МІНІСТЕРСТВО ОСВІТИ І НАУКИ УКРАЇНИ

Запорізький національний технічний університет

Методичні вказівки

до практичних занять з англійської мови для студентів спеціальності “Електромеханічне обладнання енергоємних підприємств” за напрямками електромеханіка, електротехніка, енергетика.

Ч.I

2008 р.

Методичні вказівки до практичних занять з англійської мови для студентів спеціальності “Електромеханічне обладнання енергоємних підприємств” за напрямками електромеханіка, електротехніка, енергетика. Ч.I / Укл.: В.Г. Кузьменко – Запоріжжя: ЗНТУ, 2008.- 72 с.

Укладач: В.Г. Кузьменко, ст. викладач

Рецензент: Т.О. Сокол, ст. викладач

Експерт: О.М. Расальський., зав. кафедри ЕА

Відповідальний

за випуск: В.Г. Кузьменко, ст. викладач

Затверджено

на засіданні кафедри іноземних мов

протокол № 6 від 30.12.2007 р.

Contents

Electrical Machines……………………………………………... 4

Brushed DC Electric Motor…………………………………..... 4

3-phase AC induction motor.………………………………...... 15

Transformer..………………………………………………....... 33

Supplement………………………………………………......... 57

Перелік скорочень…………………………………………….. 72

Electrical Machines

Brushed DC Electric Motor

Text A

1. Listen to the words and word combinations from the text. Pay attention to their meaning.

brush – щітка

motor – двигун

DC – постійний струм

brushed DC motor – двигун постійного струму з щітковим колектором

commutate – комутувати, перемикати

to run – працювати, експлуватувати

power source – джерело живлення

pole – полюс

coil – обмотка

to power – живити, пропускати струм

magnet – магніт

magnetic field – магнітне поле

to generate – генерувати

armature – якір

to cause – викликати, заставляти

to rotate – обертати(сь)

to align – вирівнювати

commutator – колектор, комутатор, перемикач

to reverse – змінювати напрямок на зворотній

current – струм

to wind – намотувати

core – сердечник, стержень

positive – позитивний

to act – діяти

turning – обертання

direction – напрямок

cycle – період, цикл, оберт

plane – площина.

2. Memorize the words and word combinations and their equivalents.

torque – обертаючий момент, пусковий момент

rotor – ротор

to displace – переміщати(ся), зміщувати(ся)

degree – градус

stator – статор

to start – запускати

inertia – інерція

commutator brush – колекторна щітка

commutator plates – пластини комутатора

short-circuit – коротке замикання, ланцюг короткого замикання

consume – споживати

harmful – шкідливий, небезпечний

watt – ватт

power output – вихідна енергія

overheating – перегрів

damage – пошкодження

welding – зварка

to flow – текти, протікати

shaft – вал

generator – генератор

voltage – напруга.

3. Find the words and combinations of words in the text and translate the sentences containing them.

to spin – обертатись

to apply – прикладати, застосовувати

electrical load – електричне навантаження

resistance – опір

terminal – клема, зажим, вивід

voltage drop – падіння напруги

due to – завдяки

winding – обмотка

equation – рівняння

mechanical power – механічна енергія

speed – швидкість

to reduce – зменшувати(сь)

to slow – сповільнювати(сь)

to draw – витікати, протікати

to excite – збуджувати(сь)

revolution – оберт

ampere – ампер

to help on – сприяти

to absorb – поглинати

friction – тертя

to drive – приводити в дію

commutating plane – площина комутації.

4. . Pay attention to the translation of the following.

internal – внутрішній

external – зовнішній

to result in (smth) – приводити до (чогось), мати своїм результатом (щось)

to result from (smth) – в результаті (чого-небудь), бути наслідком (чого-небудь)

to increase – збільшувати(сь), зростати

to decrease – зменшувати(сь)

electromotive force (EMF) =

= electromotive power – електрорушійна сила

counter electromotive force = counter - EMF (CEMF) = backward-flowing electromotive force = back EMF – протиелектрорушійна сила

i.e.= that is – тобто

per – за

to be refferred to as – називатись.

5. Read and translate the text.

A brushed DC motor is an internally commutated electric motor designed to be run from a DC power source.

The following graphics illustrate a two pole DC motor.

Simple Two Pole DC Motor Rotation

A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.	The armature continues to rotate.	When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. The process then repeats.

When a current passes through the coil wound around a soft iron core, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle thus causing the motor to rotate in the same direction.

The problem facing the motor shown above, is when the plane of the coil is parallel to the magnetic field; i.e. the torque is ZERO-when the rotor poles are displaced 90 degree from the stator poles. The motor would not be able to start in this position, but the coil can continue to rotate by inertia.

There is a secondary problem with this simple two-pole design; at the zero-torque position, both commutator brushes are touching across both commutator plates, resulting in a short-circuit that uselessly consumes power without producing any motion. In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful, but if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of the metallic brushes to the commutator.

Unlike the demonstration motor, above, DC motors are commonly designed with more than two poles, are able to start at any position, and do not have any position where current can flow without producing electromotive power.

If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF). During normal operation, the spinning of the motor produces a voltage, known as the counter-EMF (CEMF) or back EMF, because it opposes the applied voltage on the motor. This is the same EMF that is produced when the motor is used as a generator (for example when an electrical load (resistance) is placed across the terminals of the motor and the motor shaft is driven with an external torque). Therefore, the voltage drop across a motor consists of the voltage drop, due to this CEMF, and the parasitic voltage drop resulting from the internal resistance of the armature's windings. The current through a motor is given by the following equation:

I = (V_applied − V_cemf) / R_armature

The mechanical power produced by the motor is given by:

P = I * (V_cemf)

As an unloaded DC motor spins, it generates a backwards-flowing electromotive force that resists the current being applied to the motor. The current flow through the motor drops as the rotational speed increases, and a free-spinning motor has very little current flow. It is only when a load is applied to the motor that slows the rotor that the current draw through the motor increases. In an experiment of this kind made on a motor with separately excited magnets, the following figures were obtained:

Apparantly, if the motor had been helped on to run at 261.5 revolutions per minute, the current would have been reduced to zero. In the last result obtained, the current of 5.1 amperes was absorbed in driving the armature against its own friction at the speed of 195 revolutions per minute."

