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1、河南理工大学毕业设计(论文)说明书中英文对照翻译原文：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 purp
2、ose of transformers is to change 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 secondar
3、y is the one connected to the 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 ste
4、pped down to distribution levels, 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 o
5、ther. There is a magnetic link, 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 c
6、ore inside the windings.2. The 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 ke
7、ep losses low.IDEALIZED TRANSFORMERS 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 assu
8、me that there is no flux leakage. 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 th
9、e primary, a small current flows. 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
10、currents circulating in the core 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
11、 part of the excitation current 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. INTRO
12、DUCTIONThe high-voltage transmission 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
13、system to operate at different 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 th
14、ey link a common flux.In power 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
15、one voltage level to another. 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 per
16、iodically both in magnitude and 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 PRINCIPLES
