SINGLE- AND THREE- PHASE ALTERNATING CURRENTS

The door opened, to Kitty's fancy not quite naturally but as though it swung back of itself on its hinges, and the Mother Superior entered the little room. She stood for an instant on the threshold and a grave smile hovered upon her lips as she looked at the laughing Sister and Waddington's puckered, clownish face. Then she came forward and held out her hand to Kitty.

"Mrs. Fane?" She spoke in English with a good deal of accent, but with a correct pronunciation, and she gave the shadow of a bow. "It is a great pleasure to me to make the acquaintance of the wife of our good and brave doctor."

Kitty felt that the Superior's eyes held her in a long and unembarrassed look of appraisal. It was so frank that it was not uncivil; you felt that here was a woman whose business it was to form an opinion of others and to whom it never occurred that subterfuge was necessary. With a dignified affability she motioned to her visitors to take chairs and herself sat down. Sister St. Joseph, smiling still but silent, stood at the side but a little behind the Superior.

"I know you English like tea," said the Mother Superior, "and I have ordered some. But I must make my excuses if it is served in the Chinese fashion. I know that Mr. Waddington prefers whisky, but that I am afraid I cannot offer him."

She smiled and there was a hint of malice in her grave eyes.

"Oh, come, ma mere[3], you speak as if I were a confirmed drunkard."

"I wish you could say that you never drink, Mr. Waddington."

"I can at all events say that I never drink except to excess." The Mother Superior laughed and translated into French for Sister St. Joseph the flippant remark. She looked at him with lingering, friendly eyes.

"We must make allowances for Mr. Waddington because two or three times when we had no money at all and did not know how we were to feed our orphans Mr. Waddington came to our rescue."

The convert who had opened the door for them now came in with a tray on which we're Chinese cups, a teapot, and a little plate of the French cakes called madeleines.

"You must eat the madeleines," said the Mother Superior, "because Sister St. Joseph made them for you herself this morning."

They talked of commonplace things. The Mother Superior asked Kitty how long she had been in China and if the journey from Hong-Kong had greatly tired her. She asked her if she had been in France and if she did not find the climate of Hong-Kong trying. It was a conversation, trivial but friendly, which gained a peculiar savour from the circumstances. The parlour was very quiet, so that you could hardly believe that you were in the midst of a populous city. Peace dwelt there. And yet, all round about, the epidemic was raging and the people, terrified and restless, were kept in check but by the strong will of a soldier who was more than half a brigand. Within the convent walls the infirmary was crowded with sick and dying soldiers, and of the orphans in the nuns' charge a quarter were dead.

Kitty, impressed she hardly knew why, observed the grave lady who asked her these amiable questions. She was dressed in white and the only colour on her habit was the red heart that

burned on her breast. She was a woman of middle age, she might have been forty or fifty, it was impossible to say, for there were few wrinkles on her smooth, pale face, and you received the impression that she was far from young chiefly from the dignity of her bearing, her assurance, and the emaciation of her strong and beautiful hands. The face was long, with a large mouth and large, even teeth; the nose, though not small, was delicate and sensitive; but it was the eyes, under their thin black brows, which gave her face its intense and tragic character. They were very large, black, and, though not exactly cold, by their calm steadiness strangely compelling. Your first thought when you looked at the Mother Superior was that as a girl she must have been beautiful, but in a moment you realised that this was a woman whose beauty, depending on character, had grown with advancing years. Her voice was deep, low and controlled, and whether she spoke in English or in French she spoke slowly. But the most striking thing about her was the air she had of authority tempered by Christian charity; you felt in her the habit of command. To be obeyed was natural to her, but she accepted obedience with humility. You could not fail to see that she was deeply conscious of the authority of the Church which upheld her. But Kitty had a surmise that notwithstanding her austere demeanour she had for human frailty a human tolerance; and it was impossible to look at her grave smile when she listened to Waddington, unabashed, talking nonsense, without being sure that she had a lively sense of the ridiculous.

But there was some other quality in her which Kitty vaguely felt, but could not put a name to. It was something that, notwithstanding the Mother Superior's cordiality and the exquisite manners which made Kitty feel like an awkward school-girl, held her at a distance.

[1] badinage (French) — jesting

[2]C'est la dame du docteur? — Is she the doctor’s wife?

