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Файл:Technical English for Electrical Engineers. Учебное пособие
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the terminals of an electric battery. The only other piece of equipment was a
pivoted magnet, like a compass needle.
It had long been known that magnets have two poles – north and south.
Unlike poles attract and like poles repel. Oersted also knew that there was a
relationship between electricity and magnetism, and he showed this by
placing the magnetic needle below the wire, then connecting the wire to the
battery. The needle was deflected by the current in the wire. The wire was
acting like another magnet and influencing the magnetic needle below it.
What made the experiment so important was the next stage: when he placed
the needle above the wire the needle was again deflected, but this time in the
opposite direction.
Oersted concluded that there must be some sort of circular power or
force around the wire. This force made the magnet move in opposite
directions depending on its position relative to the electrically charged wire.
2. Are the following statements true or false? Correct any that are
wrong.
1. Oersted was trying to show that electricity and magnetism were not
related.
2. For his experiment he used a kind of compass needle, a wire bridge
and an electric generator
3. Не first placed the magnetic needle underneath the wire, then
connected the wire to the battery.
4. The needle under the wire was pushed first one way, then the other.
5. In the second part of the experiment he put the needle above the wire.
6. Oersted thought the wire was surrounded by a magnetic field.
3. Find words and expressions in the text with similar meanings to
the following:
free to turn; pushed away; beneath; connection; carrying an electric
current; apparatus; a form of; put.
4. Give one minute summary of the text.
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5. Here are the instructions for a simple experiment with a magnet.
Now write the report. Start like this:
The aim of the experiment was to show why the like poles of a magnet
repel and the unlike poles attract We took …
Continue.
Why do the like poles of magnets repel and the unlike poles attract?
Take a sheet of cardboard, a magnet, a handful of iron filings and a compass.
Put the magnet under the sheet of cardboard and scatter the iron filings on
top of the card.
Tap the edge of the card lightly.
The iron filings will make a pattern. They will form a series of loops between
the two poles of the magnet.
Place the compass on one side of the magnet, and then on the other. You will
see that the compass needle follows the loops.
This shows that there are lines of force that leave the magnet at one pole and
enter it again at the other pole.
VII
FARADAY’S EXPERIMENT
1. Read the description of one of the Faraday’s experiments and
make a summary of it.
Oersted's experiments did not have any immediate practical
application. All he had done, in effect, was to show that a wire carrying an
electric current acts like a magnet. The thing that most interested scientists
was the question of whether the opposite was true: could magnets be used to
induce an electric current?
Michael Faraday, an English scientist, carried out a series of
experiments to find the answer to this question. His work led to the
development of the electric generator and so made it possible to produce
electricity on a large scale.
In one of his experiments, Faraday connected a coil to a simple
ammeter, Then he took a bar magnet and moved it quickly towards the coil.
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The ammeter showed a momentary current. When the magnet was moved
quickly away from the coil, the ammeter again registered a current, but in
the opposite direction.
Faraday's experiments were only the first steps, but he had shown quite
clearly that magnets could be used to produce an electric current. The next
step was to show that if a momentary movement produced a momentary
current, then a continuous movement should induce a continuous current.
This is the principle on which all electric generators (and motors) are based.
ENERGY
I
1. Read the text and comment on the following: “What is really the
answer to our energy problem in the future?”.
SOLAR POWER
More energy arrives at the Earth's surface in an hour than man uses in
one year. This clean natural energy comes from sunlight and it's called
solar power. The question is... how can we use it to replace fossil fuels
and clear energy? There are three answers.
1. We can use it directly.
Many modern buildings have big windows which face south. They
collect solar power directly. In fact some buildings in North America and
Scandinavia get 100% of their energy from the sun.
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2. We can collect it on Earth.
Another way to collect the sun's power is with solar panels. These
absorb and store energy on sunny days. But there are two problems with
solar panels on Earth. (a) They're expensive; (b) They don't work very
well on cloudy days.
3. We can collect it in space.
One answer to the problems of clouds is to collect solar power in
space. The idea is expensive, but simple. Satellites with huge solar panels
collect the sun's energy. Then they send it back to Earth. A series of
satellites like this will be able to work for 24 hours a day.
WAVE POWER
25% of the world's electricity already comes from dams and rivers.
Now, scientists are learning how to use the sea's power, too. What they're
doing is collecting the energy contained in waves. Here's how it works.
First, water enters a special wave machine. This pushes all the air inside
the machine up to the top. Then the water leaves again and pulls the air
back down. This pushing and pulling makes enough energy to work an
electric motor. At the moment wave machines are small and expensive.
They don't produce much electricity, either. But in the future they will be
bigger and cheaper. One day scientists think they will produce between
25% and 30% of our electricity.
