Documentation

CHAPTER:1
INTRODUCTION
1.1 ABOUT LANCO
India currently has an installed capacity of 1,70,229 MW of power, with the projected
capacity of 1,94,703 MW by March 2012 and 3,01,173 MW by the 12
th
Five-Year Plan. The
current energy deficit stands at 8.6 percent and the peak deficit at 11.1 percent. To achieve a
Gross Domestic Product (GDP) growth of 8-9 percent, power demand is expected to grow at the
same pace and the power deficit expected to continue. Coal is projected to remain the dominant
fuel for power generation in the country. The market offers an immense potential with the
independent power producer (IPP) share in capacity addition likely to cross 60 percent in the
near future.
With its geographically diversified portfolio of thermal power projects, Lanco is uniquely
poised to contribute significantly to filling the demand-supply gap in power generation in the
country. Lanco has taken a giant leap forward in the private IPP space standing as the top private
power producer in the country by the end of FY'11 and will continue to hold its position in the
elite league of top three. Against the 11th Five-Year Plan private sector target of 19,797 MW,
Lanco is adding a 20 percent capacity.
The Lanco Thermal Division operates within the Lanco group's integrated power value
chain. This eco-system incorporates EPC and construction, development, operation and
maintenance (O&M), trading, transmission and distribution and coal mines. The Division
contributes 45 percent to the group's revenues and 76 percent to the EPC order book.
Lanco is one of the very few organisations that offers specialised O&M of thermal power
plants, and has set several benchmarks in the area. Though the initial goal is to operate group
assets, Lanco aims to become the leading O&M specialist within India and internationally.



1.2.SELETION OF PLANT SITE

The following points should be considered while selecting a site for a steam power
station.
1. Supply of water:
The steam amount of water is required for the condensers: therefore, such a plant
should be located at bank of river or near a canal to ensure the continuous supply of
water.
2. Transportation of facilities:
A modern steam power station often requires the transportation of material and
machinery. Therefore adequate transportation facilities must exist.
3. Cost and type of land:
The steam power station should be located at a place where level land is cheap and
further extension, if necessary is possible. Moreover, the bearing capacity of the ground
should be adequate so they heavy equipment could be installed
4. Nearness to load centers:
In order to reduce the transmission cost the plant should be located near the load
center. This is particularly important of D.C supply system is adopted. However if A.C
supply system is adopted this factor becomes relatively less important. It is because A.C
power can be transmitted at high voltage with consequent reduced transmission cost.
5. Distance from populated area:
A huge amount of coal is burnt a steam power station, therefore, a smoke and fumes
pollute the surrounding areas. This necessitates that the plant should be located at the
considerable distance from polluted areas.





1.3 BASIC CYCLES
BRAYTON CYCLE
Preface:

Power generation is an important issue today, especially on the West Coast. Demand is
outweighing supply because of lack of incentives for the utilities industry to build additional
power plants over the past 10-20 years. Electrical innovations (such as the personal computer)
were not accounted for in earlier predictions of power utilization and, now, the country is in dire
need of streamlining the current power plants while pushing through as many applications as
possible for new power plants. In response to this situation, power generation engineers will be
in high demand. These engineers must have a thorough understanding of thermodynamics and, in
particular, the Brayton cycle. It is the backbone of power generation. In order to deepen
knowledge of how the Brayton cycle is applied at power generation plants, an interview was
conducted via e-mail with Brian Lawson, who has obtained the P.E. designation and is the Senior
Mechanical Engineer for Sierra Pacific Power Company‘s Tracy Power Generating Station. This
station provides a total electrical power output of 454 MW and supplies the majority of the
population in northern Nevada. The italicized questions and answers asked and obtained are
integrated throughout the various topics to provide further insight and understanding for the
beginning engineer entering the power generation field. Further, bolded words are defined in
detail at the end of each paragraph.
BRAYTON CYCLE/GAS TURBINE HISTORY:

The basic gas turbine cycle is named for the Boston engineer, George Brayton, who first
proposed the Brayton cycle around 1870.Now, the Brayton cycle is used for gas turbines only
where both the compression and expansion processes take place in rotating machinery.John
Barber patented the basic gas turbine in 1791.The two major application areas of gas-turbine
engines are aircraft propulsion and electric power generation. Gas turbines are used as stationary
power plants to generate electricity as stand-alone units or in conjunction with steam power
plants on the high-temperature side. In these plants, the exhaust gases serve as a heat source for
the steam. Steam power plants are considered external-combustion engines, in which the
combustion takes place outside the engine. The thermal energy released during this process is
then transferred to the steam as heat. The gas turbine first successfully ran in 1939 at the Swiss
National Exhibition at Zurich. The early gas turbines built in the 1940s and even 1950s had
simple-cycle efficiencies of about 17 percent. This was because of low compressor and turbine
efficiencies and low turbine inlet temperature due to metallurgical limitations at the time. The
first gas turbine for an electric utility was installed in 1949 in Oklahoma as part of a combined-
cycle power plant. It was built by General Electric and produced 3.5 MW of power.

In the past, large coal and nuclear power plants dominated the base-load electric power
generation. However, natural gas-fired turbines now dominate the field because of their black
start capabilities, higher efficiencies, lower capital costs, shorter installation times, better
emission characteristics, and abundance of natural gas supplies. The construction cost for gas-
turbine power plants are roughly half that of comparable conventional fossil-fuel steam power
plants, which were the primary base-load power plants until the early 1980s. More than half of
all power plants to be installed in the foreseeable future are forecast to be gas-turbine or
combined gas-steam turbine types.
In the early 1990s, General Electric offered a gas turbine that featured a pressure ratio of
13.5 and generated 135.7 MW of net power at a thermal efficiency of 33 percent in simple-cycle
operation. A more recent gas turbine manufactured by General Electric uses a turbine inlet
temperature of 1425°C (2600°F) and produces up to 282 MW while achieving a thermal
efficiency of 39.5 percent in the simple-cycle mode. Current low prices for crude oil make fuels
such as diesel, kerosene, jet-engine fuel, and clean gaseous fuels (such as natural gas) the most
desirable for gas turbines. However, these fuels will become much more expensive and will
eventually run out. Provisions must therefore be made to burn alternative fuels.
BRAYTON CYCLE COMPONENTS:

Gas turbines usually operate on an open cycle, as shown in Figure 1. Fresh air at ambient
conditions is drawn into the compressor, where its temperature and pressure are raised. The
high-pressure air proceeds into the combustion chamber, where the fuel is burned at constant
pressure. The resulting high-temperature gases then enter the turbine, where they expand to the
atmospheric pressure through a row of nozzle vanes.

This expansion causes the turbine blade to
spin, which then turns a shaft inside a magnetic coil. When the shaft is rotating inside the
magnetic coil, electrical current is produced. The exhaust gases leaving the turbine in the open
cycle are not re-circulated.

Figure 1 – An Open Cycle Gas-Turbine Engine


Figure 2 – A Closed Cycle Gas-Turbine Engine
The open gas-turbine cycle can be modeled as a closed cycle as shown in Figure 2 by
utilizing the air-standard assumptions. Here the compression and expansion process remain the
same, but a constant-pressure heat-rejection process to the ambient air replaces the combustion
process. The ideal cycle that the working fluid undergoes in this closed loop is the Brayton cycle,
which is made up of four internally reversible processes

COMPRESSOR:
Efficient compression of large volumes of air is essential for a successful gas turbine
engine. This has been achieved in two types of compressors, the axial-flow compressor and the
centrifugal or radial-flow compressor. Most power plant compressors are axial-flow
compressors. The object of a good compressor design is to obtain the most air through a given
diameter compressor with a minimum number of stages while retaining relatively high
efficiencies and aerodynamic stability over the operating range. Compressors contain a row of
rotating blades followed by a row of stationary (stator) blades. A stage consists of a row of rotor
and a row of stator blades. All work done on the working fluid is done by the rotating rows, the
stators converting the fluid kinetic energy to pressure and directing the fluid into the next rotor.
The fluid enters with an initial velocity relative to the blade and leaves with a final relative
velocity at a different angle.


Figure 3 – An Axial-Flow Compressor
COMBUSTION/COMBUSTOR:
Combustion is the chemical combination of a substance with certain elements, usually
oxygen, accompanied by the production of a high temperature or transfer of heat. The function of
the combustion chamber is to accept the air from the compressor and to deliver it to the turbine at
the required temperature, ideally with no loss of pressure. Essentially, it is a direct-fired air
heater in which fuel is burned with less than one-third of the air after which the combustion
products are then mixed with the remaining air. For the common open-cycle gas turbine, this
requires the internal combustion of fuel. This means the problem of fuel operation, mixing and
burning, must be addressed. Fuel is commonly gaseous or liquid. Solid fuel has not yet advanced
beyond the experimental stage. Gaseous or liquid fuels are usually hydrocarbons. Gases usually
being natural gas, mostly methane, and butane. Liquids may range from highly refined gasoline
through kerosene and light diesel oil to a heavy residual oil. Combustion itself is seldom
difficult. The difficulty arises in the combination of combustion with low-pressure loss in a size
of combustor compatible with the high power-weight, high specific output potentialities, or the
rotating elements. Almost any fuel can be burnt successfully if sufficient pressure drop is
available to provide the necessary turbulence for mixing of air and fuel and if sufficient volume
is available to give the necessary time for combustion to be completed.



