Английский язык для моряков / Англ Труханова

inside and assemЫed ofsheet steel laminations needed to reduce eddy currents. А three-phase winding 3 is laid in the core slots and made either one-layered (with low powers), or douЫe-layered.

The rotor is а steel shaft 4 on which the core 5 also made of sheet steel laminations is mounted. 1n the core slots, the copper and alu­ minium legs 6 can Ье found being short-circuited from their ends Ьу rings 7. Such rotor is called а (squirrel-) cage type.

The operation of the induction motor is principally based оп the electromagnetic interaction ofits rotating magnetic field with the cur­ rents in the rotor winding. The way in which the mentioned rotating field is estaЫished Ьу means ofа set ofstationary windings may Ье briefly described as follows. Across three stator windings (AX,BY,CZ) shifted Ьу 120° relative to one another а three-phase current is flowing. The di­ rection ofthe current from the beginnings ofthe phase windings (А,В,С) towards their ends (Х,Y,Z) is presumaЫy regarded as opposite. At the time t1 the current in the winding АХ isn't flowing, but it obtains а neg­ ative direction in the winding ВУ and а positive direction in the wind­ ing CZ. The resultant magnetic field inside the stator is, therefore, di­ rected downwards. Since the N and S poles of the field are being permanently disp\aced across the inside ofthe stator, the revolving mag­ netic field is produced. The above mentioned stator winding has only one pair ofpoles, owing to which the magnetic field does one revolu­ tion during one cycle ofthe current reversal. Ifthe winding has р pairs ofpoles and is supplied Ьу the current offrequency f1, the speed ofro­

tation ofthe revolving magnetic field

60/ n1= --.

р

This speed ofrotation is called а synchronous one. The rotor speed

ofrotation is asynchronous. It is smaller than the stator speed ofrota­ tion Ьу the value ofthe slip S.

If the rotor is stationary (n2 =О), S = 1. If theoretically n2 = nl ' S = О, i.e. the slip may vary between О and 1. With the rated load

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QUESTIONS

1.Why are induction motors widely used in all industries?

2.What are induction motors afforded to do оп board ships?

3.What do we call "induction motors"?

4.What are the constructive elements of а cage motor?

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6.How is the rotating magnetic field estaЫished?

7.How many revolutions does the magnetic field do during one cycle

of the current reversal if the stator winding has one pair of poles? 8. What do we call the speed of rotation which is detected Ьу the forrnula

9. What do we call the value Ьу which the rotor speed of rotation is smaller than the stator speed of rotation?

1О. In what way сап we define the rotor speed of rotation?

11.What is the slip?

12.What exactly are the rnechanisms on board ships which are driven Ьу а three-phase cage rnotor?

5

Fig. 8. Asynchronous Cage Motor

З. ELECTRIC SPECIAL PURPOSE MACHINES

On board ships separate electrical energy consumers (radiocom­ munication, electric radionavigational instruments etc.) require special sources ofenergy , the main electrical properties ofwhich (voltage, the kind of current, frequency) are ditferent from those of shipboard elec­ tric power station. For the purposes of converting electrical parametres

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ofshipboard e\ectric power station into required ones such machines as converters are used. Rotary converters may Ье either multiarmatured or one-armatured The general disadvantage ofall rotary converters is both the moving contact in the commutator-brushgear transition an? the rotating parts, which makes the converters consideraЬ\y less reliaЬ\e and harder to operate. At present time static converters are widespread оп board ships. The are deprived ofthe drawbacks indicated above..

Another variety ofan electric special purpose machine is ampli­ fiers. They are distinguished as magnetic amplifiers and rotary amplifi­ ers. Magnetic amplifiers (МА) have acquired а wide application оп board ships being designed for automatic regulation, monit(!ring and con­ trol ofvarious marine sets. They are advantageous in not having mov­ ing parts, being simple in construction and easy in operation, possess­ ing high reliaЬility and efficiency, being characterised Ьу instant readiness and resistance to moisture and vibration. Magnetic amplifiers are pro­ vided to control а Ьig power Ьу expending а small one.

Rotary amplifiers (RA) find application in automatic control and regulating circuits ofmarine generators and servomotors included into the adjustaЬ\e-potential systems. Depending on its capacity а rotary am­ plifier may operate as either an exciter or а generator ofthe system. The most widespread type of а rotary amplifier is an amplidyne owing а cross field. lt is а d.c. generator specially constructed with а number of advantageous features: а Ьig magnification ratio, small inertia capabll­

ity, а Ьig overload capacity etc.

Another electric special purpose machine is а tacbogenerator. It is designed for converting the speed ofrotation ofthe shaft possessed Ьу machines and mechanisms into the proportional electric voltage. А tachogenerator is required to keep linearity and symmetry ofan output characteristic within the entire range ofthe change ofeither the speed ofrotation or the direction ofrotation. Оп board ships d.c. and а.с. ta­ chogenerators are used to measure the speed of rotation ofpropulsion

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shafts and other mechanisms. They are also provided in automatic sys­ tems to obtain the rotational speed feedback.

Synchronous transmission systems are called selsyn systems. Various instruments designed for controlling the operation ofthe ship base themselves on selsyns. Such instruments as engine and bridge tele­ graphs, а gyro-pilot, а gyro-compass, tachometres of propulsion shafts, logs etc. are installed to ensure the control ofsteering gear positions, the operation of the boilers, the ship's speed and the direction ofthe ship's motion.

