1. the advantages of parallel operation
The two or more than two transformers, respectively, the secondary side were connected to their respective public bus, while the load power supply. The company is located in:
Advantages:
(1) improve operational efficiency;
(2) improve the reliability of power supply;
(3) to facilitate expansion.
2.the ideal conditions for parallel operation
(1) the same ratio;
(2) the same group number of the link group;
(3) the output current of the transformer with the same phase;
(4) The impedance voltage of each transformer is equal.
The secondary side of two transformers operating in parallel forms the circuit.
If the coupling group and variable ratio are equal, you can ensure that there is no loop in this loop.
A small secondary voltage difference will also cause a large circulation in the return road, so the ratio allows only a very small deviation (0.5 to 1)%
It is inevitable that there will be a phase difference due to the different phase of the secondary voltage of two transformers with different connection groups.
When the output current of each transformer running in parallel is in phase, the output current of the entire parallel group can be maximized, and the installed capacity of each transformer can be fully utilized.
Impedance voltage is equal to the short-circuit impedance per unit value, in the case of the same current phase, the distribution of each transformer current is inversely proportional to its impedance.
IA / IB = ZKB / ZKA
(SA / SAN) = (UNIA) / (UNIAN) = IA / IAN
(SB / SBN) = (UNIB) / (UNIBN) = IB / IBN
(SA / SAN): (SB / SBN) = (IAIBN / IBIAN)
= (ZKBIBN / ZKAIAN) = (uKB * UN) / (uKA * UN)
= (1 / uKA) :( 1 / uKB)
So: (SA / SAN): (SB / SBN) = (1 / uKA): (1 / uKB)
If uKA ≠ uKB, a transformer with a lower impedance voltage reaches full load first, which limits the total capacity of the entire parallel group.
General provisions of the parallel operation of the transformer impedance voltage difference does not exceed 10%.
Transformer loss in operation itself, the more parallel, the greater the loss. The number of transformers should be adjusted according to the user's load changes in the actual operation.
(1) When the load drops to a certain extent, it is more economical to cut off a transformer
(2) When the load increases to some extent, it may be more economical to invest in one.
