Unit - I
Largest Thermal Power Plants (India)
• Vindhyachal Thermal Power Station in the Singrauli district of
Madhya Pradesh, with an installed capacity of 4,760MW, is
currently the biggest thermal power plant in India. It is a coalbased power plant owned and operated by NTPC.
• The 4,620MW Mundra Thermal Power Station located in the
Kutch district of Gujarat is currently the second biggest operating
thermal power plant in India. It is a coal-fired power plant owned
and operated by Adani Power.
• The 4,000MW Mundra Ultra Mega Power Plant (UMPP), also
located in the Kutch district of Gujarat, ranks as the third largest
thermal power plant in India.
• Talcher Super Thermal Power Station or NTPC Talcher Kaniha,
located in the Angul district of Odisha, is a 3,000MW coal-fired
power plant owned and operated by NTPC.
Largest Thermal Power Plants (World)
Taichung power plant in Longjing, Taichung, Taiwan, is the world’s biggest thermal
power station. It is a coal fired power station with an installed capacity of 5,788MW
owned and is operated by the state-owned Taiwan Power Company (Taipower).
Shoaiba Power Plant, Saudi Arabia
Shoaiba oil-fired power facility located on the Red Sea coast, around 100km south of
Jeddah in Saudi Arabia, is currently the second biggest thermal power plant in the
world. The 5,600MW power station is also the biggest in the Middle East.
Thermal Power Plants in Punjab
• Talwandi Sabo Power Project, Mansa. It is the highest capacity thermal
power plant in Punjab, with power capacity of 1980 MW (660x3).
• Nabha Power Project, Rajpura.
Power capacity of 1400 MW (700x2).
• Guru Gobind Singh Super Thermal Power Plant, Ropar. It is a 1260 MW
(6x210 MW) coal-based thermal power plant.
• Guru Hargobind Thermal Plant, Lehra Mohabbat, Bhatinda. It is a 920 MW
(2x210 MW, 2x250 MW) coal-based thermal power plant.
• Guru Nanak Dev Thermal Plant, Bhatinda. It is a 460 MW (110x2 + 120x2
MW) coal-based thermal power plant.
Guru Hargobind Thermal Plant is located at Lehra Mohabbat, Bhatinda, on National Highway No. 7 which runs
from Bathinda to Chandigarh.
Capacity (MW): 920
Hydro Power Plants in Punjab
•
•
•
•
•
•
•
•
•
•
Ranjit Sagar Dam, 600 MW
Shanan Power House. It is a 110 MW hydro power plant.
Anandpur Sahib Hydel Channel, 134 MW
Mukerian Hydel, 207 MW
UBDC Hydroelectric Power House, 45 MW
Bhakra Nangal Project, 1325MW
Pong Dam Project 396 MW
Dehar Power House 990 MW
Thein Dam Project 600 MW
Shahpur Kandi Project 206 MW
Transmission line constants
• An A.C. transmission line has resistance, inductance and
capacitance uniformly distributed along its length. These
are known as constants or parameters of the line.
• The performance of a transmission line depends to a
considerable extent upon these line constants.
• These constants determine whether the efficiency and
voltage regulation of the line will be good or poor.
• Resistance: It is the opposition of line conductors to
current flow.
• Inductance: It is the flux linkages per ampere i.e.
• Capacitance: The capacitance between the conductors is
the charge per unit potential difference i.e.
Types of Conductors
Economic Load Dispatch
I The idea is to minimize the cost of electricity generation
without sacrificing quality and reliability.
I Therefore, the production cost is minimized by operating
plants economically.
I Since the load demand varies, the power generation must vary
accordingly to maintain the power balance.
I The turbine-governor must be controlled such that the
demand is met economically.
I This arises when there are multiple choices.
Economic Distribution of Loads between the units in a Plant:
I To determine the economic distribution of load between
various generating units, the variable operating costs of the
units must be expressed in terms of the power output.
I Fuel cost is the principle factor in thermal and nuclear power
plants. It must be expressed in terms of the power output.
I Operation and Maintenance costs can also be expressed in
terms of the power output.
I Fixed costs, such as the capital cost, depreciation etc., are not
included in the fuel cost.
Let us define the input cost of an unit i ,Fi in Rs./h and the power
output of the unit as Pi . Then the input cost can be expressed in
terms of the power output as
Fi = ai Pi2 + bi Pi + ci Rs/h
Where ai , bi and ci are fuel cost coefficients.
The incremental operating cost of each unit is
i
=
dFi
= 2ai Pi + bi Rs./MWh
dPi
Let us assume that there ar N units in a plant.
N
1
PD
The total fuel cost is
FT = F1 + F2 + · · · + FN =
N
X
Fi Rs./h
i=1
All the units have to supply a load demand of PD MW.
P1 + P2 + · · · + PN = PD
N
X
Pi = PD
i=1
min FT =
N
X
i=1
Subject to
N
X
i=1
Pi = PD
Fi
It is a constrained optimization problem. Let us form the
Lagrangian function.
