Saturable current transformer

1. Magnetic flux High U has low magnetic saturation, that is, the magnetic core can withstand large current at low frequency. The larger the current, the greater the inductive reactance changes with the current and becomes capacitive reactance. The heating of the magnetic core winding means that the core loss is too large, and the power is converted into heat energy instead of magnetic energy, and the energy is consumed. Usually, the nickel core has a wide bandwidth, and there is a balance between Q value and U. The higher the U value, the lower the Q value, and vice versa. It is difficult to work at low frequency with U value, but the loss is small. It is easier to work at low frequency with high U value, but the core loss is too large, the power loss is also large, and it is basically difficult to work continuously. Using a magnetic core winding with a U value of 400 should greatly reduce the magnetic loss. Although the inductance is a bit low, it can be solved by increasing the number of winding coils. Taking a 1:4 transformer as an example, the primary of 1 coil is changed to two coils; the secondary of 2 coils is changed to 4 coils, so the total length of the winding should be doubled, and the high transmission frequency should also be reduced accordingly. 2. Curie temperature Some cheap magnetic core windings have a Curie temperature of 165℃. When this temperature is reached, they lose their magnetism immediately, just like air medium. After returning to room temperature, the magnetic properties change permanently, and the magnetic permeability decreases by 10%. If the working temperature of the magnetic material used in the output transformer of the magnetic ring exceeds the Curie temperature, the output power tube can be burned in a moment. The Curie temperature data of imported -61 and -43 materials are unknown. The domestic NXO-100 is 260℃, and the R-400 is 350℃. The point where the output power starts to decrease is the temperature limit of the magnetic ring. From the past experimental results, at 55 degrees, those EMI magnetic rings have not yet experienced a decrease in output power. 3. Working frequency The material of each magnetic core determines its optimal working frequency, so it is necessary to select the material of the magnetic core according to the specific frequency. For example, the material of NXO-100 has a magnetic flux of 100 and a working frequency of 15MHZ. The magnetic ring made of NXO-80 material has a magnetic flux of 80 and a working frequency of 30MHZ. The magnetic ring with low working frequency will have great loss and heat when it is forced to work at a high frequency. When the heat of the magnetic ring exceeds the Curie temperature, the electrical performance will change suddenly and it will not work normally. In summary, to choose the right magnetic ring, it is not enough to look at the appearance or volume. It is necessary to understand its actual parameters. Otherwise, when problems occur, such as high standing wave, too narrow bandwidth, severe heating or burning of the magnetic ring, etc., you don’t know where the cause comes from.