How to determine the parameters or dimensions of transformer?

First, identify the power transformer \x0d\ 1. Identify the cores of common power transformers from their shapes, including E-type and C-type. E-shaped iron core transformer is shell-type structure (iron core wound with coil), and the iron core is made of D4 1 and D42 high-quality silicon steel sheets, which are widely used. C-shaped iron core transformer adopts cold-rolled silicon steel sheet as iron core, which has small magnetic leakage and small volume, and is of iron core structure (coil wraps iron core). \x0d\2。 Identify the number of terminals drawn from the winding. Power transformers usually have two windings, namely primary winding and secondary winding, so there are four terminals. In order to prevent AC noise and other interference, some power transformers often add a shielding layer between the primary winding and the secondary winding, and its shielding layer is the grounding terminal. Therefore, the power transformer has at least four terminals. \x0d\3。 From the lamination mode of silicon steel sheets, it is recognized that the silicon steel sheets of E-type power transformer are alternately inserted, there is no air gap between E-sheet and I-sheet, and the whole iron core is closely attached. There is a certain air gap between E piece and I piece of audio input and output transformer, which is the most intuitive way to distinguish power supply from audio transformer. As for C-shaped transformers, they are generally power transformers. \x0d\ II。 Estimation of power \x0d\ Transmission power of power transformer depends on the material and cross-sectional area of iron core. The so-called cross-sectional area, whether it is E-shaped shell structure or E-shaped core structure (including C-shaped structure), refers to the cross-sectional (rectangular) area of the core column wrapped by the winding. After measuring the cross-sectional area S of the iron core, the power P of the transformer can be estimated according to P=S2/ 1.5. Where the unit of s is cm2. \x0d\ For example, the cross-sectional area of an iron core of a power transformer is measured to be 7 cm2, and its power is estimated to be p = S2/1.5 = 72/1.5 = 33w. Excluding all kinds of errors, the actual nominal power is 30W. \x0d\ III。 Measurement of winding voltage \x0d\ Using an unmarked power transformer, it is the most basic work to find out the primary winding and distinguish the output voltage of the secondary winding. An example is given to illustrate the judgment method. \x0d\ Example: A power transformer with *** 10 terminal is known. Try to judge the voltage of each winding. \x0d\ Step 1: Distinguish the number of windings and draw the circuit diagram. \x0d\ Measured by multimeter R× 1, each connected terminal is a winding. At present, it is measured that there are three pairs of connections, 1 group of three \x0d\, and one terminal is not connected with any other terminals. Draw the circuit diagram and number it according to the above measurement results. \x0d\ According to the measurement, the transformer has four windings, among which the windings numbered ⑤, ⑦ and ⑦ are tapped windings, and the terminal ⑩ x0d \ is a shielded terminal without any winding. \x0d\ Step 2: Determine the primary winding. \x0d\ For the step-down power transformer, the line diameter of the primary winding is smaller than that of the secondary winding, and the number of turns is more than that of the secondary winding. Therefore, in the step-down transformer shown in Figure 4, the resistance of the primary winding is the largest. \x0d\ Step 3: Determine the voltages of all secondary windings. \x0d\ Connect the AC power supply to the primary winding through the voltage regulator, and step up the voltage slowly until it reaches 220V. Measure the no-load voltage of each winding in turn and mark it on each output terminal. If the transformer does not heat for a long time under no-load condition, it shows that the performance of the transformer is basically intact, which further verifies that the primary winding is correct. \x0d\ IV。 Determination of the maximum current of each secondary winding \x0d\ The output current of the transformer secondary winding depends on the diameter d of the enameled wire of the winding. The diameter of the enameled wire can be measured directly from the lead terminal. After measuring the diameter, the maximum output current of the winding can be obtained according to formula I=2D2. Where the unit of d is mm.