ELECTRICAL SUPPLY PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 44. ELECTRICAL SUPPLY

 

A Direct current and alternating current The current from a cell is direct current (DC) – a constant flow of electricity which travels around a circuit in one direction. The electricity supplied to homes and other buildings – called mains electricity – is alternating current (AC). Unlike a DC supply, an AC supply flows backwards and forwards – its direction continually alternates. The rate at which the current alternates – called frequency – is measured in hertz (Hz). For example, in the UK, AC supply of mains electricity forms a sine wave. B AC generation and supply Mains electricity is generated (produced) at sites called power stations, which use large generators. A generator converts mechanical energy to electrical energy. A generator rotates a magnet within an iron surround. The iron – called an armature – has coils of wire around it, called field coils (or filed windings). As the magnet rotates, it causes current to flow through the field coils, due to electromagnetic induction. C DC generation and use The extract below is from a consumer magazine. Photovoltaic cells (PVs) – or solar cells – are an effective way of generating your own electricity from sunlight. The current they produce can be used immediately, may be stored in rechargeable batteries (like the ones in cars), or can be fed into the power grid and sold to the electric company. But PVs produce direct current. This is fine for charging batteries, but is not suitable for powering household appliances, which require alternating current. For this, the DC supply from PVs and batteries needs to go through an inverter – a device which converts DC to AC. EXERCISES 44.1 Complete the text about inverters using words from A opposite. Look at A, B, and C opposite to help you. Inverters convert (1)________________ _____________________ to (2)________________ _____________________. If an inverter is used to supply electrical appliances in a home, it must copy the supply of (3)________________ _____________________ electricity produced by the generators at power stations. Most inverters can produce a current 44.2 Choose the correct words from the brackets to complete the descriptions of different stages of AC generation and supply (a-f). then, put the stages in the correct order. Look at N opposite to help you. a. After the step-up transformer, the  current enters a (distribution/ transmission) line. b. Current is produced, by electromagnetic induction, in the (magnet/ filed coils) of a generator. 44.3 Decide whether the sentences below are true or false, and correct the false sentences. Look at A, B and C opposite to help you. 1. Photovoltaic cells produce direct current 2. The electricity supply from PVs can be used to charge rechargeable batteries.

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