GEO-THERMAL POWER
Several 'wind farms' already exist in Britain and other European
countries. Each farm is a group of machines which turn wind power into
electricity. The idea is popular in America, too.
The problem at the moment is money. It's very expensive to develop
and build wind farms. That's because they have to be in high places near
the coast or on islands. This makes their electricity expensive too. But in
the future, electricity from fossil fuels and nuclear power will begin to
cost more and more. Perhaps then wind farms won't look so expensive
after all.
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As well as solar, wind and wave power, there are other kinds of
natural energy, too. One is from the hot rocks and water at the centre of
the Earth. This kind of 'geo-thermal' energy already heats thousands of
buildings in Iceland, Hungary, Japan and New Zealand. (In fact, 60% of
Iceland's energy comes from under the ground.)
Is this really the answer to our energy problems in the future? This
report examines the facts.
So... what's going to happen in the 21st century? Will energy from
the sun, the wind, the sea, under the ground take the place of fossil fuels
and nuclear energy completely? The answer is probably no, but natural
energy will become more and more important. That's because:
It will become cheaper;
It will be better for the environment;
It will make it possible to conserve fossil fuels:
It will be safer than nuclear power.
2. Summarize information given in the texts.
3. Speak on: (a) different kinds of power
(b) advantages and disadvantages of this or that kind of
power.
MANUAL
a) Insulation tests to earth.
Disconnect the supply by opening the main
switch and withdrawing the main fuses.
Insert all fuses at the distribution board (see
Fig. 1).
Insert all lamps.
Close all single-pole switches.
Join together the two contacts on the installation
side on the main switch, and connect them to one
terminal of the Insulation Tester used.
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Connect the other terminal of the Tester to the conduit in which the
wiring is run or, if lead-covered cable is used, to the lead sheathing. A
second connection should also be made to the consumer's main earth. This
second connection is, however, unnecessary if the continuity and earthing
of the conduit had been previously tested.
Turn the handle of the Tester at about 160 r.p.m. and take a reading.
In case the result of the test is considered satisfactory the installation is
in proper order so far as resistance to earth is concerned.
If, however, the values obtained are not sufficiently high, withdraw all
fuses at the distribution fuse board and test again. This test should include
only the portion of the installation between the main switch and the bus bars
of the fuse board.
If the fault is not detected, one should proceed to the distribution fuse
board and test each branch circuit in turn till the faulty circuit or circuits
are discovered. These should be subjected to further tests till the actual
fault is detected.
b) Insulation test between conductors.
Remove all lamps.
The main switch should be opened, all fuses inserted at the distribution
board, and all single-pole switches in the closed or "on" position.
Connect one terminal of the Insulation Tester to fuse contact and the
other to another contact and make a test.
Two readings should be taken on an insulation containing two-way
switches, one with both switches on the "on" position and the other with
both switches in the "off" position.
If the result of the test between conductors is also satisfactory, no
further insulation tests are necessary and the insulation may be considered
to be in order.
If however, the results of the tests are unsatisfactory, proceed to the
distribution board, withdraw all fuses and test each branch circuit individually
between conductors until the faulty circuit or circuits are located.
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PRESENTATION
This is a diagram of an internal combustion engine that uses hydrogen
as a fuel. Describe this engine and explain how it works. Explain the
benefits of this kind of engine.
Energy
Good morning, everyone. Today I'm going to talk about the Wave
Energy Converter.
You're probably wondering what a Wave Energy Converter is. So,
let's have a simple definition to start with. Very simply, a Wave Energy
Converter is a system which converts the energy from sea waves into
electrical power.
Before I talk about the system itself, let me tell you where it is located,
because some systems are located on the surface of the sea, and some on
the sea shore. But not this system. The Wave Energy Converter is fixed to
the seabed.
OK, now let's look at the main components. The Wave Energy
Converter has five main components or parts. These are: a very large
flexible disc, a lever, a chamber which takes in sea water, a set of pistons,
many sea water pipes, and of course a turbine on the land.
The main specifications of the system are as follows. The whole
system on the seabed is 4. 6 metres high and 20. 4 metres long; the main
pipe is 125 millimetres wide; the pressure of the water in the pipes is
7000 kilopascals, or 1000 psi, that's pounds per square inch. The complete
system can generate 100 kilowatts of electricity.
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OK, that's enough number-crunching. Let's look at how the system
works. Here's a very simple account of the operation of the system. Let's
start with the sea. The sea wave oscillates. This oscillating motion pushes
the disc down in a linear motion. The disc makes the lever oscillate. The
oscillating lever makes the pistons move in a reciprocating motion. Then
the pistons push sea water from the chamber through the pipe at high
pressure. The high-pressure water then makes the turbine rotate? And of
course this generates electricity.
