Методическое пособие для студентов iv курса очного и заочного обучения специальности 26. 05. 07 "Эксплуатация судового электрооборудования и средств автоматики"
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UNIT VII. INDUCTION (ASYNCHRONOUS) MOTORS.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 4. Match the synonyms. a) to drive, number, to use, to install b) quantity, to employ, to mount, to operate 5. Answer the questions. 1. Why are induction motors widely used in all industries? 2. What are induction motors afforded to do on board ships? 3. What do we call "induction motors"? 4. What are the constructive elements of a cage motor? 5. What is the operation of a three-phase cage motor principally based on? 6. How is the rotating magnetic field established? 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? 9. What do we call the value by which the rotor speed of rotation smaller than the stator speed of rotation? 10. In what way can we define the rotor speed of rotation? 11. What is the slip? 12. What exactly are the mechanisms on board ships which are driven by a three-phase cage motor? 6. Speak about induction motors. |