How to operate transformers in parallel？

In power system, transformer is the key equipment to realize voltage conversion and energy transmission. In order to improve the reliability, flexibility and operation efficiency of power supply system, two or more transformers are often run in parallel. Transformer parallel connection refers to connecting the primary winding and the secondary winding of two or more transformers in parallel to supply power to the load together. However, parallel operation is not simply to connect devices together, but to meet certain technical conditions to ensure its safe, stable and efficient operation.

First, the advantages of parallel operation of transformers

Parallel operation of transformers has many advantages. First of all, it improves the reliability of power supply. When one transformer fails or needs to be overhauled, the remaining transformers can still supply power to avoid interruption. Secondly, the operation efficiency can be improved, and the transformer can be switched flexibly according to the load change, so that the equipment can run in the high-efficiency interval. In addition, when the load increases, the capacity of the transformer can be gradually increased, so as to avoid excessive initial investment and improve the economy of the system.

Second, the basic conditions for parallel operation

To realize the safe parallel operation of transformers, the following basic conditions must be met:

1. Same transformation ratio: The transformation ratios of all transformers must be consistent, otherwise, circulation will be generated on the secondary side, which will lead to heating or even damage of transformers.
2. Same connection group: The connection modes of transformers (such as Y/Y-12, Y/δ-11, etc.) must be consistent, otherwise phase difference will occur, resulting in short circuit or circulation.
3. Equal percentage impedance: The short-circuit impedance of transformers should be the same as much as possible, otherwise it will lead to uneven load distribution, and some transformers may be overloaded while others are not fully utilized.
4. The rated voltage and frequency are consistent: ensure that the transformer can work at the same voltage level and frequency.
5. The capacity ratio should not be too large: it is generally required that the capacity ratio of the transformer should not exceed 3:1, otherwise it is difficult to distribute the load reasonably.

Third, the load distribution in parallel operation

Under the premise of satisfying the above conditions, the load current can be reasonably distributed among transformers running in parallel. The load distribution is inversely proportional to the short-circuit impedance of the transformer, that is, the transformer with small short-circuit impedance bears more load. Therefore, when selecting transformers running in parallel, equipment with similar parameters should be selected as far as possible to achieve load balance.

Four, the matters needing attention in parallel operation

Although parallel operation has brought many advantages, the following points should be paid attention to in actual operation:

-Regular inspection and maintenance: to prevent parallel connection failure due to equipment aging or failure.
-Preventing circulating current: Avoid unnecessary circulating current loss by accurately adjusting the transformation ratio and wiring mode.
-Relay protection coordination: each transformer should be equipped with appropriate protection devices to prevent the spread of faults.
-Flexible switching of operation mode: if automatic switching device is adopted, quick switching can be realized in case of failure or overhaul.

V. Conclusion

Parallel operation of transformers is one of the important means to improve power supply reliability and operation efficiency in modern power system. Through scientific design and standardized operation, multiple transformers can work together to improve the stability and economy of the whole system. But at the same time, we must strictly abide by the technical conditions of parallel operation and strengthen operation management and maintenance to ensure the safe and reliable operation of the system.

In a word, the parallel operation of transformers is a highly technical work with high management requirements. Only by fully understanding its principles and conditions can we give full play to its advantages and provide a strong guarantee for the stable operation of the power system.