Parallel operation of transformers

The transformers are 500kva and 250kva. All other conditions meet the parallel connection standards.

I would appreciate some guidance from Hai Chuan’s brother.

The capacity difference is too large; the capacity of parallel transformers should not exceed a ratio of 3 to 1. It’s better if each one carries its own load.

In theory, it should be possible to connect them in parallel; I just don’t know how the output capacity will be distributed after use, and whether 90% of the total output capacity can be achieved

The parallel operation mode of transformers enhances the reliability of power supply; if one transformer fails, it can be disconnected, allowing the remaining transformers to continue supplying power to the load. In cases of excessive load, some secondary loads can also be disconnected, thereby ensuring uninterrupted power supply to the important loads. Transformers are operated in parallel, and under certain conditions, this can improve their operational efficiency. The efficiency of a transformer varies within a certain range. The transformer achieves its highest efficiency when its fixed losses are equal to its variable losses; at this point, the load on the transformer is approximately 50% of its rated capacity. Both excessive and insufficient load levels result in reduced efficiency. Controlling the number of control transformers in operation allows the transformers to operate at high efficiency under certain conditions. Transformers are operated in parallel, which has the drawback that the load rates of each transformer vary due to uneven load distribution. Although parallel operation of transformers has its advantages, not any two transformers can be operated in parallel. Transformers operating in parallel must meet certain conditions, and these conditions are: 1. The transformer connections have the same type ； 2. The voltage transformation ratios of the transformers should be equal, with the maximum allowable error not exceeding ±5% ； 3. The percentage of short-circuit impedance of the transformers should be as equal as possible, with the allowable maximum error not exceeding ±10% for each ； 4. The capacity ratio of the transformers shall not exceed 3:1. When the capacities of transformers operating in parallel differ significantly, it is easy for some transformers to become overloaded while others remain underloaded, preventing all transformers from achieving their maximum power supply capacity at the same time. To this end, it is specifically stipulated that when transformers are operated in parallel, the capacity ratio between them shall not exceed 3:1.

The capacity difference is too large (more than one-third), making it difficult to distribute the load; this can easily lead to damage to the transformer with the smaller capacity, so it’s best not to connect them in parallel.

The capacity ratio is 2:1, with a difference of no more than 3:1

2:1 is of course larger than 3:1

It is best for parallel transformers to have equal capacity, with the maximum difference not exceeding 3:1. If one transformer has a capacity of 500 kVA, the other should have a capacity of at least 333 kVA in order to ensure proper distribution of the load.