Figure 4 – A Combustion Chamber Can

TURBINE:
Gas turbines move relatively large quantities of air through the cycle at very high
velocities. Among the mechanical characteristics of gas turbine engines are very smooth
operation and absence of vibration due to reciprocating action. The high rotational speeds
utilized require very accurate rotor balancing to avoid damaging vibration. Rotor parts are highly
stressed with low factors of safety. Blades are very finely tuned to avoid resonant vibration. Gas
turbines have relatively few moving (and no sliding) parts and are not subjected to vibratory
forces. As a result, they are highly reliable when properly designed and developed. The gas
turbine in its most common form is a heat engine operating through a series of processes. These
processes consist of compression of air taken from the atmosphere, increasing of gas temperature
by the constant-pressure combustion of fuel in the air, expansion of the hot gases, and finally,
discharging of the gases to atmosphere, in a continuous flow process. It is similar to the gasoline
and Diesel engines in its working medium and internal combustion, but is like the steam turbine
in the steady flow of the working medium. The compression and expansion processes are both
carried out by means of rotating elements in which the energy transfer between fluid and rotor is
effected by means of kinetic action, rather than by positive displacement as in reciprocating
machinery.




Figure 5 – Inside a Turbine Chamber



R RA AN NK KI IN NE E C CY YC CL LE E
T Th he e R Ra an nk ki in ne e c cy yc cl le e i is s t th he e m mo os st t c co om mm mo on n o of f a al ll l p po ow we er r g ge en ne er ra at ti io on n c cy yc cl le es s a an nd d i is s
d di ia ag gr ra am mm ma at ti ic ca al ll ly y d de ep pi ic ct te ed d v vi ia a F Fi ig gu ur re es s 1 1 a an nd d 2 2. . T Th he e R Ra an nk ki in ne e c cy yc cl le e w wa as s d de ev vi is se ed d t to o m ma ak ke e u us se e o of f
t th he e c ch ha ar ra ac ct te er ri is st ti ic cs s o of f w wa at te er r a as s t th he e w wo or rk ki in ng g f fl lu ui id d. . T Th he e c cy yc cl le e b be eg gi in ns s i in n a a b bo oi il le er r ( (S St ta at te e 4 4 i in n f fi ig gu ur re e
1 1) ), , w wh he er re e t th he e w wa at te er r i is s h he ea at te ed d u un nt ti il l i it t r re ea ac ch he es s s sa at tu ur ra at ti io on n- - i in n a a c co on ns st ta an nt t- -p pr re es ss su ur re e p pr ro oc ce es ss s. . O On nc ce e
s sa at tu ur ra at ti io on n i is s r re ea ac ch he ed d, , f fu ur rt th he er r h he ea at t t tr ra an ns sf fe er r t ta ak ke es s p pl la ac ce e a at t a a c co on ns st ta an nt t t te em mp pe er ra at tu ur re e, , u un nt ti il l t th he e
w wo or rk ki in ng g f fl lu ui id d r re ea ac ch he es s a a q qu ua al li it ty y o of f 1 10 00 0% % ( (S St ta at te e 1 1) ). . A At t t th hi is s p po oi in nt t, , t th he e h hi ig gh h- -q qu ua al li it ty y v va ap po or r i is s
e ex xp pa an nd de ed d i is so oe en nt tr ro op pi ic ca al ll ly y t th hr ro ou ug gh h a an n a ax xi ia al ll ly y b bl la ad de ed d t tu ur rb bi in ne e s st ta ag ge e t to o p pr ro od du uc ce e s sh ha af ft t w wo or rk k. . T Th he e
s st te ea am m t th he en n e ex xi it ts s t th he e t tu ur rb bi in ne e a at t S St ta at te e 2 2. .
T Th he e w wo or rk ki in ng g f fl lu ui id d, , a at t S St ta at te e 2 2, , i is s a at t a a l lo ow w- -p pr re es ss su ur re e, , b bu ut t h ha as s a a f fa ai ir rl ly y h hi ig gh h q qu ua al li it ty y, , s so o i it t i is s
r ro ou ut te ed d t th hr ro ou ug gh h a a c co on nd de en ns se er r, , w wh he er re e t th he e s st te ea am m i is s c co on nd de en ns se ed d i in nt to o l li iq qu ui id d ( (S St ta at te e 3 3) ). . F Fi in na al ll ly y, , t th he e c cy yc cl le e
i is s c co om mp pl le et te ed d v vi ia a t th he e r re et tu ur rn n o of f t th he e l li iq qu ui id d t to o t th he e b bo oi il le er r, , w wh hi ic ch h i is s n no or rm ma al ll ly y a ac cc co om mp pl li is sh he ed d b by y a a
m me ec ch ha an ni ic ca al l p pu um mp p. . F Fi ig gu ur re e 2 2 s sh ho ow ws s a a s sc ch he em ma at ti ic c o of f a a p po ow we er r p pl la an nt t u un nd de er r a a R Ra an nk ki in ne e c cy yc cl le e. .

F Fi ig gu ur re e 1 1: : D Di ia ag gr ra am ms s f fo or r a a s si im mp pl le e i id de ea al l R Ra an nk ki in ne e c cy yc cl le e: : a a) ) P P- -V V d di ia ag gr ra am m, , b b) ) T T- -S S d di ia ag gr ra am m

F Fi ig gu ur re e 2 2: : S Sc ch he em ma at ti ic c o of f a a s si im mp pl le e i id de ea al l R Ra an nk ki in ne e c cy yc cl le e

R RA AN NK KI IN NE E C CY YC CL LE E A AN NA AL LY YS SI IS S
T Th hi is s e ex xp pe er ri im me en nt t h ha as s a an n i im mp po or rt ta an nt t d di if ff fe er re en nc ce e w wi it th h t th he e c cy yc cl le e s sh ho ow wn n i in n F Fi ig gu ur re e 2 2. . T Th he e
d di if ff fe er re en nc ce e i is s t th ha at t t th he er re e i is s n no ot t a a p pu um mp p t to o c co om mp pl le et te e t th he e c cy yc cl le e. . T Th hi is s i is s n no ot t e ex xa ac ct tl ly y a a c cy yc cl le e. . I In ns st te ea ad d, , i it t
i is s a an n o op pe en n s sy ys st te em m. . T Th he e w wa at te er r c cr ro os ss si in ng g t th he e c co on nd de en ns se er r i is s s st to or re ed d i in n a a t ta an nk k a as s s sh ho ow w i in n F Fi ig gu ur re e 3 3, , b bu ut t
t th he e p pr ri in nc ci ip pl le e o of f R Ra an nk ki in ne e c cy yc cl le e s st tu ud di ie ed d i in n T Th he er rm mo od dy yn na am mi ic c i is s s st ti il ll l v va al li id d. .
T Th he e b bo oi il le er r w wi il ll l b be e f fi il ll le ed d w wi it th h w wa at te er r b be ef fo or re e t th he e e ex xp pe er ri im me en nt t a an nd d t th he e e ex xp pe er ri im me en nt t w wi il ll l b be e
e en nd de ed d w wh he en n t th he e w wa at te er r i is s r re ea ac ch he es s t th he e m mi in ni im mu um m l le ev ve el l o of f c co or rr re ec ct t o op pe er ra at ti io on n, , g gi iv ve en n b by y t th he e
m ma an nu uf fa ac ct tu ur re er r. .
A An no ot th he er r i im mp po or rt ta an nt t d di if ff fe er re en nc ce e i is s t th ha at t b be et tw we ee en n t th he e b bo oi il le er r a an nd d t tu ur rb bi in ne e t th he er re e i is s a a v va al lv ve e t th ha at t
g ge en ne er ra at te es s a a t th hr ro ot tt tl li in ng g e ef ff fe ec ct t. . T Th he e t th hr ro ot tt tl li in ng g p pr ro oc ce es ss s i is s a an na al ly yz ze ed d a as s a an n i is se en nt th ha al lp pi ic c p pr ro oc ce es ss s. . T Th hi is s
p ph he en no om me en no on n w wi il ll l b be e a an na al ly yz ze ed d m mo or re e i in n d de et ta ai il l. . A Al ls so o, , t th he e b bo oi il le er r g ge en ne er ra at te es s a a s su up pe er rh he ea at te ed d v va ap po or r. .

F Fi ig gu ur re e 3 3: : S Sc ch he em ma at ti ic c o of f R Ra an nk ki in ne e c cy yc cl le e s st te ea am m t tu ur rb bi in ne e a ap pp pa ar ra at tu us s
I I. . Mass Flow Rate of the Rankine Cycle.
Evaluating the time of operation and volume of consumed water, the mass flow rate can
be measured as:
water
water
water water water
time
q m µ µ
¬
= = 

Here, time is measured with a chronometer for a known volume of water
water
¬ in the
boiler.
I II I. . Work and Heat Transfer
For this analysis, it is assumed that the process is ideal and there are not pressure losses
occurring in the piping, but as has been said previously the boiler generates superheated vapor
and there is a throttling process in the valve. Figure 4 shows the modified cycle of the plant.
The evaporator, in this case a fire-tube boiler, produces a superheated vapor (Stage1' ).
Taking a control volume enclosing the boiler tubes and drums, the energy rate balance gives:
( )
(
¸
(

¸

÷ +
÷
+ ÷ + =
' 2 1
2
2
2
1
4 1
2
0 z z g
V V
h h m Q
water in



neglecting kinetic and potential energy, the energy equation reduce to:
( )
4 1
h h m Q
water in
÷ =
'



Then, vapors pass through the valve, states1‘-1‖. For a control volume enclosing the
valve, the mass and energy rate balance reduces under steady state to:
| |
1 1
0
' ' '
÷ + = h h m Q
water v



