Tansformer are nearly used in all electronic products. Its principal is simple yet the winding technology is different according to the different use places. The main functions of the
transformers are: voltage transfer, impedance transfer, isolating, voltage regulation (magnetic saturation
transformer) and so on. And the main used core shape includes E-type and C-type.
一、The basic principles of transformers
Picture 1 is the principal minic diagram. When sine AC voltage (V1) added to the two ends of the primary coil, then there is alternating current (I1) in the wire and alternating flux (ф1) produced, which forms the magnetic circuit by along the core through the primary coil and secondary circuit. And the mutual inductance electric potential (U2) is produced in the secondary coil, and at the same time ф1 will induces a self-induced potential E1 in the primary coil, and the direction of E1 is opposite to that of voltage (U1), and yet the amplitude of the two is similiar and thus limit the I1. There is a need of energy consumption in order to maintain the existance of ф1, and the
transformer itself has a certain loss, and therefore even the secondary arr not connected with load, there is current in the primary coil. And the current is what we called no-load current.
If the secondary is connected with load, current (I2) and magnetic flux (ф2) is produced in the secondary coil, the direction of ф1 and ф2 is opposite, and thus has a function of equits and therefore reduces the magnetic flux in the core, and therefore the self-induced voltage E1 is reduced, and the I1 increased. When the secondary load current increase, I1 and ф1 increase, and the increased part of ф1 replenish the magnetic flux counteracted by ф2 in order to maintain the total number of magnetic flux. In spite of
transformer loss, the load loss power in the secondary coil is that get fron the primary coil of an ideal
transformer. The change of cyclomatic number of secondary coil can change the secondary voltage, yet the allowance load loss power can not be changed.
When the primary winding is switched on, the magnetic flux produced by coil flows in the core, and for the core is also an inductor, and can induce the potential on the surface which is perpendicular to the magnetic line, the potential forms the closed circuit in the cross-section of the core and yield the current, which is like a swirl and so is called wortex. The wortex increases the transformer loss, and causes transformer core heating and therefore the transformer temperature rise increases. The loss yielded by the wortex is called iron loss. And there is a large demand of copper for winding the transformer, and there exist resistance in the copper conductor, and it will consumption a certain power when the current switch on, and the consumption always transform the heat and we call the heat loss as copper loss. And therefore the transformer temperature rise incluses iron loss and copper loss. And for the existance of the two losses, the output power is smaller than the input power, and we use the efficiency parameter to descripe the phenomenon η=output power/ input power.
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