Undergraduate Internship Report

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Acknowledgement

First of all, we would like to thanks our heartfelt gratitude to Almighty Allah for His help to
complete our internship successfully.

We would like to thank our honorable supervisor Sanaul Haque, Senior lecturer, Department of
Electrical & Electronic Engineering, East West University, for her constant
support, cooperation and generosity.

We would like to thank our honorable chairperson Dr. Mohammad Mojammel Al Hakim,
Professor, Department of Electrical & Electronic Engineering, East West University, for being so
kind during the period of our internship.

We would like to express our sincere gratitude to the authority of Bangladesh Power Development
Board for providing us the precious opportunity to work in the field of power plant maintenance
and operation at Ghorashal Power Station.

We would like to acknowledge the advice and guidance of Engr. Mohammad Ali Firoz, Director
in Ghorashal Training Center. We also thank all the engineers and members of Ghorashal Power
Station for their guidance and suggestions.

I want to show our gratefulness to all the respondents who spared their precious time in answering
our questionnaires.

Finally we want to thank all of our teachers, friends and family for their inspiration and co-
operation throughout our whole academic life in East West University.

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Executive Summary

We did our internship at Ghorashal Power Station (GPS), located on the Eastern bank of river
Shitalakkha at North East of Dhaka under Palash, Narsingdi district from 18th April 2018 to 6th
May 2018.

In Ghorashal Power Station we visited the whole power plant and achieved a clear idea about its
generation, controlling and maintenance process. Six units at GPS are steam power plant and one
is combine cycle power plant, so water for its purpose is gathered from the Shitalakkha River.
Water is boiled by burning gas which is supplied by Titas Gas Distribution Company to produce
steam. Substation is an important part of a power station to distribute power and protection
purpose. We acquired knowledge about various types of transformers, bus-bars, circuit breakers,
lightning arresters, instrument transformer and other equipment of the substation which were
clearly shown by the senior engineers of the substation at Ghorashal Power Station.

During our internship period we observed and gathered various knowledge and experiences over
the topics which we have learned inside the class room or from books. In this report we have
focused on the process which is used in Ghorashal Power Station for power generation.

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TRAINING SCHEDULE

The table of our training schedule in Ghorashal Power Station (GPS) is given below:
Date Subjects Time Mentor

Engr. Abdullah Bin Aziz

Generation, Transmission &
Distribution.
18.04.2018 09am to 05pm
Engr. Md. Niaz Morshed
(Wednesday) Thermal Diagram of 210MW
Unit.
Engr. Md. Asraful Islam
Start up procedure of 210MW
steam turbine power plant.
Shut down procedure of 210MW Engr. Kartick Chandra
19.04.2018 09am to 05pm
steam turbine power plant.
(Thursday)
Chemical plant and its control, Mr. Md. Abdul Mannan
demi water and its different stage.
20.04.2018 Gas turbine operation & 09am to 05pm Engr. Md. Istiak Hossain
(Friday) maintenance.
Practical visit at 4th unit Re- Engr. Jasim Uddin Khadem
21.04.2018 powering project.
(Saturday) Practical visit at 365MW CCPP. 09am to 05pm Engr. Md. Rukanuzzaman

CCPP, Their flow diagram and Engr. Md. Sultan Salahuddin

22.04.2018 working principle.
(Sunday) Transformer failure, their causes 09am to 05pm Engr. Md. Masud Rana
remedies.
Synchronization system,
condition, generation, grid Engr. Md. Delower Hossain

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voltage relation, problem and Khalifa

solution of 210MW unit. 09am to 05pm
23.04.2018 Turbine rolling, synchronization,
(Monday) load shearing, load reduction, Engr. Md. Aminul Haque
emergency shutdown of turbine.
Relays, their functions and Engr. Md. Sariful Islam
24.04.2018 characteristics.
(Tuesday) Generator, Exciter & Motors. 09am to 05pm Engr. Md. Amirul Momenin

Transmitter, controller, control Engr. Dilip Kumer Biswas

loop, control valve.
25.04.2018 Circuit breaker, Isolator, Bus bar 09am to 05pm
(Wednesday) and Lightning arrestor, Engr. Md. Abul Basher
Grounding. Feeder and their
functions.
Substation, Switchgear & Engr. Md. Abu Baker
protection of high voltage system. Siddique
26.04.2018
(Thursday) Construction and working 09am to 05pm
Engr. Khirod Mohan Bose
principle of Boiler and its
Auxiliaries.

HFO plant and impact of IPP.

27.04.2018
Sustainable development goals 09am to 05pm Engr. Md. Azzizul Haque
(Friday)
and its impact in power sector.

Basic principle of DCS and Engr. Kh. Mokammel Hossain

28.04.2018 09am to 05pm
Networking.
(Saturday)
Thermometer, Monometer. Engr. Md. Towhidur Rahman

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Discussion on power plant

Engr. Md. Enamul Haque
Simulator at Simulator lab.
30.04.2018
Demonstration of gas turbine
(Monday) 09am to 05pm Engr. Md. Jewel Hossain
power plant using power plant
Serazi
Simulator at Simulator lab.
03.05.2018 Different test procedure of
(Thursday) transformer and practical 09am to 05pm Engr. Abu Baker
demonstration at electrical lab.
04.05.2018 Different types of protection Engr. Md. Mahabubur
(Friday) system used in Boiler, Turbine 09am to 05pm Rahman
and Generator.
05.05.2018 Examination, Round Table
09am to 05pm Engr. Mohammad Ali Firoz
(Saturday) conference & Evaluation.

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Table of Content
TRAINING SCHEDULE .................................................................................................................................... 5
Chapter 1: Introduction .............................................................................................................................. 14
1.1 Objective of the Internship ............................................................................................................... 14
1.2 Company Profile ................................................................................................................................ 14
1.3 Mission and Vision ............................................................................................................................ 14
1.4 Production Capacity .......................................................................................................................... 14
1.6 Future Projects of GPS ...................................................................................................................... 15
Chapter 2: Power Generation, Transmission and Distribution ................................................................... 16
2.1 Introduction ...................................................................................................................................... 16
2.2 Generation ........................................................................................................................................ 16
2.2.1 Steam Turbine Power Plant ....................................................................................................... 17
2.2.1.1 Components of STPP ............................................................................................................... 17
2.2.1.2 Steam Turbine ......................................................................................................................... 19
2.2.2 Gas Turbine ................................................................................................................................ 21
2.2.3 Working Principle of Combined Cycle Power Plant ................................................................... 23
2.3 Transmission ..................................................................................................................................... 23
2.4 Distribution ....................................................................................................................................... 24
CHAPTER 3: Steam Turbine Power plant .................................................................................................... 25
3.1 Introduction ...................................................................................................................................... 25
3.2 Working Principle of Steam Turbine at GPS...................................................................................... 25
3.3 Pumps Used in STPP .......................................................................................................................... 26
3.3.1 Circulating Water Pump ............................................................................................................. 26
3.3.2 Feed Water Pump ...................................................................................................................... 26
3.3.3 Lube Oil Pump ............................................................................................................................ 27
3.4 Water Treatment Plant ..................................................................................................................... 27
3.5 Boiler ................................................................................................................................................. 27
3.5.1 Economizer................................................................................................................................. 28
3.5.2 Super Heater .............................................................................................................................. 28
3.6 Steam Turbine ................................................................................................................................... 29

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3.6.1 High Pressure Turbine ................................................................................................................ 29

