43. /10 мин./ Из следующих предложений выпишите 9 словосочетаний, состоящих из двух существительных. Переведите их.
1. Squirrel-cage motors have two main parts. 2. The stator is contained in the motor’s stationary frame. 3. The rotor is mounted on the drive shaft. 4. The flow of ac sets up a magnetic field. 5.The rotor of a squirrel-cage motor consists of laminated iron & the squirrel-cage conductors. 6. The conductors recess into slots in the laminated core. 7. All conductors of a squirrel-cage rotor are mechanically & electrically connected by end rings. 8. The cage conductors & end rings of smaller rotors are generally die cast into the rotor. 9. With larger machines, rotor conductors are brazed or welded to end rings. lO.-Experiments with aluminium die casting of rotor cages started in the early 30’s.
44. /35 мин./ Прочтите текст и ответьте на вопросы.
1. Which is the most obvious way to convert ac to dc? /1/ 2. How are motor & generator copnnected in a motor-generator set? /2/ 3. There are several ways to dampen surges on the generator.. What are they? /2/ 4. Why are most motor-generator sets designed as units? /З/б. What kind of dc motors may advantageously be supplied by motor-genera for sets/4/ 6. How can dc terminal voltage be adjusted? /5/ 7. Where are booster often used? 8. What can be done when load overhauls the direct current-drive generator? /6/ 9. How can the power factor of the ac supply be improved? /7/
Motor-Generator Sets /т-g sets/
1. Most obvious way to convert ac to dc current is with a m-g set. The generator can be designed to suit load requirements. While it is probably possible to design a rectifier circuit to take care of any dc load requirements, m-g sets have certain definite advantages for some applications with special needs.
. 2. Motor & generator are electrically separate but shaft connected. Surges on generator are transmitted to motor, then to the ac supply. Surges may be damped somewhat by the m-g sets’ inertia. For some applications a fly-wheel can be added to the m-g set to store energy to dampen generator load surges, to give smoother operation.
3. Most sets are designed as units, rather than just a motor & generator coupled together. Overhall size is reduced, two or three bearings are required instead of four, all alignment problems are simplified in this way.
4. Converter-inverter machine, formerly popular for ac-to-dc conversion, is now mostly used as dc-to-ac inverter for special applications such as ac control system operated from batteries. As an inverter machine is operated as a dc motor, the commutator changes dc to ac in winding & ac is tapped off through slip rings. Frequency is dependent on armature speed. As rotary converter,machine may be accelerated in a number of ways after which it runs off ac lines similar to synchronous motor. Ac is fed to windings through slip rings & is changed to dc commutator. Dc voltage is fixed by ac supply voltage. Larger units are polyphase, with 6-phase armature connections favoured for most applications.
5. Adjustable-speed dc motors may often be supplied to advantage by m-g sets. Dc terminal voltage is readily adjustable by generator field control. Armature control of the motor driving load
.'is accomplished without an armature-circuit rheostat. Complicated speed-control systems often employ booster generators. Booster armature is hooked up in series with the armature of an individual dc-drive motor.
6. Regeneration is a natural advantage of m-g sets, & suitable controls for regeneration are normally simple. Dynamic braking & return of power to the ac lines can be accomplished when load overhauls the dc-drive motor, forcing it to act as a generator. Motor & generator of the m-g set in turn reverse their functions.
7. Power factor of the ac supply can be improved if a synchronous motor with leading power factor is used to drive the m-g set.
Ключи.
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8 - bcefijlmo
9 - 2, 3, 6, 7
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