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