Since there is not work done in the valve and heat transfer
v
Q

can be neglected, last equation
reduces to:
1 1 ' ' '
= h h
which means that there is an isenthalpic expansion in the valve.
Making a similar analysis for the pump and condenser, the work and heat transfer are:
( )
3 2
h h m Q
water out
÷ = 

and ( )
3 4
h h m W
water p
÷ = 


The energy balance for a control volume around the turbine under steady state condition is:
| |
2 1
0
' ' ' '
÷ + ÷ = h h m W Q
water t cv

 

Neglecting heat transfer
cv
Q

to the surrounding, the process in the turbine is assumed adiabatic
and reversible, so isentropic (
1 2 ' ' ' '
= S S ) and the energy equation reduces to:
( )
2 1 ' ' ' '
÷ = h h m W
water t



Then, knowing that
1 2 ' ' ' '
= S S and also
2
f
S and
2
g
S which could be estimated with the pressure
and temperature at outlet of the turbine, the quality of the vapor can be calculated as:
2 2
1
2
2
f g
g
S S
S S
x
÷
÷
=
' '

with
2
x , the enthalpy
2
h is calculated as:
( )
2 2
2
2
2 f g g
h h x h h ÷ ÷ =
where
2
f
h and
2
g
h are calculated with the outlet temperature. It is important to emphasize
that the valve generates entropy from state 1' to the state1' ' . Without the expansion valve the
cycle would be close to an isentropic expansion 2 1 ' ÷ ' in the turbine. All parameters
1'
h ,
1' '
h ,
1'
S
,
1' '
S ,
1
S ,
B
h and
4
S can be determined from temperatures and pressures at each stage.
I II II I. . Thermal Efficiency of Cycle
The net work of the cycle is defined by the difference between the turbine work and the
pump work:
( ) ( )
3 4 2 1
h h m h h m W W W
water water p t cycle
÷ ÷ ÷ = ÷ =
' ' ' '
 
  

If the pump work is neglected, the net work of the cycle reduces to:
( )
2 1 ' ' ' '
÷ = h h m W
water cycle



Then the thermal efficiency of this system is defined by the rate between the net work
and heat transfer from the boiler:
( )
( )
4 1
2 1
h h
h h
Q
W
in
t
÷
÷
= =
' ' ' '

q
I IV V. . Air -Fuel ratio and Air Excess.
The chemical composition of the gases at the outlet of boiler is:
( ) ( ) ( ) ( ) ( ) ( ) ( ) O H M N G NO F O D NO C CO B CO A
water 2 2 2 2 2
+ + + + + +
at the inlet, there are dry air and fuel (butane):
| | | |
10 4 2 2
76 . 3 H C M N O M
fuel air
+ +
Then, making a balance between inlet and outlet:
| | | | ( ) ( ) ( ) ( ) ( )
( ) ( ) O H M N G
NO F O D NO C CO B CO A H C M N O M
water
fuel air
2 2
2 2 2 10 4 2 2
76 . 3
+ +
+ + + + = + +

so,
4
B A
M
fuel
+
=
76 . 3
2G F C
M
air
+ +
=
5
fuel
water
M
M =
Where the coefficients (A, B, C, D, F, G and M
i
) are the molar mass necessary to balance
the equation. Then the air excess is:
100
) (ideal M
M
E
air
air
air
=
the ) (ideal M
air
is the molar mass of air when the chemical reaction is complete, and there is not
formation of water and intermediate compounds:
| | | | ( ) ( ) ( ) O H M N G CO A H C N O ideal M
water air 2 2 2 10 4 2 2
76 . 3 ) ( + + = + +
Balancing this equation:
2
13
) ( = ideal M
air
, 44 . 24 = G , 4 = A and 5 =
water
M , which is:
| | | | ( ) ( ) ( ) O H N CO H C N O
2 2 2 10 4 2 2
5 44 . 24 4 76 . 3
2
13
+ + = + +
Then, the Air-Fuel ratio is defined by:
fuel fuel
air air
P M
P M
AF =
Where
air
P and
fuel
P are the atomic weight of air and combustible, respectively. The 29 =
air
P
kg/Kmol and the 12 . 58 10 4 = + =
H c fuel
P P P kg/Kmol.
V V. . Mass flow rate in the turbine
From the generated amperage and voltage:
VI W
t
=


so, the mass flow rate in the turbine is:
( )
2 1 ' ' ' '
÷
=
h h
VI
m
t
q

Where
t
q is the efficiency of the turbine. Here, we will assume this efficiency equal to one.
V VI I. . Boiler analysis
From the chemical equation of combustion, balanced in term of moles:
| | | | ( ) ( ) ( ) ( ) ( )
( ) ( ) O H M N G
NO F O D NO C CO B CO A H C mass N O mass
comb air
2 2
2 2 2 10 4 2 2
76 . 3
+ +
+ + + + = + +

the first law of thermodynamics for a volume enclosing the boiler is:
( ) ( )
¿ ¿
= +
P
comb
R
mh Q mh
where
¿
R
and
¿
P
are the sum for each reactants and products of combustion. Remember that
i i i
M n m = , where
i
m is mass,
i
n is number of moles and
i
M is the molar mass of the i-th
component. Last equation is written in the form:
( ) ( )
¿ ¿
= +
P
comb
R
nMh Q nMh
Here, h is the enthalpy of reactants and products at the temperature of inlet and outlet of the
boiler. They could be found in the table of enthalpies of formation.
A An no ot th he er r f fo or rm m t to o w wr ri it te e t th he e f fi ir rs st t l la aw w i is s: :
( ) | | ( ) | |
¿ ¿
A + = + A +
P
f comb
R
f
h h nM Q h h nM
0 0

w wh he er re e
0
f
h i is s t th he e e en nt th ha al lp py y o of f r re ea ac ct ta an nt ts s a an nd d p pr ro od du uc ct ts s, , r re es sp pe ec ct ti iv ve el ly y, , a at t t th he e s st ta an nd da ar rd d t te em mp pe er ra at tu ur re e a an nd d
p pr re es ss su ur re e. . R Re ea ar rr ra an ng gi in ng g: :
( ) | | ( ) | |
( ) | | ( ) | | ( ) | | ( ) | |
¿ ¿ ¿ ¿
¿ ¿
A ÷ A + ÷ =
A + ÷ A + =
R P R
f
P
f
R
f
P
f comb
h nM h nM h nM h nM
h h nM h h nM Q
0 0
0 0

T Th he e f fi ir rs st t t tw wo o t te er rm ms s a ar re e t th he e e en nt th ha al lp py y o of f c co om mb bu us st ti io on n ( (
0
PR
h ) ) a at t s st ta an nd da ar rd d t te em mp pe er ra at tu ur re e a an nd d p pr re es ss su ur re e. .
( ) | | ( ) | |
¿ ¿
A ÷ A + =
R P
PR comb
h nM h nM h Q
0

T Th he e e en nt th ha al lp py y o of f c co om mb bu us st ti io on n a al ls so o i is s c ca al ll le ed d h he ea at ti in ng g v va al lu ue e ( (H HV V) ), , a an nd d t th hi is s i is s n nu um mb be er r
i in nd di ic ca at ti iv ve e t to o t th he e u us se ef fu ul l e en ne er rg gy y c co on nt te en nt t o of f d di if ff fe er re en nt t f fu ue el ls s. . T Th he er re e a ar re e t tw wo o t ty yp pe es s o of f h he ea at ti in ng g v va al lu ue e: :
h hi ig gh he er r h he ea at ti in ng g v va al lu ue e ( (H HH HV V) ) a an nd d t th he e l lo ow we er r h he ea at ti in ng g v va al lu ue e ( (L LH HV V) ). . T Th he e H HH HV V i is s o ob bt ta ai in ne ed d w wh he en n a al ll l
t th he e w wa at te er r f fo or rm me ed d b by y c co om mb bu us st ti io on n i is s a a l li iq qu ui id d. . T Th he e L LH HV V i is s o ob bt ta ai in ne ed d w wh he en n a al ll l t th he e w wa at te er r f fo or rm me ed d b by y
t th he e c co om mb bu us st ti io on n i is s a a v va ap po or r. . F Fo or r t th ha at t H HH HV V i is s m mo or re e t th ha an n L LH HV V ( (s se ee e T Ta ab bl le e 1 1) ). . F Fo or r c ca al lc cu ul la at ti io on ns s, , w we e
w wi il ll l a as ss su um me e t th ha at t w wa at te er r f fo or rm me ed d i is s i in n t th he e l li iq qu ui id d s st ta at te e a an nd d t th he e H HH HV V w wi il ll l b be e u us se ed d f fo or r
0
PR
h . . N No ow w, , w we e
c ca an n c ca al lc cu ul la at te e t th he e e ef ff fi ic ci ie en nc cy y o of f t th he e b bo oi il le er r a as s: :
comb
in
boiler
Q
Q
= q

V VI II I. . Cost of Generating Steam and Energy.
T Th he e m ma as ss s f fl lo ow w o of f f fu ue el l i is s t th he e p pr ro od du uc ct t b be et tw we ee en n t th he e d de en ns si it ty y a an nd d f fu ue el l f fl lo ow w m ma as ss s a an nd d t th he e t ti im me e
o of f o op pe er ra at ti io on n: :
fuel fuel fuel
q m µ = 

w wh he er re e
fuel
µ i is s t th he e d de en ns si it ty y o of f b bu ut ta an ne e g ga as s a at t a at tm mo os sp ph he er ri ic c p pr re es ss su ur re e. . T Th he en n t th he e c co os st t o of f g ge en ne er ra at ti in ng g
s st te ea am m p pe er r u un ni it t m ma as ss s o of f s st te ea am m i is s: :
water
fuel fuel
m
ice m
t STEAM

