Tiếng anh chuyên nghành điện chương 7

Unit 7: Type of Generator
I

READING AND COMPREHENSION

TYPES OF GENERATORS

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Steam Units:  Steam-electric (thermal) generating units are typically the large base
load plants. Steam produced in a boiler turns a turbine to drive an electric generator
(Figure 3a). Fossil fuels (coal, petroleum and petroleum products, natural gas or other
gaseous fuels) and other combustible fuels, such as biomass and waste products, are
burned in a boiler to produce the steam. Nuclear plants use nuclear fission as the heat
source to make steam. Geothermal or solar thermal energy also produce steam. The
thermal efficiency of fossil-fueled steam-electric plants is about 33 to 35 percent. The
waste heat is emitted from the plant either directly into the atmosphere, through a
cooling tower, or sent to a lake for cooling. A water pump brings the residual water
from the condenser back to the boiler.

Figure 3a. Schematic of generic thermal generator

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Gas Units: Gas turbines and combustion engines use the hot gas from burning fossil
fuels, rather than steam, to turn a turbine that drives the generator. These plants can be
brought up quickly, and so are used as peaking plants. The number of gas turbines is
growing as technological advances in gas turbine design and declining gas prices have
made the gas turbine competitive with the large steam-electric plants. However,

thermal efficiency is slightly less than that of the large steam-electric plants (Figure
3b). The gas wastes are disposed of through an exhaust stack.

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Figure 3b. Schematic of gas turbine

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Combined-Cycle Units: Combined cycle plants first use gas turbines to generate
power and then use the waste heat in a steam-electric generator to produce more
electricity. Thus, combined-cycle plants make more efficient use of the heat energy in
fossil fuels. New technology is improving the thermal efficiency of combined-cycle
plants, with some reports of 50 to 60 percent thermal efficiency (Figure 3c).

Figure 3c. Schematic of combined cycle

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30

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Cogenerating Units: Cogenerators, also known as combined heat and power
generators, are facilities that utilize heat for electricity generation and for another form
of useful thermal energy (steam or hot water), for manufacturing processes or central
heating. There are two types of cogeneration systems: bottom-cycling and top-cycling.
In a bottom-cycling configuration, a manufacturing process uses high temperature
steam first and a waste-heat recovery boiler recaptures the unused energy and uses it to

drive a steam turbine generator to produce electricity. In one of two top-cycling
configurations, a boiler produces steam to drive a turbine-generator to produce
electricity, and steam leaving the turbine is used in thermal applications such as space
heating or food preparation. In another top-cycling configuration, a combustion
turbine or diesel engine burns fuel to spin a shaft connected to a generator to produce
electricity, and the waste heat from the burning fuel is recaptured in a waste-heat
recovery boiler for use in direct heating or producing steam for thermal applications
(Figure 3d).

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Figure 3d. Cogeneration Schematic
Other Units: The kinetic energy in moving water and wind is used to turn turbines
at hydroelectric plants and wind facilities to produce electricity. Other types of
energy conversion include photovoltaic (solar) panels that convert light energy
40 directly to electrical energy, and fuel cells that convert chemical energy directly to
electrical energy.

Task 1

Rephrasing
Rewrite the following sentences, replacing the words in italics with expressions
from the passage which have similar meanings:
1. Steam produced in a boiler spins a turbine to drive an electric generator.
2. Fossil fuels (coal, petroleum and petroleum products, natural gas or other
gaseous fuels) and other flammable fuels, such as biomass and waste products,
are burned in a boiler to produce the steam.
3. The waste heat is discharged from the plant either directly into the atmosphere,
through a cooling tower, or sent to a lake for cooling.

4. The gas wastes are disposed of through an chimney.
5. The number of gas turbines is growing as technological progress in gas turbine
design and declining gas prices have made the gas turbine competitive with the
large steam-electric plants.