3.6.2 Intermediate Pressure Turbine .................................................................................................. 29
3.6.3 Low Pressure Turbine................................................................................................................. 30
3.7 Exhaust stack..................................................................................................................................... 30
3.8 Generator .......................................................................................................................................... 31
3.8.1 Major Components of the Generator ........................................................................................ 32
3.8.3 Generator Cooling System ......................................................................................................... 34
3.8.4 Protection System of Generator ................................................................................................ 34
3. Stator Earth Fault Protection .......................................................................................................... 35
3.9 Control Room .................................................................................................................................... 35
Chapter 4: Combined Cycle Power Plant .................................................................................................... 37
4.1 Introduction ...................................................................................................................................... 37
4.2 Working Principle of Combined Cycle Power Plant .......................................................................... 37
4.3 Equipment’s of Gas Turbine .............................................................................................................. 37
4.3.1 Combustion Chamber ................................................................................................................ 37
4.3.2 Compressor ................................................................................................................................ 38
4.3.3 Diesel Engine .............................................................................................................................. 38
4.3.4 Gas Turbine ................................................................................................................................ 38
4.3.5 Alternator ................................................................................................................................... 38
4.3.6 Exhaust Stack ............................................................................................................................. 38
4.3.7 Torque Convertor ....................................................................................................................... 39
4.3.8 Intercooler.................................................................................................................................. 39
4.3.9 Regenerator ............................................................................................................................... 39
4.3.10 Air Intake Filter......................................................................................................................... 39
4.4 Equipment’s of Steam Turbine ......................................................................................................... 40
4.4.1 Boiler Drum ................................................................................................................................ 40
4.4.2 Cooling Tower ............................................................................................................................ 40
4.4.3 Demi Water Tank ....................................................................................................................... 41
4.4.4 Economiser................................................................................................................................. 41
4.4.5 Super Heater .............................................................................................................................. 42

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4.4.6 Condenser .................................................................................................................................. 42

4.4.7 Deaerator ................................................................................................................................... 42
4.5 Control Room .................................................................................................................................... 42
Chapter 5: Substation ................................................................................................................................. 43
5.1 Introduction ...................................................................................................................................... 43
5.2 Types of Transformer ........................................................................................................................ 43
5.2.1 Power Transformer .................................................................................................................... 43
5.2.2 Current Transformer .................................................................................................................. 44
5.2.3 Potential Transformer ................................................................................................................ 45
5.2.4 Auxiliary Transformer ................................................................................................................ 45
5.2.5 Auto Transformer....................................................................................................................... 45
5.3 Bus Bar .............................................................................................................................................. 45
5.4 Types of Circuit Breaker in GPS ......................................................................................................... 46
5.4.1 Air Blast Circuit Breaker ............................................................................................................. 46
5.4.2 SF6 Circuit Breaker ..................................................................................................................... 47
5.5 Lightning Arresters ............................................................................................................................ 47
5.6 Wave Traps ....................................................................................................................................... 48
5.7 Isolator .............................................................................................................................................. 48
5.8 Types of Relay at GPS ........................................................................................................................ 48
5.8.1 Differential Relay........................................................................................................................ 48
5.8.2 Over Current Relay ..................................................................................................................... 49
5.9 Transformer Oil Test ......................................................................................................................... 49
5.10 Load Loss and Impedance Test ....................................................................................................... 50
5.11 Transformer Tap Changer ............................................................................................................... 50
5.12 Transformer Bushing....................................................................................................................... 51
5.13 Conservator Tank ............................................................................................................................ 51
5.14 Radiator........................................................................................................................................... 52
Chapter 6: Conclusion ................................................................................................................................. 53
6.1 Discussion.......................................................................................................................................... 53
6.2 Problems ........................................................................................................................................... 53

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6.3 Recommendations ............................................................................................................................ 53

Reference .................................................................................................................................................... 54

List of Figure
Figure 2.1: Schematic of Power Generation, Transmission and Distribution……….……16
Figure 2.2: Flow Diagram of Water Treatment Process …………………………….……17
Figure 2.3: Impulse Turbine and Reaction Turbine ………………………………….…...19
Figure 2.4: Working Principle of Gas Turbine………………………………………... …21
Figure 2.5: Working Principle of Combustion Chamber………………………………….22
Figure 2.6: Working Principle of Combined Cycle Power Plant………………………….23
Figure 3.1: Steam Turbine Power Plant at GPS …………………………………………..25
Figure 3.2: Circulating Water Pump………………………………………………...…….26
Figure 3.3: Feed Water Tank………………………………………………………..…….26
Figure 3.4: Lube Oil Pump………………………………………………………..………27
Figure 3.5: Clarified Process of Water Treatment Plant at GPS………………………….27
Figure 3.6: Boiler Drum at GPS…………………………………………………………..28
Figure 3.7: Rotor Blade of HPT at GPS…………………………………………………..29
Figure 3.8: Rotor Blade of IPT at GPS……………………………………………………30

Figure 3.9: Rotor Blade of LPT at GPS…………………………………………………...30

Figure 3.10: Exhaust Stack of Steam Turbine at GPS…………………………………….31

Figure 3.11: Generator of 4th Unit at GPS………………………………………………..31

Figure 3.12: The Stator of Unit-4 Generator at GPS……………………………………...33

Figure 3.13: Rotor of Unit-4 Generator at GPS…………………………………………...33

Figure 3.14: Control Room of 1&2 Unit at GPS…………………………………………..36

Figure 4.1: Combined Cycle Power Plant…………………………………………………37

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Figure 4.2: Diesel Engine. .……………………………………………………………..... 38

.
Figure 4.3: Exhaust Stack……………………………………………………………….....39

Figure 4.4: Air Intake Filter………………………………………………………………..40

Figure 4.5: Cooling Tower…………………………………………………………………41
Figure 4.6: Demi Water Tank……………………………………………………………....41
Figure 4.7: Control Room…………………………………………………………………..42
Figure 5.1: Substation…………………………………………………………………….....43
Figure 5.2: Power Transformer……………………………………………………………...44
Figure 5.3 Current Transformer……………………………………………………………..44
Figure 5.4 Potential Transformer……………………………………………………………45
Figure 5.5: Bus Bar………………………………………………………………………….46
Figure 5.6: Air Blast Circuit Breaker………………………………………………………..46
Figure 5.7: SF6 Circuit Breaker……………………………………………………………..47
Figure 5.8: Lightning Arresters……………………………………………………………...47
Figure 5.9: Wave Trap……………………………………………………………………….48
Figure 5.10: Isolator………………………………………………………………………….48
Figure 5.11: Differential Relay………………………………………………………………49
Figure 5.12: Over Current Relay……………………………………………………………..49
Figure 5.13: Transformer Oil Test……………………………………………………………50
Figure 5.14: Load Loss and Impedance Test…………………………………………………50
Figure 5.15: Transformer Tap Changer………………………………………………………51
Figure 5.16: Transformer Bushing……………………………………………………………51
Figure 5.17: Conservator Tank………………………………………………………………..52
Figure 5.18: Radiator………………………………………………………………………….52

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List of Table
Table 1.1: Production Capacity of All Units at GPS…………………………………………..14
Table1.2: Project at a Glance…………………………………………………………………..15
Table 2.1: Number of Substation across the Country………………………………….………23
Table 2.2: Length of Transmission Line across the Country…………………………………..24
Table 3.1: Capacity and Efficiency of Boiler…………………………………………………..28
Table 3.2: Ratings of Boilers of 55MW and 210 MW Units of GPS…………………………..28
Table 3.3: Ratings of 55 MW and 210 MW Generators………………………………………..32

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Chapter 1: Introduction
1.1 Objective of the Internship

The main objective of this internship is to achieve practical knowledge and experience about power
station. It is our academic requirement also. It is a great opportunity to do internship at Ghorashal
Power Station. It is the second largest power station of Bangladesh [1]. It has started its operation
in the year of 1974 [2]. The total capacity of the GPS is 1315 MW which is generated by 7 units.
We started our internship on 18th April 2018 and completed on 5th May 2018. During this time
we have achieved practical knowledge about power generation, transmission and distribution
process of GPS. We could relate the theoretical knowledge with the practical activities at GPS. In
this report we will discuss what we have observed and learnt at GPS.

