The Transformer University of Ottawa（变压器渥太华大学）.pdf

The Transformer The principle parts of a transformer and their functions are: • The core, which makes a path for the magnetic flux. • The primary coil, which receives energy from the ac source. • The secondary coil, which receives energy from the primary winding and delivers it to the load. • The enclosure, which protects the transformer from dirt, moisture, and mechanical damage. 1 Transformer Core • The composition of a transformer core depends on voltage, current, and frequency. Commonly used core materials are air, soft iron, and steel. Each of these materials is suitable for certain applications. Generally, air-core transformers are used when the voltage source has a high frequency (above 20 kHz). Iron-core transformers are usually used when the source frequency is low (below 20 kHz). • A soft-iron-core transformer is very useful where the transformer must be physically small, yet efficient. The iron-core transformer provides better power transfer than does the air-core transformer. A transformer whose core is constructed of laminated sheets of steel dissipates heat readily; thus it provides for the efficient transfer of power. • The majority of transformers contain laminated-steel cores. These steel laminations are insulated with a nonconducting material, such as varnish, and then formed into a core. It takes about 40 laminations to make a core of 2 cm thick. The purpose of the laminations is to reduce losses which will be discussed later in this chapter. • The most efficient transformer core is one that offers the best path for the most lines of flux with the l