ISBsRMHSPROCESS FLOW CHART OF TPP &

BH

ESP

PA Fan FD Fan

ID FanAsh

Water Pump Hse

Ash Slurry Pump Hse

Chimney

Ash Pond

De-aerat

Condenser

GSB-1

101 Ata Main Steam Header

Boiler 5Econo

mizerTub. Air

Heater

Air Heate

r

TRANSCO S/Stun

LBSS 5MRS Tie Lines

90 MVA

63 MVAGen. TransformersDM Plant

BFPHPH

LPHCEP

PH 4Raw Water

Blast Air to BF

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

13 Ata Process Steam4 Ata Process Steam

~ ~ ~ ~

7

2.BOILERS:

INTRODUCTIONBoiler is a major component in a steam power plant. Combustion of fuel takes place inside the boiler and water by taking up the heat of combustion turns into steam.A simple boiler is a closed vessel strongly constructed of steel in which steam is generated from water by the application of heat. The function of steam boiler is to convert chemical energy of fuel into heat by combustion and thus to produce steam which is then available for different purposes.The boiler with accessories is called as steam generator.Steam generation is done by evaporating water at constant pressure. The heat required for vaporizing may be obtained from any source-solid, liquid or gaseous fuels. Heat obtainable from electricity, atomic reactors and exhaust of engines may also be used.The generated steam may be employed for the following purposes:1. Power Generation: Electrical power or mechanical work may be obtained by expandingSteam in steam engines or steam turbines.2. Process Work: At low pressures, steam is used in many industries for different purposes.For drying paper in paper industry, bleaching, sizing etc. in Textile, sugar and chemical industries.3. Heating: Steam is also used for heating residential and industrial buildings in winter and for producing hot water.

BOILERS : 5 (4 working + 1 Standby)

TYPE : Water Tube Boiler

CAPACITY : 330 Tons/ Hr.

PRESSURE : 101 Atm.

TEMPERATURE : 540o C

FUEL : Pulverized coal, BF Gas,

CO Gas, Furnace oil/LSHS

8

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 desecrated and 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

temperatures is at top. On an average, the temperature of the boiler is 318°c. 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.

9

Fig (3.2.3

3.3 Fuel comparison:

Fuel Calorific value

Coal 3200-4500 Kcal/KG

Coke-oven gas 4425 Kcal/NM³

Blast Furnace gas 800 Kcal/NM³

Fuel oil 10000Kcal/KG

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

10

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).

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.

4. LOAD MANAGEMENT:

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

5. TURBO GENRATOR

3. TURBO GENERATORS

5 TGs : ( 3 × 60MW + 2 × 67.5MW ).

3.4.1 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.

46.8%

30%

23% 0.07%

Typical Fuel Mix in Boilers

COAL COG

BFG

OIL

11

Air cooled Generators.

3.4.2 Operational limits:

For analysing the operational problems and taking necessary steps,

operational limits of the generator should be known to be operator. If the 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. Overvoltage and overcurrent trips.

d. Fault in static extension equipment and pole slipping trips.

e. Fault in Automatic Voltage Regulator.

f. Stator or rotor temperature high.

3.4.3 Variation of terminal voltage:

Generator can develop rated power factor when 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 4130A

corresponding to 105% of the rated value.

3.4.4 Variation in frequency:

The generator can be operated continuously at 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.

Generation>demand: high frequency

Demand>generation: low frequency

3.4.5 Overloading:

12

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.

3.4.6 Operation under unbalanced load:

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.

3.4.7 Synchronization:

A generator requires to be synchronized if it to be run in parallel with

others. Before it is connected electrically to energize bulbar, the following conditions must

be satisfied.

a. Equality of voltage

b. Equality of frequency

c. Synchronization 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.

3.4.8 Synchronization procedures:

1. Ensure that the machine has attained the rated speed of 3000 rpm.

2. Obtain clearance from MCR to synchronize the machine.

3. Put the common “SYN SELECTOR” switch to “Manual with check” position.

4. Put the generator “Synch” switch to “Synch’ position.

13

5. See that bus voltage and frequency appears in “SYNCH TROLLEY”.

6. Give a closing command for the field breaker to close. Observe the “Red lamp” glows on

the control desk indicating the closing of field breaker.