1.2 Company Profile

Ghorashal Power Station (GPS) is the second largest power station in Bangladesh. It has started
its operation in the year of 1974. It is situated at the Eastern bank of river Shitalakkha at North
East of Dhaka under Palash, Narsingdi district. GPS has installed capacity of 1315MW. It has six
units of steam turbines and 1 unit of combine cycle. In this power station, natural gas (CH4) is
used as fuel from Titas Gas Transmission and Distribution Company [2].

1.3 Mission and Vision

The mission of Ghorashal Power Station is to deliver quality electricity at reasonable price with
excellent professional service. The vision of Ghorashal power plant is to increase power generation
capacity within 2022 with the help of re powering project of unit-4 [3].

1.4 Production Capacity

Ghorashal Power Station has total 7 units. 6 units are steam turbine power plant and 1 is combined
cycle power plant. For the steam turbine power plant Russian technology and for the combined
cycle power plant Chinese technology is used at GPS. Generated voltage of unit 1 and 2 is 10.5
kV with the capacity of 55 MW each. For unit 3, 4, 5 and 6 the generated voltage is 15.75 kV with
the capacity of 210 MW each and for unit 7 the generated voltage is 20 kV with the capacity of
365MW. This generated voltage is increased by step up transformer for transmission. The table
1.1 shows the production capacity of all units at GPS.
Table 1.1: Production Capacity of All Units at GPS
Unit No Installed Capacity (MW)

Unit-1 55
Unit-2 55

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Unit-3 210
Unit-4 210

Unit-5 210
Unit-6 210
Unit-7 365

1.6 Future Projects of GPS

GPS installed generation capacity is 1315 MW. A plan has been taken to increase the total
established generation capacity. In order to achieve this target, GPS has decided to set up a new
power plant project named ‘Bangladesh Ghorashal Unit 4 Repowering Project’ [4].
Table1.2: Project at a Glance [2]
Project ID P128012

Country Bangladesh

Region South Asia

Status Active

Approval Date (as of board December 21, 2015

presentation)

Closing Date March 31, 2022

Total Project Cost US$ 263.00 million

Commitment Amount US$ 217.00 million

Team Leader Mohammad Anis

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Chapter 2: Power Generation, Transmission and

Distribution
2.1 Introduction
The main objective of a power plant is to generate electricity. The generated electricity needs to
be transmitted and distributed to serve the users. This chapter briefly discusses the generation,
transmission and distribution of electricity.

2.2 Generation
There are different types of power plants in Bangladesh which generate electricity and synchronize
it with the national grid. Bangladesh's total installed electricity generation capacity has reached
nearly 16,833 megawatts (MW) [1]. Bangladesh Power Development Board (BPDB) has taken a
great capacity expansion plan to add about 11,600 MW generation capacities within next 5 years
to achieve 24,000 MW capacities. The figure 2.1 shows the general overview of a power system.
After the generation with the help of power transformer voltage level is increased. It’s also called
unit transformer. Then electricity is transmitted to the substation through transmission line. In sub-
station, a step down transformer is used to decrease the voltage level and then electricity is
transmitted to the distribution substation. According to BPDB the transmission lines are reportedly
raised to 10,436 km while the distribution line to 401,000 km. Finally the distribution substation
provides electricity to their consumers.

Figure 2.1: Schematic of Power Generation, Transmission and Distribution [5]

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2.2.1 Steam Turbine Power Plant

Steam Turbine Power Plant (STPP) is known as Thermal power plant. Steam is used as prime
mover. Here, the main element for production is steam. STPP convert heat energy of coal
combustion into electrical energy.

2.2.1.1 Components of STPP

The major components of an STPP are:

(a) Water Treatment Plant

For safety of blades and to avoid ionization, the water needs to be de-mineralized. At first the raw
water is rise to the clarifier tank with the help of Circulating Water Pump to remove suspended
matter of water. After this process, the water is known as coagulated water. This water is partially
clear and contains some floating coagulant and other floating substances. The next filter is sand
filter. Water is filtered here by mechanical process. After this process the water is known as
clarified water or filtered water. By the cation exchange resin and anion exchange resin all ion of
water is removed. Then it goes to de gasifier where gaseous substances specially carbon dioxide
is remove mechanically and chemically. For the over purification water is filtered again by cation
exchange resin and anion exchange resin. It’s called 2nd stage of cation and anion stage filter. the
water is formed as semi-de-mineralized water. This water is used for cooling and for the production
of de-mineralized water. The semi-de-mineralized water contains trace amounts of cation & anion
which are removed by the mixed bed exchanger.
After mixed bed exchanger the water is known as De-mineralized water. This water is use for
Boiler feeding.

Figure 2.2: Flow Diagram of Water Treatment Process

(b) Boiler
A boiler is a device which is used to produce steam. The main purpose of the boiler section is to
produce necessary and good quality steam which is rotate the turbine blades. To produce steam,
the boiler has some requirements. The primary requirements of the boiler are:

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1. Water must be safely contained.

2. Steam must be delivered at rated pressure, temperature.

(c) Types of Boiler

According to the relative position of hot gases and water, boilers are two of types.

 Fire Tube Boiler: A fire-tube boiler contains hot gases from a fire pass through many
tubes running through a sealed container of water. The heat of the gases is transferred
through the walls of the tubes by thermal conduction [6].

 Water Tube Boiler: A water tube boiler is a type of boiler in which water circulates in
tubes heated externally by the fire. Fuel is burned inside the furnace which creating hot gas
and heats water in the tubes [7].

(d) Component of Boiler

1. Furnace
Furnace is the chamber inside boiler where natural gas or coal is burned with the presence of air
for producing heated gas or flue gas. The ratio of gas and air is 1:10. The temperature inside the
furnace chamber is 1500-1800°c. The treated water from the feed water tank first passes through
economizer and then enters into the furnace through tubes and the flue gas, produced inside the
furnace, passes around the tubes. By this way flue gas releases heat to the water and water becomes
saturated steam.

2. Boiler Drum
Water is reserved in the boiler drum which is converted to the saturated steam. A level transmitter
is used inside the boiler drum to measure the level of water. The plant will trip If the water level
is crosses the limit. So, it is very important to control the level of water. This is done by an
automatic system. From the boiler drum the saturated steam is transferred into the super heater.

3. Economizer
The economizer is a device which recovers some of the heat which is carried by exhaust flue gas.
The recovered heat is utilized to increase the temperature of feed water. As a result consumption
of fuel is decreases.

4. Super Heater
Super heater is a part inside the furnace where saturated steam is converted to super heated steam.
There are 3 types of super heater-
a. Radiant Super heater
b. Platen Super heater
c. Convective Super heater (1 and 2)

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There will be no water content in the super heated steam. So, the super heater converts the wet
saturated steam into dry high temperature steam. The temperature of the super heated steam inside
the super heater is about 540°C. This super heated steam is then supplied to the high pressure
turbine at a pressure of 130 bar. There are bundle of tubes inside the super heater which carries the
saturated steam and the flue gas passes around these tubes. While passing around the tubes the flue
gas releases heat and the saturated steam receive the heat and become dry and super heated.

