The design of a typical transformer is simple. It consists of a steel core, two coils with wire winding. One winding is called primary, the second - secondary. The appearance of an alternating voltage (U1) and current (I1) in the first coil form a magnetic flux in its core. It creates an EMF directly in the secondary winding, which is not connected to the circuit and has an energy strength equal to zero.
If the circuit is connected and consumption occurs, this leads to a proportional increase in the current strength in the first coil. Such a model of communication between the windings explains the process of transformation and redistribution of electrical energy, which is included in the calculation of transformers. Since all the turns of the second coil are connected in series, the total effect of all the EMF that appears at the ends of the device is obtained.
Transformers are assembled in such a way that the voltage drop in the second winding is a small fraction (up to 2 - 5%), which allows us to assume that U2 and EMF are equal at its ends. The number U2 will be more/less as much as the difference between the number of turns of both coils - n2 and n1.
Dependencybetween the number of wire layers is called the transformation ratio. It is determined by the formula (and is denoted by the letter K), namely: K=n1/n2=U1/U2=I2/I1. Often this indicator looks like a ratio of two numbers, for example 1:45, which shows that the number of turns of one of the coils is 45 times less than that of the other. This proportion helps in the calculation of the current transformer.
Electrotechnical cores are produced in two types: W-shaped, armored, with a branching of the magnetic flux into two parts, and U-shaped - without division. To reduce probable losses, the rod is not made solid, but is made up of separate thin layers of steel, insulated from each other with paper. The most common type is cylindrical: a primary winding is applied to the frame, then balls of paper are mounted, and a secondary layer of wire is wound on top of this.
Calculation of a transformer can cause some difficulties, but the simplified formulas below will come to the aid of an amateur designer. It is first necessary to determine the levels of voltages and currents individually for each coil. The power of each of them is calculated: P2=I2U2; P3=I3U3; P4=I4U4, where P2, P3, P4 are powers (W) increased by windings; I2, I3, I4 - current strengths (A); U2, U3, U4 - voltages (V).
To establish the total power (P) in the calculation of the transformer, you need to enter the sum of the indicators of the individual windings, and then multiply by a factor of 1.25, which takes into account losses: P=1.25(P2+P3+P4+…). By the way,the value of P will help calculate the cross section of the core (in sq.cm): Q \u003d 1.2short square P
Then follows the procedure for determining the number of turns n0 per 1 volt according to the formula: n0=50/Q. As a result, the number of turns of the coils is found out. For the first one, taking into account the voltage loss in the transformer, it will be equal to: N1=0.97n0U1For the rest: N2=1.3n0U2; n2=1.3n0U3… The diameter of the conductor of any winding can be calculated by the formula: d=0.7short square 1 where I is the current strength (A), d is the diameter (mm).
Transformer calculation allows you to find the current strength from the total power: I1=P/U1. The size of the plates in the core remains unknown. To find it, it is necessary to calculate the winding area in the core window: Sm=4(d1(sq.)n1+d2(sq.)n2+d3(sq.)n3+…), where Sm is the area (in sq. mm), all windings in the window; d1, d2, d3 and d4 - wire diameters (mm); n1, n2, n3 and n4 are the number of turns. Using this formula, the winding unevenness, the thickness of the wire insulation, the area occupied by the frame in the gap of the core window are described. According to the area obtained, a special plate size is selected for free placement of the coil in its window. And the last thing you need to know is the thickness of the core set (b), which is obtained by the formula: b \u003d (100Q) / a, where a is the width of the middle plate (in mm); Q - in sq. see The most difficult thing in this method is to calculate the transformer (this is the search for a rod element with a suitable size).