Task 2

Contextual reference
What do the pronouns in italics in these sentences refer to?
1. Gas turbines and combustion engines use the hot gas from burning fossil fuels,
rather than steam, to turn a turbine that drives the generator. (line 12)
(a) Gas turbines and combustion engines
(b) The hot gas
(c) Steam
(d) A turbine

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2. However, thermal efficiency is slightly less than that of the large steam-electric
plants. (line 16)
(a) Gas turbine design
(b) The gas turbine
(c) The large steam-electric plants
(d) Thermal efficiency
3. In a bottom-cycling configuration, a manufacturing process uses high temperature
steam first and a waste-heat recovery boiler recaptures the unused energy and uses
it to drive a steam turbine generator to produce electricity. (line 28)
(a) High temperature steam
(b) A waste-heat recovery boiler

(c) The unused energy
(d) A manufacturing process
4. Other types of energy conversion include photovoltaic (solar) panels that convert
light energy directly to electrical energy, and fuel cells that convert chemical
energy directly to electrical energy. (line 39, 40)
(a) Other types of energy conversion; fuel cells
(b) Photovoltaic panels; fuel cells
(c) Energy conversion; electrical energy
(d) Photovoltaic panels; light energy

Task 3

Checking facts and ideas
Decide if these statements are true or false. Quote from the passage to support your
decisions.
1. Combined cycle plants first use gas turbines to generate power and then use the
waste heat in a steam-electric generator to produce more electricity.
2. Coal, petroleum and petroleum products, natural gas are combustible fuels .
3. Biomass and waste products are combustible fuels.
4. The thermal efficiency of fossil-fueled steam-electric plants is not over 50 percent.
5. Cogenerators only utilize heat for electricity generation.
6. In a top-cycling configuration, the waste heat from the burning fuel is recaptured
in a waste-heat recovery boiler for producing electricity.
7. The moving water provides kinetic energy for generating electricity.
8. Combined-cycle units could be reached 50 to 60 percent thermal efficiency.
9. The waste heat is emitted from the plant directly into the atmosphere.
10. Gas turbines mainly use the steam from burning fossil fuels to drive generators.

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II USE OF LANGUAGE

Task 4

Describing function
To describe the function of X (an apparatus, a device, equipment and so on), we
answer the question What does X do?
EXAMPLE

What does a switch do? It changes the condition of a circuit.
We can emphasize function by using this pattern:
The function of X is to do sth.
The function of a switch is to change the condition of a circuit.
Now identify the following components and explain the function of each component
with the help of this list.
1. A boiler
2. A nuclear plant
3. A gas turbine
4. An electric generator
5. A cooling tower
6. A water pump
7. A condenser
8. An exhaust stack
9. Photovoltaic panels
10. Fuel cells
(a)
(b)
(c)
(d)

(e)
(f)
(g)
(h)
(i)
(j)

converts chemical energy directly to electrical energy
turns a turbine to drive an electric generator
converts light energy directly to electrical energy
uses nuclear fission to make steam
disposes the gas wastes
generates steam
brings the residual water from the condenser back to the boiler
emits the heat wastes from the plant directly into the atmosphere
extracts energy from a flow of combustion gas
converts mechanical energy into electrical energy

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Task 5

Describing position and connection
When describing the position of a component or how it is connected in a circuit,
phrases of this pattern are used:
Be + participle + preposition
Attached to
Applied to
Connected across

Connected between
Connected to
Located within
Mounted on
Mounted under
Wired to
Wound round
EXAMPLES

Battery

Bulb

1. The bulbs are connected across the battery

Helicopter

Microwave Radar antenna

2. Microwave radar antenna is mounted under helicopter.
10 GHz Radar antenna

van

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1. 10 GHz Radar antenna (1)…….. van during non-contact experiment at Skagit
River.

2. When a number of solar cells (2)…… each other and mounted in a support frame,
it is referred to as a module.
wires

steel core

3. Wires (3)……….. a steel core.

4.
5.
6.
7.

Air preheater (4)…. the boiler.
Turbine (5)…. the generator.
Pulverizer (6)….. stoker and boiler.
Turbine and generator (7)…. powerhouse.

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III INFORMATION TRANSFER

Task 6

Reading generator rating plates
The capacity of a synchronous generator is equal to the product of the voltage per
phase, the current per phase, and the number of phases. It is normally stated in
megavolt-amperes (MVA) for large generators or kilovolt-amperes (kVA) for small
generators. Both the voltage and the current are the effective, or rms, values (equal

