Solution for zero-line burning of three-phase transformer

The three-phase transformer has a zero-line blow, and the internal reasons are: quality defect, excessive neutral current; external zero line: poor contact (not firmly crimped or aluminum-copper crimped electrification reaction leads to increased contact resistance), load Unbalance leads to a large zero current, which causes the contact in poor contact to continue to heat up, the contact resistance is further increased, and the heat is more serious.

Under normal conditions (three-phase balance), there should be no current on the zero line of the transformer. Even in the case of normal distributed load, even if there is a certain imbalance, the current on the zero line should be small. Based on this, The cross-sectional area of ​​the zero line is smaller than that of the fire line. In the past, 30% of the section of the fire line was generally selected. Now with the increasing load of the type, the cross section of the subscriber line is getting larger and larger. Now the user is required to enter the line of 6 square copper wire. This makes the load of different users different after entering the household, so now the general zero line is 60% of the fire line. For example, the type of a cable is 3*16+1*10.

To solve the zero-line burn, the clamp-type ammeter should be used first. There is no zero-sequence current. If it is indeed larger than the current-carrying flow of the zero-line section, consider increasing the zero-line cross section on the one hand, but it is more important to adjust the load distribution. As for the blow caused by the single-phase short circuit, it is sufficient to find the short-circuit point.