So, that's how it works. And of course this system has great benefits.
The most important benefit is that wave energy is a renewable energy
resource; and of course it uses no fossil fuels.
CIGRE
Tidal power plant bulb unit management through air gap monitoring
M. JEAN-LOUIS DROMMI, M. ANDRÉ TÉTREAULT
Électricité de France VibroSystM Inc.
France, Canada
The La Rance tidal power plant, the first of its kind, located in SaintMalo on the northern shore of Brittany, France, is a unique example of
engineering in regards to power generation. Its unique management of
tidal waters in order to produce electrical energy is a clear example of
applied engineering, in order to make use of existing geography to produce
clean, renewable energy for the future. After 2 rotor/stator rubs on its bulb
Units, one in 1995 and a second one in 2005, it became clear that
unexpected displacements and/or deformations were occurring in these
Units. With the help of an on-line monitoring system, which included a
dynamic air gap monitoring system, the utility was able to record and
analyse particular behaviour, which allowed for actions to be undertaken
ensuring the long term operation of these Units. In fact, the correlation of
air gap, vibration and associated machine parameters allowed for a better
understanding of rotor displacement and shape, as well as stator position
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and shape, by revealing the mechanisms involved and provided the
necessary information to intervene efficiently. The monitoring system
consisted of sensors, signal processing and data management. Various
issues were raised and analysed during this process. Initially, 3 bulb units
were fitted with dynamic air gap monitoring in order to quantify the
suspected rotor deformations. The first issue raised was fretting corrosion,
which had been occurring at the shrink fit areas between the rim and the
rotor hub, leading to shrink fit reduction (but without any possible
quantification). The air gap monitoring system provided clear data so as to
determine the actual situation in regards to the fretting of the rim. The
second issue was the confirmation of a rotor clover deformation, which
was expected however, the amplitude observed was surprising. The third
issue raised was the discovery of the air gap behaviour in reference to
thermal variations, which was contrary to common expected behaviour.
Application of Sweep Frequency Response Analysis (SFRA)
for inter-turn detection of in medium-voltage coils manufacturing
C.A. PLATERO (*), F. BLÁZQUEZ, F.R. BLÁNQUEZ, E. REBOLLO
Universidad Politécnica de Madrid
Spain
It is known that for some years it has been developed a technique
based on the sweep frequency response analysis (SFRA) for the diagnosis
of power transformer windings. Since the first works to nowadays many
developments and improvements have been made. The relevance of this
method has resulted in the creation of new standards for applying the
method, such as CIGRE and IEEE. Since its appearance, the industrial
interest of this technique lies in the possibility of identifying small strains
that could appear in the coils of power transformers, as a result of forces
that occur during a short circuit or any possible shock during transport.
Basically, this technique is based on the analysis of the impedance of the
windings in the frequency domain. Given that the winding can be modeled
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as an equivalent circuit with a complex network of capacities, inductances
and resistances, its frequency response is unique. Thus, any alteration in
the winding results in a variation of the equivalent circuit and therefore its
frequency response changes too. However, despite its apparent advantages
in power transformers, the SFRA technique has been practically unused in
the diagnosis of rotating machines. This is because the high frequency
equivalent circuit of the windings rotating machines is more complex than
the transformers: the stator winding is divided into slots, and there is a
rotor winding. Moreover, in some cases the relative position between rotor
and stator can significantly influence the measurements. The authors of
this paper conducted a preliminary study using the SFRA for detecting and
locating faults in the stator windings of synchronous machines. This study
concluded the high potential of SFRA to locate and identify a fault in
salient poles rotating machine, maintaining the position of the rotor to
avoid variations in the magnetic circuit structure. The complete and correct
interpretation of the results is difficult. It will be necessary to carry out
many tests on different machines, in order to have a large database and
interpret the results of SFRA correctly. A first step in this verification
process would be to use the SFRA to test form coils during the
manufacturing phase. Thus, the purpose of the present studies has been the
detection of deformations and inter-turn faults within the coils. Using real
medium-voltage coils, the first stage of this project has been the study of
the grounding connections. Given that the coil is normally inside the stator
of the machine, the grounding conditions of the individual coil in study
could be relevant. In this paper the results of the tests that have been
carried out related to this topic are described. Once the grounding
conditions were fixed, the coil under test has been modified, as it will be
described, in order to perform inter-turn faults. After conducting several
tests, the results have been analyzed and the conclusions allow
corroborating that the inter-turn faults in motor medium voltage coils can
be detected and, in further studies, the faults could be located.
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