7. Voltage will start building up due to field flashing and it builds up to 6 to 7KV is the

regulation is in manual mode. Then check the voltage of all 3 phases of voltages are not

equal then check the PT fuses and replace the blown one if any. If every aspect is normal,

then start increasing the voltage by giving ‘raise’ command through ‘Regulation manual’

switch in TG control desk. Raise the voltage till it matches with the bus voltage.

8. If the regulation is in auto, voltage will automatically go to 11KV while raising the voltage

in auto, please observe carefully so that it should not go high abruptly. I if that happens

then immediately change the regulation to manual and adjust the voltage manually.

9. Once the voltage is adjusted, see that frequency of TG is approximately equal to bus

frequency. If difference is there then give impulse to the speed controller by pressing the

speed raise and lower button desk accordingly to bring the frequency approximately equal

to bus frequency.

10. Switch on the “SYNCHROSCOPE” of the frequency of TG is higher than the system

frequency, synchroscope pointer will move in clockwise direction and if the frequency is

lower, it will move in the anti-clockwise direction speed of rotation of pointer will depend

upon the difference in frequencies.

11. When the voltage and frequency match, the synchroscope will move very slowly in the

clockwise direction. This positions shown that:

Phase sequences of generated voltage and system voltage are same.

Effective values of both the voltage are same.

Frequencies of both are same.

12. Give closing impulse to generator breaker the instance when the synchroscope pointer

is in between 11 &12 0’clock position and the red lamp on “Synchronal Trolley” glows

indicating synchronized condition between TG and system.

14

13. Once TG breaker is closed load the machine from ECR by pressing “Speed raise”

button up to 10-15 MW.

14. Inform MCR and MRS regarding the synchronization of the set.

15. Put synchroscope switch to ‘OFF’ position. Remove the trolley and put back in proper

place. Put TG synchronizing switch to ‘OFF’ position.

16. Observe the voltage of generator and see that the generator delivers lagging MVAR. If

the generator is delivering leading MVAR then make the TG deliver lagging MVAR by

adjusting the excitation.

17. If the AVR is normal mode then adjust the ‘auto’ position till the ‘Null voltmeter’ for

A/M changeover reads ‘Zero’. Then change the regulation to auto

3.4.9 Asynchroscope operation:

Asynchroscope 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

normally. If it cannot be restored then the set has to be switched off. Then the set should

switched over to the reserve excitation.

15

3.4.10 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:

BLOWER - 3(2 working + 1 standby)

CAPACITY - 6067 m³/min

3.5.1 Special features:

Constant speed with EHTC (Electro Hydraulic Turbine Governing System)

Inlet Guide Vane Control

16

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.

3.6 Auxiliaries of TPP:

These include coal conveyors, cooling towers and pump no.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.

Transformer:

TRANSFORMERS CONNECTED TO 60MW GENERATORS

Make : May & Christ W.G.

Type : Dry type air cooled

Connection symbol : DYN5

Class of insulation : F

Power rating : 650 KVA

17

Primary voltage : 11 KV

Secondary voltage : 480Volts

TRANSFORMERS CONNECTED TO 67.5MW GENERATORS

Make : BHEL, JHANSI

Type : Dry type air cooled

Connection symbol : DYN5

Class of insulation : F

Power rating : 500 KVA

Primary voltage : 11 KV

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.

The transformer consists of a conservator tank, breather, backhauls relay, and

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

18

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

due to change in temperature in insulation.

For the contract 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 Bocholt 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 50MVA during natural cooling and 63MVA during forced cooling

4.LOAD MANAGEMENT

19

SHOP AVERAGE DEMAND(MW)

RMPH 4.0

CO&CCP 19.5

SINTER PLANT 29.0

BLAST FURANCE 24.0

SMS&CCM 14.5

LMMM 11.5

WRM 13.5

MMSM 11.5

CRMP 4.0

TPP 35.0

WATER SUPPLY 2.0

ASP 29.5

TOTAL 221.0

3.2 Sources of power for vsp:

20

CAPTIVE POWER PLANT

STATE ELECTRICITY GRID

DIESEL GENERATORS

3.2.1 There are three Captive Generation Sources:

The main source is the Thermal Power Plant (TPP) with 5 boilers, 4 generators ( 3

of 60MW capacity and 1 67MW capacity) and 2 turbo blowers

A Back Pressure Turbine Station with 2 alternators, each of 7.5MW capacity.