L = FT + (PD
N
X
Pi )
i=1
To find the optimum,
@L
= 0 i = 1, 2, · · · , N
@Pi
@L
=0
@
dFi
=
dPi
i = 1, 2, · · · , N
N
X
i=1
Pi = PD
N + 1 linear equations need to be solved for N + 1 variables.
For economical division of load between units within a plant, the
criterion is that all units must operate at the same incremental fuel
cost.
dF1
dF2
dFn
=
= ··· =
=
dP1
dP2
dPn
dF2
(Rs/MWhr)
dP2
dF1
(Rs/MWhr)
dP1
This is called the coordination equation.
⇤
P1⇤
P1 (MW)
P2⇤
P2 (MW)
Example : Consider two units of a plant that have fuel costs of
F1 = 0.2P12 + 40P1 + 120 Rs./h
F2 = 0.25P22 + 30P2 + 150 Rs./h
1. Determine the economic operating schedule and the
corresponding cost of generation for the demand of 180 MW.
2. If the load is equally shared by both the units, determine the
savings obtained by loading the units optimally.
1. For economical dispatch,
dF1
dF2
=
dP1
dP2
0.4P1 + 40 = 0.5P2 + 30
and
P1 + P2 = 180
On solving the above two equations,
P1 = 88.89 MW;
P2 = 91.11 MW
The cost of generation is
FT = F1 + F2 = 10, 214.43 Rs./h
2. If the load is shared equally,
P1 = 90 MW;
P2 = 90 MW
The cost of generation is
FT = 10, 215 Rs./h
Therefore, the saving will be 0.57 Rs./h
Generator Limits:
The power generation limit of each unit is given by the inequality
constraints
Pi,min  Pi  Pi,max i = 1, · · · , N
I The maximum limit Pmax is the upper limit of power
generation capacity of each unit.
I Whereas, the lower limit Pmin pertains to the thermal
consideration of operating a boiler in a thermal or nuclear
generating station.
How to consider the limits
I If any one of the optimal values violates its limits, fix the
generation of that unit to the violated value.
I Optimally dispatch the reduced load among the remaining
generators.
Example: The fuel cost functions for three thermal plants are
F1 = 0.4P12 + 10P1 + 25 Rs./h
F2 = 0.35P22 + 5P2 + 20 Rs./h
F3 = 0.475P32 + 15P3 + 35 Rs./h
The generation limits of the units are
30 MW  P1  500 MW
30 MW  P2  500 MW
30 MW  P3  250 MW
Find the optimum schedule for the load of 1000 MW.
For optimum dispatch,
dF1
dF2
dF3
=
=
dP1
dP2
dP3
0.8P1 + 10 = 0.7P2 + 5
0.7P2 + 5 = 0.9P3 + 15
and
P1 + P2 + P3 = 1000
On solving the above three equations,
P1 = 334.3829 MW;
P2 = 389.2947 MW;
Since the unit 3 violates its maximum limit,
P3 = 250 MW
P3 = 276.3224 MW
The remaining load (750 MW) is scheduled optimally among 1 and
2 units.
0.8P1 + 10 = 0.7P2 + 5
P1 + P2 = 750
On solving the above equations,
P1 = 346.6667 MW;
P2 = 403.3333 MW
Therefore, the final load distribution is
P1 = 346.6667 MW;
P2 = 403.3333 MW;
P3 = 250 MW
Series
and
Shunt
Compensation
Series Compensation
Series compensation is basically a powerful tool
to improve the performance of EHV lines. It
consists of capacitors connected in series with
the line at suitable locations.
Advantages of Series Compensation
1. Increase in transmission capacity
– The power transfer capacity of a line is given by
E.V
P=
sin d
X
where, E is sending end voltage
V is receiving end voltage
X is reactance of line
δ is phase angle between E and V
Power transfer without and with compensation:
E.V
P1 =
sin d
XL
E.V
P2 =
sin d
(X L - XC )
P2
XL
1
1
=
=
=
P1 ( X L - X C ) (1 - X C / X L ) 1 - K
where K is degree of compensation.
The economic degree of compensation lies in the range of 40-70%
(K < 1, i.e. 0.4-0.7)
2. Improvement of System Stability
• For same amount of power transfer and same value of E
and V, the δ in the case of series compensated line is less
than that of uncompensated line.
P=
E.V
sin d1
XL
P=
E.V
sin d 2
(X L - XC )
sin d 2 ( X L - X C )
=
sin d1
XL
• A lower δ means better system stability
• Series compensation offers most economic solution for
system stability as compared to other methods (reducing
generator, x-mer reactance, bundled conductors, increase
no. of parallel circuits
Disadvantages
1. Increase in fault current
2. Mal operation of distance relay- if the degree
of compensation and location is not proper.
3. High recovery voltage of lines- across the
circuit breaker contacts and is harmful.
