Abstract: The parallel running of transformers needs to consider how to solve the rationality of the load distribution matching with the rated capacity of each transformer, and the short-circuit impedance is the main factor affecting the load distribution ratio. The advantages and disadvantages of parallel running of transformers and the ideal conditions for parallel running are introduced in this paper. Taking the parallel running of two transformers as an example, the relationship between the load distribution ratio and the short-circuit impedance is analyzed.The results show that, when two transformers with unequal rated capacity run side by side, it is necessary to ensure that their short-circuit impedance is equal as far as possible, so that the load carried by each transformer is distributed proportionally according to their respective rated capacity. However, when the short-circuit impedance cannot be completely equal, the short-circuit impedance of the transformer with smaller rated capacity should be larger, and the short-circuit impedance of the transformer with larger rated capacity should be smaller, so that the total transmission capacity of the system after parallel operation is greater than the sum of the rated capacity of the two transformers,so as to improve the economy and safety of the system operation.

    Key words: transformer; parallel running; load distribution ratio; short-circuit impedance; full load operation; transmission capacity