Three common problems of rectifier transformers

1. What is the capacity of the transformer?

From the above analysis of the second problem, it can be seen that the selection of the core is related to the voltage, and the choice of the conductor is related to the current, that is, the thickness of the conductor is directly related to the amount of heat generated. In other words, the capacity of the transformer is only related to the amount of heat generated. For a well-designed transformer, if it is working in a poorly-cooled environment, if it is 1000KVA, it may work at 1250KVA if the cooling capacity is enhanced. In addition, the nominal capacity of the transformer is also related to the allowed temperature rise. For example, if a 1000KVA transformer allows a temperature rise of 100K, if it can be allowed to work up to 120K under special circumstances, the capacity is more than 1000KVA. . It can also be seen that if the heat dissipation conditions of the transformer are improved, its nominal capacity can be increased. Conversely, for the same capacity inverter, the size of the transformer cabinet can be reduced.

Therefore, in some bidding processes, the competitors intentionally designate a larger transformer capacity, giving the user a large margin of illusion design, in fact, there is no sense, the key depends on the size and cooling method of the transformer.

2. What are the cooling mediums of the rectifier transformer?

To bring heat out of the inverter, there are generally three types of media that can be used: air, water, and oil. The heating components of the high-voltage inverter are mainly two parts: one is a rectifier transformer and the other is a power element. In the early stage of the transformer, the oil cooling method was mainly adopted, ie, the transformer was immersed in the oil tank. Since the specific heat of the oil is higher than air and the insulation strength is high, this heat dissipation method is the main heat dissipation of the high-power transformer. However, due to the need for maintenance of the oil product, the seal at the lead-out line is not well resolved. With the advancement of insulating materials, dry-type transformers have dominated the medium and low power levels. Dry-type transformers are cooled by air. The transformer can also be water-cooled, that is, the coil of the transformer is made hollow, and the interior of the transformer is pure water, and pure water is used to take away the heat.

3. What are the basic problems in transformer design?

The basic problem of transformer design is magnetic flux and current density. The current and the capacity of the transformer are proportional to each other, and the magnitude of the current density (ie, the thickness of the wire) is taken into consideration in terms of the amount of heat generated by the conductor. For magnetic flux, the basic relation of electromagnetism is u = 4.44fwΦ, where u is the voltage; f is the frequency, here is 50Hz, the fixed value; w is the number of turns of the coil; Φ is the magnetic flux. Since the magnetic flux density B of the silicon steel sheet is limited by the material, generally only 1.4-1.8 Tesla can be designed, and Φ=BS. Therefore, to increase Φ, the sectional area of ​​the core can generally only be increased. The core of the transformer is generally a three-phase column. The cross-sectional area of ​​the core can be determined according to the above formula. The size of the core window must consider the principle of putting the coil in. The larger the capacity of the transformer, the thicker the wire, the larger the core's window needs to be. China Power Electronics Industry Network In the transformer design, the amount of copper and iron can be balanced. Because once the capacity of the transformer is determined, the current is determined, and the thickness of the wire is also determined. By increasing the number of turns W, the magnetic flux Φ can be smaller, and the cross-sectional area of ​​the core can be smaller, but these must be reduced. The number of turns of the iron core is larger. On the other hand, reducing the number of turns, the magnetic flux Φ is larger, and the cross-sectional area of ​​the iron core is larger, but the window of the iron core can be smaller.