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Language study. Describing function.

 

Try to answer this question:

What does an electric motor do?

When we answer a question like this, we describe the function of something, we can describe the function of an electric motor in this way.

An electric motor converts electrical energy to mechanical energy.

We can emphasis the function like this.

The function of an electric motor is to convert electrical energy.

 

Step 3.

Match each of these motor components to its function, and then describe its function in a sentence

Component Function

1 armature a) transfers rotation from the motor;

2 bearing b) create an electromagnetic field;

3 brushes ) converts electromagnetic energy to rotation;

4 commutator d) reverses the current to the armature

5 drive shaft e) support the drive shaft;

6 field windings f) supply current to the armature;

Step 4. Complete the text. Use the following words: are made up; is placed; is composed; consists.

 

A transformer ... of two coils, a primary and a secondary. The coils are wound on a former which is mounted on a core. The coils ...of a number of loops of wire. The core ... of thin pieces of soft iron.

U- and T- shaped pieces are used.

 

Word study

Study these expressions for describing how components are connected to each other.

 

A is bolted to B. = A is connected to with bolts.

A is welded to B. = A is connected to B by welding.

A is fixed to B. = no specific method given.

 

Step 5.

Explain each of these methods of connection

1 screwed 2 soldered 3 attached 4 wired 5 bonded   6 nailed 7 brazed 8 welded 9 riveted 10 glued  

 

 

LESSON 6.

Step 1.

List the different ways in which electricity can be generated

 

Step 2.

Answer these questions about a portable generator using your own knowledge of engineering.

1 What are its main parts?

2 What does the engine run on?

3 What are the four strokes called?

4 What is the function of the crankshaft?

5 What do both stator and rotor have?

6 What is the difference between stator and rotor?

 

Step 3.

Read this text to check as many of the answers as you can. You will not find complete answers to all of the questions.

 

PORTABLE GENERATOR.

 

Although most electricity comes from power stations power can also be generated by far smaller means. Nowadays, electricity generators can be small enough to hold in the hand.

Portable generators are made up of two main parts: an engine, which powers the equipment, and an alternator, which converts motion into electricity.

The engine shown (Fig.1) runs on petrol. It is started by pulling a cord. This creates a spark inside which ignites the fuel mixture. In a typical four-stroke engine, when the piston descends, the air inlet valve opens and a mixture of air and petrol is sucked in through a carburetor. The valve closes, the piston rises on the compression stroke and a spark within the upper chamber ignites the mixture. This mini-explosion pushes the piston back down, and as it rises again the fumes formed by the ignition are forced out through the exhaust valve.

This cycle is repeated many times per second. The moving piston makes the crankshaft rotate at great speed.

The crankshaft extends directly to an alternator, which consists of two main sets of windings - coils of insulated copper wire wound closely around an iron core. One set, called stator windings, is in a fixed position and shaped like a broad ring. The other set, the armature windings, is wound on the rotor, which is fixed to the rotating crankshaft. The rotor makes about 3,000 revolutions per minute.

The rotor is magnetized and as it spins round, electricity is generated in the stator windings through the process of electromagnetic induction. The electric current is fed to the output terminals or sockets. This type of generator can produce a 700watt output, enough to operate lights, television, and some domestic appliances. Larger versions provide emergency power to hospitals and factories. Source adapted from Inside out: Portable generator. Education Guardian.

Step 4.

Study this text on the four-stroke cycle. Then label each stroke correctly.

 

In the four-stroke cycle, the piston descends on the intake stroke, during which the inlet valve is open. The piston ascends on the compression stroke with both valves closed and ignition takes place at the top of the stroke. The power or expansion stroke follows. The gas generated by the burning fuel expands rapidly, driving the piston down, both valves remaining closed. The cycle is completed by the exhaust stroke, as the piston ascends once more, forcing the products of combustion out through the exhaust valve. The cycle then repeats itself.

 

Language study: Cause and effect.

Study these pairs of actions, what is the link between each pair?

1 Cause: The gas expands.

2 Effect: This drives the piston down.

3 Cause: The piston ascends.

4 Effect: This forces the products of combustion out.

 

We can show both the time link and the cause and effect link like this:

1+2 The gas expands, driving the piston down.

3+4 The piston ascends, forcing the products of combustion out.

 

Step 5. Link these actions in the same way.

Cause 1. The piston moves down the cylinder. 2. The piston creates a vacuum. 3. The piston moves up the cylinder. 4. The gas expands quickly. 5 The piston moves up and down. 6 The crankshaft spins round. 7The armature of the alternator rotates   8 The alternator runs at a steady 3000rpm.   Effect This creates a partial vacuum. This draws in fuel from the carburetor. This compresses the mixture. This pushes the piston down. This rotates the crankshaft This turns the rotor at 3000rpm. This induces a current in the stator windings. This generates around 700 watts.  

