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Welding transformers are applied for arc welding by using an alternating one-phase current. Their external characteristic is steeply drooping. The voltage in the secondary winding ranges between 30- 70V. They supply the arc across the reactive resistance, i.e. the reactor. The current value may be adjusted by varying the air-gap of the reactor magnetic conductor the current value of which may rise to 2,500A high.
On board ships only air-cooled transformers are in use. They differ in the following types:
- one-phase dry open transformer,
- one-phase dry waterproof transformer,
- one-phase dry splashproof transformer,
- three-phase dry waterproof transformer,
- three-phase dry splashproof transformer,
- one-phase dry ironclad waterproof type.
6. Answer the questions.
1. What types are special transformers available in?
2. What are current measuring transformers and voltage measuring transformers designed for?
3. In accordance with what should measuring transformers be rated?
4. Why are fuses not mounted in current transformers' secondary circuits?
5. In what case are the measuring transformers' secondary windings and bodies grounded?
6. How is the value of the primary voltage obtained?
7. What are welding transformers applied for?
8. What range does the voltage in the welding transformer's secondary winding vary in?
9. How can the welding transformer's current value be adjusted?
10. What types of air-cooled transformers are in use on board ships?
7. Read and translate the text.
AUTOTRANSFORMERS
The primary and the secondary windings of ordinary transformers interact electromagnetically. Autotransformers only have one winding which is primary and secondary at the same time. This winding is arranged on a closed magnetic conductor; therefore, the conventional primary and secondary windings of an autotransformer are not only connected electromagnetically, but also electrically. The common part of an autotransformer winding is wound by the wire of smaller section, which makes it possible to save the mass and the volume of the copper expended and, therefore, to reduce the steel mass. When the steel mass is decreased, the magnetic losses are decreased too; this being so, autotransformers are cheaper, but their efficiency level is higher in comparison with that of ordinary transformers of the same power.
The ratio between voltages and currents in an autotransformer is identical to that of an ordinary transformer:
Autotransformers are used for starting a.c. electric motors, regulating light, etc. Their use is prohibited, however, in low voltage portable lighting because of the electrical type of connection between the windings of lower and upper voltage, which can lead to the penetration of high voltage in a low voltage network and cause injury of attending personnel.
Autotransformers may be of a step-down and step-up type, one- phased and multiphased. If the autotransformer winding possesses a large number of tappings, the secondary voltage may be adjusted in the range between zero and the mains voltage.
The disadvantage of autotransformers is the electrical type of connection between the secondary and primary circuits, which makes their field of application narrower.
8. Answer the questions.
1. How many windings does an autotransformer have?
2. Is the autotransformer winding primary and secondary at the same time?
3. Where is the autotransformer winding arranged?
4. In what way are the conventional autotransformer windings connected to each other?
5. What makes it possible to save the mass and the volume of the copper expended in autotransformers?
6. Why are autotransformers cheaper but their efficiency level is higher than that of ordinary transformers of the same power?
7. Where are autotransformers used?
8. What can lead to the penetration of high voltage in a low voltage network and injure the attending personnel?
9. What types of autotransformers do you know?
10. What is the disadvantage of autotransformers?
9. Complete the sentences with the correct form of Present Simple Active. Choose from the verbs in the box. Use each verb only once.
become, show, provide, supply, have, range, interact, be, cause
1) Figure 12 in the last column . . . that the shift is equal to 360.
2) Current and voltage measuring transformers . . . operational safety of ammetres, voltmetres, wattmetres etc.
3) The winding insulation breakdown and the overheating of the сonductor . . . possible.
4) The voltage in the secondary windings . . . between 30 70 V.
5) Welding transformers ... the arc across the reactor.
6) Autotransformers only . . . one winding.
7) The transformer primary and secondary windings . . . electromagnetically.
8) The penetration of high voltage in a low voltage network … injury of an attending personnel.
9) The welding transformers' external characteristic ... steeply drooping.
10. Make one sentence from two using the Participle.
1) A transformer is an electromagnetic device. It converts an alternating current of one voltage into an alternating current of another voltage.
2) The current produces the alternating magnetic flux in the core. It passes through the primary winding.
3) We obtain the transformer ratio. We divide one equation by another.
4) The alternating magnetic flux in the core induces the emf of self-induction. It cuts the turns of the primary winding.
5) We obtain the value of the primary voltage U1 in a measuring circuit. We multiply U2 of the secondary winding by the transformer ratio k.
6) An autotransformer is a device. It has one winding - the primary and the secondary at the same time.
7) The transformer magnetic flux and the emf of the secondary open winding go up to dangerous values. They cause the insulation breakdown of the winding and the overheating of the core.