5. Induced Draught Fan

In this system a fan or blower is located at or near the base of the chimney. The pressure of the
furnace is reduced below that of the atmosphere. By creating a partial vacuum in the furnace and
flue gas pipe, the products of combustion are drawn from the main flue gas pipe and they pass up
the chimney. This draught is used usually when economizers and air pre heaters are incorporated
in the system.

6. Forced Draught Fan

Forced draught fan is known as FD fan. At first it sucks the air and then passes it through the pre
heater. Finally, the fans draw warm air from the top of the boiler house through large air heaters.
Dampers are used to control the quantity of air admitted to the furnace. Forced draught furnaces
usually have a positive pressure.

7. Water Wall
Furnace chamber is surrounded by many tubes with water inside. These surrounded water tubes
are called water wall. Steam is generated in the tubes and then goes to the boiler drum.

8. Flue Gas Stack / Chimney

A chimney is a structure which provides ventilation for hot flue gases or smoke from a boiler to
outside atmosphere.

2.2.1.2 Steam Turbine

Steam turbine converts thermal energy to mechanical energy. In a power plant, steam turbine is
attached to a generator to act as the prime mover.

Figure 2.3: Impulse Turbine and Reaction Turbine [19]

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The turbine acts as the more mechanical side of the system by providing the rotary motion for the
generator, while the generator acts as the electrical side by employing the laws of electricity and
magnetism to produce electrical power. Steam turbine is generally classified into two types
according to the action of steam on moving blades.

2.2.1.2.1 Turbine Parts and Auxiliaries

1. Turbine Rotor
Running through the center of the turbine is a sturdy axle called the rotor; it takes power from the
turbine to an electric generator. The blades are the most important part of a turbine, they capturing
as much energy as possible from the steam and converting it into rotational energy by spinning the
rotor. The size and characteristics of the blades of the turbines in these sections are different from
each other. These are,

1. High pressure turbine (HPT),

2. Intermediate pressure turbine (IPT)
3. Low pressure turbine (LPT)

2. Nozzle
A nozzle is a duct of smoothly varying cross-sectional area in which a steadily flowing fluid can
be made to accelerate by a pressure drop along the duct. The nozzle expands the steam, increasing
its velocity and redirecting the flow into the turbine blades.

3. Bearing
Two types of bearings are used to support and locate the rotors of steam turbines. It is journal and
thrust bearings. Journal bearings are used to support the weight of the turbine rotors. A journal
bearing consists of two half-cylinders that enclose the shaft and are internally lined with Babbitt,
a metal alloy usually consisting of tin, copper and antimony. Thrust bearings axially locate the
turbine rotors. A thrust bearing is made up of a series of Babbitt lined pads that run against a
locating disk attached to the turbine rotor. High-pressure oil is injected into the bearings to provide
lubrication. The oil is carefully filtered to remove solid particles. Specially designed centrifuges
remove any water from the oil.

4. Condenser
Condenser is a device that condenses the steam which is coming from the turbine exhaust for re
using. Condenser serves two important functions; it creates a very low pressure at the exhaust of
the turbine causing the expansion of the steam in the prime mover at a very low pressure. It’s a
one kind of heat exchanger.

5. Governing System
The governor system is the most important element of fuel system. It keeps the engine running at
the demand speed regardless of changes in the load. It controls the amount of fuel supply and the
level of fuel in the power station.

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2.2.2 Gas Turbine

A gas turbine is also known as combustion turbine. There are three main components:
1. An upstream rotating gas compressor.
2. A downstream turbine on the same shaft;
3. A combustion chamber or area, called a combustor, in between 1and 2 above.

2.2.2.1 Working Principle of Gas Turbine

At first through air intake filter take fresh air from atmosphere. Then this fresh air goes to the
compressor and compressed air through air volume decreased and increased air presser.
Compressed air come out from compressor and go to the combustion chamber which compressed
air and fuel are mixed where produce flue gas. This flue gas goes to the turbine stages when the
flue gas passed turbine blade the heat energy convert into mechanical energy. This mechanical
energy converts into electrical energy by the alternator where alternator coupled with gas turbine.
When turbine heat energy convert into mechanical energy and come out exhaust flue gas from
turbine.

Figure 2.4: Working Principle of Gas Turbine [18]

2.2.2.2 Equipment of Gas Turbine

1. Air Intake Filter: The compressor function is natural air compressed that’s mean increased
pressure which come out through air intake filter. Air intake filter is devices which remove
unwanted partials from the natural air so that compressed is easy and ensure good quality
combustion products or flue gas.

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2. Compressor: The compressor is playing a very important role for a gas turbine. For a gas
turbine the compressor function are supplying air where sufficient amount of needed for a
combustion burner and increases pressure.
3. Intercooler: The compressed high pressure air come out the compressor and goes to the
intercooler. Intercooler is a device which air is cooling so that air volume is decreased for this
reason rise in pressure. Through the intercooler uses we get two benefited one of them overall
thermal efficiency and another one is steam capacity increased per square cm.
4. Regenerator: The high pressure air is come out the intercooler and goes to the regenerator. The
Regenerator is device which rises in temperature of an exhaust flue gas. The regenerator is
increased thermal efficiency of a power plant.
5. Combustion chamber: Combustion chamber is very important stage for a gas turbine power
plant. In a chamber air and fuel are mixed which produces combustible matter or flue gases.

Figure 2.5: Working Principle of Combustion Chamber [17]

6. Alternator: The gas turbine is shafted with alternator. Alternator is converted mechanical
energy into electrical energy. This electrical energy come out and goes to the power transformer
which is step up transformer.
7. Exhaust stack: The exhaust stack come out from gas turbine. In only gas turbine power plant
where exhaust flue gas go to the atmosphere. At the same time for combine cycle power plant
exhaust flue gas not come out atmosphere where flue gas reuses for increased boiler temperature.
8. Gas turbine: The combustion chamber exhaust flue gas come out and go to the gas turbine
when high temperature exhaust flue gas passes through turbine blade then gas turbine heat energy
converted into mechanical energy. Gas turbine coupled with alternator and its providing
mechanical energy so that rotating for alternator and it convert into electrical energy.

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2.2.3 Working Principle of Combined Cycle Power Plant

At first, by the air intake filter collect fresh air from atmosphere. Then this fresh air goes to the
compressor and compressed the air by decreased the air volume and increased pressure of air.
Compressed air come out from compressor and goes to the combustion chamber. Compressed air
and fuel are mixed here and produce flue gas. This flue gas goes to the turbine stages when the
flue gas passed turbine blade the heat energy convert into mechanical energy. This mechanical
energy converts into electrical energy by the alternator where alternator coupled with gas turbine.
When turbine heat energy convert into mechanical energy and come out exhaust flue gas from
turbine. The heat of the gas turbine’s exhaust is used to generate steam by passing it through a heat
recovery steam generator (HRSG) with a live steam temperature around 600°C.

Figure 2.6: Working Principle of Combined Cycle Power Plant [16]

The heat Recovery Steam Generator quite fresh water flows in tubes and the hot gases passes a
around that and thus producing steam. The steam then rotates the steam turbine and coupled
generator to produce Electricity. The hot gases leave the HRSG at around 100 degrees centigrade
and are discharged into the atmosphere.

