Урок 3. Unit 3.

1. Прочитайте слова, обращая внимание на чтение подчеркнутых букв и

буквосочетаний.

Refer, certain, circuit, turn, third, tertiary, serve, commercial, purpose.

Previously, between, field, means, increase, decrease, keep, metering,

easily.

Flux, conductor, current, induction, one, but, enough, much, nothing.

Prevalent, basis, change, great, able, same.

Comprise, winding, behind, likewise, high, why, primary, cycle, supply.

Vicinity, consider, single, significance, equipment, ability, system.

Source, more, cause, call, small, important.

Produce, mutual, distribution, neutral, value, use, induced.

Rapidly, bank, value, capacity, manner tap.

Amount, how, found, down, now, round.

Desired, required, higher, wire.

Regard, retard, far, example.

Transformer, whenever, relative, secondary, another, property.

2. Прочитайте и запомните следующие слова и словосочетания.

a bank – батарея;

losses – потери;

to step up –повышать (напряжение);

to step down – понижать (напряжение);

a transmission system – система передачи;

a tertiary winding – третичная обмотка;

an instrument transformer – измерительный трансформатор;

a current transformer – трансформатор тока;

a potential transformer – трансформатор напряжения;

a distribution transformer – трансформатор распределительной сети,

распределительный трансформатор;

a power transformer – мощный (силовой) трансформатор;

a one-to-one transformer – разделительный трансформатор с коэффициентом

трансформации, равным единице;

potential – электрический потенциал, разность потенциалов, напряжение;

metering equipment – измерительное оборудование, аппаратура;

relaying equipment – оборудование релейной защиты;

the primary – первичная обмотка;

the secondary – вторичная обмотка;

opposition – противофаза; сопротивление;

a stack – набор, комплект; блок, батарея;

capacitance – электрическая емкость; емкостное сопротивление;

resistance – (активное) сопротивление; сопротивление;

impedance – полное сопротивление;

billing – составление счетов; расчеты;

utilities – энергостанции (энергосистемы) общего пользования;

a tap changer – переключатель ответвлений (обмоток трансформатора);

a load tap changer – переключатель ответвлений (обмоток трансформатора)

под нагрузкой;

excitation – возбуждение; подмагничивание;

to shut down – остановить; выключить; отключить;

setting – уставка.

3. Прочитайте текст 3 “Transformers”. Во всех предложениях подчеркните

глагол-сказуемое. Укажите предложения, глагол-сказуемое которых 1) содержит модальные глаголы или их эквиваленты, 2) употребляется в страдательном залоге. Переведите эти предложения письменно.

TEXT 3. TRANSFORMERS

Part I

To understand the operation of a transformer, one must refer to certain basics which were previously explained. Voltage is produced whenever there is relative motion between a magnetic field and a conductor. Whenever current flows in a conductor, a magnetic field (flux) is established surrounding that conductor. The magnetic field (flux) is most prevalent in the vicinity of that conductor.

These basics are the basis for transformation of currents and voltages. A transformer may be defined as a piece of apparatus without continuously moving parts which by electromagnetic induction transforms alternating voltage and current in one winding into alternating voltage and current in one or more other windings, usually at different values of voltage and current. It consists essentially of an iron core on which are wound the primary and the secondary windings. The core comprises the means by which the flux is concentrated. The rapidly changing alternating current produces rapidly changing flux. As this flux increases and decreases, there is relative motion between flux from windings of the source side of the bank and the secondary windings. This produces mutual inductance. Mutual inductance is the ability to transfer energy from one circuit to the other circuit without a direct connection.

Transformers do not produce electricity. They merely transform it from one level to another. The total amount of power does not increase. There are losses which are associated with transformers. Anytime the voltage is stepped down, the current is stepped up by the same ratio. Likewise, when the voltage is stepped up, the current is stepped down by the same ratio. This is why transmission systems utilize high voltage. The higher the voltage the less the current for a given value of power. Less AC decreases losses.

The winding of a transformer which is electrically connected to the source of power is called the primary winding. The load side winding of a transformer is termed the secondary winding. Transformers with a third winding require a term other than primary and secondary. The third winding of a power transformer is termed the tertiary winding. A transformer may be used to step the voltage up or down. It may also serve to step the current up or down.

Let us consider the basic types of transformers. First, instrument transformers are of significance. Current transformers and potential transformers are instrument transformers. Instrument transformers transform potential or current to values which can be easily used on metering and relaying equipment. The potential transformer transforms voltage from a high value to a lower value, the most common of which is 120 volts AC. The potential transformer is similar to a power transformer, but can only handle small volt-ampere values. The load of a potential transformer must be considerably less than that normally found on a power transformer. A potential transformer will transform voltage. It can only handle enough current for metering and relaying.

Another type of instrument transformers is the current transformer. The current transformer transforms current from higher values to lower values. High values cannot easily be used in metering and relaying circuits. Low values may easily be used in metering and relaying circuits. The current transformer is rated in ratio of, for example 600:5. “MR” represents a multi-ratio current transformer. The “5” is not the maximum of current that can flow in the secondary, but is an easy reference to what is commonly referred to as a full scale deflection on an ammeter. Unlike a potential transformer a current transformer is a very low impedance device. The secondary of the current transformer offers very little opposition to the current flow. The primary may be the conductor and the secondary may represent a number of turns around that conductor. The current flow through the primary establishes flux. Based upon the number of turns, the secondary produces a current flow proportional to but much less than the primary current.

If the current is stepped down, the voltage must be stepped up. Anytime the current is stepped up, the voltage must be stepped down. The voltage is stepped down on a potential transformer and the current is stepped up. On a current transformer, the current is stepped down and the voltage is stepped up.

There is very little voltage associated with a CT secondary voltage. This is true because the primary of that current transformer is actually nothing more than one phase of the conductor itself. The voltage across two points on one phase of the primary is no more than millivolts.

4. Найдите в тексте эквиваленты следующих фраз, составьте с ними свои

предложения, описывая работу электрооборудования:

1. всякий раз, когда имеется;

2. всякий раз, когда ток течет;

3. состоит, по-существу из;

4. средства с помощью которых;

5. подобным же образом, когда напряжение;

6. вот почему системы передачи электроэнергии;

7. чем выше …, тем меньше;

8. он также может служить для того, чтобы;

9. могут легко использоваться;

10)должна быть значительно меньше (больше).

5. Назовите основные части трансформатора и расскажите о их

назначении.

6. Переведите текст на русский язык.