2023.1.30 Articles

The losses of magnetic components are mainly iron loss and copper loss. The relationship between copper loss, iron loss and load of magnetic components is shown in the figure1.

Fig 1. Relationship between copper loss, iron loss and load of magnetic components.

Iron loss is a fixed loss, mainly eddy current loss and magnetic hysteresis loss, which is a loss that will inevitably occur in the magnetic circuit of the transformer; while the iron loss is proportional to the square of the voltage, but the working voltage of the transformer does not change much and will not change with the load. And the change, the power loss is fixed, so the iron loss is a fixed loss.

The copper loss is a variable loss, such as the copper loss formula, the copper loss will change with the current and the load time, and the copper loss is proportional to the square of the current and the load.

The copper loss is a variable loss, such as the copper loss formula, the copper loss will change with the current and the load time, and the copper loss is proportional to the square of the current and the load.

• t is the duration of the current in seconds

• I is the current flowing through the wire in amperes

• R is the resistance of the wire in ohms

• Calculated copper losses in watts

The main components of magnetic components are copper wire and iron core, and the copper wire has resistance; the larger the cross-sectional area of the copper wire, the smaller the resistance value, the greater the current that can be allowed to flow, and the longer the distance of the copper wire. , the greater the resistance value, the greater the loss; so the loss generated when the current flows through the resistor will be converted into heat energy, and this loss is called "copper loss".

The copper loss is mainly determined by the size of the load current and the operating frequency. If the current is high frequency, the copper loss will be affected by the proximity effect and the skin effect.

Therefore, the size of the copper loss is actually determined by the size of the load, power factor and operating frequency to decide.

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The rated current according to the rate of change of the inductance value is called the saturation current. The saturation current is the rated current with the decrease of the inductance value as the index. The increase of wave current leads to unstable IC control. Generally, the saturation current takes the inductance value to drop by 20-30%. DC superposition can be used to judge the attenuation of the inductance value to the saturation current.

Refers to the application of magnetic component products, the change of rated current to temperature, called temperature rise current, when the magnetic component is superimposed with DC, the surface temperature reaches a certain temperature and rises to 20、40 or 60 degrees of current, There will be different definitions of temperature rise due to different considerations in the design environment.

There is no uniform standard for Isat and Irms in the industry.

The design side can refer to the parameters of Isat and Irms to determine whether the part meets the design requirements.

The skin effect is also known as the skin effect. When the copper wire conductor has an AC or alternating electromagnetic field, the current distribution of the copper wire conductor is uneven, so that the current is concentrated on the surface skin of the copper wire conductor, resulting in a large current density on the surface of the conductor and a small current in the center of the copper wire conductor.

This phenomenon increases the resistance and power loss of the conductor, which is called the skin effect; and the higher the frequency of the current, the more obvious the skin effect is.

Use smaller multi-strand wires to improve the use efficiency of copper wire conductors to solve the skin effect problem, such as the schematic diagram of the skin effect of 36-strand multi-strand wires and single-core wires.

6-strand multi-strand wire and single-core wireSchematic diagram of skin effect of 3

• Resistivity of ρ Conductor (Ω-m)

• Relative permeability of μr conductors

• f is the frequency in Hz

• sqrt ( ) stands for square root

The amount of current distribution on the cross-sectional area of the wire is called the current density, and the unit is A/m².

The higher the density, the stronger the current.

The current density is equal to the current divided by the cross-sectional area of the wire, that is, the current is equal to the product of the current density and the cross-sectional area of the wire.

Therefore, the cross-sectional area of the wire is proportional to the current, and the larger the cross-sectional area of the wire, the greater the current.

Different materials have different current density values. For example, the current density of copper wires can be higher than that of aluminum wires. At the same time, when the cross-sectional area of the wire is larger, the value of the current density is also smaller due to the influence of heat dissipation factors and skin effect.

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