2.3 Transmission
For transmission and distribution system substation is an important part of an electricity
generation. Transformers are used to transform voltages from high level or medium level to low
level or vice-versa. For the operation, maintenance and development of transmission line all
responsibility goes to the Power Grid Company of Bangladesh (PGCB).
Table 2.1: Number of Substation across the Country [14]

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Name Number
400 kV 1
400/230 kV 4
400/132 kV 1
230/132 kV 20
132/33 kV 98

Table 2.2: Length of Transmission Line across the Country [15]

Name of Line Length
400KV Transmission Lines 348.88 Route km.
230 KV Transmission Lines 1633.853 Route km.
132 KV Transmission Lines 4278.494 Route km.

Route km is the distance taken by the mode of transport referred to.

2.4 Distribution
Distribution of power in Bangladesh is done by three organizations. They are
1. Bangladesh Power Development Board (BPDB): BPDB is in charge of distribution of electricity
in district towns.
2. Rural Electrification Board (REB): REB is in charge of distribution of electricity in rural areas
through 70 rural electric cooperatives.
3. The third one is also a combination of three companies. The companies are,
 Dhaka Power Distribution Company (DPDC): DPDC is in charge of power distribution
to the customers of the Dhaka City Corporation.

 Dhaka Electric Supply Company (DESCO): DESCO is in charge of power distribution

in Dhaka Metropolitan and Naraynganj.

 Western Zone Power Distribution Company Ltd. (WZPDCL): WZPDCL covers the
distribution of electricity in Khulna and Barisal Divisions.

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CHAPTER 3: Steam Turbine Power plant

3.1 Introduction
Steam turbine power plant of Ghorashal Power Station (GPS) has 7 units. The installed capacity
of unit 1 and 2 is 55 MW each and installed capacity of unit 3 to 6 is 210 MW each. This power
plant uses natural gas as fuel to produce steam from water. This steam is then used to drive the
steam turbine. Figure 3.1 shows the steam turbine power plant at Ghorashal Power Station.

Figure 3.1: Steam Turbine Power Plant at GPS

3.2 Working Principle of Steam Turbine at GPS

Boiler of Ghorashal Power Station produces steam by using water from the Shitalakshya river. At
first water is collected from the Shitalakshya River and then sent it to the water treatment plant.
The raw water passes through several processes to produce de-mineralized (demi) water. Demi
water is highly purified for generating steam. Then this water is taken to the boiler using a pump.
At Ghorashal Power Station water tube boiler uses natural gases in the presence of air. The ratio
of gas and air is 1:10. The air through forced draft fan (FDF) and methane (CH4) gas is used as
fuel which is supplied by ‘Titas Gas Transmission and Distribution Company Limited’. The steam
is taken from the boiler to the super heater, where its temperature increases to 540° C and pressure
becomes 130 bar. After that this steam goes to the high pressure turbine (HPT) and the exhaust
steam is taken to re-heater (RH) where exhaust steam decreases to 336`° C and pressure decreases
to 28.4 bar. At RH the temperature of steam becomes 540° C and pressure becomes 24.8 bar. After
that the steam is sent to the intermediate pressure turbine (IPT) and then to the low pressure turbine
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(LPT). At this time the turbine starts to rotate the generator shaft and a speed of 3000 rpm is
maintained. The turbine shaft is coupled with the rotor of generator and electricity is produced.

3.3 Pumps Used in STPP

Circulating water pump, feed water pump and lube oil pump are used in GPS.

3.3.1 Circulating Water Pump

Ghorashal Power Station uses both open and closed system of water flow. There are two pump
houses, one is used as open system when water is available from Sitalakhya River and another one
is used as closed system during dry season. There are three 4MW pumps used to flow water into
condenser.

Figure 3.2: Circulating Water Pump

3.3.2 Feed Water Pump

Feed water pump is used to supply demi-water to boiler drum. In steam power plant of Ghorashal
Power station there are two feed pumps in each of boilers. Figure 3.3 shows the operating feed
water tank at STPP.

Figure 3.3: Feed Water Tank

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3.3.3 Lube Oil Pump

It is mainly used for pumping lube oil for lubrication purpose of turbine and generator bearing. It
pumps more lube oil into the system. Figure 3.4 shows a lube oil pump.

Figure 3.4: Lube Oil Pump

3.4 Water Treatment Plant

Water is the most important element of steam turbine power plant. The source of the raw water is
Shitalakhya River. This raw water is purified by mechanical and chemical processes. Then it is
supplied to the system. The figure 3.5 shows the clarified process at Ghorashal Power Plant.

Fig 3.5: Clarified Process of Water Treatment Plant at GPS

3.5 Boiler
A boiler or steam generator is a device which is used to produce steam. The main purpose of the
boiler section is to produce necessary and good quality steam which rotates the turbine blades.
There are six boilers at GPS and all boilers are water tube boiler.

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Table 3.1: Capacity and Efficiency of Boiler

Description Unit 1,2 Unit 3,4,5,6

Maximum capacity 170 ton/hr 670 ton/hr

Efficiency 90% 93%

Table 3.2: Ratings of Boilers of 55MW and 210 MW Units of GPS

Description 55 MW unit 210 MW unit

Model No. T. M-157 TGME-206/COB

Steam generating capacity 230 670
(Ton/hr)
Steam pressure at boiler out 100 140
let (Kgf/ cm²)
Rated live steam temperature 540 540
(º C)
Secondary steam N.A. 540
temperature (º C)
Efficiency (in %) 90.5 93
Flue gas temperature (º C) 120 132

Figure 3.6: Boiler Drum at GPS

3.5.1 Economizer
The economizer is a device which recovers some of the heat which is carried by exhaust flue gas.
The recovered heat is utilized to increase the temperature of feed water. As a result consumption
of fuel is decreases.

3.5.2 Super Heater

Super heater is a part inside the furnace where saturated steam is converted to super heated steam.
There are 3 types of super heater-
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a. Radiant Super heater b. Platen Super heater c. Convective Super heater (1 and 2)
There will be no water content in the super heated steam. So, the super heater converts the wet
saturated steam into dry high temperature steam. The temperature of the super heated steam inside
the super heater is about 540°C. This super heated steam is then supplied to the high pressure
turbine at a pressure of 130 bar. There are bundle of tubes inside the super heater which carries the
saturated steam and the flue gas passes around these tubes. While passing around the tubes the flue
gas releases heat and the saturated steam receive the heat and become dry and super heated

3.6 Steam Turbine

The steam turbines used in GPS have three different sections. The size and characteristics of the
blades of the turbines in these sections are different from each other. These are,

3.6.1 High Pressure Turbine

From the super heater, steam with 130 kg/ cm² pressure and 540°C temperature first enters the
high pressure turbine and then hits the high pressure turbine blades. The high pressure turbine has
twelve stages with moving and fixed blades. After completing twelve stages, the temperature of
steam falls to 332°C and pressure 28 kg/ cm². Steam again goes to super heater to gain heat. High
pressure turbine rotor of unit-4 is shown in figure 3.7

Figure 3.7: Rotor Blade of HPT at GPS

3.6.2 Intermediate Pressure Turbine

From the re-heater steam goes to the intermediate pressure turbine. This turbine has eleven stages.
Here, steam pressure is 25 kg/ cm² and the temperature is 540ºC. If the temperature falls below
440º C or raise above 565º C then the intermediate pressure turbine (IPT) valve will trip and the
steam will go to the boiler for gaining more heat. After completing eleven stages, the temperature
of steam falls to 171ºC and pressure 1.34 kg/ cm². Intermediate pressure turbine rotor of unit-4 is
shown in figure 3.8

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Figure 3.8: Rotor Blade of IPT at GPS

3.6.3 Low Pressure Turbine

From the intermediate pressure turbine, steam enters the low pressure turbine and continues its
expansion. Here, the pressure is about 1.34 kg/ cm² and the temperature is about 171ºC. In low
pressure turbine blades are larger than the previous two sections but the energy of steam is less
than the previous two sections. LPT is divided into two sections and each section contains 3 or 4
stages at GPS.