to the peak value divided by 2 ).
The voltage rating of the generator is normally stated as the operating voltage
between two of its three terminals—i.e., the phase-to-phase voltage. For a winding
connected in delta, this is equal to the phase-winding voltage. For a winding connected
in wye, it is equal to 3 times the phase-winding voltage.
The capacity rating of the machine differs from its shaft power because of two factors
—namely, the power factor and the efficiency. The power factor is the ratio of the
real power delivered to the electrical load divided by the total voltage–current product
for all phases. The efficiency is the ratio of the electrical power output to the
mechanical power input. The difference between the two power values is the power
loss consisting of losses in the magnetic iron due to the changing flux, losses in the
resistance of the stator and rotor conductors, and losses from the winding and bearing
friction. In large synchronous generators, these losses are generally less than 5 percent
of the capacity rating. These losses must be removed from the generator by a cooling
system to maintain the temperature within the limit imposed by the insulation of the
windings.
SYNCHRONOUS GENERATOR DATA
Unit Number: ______ Total number of units with listed specifications on site: _________
Manufacturer: ____________________________________________________________
Type: ____________________________Date of manufacture: _____________________
Serial Number (each):______________________________________________________
Phases: Single Three R.P.M.: __________________ Frequency (Hz): _____________
Rated Output (for one unit): _______________Kilowatt _____________Kilovolt-Ampere
Rated Power Factor (%): ________Rated Voltage (Volts): _______Rated Amperes: ____
Field Volts: ________Field Amps: __________ Motoring power (kW): ______________
Synchronous Reactance (Xd): ________________% on __________________KVA base
Transient Reactance (X’d): __________________% on __________________KVA base
Subtransient Reactance (X’d); ________________% on __________________KVA base
Negative Sequence Reactance (Xs): ___________% on __________________KVA base
Zero Sequence Reactance (Xo): ______________% on __________________KVA base

Neutral Grounding Resistor (if applicable): _____________________________________
________________________________________________________________________
I 22 t or K (heating time constant): _____________________________________________
Additional information: ____________________________________________________
________________________________________________________________________

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IV GUIDED WRITING

Task 7 Sentence building
Join the following groups of sentences to make the longer sentences. Use the words
printed in italics at the beginning of each group. You may omit words and make
whatever changes you think are necessary in the word order and punctuation of the
sentences.
1. while
In any generator, the whole assembly carrying the coils is called the armature, or
rotor.
The stationary parts constitute the stator.
2. but
There are advantages and disadvantages to all types of generators.
Consumer generators most often run on either gasoline, diesel, or propane.
3. that
A direct-current (DC) generator is a rotating machine.
A rotating machine supplies an electrical output with unidirectional voltage and
current.
4. if
An induction machine can operate as a generator.
The induction machine is connected to an electric supply network operating at a

substantially constant voltage and frequency.
5. when
Generators offer a level of safety and security.
A power supply is unstable.
6. because
These three factors -- energy, environment, and economy -- are interdependent.
Advances in one must be compatible with the others.

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V READING AND SUMMARIZING
Study this passage carefully and answer the questions which follow:
STRUCTURE AND PRINCIPLE OF ENGINES
We have used thermal engines widely since they invented in the 17th century. There
are many kinds of the engine, and they are used in our life. In this session, the
structure, the principle and the characteristics of the thermal engines and the power
source are presented.
•

1769: J. Watt invented a reciprocating steam engine with a condenser.

•

1816: R. Stirling invented a hot air engine (Stirling engine) which utilizes a
reheat energy.

•

1839: J. Ericsson developed several hot air engines (Ericsson engine) in these

days.

•

1876: N. Otto developed a spark ignition engine (gasoline engine).

•

1883: C. Laval developed a steam turbine.

•

1892: R. Diesel invented the principle of a compression ignition engine (Diesel
engine).

•

1930: F. Whittle invented a gas turbine for an airplane.

•

1944: A practical rocket engine is developed in Germany.

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1952: F. Bacon invented a fundamental fuel cell.

Reciprocating Steam Engine
The
reciprocating

steam
engine is the first engine
which was reached practical
use. This engine obtains a
mechanical power using static
pressure of the steam. After
the Industrial Revolution, it
had been used as the power
sources for industries and
transportations while a long time. But it is replaced by internal combustion engines,
and not used nowadays.
Generally, the steam engine consists of a boiler, a heater, a piston, a cylinder,
condenser and a water pump as shown in a right figure. An intake and an exhaust
valve are located on the top of the cylinder.

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Stirling Engine
The Stirling engine consists of two
pistons as shown in a right figure. It is
a closed cycle external combustion
engine which uses the working gas
repeatedly without any valve. A
memorable characteristic of this engine
is that a regenerator is adopted in order
to obtain a high efficiency. In those
days invented the engine, this had been
called 'Hot air engine' together with an
Ericsson engine described bellow.

