The Impact of Short Circuit Impedance of Transformers on Cost

When the power factor of the load is constant, the voltage regulation rate of the transformer is basically proportional to the short-circuit impedance, and the reactive power loss of the transformer is proportional to the reactive component of the short-circuit impedance. Transformers with high short-circuit impedance have a high voltage regulation rate, so a low short-circuit impedance is more suitable. However, the short-circuit current multiple is inversely proportional to the short-circuit impedance. The smaller the short-circuit impedance, the greater the short-circuit current multiple, and the greater the impact on the power grid. The short-circuit current caused by switch interruptions in the system is also greater. For transformers, when the transformer is short circuited, the winding will experience tremendous electrical force and generate a higher short-circuit temperature rise. In order to limit short-circuit current, a larger short-circuit impedance is desired.

However, for core transformers, when taking a larger short-circuit impedance, it is necessary to increase the number of turns of the winding, which increases the weight of the wire, or increases the leakage area and reduces the reactance height of the winding, thereby increasing the weight of the iron core. From this, it can be seen that the manufacturing cost of high impedance transformers needs to be correspondingly increased.

As the short-circuit impedance increases, the load loss also increases accordingly. So, choosing short-circuit impedance should consider both electric power and manufacturing costs, taking into account both.

Shell type transformers can be divided into several ampere turn groups due to their winding ampere turns, and their impedance can vary over a large range without causing significant changes in transformer costs.