Учебное пособие предназначено для бакалавров всех специальностей и направлений подготовки радиотехнического факультета. В нем представлены материалы для аудиторной и самостоятельной работы
 Скачать 1.03 Mb.
|
UNIT 11Task 1. Study new words and word combinations.
TASK 2. Read the text and translate it from English into Russian. TRANSFORMERS A transformer is a device which is used to transfer electrical energy from one circuit to another. Besides, a transformer is used to change the voltage and current in a circuit. A transformer is based on the fundamental principle of mutual induction. A simple transformer consists of two coils and a core. The coils are called the primary and the secondary. These coils are wound over a common core. Transformers can have either air or magnetic cores. It depends on the frequency at which they are to be operated. The primary winding is connected to the voltage source. It receives energy. The secondary winding is connected to the load resistance and supplies energy to the load. There are two types of transformers: a step-up transformer and a step-down transformer. In a step-down transformer the number of turns in the primary is greater than the number of turns in the secondary. This transformer steps down the voltage. In a step-up transformer the number of turns in the secondary is greater than in the primary. The important thing in transformer design is the insulation of windings. There are 3 main classifications of transformers: for power-frequency circuits, for audio-frequency and for radio frequency. TASK 3. Complete the sentences. 1. A transformer is a device which is used to . . . 2. A transformer is based on . . . 3. The coils of the transformer are called . . . 4. The primary winding of the transformer is connected . . . 5. The important thing in transformer design is . . . TASK 4. Answer the following questions and retell the text. 1. What is a transformer used for? 2. What principle is a transformer based on? 3. What cores can transformers have? 4. What is the function of a primary winding? 5. What two types of transformers does the text discuss? 6. What is the important thing in transformer design? 7. What three main classifications of transformers do you know? TASK 5. Make up the sentences using the following words and word combinations. A transformer, a device, to transfer electrical energy, to change voltage and current in a circuit, mutual induction, two coils, a core, the primary winding, the secondary winding, to receive energy, to supply energy, a step-up transformer, a step-down transformer, the number of turns, the insulation of windings. TASK 6. Translate the sentences, pay attention to the degrees of comparison. The simplest condenser consists of two plates separated by an insulator. 2. In practice the most common types of dielectrics are: air, mica, paper. 3. We think that he is the best inventor of our plant. 4. I work worse than he does. 5. This new device works better that the old one. 6. Scientists try to get better knowledge of the mineral resources of this region. 7. The proton was found to be 1,840 times heavier than the electron. 8. Radio is one of the greatest achievements of modern engineering. TASK 7. Read the text about transformers and complete it with the following words and phrases.
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) … .
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(VS) is in proportion to the 6) … (VP), and is given by the ratio of the 7) … in the secondary (NS) to the number of turns in the primary (NP) 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 NS greater than NP, or “stepped down” by making NS less than NP. In the vast majority of transformers, the windings are coils wound around a 8) … , air-core transformers being a notable exception.
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. TASK 8. 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. 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. TASK 9. 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 …. 6. 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 …. 10. Manufacturing process can be accommodated to special … , such as cooling systems, …, …, … on load tab changers and …. 11. Transformers can be tested in following types of tests: … and switching impact test; induced …tests; … tests. TASK 10. Match the words in column A with the words from column B to create whole phrases. Expressions with verbs:
|