Word study: Verbs with -ise /-ize

Study these statements:

The rotor is magnetized.

What does it mean? Can you say it another way? We can rewrite this statement as:

The rotor is made magnetic.

Verbs ending in -ise/-ize have a range of meanings with the general sense of

make + adjective.

 

Step6.

Rewrite these sentences replacing the phrases in italics with appropriate -ise/-ize verbs.

1. Some cars are fitted with a security device, which makes the engine immobile.

2. In areas where the power supply fluctuates, for sensitive equipment a device to make the voltage stable is required.

3. Manufacturers seek to keep costs to a minimum and profits to a maximum.

4. Most companies have installed computers to control their production line.

5. Companies may make their operation more rational by reducing the variety of products they make.

 

Step 7.

The statements that follow describe the distribution of power from power station to consumer. Put the statements in the correct order. The first one has been done for you.

a) It is fed to substations.

b) It is stepped up by a transformer to high voltages for long-distance distribution.

c) It is distributed via the grid to supply points.

d) It is distributed to the domestic consumer.

e) Electricity is generated at the power station at 25 kV.

f) It passes via the switching compound to the grid.

g) It is distributed via overhead or underground cables to intermediate substations.

 

Step 8.

Mark the sequence of stages using appropriate sequence words where you think this is helpful. Add the following information to your statement and make them into a text.

1. At the main grid supply points, power is stepped down to 33kV for distribution to heavy industry.

2. At intermediate substations, power is reduced to 11 Kv for light industry.

3. At the distribution substations, power is stepped down to 415 V. 3-phase, and 240 V, 1-phase.

 

Technical reading.

 

Step 9.

The two texts, which follow describe two plants for generating electricity from wave power. Note the similarities and differences between the plants.

WAVE POWER.

 

This prototype wave-power plant on the Scottish island of Islay was constructed by building a concrete water column across a natural gully on the shoreline. Waves flowing in and out of the gully cause water in the column to move up and down. As the water moves up it compresses the air above and forces it through a wide tube at the back of the water column. As the water moves down air is drawn into the water column. The moving air passes through a turbine coupled to a generator. Both the turbine and generator are unusual. The turbine is a Wells turbine (named after its inventor) that keeps turning in one direction even though the air flow is constantly changing direction. It has two rotors, each with four blades.

The generator is a wound rotor induction motor, which acts as a generator when it is turning at speeds greater than 1,500 rpm. Below that speed it operates as a motor and takes power from the grid. This motor/generator is used because the turbine takes some time to build up to a speed where it can generate electricity. When the turbine slows down due to a lull in wave activity, the generator becomes an electric motor and keeps the turbine running at a minimum speed so that it is ready to accept the power from the next batch of waves.

The plant is controlled by a computer. It includes a PLC (programmable logic controller), which monitors the operation of the motor/generator and the amount of electricity going to or being taken from the grid. There is also testing equipment to monitor how much electricity the plant is producing and the efficiency of the water column, turbine, and generator.

This experimental plant generates 150 kW. Plans have been approved for the construction of a 1 MW.

Sources scheme: Adapted from Inside out; Wave power; Education Guardian.

 

High hopes for wave power project

The worlds first power station in the open sea is to be stationed off do unreal in Scotland. The machine, called Osprey (Ocean Swell-Powered Renewable Energy), will stand in 18 meters of water a kilometer out and not only harvest the larger waves, which produce higher outputs, but also gain power with waves from any direction. The device is known as an oscillating water column. As a wave rises, air is pushed through an air turbine and sucked back again as the wave falls.

The turbine has been designed by Professor Alan Wells, of Queens University, Belfast. It will generate 2 megawatts. There is potential for 300 Ospreys in Scottish waters, which could provide 10 percent of the countrys peak electricity demand.

 

LESSON 7.

SUMMARY OF IMPORTANT FACTS.

Principles of Electricity

 

A chemical element is built up from atoms. Each atom is made up of electrons, protons and neutrons. The electron has a negative charge and the proton a positive charge; the two electrical charges are equal and opposite, but the mass of proton is 1840 times greater than that of the electron. Current flow is a combination of electron flow (negative charge carries) and hole flow (positive charge carries).

A conductor offers low resistance to current flow, an insulator offers high resistance. The resistance of semiconductor is mid-way between the two extremes .

Voltage or e. m. f. is a measure of the potential of an electric circuit to produce current flow. The conductance (G) of an electrical circuit is measured in simians (S) and resistance (R in ohms).

A linear circuit element is one whose resistance is constant despite fluctuations of voltage and current. The resistance of a non-linear circuit element varies with fluctuations of voltage and current. A direct current or unidirectional current always flows in the same direction around a circuit. An alternating current periodically reverses its direction of flow if the periodic time of an alternating wave is T.

1 second, the frequency of the alternating wave is f = z.

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