What is an air gap?
2022.12.15
Articles
GOTREND Technology Co.,Ltd
A.What is an air gap?
It exists in the gap between the iron core and the iron core, so that part of the magnetic circuit of the iron core is composed of air, so it can also be called an air gap (AIR GAP), such as combined iron core EE, PQ, EFD Core, etc., not a The closed body is formed by the butt joint of two sets of iron cores, and the gap generated by the butt surface is the air gap of the magnetic core. And the iron core of the closed body, such as T, SQ CORE, etc., has no air gap.
B.What is the air gap for?
When there is an air gap in the iron core of the transformer, since the permeability of the air is much lower than the permeability of the iron core, the magnetomotive force will stay on the air gap, increasing the magnetic resistance, greatly reducing the permeability and reducing the remanence. , and the maximum magnetic flux density Bm can reach the saturation magnetic flux density Bs, so that the magnetic flux increment increases, and the iron core is not prone to magnetic saturation.
1. The size of the air gap can reduce the permeability and control the inductance.
2. The air gap can increase the saturation current and prevent the magnetic saturation of the iron core.
3. Appropriate air gap size can increase the effect and upper limit of energy storage.
4. Air gap can reduce residual magnetism (Br)
5. Opening the air gap will increase the leakage inductance and increase the excitation current.
C. Air gap energy can increase the capacity of energy storage
The magnetic field energy per unit volume is called the magnetic field energy density.
Definition : ω=W/V=(BH)/2.
V is the volume.
When the square of B intensity is divided by 2μ, the energy storage remains unchanged, and the permeability μ of the iron core at the air gap is transformed into the permeability of air. The energy storage density is increased by hundreds to thousands of times, so the air gap can increase the energy storage capacity.
Because the energy density = 1/2 μ times the square of H, when the current is the same, the H is the same, and the permeability without the air gap is higher; if the air gap is too large, the inductance will be too low due to the low permeability.
The amount of inductance is becoming more and more difficult to increase, which increases the copper loss, so we need to choose the appropriate air gap size.
Because the energy density = 1/2 μ times the square of H, when the current is the same, the H is the same, and the permeability without the air gap is higher; if the air gap is too large, the inductance will be too low due to the low permeability.
The amount of inductance is becoming more and more difficult to increase, which increases the copper loss, so we need to choose the appropriate air gap size.
D. Change of BH value after adding air gap
The X-axis is the magnetic field intensity (H) generated by the current, the Y-axis is the magnetic induction intensity (B) of the iron core, and the B-H table represented by three different air gaps.
1.The residual magnetism (Br) decreases as the air gap decreases.
2. The magnetic field strength (H) is the magnetic field strength generated by the current, and the current strength increases with the increase of the air gap.
3. Since the energy storage density is 1/2BH, the energy storage capacity is half of the BH area, so the energy storage capacity increases with the increase of the air gap.
E. What is the principle of air gap avoidance?
Magnetic lines of force will be generated around the air gap. When the magnetic lines of force hit the copper wire, heat loss will occur, and when the copper wire is at the bottom of the skeleton, it is also the most difficult to dissipate heat.
Therefore, there are application designs that require multiple air gap avoidance, such as using insulating materials or gaskets next to the air gap, using iron core I-pieces or R rods to control the air gap at the top layer and avoiding copper wires on the top layer, etc. Design process.
1.The residual magnetism (Br) decreases as the air gap decreases.
2. The magnetic field strength (H) is the magnetic field strength generated by the current, and the current strength increases with the increase of the air gap.
3. Since the energy storage density is 1/2BH, the energy storage capacity is half of the BH area, so the energy storage capacity increases with the increase of the air gap.
E. What is the principle of air gap avoidance?
Magnetic lines of force will be generated around the air gap. When the magnetic lines of force hit the copper wire, heat loss will occur, and when the copper wire is at the bottom of the skeleton, it is also the most difficult to dissipate heat.
Therefore, there are application designs that require multiple air gap avoidance, such as using insulating materials or gaskets next to the air gap, using iron core I-pieces or R rods to control the air gap at the top layer and avoiding copper wires on the top layer, etc. Design process.
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