A New Engineering Design Method Of220kV High-impedance Transformer

As the hub equipment of power system, transformer would bring serious harm to the grid and cause great loss once it is damaged. As the increase of the power system capacity, the current of short circuit is also growing. In order to reduce the damage to the power equipment brought by short current, high-impedance transformer is gradually applied in power system. According to the statistical data, the application of three-winding transformer which is high impedance in power grid is more and more widely in recent years. The transformer has many disadvantages, such as, high cost and loss, hard maintenance etc. So, the manufacturing of the transformer which is economical and easy to maintain has great theoretical and engineering practical significance.This paper shows a new design method of220kV three-winding on-load voltage regulation high-impedance transformer. This method demands that high voltage winding should be near to the core, and from the inside to the outside, the sequence is medium voltage winding, regulating winding and low voltage winding. The essence of the new high-impedance transformer is to enlarge the longitudinal magnetic leakage area through enlarging the main space dimension between medium and low voltage windings, thus, the impedance is also increased. This method only increases the space dimension between medium and low voltage windings, during increasing high-low and medium-low impedance, the high-medium impedance is not influenced. Because of the internal installed high voltage winding, the high voltage winding diameter is greatly reduced, and the high voltage winding conductor resistance is also reduced, thus, load loss during working caused by high voltage to medium voltage winding is reduced.Combined with the traditional calculation method, this paper deduces the impedance engineering calculation method of high impedance transformer in detail, so as to give the electromagnetic calculation scheme. Considering the particularity of the product, simulation verification is carried out to the impedance through magnetic field energy calculation by the finite-element analysis method. Because the transformer changes winding arrangement method and capacitance distribution, this paper also calculates full-wave lightning impulse voltage distribution state. During the design of the structure, special design is carried out to the special parts such as active part and insulation part, and then test is carried out to the sample product. The final result shows that, this design fully meet the requirements of the specified parameters, it is economical and can reach the anticipated purpose, so it is an ideal design method for high-impedance transform.