А selsyn is composed of,both the stator and the rotor. In con­ struction, selsyns are divided into those provided with slip-rings and those deprived of them. Slip-ringed selsyns, in their turn, may Ье equipped with either the primary one-phase field winding mounted on the stator and having salient poles or the secondary three-phase synchro­ nisation winding mounted on the rotor and having non-salient poles.

VOCABULARY

automatic control and regulating схемы авrоматическоrо управления

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QUESTIONS

1.For what purposes are converters used?

2.What types of converters do you know?

3.Which type of converter is advantageous on board ships ? Why?

4.What types of amplifier do you know?

5.Why has а magnetic amplifier acquired а wide application on board ships?

6.What is а magnetic amplifier designed for?

7.Where does а rotary amplifier find application?

8.What may а rotary amplifier operate as depending on its capacity?

9.Which type of rotary amplifier is the most widespread on board ships? Why?

10. What is а tachogenerator designed for?

11. What are d.c. tachogenerators and а.с. tachogenerators used for on board ships?

12.What types of synchronous transmission system do you know?

13.What instruments base themselves on а selsyn? What are they responsiЫe for?

14.What parts is а selsyn composed of?

15.What types of selsyn do you know?

EXERSISES

/. Check yourselfin your vocabulary.

What doуои cal/:

1. the machine which is designed to convert the electrical parametres of shipboard electric power station into the required ones?

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2.the field with which an amplidyne is provided?

3.the frequency which is important for а synchronous a\ternator and equal to 50 Нz?

4.the type of alternator which doesn't have either а commutator, slip­ rings or brushes?

5.the magnetic field which is estaЬ\ished inside the motor stator and directed downwards?

6.the type of a\temator the number of revolutions of which with stan­ dard frequency is co-ordinated with the number of pair of poles?

7.the alternator characteristic which makes it possiЬ\e to judge the degree of stee\ saturation?

8.the type of converter that doesn't have either moving contacts or rotating parts?

9. the circuits in which rotary amplifiers find app\ication?

10.the type of motor which makes 80-90% of the total number of the electric motors insta\led on board ships?

11.the property owing to which magnetic amplifiers get instantly prepared for operation?

12.the type of rotary amplifier that owns а Ьig magnification ratio?

13.the contacts Ьу means of which small power is collected in synchronous alternators?

14.the type of amp\ifier which is constructed for automatic regulation, monitoring and control of various marine sets?

15.the value which shows the ratio between the speed of rotation of the magnetic field п1 and the rotor speed of rotation n2 ?

IL Make sure уои have properly understood the texts given above:

1. Synchronous alternators are machines which:

а) convert the speed of rotation of the shaft possessed Ьу mechanisms into the proportional electric voltage;

Ь) have the number of revolutions co-ordinated with the number of poles with standard frequency;

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с) regulate, monitor and control various marine sets. 2. Induction motors are machines which:

а) convert mechanical energy into electrical energy;

Ь) find application in automatic control and regulating circuits included into the adjustaЫe-potential systems;

с) have the rotor moving asynchronously with the magnetic field. 3. Converters are used for:

а) transforming electrical parametres of shipboard electric power station into the required ones;

Ь) driving ships auxiliaries, anchor-mooring mechanisms, cranes, winches;

с) converting electrical energy into mechanical one.

4.Amplifiers may Ье distinguished as those of: а) а magnetic type and а rotary type;

Ь) а static type and а rotary type;

с) а one-layer type and а douЫe-layer type. 4. Tachogenerators are machines which are used:

а) to drive various machines, mechanisms and devices; Ь) to measure the speed of rotation of propulsion shafts;

с) to convert cuпent and voltage parametres of shipboard electric power station into required ones.

5. Selsyns are systems:

а) provided with air-cooling;

Ь) which realize "generator-motor" interaction;

с) on which various instruments constructed for controlling the operation of the ship base themselves.

JIJ. Mindyour Grammar.

1. Complete the following sentences with the correct -ing and - ed forms. Se/ect the right verbfrom the Ьох using it опсе оп/у:

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l). The stator is found in the frame with the core . . . inside and of 0,35-0,5mm electrical steel laminations.

2). А lot of shipboard alternators operate at the speed of rotation from 500 to l 500rev/min.

3). Magnetic amplifiers are electric special-purpose machines . Ьу instant readiness and resistance to moisture and vibration.

4). An amplidyne is а d.c. generator specially . . . with а number of advantageous features.

5). The most widespread type of rotary amplifier is an amplidyne . .

. а cross field.

6). Slip-ringed selsyns may have either the primary one-phase field winding . . . salient poles or the secondary three-phase synchro­ nization winding . . . non-salient poles.

7). Three-phase cage motors are induction motors . . . ship's auxil­ iaries , anchor-mooring mechanisms, cranes, winches.

8). The core and aluminium legs . . . from their ends can Ье found in the core slots.

9). The cores of the poles have the field windings through slip-rings and brushes.

10). А great deal of ship alternators have the rotor poles.

2. Fill the gaps after the moda/ verbs with the Passive lnfinitive:

\). The copper and aluminium \egs can . . . (find) in the core slots. 2). The way in which the rotating field is estaЫisl1ed in the stator may

. . . (describe) as follows.

3). The current value can . . . (adjust) Ьу varying the air-gap of the

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withstand а working voltage of an electrical set.

8). If the rules of the electrical maintenance and safety are not observed, the normal state of the equipment may . . . (break).

9). The trouЫes must ... (eliminate) in time.

10). The test procedure of this autotransformer should . . . (do) in accordance with the safety rules.

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