INTRODUCTION TO GAS POWER STATION
HOW DOES A COMBINED-CYCLE POWER PLANTWORK?
GAS TURBINE STARTING SYSTEM
TRANSMISSION OF GENERATED POWER ONTO THE THE
CONDESOR AND COOLING TOWER
NTPC ,the largest power company in india ,was setup in 1975 to accelerate power
development in country.
NTPC Dadri is a unique power plant of NTPC group which has coal based thermal
plant and gas based thermal plant of 1820 MW ,817 MW and solar based plant
NTPC has installed capacity of 29,397MW.
It has 15 coal based power station ,7 gas based power stations and 1 solarbased
It plans to be 75,000MW company by 2017.
INTRODUCTION TO GAS POWER
The gas turbine has found increasing application due to the
following potential advantages over competive equipment.
• Small size and weight per horsepower
• Rapid loading capability
• Self-contained packaged unit
• Moderate first cost
• No cooling water required
• Easy maintenance
• High reliability
• Waste heat available for combined cycle application.
• Low Gestation Period
• Low Pollution Hazard
Combined Cycle Power Plants
GT1 GT2 GT3 GT4
MODULE 1 MODULE 2
Combined Cycle Power Plants integrates two power
conversion cycles namely.
1.Brayton Cycle(Gas Turbines)
2.RankinCycle(Conventional steam power plant)
with the principal objective of increasing overall plant
Gas Turbine plant-operate on Brayton Cycle in which air
iscompressed this compressed air is heated in the
combustor by burning fuel combustion produced is
allowed to expand In theTurbine and the turbine is
coupled with the generator
The conversion of heat energy to mechanical energy with the aid of steam is carried
out through this cycle
The initial state of the working fluid is water (point-3) which, at a certain temperature
is compressed by a pump (process 3-4) and fed to the boiler.
In the boiler the compressed water is heated at constant pressure (process 4-5-6-1).
Modern steam power plants have steam temperature in the range of 500C to 550C at
the inlet of the turbine
HOW DOES A COMBINED CYCLE
POWER PLANT WORK
The amount of air needed for combustion is800,000 cubic feet per
This air is drawn though the large air inlet section where it is cleaned,
cooled and controlled, in order to reduce noise.
The air then enters the gas turbine where it is compressed, mixed with
natural gas and ignited , which causes it to expand. The pressure created
from the expansion spins the turbine blades , which are attached to a
shaft and a generator , creating electricity.
Each gas turbine produces 185 megawatts (MW)of electricity.
GAS TURBINE STARTING SYSTEM
A typical hydraulic starting system for each gas turbine is consist of:
Starting motor, electric AC induction motor
Hydraulic torque converter
The electric starting motor drives the hydraulic torque generator
through a coupling.
The static frequency converter serves the same
function of starting, accelerating running at preset speed by
starting the generator as a synchronous motor by feeding variable
frequency current drawn from the connected grid.
The steam turbine is capable of producing upto 240 MW. It is located
on top of the condenser, across from the cooling tower.
Steam enters the turbine with temperatures as high as 1200 degrees C
and pressure as strong as 2,200 pounds per square inch. The pressure
of the steam is used to spin turbine blades that are attached to a rotor
and a generator, producing additional electricity, about100 megawatts
per HRSG unit.
After the steam is spent in the turbine process , the residual steam
leaves the turbine at low pressure and low heat, about 100 degrees.
This exhaust steam passes into a condenser, to be turned back into
By using this “combined-cycle” process, two gasturbines and one
steam turbine, we can producea total of about 600 megawatts of
Transmission of Generated Power Onto
the Grid Transformers
The transformers take the generated 13,000 volts and
“transform” them to 230,000 volts, which is the required
voltage needed for transmission to the nearby tower that
sends power to the substation.
A small amount of generation is directed to “Auxiliary
transformers” which “transform” the generated voltage to a
lower voltage, so it may be used by the plant to power our own
pumps, fans, and motors. The Metcalf Energy Center requires
12 – 15 megawatts to operate
From each transformer, the power passes underground into our
switchyard. The power from all of the generators comes together there
, where it is measured, metered and directed on to the grid.
The proximity of the site to a large, existing PG&T substation makes it
a good place to build a power plant and the nearest transmission
tower is only about 200 feet away.
Condenser and Cooling Tower
The purpose of the condenser is to turn low energy steam back
into pure water for use in the Heat Recovery Steam Generator.
The purpose of the cooling tower is to cool the circulating water
that passes through the condenser. It consists of ten cells with
large fan son top, inside the cone-like stacks, and a basin of water
Natural gas fuels the combustion turbines. Each turbine can consume up to
2,000 MMBTU per hour
The pipeline was built 60 feet underground and passed under highways,
creek, train tracks, and environmentally sensitive areas.
The pipeline enters the site just behind the water tanks, where equipment
regulates and measures the natural gas composition, flow and pressure.
From the control room, the plant operators monitor and operate the facility, via
the plant’s “ Distributed Control System”, with the click of a mouse, viewing
graphic representations of all MEC systems on various screens.
The system gives operators both audible and visual signals to keep them
informed of plant conditions at all times and to determine when preventative
maintenance is required