Tiếng Anh chuyên ngành Kỹ thuật điện (Phần 2) - Nguyễn Quốc Hùng
Exercise 4 Read the passage carefully and decide whether the statements
are true (T) or false (F)
A variant of the wound field DC motor is the universal motor. The name derives
from the fact that it may use AC or DC supply current, although in practice they
are nearly always used with AC supplies. The principle is that in a wound field
DC motor the current in both the field and the armature (and hence the resultant
magnetic fields) will alternate (reverse polarity) at the same time, and hence the
mechanical force generated is always in the same direction. In practice, the
motor must be specially designed to cope with the AC current (impedance must
be taken into account, as must the pulsating force), and the resultant motor is
generally less efficient than an equivalent pure DC motor. Operating at normal
power line frequencies, the maximum output of universal motors is limited and
motors exceeding one kilowatt are rare. But universal motors also form the basis
of the traditional railway traction motor in electric railways. In this application,
to keep their electrical efficiency high, they were operated from very low
frequency AC supplies, with 25 Hz and 16 2/3 hertz operation being common.
Because they are universal motors, locomotives using this design were also
commonly capable of operating from a third rail powered by DC.
The advantage of the universal motor is that AC supplies may be used on motors
which have the typical characteristics of DC motors, specifically high starting
torque and very compact design if high running speeds are used. The negative
aspect is the maintenance and short life problems caused by the commutator. As
a result such motors are usually used in AC devices such as food mixers and
power tools which are used only intermittently. Continuous speed control of a
universal motor running on AC is very easily accomplished using a thyristor
circuit, while stepped speed control can be accomplished using multiple taps on
the field coil. Household blenders that advertise many speeds frequently
combine a field coil with several taps and a diode that can be inserted in series
with the motor (causing the motor to run on half-wave rectified AC).
1. The universal motor can operate in AC only.
2. Impedence is not important in designing a universal motor.
3. It is dificult for a universal motor to produce the output of over one
kilowatt when operating at normal power line frequencies.
4. The commutator can work for a short time.
5. A thyristor circuit is a solution to continuous speed control of a universal
motor running on AC
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Tiếng Anh chuyên ngành Kỹ thuật điện 27 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Unit 6 Electric Motors Vocabulary and Pronunciation Exercise 1 Match English terms and Vietnamese translations English Vietnamese 1. mechanical energy Cổ góp 2. armature Cơ năng 3. reverse polarity cuộn dây kích thích 4. impedance đảo cực 5. pulsating force đầu máy xe lửa 6. traction motor Động cơ kéo 7. electric railways Động cơ xén cỏ 8. locomotives Đường xe điện 9. torque lực mạch động 10. compact design Mạch tyristo 11. commutator mô men xoắn, mô men quay 12. thyristor circuit nửa chu kỳ 13. half-wave Phần ứng 14. revolutions per minute (rpm) Ray tiếp xúc 15. weed trimmer motors số vòng quay trong một giây 16. field windings thiết kế nhỏ gọn 17. third rail Trở kháng Tiếng Anh chuyên ngành Kỹ thuật điện 28 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 2 T.S 1 Listen and practise 1. mechanical energy 7. electric railways 13. half-wave 2. armature 8. locomotives 14. revolutions per minute (rpm) 3. reverse polarity 9. torque 15. weed trimmer motors 4. impedance 10. compact design 16. field windings 5. pulsating force 11. commutator 17. third rail 6. traction motor 12. thyristor circuit Exercise 3 T.S 2 Listen and complete the sentences by selecting the correct word from the box to fill in the gap mechanical energy electric railways half-wave armature locomotives revolutions per minute (rpm) reverse polarity torque weed trimmer motors impedance compact design field windings pulsating force commutator third rail traction motor thyristor circuit 1. An inside rotor attached to the output shaft that is given a by the rotating field. 2. An electric motor uses electrical energy to produce 3. Universal motors can rotate at relatively ..(rpm). 4. a small fan blade attached to the acts as an artificial load to limit the motor speed to a safe value. 