Thermal Steam-turbine Power Plants

Aviation Signal

A glass tube filled with neon gas was found to be suitable for this kind of work. Instead of a neon lamp, in some cases, a low current filament lamp may also be used as a signalling source.

In order to assist the aviator in locating the transmission line, a sig­nal marking its position is provided; this signal is a luminous lamp at­tached to the conductors of the transmission line; the lamp is lighted by the potential on the line and serves to indicate its position. This signal also makes a safety device. If the line is under tension, the attending personnel working on it will know that potential is on the line.

A high tension transmission line leading from one city to another makes a guideway for aviators during the day time, since it is visible from great distances. However, at night the high tension transmission line becomes a danger for the aviator, rather than a help.

21. Read the text and find in it the answers to the questions that follow it.

Large steam-turbine plants have two forms: condensing plants or electric power plants.

The great masses of hot steam, having accomplished the mechanical work in the turbines of condensing steam-turbine plants, are condensed, i.e. are cooled down and turned back into distilled water, and returned to the boiler for production of steam to activate the turbine.

Condensation of steam takes place in condensers where the hot steam is cooled when it comes in contact with tubes through which cold water, supplied from a water reservoir (river or lake), is circulated. This cooling water, after it takes the heat from the spent steam, is returned to the water source carrying along with it the unutilized heat energy. This water is called the circulating water. The importance of the distilled water for feeding steam boilers is extremely great since chemically clean water decreases the formation of scale in the boiler tubes, and, thus, makes their service life longer.

Condensing plants of large generating capacity are built close to sources of fuel, in order not to transport large quantities of fuel over considerable distances.

The electric power generated in such plants is transmitted over long distances for the supply of large industrial regions. So these plants are called regional thermal power plants.

Heat and electric power plants, in addition to electric power genera­tion, also supply heat to, closely located consumers (within a radius of 50 km), i.e. serve as district heat plants. To such heat consumers belong all kinds of industrial enterprises that require heat for production pur­poses, and also municipal consumers such as baths, laundries and the heating systems of dwelling houses and other buildings.

The electric power developed by the generators is fed to the switch­board of the plant, whence it is delivered by overhead transmission and cable lines to the consumers.

1. In what part of the power plant does condensation of steam take place?

2. Why is distilled water used for feeding steam boilers?

22. Arrange the paragraphs of the text below in the logical order. Testing Motors and Generators

It is of great importance, therefore, to make regular tests of insula­tion resistance of all machinery so as to detect possible faults. Different conditions may influence the value of the insulation resistance.

It is advisable, therefore, to make the test of the machine as soon after it has been shut down as possible, when the insulation resistance is likely to be lowest. If, after the motor has just been shut down, the in­sulation resistance is found to be satisfactory, it may be assumed that it will be better at any other time provided that the machine does not stand idle for long in a humid atmosphere.

Faults on electrical machinery must be due to one of two causes. One is the absence of continuity in the conductor which is supposed to be carrying the current. The other is the absence, or partial absence, of insulation. The latter is by far the more common and the more danger­ous of the two. A burnt out armature, for example, is usually due to in­sulation failure.

A drop in insulation resistance may often be accounted for, for ex­ample, by damp weather.

As regards the effect of temperature it should be noted that the in­sulation resistance of motors and generators is generally lower when they are hot than when they are cold as the insulating varnishes used in the building of the machines have a lower resistance when hot than when cold.

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23. Read the text and find in it the answer to the question that follows it. How to Make Tests on Installations

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. 22).

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.

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.

Conductors to other branch circuits All fuses in

In case the result of the test is considered satisfactory the instal­lation is in proper order so far as resistance to earth is concerned.

Lamp in position

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 busbars 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. _Fig22. Insulation test to earth

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.

What elements should be disconnected, inserted, closed, joined together, con­nected, etc. fcr making test on installations?

24. Read the text and find in it the answers to the questions that follow it.

Contactors Type 370

These contactors consist of the following main parts:

• one fixed bar

• one magnetic circuit which may be either a.c. or d.c.

• one or more auxiliary contacts (the maximum number of auxil­iary contacts is 4)

• one or more poles for use with a.c. or d.c. loads.

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These components are to be in­stalled.

X

JX

Fig. 23. Schematic position­ing of the different contactor components: 1 -fixed bar; 2 - magnetic circuit; 3 - auxiliary contacts; 4 -poles

1. What are the main parts of the contactors? 2. Which are the functions of each of these parts? 3. Describe Fig. 23.

Their functions are as follows: fixed bar has the function of sup­porting all the stationary parts of the contactor. At both ends it is provided with holes for mounting the contac­tor. Moving shaft is made of steel. It is insulated for the installation of both main pole and auxiliary moving contacts.

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25. Read the text and And in it the answers to the questions that follow it.

Disconnecting Switches

Application. Indoor disconnecting switches are devices that are in­tended to make and break electric circuits rated at 6 to 10 kV, a.c. with no load currents. The single-pole disconnecting switches are controlled manu­ally, by means of an insulated rod. The triple-pole disconnecting switches are controlled by means of manual lever-type operating mechanisms.

Mounting Instructions. 1. Clean the switch from dust and dirt. 2. In­spect it on the outside. 3. When insulating the switch, see that the bolts and switch terminals are reliably protected.

1. What are indoor disconnecting switches intended for?

2. What means are the single-pole switches controlled by?

3. What means are the triple-pole switches controlled by?

4. What recommendations do the mounting instructions include?

26. Think of 8-10 questions covering the contents of the text below. Use
them in a talk with your groupmate.

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