 Pr
cos =
w wh he er re e
fuel
ice Pr i is s t th he e p pr ri ic ce e o of f t th he e f fu ue el l. . A Al ls so o i it t i is s p po os ss si ib bl le e t to o d de et te er rm mi in ne e t th he e c co os st t o of f g ge en ne er ra at ti in ng g
e en ne er rg gy y b by y: :
VI
ice m
t ENERGY
fuel fuel
Pr
cos

=
POWER PLANT DEVIATIONS AND COMPONENT EFFICIENCIES
The study of a thermal power plant reveals the eddy turbulence, fluid friction, and
pressure/temperature dependent viscosity variations of working fluid, which are not considered
under ideal conditions. Decisions regarding the analysis and technological advancements for
these effects become vital while looking for the improvement of the efficiency of thermal power
plants. Turbine, steam generator (boiler) and a pump are the basic components of a steam
thermal power plant. An analytical discussion about the steam turbine and pump functions has
been taken up as these affect the Rankine cycle efficiency.
STEAM TURBINE
The adiabatic steam turbine with irreversible flow exhibits the same thermodynamic
results as in the case of an isentropic turbine shown in the equation below;
Wt = h1- h2 [kJ/kg]
Here h2 represents the actual exit enthalpy and wt is the actual work of an adiabatic
turbine where all the above discussed non-ideal irreversible components working under non-
ideal conditions that exist. The efficiency of a real turbine, known as isentropic efficiency, is
defined as the ratio of the actual shaft work to the shaft work for an isentropic expansion
between the same inlet and exit pressure (Figure 4).
The turbine efficiency is:
Efficiency_turb = (h1- h2) / (h1- h2s) (2.8)
where h2s is enthalpy evaluated at the turbine inlet entropy and at the exit pressure.
Under ideal conditions, h2 = h2s – the efficiency becomes 1. In Figure 4, points 2 and 2
represent work lost due to irreversibility.

Figure 4: Turbine efficiency
PUMP:
The turbine condensate is recycled by using a pressure centrifugal pump. External work
must be supplied to a pump to move liquid from a low pressure to a high pressure. The sensible
internal energy of the liquid water is enhanced by means of doing work through pumping,
however, considerable work energy is lost due to irreversibility. Therefore, the remaining
effective work to raise the pressure is less than supplied. Pump efficiency is the ratio of the
isentropic work to the actual work input when operating between two given pressures. Applying
equation and the notation of Figure 5, the isentropic pump work, wps = h3 – h4s, and the
pump isentropic efficiency is;
Efficiency_ pump = wps /wp = (h4s – h3)/(h4 – h3)

With reference to Figure 5, it would seem that the pump lost work, given by h4 – h4s
decreases and that the actual discharged state approaches the isentropic discharge state. States 4
and 4s are usually sub-cooled liquid states and as a first approximation their enthalpies may be
taken to be the saturated liquid enthalpy at T3.

Figure 5: Pump efficiency
More accurate approximations for these enthalpies may be obtained by applying the First
Law for a closed system undergoing a reversible process, equation: Tds = dh – vdp. For an
isentropic process, it follows that dh = vdp as ds = 0. Because a liquid is almost incompressible,
its specific volume, v, is almost independent of pressure. Thus, using the notation of Figure 5 for
dh = vdp where, dh = h4s – h3 , and dp = p4 – p3. This equation on integration with respect to
constant specific volume gives h4s = h3 + v3 (p4 – p3) [kJ/kg], where the knowledge of State 3
and p4 determines h4s. Using Equation, pump work can be calculated for a given efficiency of
the pump.












COMBINED CYCLES

Combined Cycle Basic Components, Terminology and Heat Cycle(s)
The term combined cycle (CC) refers to a system that incorporates a gas turbine (GT), a
steam turbine (ST), a heat recovery steam generator (HRSG), where the heat of the exhaust gases
is used to produce steam and a generator. The shaft power from the gas turbine and that
developed by the steam turbine both run the generator that produces electric power.
The term ―cogeneration‖ means generation of both work (shaft power) and heat (steam,
in the case of a CC). So a combined cycle is a form of cogeneration.
Fig. 68. Single and Multi shaft arrangements for CC plants

The following figure shows a single shaft CC cycle block diagram in more detail.
Combined cycle plants are generally open cycle systems, however CC closed systems are
possible if not that common.
The plant system may also incorporate other accessories, such as a gear box (often used
to ―convert‖ 60 Hz models to 50Hz models), and/ or subsystems (that may themselves be closed
or open systems) such as:
• Condensing units, intercooling heat exchangers (for the GT compressor air),
• A regeneration (heat addition) heat exchanger to preheat the GT compressor discharge air,
• Reheat heat exchangers (for adding heat to the GT turbine module products of combustion),
• Inlet cooling and/or water or steam injection on the GT for power augmentation and/or NOx
reduction,
• A closed or open steam (and/ or air) cooling system (for the hottest areas of the GT turbine
module), and
•A supplementary firing system positioned downstream of the GT exhaust to maximize
combustion of the exhaust gases (which will include unburned fuel hydrocarbons).
See the block diagram figures below for a representation of GT closed systems, one with
regeneration and intercooling, and one with reheat and regeneration. They are followed by a
figure that represents a GT open system with water injection and regeneration.



Gas flapper valves allow the gas turbine exhaust to bypass the heat recovery boiler
(HRSG) allowing the gas turbine to operate if the steam unit is down for maintenance. In earlier
designs supplementary oil or gas firing was also included to permit steam unit operation with the
gas turbine down. This is not generally included in contemporary combined-cycle designs, as it
adds to capital cost, complicates the control system, and reduces efficiency.
Sometimes as many as four (but most frequently two) gas turbines, each with individual
boilers may be associated with a single steam turbine. As stated previously, the gas turbine,
steam turbine, and generator may be arranged as a single-shaft design. A multi-shaft arrangement
can also be used: Each gas turbine drives a generator and has its own HRSG, and steam turbine,
which in turn, may also add power to the generator.
In areas such as Scandinavia, additional criteria such as cogeneration in combined heat
and power plants (CHP) or district heating, as well as demanding conditions (e.g. available
space, emissions, noise level, architecture, environmental permits) associated with existing sites
and available infrastructure must also be considered. A customer‘s preferences regarding fuel
election, personnel training level required and service requirements must also be accommodated.
Fuels for Combined Cycles
Gas turbine operators prefer to burn natural gas and light oil. As we saw previously,
crude oil, residual and ―bunker fuel contain corrosive components. They require fuel treatment
equipment. Also, ash deposits from these fuels can result in gas turbine derating of up to 15
percent. As we also saw previously (in the case of the Shunde plant in south China), they may
still be economically attractive fuels, particularly in combined-cycle plants.
Sodium and potassium are removed from residual, crude and heavy distillates by a water
washing procedure. A simpler and less expensive purification system will do the same job for
light crude and light distillates. A magnesium additive system reduces vanadium.
Note that reduced availability will result due to water cleaning shutdowns to remove
blade deposits, as on-line washing, even at reduced speeds, is not effective. A shutdown with a
crank soak every 100 to 120 hours is required. Reduced component life due to hot gas path
corrosion caused by vanadium deposits and other corrosion is another factor to consider.
Design and operation of these plants requires more attention than natural gas fired plants
particularly in relation to fuel variables such as calorific content, density, composition,
concentration of contaminants and emissions, as well as different burning behaviors (e.g.
ignitability, flame velocity and stability).
To overcome these difficult fuel properties, technological adaptation, additional
equipment and operational requirements are necessary. These include GT layout (compressor,
turbine) for the changed mass flows, different burner technology (burner design, burner nozzles),
additional startup/shutdown fuel system, and safety measures. Performance, availability and
operation & maintenance (O&M) expenses can be affected.
Factors that affect Costs per Fired Hour
Fuel type and mode of operation (steady load/ partial load) will determine maintenance
intervals and the maintenance work items required. Some estimate that burning residual or crude
oil will increase maintenance costs by a factor of 3, (assuming a base of 1 for natural gas, and by
a factor of 1.5 for distillate fuel) and that those costs will be three times higher for the same
number of fired hours if the unit is started every fired hour, instead of starting once very 1000
.fired hours. ―Peaking‖ at 110 percent rating will increase maintenance costs by a factor of 3
relative to base-load operation at rated capacity, for any given period.
The control system on combined cycle units is automatic. When an operator starts the
unit, it accelerates, synchronizes and loads ―by itself‖. Fewer operators are required than in a
steam plant.



















CHAPTER:2

TURBINES USED IN LANCO POWER PLANT

2.1. GAS TURBINE:
The gas turbine is the most versatile item of turbomachinery today. It can be used in
several different modes in critical industries such as power generation, oil and gas, process
plants, aviation, as well domestic and smaller related industries.
A gas turbine essentially brings together air that it compresses in its compressor module,
and fuel, that are then ignited. Resulting gases are expanded through a turbine. That turbine‘s
shaft continues to rotate and drive the compressor which is on the same shaft, and operation
continues. A separate starter unit is used to provide the first rotor motion, until the turbine‘s
rotation is up to design speed and can keep the entire unit running.
The compressor module, combustor module and turbine module connected by one or
more shafts are collectively called the gas generator. The figures below (Figures 1 and 2)
illustrate a typical gas generator in cutaway and schematic format.

Fig. 1. Gas Turbine

Fig. 2. Schematic of modules: f: fan section, ag: low pressure compressor, bg: high pressure
compressor, c: turbine, e: shaft, h: combustor

Figure 3 below shows a gas turbine cutaway with its basic operating specification. Note this
particular turbine model can be used for both 50 and 60Hz power generation.