A Gas Expansion Turbine Station with 2 alternators, each of 12 MW capacity.

These are gas powered alternators unlike alternators in other units which are steam

powered.

Fig (3.2.1)

5. INTRODUCTION OF POWER SYSTEM IN

VSP

 Distribution networks:-

 

21

Distribution networks (D.N.W) department is a service sector in Vishakhapatnam

steel plant. It plays a vital role as it supplies power to all the sections in the plant. The

major sections of this department include

     Main receiving station (M.R.S)

     Load block step-down substations (L.B.S.S)

     Relays Testing Laboratory

The brief introduction of these sections is mentioned below,

 Main Receiving Station (M.R.S):- This is a place where power (220kv ac) from A.P.TRANSCO and from Thermal

Power Plant are received. From here the power is distributed to various load block step

down substations such as L.B.S.S-2, L.B.S.S-3, and L.B.S.S-4.

  This is a 220kv substation receives power from VSPSS of APTRANSCO through a

double circuit transmission line and capacitive power plant TPP through 220kv lines.

The following are the loads connected to the BUS BARS:

S. No1.

2.

BUSBUS-1

BUS-2

LOADS CONNECTEDTIE-1TIE-3LBSS-3LBSS-4TOWNSHIP

TIE-2LBSS-2

This substation supplies power at 220kv through double circuit transmission line to

LBSS-2, LBSS-3, and LBSS-4. MRS also supplies power to LBSS-2, LBSS-3, and LBSS-4.

MRS also supplies power to township through CPRS(Construction Power Receiving

Station) by stepping down from 220kv to 33kv and then 33kv to 11kv and further

distributed and step down to working voltage. The scope includes operation and

22

maintenance of equipment at MRS and coordination with TPP for import and export of

power.

220 kV TRANSMISSION LINES IN VSP

Fig (6.1)

70 MW

50 MW10 MW

50 MW

70 MW

1.1 KM

3.4 KM

2.1 KM1.6 KM

8.3 KM

LBSS 5

LBSS 1

LBSS 2

LBSS 4LBSS 3

MRS

23

Fig (6.1)

24

APTRANSCO SUPPLY NETWORK:

The Power Grid Corporation’s Sub-station adjacent to Ukkunagaram is connected

to Vijayawada by a 400 kV line. It is also being connected to Jaipur, Orissa (Eastern Grid)

through DC back to back arrangement of 500 MW capacity and by 400 kV AC double

circuit line.

Power is stepped down through a 315 MVA, 400/220 kV auto transformer at Power

Grid Corporation Sub-station and is fed to the adjacent APTRANSCO switching station.

This switching station is also connected to Bommuru and Gajuwaka sub-stations by 220

kV double circuit lines. Bommuru sub-station is connected to generating stations at

Vijayawada, Lower Sileru, Vijjeswaram, Kakinada and Jegurupadu. Gajuwaka sub-

station is connected to Upper Sileru. Two 1000 MW Thermal Power Stations are expected

to come up in the next few years at Visakhapatnam and close to steel plant.

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 (220kv):

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

entire plant is configured as five electrical Load Blocks and Steps down sub-stations are

provided in each block (designated as LBSS 1 to 5) with 220KV transformers to step down

power to 33/11/6.6 KV and for further distribution as indicated below

:

STATION DESIGNATION AREAS COVERED

25

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 inter

connected 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. To ensure continuity of supply and also facilitate maintenance, the stations are

connected by double circuit line. 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 lines and two transformer in service, all the loads can

be catered to.

.

26

CONCLUSION

VSP is having its own captive power plant through which the power is

distributed to all the units in VSP. In addition to its own captive power plant, AP TANSCO

grid is also kept synchronized with its power system. In recent stage latest technology and

equipment’s are also being introduced.

This project is the result of our study on the generation and distribution of

Electrical power in Visakhapatnam Steel Plant. The whole generation and distribution

process is thoroughly studied and the report is presented.