11. Speak about transformers.
1. Read and remember the following words and word combinations.
2. Read and translate the text.
SYNCHRONOUS ALTERNATORS
This term refers to a particular type of generator the number of revolutions of which with standard frequency is coordinated with the number of pairs of poles.
Synchronous alternators of small power are sometimes built like D.C. generators equipped with stationary poles and a rotating armature. The difference is that not the commutator but the armature winding is connected to the slip-rings causing its alternating current to flow into the external circuit.
Taking into account that it is difficult to collect large power by means of sliding contacts, synchronous alternators are usually provided with rotating poles (the rotor) and a stationary armature (the stator). The power of such alternators is practically unlimited (1,400,000 kVA).
The stator is found in a steel frame with the core mounted inside and assembled of 0,35 - 0,5 mm electrical steel laminations. The stator winding is laid in the core slots, its leads being brought out to the terminal box. Synchronous alternators may be either one-phased or three- phased. A three-phase alternator has the stator windings either star- or delta-connected in the terminal box.
The greater part of shipboard alternators operates at the speed of rotation ranging from 500 to 1500 rev/min and has the rotor equipped with salient poles.
The rotor is a steel shaft on which the cores of the poles with mounted on them excitation windings are fixed, their supply being obtained through slip-rings and brushes. The source of direct current is usually a shunt-wound generator (the exciter) which is mounted with asynchronous alternator on the same shaft.
Synchronous alternators in marine application are those with silicon rectifiers in the excitation system, those with static excitation system, brushless alternators etc. Self-excited brushless alternators are the most widespread because they do not have either a commutator, slip-rings or brushes, which makes them more reliable and easier to operate.
3. Match the following English and Russian word combinations.
a) standard frequency,stationary armature,slip ring, shipboard alternator , external circuit, sliding contacts, brushless alternator, steel frame, salient pole, terminal box, marine application
b) стальной корпус, клеммный щит (коробка), скользящие контакты, морское исполнение, внешняя цепь, стандартная частота, токосъёмное кольцо, явный полюс, неподвижный якорь, бесщёточный генератор, судовой генератор переменного тока.
4. Match the synonyms.
a) to refer, number, to mount, to operate, widespread, to get,
b) to obtain, common, to install, to work, to call, amount
5. Answer the questions.
1. What does the term of “synchronous alternator” refer to?
2. What is the standard frequency for synchronous alternators equal to?
3. What are synchronous alternators equipped with when they are built like dc generators?
4. What are the main constructive elements of synchronous alternators?
5. How is the stator constructed?
6. What types of synchronous alternators can be distinguished according to their number of phases?
7. How is the rotor of shipboard alternators constructed?
8. What speed do shipboard alternators operate at?
9. What types of synchronous alternators in marine application do you know?
10. Which of synchronous alternators in marine application are the most widespread on board ship and why?
6. Speak about synchronous alternators.
1. Read and remember the following words and word combinations.
2. Read and translate the text.
INDUCTION (ASYNCHRONOUS) MOTORS
Induction motors are simple in construction, economical and reliable in operation, owing to which they are widely used in all industries. On board ships they are afforded to drive various machines, mechanisms and devices; they make 80-90% of the total number of the electric motors installed.
Induction motors are the machines the rotor of which rotates asynchronously with the magnetic field. The rotor speed of rotation varies with the change in the load on the shaft of the asynchronous motor.
The construction of induction motors provides for two main parts: the stator which is the stationary part and the rotor which is the moving part. The stator is a steel frame with the core mounted a three-phase cage motor inside and assembled of sheet steel laminations needed to reduce eddy currents. A three-phase winding is laid in the core slots and made either one-layered (with low powers), or double-layered.
The rotor is a steel shaft on which the core also made of sheet steel laminations is mounted. In the core slots, the copper and aluminium legs can be found being short-circuited from their ends by rings. Such rotor is called a squirrel-cage type.
On board ships three-phase cage motors are used for driving ship's auxiliaries, anchor-mooring mechanisms, cranes, winches etc.
3. Match the following English and Russian word combinations.
a) reliable in operation, to vary, squirrel-cage motor, winch, induction motor, double-layer winding, short-circuited, anchor-mooring mechanisms
b) якорно-швартовые механизмы, асинхронный двигатель, надежный в эксплуатации, лебедка, закороченный, двухслойная обмотка, меняться, двигатель с короткозамкнутым ротором
On board ships only air-cooled transformers are in use. They differ in the following types:
- one-phase dry open transformer,
- one-phase dry waterproof transformer,
- one-phase dry splashproof transformer,
- three-phase dry waterproof transformer,
- three-phase dry splashproof transformer,
- one-phase dry ironclad waterproof type.
