2021-11-09
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Unit 2. Types of current
Vocabulary
alternating переменный (ток)
to apply применять, прилагать
to consider рассматривать, обсуждать
cycle цикл
direct постоянный (ток)
direction направление
frequency частота
mains electricity сетевое электричество
necessary необходимый, нужный
provided (that) при условии, что
sine wave синусоидальная волна
single-phase однофазный
three-phase трехфазный
to use использовать
Text
Current is flow of electricity through a circuit. Let us consider two
main types of current: direct and alternating. Direct current (DC) flows through a conducting circuit in one direction only. It flows provided a di- rect voltage source is applied to the circuit. The current from a cell is direct current.
Alternating current (AC) is current that changes its direction of flow through a circuit. It flows provided an alternating voltage source is applied to the circuit. The electricity supplied to homes and other buildings – called mains electricity – is alternating current. Alternating current flows in cycles. The number of cycles per second is called the frequency of the cur- rent. For example, in the UK, AC supply is 50 Hz – it alternates 50 times per second.
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The current supplied to most homes is single-phase – it forms one si- ne wave. In factories and large buildings, which have powerful electrical equipment, the supply if often three-phase – effectively three currents, each with a different phase (timing). This provides a smoother supply as it re- duces the gaps between the voltage peaks.
It is easy to transform AC power from one voltage to another using a transformer. Transformers are also used to step down the voltage at the re- ceiving point of the line to the low values that are necessary for use.
AC can be changed into DC but this is seldom necessary.