After many developments, the Stirling
engines in the present come to get a
high power and a high efficiency by using high pressure helium or hydrogen as the
working gas. But this engine has not reached practical use yet, because it has several
problems such as a heavy weight and a high production cost.
Ericsson Engine
J. Ericsson developed several engines by
reforming the Stirling engine (called the
hot air engine in these days). One of them
is called the Ericsson engine nowadays. It
is an opened cycle external combustion
engine with two valves at a supply cylinder
and power cylinder as shown in a right
figure. Also, most of the engines invented
by J. Erickson were used the regenerator.
Gasoline Engine
Nowadays, the gasoline engine (spark ignition
engine) is used widely as the power source of
automobiles. As the principle of this engine, a
mixture gas of the fuel and the air is compressed in
the cylinder at the first. And the gas explodes by use
of an ignition plug, and generates the output power.
As good characteristics of the engine, it can be
realized a smaller and light weight engine, and has a
possibility of the high engine speed and high power.
Also, the maintenance of the engine is very simple.

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Steam Turbine
The steam turbine has rotating blades
instead of the piston and the cylinder of
the reciprocating steam engine. This
engine is used as the power source in the
thermal and nuclear power plants. The
steam turbine utilizes dynamic pressure
of the steam, and converts a thermal
energy to a mechanical energy, though
the reciprocating steam engine utilizes
the static pressure of the steam. The both
engines use the energy that is obtained at the expansion of the steam.
Diesel Engine
The Diesel engine (compression ignition engine) is the
internal combustion engine as well as the gasoline
engine, and used widely as the power source of the ship
and the automobile. As the principle of this engine, the
air is entered in the cylinder, and it is compressed
adiabatically to a high temperature at the first. When the
mists of the fuel are jetted into the high temperature
cylinder, it combusts automatically, and the engine
obtains the output power. It can get the higher
efficiency than that of the gasoline engine for a high
compression ratio. Also this engine has economical
advantage because it can use inexpensive light oil and
heavy oil as the fuel. However it may have the problems
such as large vibrations and noises, and increase of the engine weight for the high
pressure in the cylinder.
Gas Turbine
As the principle of the gas turbine, a working gas

(air) is compressed by a compressor and heated by
combustion energy of the fuel at the first. The
working gas becomes the high temperature and
high pressure. The engine converts the energy of
working gas into the rotating energy of the blades,
making use of the interaction between the gas and
the blades.

a

As shown in the below figure, there are two types
of the gas turbine. One is the open cycle type (internal type), and another is the closed
cycle type (external type). Basic components of both types are the air compressor, a
combustor and the turbine.
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The gas turbine can handle a larger gas flow than that of the reciprocating internal
combustion engines, because it utilizes a continued combustion. Then the gas turbine
is suitable as the high power engine. The gas turbine for airplanes (called a jet engine)
makes use of this advantage.

Rocket Engine
The rocket engine obtains a
combustion gas of high
temperature and high pressure
from the fuel and an oxidizer in
combustor. The combustion gas
becomes high speed with an
adiabatic expansion through a

nozzle, and is jetted to the rear
the engine. It is obtained a
propulsive force by a reaction of the high speed gas.

a

of

The jet engine and the rocket engine obtains the propulsive force in the same way by
using the reaction of the working gas. However, it is difference from the jet engine that
the rocket engine has the total gas including the oxidizer itself. Then it can get the
propulsive force even if there is no air, so it is used as the propulsive power source in
the space.
Fuel Cell
Above thermal engines change the energy of
the fuel to the mechanical power by way of
thermal energy. On the other hand, the fuel
cell changes the chemical energy of the fuel
to the electric energy directly.
The fuel cell consists of the anode and the
cathode which are separated by an electrolyte
layer. When the fuel is supplied to the anode,
and the oxidizer is supplied to the cathode, it generates the electric energy.
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1.
2.
3.
4.

How the steam turbine converts a thermal energy to a mechanical energy?
What is called 'Hot air engine' ?
Can jet engine get the propulsive force even in case of without air? Why?
Where does the rocket engine obtains a combustion gas of high temperature and
high pressure ?
5. Why can the gas turbine handle a larger gas flow than that of the reciprocating
internal combustion engines?

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