Figure 3.9: Rotor Blade of LPT at GPS

3.7 Exhaust stack

It is the way of exit of exhaust gas at power plant. The figure 3.10 shows the exhaust stack of
steam turbine power plant at Ghorashal Power Station.

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Figure 3.10: Exhaust Stack of Steam Turbine at GPS

3.8 Generator
The main working principle of generator is convert mechanical energy to electrical energy. There
are two types of generator in GPS. These are 55 MW generators and 210 MW generators. Unit 1
and 2 have 55 MW generators and unit 3-6 have 210 MW generators.

Figure 3.11: Generator of 4th Unit at GPS

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Table 3.3: Ratings of 55 MW and 210 MW Generators.

Description 55 MW unit 210 MW unit
Type TB-60-2 TΓB-200 MT3

KVA 68750 247000

KW 55000 210000

Power factor 0.80 0.85

Frequency 50 Hz 50 Hz

RPM 3000 3000

Number of Phase 3 3

Phase connection Y (star) Y (star)

Rotor voltage 400 V 430 V

Rotor current 1445 A 1950 A

Stator voltage 11.5 KV 15.75 KV

Stator current 2761 A 7698 A

3.8.1 Major Components of the Generator

The major components of generator are discussed below.

1. Stator
Stator is the stationary part of a generator. It contains either an electromagnet or a permanent
magnet. When the stator is an electromagnet, it contains wire winding which are energized with
the help of AC or DC supply. In GPS, stator is electromagnet type. A moving magnetic field
induced a voltage difference between the windings of the stator and it produces AC current as
output of the generator.

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Figure 3.12: The Stator of Unit-4 Generator at GPS

2. Rotor
The rotor is the rotating part of a generator. In this generator, rotor is an electromagnet. Coil
energizes the rotor and makes it an electromagnet. The coil that energies the rotor is known as the
field coil. At GPS the rotor is used as the field exciter and the rotor is driven by the generator prime
mover.

Figure 3.13: Rotor of Unit-4 Generator at GPS

3. Slip Ring
Slip rings are metal rings which are fitted over the shaft of the rotor and are insulated from the
rotor. They rotate as the rotor shaft rotates and one end of the rotor winding is connected to the
slip ring. These rings help transfer of electricity from the stationary brushes to the rotating rotor.

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4. Carbon Brush
Carbon brush is a block which is made of carbon compound. Carbon brushes are placed over the
slip rings and these brushes glide over the slip rings and conduct electricity. The carbon brushes
are also fitted with springs, so that when brushes go down by friction over time, carbon brushes
will still remain in contact with the slip rings.

5. Armature Winding
The armature winding is the main current-carrying winding in which the electromotive force or
counter electromotive force of rotation is induced. The current in the armature winding is known
as the armature current.

3.8.3 Generator Cooling System

Generator deals with very high power. So the temperature of generator rises while running. Too
much heat affects the performance and lifetime of the generator. In GPS, there are cooling systems
installed for the generator which absorb the temperature of the generator while it is running.

1. Water Cooling
Water flow is used in generator for cooling purpose. This type of cooling system is used for stator
cooling. Stator is surrounded by the water. The water absorbs heat and then carries the heat away.
Water flows continuously by a motor to dissipate the heat.

2. Hydrogen Cooling
Hydrogen cooling system is used for rotor cooling. In this system hydrogen gas is used to dissipate
the heat from the rotor. As hydrogen gas is lighter than air, it does less interruption with the rotating
speed of the rotor than air. For this cooling system hydrogen gas is supplied by a hydrogen plant.
In this hydrogen plant, water is electrolyzed into hydrogen and oxygen.

3.8.4 Protection System of Generator

1. Over Speed Protection
Over speed protection is generally provided for prime mover driven generators. All generators in
GPS are prime mover driven generator. Prime mover is the part that rotates the rotor of the
generator. In GPS, a steam turbine works as a prime mover. If the prime mover speed increases
then the generator frequency increases. The speed governor normally controls the speed of the
rotor. If any abnormality exists, it trips the circuit breaker of the generator.

2. Over Current / Under Voltage Protection

In grid system more than one generators supply the load and if for any reason one or more
generators suddenly trip, other generators try to supply the load and each of these generators will
experience a sudden increase in current and thus decrease in voltage. In GPS, automatic voltage
regulator is connected to the system which tries to restore the voltage. Under voltage relay is also
used for the under voltage protection. In GPS, over current relay is used for over current protection.
To construct this relay only current coil is needed; there is no need of voltage coil.
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3. Stator Earth Fault Protection

This fault occurs when the stator of the generator becomes shorted with the ground. Generally the
stator of a generator is very close to the ground. So, this fault can occur. Stator earth faults can
also be caused by the degradation of insulation in the windings. If this fault occurs, the normal low
neutral voltage will rise as high as line-to-neutral voltage. This fault may cause the serious damage.
This fault can be detected by measuring secondary voltage of neutral grounding transformer.

4. Rotor Earth Fault Protection

Rotor field winding of the generator is electrically isolated from the ground. Rotor earth fault may
be caused due to insulation failure of winding. Two methods are available to detect this type of
fault. The first method is that one resistor is connected to the field winding and exciter. The resistor
is centrally tapped and grounded with a voltage sensitive relay. If any earth fault occurs, the relay
senses and closes the path. In second method, one voltage sensitive relay is connected to the field
and exciter circuit. Other terminal of the voltage sensitive relay is grounded. A capacitor and
secondary of one auxiliary transformer is installed between ground and relay. When earth fault
occurs, a secondary voltage will appear across the secondary winding of the auxiliary transformer.
The relay will be operated by sensing the voltage. In GPS, these two methods are used in all six
units.

5. Temperature Protection
Temperature protection is needed to protect the generator from overheating. Overheating is caused
due to overload in grid system or failure in cooling system. It could cause serious damage to the
generator. To protect the stator against overheating, embedded resistance temperature detector or
thermocouples are used. In GPS, thermocouple is used to detect the temperature. When it starts to
overheat, the temperature change is detected and the relay operates an alarm.

6. Frequency Protection
The generator needs to be operated within a certain frequency range. If generator operates over or
under this limit, vibration occurs in the generator which can damage the rotor. This occurs because
of sudden load change in the grid. This relay operates, if the frequency falls below 48 Hz or goes
over 52 Hz.

7. Over Voltage Protection

Over voltage occurs due to sudden loss in the load on the generator. If suddenly load decreases
then the voltage start to rise and causes over voltage. Here, prime mover speed does not change
with the load change. The over voltage protection is provided by two over voltage relays. They are
instantaneous relay and IDMT (Inverse Definite Minimum Time) relay. Instantaneous relay
operates for 130 to 150 % of the rated voltage and IDMT relay operates for 110% of rated voltage.

3.9 Control Room

At Ghorashal power plant, Steam turbine power plant has 3 control room in total. Each of the
room is individually known as unit control room. Unit 1 and 2 are operated by the control room
1. Unit 3 and 4 are operated by the control room 2 and unit 5 and 6 are operated by the control
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room 3. There are 3 sections in the control room. These are defined by Boiler desk, Turbine desk
and Generator desk. .The engineers are monitoring the desk and control a particular unit. All
units are analogue system.