In a DC motor, the contact point of where a pair of brushes touch the commutator is referred to as the commutating plane. In this diagram the commutating plane is shown for just one of the brushes.

Commutating plain for just one of the brushes

6. Translate the word combinations from the text:

two pole DC motor; internally commutated electric motor; soft iron core; Fleming's left hand rule; two-pole design; zero-torque position; low-current battery-powered demonstration; backwards-flowing electromotive force; free-spinning motor; excited magnets; severe commutator overheating.

7. Point out the sentences in the text in which the word “to make” should be translated as “примушувати”.

8. Answer the questions.

1. What is a brushed DC motor?

2. When is a magnetic field generated around the armature?

3. What causes the rotation?

4. When does the commutator reverse the direction of current through the coil?

5. According to which rule is a turning effect caused on the coil?

6. What makes the motor rotate in a constant direction?

7. What will the motor produce if the shaft is turned by an external force?

8. What does the spinning of the motor produce during normal operation?

9. What does the voltage drop across a motor consists of?

10. What does an unloaded spinning DC motor generate?

11. When does the current draw through the motor increase?

12. What is is referred to as the commutating plane?

9. Find the sentences in the text telling you about two problems facing the simple two pole DC motor.

Text B

Compensation for stator field distortion

1. Make sure that you know these words and word combinations.

dynamo – генератор постійного струму

compensation – корекція, вирівнювання

field distortion – викривлення (зміщення) поля

uniform – однорідний

to induce – індукувати, викликати, збуджувати

field effect – ефект поля

to drag – тягнути

magnetic lines – магнітні силові лінії

outer – зовнішній

exaggerated – збільшений

iron filings – залізні ошурки

degree – ступінь

right angle – прямий кут

to retard – затримувати (ся)

to advance – випереджати

position – положення

reversible commutated – з реверсивною комутацією

neutral – нейтральний

normal – перпендикулярний

fixed – постійний, фіксований

timing – розподіл (регулювання) моментів запалювання

internal combustion engine – двигун внутрішнього згорання.

2. Read and translate the text.

In a real dynamo, the field is never perfectly uniform. Instead, as the rotor spins it induces field effects which drag and distort the magnetic lines of the outer non-rotating stator.

Exaggerated example of how Iron filings show the distorted field

the field is distorted by the across the rotor.

rotor.

The faster the rotor spins, the further the degree of field distortion. Because the dynamo operates most efficiently with the rotor field at right angles the stator field, it is necessary to either retard or advance the brush position to put the rotor's field into the correct position to be at a right angle to the distorted field.

Centered position of the commutating plane if there were no field distortion effects

Actual position of the commutating plane to compensate for field distortion.

These field effects are reversed when the direction of spin is reversed. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it is necessary to move the brushes to the opposite side of the normal neutral plane.

The effect can be considered to be somewhat similar to timing advance in an internal combustion engine. Generally a dynamo that has been designed to run at a certain fixed speed will have its brushes permanently fixed to align the field for highest efficiency at that speed.

3. Answer the questions.

1. Is the field perfectly uniform in the motor?

2. What distort the magnetic lines of the non-rotating stator?

3. What does the degree of field distortion depend on?

4. When does the motor operate most efficiently?

5. What is necessary to do to put the rotor field at a right angle to the distorted field?

6. When are the field effects reversed?

7. Is it difficult to build an efficient reversible commutated dynamo? Why?

8. Why will a dynamo designed to run at a certain fixed speed have its brushes permanently fixed?

Text C

Dynamo Design Variations

1. Read and memorise the words and word combinations.

wound rotor – фазний ротор (з обмоткою збудження)

wound stator – фазний статор (з обмоткою збудження)

permanent magnet stator – статор з постійним магнітом

field coil – обмотка збудження

series wound – обмотка послідовного збудження

shunt wound – обмотка паралельного збудження

permanent magnet motor – двигун з постійним магнитом

advantage – перевага

performance – продуктивність

horsepower – потужність в кінських силах

fractional – менше однієї кінської сили

application – застосування

efficient – ефективний, продуктивний

reliable – надійний

industrial – промисловий

wound field – обмотка збудження

rotor magnet – магнітний ротор

retain – зберігати, утримувати

field strength – напруженість поля

high-strength field – поле великої напруженості

high-intensity permanent magnet – постійний магніт з полем великої напруженості

high-power motor – двигун великої потужності.

2. Read and translate the text.

DC motors are commonly constructed with wound rotors and either wound or permanent magnet stators.

Wound stators. The field coils have traditionally existed in three basic formats: series wound, shunt wound, and a combination of the two.

Permanent Magnet Motors. Permanent magnet types have some performance advantages over wound stator types, and have become predominant in fractional horsepower applications. They can be smaller, lighter, more efficient and reliable.

Originally all large industrial DC motors used wound field or rotor magnets. Permanent magnets have traditionally only been useful on small motors because it was difficult to find a material capable of retaining a high-strength field. Only recently advances in materials technology have allowed the creation of high-intensity permanent magnets, such as neodymium magnets, allowing the development of compact, high-power motors without field coils.