Fig. 5. The basic gas turbine cycle (Source: The Aircraft Engine Book, Rolls Royce UK)

The basic gas turbine cycle is illustrated (PV and T-s diagrams) in Figure 5. A
comparison can be drawn between the gas turbine‘s operating principle and a car engine‘s. See
Figures 5 and 6. A car operates with a piston engine (reciprocating motion) and typically handles
much smaller volumes than a conventional gas turbine.

2.2. HEAT RECOVERY STEAM GENERATOR TURBINE:

Many industrial processes and power generation systems produce a high temperature
exhaust gas which, if released straight to atmosphere, represents a large loss of energy. For a
typical gas turbine, the exhaust heat loss can be greater than 60% of the lower heating value
(LHV) of the fuel. In other industrial processes, the process itself may require that a gas stream
be cooled. Heat recovery steam generators (HRSGs) can convert heat in these exhaust gases to
useful energy and hence improve process efficiency with economic and environmental benefits.
HRSGs are employed in a number of applications. The larger units (utility HRSGs) are
used in utility combined cycle gas turbine (CCGT) power plants, while medium-tosmaller units
(industrial HRSGs) are used with other engines and in various industrial processes.
Utility scale HRSGs operate at high pressure (HP) steam conditions of up to
124bar/565°C with the associated CCGTs delivering electrical power with a net efficiency
approaching 60%. During the last ten years, over 30 CCGT power plants have been built and are
operating in the UK. This has helped the UK to develop a great deal of expertise in the design,
manufacture and operation of utility HRSGs. The UK has also been involved in the development
of HRSGs for use in integrated gasification combined cycle (IGCC) power plant.
Industrial HRSGs generally operate at lower steam conditions and often include
provision for supplementary or auxiliary firing. Lower pressure industrial boilers are usually of
shell (rather than water tube) design. HRSG applications are more diverse at the industrial scale,
eg industrial gas turbines use essentially the same HRSG technology as at the utility scale, while
reciprocating engines generating electricity on a small scale use small HRSGs to usually recover
low-grade heat as hot water from the engine cooling circuit to operate in combined heat and
power (CHP) mode. Higher-grade heat may also be recovered from the engine exhaust gas as
steam using HRSGs. Heat recovery, using HRSGs, is also achieved from other industrial exhaust
gases such as glass/metallurgical furnaces, kilns, roaster based plants, smelters and converters,
coke ovens, and solid/liquid/gas waste incinerators.
In the current competitive HRSG market, UK companies have been involved in licensing
agreements and collaborative partnerships to compete in the global market. The continual
development of new technologies, eg once-through technology, the effects of flexible operation,
new forms of gasification and the use of HRSGs in novel low emission power cycles are also
vital for new business.
Utility HRSGs
A utility HRSG is essentially a counterflow heat exchanger consisting of a series of
superheater, boiler (or evaporator) and economiser tube sections, arranged from the gas inlet to
the gas outlet to maximise heat recovery from the gas turbine exhaust gas. The heat transfer rate
on the water side of the tubes is far greater than the transfer rate on the gas side. The outside heat
transfer rate is said to be ‗controlling‘ and is therefore responsible for the overall heat transfer
rate. In an HRSG, this overall heat transfer rate is lower than that for plant life and reliability,
and there is no marked cost difference between them.
To maximise heat recovery, the final flue gas temperature should be as low as possible
(whilst remaining above the dew point). To maximise steam turbine efficiency, the steam
pressure and temperature should be as high as possible. The temperature of the evaporator
section is the saturated water temperature, which increases with pressure. Increasing the pressure
therefore increases the temperature at which heat exchange is occurring, which limits the amount
of heat recovery. The way around this conflict is to use a multi-pressure system.

With a dual pressure cycle, the high-pressure circuit ensures high steam pressure delivery
whilst the low-pressure circuit ensures that maximum heat is extracted from the GT exhaust.
Efficiency can be further enhanced by adding more pressure levels, but extra capital cost will be
incurred and, in practice, no more than three are generally used.
In a fired boiler due to the lower flue gas temperatures and the reduced effect of
radiation. In order to increase the rate of heat exchange, the surface area on the outside of the
tubes is increased by ‗finning‘.
An HRSG may have either a horizontal or a vertical gas pass. In the first case, the gas
turbine (GT) exhaust is ducted horizontally through the HRSG casing, before being turned
vertically up a stack. The vertical evaporator tubes allow natural circulation. In the second case,
when the gas pass is vertical, the evaporator tubes are horizontal and circulation is usually forced
to ensure a more consistent flow of water. However, natural circulation HRSGs have been built
with vertical gas flows and horizontal heating surfaces. The two design types have their own
advantages and disadvantages, but both manage to compete successfully in the same markets.
Both hold similar records Steam, which has initially passed through the high-pressure section of
a steam turbine, may be reheated, improving the lower pressure end of the steam turbine
performance. The overall cycle efficiency of a triple pressure system with reheat is typically 3%
higher than that of a single pressure system.
As a gas turbine exhaust contains sufficient oxygen to support further combustion
(approximately 15% w/w), additional burners may be positioned in the exhaust stream across the
transition duct to allow supplementary or auxiliary firing. ‗Supplementary-fired‘ HRSGs have
additional firing capability to increase the flue gas temperature, which, in turn, increases steam
production and raises the superheated steam temperature. The normal exhaust temperature of a
large GT is up to ~600°C. This temperature can be raised to ~815°C by supplementary firing in a
standard HRSG design. Higher temperatures up to around 1100°C are possible if a refractory
lining is fitted. Above this temperature, water cooled walls are needed. An increase in exhaust
gas temperature to ~815°C is associated with an increase in steam production of approximately
50%.
‗Supplementary-fired‘ HRSGs allow steam to be generated in the HRSG when the gas
turbine itself is not in operation. This allows maintenance to be undertaken on the gas turbine
whilst still generating electricity with the steam turbine. A separate air inlet duct
is needed in this case.

OPERATION
The main operational issues experienced by users are usually dependent on HRSG
design, quality of fabrication and supplier experience. These issues are:
Economiser Steaming
Steam ‗locking‘ is a risk on horizontal gas flow designs, some of which have high points
in the tubing that cannot be vented adequately. This can result in differential tube expansion,
poor drum level control, chemical deposition (with an associated corrosion risk) and economizer
under performance.
Dew-Point Corrosion
External dew-point corrosion due to low back-end temperatures on start-up and during
low load operation is a risk on pre heaters and, to a lesser extent, on economisers. Typically, a
pumped condensate pre heater recirculation system can be used to maintain inlet temperature
above acid dew point.
Flexible Operation
Flexible operation introduces a greater number of ‗events‘ where differential
temperatures exist within boiler components, and this reduces the fatigue life of the boiler. Some
of these effects are:
Economisers
Thermal fatigue and corrosion fatigue of economisers is usually start-related and
exacerbated under a flexible operation regime. During start-up, it takes some time for the drum
swell to subside after steam formation has commenced. The economizer header and tubes may,
therefore, be 100- 150°C above the temperature of the feedwater by the time the feedwater is
required. Depending on the header geometry, these mechanisms may be substantial enough to
cause low cycle fatigue.
When a unit is ‗boxed-up‘ (during an overnight shutdown, for example), heat radiates
from the hotter components to cooler ones such as the economiser and preheater. The
economiser and preheater tube banks warm up as heat is redistributed within the boiler,
particularly if a stack damper is used to reduce cooling rates and pressure decay whilst off-load.
On start-up, thermal down-shock can occur on the internal surfaces of economiser and
preheater headers as relatively cold feedwater enters these components. Thermal stratification
within the economizer headers can occur when off-load. A temperature differential is established
in the vertical plane causing the upper part of the header to expand relative to the lower part,
leading to header ‗hogging‘ and loading of the stub-to-header welds.
Evaporators
There can be difficulties in maintaining drum levels within allowable limits on startup;
using different drum levels for different start types can make this more manageable. The drum is
usually the thickest-walled component and therefore most vulnerable to stresses due to through
wall temperature differentials. The use of the newer higher strength alloys allows
thinner sections to be used, reducing this problem. However, the use of once-through technology
will have a greater effect, as it removes the need for a drum.
Super heaters & Re heaters
As the first heat exchanger in the gas path, the final stage super heater inevitably sees the
most severe temperature cycling. On utility-scale units, the GT exhaust temperature can increase
from 80°C to 450°C in five minutes. This results in high stress concentrations in the headers at
the tube stub positions and uses up the fatigue life of the component.
The tubes can reach temperatures above those experienced during normal operation and
so may be at risk of creep (as well as fatigue) damage during this period. The ramp up in
temperature is followed by a temperature drop when the drum pressure has risen sufficiently to
initiate a substantial cooling steam flow.
Re heaters are also susceptible to thermal fatigue damage on cold starts. Gas turbine
purge sequences rapidly cool the HP super heater (and re heater, if applicable), particularly on a
hot restart following a GT trip. This results in condensate formation, which can collect in, and
thermally shock the lower headers/tubes of horizontal gas-flow HRSGs. Damage is exacerbated
if drains are not sized or operated adequately to remove the condensate at the rate that it forms.
The unequal distribution of this condensate can result in tube distortion and differential
expansion between different parts of the header, which, depending upon the flexibility of the stub
to header attachments and/or header support system, may result in substantial loads on the stub-
to-header welds.
Attemperators
Attemperator sprays are used to control the temperature of the main steam leaving the
final super heater/ re heater outlet header. Poor attemperator control can result in quenching of
super heater/ re heater headers, tube distortion and damage to downstream pipework.
Attemperators can be particularly problematic on start-up or when an HRSG is being operated at
part-load. Modern multi nozzle, piston-controlled sprays or similar sophisticated systems allow
finer attemperation control and reduce the risk of these problems.
Tube Damage
Tube fretting is the abrasion of tubes against the tube sheets through which they pass. It
may cause wall thinning and eventual failure. Fretting can occur during expansion/contraction on
startup/ shutdown, particularly where finned tubing is used and/or where tube or tube plate
distortion has occurred. This may also result in increased stress on the stub-to header welds.
Tube failures have also resulted from gas bypassing via the sides of the HRSG casing.
Bypassing leads to a reduction in HRSG thermal performance, casing distortion and excessive
heating of the wing tubes downstream. It can also have an adverse effect on the water/steam-side
chemistry of evaporator tubes. The correct positioning and construction of tube sheets and
baffles reduce this problem.