Figure 3.14: Control Room of 1 and 2 Unit at GPS

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Chapter 4: Combined Cycle Power Plant

4.1 Introduction
The 7th Unit of Ghorashal Power Station is combined cycle power plant. The total capacity of
combined cycle power plant is 365MW. The Gas turbine produces 254 MW and steam turbine
produces 109 MW which is run by the exhaust gas of a gas turbine. The working principle and
components of combined cycle power plant of GPS are described in this chapter.

4.2 Working Principle of Combined Cycle Power Plant

The combined cycle power plant of Ghorashal Power Station operates in two ways. one is gas
turbine unit and another one is steam turbine unit. At first pure air is compressed by the compressor
and then this compressed air is sent to the combustion chamber. In the combustion chamber the
compressed air is used to burn the natural gas, which produces burnt gas with high amount of heat
energy. This burnt gas is used to rotate the turbine. The exhaust gas that comes out of the turbine
has enough energy to boil water to produce steam. This steam is used to rotate the steam turbine.

Figure 4.1: Combined Cycle Power Plant at GPS

4.3 Equipment’s of Gas Turbine

4.3.1 Combustion Chamber
Combustion chamber is an enclosed vessel where air and gas are burnt to produce burnt gas. The
ratio of gas and air is 1:20 at Ghorashal Power Station. For combustion chamber, it is required to
have high temperature and high pressure so that turbine blade can rotate. In a combustion chamber
the pressure of air is 7 bar and the pressure of fuel is 31.5 bar at GPS.
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4.3.2 Compressor
For a gas turbine the compressor supplies sufficient amount of air needed for a combustion burner
and increases pressure. The Ghorashal gas power plant compressed pressure is 17.5 bar.

4.3.3 Diesel Engine

Diesel engine is used to run the compressor. The compressor, turbine and the diesel engine all are
connected to the same shaft. When turbine speed reaches 1800 rpm, the diesel engine is
disconnected. Figure 4.2 shows a diesel engine of gas turbine section.

Figure 4.2: Diesel Engine

4.3.4 Gas Turbine

The combustion chamber produces burnt gas and this brunt gases sent to the gas turbine. When
high temperature and pressure brunt gas passes through turbine blade then the energy is converted
into mechanical energy. Gas turbine is coupled with the rotor of the alternator and it provides
mechanical energy for rotation which is then converted into electrical energy.

4.3.5 Alternator
The gas turbine is same shaft with alternator. Alternator converts mechanical energy into electrical
energy. This electrical energy is sent to the power transformer (step up transformer) and this
transformer is directly connected with bus bar.

4.3.6 Exhaust Stack

The exhaust gas that comes out of the gas turbine is normally used for steam turbine section in
GPS. In GPS exhaust gas temperature around 600°c which is used in the boiler to generate steam

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which rotates the steam turbine. After this the gas is released to the atmosphere by the exhaust
stack.

Figure 4.3: Exhaust Stack

4.3.7 Torque Convertor

Torque convertor is one kind of coupling that is used between the diesel engine and the gas turbine
shaft. Initial stage rotating gas turbine is not sufficient running speed. When gas turbine reaches
sufficient speed then torque convertor automatically disconnects from diesel engine in GPS.

4.3.8 Intercooler
The compressed high pressure air is sent to the intercooler. Intercooler is a device where air is
cooled so that air volume decreases and pressure rises. GPS gets two benefits by using intercooler;
one is thermal efficiency and another one is increased steam capacity per square cm.

4.3.9 Regenerator
The high pressure air comes out of the intercooler and is sent to the regenerator. The Regenerator
is a device which rises the temperature of an exhaust flue gas. The regenerator increases thermal
efficiency at GPS.

4.3.10 Air Intake Filter

Air intake filter first receives pure air from the atmosphere then it is sent to the compressor. It
removes any unwanted particles coming in with the air so that it does not cause improper
combustion.
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Figure 4.4: Air Intake Filter

4.4 Equipment’s of Steam Turbine

Equipment’s of steam turbine are given below:

4.4.1 Boiler Drum

The boiler drum of the steam turbine unit of GPS is used for the same purpose as that of the steam
turbine power plant. Compared to the steam turbine power plant, the size of the combine cycle
power plant boiler drum at GPS is smaller.

4.4.2 Cooling Tower

In GPS combine cycle power plant needs large amount of water for steam turbine. Water
purification is highly expensive way. So at GPS, cooling tower is used such that thepurified water
can be easily reused.

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Figure 4.5: Cooling Tower

4.4.3 Demi Water Tank

Demi water is de-mineralized water which does not contain dust particle. The demi water tank
storesde-mineralized water that is needed for steam turbine. At GPS, demi water is used so that
turbine section does not get damaged easily.

Figure 4.6: Demi Water Tank

4.4.4 Economiser
Economizer is used to raise the temperature of feed water that comes from the deaerator storage
vessel. This economizer is capable of raising the temperature of the feed water to 220-230˚C. The
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thermal energy of the exhaust gas from the gas turbine is used to raise the temperature of the feed
water at GPS.

4.4.5 Super Heater

The super heater is a device that is used to convert the wet steam into dry steam. The super heater
is placed at the bottom of the boiler because at this place the temperature of the exhaust gas entering
the boiler is highest and has a value of 600˚c. The super heater also increases the pressure of the
steam. At GPS, from the super heater the super-heated steam is supplied to the steam turbine.

4.4.6 Condenser
At GPS, the condenser is used to condense the exhaust steam coming out of the steam turbine.
This is done so that the steam that is condensed to water can be re-used. There are two condensers,
the first condenser is active all the time and the other is used only when the first one fails.

4.4.7 Deaerator
Deaerator is a device that is used to remove air and other dissolved gases from the feed water.
The feed water that enters the deaerator has a temperature of 40˚c. From the deaerator the feed
water is stored in the dearator storage vessel, where the water has a temperature of 50˚c at GPS.

4.5 Control Room

Control room of combined cycle power plant uses digital technology. Here the operation desk,
displaying different readings of the system, and controlling systems of this plant are maintained.
In the control room, equipments are operated from operating desk.

Figure 4.7: Control Room

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Chapter 5: Substation

5.1 Introduction
Substation is playing important role in electricity generation, transmission and distribution system.
It mainly works at some electrical characteristic such as synchronic voltage, improve power factor
and frequency. There are many equipment in a substation such as relay, circuit breaker,
transformer, bas bar, lighting arrester, CT, PT, isolator, insulator etc. The electrical energy
generated in any power plant first goes to the substation. After that substation transmits the
generated power by step-up transformer so that reduce line loss and transmutation loss and
distribution to the consumer by step down transformer. GPS has an outdoor type substation.

Figure 5.1: Substation

5.2 Types of Transformer

5.2.1 Power Transformer
The power transformers are used in the substation to step up or step down the voltage level while
the power and the frequency remain constant. At GPS, there is a power transformer which is
directly connected generator where generator voltage 11kv by stepped up to 220kv and this line
connected with bus bar.

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Figure 5.2: Power Transformer

5.2.2 Current Transformer

Current transformer transforms current from higher to lower value. Current transformer is a step
up transformer. At GPS, substation use large number of current transformer which is mainly used
for current measurement and over current protection. Here current transformer is in series
connection with other equipment’s of a substation.

Figure 5.3 Current Transformer

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5.2.3 Potential Transformer

Potential transformer transforms voltage from higher to lower value. Potential transformer is a step
down transformer. So, it steps down voltage in a required ratio so that it can be measurable. At
GPS, substation use large number of potential transformer which main purpose for voltage
measurement and high voltage protection. Here potential transformers are parallel connection with
others equipment.