Location of Series Capacitor
• The choice of the location of the series
capacitor depends on many technical and
economical consideration.
• In each case, a special system study
concerning load flow, stability, transient
overvoltage, protection requirements, system
voltage profile etc. is necessary before the
optimal location is chosen.
Shunt Compensation
• For high voltage transmission line the line
capacitance is high and plays a significant role in
voltage conditions of the receiving end.
• When the line is loaded then the reactive power
demand of the load is partially met by the reactive
power generated by the line capacitance and the
remaining reactive power demand is met by the
reactive power flow through the line from sending
end to the receiving end.
Shunt Compensation (continued…)
• When load is higher then a large reactive
power flows from sending end to the receiving
end resulting in large voltage drop in the line.
• To improve the voltage at the receiving end
shunt capacitors may be connected at the
receiving end to generate and feed the reactive
power to the load so that reactive power flow
through the line and consequently the voltage
drop in the line is reduced.
Shunt Compensation (continued…)
• To control the receiving end voltage a bank of
capacitors (large number of capacitors
connected in parallel) is installed at the
receiving end and suitable number of
capacitors are switched in during high load
condition depending upon the load demand.
• Thus the capacitors provide leading VAr to
partially meet reactive power demand of the
load to control the voltage.
Shunt Compensation (continued…)
• If XC = 1/ωC be the reactance of the shunt
capacitor then the reactive power generated of
leading VAr supplied by the capacitor:
QC =
V2
2
XC
2
= V2 wC
where, |V2| is the magnitude of receiving end
voltage.
Shunt Compensation (continued…)
• When load is smaller then the load reactive power
demand may even be lesser than the reactive power
generated by the line capacitor. Under these conditions
the reactive power flow through the line becomes
negative, i.e., the reactive power flows from receiving
end to sending end, and the receiving end voltage is
higher than sending end voltage (Ferranti effect).
• To control the voltage at the receiving end it is
necessary to absorb or sink reactive power. This is
achieved by connecting shunt reactors at the receiving
end.
Shunt Compensation (continued…)
• If XL = ωL be the reactance of the shunt reactor
(inductor) then the reactive VAr absorbed by
the shunt rector:
QL =
V2
2
XL
2
= V2 / wL
• where, |V2| is the magnitude of receiving end
voltage.
Shunt Compensation (continued…)
• To control the receiving end voltage generally
one shunt rector is installed and switched in
during the light load condition.
• To meet the variable reactive power demands
requisite number of shunt capacitors are
switched in, in addition to the shunt reactor,
which results in adjustable reactive power
absorption by the combination.
Present Day Scenario of Transmission
Systems
ü Increased demand on Transmission Networks
ü Lack of New Right-of-Way.
ü Need to provide Open Access to generating stations and
Customers.
ü Absence of Long term planning
ü All together created less security and reduced quality of
supply.
15
Introduction to Flexible AC Transmission
Systems (FACTS)
Ø FACTS concept is based on the incorporation of power
electronic devices into the high-voltage side of the
network, to make it electronically controllable
(IEEE/CIGRE´ , 1995).
Ø Controllable Parameters are Line Impedance, Voltage
Magnitude, Phase angle and Current flowing through the
line.
17
Benefits of FACTS controllers
ü Reduction of operation and transmission investment cost.
ü Increased system security and reliability.
ü Increased power transfer capabilities.
ü An overall Enhancement of the quality of the electric
energy delivered to customers.
18
Basic Types of FACTS Controllers
Ø Series Controllers (TCSC, SSSC)
Ø Shunt Controllers (SVC, STATCOM)
Ø Combined Series - Series Controllers (IPFC)
Ø Combined Series - Shunt Controllers (UPFC)
19
• Thyristor-Controlled Series Compensation (TCSC) is used in power
systems to dynamically control the reactance of a transmission line
in order to provide sufficient load compensation.
• A static synchronous series compensator or SSSC is a kind of
flexible AC transmission system, which is consists of a solid-state
voltage source inverter coupled with a transformer that is
connected in series with a transmission Line.
• Recent developments of FACTS research have led to a new device:
the Interline Power Flow Controller (IPFC). This element consists of
two (or more) series voltage source converter-based devices
(SSSCs) installed in two (or more) lines and connected at their DC
terminals.
• A unified power flow controller (or UPFC) is an electrical device for
providing fast-acting reactive power compensation on high-voltage
electricity transmission networks. It uses a pair of three-phase
controllable bridges to produce current that is injected into a
transmission line using a series transformer. The controller can
control active and reactive power flows in a transmission line.
Active Compensation
• Synchronous condensers are the active shunt
compensators and have been used to improve the
voltage profile and system stability.
• When machine is overexcited, it acts as shunt
capacitor as it supplies lagging VAr to the system
and when under excited it acts as a shunt coil as it
absorbs reactive power to maintain terminal
voltage.
• The synchronous condenser provides continuous
(step less) adjustment of the reactive power in
both under excited and overexcited mode.