Transformers are the most important electrical equipment in power systems and are generally operated for long periods of time. In order to make the transformer safe and economical to operate and improve the reliability of operation, two or more transformers are generally operated in parallel.
The parallel operation of the transformer is a complicated calculation process, and its essence is to increase the total capacity of the transformer. However, when the transformers are operated in parallel, it is not easy to connect the secondary side to one. Before the transformers are operated in parallel, be sure to carefully check the nameplate of the transformer to see if it meets the basic conditions for parallel operation. The conditions for the parallel operation of the transformer are:
1. The wiring group is the same.
2. The 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 does not exceed 3:1.
Parallel operation of the transformer is a 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 power, but also brings great safety hazards.
In addition, when the transformers are running in parallel, since their impedances are connected in parallel, the total impedance will decrease, the short-circuit current of the system will be greatly increased, and the selection of the upstream switching equipment will be higher. This problem is in design. It should have been considered.
If the original system is not running in parallel, for example, most enterprises' power systems are single busbar segmentation wiring. In general, from the device management level, when both incoming switches H2 and H3 are closed, segmentation The switch H1 is not allowed to be closed, and is generally stipulated in the power supply and contract contract signed by the enterprise and the power supply company. However, from a technical point of view, in the case where both 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 simultaneously closed. The time should be as short as possible. After confirming that H1 is closed successfully, it is necessary to open H2 or H3 as soon as possible.
Of course, in order to make the transformer safe and economical, and to improve the reliability of the power supply, two or more transformers are often used in parallel. The significance of parallel operation of transformers is:
1. When a transformer fails, the transformer differential protection action will jump 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 the user's power consumption.
2. When the transformer is subjected to preventive test or overhaul, it can be removed from the parallel system, and the rest of the transformer will 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. The reliability of the system power supply.
3. Improve the capacity of the grid and facilitate scheduling. We know that the seasonality of the electrical load is very strong, generally the load is relatively large in summer, and the electrical load is small in winter. In this way, when the load in winter is small, the parallel transformer that is partially operated can be exited, 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, a peak load of a power supply network requires a transformer of 40000 KVA. If a transformer of 50000 KVA is selected, the transformer needs to operate normally at any time. If the transformer fails, it will affect the normal power consumption of all the equipment downstream of the transformer. For some power users that do not allow power to be cut off, it will cause huge losses and even cause safety accidents. For example, the data storage device of the big data room. Moreover, when the load is reduced in winter, the transformer will have a large horse-drawn carriage. 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 of the transformer, and greatly improve the power supply reliability of the power system.
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