Figure 5.4 Potential Transformer

5.2.4 Auxiliary Transformer

Auxiliary transformer is a power transformer that provides power to the auxiliary equipment of a
power station during its normal operation. At GPS, this transformer is connected directly to the
generator output.

5.2.5 Auto Transformer

Auto transformer is an electrical transformer with only one winding. In an autotransformer,
portions of the same winding act as both the primary and secondary sides of the transformer. Auto
transformer generally used in the situation where primary and secondary voltage ratio is almost
same. At GPS, auto transformer is used between 132kv and 230kv transmission lines.

5.3 Bus Bar

The incoming and outgoing lines in a substation are connected to the bus bars. At GPS, substation
single bus bar arrangement for 132kv and 230kv system and double bus bar system between 132kv
and 230kv system.

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Figure 5.5: Bus Bar

5.4 Types of Circuit Breaker in GPS

5.4.1 Air Blast Circuit Breaker
Air blast circuit breaker sweeps away the arching products in to the atmosphere. Under normal
condition the contacts are closed. When a fault occurs contacts are opened. Most of the old circuit
breakers of GPS are air blast circuit breaker.

Figure 5.6: Air Blast Circuit Breaker

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5.4.2 SF6 Circuit Breaker

In Sulpher Hexafluoride or SF6 Circuit Breaker is used as an insulating and arc extinguish medium.
In the normal operating conditions, the contacts of the breaker are closed. When the fault occurs
in the system, the contacts are open, and an arc is beaten between them.

Figure 5.7: SF6 Circuit Breaker

5.5 Lightning Arresters

In GPS, have large amount of lightning arresters. This lightning arresters will bypass this high
voltage to the ground so that the nearby transformer and other equipment will not be damaged.

Figure 5.8: Lightning Arresters

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5.6 Wave Traps

Wave Traps are used at sub-stations for communicating with other sub-stations. This system is
used to transmit communication and control information at a high frequency over the power lines.
Through the wave traps in GPS substation control room comminute others substation.

Figure 5.9: Wave trap

5.7 Isolator
The isolator is a mechanical switch which is used to isolate a section from any energized conductor.
It is used for safety purpose.

Figure 5.10: Isolator

5.8 Types of Relay at GPS

5.8.1 Differential Relay
The differential relay operation between the current entering the winding and current leaving the
winding is used for sensing relay operation. At GPS, differential relay is used to protect generators,
transformers, bas, and transmission lines from the effects of internal faults.

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Figure 5.11: Differential Relay

5.8.2 Over Current Relay

The over current relay is used for protection purpose. Over current relay first senses the current
flow and trips the circuit breaker if over current flow is detected. In an over current relay here
present current coil. Through this coil normal current is flow but when over current flow by this
coil moving to change the contact position in the relay trips the circuit breaker.

Figure 5.12: Over Current Relay

5.9 Transformer Oil Test

Transformer oil testing is an important part for protection of a transformer. Transformer oil is
playing very good insulation system for a transformer. At GPS periodically perform tests on the
oil and observe is capable of fulfill insulation.

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Figure 5.13: Transformer Oil Test

5.10 Load Loss and Impedance Test

In GPS these two tests are carried out simultaneously. A low-voltage is applied to the HV winding
and LV winding being short-circuited. Ammeter is connected in one phase. The applied voltage is
increased gradually until the ammeter indicates the full load current. The voltage at which the rated
current flows is to be recorded. The impedance voltage can be calculated as follows, % Impedance
= Voltage at which rated current flow. X 100/ Rated Voltage.

Figure 5.14: Load Loss and Impedance Test

5.11 Transformer Tap Changer

A tap changer of a transformer which can be variable turn’s ratio and enable stepped voltage
regulation of the output. This tap changer is an automatic or manual tap changer mechanism. In
GPS tap changer is an automatic mechanism.
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Figure 5.15: Transformer Tap Changer

5.12 Transformer Bushing

Bushing is an important part of power transformer. It is used to insulate the incoming or outgoing
conductor. At GPS, the bushings connect the windings of the transformer to the supply line and
insulate the feed through conductor from the transformer main tank.

Figure 5.16: Transformer Bushing

5.13 Conservator Tank

In GPS a conservator tank of transformer provides adequate space to this expanded transformer
oil. It also acts as a reservoir for transformer insulating oil. This is a cylindrical tank on supporting
structure on the roof the transformer.
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Figure 5.17: Conservator Tank

5.14 Radiator
Radiators are connected in every power transformer at GPS. Radiator is a heat exchangers used to
transfer thermal energy from one medium to another. Its release the heat from the transformer to
atmosphere and cool the transformer.

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Figure 5.18: Radiator

Chapter 6: Conclusion
6.1 Discussion
In Bangladesh, electricity plays a major role in the growth of economy. Government is trying to
provide a stable of supply of electricity. Ghorashal Power Station is one of the main contributors
to the national grid. At GPS, the main fuel source is natural gas. GPS has two kinds of power plant.
One is steam power plant which has total generation capacity around 910MW and another one is
combine cycle power plant which has total generation capacity around 365MW. In combine cycle
power plant, gas turbine produces 209 MW and steam turbine produces 155 MW. At GPS, 6 units
generate power by steam turbine power plant. During our internship period we gathered practical
knowledge on how Ghorashal Power Station generates electricity and feeds it to the national grid.

6.2 Problems
We faced the following problems during our internship:
1. The technology behind a power station is a mixture of both electrical and mechanical
engineering. As there is no mechanical course in our curriculum, it was difficult to understand the
terms related to mechanical engineering.
2. Internship period was too short.

6.3 Recommendations
1. A student should complete EEE441 and EEE442 to be eligible for internship in power sector.
2. 15 days are not sufficient to observe the functionality of all equipments at a power plant. So the
department should take necessary steps to extend the duration of internship for achieving sufficient
practical knowledge.

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Reference
1. http://www.bpdb.gov.bd/bpdb_new/index.php/site/power_generation_unit
2. http://globalenergyobservatory.org/form.php?pid=40454
3. https://www.genewsroom.com/press-releases/ge-repower-bpdb%E2%80%99s-ghorashal-
station-bangladesh-283107
4. http://www.xinhuanet.com/english/2017-09/13/c_136607232.htm
5. http://www.mechmore.com/images/mep/big/9.jpg

6. https://en.wikipedia.org/wiki/Fire-tube_boiler

7. https://en.wikipedia.org/wiki/Water-tube_boiler

8. http://www.daviddarling.info/encyclopedia/I/AE_impulse_turbine.html

9. https://www.siemens.com/global/en/home/products/energy/power-generation/gas-turbines/_.

10. https://en.wikipedia.org/wiki/Gas_turbine

11. https://en.wikipedia.org/wiki/Diesel_engine

12.http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Four%20Stroke%2
0Cycle%20Engines.htm

13. http://www.mechscience.com/wp-content/uploads/2017/10/image-18.png

14. https://www.pgcb.org.bd/PGCB/?a=pages/substations.php

15. https://www.pgcb.org.bd/PGCB/?a=pages/transmission_line.php

16. https://www.researchgate.net/figure/a-Gas-turbine-combined-with-conventional-steam-turbine-
forming-CC-1_fig2_276418409

17. https://understandingchp.com/files/2016/10/CHP-Gas-Turbine-System.jpg

18. http://mechanical-engineering-info.blogspot.com/2012/01/gas-turbine-power-plant.html

19. https://www.mecholic.com/2015/10/comparison-between-impulse-and-reaction-turbine.html

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