5. By changing the connected to the rotor circuit, the speed/current and speed/torque curves can be altered. Tiếng Anh chuyên ngành Kỹ thuật điện 29 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi reading: Universal motors Exercise 4 Read the passage carefully and decide whether the statements are true (T) or false (F) A variant of the wound field DC motor is the universal motor. The name derives from the fact that it may use AC or DC supply current, although in practice they are nearly always used with AC supplies. The principle is that in a wound field DC motor the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) at the same time, and hence the mechanical force generated is always in the same direction. In practice, the motor must be specially designed to cope with the AC current (impedance must be taken into account, as must the pulsating force), and the resultant motor is generally less efficient than an equivalent pure DC motor. Operating at normal power line frequencies, the maximum output of universal motors is limited and motors exceeding one kilowatt are rare. But universal motors also form the basis of the traditional railway traction motor in electric railways. In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 Hz and 16 2/3 hertz operation being common. Because they are universal motors, locomotives using this design were also commonly capable of operating from a third rail powered by DC. The advantage of the universal motor is that AC supplies may be used on motors which have the typical characteristics of DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. As a result such motors are usually used in AC devices such as food mixers and power tools which are used only intermittently. Continuous speed control of a universal motor running on AC is very easily accomplished using a thyristor circuit, while stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC). 1. The universal motor can operate in AC only. 2. Impedence is not important in designing a universal motor. 3. It is dificult for a universal motor to produce the output of over one kilowatt when operating at normal power line frequencies. 4. The commutator can work for a short time. 5. A thyristor circuit is a solution to continuous speed control of a universal motor running on AC Tiếng Anh chuyên ngành Kỹ thuật điện 30 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 5 Choose a correct word to fill in the gap useful rotate limit cost into permanent due to exceed Universal motors can . (1)at relatively high revolutions per minute (rpm). This makes them . (2)for appliances such as blenders, vacuum cleaners, and hair dryers where high-speed operation is desired. Many vacuum cleaner and weed trimmer motors exceed 10,000 rpm, Dremel and other similar miniature grinders will often .(3)30,000 rpm. Motor damage may occur . (4)overspeed (rpm in excess of design specifications) if the unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated (5)the motor's protection and control schemes. Often, a small fan blade attached to the armature acts as an artificial load to (6)the motor speed to a safe value, as well as provide cooling airflow to the armature and field windings. With the very low (7)of semiconductor rectifiers, some applications that would have previously used a universal motor now use a pure DC motor, sometimes with a . (8)magnet field. Exercise 6 Complete the sentences by finding the missing letters 1. The energy acquired by the objects upon which work is done is known as m.l energy. 2. In electrical engineering, an a.e is one of the two principal electrical components of an electromechanical machine--a motor or generator. 3. Electrical ie describes a measure of opposition to a sinusoidal alternating current (AC). 4. A t.n motor is a type of electric motor used to power the driving wheels of a vehicle such as a railroad locomotive, electrical multi-unit train (such as a subway or light rail vehicle train), a tram, or an automobile. 5. A le is a railway vehicle that provides the motive power for a train. Tiếng Anh chuyên ngành Kỹ thuật điện 31 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi 6. A te (τ) in physics, also called a moment, is a vector that measures the tendency of a force to rotate an object about some axis. 7. A c.r is an electrical switch that periodically reverses the current direction in an electric motor or electrical generator. 8. R.ns per minute (abbreviated rpm, RPM, r/min, or r·min−1) is a unit of frequency: the number of full rotations completed in one minute around a fixed axis. Tiếng Anh chuyên ngành Kỹ thuật điện 32 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Unit 7 Batteries Vocabulary and Pronunciation Exercise 1 Match English terms and Vietnamese translations English Vietnamese Battery pin sơ cấp Charge pin địên phân charging current có thể nạp lại chemical energy pin thứ cấp chemical reaction pin nhiên liệu Discharge nạp, sạc Disposable dòng điện nạp (sạc) electrochemical pin, ắc quy electrolytic cell phản ứng hóa học fuel cell pin vonta irreversible reaction dùng một lần primary cell phản ứng không thuận nghịch Rechargeable hóa năng secondary cell xả, phóng điện voltaic pile điện hóa Exercise 2 T.S 1 Listen and practise 1. battery 6. discharge 11. irreversible reaction 2. charge 7. disposable 12. primary cell 3. charging current 8. electrochemical 13. rechargeable 4. chemical energy 9. electrolytic cell 14. secondary cell 5. chemical reaction 10. fuel cell 15. voltaic pile Tiếng Anh chuyên ngành Kỹ thuật điện 33 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 3 T.S 2 Listen and complete the sentences by selecting the correct word from the box to fill in the gap fuel cell secondary cells irreversible reaction Charge electrolytic cell primary cell charging current electrochemical rechargeable 1. A is an electrochemical conversion device. 