Expansion Joints
Gas duct fabric expansion joints are typically located at the HRSG inlet, the outlet to the
main stack and, if applicable, at the bypass stack inlet. Expansion joints often represent the most
pressing obstacle to more flexible operation, as low cycle fatigue exacerbates existing defects
and can lead to the creation of new ones. High temperature fabric expansion joints are
often of relatively complex design and experience onerous operating conditions. Large
temperature differences between the inner and outer flanges of a joint may occur, particularly
during start-up, and this can result in steelwork deterioration and subsequent fabric damage.
More severe defects have been experienced on square joints than on round joints - square joints
inherently tend to concentrate stresses at certain points within the frame.

Heat recovery steam generator turbine



2.3. STEAM TURBINE.

Steam turbines for combined-cycle power plants generally are of two styles. Steam
turbines with different exhaust annulus areas are available to permit optimization to meet
specific condenser cooling conditions. Steam turbines with large annulus areas are more
expensive, but provide increased capability and may be the most economical selection for
applications with low steam turbine exhaust pressures. Steam turbines with small exhaust
annulus area provide comparable or higher capability and low cost and are the more economical
choice when steam turbine exhaust pressures are high.
Combined cycle steam turbines have features that include but are not limited to:
 Modules assembled where they can be shipped and field assembled with a low profile
installation, reducing installation time and cost.
 Borescopic inspection access ports where the upper turbine casing does not have to be
removed during inspection.
 Main cold and hot reheat pipes as well as the main steam pipes connect to the lower half
of the shell. This allows removal of the upper half shell for maintenance.

A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to
do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir
Charles Parsons in 1884.
Because the turbine generates rotary motion, it is particularly suited to be used to drive
an electrical generator – about 90% of all electricity generation in the United States is by use of
steam turbines. The steam turbine is a form of heat engine that derives much of its improvement
in thermodynamic efficiency through the use of multiple stages in the expansion of the steam,
which results in a closer approach to the ideal reversible process.

A rotor of a modern steam turbine, used in a power plant

HISTORY

The first device that may be classified as a reaction steam turbine was little more than a
toy, the classic Aeolipile, described in the 1st century by Greek mathematician Hero of
Alexandria in Roman Egypt. In 1551, Taqi al-Din in Ottoman Egypt described a steam turbine
with the practical application of rotating a spit. Steam turbines were also described by the
Italian Giovanni Branca (1629) and John Wilkins in England (1648). The devices described by
al-Din and Wilkins are today known as steam jacks.
The modern steam turbine was invented in 1884 by the Anglo-Irish engineer Sir Charles
Parsons, whose first model was connected to a dynamo that generated 7.5 kW (10 hp) of
electricity. The invention of Parson's steam turbine made cheap and plentiful electricity possible
and revolutionized marine transport and naval warfare. His patent was licensed and the turbine
scaled-up shortly after by an American, George Westinghouse. The Parsons turbine also turned
out to be easy to scale up. Parsons had the satisfaction of seeing his invention adopted for all
major world power stations, and the size of generators had increased from his first 7.5 kW set up
to units of 50,000 kW capacity. Within Parson's lifetime the generating capacity of a unit was
scaled up by about 10,000 times and the total output from turbo-generators constructed by his
firm C. A. Parsons and Company and by their licensees, for land purposes alone, had exceeded
thirty million horse-power

Parsons turbine from the Polish destroyer ORPWicher.

A number of other variations of turbines have been developed that work effectively with
steam. The de Laval turbine (invented by Gustaf de Laval) accelerated the steam to full speed
before running it against a turbine blade. Hence the (impulse) turbine is simpler, less expensive
and does not need to be pressure-proof. It can operate with any pressure of steam, but is
considerably less efficient.
One of the founders of the modern theory of steam and gas turbines was also Aurel
Stodola, a Slovak physicist and engineer and professor at Swiss Polytechnical Institute
(now ETH) in Zurich. His mature work was Die Dampfturbinen und ihre Aussichten als
Wärmekraftmaschinen (English The Steam Turbine and its perspective as a Heat Energy
Machine) which was published in Berlin in 1903. In 1922, in Berlin, was published another
important book Dampf und Gas-Turbinen (English Steam and Gas Turbines).
The Brown-Curtis turbine which had been originally developed and patented by the U.S.
company International Curtis Marine Turbine Company was developed in the 1900s in
conjunction with John Brown & Company. It was used in John Brown's merchant ships and
warships, including liners and Royal Navy warships.
Steam supply and exhaust conditions
These types include condensing, non-condensing, reheat, extraction and induction.
Condensing turbines are most commonly found in electrical power plants. These turbines
exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well
below atmospheric to a condenser.
Non-condensing or back pressure turbines are most widely used for process steam
applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the
process steam pressure. These are commonly found at refineries, district heating units, pulp and
paper plants, and desalination facilities where large amounts of low pressure process steam are
available.
Reheat turbines are also used almost exclusively in electrical power plants. In a reheat
turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler
where additional superheat is added. The steam then goes back into an intermediate pressure
section of the turbine and continues its expansion.
Extracting type turbines are common in all applications. In an extracting type turbine,
steam is released from various stages of the turbine, and used for industrial process needs or sent
to boiler feed water heaters to improve overall cycle efficiency. Extraction flows may be
controlled with a valve, or left uncontrolled.
Induction turbines introduce low pressure steam at an intermediate stage to produce
additional power.
CASING OR SHAFT ARRANGEMENTS
These arrangements include single casing, tandem compound and cross compound
turbines. Single casing units are the most basic style where a single casing and shaft are coupled
to a generator. Tandem compound are used where two or more casings are directly coupled
together to drive a single generator. A cross compound turbine arrangement features two or more
shafts not in line driving two or more generators that often operate at different speeds. A cross
compound turbine is typically used for many large applications.

Mounting of a steam turbine
TWO-FLOW ROTORS

The moving steam imparts both a tangential and axial thrust on the turbine shaft, but the
axial thrust in a simple turbine is unopposed. To maintain the correct rotor position and
balancing, this force must be counteracted by an opposing force. Either thrust bearings can be
used for the shaft bearings, or the rotor can be designed so that the steam enters in the middle of
the shaft and exits at both ends. The blades in each half face opposite ways, so that the axial
forces negate each other but the tangential forces act together. This design of rotor is called two-
flow or double-exhaust. This arrangement is common in low-pressure casings of a compound
turbine.

A two-flow turbine rotor. The steam enters in the middle of the shaft, and exits at each end,
balancing the axial force.
PRINCIPLE OF OPERATION AND DESIGN
An ideal steam turbine is considered to be an isentropic process, or constant entropy
process, in which the entropy of the steam entering the turbine is equal to the entropy of the
steam leaving the turbine. No steam turbine is truly isentropic, however, with typical isentropic
efficiencies ranging from 20–90% based on the application of the turbine. The interior of a
turbine comprises several sets of blades, or buckets as they are more commonly referred to. One
set of stationary blades is connected to the casing and one set of rotating blades is connected to
the shaft. The sets intermesh with certain minimum clearances, with the size and configuration of
sets varying to efficiently exploit the expansion of steam at each stage.
TURBINE EFFICIENCY
To maximize turbine efficiency the steam is expanded, doing work, in a number of
stages. These stages are characterized by how the energy is extracted from them and are known
as either impulse or reaction turbines. Most steam turbines use a mixture of the reaction and
impulse designs: each stage behaves as either one or the other, but the overall turbine uses both.
Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.
OPERATION AND MAINTENANCE
When warming up a steam turbine for use, the main steam stop valves (after the boiler)
have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up
the lines in the system along with the steam turbine. Also, a turning gear is engaged when there
is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven
expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to
assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to
the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10–
15 RPM (0.17–0.25 Hz) to slowly warm the turbine.
Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a
blade breaking away from the rotor at high velocity and being ejected directly through the
casing. To minimize risk it is essential that the turbine be very well balanced and turned with dry
steam - that is, superheated steam with a minimal liquid water content. If water gets into the
steam and is blasted onto the blades (moisture carry over), rapid impingement and erosion of the
blades can occur leading to imbalance and catastrophic failure. Also, water entering the blades
will result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along
with controls and baffles in the boilers to ensure high quality steam, condensate drains are
installed in the steam piping leading to the turbine. Modern designs are sufficiently refined that
problems with turbines are rare and maintenance requirements are relatively small.

