Unit 6 Transformers. Lead-in. Basic principles. Task 1. Task 2. What applications of transformers do you know?

Transcription

1 Unit 6 Transformers Lead-in What applications of transformers do you know? Basic principles Task 1 Match the words and phrases with the translations. 1. magnetic field 2. induced voltage 3. conductors 4. primary voltage 5. circuit 6. number of turns 7. winding 8. stepped up 9. power transmission 10. ferromagnetic core 11. electronic circuits 12. stepped down 13. coils 14. mutual induction 15. power grids 16. magnetic flux 17. electromotive force a) strumień magnetyczny b) rdzeń ferromagnetyczny c) obwód d) napięcie pierwotne (zasilające) e) cewki f) (tutaj) zwiększany g) pole magnetyczne h) napięcie indukowane i) przewodniki j) sieci elektryczne k) ilość zwojów l) przesyłanie energii m) obwód elektroniczny n) (tutaj) zmniejszany o) indukcja wzajemna p) siła elektromotoryczna q) uzwojenie Task 2 Read the text about transformers and complete it with the words and phrases from Task 1. magnetic field winding mutual induction conductors A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled (1) the transformer s coils. A varying current in the first or primary (2).creates a varying magnetic flux in the transformer s core, and thus a varying (3).. through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding. This effect is called (4).. number of turns primary voltage ferromagnetic core induced voltage If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the (5).. in the secondary winding 1

2 (V S ) is in proportion to the (6). (V P ), and is given by the ratio of the (7) in the secondary (N S ) to the number of turns in the primary (N P ) as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be stepped up by making N S greater than N P, or stepped down by making N S less than N P. In the vast majority of transformers, the windings are coils wound around a (8), air-core transformers being a notable exception. power transmission power grids electronic circuits Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of (9).. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some (10)., transformers are still found in nearly all electronic devices designed for household ( mains ) voltage. Transformers are essential for high voltage (11).., which makes long distance transmission economically practical. Adapted from Task 3 Label the diagram of an ideal transformer. Primary voltage Secondary current Transformer core Secondary voltage Primary winding Primary current Secondary winding Adapted from 2

3 Types and construction of transformers Task 4 a) Match the names with the descriptions. Power transformers Auto transformer Instrument potential transformer Distribution transformers Instrument current transformer Control transformers Isolation transformers Transformers are constructed so that their characteristics match the application for which they are intended. The differences in construction may involve the size of the windings or the relationship between the primary and secondary windings. Transformer types are also designated by the function the transformer serves in a circuit. A... are generally used in electrical power distribution and transmission systems. This class of transformers has the highest power, or volt-ampere ratings, and the highest continuous voltage rating. The power rating is normally determined by the type of cooling methods the transformer may use. Some commonly-used methods of cooling are by using oil or some other heat-conducting material. Ampere rating is increased in a distribution transformer by increasing the size of the primary and secondary windings; voltage ratings are increased by increasing the voltage rating of the insulation used in making the transformer. B... are used in electronic circuits and come in many different types and applications. Electronics or power transformers are sometimes considered to be those with ratings of 300 volt-amperes and below. These transformers normally provide power to the power supply of an electronic device, such as in power amplifiers in audio receivers. C... are generally used in electronic circuits that require constant voltage or constant current with a low power or volt-amp rating. Various filtering devices, such as capacitors, are used to minimize the variations in the output. This results in a more constant voltage or current. D The... is generally used in low power applications where a variable voltage is required. The auto transformer is a special type of power transformer. It consists of only one winding. By tapping or connecting at certain points along the winding, different voltages can be obtained (Figure 8). Figure 8... Schematic 3

4 E... are normally low power transformers used to isolate noise from or to ground electronic circuits. Since a transformer cannot pass DC voltage from primary to secondary, any DC voltage (such as noise) cannot be passed, and the transformer acts to isolate this noise. F The... (PT) steps down voltage of a circuit to a low value that can be effectively and safely used for operation of instruments such as ammeters, voltmeters, watt meters, and relays used for various protective purposes. G The... (CT) steps down the current of a circuit to a lower value and is used in the same types of equipment as a potential transformer. This is done by constructing the secondary coil consisting of many turns of wire, around the primary coil, which contains only a few turns of wire. In this manner, measurements of high values of current can be obtained. A current transformer should always be short-circuited when not connected to an external load. Because the magnetic circuit of a current transformer is designed for low magnetizing current when under load, this large increase in magnetizing current will build up a large flux in the magnetic circuit and cause the transformer to act as a step-up transformer, inducing an excessively high voltage in the secondary when under no load. Adapted from b) Complete the expressions with appropriate prepositions. What other prepositions can be used? 1. differences 2. relationship 3. designated used result 6. consist isolate... c) Find words in the text which match the following definitions the rate at which a device converts electrical energy into another form of energy, such as light, heat, or motion or maximum power to be used with that device (par. A) 2. material material which allows heat to go through (par. A) 3.. a piece of equipment that changes radio and television signals into sounds and pictures (par. B) 4.. a device which collects and stores electricity (Par. C) 5.. an amount of something produced by a person, machine, factory, country, etc (par. C) 6.. a conducting connection between an electric circuit or equipment and the earth or some other conducting body (par. E) 7.. a device that reacts to a small change in an electrical current by moving switches or other devices in an electrical circuit (par. F) 8.. giving protection (par. F) 9.. continuous change (par. G) 4

5 d) Now complete the following sentences with expressions from part a) 1. It comprises a transmitter and a portable which is designed to be moved from one location to another as required. 2. A..ed wire on a lightning rod leads large electric charges from the atmosphere directly to Earth, preventing them from taking other paths that might result in damage to property or injury to persons. 3. If several powerheads are being used, they should all be of the same make and to provide maximum efficiency. 4. Ramtron aims in future to actually replace the.. with a small amount of ceramic embedded in the chip. 5. The BBC has always maintained that it needs more spectrum for each service to be able to provide more. stations in remote areas. 6. Researchers will present this plastic at the Composites trade fair in October. 7. Our plans are in a state of.. at the moment. 8. Last year British manufacturing. fell by 14%. 9. The crash crew person had to don the.. clothing after arriving at the scene. Task 5 Write three questions based on the text to check your partner s comprehension Task 6 Watch the video about ABB transformers presenting the process of design and construction and complete the sentences with appropriate words and phrases. 1. Transformer designers. the important data. 2. The core is made up of. laminations. 3. The highest level of precision is guaranteed because of of sheets 4. For the windings the manufacturers use insulated electrolytic. 5. Factors taken into account during production are.., expectations and electric and During the work any kind of. should be avoided. 7. Drying process is crucial as... may deteriorate performance. 8. Tank designs are affected by such factors as the,. and. 9. Weld testing usually includes:..,.. and ultrasonic Manufacturing process can be accommodated to special...., such as cooling systems,...,...,... onload tab changers and... 5

6 11. Transformers can be tested in following types of tests: -.. and switching impact test - induced.tests -.. tests. Recording from Task 7 Match the words in column A with the words from column B to create whole phrases and translate the phases into Polish. expressions with verbs A 1. to evaluate 2. to take 3. to jeopardize 4. to meet 5. to subcontract out 6. to exercise 7. to accommodate B a) special customer requirements b) responsibility c) relevant data d) transformer performance e) requirements f) work g) precautions to avoid sth expressions with adjectives A 1. tailor- 2. highly- 3. cost- 4. closely- 5. stringing 6. on- B a) overseen b) efficient c) made designs d) standards e) site test f) trained staff 6