 |
1. Does the system described have any advantages? What are they?
|
|
|
|
1. Does the system described have any advantages? What are they?
2. What gas is the space filled with?
3. Why should the system be protected?
18. Read the text and find in it the answers to the questions that follow it.
Starting Resistors Types 50-51
The electrical block resistors are generally used in starting and regulating installations for motors of any type and power.
Starting resistors have the capacity to support very high temperature variations, to which they are subjected due to their operating duty, without alteration or distortion.
Resistors consist of silicon sheet-steel or of special cast iron elements. Said elements are grouped in an assembly by means of steel rods interlocked by bolts in order to obtain rigid assemblies. These units are suitable for use in any type of machine and operate under high vibration conditions. For protection purposes, the resistor units are assembled in sheet-steel cases supplied with ventilation slits.
Starting resistors have a number of advantages; they are unbreakable, light, rigid; they can withstand, without variation, vibration and shocks. They are also easily detachable; their elements are interchangeable. Resistors are intended for operation in an ambient temperature of up to 300°C.
1. What device is described in the article?
2. What is the device used for?
3. What elements does it consist of?
4. What are the advantages of the device?
19. Study Fig. 21 and complete the sentences stating what metals are used for producing the devices a-e.
What Metals Are Used in Making Electrical Devices?
1. Alnico is an alloy of iron, aluminium, nickel, and cobalt used in making ….
2. Phosphor bronze springs are used to produce ….
3. Tungsten is used in ….
4. Nickel and cadmium are used in … rechargeable.
5. Nichrome is high-resistance alloy of nickel and chromium used for ….
Fig. 21
20. Arrange the paragraphs of the text in the logical order.
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.
Thermal Steam-turbine Power Plants
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.
|
|
|