2. An is an reaction which cannot be changed. 3. . is the current that flows into a capacitor when a voltage is first applied. 4. A rechargeable battery is a group of two or more . . 5. The anode of an is positive, and the cathode is negative. Reading: Battery In electronics, a battery is two or more electrochemical cells which store chemical energy and make it available as electrical energy. Common usage has evolved to include a single electrical cell in the definition. There are many types of electrochemical cells, including galvanic cells, electrolytic cells, fuel cells, flow cells and voltaic piles. A battery's characteristics may vary due to many factors including internal chemistry, current drain and temperature. One common division of batteries distinguishes two types: primary (disposable) and secondary (rechargeable). Primary batteries are designed to be used once only because they use up their chemicals in an effectively irreversible reaction. Secondary batteries can be recharged because the chemical reactions they use are reversible; they are recharged by running a charging current through the battery, but in an opposite direction to the discharge current. Secondary, also called rechargeable batteries can be charged and discharged many times before wearing out. After wearing out some batteries can be recycled. Tiếng Anh chuyên ngành Kỹ thuật điện 34 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi The name "battery" was coined by Benjamin Franklin for an arrangement of multiple Leyden jars (an early type of capacitor) after a battery of cannon. Although an early form of electrochemical battery may have been used in antiquity, the modern development of batteries started with the Voltaic pile, invented by the Italian physicist Alessandro Volta in 1800. Since then, batteries have gained popularity as they became portable and useful for many purposes. The widespread use of batteries has created many environmental concerns, such as toxic metal pollution. Many reclamation companies recycle batteries to reduce the number of batteries going into landfills. Exercise 4: Are these sentences true (T) or false (F)? 1. A battery is two or more electrochemical cells which store electrical energy and make it available as chemical energy. 2. Internal chemistry, current drain and temperature are factors that contribute to a battery's characteristics. 3. A primary battery is rechargeable while a secondary is disposable. 4. In primary batteries, the chemical reactions are reversible while in secondary batteries, the chemical reactions are irreversible. 5. Secondary batteries can be charged and discharged many times before wearing out. 6. An early form of electrochemical battery was invented by the Italian physicist Alessandro Volta in 1800 7. Since the invention of the Voltaic pile, batteries have gained popularity as they became portable and useful for many purposes. 8. One of the environmental concerns caused by use of batteries is toxic metal pollution. listening: Exercise 5 Listen to T.S3 and fill in the blanks with the words given Environment chemicals purchase Landfills regulations materials Services harmful elements Mercury Batteries - Environmental concerns Battery manufacture consumes resources and often involves hazardous (1) . Used batteries also contribute to electronic waste. Some areas now have battery recycling (2) available to recover some of the (3) Tiếng Anh chuyên ngành Kỹ thuật điện 35 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi from used batteries. Batteries may be (4) .. or fatal if swallowed. Recycling or proper disposal prevents dangerous (5) .. (such as lead, mercury, and cadmium) found in some types of batteries from entering the (6) . In the United States, Americans (7) .. nearly three billion batteries annually, and about 179,000 tons of those end up in (8) .. across the country. In the United States the Environmental Protection Agency’s Mercury-Containing and Rechargeable Battery Management Act of 1996, has reduced the amount of (9) . in regular household batteries. Recycling programs for lead and cadmium batteries have been put in place. Recycling and disposal (10) .. may in the future apply to alkaline and nickel-metal hydride batteries. Language work We use CAN to express possiblity or ability: S + CAN + V infinitive E.g We can produce electricity using a generator. Exercise 6 Match a line in A with a line in B to make meaningful sentences. A B 1. We can recharge a. light bulbs to either AC or DC sources. 