A modern steam turbine generator installation

SPEED REGULATION
The control of a turbine with a governor is essential, as turbines need to be run up slowly,
to prevent damage while some applications (such as the generation of alternating current
electricity) require precise speed control. Uncontrolled acceleration of the turbine rotor can lead
to an over speed trip, which causes the nozzle valves that control the flow of steam to the turbine
to close. If this fails then the turbine may continue accelerating until it breaks apart, often
spectacularly. Turbines are expensive to make, requiring precision manufacture and special
quality materials.
During normal operation in synchronization with the electricity network, power plants are
governed with a five percent droop speed control. This means the full load speed is 100% and the
no-load speed is 105%. This is required for the stable operation of the network without hunting
and drop-outs of power plants. Normally the changes in speed are minor. Adjustments in power
output are made by slowly raising the droop curve by increasing the spring pressure on
a centrifugal governor. Generally this is a basic system requirement for all power plants because
the older and newer plants have to be compatible in response to the instantaneous changes in
frequency without depending on outside communication.
THERMODYNAMICS OF STEAM TURBINES
The steam turbine operates on basic principles of thermodynamics using the part of
the Rankine cycle. Superheated vapor (or dry saturated vapor, depending on application) enters
the turbine, after it having exited the boiler, at high temperature and high pressure. The high
heat/pressure steam is converted into kinetic energy using a nozzle (a fixed nozzle in an impulse
type turbine or the fixed blades in a reaction type turbine). Once the steam has exited the nozzle
it is moving at high velocity and is sent to the blades of the turbine. A force is created on the
blades due to the pressure of the vapor on the blades causing them to move. A generator or other
such device can be placed on the shaft, and the energy that was in the vapor can now be stored
and used. The gas exits the turbine as a saturated vapor (or liquid-vapor mix depending on
application) at a lower temperature and pressure than it entered with and is sent to the condenser
to be cooled. If we look at the first law we can find an equation comparing the rate at which
work is developed per unit mass. Assuming there is no heat transfer to the surrounding
environment and that the change in kinetic and potential energy is negligible when compared to
the change in specific enthalpy we come up with the following equation


where
 Ẇ is the rate at which work is developed per unit time
 ṁ is the rate of mass flow through the turbine

Rankine cycle with superheat
 Process 1-2: The working fluid is pumped from low to high pressure.
 Process 2-3: The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapor.
 Process 3-3': The vapour is superheated.
 Process 3-4 and 3'-4': The dry saturated vapor expands through a turbine, generating
power. This decreases the temperature and pressure of the vapor, and some condensation
may occur.
 Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant
pressure to become a saturated liquid.

ISENTROPIC TURBINE EFFICIENCY
To measure how well a turbine is performing we can look at its is entropic efficiency.
This compares the actual performance of the turbine with the performance that would be
achieved by an ideal, isentropic, turbine. When calculating this efficiency, heat lost to the
surroundings is assumed to be zero. The starting pressure and temperature is the same for both
the actual and the ideal turbines, but at turbine exit the energy content ('specific enthalpy') for the
actual turbine is greater than that for the ideal turbine because of irreversibility in the actual
turbine. The specific enthalpy is evaluated at the same pressure for the actual and ideal turbines
in order to give a good comparison between the two.
The isentropic efficiency is found by dividing the actual work by the ideal work.

where
 h
1
is the specific enthalpy at state one
 h
2
is the specific enthalpy at state two for the actual turbine
 h
2s
is the specific enthalpy at state two for the isentropic turbine

DIRECT DRIVE
Electrical power stations use large steam turbines driving electric generators to produce
most (about 80%) of the world's electricity. The advent of large steam turbines made central-
station electricity generation practical, since reciprocating steam engines of large rating became
very bulky, and operated at slow speeds. Most central stations are fossil fuel power
plants and nuclear power plants; some installations use geothermal steam, or use concentrated
solar power (CSP) to create the steam. Steam turbines can also be used directly to drive large
centrifugal pumps, such as feed water pumps at a thermal power plant.
The turbines used for electric power generation are most often directly coupled to their
generators. As the generators must rotate at constant synchronous speeds according to the
frequency of the electric power system, the most common speeds are 3,000 RPM for 50 Hz
systems, and 3,600 RPM for 60 Hz systems. Since nuclear reactors have lower temperature
limits than fossil-fired plants, with lower steam quality, the turbine generator sets may be
arranged to operate at half these speeds, but with four-pole generators, to reduce erosion of
turbine blades.




CHAPTER:3

GENERATION OF POWER AT LANCO.
















CHAPTER:4
TYPES OF TRANSFORMERS
TRANSFORMER:
A transformer is a device that transfers electrical energy from one circuit to another
through inductively coupled conductors—the transformer's coils. A varying current in the first or
primary winding creates a varying magnetic flux in the transformer's core and thus a
varying magnetic field through the secondary winding. This varying magnetic field induces a
varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is
called inductive coupling.
If a load is connected to the secondary, current will flow in the secondary winding, and
electrical energy will be transferred from the primary circuit through the transformer to the load.
In an ideal transformer, the induced voltage in the secondary winding (V
s
) is in proportion to the
primary voltage (V
p
) and is given by the ratio of the number of turns in the secondary (N
s
) to the
number of turns in the primary (N
p
) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating
current (AC) voltage to be "stepped up" by making N
s
greater than N
p
, or "stepped down" by
making N
s
less than N
p
.
In the vast majority of transformers, the windings are coils wound around a ferro
magnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a
stage microphone to huge units weighing hundreds of tons used to interconnect portions
of power grids. All operate on the same basic principles, although the range of designs is wide.
While new technologies have eliminated the need for transformers in some electronic circuits,
transformers are still found in nearly all electronic devices designed for household ("mains")
voltage. Transformers are essential for high-voltage electric power transmission, which makes
long-distance transmission economically practical.

INDUCTION LAW
The voltage induced across the secondary coil may be calculated from Faraday's law of
induction, which states that:

where V
s
is the instantaneous voltage, N
s
is the number of turns in the secondary coil and
Φ is the magnetic flux through one turn of the coil. If the turns of the coil are oriented
perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux
density B and the area A through which it cuts. The area is constant, being equal to the cross-
sectional area of the transformer core, whereas the magnetic field varies with time according to
the excitation of the primary. Since the same magnetic flux passes through both the primary and
secondary coils in an ideal transformer, the instantaneous voltage across the primary winding
equals

Taking the ratio of the two equations for V
s
and V
p
gives the basic equation for stepping
up or stepping down the voltage

N
p
/N
s
is known as the turns ratio, and is the primary functional characteristic of any
transformer. In the case of step-up transformers, this may sometimes be stated as the
reciprocal, N
s
/N
p
. Turns ratio is commonly expressed as anirreducible fraction or ratio: for
example, a transformer with primary and secondary windings of, respectively, 100 and 150 turns
is said to have a turns ratio of 2:3 rather than 0.667 or 100:150.
IDEAL POWER EQUATION

The ideal transformer as a circuit element
If the secondary coil is attached to a load that allows current to flow, electrical power is
transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly
efficient. All the incoming energy is transformed from the primary circuit to the magnetic
field and into the secondary circuit. If this condition is met, the input electric power must equal
the output power:

giving the ideal transformer equation

This formula is a reasonable approximation for most commercial built transformers
today.
If the voltage is increased, then the current is decreased by the same factor. The
impedance in one circuit is transformed by the square of the turns ratio. For example, if an
impedance Z
s
is attached across the terminals of the secondary coil, it appears to the primary
circuit to have an impedance of (N
p
/N
s
)
2
Z
s
. This relationship is reciprocal, so that the
impedance Z
p
of the primary circuit appears to the secondary to be (N
s
/N
p
)
2
Z
p
.


ENERGY LOSSES
An ideal transformer would have no energy losses, and would be 100% efficient. In
practical transformers, energy is dissipated in the windings, core, and surrounding structures.
Larger transformers are generally more efficient, and those rated for electricity distribution
usually perform better than 98%.
Experimental transformers using superconducting windings achieve efficiencies of
99.85%. The increase in efficiency can save considerable energy, and hence money, in a large
heavily loaded transformer; the trade-off is in the additional initial and running cost of the
superconducting design.
Losses in transformers (excluding associated circuitry) vary with load current, and may
be expressed as "no-load" or "full-load" loss. Winding resistance dominates load losses,
whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-
load loss can be significant, so that even an idle transformer constitutes a drain on the electrical
supply and a running cost. Designing transformers for lower loss requires a larger core, good-
quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost
so that there is a trade-off between initial cost and running cost (also see energy efficient
transformer).
Transformer losses are divided into losses in the windings, termed copper loss, and those
in the magnetic circuit, termed iron loss. Losses in the transformer arise from:



Winding resistance
Current flowing through the windings causes resistive heating of the conductors. At
higher frequencies, skin effect and proximity effect create additional winding resistance and
losses.
Hysteresis losses
Each time the magnetic field is reversed, a small amount of energy is lost due
to hysteresis within the core. For a given core material, the loss is proportional to the frequency,
and is a function of the peak flux density to which it is subjected.
Eddy currents
Ferromagnetic materials are also good conductors and a core made from such a material
also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore
circulate within the core in a plane normal to the flux, and are responsible for resistive heating of
the core material. The eddy current loss is a complex function of the square of supply frequency
and inverse square of the material thickness. Eddy current losses can be reduced by making the
core of a stack of plates electrically insulated from each other, rather than a solid block; all
transformers operating at low frequencies use laminated or similar cores.
Magnetostriction
Magnetic flux in a ferromagnetic material, such as the core, causes it to physically
expand and contract slightly with each cycle of the magnetic field, an effect known
as magnetostriction. This produces the buzzing sound commonly associated with
transformers that can cause losses due to frictional heating. This buzzing is particularly familiar
from low-frequency (50 Hz or 60 Hz) mains hum, and high-frequency (15,734 Hz (NTSC) or
15,625 Hz (PAL)) CRT noise.
Mechanical losses
In addition to magnetostriction, the alternating magnetic field causes fluctuating forces
between the primary and secondary windings. These incite vibrations within nearby metalwork,
adding to the buzzing noise and consuming a small amount of power.
Stray losses
Leakage inductance is by itself largely lossless, since energy supplied to its magnetic
fields is returned to the supply with the next half-cycle. However, any leakage flux that
intercepts nearby conductive materials such as the transformer's support structure will give rise
to eddy currents and be converted to heat. There are also radiative losses due to the oscillating
magnetic field but these are usually small.

