Compressed-gas-insulated Transmission

Transmission lines in which compressed gas is used as insulator have a number of advantages. The main advantages are simplicity of construction and low cost.

What is the construction of compressed-gas-insulated transmission lines? It is rather simple. They comprise a number of phase conductors; each phase conductor is placed inside a tube and centered by means of circular spacers. The tube space is filled with compressed gas - usually sulphurhexafluoride. Each tube in a 345-kV line has a diameter about 50 cm.

The system including compressed-gas-insulated transmission has the following advantages: its losses are rather low, they are considerably lower than those of cable transmission. Unlike cables, compressed-gas- insulated transmission system can be designed for ultra high frequencies. No external electric field appears in the system. The shunt capacitance is considerably less for a gas-insulated line than for a cable. A gas-insulated line can thus transmit power over larger distances than cable lines.

The system should be protected against metallic particles. In case metallic particles get into the system, they cause a fault - a dielectric breakdown.

Does the system described have any advantages? What are they?

What gas is the space filled with?

Why should the system be protected?

 

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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.

What device is described in the article?

What is the device used for?

What elements does it consist of?

What are the advantages of the device?

 

 

19. Study Fig. 21 and complete the sentences stating what metals are used forproducing 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

 

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.

 

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