2. We can extended b. a simple wet zinc-carbon battery in the laboratory using dilute sulphuric acid as an electrolyte solution. 3. We can make c. the simple half wave rectifier in two versions with the diode pointing in opposite directions. 4. We can connect d. secondary batteries by applying electrical current. 5. We can build e. battery life by storing the batteries at a low temperature. When we change the sentence into passive, we can use the fomula: S + CAN + BE + PAST PARTICIPAL E.g. Active: We can produce electricity using a generator. Passive: Electricity can be produced using a generator. Tiếng Anh chuyên ngành Kỹ thuật điện 36 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 7 Change the following sentences into passive 1. We can recharge secondary batteries by applying electrical current. 2. We can extend battery life by storing the batteries at a low temperature. 3. We can make a simple wet zinc-carbon battery in the laboratory using dilute sulphuric acid as an electrolyte solution. 4. We can connect light bulbs to either AC or DC sources. 5. We can build the simple half wave rectifier in two versions with the diode pointing in opposite directions. Tiếng Anh chuyên ngành Kỹ thuật điện 37 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Unit 8 Incandescent light bulb Vocabulary and Pronunciation Exercise 1 Match English terms and Vietnamese translations English Vietnamese 1. incandescence bóng thủy tinh 2. filament quang phổ liên tục 3. glass bulb dây tóc 4. headlamp đèn huỳnh quang 5. tungsten nóng sáng 6. fluorescent light đui cài 7. high-intensity ánh sáng nhìn thấy 8. inert gas vonfram 9. continuous spectrum cường độ cao 10. visible light đèn pha 11. screw base khí trơ 12. bayonet base tiếp xúc 13. leak (n,v) rò rỉ 14. insulation cách (điện ... centrically) 2. directly connected resistor (A resistor which is connected directly) 3. positively charged atom (An atom which carries positive charge) 4. electrically operated mechanism (A mechanism which is operated electrically) 5. manually operated bridge (A bridge which is operated manually) 6. eletromagnetically coupled detector (A detector which is coupled eletromagnetically) Tiếng Anh chuyên ngành Kỹ thuật điện 42 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Unit 9 Circuit breaker Vocabulary and Pronunciation Exercise 1 Match English terms and Vietnamese translations English Vietnamese 1. arc lỗi, trục trặc, hư hỏng 2. circuit breaker bộ biến đổi, biến thế, biến áp 3. compressed air đoản mạch, ngắn mạch 4. electrical circuit công tắc 5. fault không khí nén 6. fuse mạch điện 7. latch cắt điện, cầu giao 8. overload hồ quang 9. Relay cơ cấu đóng mạch, chuyển mạch 10. self-contained chốt, then 11. short circuit độc lập, có đủ các bộ phận 12. Spring Quá tải 13. switch rơ le 14. switchgear lò xo 15. transformer cầu chì Exercise 2 T.S 1 Listen and practise 1. arc 6. fuse 11. short circuit 2. circuit breaker 7. latch 12. spring 3. compressed air 8. overload 13. switch 4. electrical circuit 9. relay 14. switchgear 5. fault 10. self-contained 15. transformer Tiếng Anh chuyên ngành Kỹ thuật điện 43 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 3 T.S 2 Listen and complete the sentences by selecting the correct word from the box to fill in the gap Transformer fuses short circuit circuit breakers switch spring electrical circuit Relay switchgear 1. An . is a path which electrons from a voltage or current source follow. 2. A usually consists of two coils of wire wound on the same core. 3. A allows a current along a different path from the one intended. 4. A is an electrical . that opens and closes under the control of another electrical circuit. 5. The term refers to the combination of electrical disconnects, .. and used to isolate electrical equipment. Listening Exercise 4 Listen to T.S3 and fill in the blanks with the words given Operation circuits replaced Application switch overload fuses short-circuits switchgear A 2 pole miniature circuit breaker Photo of inside of a circuit breaker Tiếng Anh chuyên ngành Kỹ thuật điện 44 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Circuit Breakers A circuit breaker is an automatically-operated electrical (1) designed to protect an electrical circuit from damage caused by (2) . or short circuit. Unlike a fuse, which operates once and then has to be (3) , a circuit breaker can be reset either manually or automatically to resume normal (4) .. . Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large (5) . designed to protect high voltage (6) feeding an entire city. An early form of circuit breaker was described by Edison in an 1879 patent (7) , although his commercial power distribution system used (8) . . Its purpose was to protect lighting circuit wiring from accidental (9) . and overloads. reading Operation of Circuit Breakers All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high- voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically stored energy within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. The stored energy may be in the form of springs or compressed air. Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature circuit breakers are usually discarded when the Tiếng Anh chuyên ngành Kỹ thuật điện 45 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts. When a current is interrupted, an arc is generated - this arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms. Exercise 5: Are the following sentences true (T) or false (F)? 1. All circuit breakers have common features in their operation, but details are not always the same. 2. In low-voltage circuit breakers a fault condition is detected within the breaker enclosure. 3. The only function of pilot devices is to sense a fault current. 4. The trip solenoid that releases the latch is self-contained with current transformers, protection relays, and an internal control power source. 5. Contacts within the circuit breaker must open to interrupt the circuit when some mechanically stored energy within the breaker is used to separate the contacts. 6. The circuit breaker contacts must withstand the heat of the arc produced when interrupting the circuit. 7. The erosion due to interrupting the arc limits the service life of the contacts. 8. Miniature circuit breakers are usually replaced when the contacts are worn. 9. When a current is interrupted, an arc is extinguished in a controlled way by the current. 10. Vacuum, air, insulating gas, or oil can be used in different circuit breakers. Language work: Noun phrase (2) A noun phrase in English may take the following structure: Noun + Past Participle + Noun E.g: A hand operated valve The noun phrase ‘A hand operated valve’ means “a valve which is operated by hand” Tiếng Anh chuyên ngành Kỹ thuật điện 46 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 6 Now convert each of the following clauses into a noun phrase E.g: A valve which is operated by hand Æ a hand operated valve 1. transformer which is cooled by air 2. engineering which is aided by a computer 3. switchgear which is insulated by gas 4. end which is sprayed with metal 5. valve which is operated by a motor 6. screen which is coated with phosphor Exercise 7 Translate the noun phrases into Vietnamese E.g: hand operated valve (valve which is operated by hand) Æ van được thao tác bằng tay 1. air-cooled transformer (transformer which is cooled by air) 2. computer-aided enginnering (engineering which is aided by a computer) 3. gas-insulated switchgear (switchgear which is insulated by gas) 4. metal-sprayed end (metal sprayed end) 5. motor-operated valve (valve which is operated by a motor) 6. phosphor-coated screen (screen which is coated with phosphor) Tiếng Anh chuyên ngành Kỹ thuật điện 47 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Unit 10 Rectifier Vocabulary and Pronunciation Exercise 1 Match English terms and Vietnamese translations English Vietnamese 1. alternating current dạng sóng 2. anode bộ chỉnh lưu, bộ nắn dòng 3. arc dòng xoay chiều 4. cathode chỉnh lưu cả sóng 5. center-tapped hồ quang 6. direct current phân cực, cực tính 7. full-wave rectification cực dương 8. half wave rectification nửa dương 9. inverter đèn chân không 10. negative half dòng một chiều 11. polarity cực âm 12. positive half nửa âm 13. rectifier bộ đảo điện, bộ đảo lưu 14. vacuum tube trích giữa 15. waveform chỉnh lưu nửa sóng Exercise 2 T.S 1 Listen and practise 1. alternating current 6. direct current 11. polarity 2. anode 7. full-wave rectification 12. positive half 3. arc 8. half wave rectification 13. rectifier 4. cathode 9. inverter 14. vacuum tube 5. center-tapped 10. negative half 15. waveform Tiếng Anh chuyên ngành Kỹ thuật điện 48 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Exercise 3 T.S 2 Listen and complete the sentences by selecting the correct word from the box to fill in the gap. alternating current direct current anode arc center-tapped rectifier cathode inverter vacuum tube 1. A transformer is a transformer with a tap in the middle of the secondary winding. 2. An .. is an electrical device that converts to . 3. Some special function are filled with low-pressure gas. 4. An .. is an electrode through which electric current flows into a polarized electrical device. 