CORE FORM AND SHELL FORM TRANSFORMERS


Core form = core type; shell form = shell type
As first mentioned in regard to earliest ZBD closed-core transformers, transformers are
generally considered to be either core form or shell form in design depending on the type of
magnetic circuit used in winding construction (see image). That is, when winding coils are
wound around the core, transformers are termed as being of core form design; when winding
coils are surrounded by the core, transformers are termed as being of shell form design. Shell
form design may be more prevalent than core form design for distribution transformer
applications due to the relative ease in stacking the core around winding coils. Core form design
tends to, as a general rule, be more economical, and therefore more prevalent, than shell form
design for high voltage power transformer applications at the lower end of their voltage and
power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and
power ratings, shell form transformers tend to be more prevalent. Shell form design tends to be
preferred for extra high voltage and higher MVA applications because, though more labor
intensive to manufacture, shell form transformers are characterized as having inherently better
kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit
damage.
EQUIVALENT CIRCUIT
The physical limitations of the practical transformer may be brought together as an
equivalent circuit model (shown below) built around an ideal lossless transformer. Power loss in
the windings is current-dependent and is represented as in-series resistances R
p
and R
s
. Flux
leakage results in a fraction of the applied voltage dropped without contributing to the mutual
coupling, and thus can be modeled as reactances of each leakage inductance X
p
and X
s
in series
with the perfectly coupled region.
Iron losses are caused mostly by hysteresis and eddy current effects in the core, and are
proportional to the square of the core flux for operation at a given frequency. Since the core flux
is proportional to the applied voltage, the iron loss can be represented by a resistance R
C
in
parallel with the ideal transformer.
A core with finite permeability requires a magnetizing current I
m
to maintain the mutual flux
in the core. The magnetizing current is in phase with the flux. Saturation effects cause the
relationship between the two to be non-linear, but for simplicity this effect tends to be ignored in
most circuit equivalents. With asinusoidal supply, the core flux lags the induced EMF by 90° and
this effect can be modeled as a magnetizing reactance (reactance of an effective
inductance) X
m
in parallel with the core loss component, R
c
. R
c
and X
m
are sometimes together
termed the magnetizing branch of the model. If the secondary winding is made open-circuit, the
current I
0
taken by the magnetizing branch represents the transformer's no-load current.
The secondary impedance R
s
and X
s
is frequently moved (or "referred") to the primary side
after multiplying the components by the impedance scaling factor (N
p
/N
s
)
2
.


Transformer equivalent circuit, with secondary impedances referred to the primary side
The resulting model is sometimes termed the "exact equivalent circuit", though it retains a
number of approximations, such as an assumption of linearity. Analysis may be simplified by
moving the magnetizing branch to the left of the primary impedance, an implicit assumption that
the magnetizing current is low, and then summing primary and referred secondary impedances,
resulting in so-called equivalent impedance.
The parameters of equivalent circuit of a transformer can be calculated from the results of
two transformer tests: open-circuit test and short-circuit test.
CURRENT TRANSFORMER:
In electrical engineering, a current transformer(CT) is used for measurement of electric
currents. Current transformers, together with voltage transformers (VT) (potential
transformers (PT)), are known as instrument transformers. When current in a circuit is too high
to directly apply to measuring instruments, a current transformer produces a reduced current
accurately proportional to the current in the circuit, which can be conveniently connected to
measuring and recording instruments. A current transformer also isolates the measuring
instruments from what may be very high voltage in the monitored circuit. Current transformers
are commonly used in metering andprotective relays in the electrical power industry.

VOLTAGE TRANSFORMERS
Voltage transformers (VT) or potential transformers (PT) are another type of instrument
transformer, used for metering and protection in high-voltage circuits. They are designed to
present negligible load to the supply being measured and to have a precise voltage ratio to
accurately step down high voltages so that metering and protective relay equipment can be
operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 V
or 120 V at rated primary voltage, to match the input ratings of protective relays.
The transformer winding high-voltage connection points are typically labeled as H
1
,
H
2
(sometimes H
0
if it is internally grounded) and X
1
, X2 and sometimes an X
3
tap may be
present. Sometimes a second isolated winding (Y
1
, Y
2
, Y
3
) may also be available on the same
voltage transformer. The high side (primary) may be connected phase to ground or phase to
phase. The low side (secondary) is usually phase to ground.
The terminal identifications (H
1
, X
1
, Y
1
, etc.) are often referred to as polarity. This
applies to current transformers as well. At any instant terminals with the same suffix numeral
have the same polarity and phase. Correct identification of terminals and wiring is essential for
proper operation of metering and protective relays.
Some meters operate directly on the secondary service voltages at or below 600 V. VTs
are typically used for higher voltages (for example, 765 kV for power transmission) , or where
isolation is desired between the meter and the measured circuit.
CHAPTER:5

TRANSFORMERS USED IN LANCO POWER PLANT.

4.1. GENERATOR TRANSFORMER.

The generators are connected to the 220KV switchyard through 15KV/220KV step-up
generator transformers. Generator transformers are designed to deliver the total output of the
generating unit into the system covering the entire operating range of generator capability and
have the following salient technical features.
Type : Oil filled, outdoor type
Voltage ratio : 220KV/15KV
Frequency : 50Hz
Vector group : YNd1
% Impedance : 15%
Capacity : 98/128/160 MVA
Type of cooling : ONAN/ONAF/OFAF
The generator transformers are provided with 10% ON-LOAD Tap changer on HV
winding suitable for unidirectional power flow.

Generator transformer is the key equipment for electric power generation and power
transmission. The generator transformer, designed and manufactured by XD, fully complies wit
requirements of power design with its excellent performances of low loss, low noise, low partial
discharge, good ability of short-circuit withstand, and reliable operation. The voltage class
covers a range from 110 kV to 500 kV with the biggest capacity of 420 MVA for three-phase
transformer. XD also provides single-phase generator transformer and various types of combined
transformers capable of overcoming harsh transportation conditions. XD can provide varied
products to match all kinds of thermal power sets and water power sets, such as 200MW,
250MW, 300MW and 600MW, etc. Among them, two new types of generator transformers of
SFP10-370 MVA/220 kV and SFP9-420 MVA/220 kV have passed the appraisal for new
products given by the National Machinary Department and the National Power Department. The
specification and the performance of SFP10-400 MVA/500 kV power transformer have reached
to the leading level in the world. SFP-160 MVA/420 kV transformer exported to lraq is so far the
product with the highest voltage level amon all exported transformers in China, with its technical
level has ranked in the international leading list.



3.2. UNIT AUXILIARY TRANSFORMERS:
Unit transformers are sized to cater to unit auxiliaries for full load operation of both gas
turbine generating units and unit auxiliaries of one steam generating unit. The loads are
calculated on the basis of running load with sufficient margin. While arriving at the rating of
transformer and impedance value, due considerations are given to short circuit level at the unit
HT bus and also the voltage drop at the unit buses when the largest motor (BFP-1500KW)
connected to unit bus is started with all other operating loads of unit bus in running condition.
The unit transformer is having the following salient technical features.
Type : Oil filled, outdoor type
Voltage ratio : 15KV/6.6KV
Frequency : 50Hz
Vector group : Dyn11
% Impedance : 10%
Capacity : 12/15MVA
Type of cooling : ONAN/ONAF
The unit transformer is provided with 10% ON-LOAD Tap changer on HV winding
suitable for unidirectional power flow.

3.3. STATION TRANSFORMER:
The transformer are used to supply power for the start-up as well as station auxiliaries.
The size of the station transformer is calculated on the basis of running load with good margin.
Type : Oil filled, outdoor type
Voltage ratio : 220KV/6.6KV
Frequency : 50Hz
Vector group : Ynyn0
% Impedance : 10%
Capacity : 10/12 MVA
Type of cooling : ONAN/ONAF
The station transformer is provided with 10% ON-LOAD Tap changer on HV winding.
A hallow insulating with ceramic support column through which passes the insulating tie
rod and which is attached to the one-minute power-Frequency
With stand voltage : 20KV(RMS)
1.2/50µS,Impulse With Stand Voltage : 60KV(Peak)

Remote Auto Operation Of Fans:
For remote operation of fans (fan1 to fan8) fans (on RTCC panel) kept on auto mode.
Coil of contactor will get energies & it is normally open contact closes.
Operation of pumps:
For checking the healthiness of individual pump ―test‖ mode can be adopted. Based on
requirement if the internal temperature high we can run the pumps.
1)Local manual operation of pumps:
All the 4-pumps (P1 to P4) operate when pump switch is kept on local manual mode &
pump switch are kept on in service mode. Bus wired out in the circuit as pump contractor get
energized and pump1 to pump4 starts running.
2) Local operation of pumps:
For automatic operation of pump group ‗A‘, ‗B‘, ‗C‘ & ‗D‘ pump switch is kept on local auto
mode & pump switches are kept on in service mode. When the temperature of windings attains
preset value, normally open contact of will close and another contactor gets energized.
3) Remote auto operation of pumps:
For remote auto operation of pumps (pump1 to pump4) pump switch (on RTCC panel)
kept on auto mode. Coil of contactor will get energized and its number contact closes. Pump
group-‗A‘, ‗B‘, ‗C‘ & ‗D‘ start running as described above.