6. Answer the questions.
1. What types are special transformers available in?
2. What are current measuring transformers and voltage measuring transformers designed for?
3. In accordance with what should measuring transformers be rated?
4. Why are fuses not mounted in current transformers' secondary circuits?
5. In what case are the measuring transformers' secondary windings and bodies grounded?
6. How is the value of the primary voltage obtained?
7. What are welding transformers applied for?
8. What range does the voltage in the welding transformer's secondary winding vary in?
9. How can the welding transformer's current value be adjusted?
10. What types of air-cooled transformers are in use on board ships?
7. Read and translate the text.
AUTOTRANSFORMERS
The primary and the secondary windings of ordinary transformers interact electromagnetically. Autotransformers only have one winding which is primary and secondary at the same time. This winding is arranged on a closed magnetic conductor; therefore, the conventional primary and secondary windings of an autotransformer are not only connected electromagnetically, but also electrically. The common part of an autotransformer winding is wound by the wire of smaller section, which makes it possible to save the mass and the volume of the copper expended and, therefore, to reduce the steel mass. When the steel mass is decreased, the magnetic losses are decreased too; this being so, autotransformers are cheaper, but their efficiency level is higher in comparison with that of ordinary transformers of the same power.
The ratio between voltages and currents in an autotransformer is identical to that of an ordinary transformer:
Autotransformers are used for starting a.c. electric motors, regulating light, etc. Their use is prohibited, however, in low voltage portable lighting because of the electrical type of connection between the windings of lower and upper voltage, which can lead to the penetration of high voltage in a low voltage network and cause injury of attending personnel.
Autotransformers may be of a step-down and step-up type, one- phased and multiphased. If the autotransformer winding possesses a large number of tappings, the secondary voltage may be adjusted in the range between zero and the mains voltage.
The disadvantage of autotransformers is the electrical type of connection between the secondary and primary circuits, which makes their field of application narrower.
8. Answer the questions.
1. How many windings does an autotransformer have?
2. Is the autotransformer winding primary and secondary at the same time?
3. Where is the autotransformer winding arranged?
4. In what way are the conventional autotransformer windings connected to each other?
5. What makes it possible to save the mass and the volume of the copper expended in autotransformers?
6. Why are autotransformers cheaper but their efficiency level is higher than that of ordinary transformers of the same power?
7. Where are autotransformers used?
8. What can lead to the penetration of high voltage in a low voltage network and injure the attending personnel?
9. What types of autotransformers do you know?
10. What is the disadvantage of autotransformers?
9. Complete the sentences with the correct form of Present Simple Active. Choose from the verbs in the box. Use each verb only once.
become, show, provide, supply, have, range, interact, be, cause
1) Figure 12 in the last column . . . that the shift is equal to 360.
2) Current and voltage measuring transformers . . . operational safety of ammetres, voltmetres, wattmetres etc.
3) The winding insulation breakdown and the overheating of the сonductor . . . possible.
4) The voltage in the secondary windings . . . between 30 70 V.
5) Welding transformers ... the arc across the reactor.
6) Autotransformers only . . . one winding.
7) The transformer primary and secondary windings . . . electromagnetically.
8) The penetration of high voltage in a low voltage network … injury of an attending personnel.
9) The welding transformers' external characteristic ... steeply drooping.
10. Make one sentence from two using the Participle.
1) A transformer is an electromagnetic device. It converts an alternating current of one voltage into an alternating current of another voltage.
2) The current produces the alternating magnetic flux in the core. It passes through the primary winding.
3) We obtain the transformer ratio. We divide one equation by another.
4) The alternating magnetic flux in the core induces the emf of self-induction. It cuts the turns of the primary winding.
5) We obtain the value of the primary voltage U1 in a measuring circuit. We multiply U2 of the secondary winding by the transformer ratio k.
6) An autotransformer is a device. It has one winding - the primary and the secondary at the same time.
7) The transformer magnetic flux and the emf of the secondary open winding go up to dangerous values. They cause the insulation breakdown of the winding and the overheating of the core.
11. Speak about transformers.
UNIT VI. SYNCHRONOUS ALTERNATORS
1. Read and remember the following words and word combinations.
| synchronous alternator | синхронный генератор переменного тока |
| standard frequency | стандартная частота |
| synchronous number of revolutions | синхронное число оборотов |
| external circuit | внешняя цепь |
| sliding contacts | скользящие контакты |
| steel frame | стальной корпус |
| terminal box | клеммный щиток |
| salient poles | явные полюса |
| steel shaft | стальной вал |
| marine application | морское исполнение |
| silicon rectifier | кремниевый выпрямитель |
| brushless alternator | бесщеточный генератор |
2. Read and translate the text.
SYNCHRONOUS ALTERNATORS
This term refers to a particular type of generator the number of revolutions of which with standard frequency is coordinated with the number of pairs of poles.
