What is the condition of transformers running side by side

(1) The parallel operation of transformers shall meet the following conditions:

 

1) The winding wiring groups are the same.

 

2) The variable voltage ratio is the same (allowable error ± 0.5 %).

 

3) The impedance voltage is the same (allowable error ±10%).

 

4) Capacity ratio should not exceed 3:1 in general.

 

 

(2) If the above parallel operation conditions are not met, the following consequences will occur:

 

1) If the winding wiring groups are different, there will be a large potential difference on the secondary side of the transformer in the same phase. Because the impedance of the secondary side of the transformer is very small, there will be a large circulation and the transformer will be burned down.

 

2) if the variable voltage ratio exceeds the specified error, there must be circulating current between the two transformer windings because of the potential difference. The larger the variation ratio error, the larger the circulation. This not only causes a large power loss, but also burns down the transformer in serious cases.

 

3) If the impedance voltage (also known as the short-circuit voltage percentage) exceeds the specified error value, it will cause unbalanced load distribution, that is, the transformer with large capacity is under load and the transformer with small capacity is overloaded.

 

4) If the capacity ratio exceeds 3:1, the impedance voltage also differs greatly, which also fails to meet condition 3).