外文翻譯---發(fā)電機(jī)和變壓器-在線瀏覽
2025-03-06 23:07本頁面
【正文】 rmers have cooling fins to keep them from overheating. Other transformers are located near points where the electric power is used.The coils of transformer are electrically are electrically insulated from each other. 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: CORE type has the core inside the windings. 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 different in their operation, however.Coils are wound with copper wire. The resistance is kept as low as possible to keep losses low.Transformers are very efficient. The losses are often less than 3 percent. This allows us to assume that they are perfect in many putations.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 leakAge. That is, all of the magnetic flux links all of the turns on each coil.To 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 flows. Typically, this excitation current is less than 3 percent of rated current supplies the power lost in the core. Core losses are due to EDDY CURRENTS and HYSTERESIS.Eddy 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 part of the excitation current magnetizes the core. It is this magnetizing current that supplies the “shuttle power”. Shuttle power is power stored in the magnetic field and returned to the source twice each cycle. Magnetizing current is quadrature with the applied voltage.Excitation current is made up of two parts. One part is in phase with the voltage. The lo
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