Synchronous alternators of small power are sometimes built like D.C. generators equipped with stationary poles and a rotating armature. The difference is that not the commutator but the armature winding is connected to the slip-rings causing its alternating current to flow into the external circuit.
Taking into account that it is difficult to collect large power by means of sliding contacts, synchronous alternators are usually provided with rotating poles (the rotor) and a stationary armature (the stator). The power of such alternators is practically unlimited (1,400,000 kVA).
The stator is found in a steel frame with the core mounted inside and assembled of 0,35 - 0,5 mm electrical steel laminations. The stator winding is laid in the core slots, its leads being brought out to the terminal box. Synchronous alternators may be either one-phased or three- phased. A three-phase alternator has the stator windings either star- or delta-connected in the terminal box.
The greater part of shipboard alternators operates at the speed of rotation ranging from 500 to 1500 rev/min and has the rotor equipped with salient poles.
The rotor is a steel shaft on which the cores of the poles with mounted on them excitation windings are fixed, their supply being obtained through slip-rings and brushes. The source of direct current is usually a shunt-wound generator (the exciter) which is mounted with asynchronous alternator on the same shaft.
Synchronous alternators in marine application are those with silicon rectifiers in the excitation system, those with static excitation system, brushless alternators etc. Self-excited brushless alternators are the most widespread because they do not have either a commutator, slip-rings or brushes, which makes them more reliable and easier to operate.
3. Match the following English and Russian word combinations.
a) standard frequency,stationary armature,slip ring, shipboard alternator , external circuit, sliding contacts, brushless alternator, steel frame, salient pole, terminal box, marine application
b) стальной корпус, клеммный щит (коробка), скользящие контакты, морское исполнение, внешняя цепь, стандартная частота, токосъёмное кольцо, явный полюс, неподвижный якорь, бесщёточный генератор, судовой генератор переменного тока.
4. Match the synonyms.
a) to refer, number, to mount, to operate, widespread, to get,
b) to obtain, common, to install, to work, to call, amount
5. Answer the questions.
1. What does the term of “synchronous alternator” refer to?
2. What is the standard frequency for synchronous alternators equal to?
3. What are synchronous alternators equipped with when they are built like dc generators?
4. What are the main constructive elements of synchronous alternators?
5. How is the stator constructed?
6. What types of synchronous alternators can be distinguished according to their number of phases?
7. How is the rotor of shipboard alternators constructed?
8. What speed do shipboard alternators operate at?
9. What types of synchronous alternators in marine application do you know?
10. Which of synchronous alternators in marine application are the most widespread on board ship and why?
6. Speak about synchronous alternators.
UNIT VII. INDUCTION (ASYNCHRONOUS) MOTORS.
1. Read and remember the following words and word combinations.
| induction (asynchronous) motor | асинхронный двигатель |
| economical | экономичный |
| reliable in operation | надежный в эксплуатации |
| slip | скольжение |
| one-layer winding | однослойная обмотка |
| double-layer winding | двухслойная обмотка |
| short-circuited | закороченный |
| leg | стержень |
| end | торец |
| (squirrel-) cage motor | двигатель с короткозамкнутым ротором |
| anchor-mooring mechanisms | якорно-швартовые механизмы |
2. Read and translate the text.
INDUCTION (ASYNCHRONOUS) MOTORS
Induction motors are simple in construction, economical and reliable in operation, owing to which they are widely used in all industries. On board ships they are afforded to drive various machines, mechanisms and devices; they make 80-90% of the total number of the electric motors installed.
Induction motors are the machines the rotor of which rotates asynchronously with the magnetic field. The rotor speed of rotation varies with the change in the load on the shaft of the asynchronous motor.
The construction of induction motors provides for two main parts: the stator which is the stationary part and the rotor which is the moving part. The stator is a steel frame with the core mounted a three-phase cage motor inside and assembled of sheet steel laminations needed to reduce eddy currents. A three-phase winding is laid in the core slots and made either one-layered (with low powers), or double-layered.
The rotor is a steel shaft on which the core also made of sheet steel laminations is mounted. In the core slots, the copper and aluminium legs can be found being short-circuited from their ends by rings. Such rotor is called a squirrel-cage type.
On board ships three-phase cage motors are used for driving ship's auxiliaries, anchor-mooring mechanisms, cranes, winches etc.
3. Match the following English and Russian word combinations.
a) reliable in operation, to vary, squirrel-cage motor, winch, induction motor, double-layer winding, short-circuited, anchor-mooring mechanisms
b) якорно-швартовые механизмы, асинхронный двигатель, надежный в эксплуатации, лебедка, закороченный, двухслойная обмотка, меняться, двигатель с короткозамкнутым ротором