外文翻译变压器Word下载.docx

1、TRANSFORMERTransformers come in many sizes. Some power transformers are as big as a house. Electronic transformers, on the other hand, can be as small as a cube of sugar. All transformers have at least one coil. Most have two although they may have many more.The usual purpose of transformers is to c

2、hange the level of voltage. But sometimes they are used to isolate a load from the power source.TYPES OF TRANSFORMERSStandard power transformers have two coils. These coils are labeled PRIMARY and SECONDARY. The primary coil is the one connected to the source. The secondary is the one connected to t

3、he load. There is to no electrical connection between the primary and secondary. The secondary gets its voltage by induction.The only place where you will see a STEP-UP transformer is at the generating station. Typically, electricity is generated at 13,800 volts. It is stepped down to distribution l

4、evels, around 15,000 volts. Large substation transformers have cooling fins to keep them from overheating. Other transformers are located near points where the electric power is used. TRANSFORMER CONSTRUCTIONThe coils of a transformer are electrically insulated from each other. There is a magnetic l

5、ink, however. The two coils are wound on the same core. Current in the primary magnetizes the core. This produces a magnetic field in the core. The core field then affects current in both primary and secondary.There are two main designs for cores:1.The CORE type has the core inside the windings.2.Th

6、e SHELL type has the core outside.Smaller power transformers are usually of the core type. The very large transformers are of the shell type. There is no difference in their operation, however.Coils are wound with copper wire. The resistance is kept as low as possible keep losses low.IDEALIZED TRANS

7、FORMERS Transformers are very efficient. The losses are often less than 3 percent. This allows us to assume that they are perfect in many computations.Perfect means that the wire has no resistance. It also means that there are no power losses in the core.Further, we assume that there is no flux leak

8、age. That is, all of the magnetic flux links all of the turns on each coil.EXCITATION CURRENTTo get an idea of just how small the losses are, we can take a look at the EXCITATION CURRENT. Assume that nothing is connected to the secondary. If you apply rated voltage to the primary, a small current fl

9、ows. Typically, this excitation current is less than 3 percent of rated current.Excitation current is made up of two part is in phase with the voltage. This is the current that supplies the power lost in the core. Core losses are due to EDDY CURRENTS and HYSTERESIS.Eddy currents circulating in the c

10、ore result from induction. The core is, after all, a conductor within a changing magnetic field.Hysteresis loss is caused by the energy used in lining up magnetic domains in the core. The alignment goes on continuously, first in one direction, then in the other.The other part of the excitation curre

11、nt magnetizes the core. It is this magnetizing current that supplies the “shuttle power”. Shuttle power stored in the magnetic field and returned to the source twice each cycle. Magnetizing current is quadrature （90 degrees out of phase） with the applied voltage.1. INTRODUCTIONThe high-voltage trans

12、mission was need for the case electrical power is to be provided at considerable distance from a generating station. At some point this high voltage must be reduced, because ultimately is must supply a load. The transformer makes it possible for various parts of a power system to operate at differen

13、t voltage levels. In this paper we discuss power transformer principles and applications.2. TOW-WINDING TRANSFORMERSA transformer in its simplest form consists of two stationary coils coupled by a mutual magnetic flux. The coils are said to be mutually coupled because they link a common flux.In powe

14、r applications, laminated steel core transformers （to which this paper is restricted） are used. Transformers are efficient because the rotational losses normally associated with rotating machine are absent, so relatively little power is lost when transforming power from one voltage level to another.

15、 Typical efficiencies are in the range 92 to 99%, the higher values applying to the larger power transformers.The current flowing in the coil connected to the ac source is called the primary winding or simply the primary. It sets up the flux in the core, which varies periodically both in magnitude a

16、nd direction. The flux links the second coil, called the secondary winding or simply secondary. The flux is changing; therefore, it induces a voltage in the secondary by electromagnetic induction in accordance with Lenzs law. Thus the primary receives its power from the source while the secondary supplies this power to the load. This action is known as transformer action.3. TRANSFORMER PRINCIPLESWhen a sinusoidal