Why does the low-voltage coil of transformers of 500kVA and above use foil winding, while the coils of 500kVA and below use wire wind?

If the high-voltage coil adopts foil winding, it will bring the following problems

1) The process is complex, and the production technology is immature. It is difficult to ensure quality control, such as: end insulation, burrs, and inter-segment connection will become the weak points of the product

2) The supply time of raw materials is long and cannot meet the requirements of general users;

3) The purpose of foil wind is to solve the problems of impulse voltage distribution and large current. The use of wire winding for high-voltage coils can fully meet the requirements.

Low-voltage coils use foil wind to solve the problem of large currents and sudden short circuits. On small-capacity transformers, the above problems are not prominent, and the use of wire windings has fully met the requirements; low-volume transformers use low-voltage foil windings, which are not economical and costly.

Advantages of low-voltage foil winding:

1). The low voltage adopts foil winding, there is no helix angle at both ends of the coil, so the unbalanced ampere turns are greatly reduced. During short circuit, the axial electromotive force due to amplitude magnetic flux leakage is greatly reduced.

2) The winding turns are arranged according to the width direction, the air duct setting can be more flexible and applicable, and the heat dissipation performance can be better.

3). The winding turns-to-turn capacitance is large, the potential gradient is small, and the ability to resist surge voltage is strong.