Why can t there be gaps in the main magnetic circuit of the transformer?

With a fixed magnetic core, the magnetic circuit is also fixed, just like the wire in the circuit, no matter how large the current is, it must go from the wire, and the magnet can only go in the magnetic circuit. Whereas, the magnetic circuit gap is like a resistor in a circuit.

In order to reduce the eddy current loss, the core is divided into many thin sheets insulated from each other, and when these thin sheets are superimposed into the core, there is a certain gap between each other, and the gap is called the magnetic circuit gap. It can be seen that the magnetic circuit gap is conducive to reducing eddy current losses.

1) The main magnetic circuit of the transformer can have gaps, and the switching power supply transformer is a typical example.

The transformer gap is mainly to prevent the transformer from being unsaturated when the voltage is overloaded.

2) When the core of the transformer is working, there is eddy current loss, and the direction of the eddy current is perpendicular to the direction of the magnetic field lines.

If a whole core is used, in the direction of the perpendicular magnetic field lines, the resistance is small, the eddy current will be large, and the loss will be large.

Therefore, the core is usually made of materials with high resistivity, or processed into sheet superposition to increase it.

The resistance value in the direction of the perpendicular magnetic field line is added to reduce the eddy current loss.

The surface of the sheet silicon steel sheet is covered with an insulating coating, and the thinner the silicon steel sheet, the smaller the eddy current loss).

When there is a gap, the permeable medium changes from iron to air, and the permeability of air is very small. In addition, the core of the whole piece of iron will cause eddy current loss and iron loss 、、、

The rest of the people are so comprehensive, let me add one more point, there is a gap that will make noise!

Unsaturated, the efficiency will be reduced, and now it is possible to study the broken factories in Shenzhen, and the motor newspaper has time to take a look.

Generally, the switching power supply transformer core needs to leave a certain gap in the design. The gap is left in the firing of the core, the core is completely disassembled and put together, you will find that the core column in the middle does not coincide but has an air gap of 1 to 2 mm, if some cores do not leave a gap, you can pad some paper in the middle to solve the problem, the thickness is about 1 to 2 mm. The purpose of the air gap is to prevent magnetic saturation.

If the core is used for other productions and does not need the original air gap, there are these methods to eliminate it: 1. Use crushed magnetic powder (preferably the powder made after the same type of core is broken), mix it with varnish or glue, and wipe it on the shortage of cores; 2. Flatten the fragments of other cores (flakes) with sandpaper to an appropriate thickness and pad them in the air gap (firmly bonded with glue or varnish); 3. Smooth the raised cores with sandpaper until the air gap is eliminated when it is the same length as the shortest core. It is very easy to grind the core with fine sandpaper, even faster than grinding the core of the same diameter The temperature of the core of the switching power transformer, simply put, the general switching power supply is mainly copper loss and iron loss, and the copper loss comes from the loss and heating of the coil itself, after all, the enameled wire is impeded.

The iron loss comes from the magnetoresistance of the core, which of course also contains some eddy currents. The solution can be like this, if your load is not very large, then your primary inductor can be designed to be larger, and the wire diameter can be thicker in the case of winding, so that the no-load current is relatively small, the copper loss is relatively small, and of course there is a degree, not absolute. In the same way, the secondary wire diameter should be thicker as much as possible.

The enlargement of the core seam will not affect the main magnetic flux, because the main magnetic flux is determined by voltage, frequency, and turns, and if these three remain the same, the main magnetic flux will not change.

However, if the seam becomes larger, the local magnetic flux density at the joint will increase, because the magnetic resistance of the air gap is very large, and the magnetic flux generally does not pass through the air gap, but passes through the adjacent silicon steel sheets, and the magnetic density at the crossing place increases. Therefore, the no-load current, no-load loss, and noise will increase.

Basically, it does not affect the main magnetic flux in the core.

General power supply or power transformer does not deliberately leave an obvious, neat, complete air gap, but when the seam of one layer is staggered with the seam of another layer during lamination, there will inevitably be a small joint in each layer. Its influence on the parameters of the transformer is mainly to slightly increase the leakage inductance and no-load current. (The air gap deliberately set aside will significantly increase the leakage inductance and no-load current, such as AC welding machines).

The main magnetic flux in the core is mainly determined by the voltage connected at the time (as well as the frequency of the power supply, the number of turns of the winding).

When there is no load, u1 e1=, is visible.

At the time of load, there is no major effect due to the small resistance and leakage inductance in the windings.

Answer: When a prepared transformer is running at the rated voltage, the size of the main magnetic flux in the core is certain. According to Ohm's law of magnetic circuits, if the magnitude of the magnetic flux in the magnetic circuit is constant, the magnetic flux potential is small if the magnetic resistance is small, and the i0r in the excitation current is small. If the transformer core is closed, the magnetic resistance is much smaller than if there is a gap in the circuit, and the I0R is much smaller.

If there is a gap in the core circuit, whether it is filled with air or transformer oil, due to the large magnetic resistance, the excitation flux potential required to generate the main magnetic flux of the same size is very large, and the result is a large I0r. The power factor of the ambassador transformer decreases, and the transformer performance deteriorates. By the way, since the i0a is small and the i0r is large, it can generally be said that the i0r is large when the magnetoresistance is large.