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TRANSFORMERS

A transformer is a device for decreasing or increasing voltage in an alternating current system without change in the frequency. An elementary transformer consists of a steel core which carries two windings insulated from both the core and each other. The winding connected to the supply circuit is called the primary and the winding connected to the receiver circuit (load) is called the secondary. When the transformer reduces the applied voltage it is called step-down transformer. When the transformer raises the applied voltage it is called step-up transformer.

The transformer forms one of the main parts of a substation.

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The principle of operation is as follows. One should remember that the transformer can be used only with alternating current. No current will be induced in the case of direct current, that is, when the magnetic field does not change.

The alternating current transversing the primary sets up an alternating magnetic field which induces the electromotive force (e.m.f.) in the secondary. The alternating magnetic field cuts across both the secondary and the primary, so an electromotive force is also induced in the primary. The magnitudes of two electromotive forces depend on the frequency of the magnetizing current, the number of turns in the respective windings and the magnetic flux in the core.

Vocabulary:

transformer - трансформатор

device - прибор, устройство

decreaseуменьшать

Increase - увеличивать

alternating current (a.c.) – переменный ток

direct current (d.c.) – постоянный ток

change – изменять

frequency – частота

steel core – стальной сердечник

carry – нести

winding – обмотка

insulate – изолировать

connect – соединять

supply circuit – питающая цепь

receiver circuit – потребитель

load - нагрузка

primary – первичный

secondary – вторичный

reduce – понижать

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apply – прикладывать step-up – повышающий step-down- понижающий raise – повышать

form –образовывать substation – подстанция operation – работа

as follows – следующий

induce – индуцировать, наводить case – случай

magnetic field – магнитное поле transverse – пересекать

set upсоздавать, образовывать

e.m.f. (electromotive force) – э.д.с. (электродвижущая сила) cut across – пересекать

magnitude – величина depend on – зависеть the number of – число turn – виток

respective – соответствующий flux – поток

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GENERATORS

Synchronous generators consist of the member which supplies a magnetic field (field structure) and the member in which an e.m.f. is induced (the armature). Practically all large generators are made with the revolving field. The direct current required to excite the field coils is usually supplied by a d.c. generator. This generator is mounted on a common shaft with the field structure. The prime mover of a synchronous generator may be a steam turbine, a water wheel, an electric motor, etc. Synchronous generators may be cooled either by water or by hydrogen. Hydrogen cooling is far better method of generator ventilation.

A direct-current generator is an electric machine that converts the mechanical energy of its prime mover into the electrical energy. For its operation a d.c. generator depends on the electromagnetic induction. It consists of a rotating armature which carries a winding and a stationary field structure with electromagnets. These electromagnets produce the magnetic field. When the armature rotates, its winding cuts across the magnetic field. The e.m.f. is induced in the armature winding due to the magnetic induction. If a d.c. generator is fitted with both a commutator and slip rings, it may be used as a source of both alternating and direct current.

Vocabulary:

generator – генератор

synchronous – синхронный

member – элемент

supply – питать, обеспечивать

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magnetic field – магнитное поле

field structure – индукторная станина, конструкция полюсов armature – якорь

revolve – вращать require – требовать excite – возбуждать coil – катушка

mount – монтировать common – общий shaft – вал

prime mover – привод

steam turbine – паровая турбина water wheel – водяное колесо etc. (and so on) – и так далее cool – охлаждать

air – воздух hydrogen – водород

convert into – превращать, преобразовывать induction – индукция

due to – благодаря, из-за

fit with – оснащать, оборудовать commutator – коллектор

slip rings – контактные кольца use – использовать

source – источник

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MOTORS

An induction motor can operate as both a motor and a generator. Normally it consists of an annular core (the stator), which carries the primary winding in slots on the inner periphery. The cylindrical rotor inside the stator carries the secondary winding in slots on its outer periphery. Both the stator and the rotor are assembled of silicon steel punching coated with the varnish in order to reduce eddy-current losses. The air-gap between the stator and rotor is very small. When the primary (the stator) winding is connected to a three-phase power supply, a revolving magnetic field is produced within the stator. The field cuts across the secondary (rotor) winding and induces the e.m.f. in it. The rotor winding may be of two types: squirrel-cage and slip-ring.

A squirrel-cage induction motor is one of the most widely used types. It consists of the stator carrying the primary winding. The primary winding is enclosed in a cast iron frame. The rotor winding is connected to copper and rings on both ends, those forming a squirrel-cage structure.

A slip-ring (wound rotor) induction motor. The only difference in the construction between the squirrel-cage and the slip-ring types lies in their rotors. The slip-ring rotor has a three-phase winding which may be either star or delta connected. The insulated ends of the phases are brought out to three slip-rings on the rotor shaft.

Vocabulary:

induction motor – асинхронный двигатель

annular – кольцевой

core – сердечник

slot – паз

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inner – внутренний

periphery – окружность, периферия inside – внутри

outer – наружный assemble – монтировать

silicon steel – кремнистая сталь punching – штамповка

coat – покрывать varnish – лак reduce – уменьшать

eddy current – вихревой ток loss – потеря

air gap –воздушный зазор connect – соединять three-phase – трехфазный

power supply – источник питания within –внутри

squirrel-cage – короткозамкнутый; “беличья клетка” enclose – помещать(ся) в

cast iron – чугун

frame – корпус, станина copper – медь

wound – фазный ротор the only – единственный difference – различие delta – треугольник bring out – выводить shaft – вал, ось

slip-ring (induction )motor

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