5. A is an electrode through which electric current flows out of a polarized electrical device. listening: Exercise 4 Listen to T.S3 and fill in the blanks with the words given detectors convert diodes components arrangement difference converts rectification development function A rectifier is an electrical device that (1) alternating current (AC) to direct current (DC), a process known as (2) .. . Rectifiers have many uses including as components of power supplies and as (3) .. of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other (4) . . A device which performs the opposite (5) .. (converting DC to AC) is known as an inverter. When only one diode is used to rectify AC (by blocking the negative or positive portion of the waveform), the (6) between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to (7) .. AC to DC. Almost all rectifiers comprise a number of diodes in a specific (8) for more efficiently converting AC to DC than is possible with only one diode. Before the (9) of silicon semiconductor rectifiers, vacuum tube (10) and copper(I) oxide or selenium rectifier stacks were used. Tiếng Anh chuyên ngành Kỹ thuật điện 49 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi Reading Half-wave rectification In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a single diode in a one phase supply, or with three diodes in a three-phase supply. Full-wave rectification A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center tapped transformer, four diodes are required instead of the one needed for half-wave rectification. (See semiconductors, diode). Four rectifiers arranged this way are called a diode bridge or bridge rectifier: For single-phase AC, if the transformer is center-tapped, then two diodes back- to-back (i.e. anodes-to-anode or cathode-to-cathode) form a full-wave rectifier (in this case, the voltage is half of that for the non-tapped bridge circuit above, and the diagram voltages are not to scale). A very common vacuum tube rectifier configuration contained one cathode and twin anodes inside a single envelope; in this way, the two diodes required only Tiếng Anh chuyên ngành Kỹ thuật điện 50 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi one vacuum tube. The 5U4 and 5Y3 were popular examples of this configuration. Full-wave rectifier, with vacuum tube having two anodes. For three-phase AC, six diodes are used. Typically there are three pairs of diodes, each pair, though, is not the same kind of double diode that would be used for a full wave single-phase rectifier. Instead the pairs are in series (anode to cathode). Typically, commercially available double diodes have four terminals so the user can configure them as single-phase split supply use, for half a bridge, or for three-phase use. Exercise 5: Are the following sentences true (T) or false (F)? 1. In half wave rectification, only one half of the AC wave is passed, while the other half is blocked. 2. Half-wave rectification can only be achieved with a single diode in a one phase supply. 3. Full-wave rectification converts both halves of the AC wave to DC. 4. Full-wave rectification is more efficient than half-wave rectification. 5. In half-wave rectification, more diodes are used than in full-wave rectification. 6. A recfifier with a center-tapped transformer requires more diodes than a rectifier with a non-center tapped transformer. Tiếng Anh chuyên ngành Kỹ thuật điện 51 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi 7. A recfifier with a center-tapped transformer is more efficient than a rectifier with a non-center tapped transformer. 8. A common vacuum tube rectifier configuration contained one anode and twin cathodes inside a single envelope. 9. For three-phase AC, three pairs of diodes are used. Language work: Noun phrase (3) A noun phrase in English may take the following structure: Noun + Present Participle + Noun E.g: A current-carrying conductor The noun phrase ‘A current-carrying conductor’ means “a conductor which is carrying a current” Exercise 6 Now convert each of the following clauses into a noun phrase E.g: a conductor which is carrying a current Æ A current-carrying conductor 1. radar which can find direction 2. material which conducts current 3. material which insulates heat 4. device which can sense temperature 5. pump which feeds oil 6. system which processes data Exercise 7 Translate the noun phrase into Vietnamese A current-carrying conductor (a conductor which is carrying a current) Æ vật dẫn mang dòng 1. direction finding radar (radar which can find direction) 2. current conducting material (material which conducts current) 3. heat insulating material (material which insulates heat) 4. temperature sensing device (device which can sense temperature) 5. oil feeding pump (pump which feeds oil) 6. data processing system (which processes data) Tiếng Anh chuyên ngành Kỹ thuật điện 52 www.bea.vn: Caùch hoïc môùi – Tri thöùc môùi REFERENCES http//wiki pedia.org/ Jump to: navigation, search www.viasatellite.com/glossary/glossary2.html
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