[3] ma mere — (reverend) mother

SINGLE- AND THREE- PHASE ALTERNATING CURRENTS

Subtechnical vocabulary

reactance ( noun)

reactive resistance

Inductance of a current flow and the inductive reactance are directly proportional to the

magnetic flux linked with it.

skin (adjective)

outer, external

Skin effect occurs when the effective resistance is high.

counteract (verb)

to reduce or prevent bad effect of something

The applied voltage should be high enough to counteract both the resistive voltage

drop and the EMF of self-induction in the coil.

theorem (noun)

a statement, that can be proved

The theorem of Pythogoras explains that the square on the hypotenuse of a right-

angled triangle is equal to the sum of the squares on the other two sides.

in series (adverb)

to be connected with one after another so that electricity passes through the parts of

something electrical in the correct order

A circuit contains resistance and capacitance connected in series.

in parallel (adverb)

if two electrical circuits are connected so that any electric current is divided equally

between them

Circuits can contain inductance and capacitance if they are connected in parallel.

impedance (noun)

full resistance

Impedance is a measure of the power of a piece of electrical equipment to stop the flow

of an alternating current.

oscillatory (adjective)

changing direction very regularly and frequently

The alternate exchange of energy between the circuit and the magnetic field is basic of

electromagnetic oscillations, such circuits are called oscillatory circuits.

transmitter (noun)

equipment that sends out radio or television signals

The oscillatory circuit is the basis of radio transmitters and receivers.

detection ( noun)

discovering of something, that is not easy to see, to hear

Detection is accomplished by crystal detectors, by radio valves, or by semiconductor

devices.

require (verb)

to demand, to need something

Reactive power is required for the production of alternating magnetic fields.

high-speed ( adjective)

operating very fast

High-speed motors have large power factor.

Poly-phase (adjective)

having many phases

A poly-phase system has many advantages.

A. Improve your vocabulary. Fill in the following sentences with English equivalents

of words and phrases in brackets, translate the given sentences from English into

Russian.

1. As the conductor cuts across the lines of (магнитная индукция), an EMF is induced in it.

2. (величина) of this EMF depends on the flux density.

3. The ЕMF induced in the conductor rises from zero to a maximum, falls to zero, to reverse its

direction, rises to a maximum in the opposite direction and again drops zero, repeating this

cycle of changes every complete revolution of the conductor continuously, such an EMF is

called (переменный).

4. The continuous curve connecting the values of the EMF at any given (угол) is called

a sinusoidal curve or wave.

5. Electrical engineering gives preferences to sine-wave currents and (напряжение) in many

applications.

6. The current varies both in (направление) and magnitude regularly with time and is called

an alternating current.

7. Real electric machines have a steel drum placed between the poles of an (электромагнит).

8. The winding where the EMF is induced is arranged on the moving part of the machine, called

the ( ротор), and the pole pieces are on the stationary part, termed the ( статор ).

9. The direct current necessary to energize the field winding can be supplied by an outside

exciter mounted on a common shaft with AC generator, or by a ( выпрямитель).

B. Translate the following words and expressions , explain their meanings.

magnetic induction, EMF, magnitude, flux density, induce, drop, revolution, alternative

current, direct current, curve, sine wave, voltage, electromagnet, winding, stator, rotor,

supply, mount, shaft, rectifier, instantaneous, frequently, resistance, mean, self-induction,

inductance.

C. Find the English equivalents for the following words and word combinations.

реактивное сопротивление, индуктивность, резистивное сопротивление, самоиндукция,

электродвижущая сила, катушка, гипотенуза, треугольник, квадрат, цепь ( схема),

полное сопротивление, емкость, мгновенное значение, непрерывный, обмотка,

выпрямитель, частота.

D. Read and translate the given sentences from English into Russian, paying attention to

the new lexical stock.

1. An alternating EMF and an alternating current reverse their direction and sign at regular

intervals and vary in magnitude continuously.

2. The value of an alternating current, voltage, etc., at any given moment is known as the

instantaneous value and is designated by a small letter ( I for current, V for voltage, and

E for EMF).

3. The time occupied by one complete cycle of change in EMF, current or voltage is called the

period.

4. The number of cycles of complete change repeated within one second is the frequency.

5. Telephony uses frequencies from several hundred to a few thousand cycles while radio

engineering employs frequencies running into many millions of cycles per second.

6. AC ampere is defined as an alternating current of 1 A which, flowing in resistance,

produces heat energy at an average rate equal to that produced by 1 A direct current in the

same resistance.

7. The mean value of a sine wave over a complete cycle is zero.

8. Ohm’s law is valid for alternating current as it is for direct current.

9. Whenever an electric circuit is being closed or opened or its current is being varied,

the EMF of self-induction is induced in it due to the magnetic field set up around

the conductor.

10 .The EMF of the self-induction depends on the rate of change in the current and

the inductance of the circuit.

11.The supply voltage at any time should be equal and opposite to the emf of self-induction.

E. Translate the micro text in written form, describe in English the main idea of this

microtext.

Date: 2014-12-28; view: 1151