Transformer is an important power equipment in the power system, which generally runs for a long time. In order to make the transformer run safely and economically and improve the reliability of operation, generally two or more transformers are run in parallel.

The parallel operation of transformers is a complex calculation process, and its essence is to increase the total capacity of the transformers. However, when the transformers are operated in parallel, it is not simply to connect the secondary side to one piece. Before parallel operation of transformers, be sure to carefully check the nameplates of the transformers to see if they meet the basic conditions for parallel operation. The conditions for parallel operation of transformers are:

1. The wiring group is the same.

2. The transformation ratio is the same, and the difference does not exceed ±0.5.

3. The short-circuit voltage is the same, and the difference does not exceed ±10.

4. The capacity ratio of the two transformers should not exceed 3:1.

The parallel operation of the transformer is the parallel operation of the "power supply", and its complexity is far greater than the parallel operation of the load. If the transformers do not meet the parallel conditions and are forcibly connected in parallel, there will be a large "circulation" between the two transformers, which not only wastes electricity, but also brings great potential safety hazards.

In addition, when the transformers are operated in parallel, since their impedances are connected in parallel, the total impedance will be reduced, and the short-circuit current of the system will be greatly increased, which puts forward higher requirements for the selection of upstream switchgear. should have been considered.

If the original systems are not running in parallel, for example, the power systems of most enterprises are single-bus segmented wiring, as shown in the figure below, in general, from the equipment management level, the two incoming switches H2 and H3 are closed. Under the circumstance, the sectional switch H1 is not allowed to close, which is generally stipulated in the power supply contract signed by the enterprise and the power supply company. However, from a technical point of view, when the two incoming switches H2 and H3 are closed, the sectional switch H1 can be closed. This operation realizes the undisturbed switching of the operating load, but the three switches are closed at the same time. The time should be shortened as much as possible. After confirming that H1 is successfully closed, H2 or H3 should be opened as soon as possible.

Of course, in order to make the transformer run safely and economically and improve the reliability of power supply, two or more transformers are often used in parallel. The significance of parallel operation of transformers is as follows:

1. When a transformer fails, the differential protection of the transformer will trip the high and low voltage side switches of the transformer to cut off the transformer, while other transformers running in parallel can continue to operate to ensure the continuity of power consumption by users.

2. When the transformer is undergoing preventive test or maintenance, it can be removed from the parallel system, and the rest of the transformers can bear all the power load, which not only ensures the planned maintenance of the transformer, but also ensures the uninterrupted power supply of the load. Reliability of system power supply.

3. Increase the capacity of the power grid and facilitate dispatching. We know that the seasonality of electricity load is very strong. Generally, the load is relatively large in summer, and the electricity load is relatively small in winter. In this way, when the load is small in winter, the partially running parallel transformer can be withdrawn, which reduces the no-load loss caused by the operation of the large-capacity transformer and improves the efficiency of the entire power grid.

For example, the peak load of a power supply grid requires a 40000KVA transformer. If a 50000KVA transformer is selected, the transformer needs to operate normally at all times. If the transformer fails, it will affect the normal power consumption of all equipment downstream of the transformer, and it will cause huge losses and even safety accidents to some power-consuming departments that are not allowed to cut off power. For example, the data storage device in the big data room. Moreover, when the load is reduced in winter, the phenomenon of a large horse-drawn trolley will appear in the transformer. If three 25000KVA transformers are used in parallel operation, one transformer can be cut off when the load is small, so as to reduce the no-load loss and reactive load expenses of the transformer, and at the same time greatly improve the power supply reliability of the power system.