Working principle and wiring method of power transformer

The high-voltage windings used in domestic transformers are generally connected to the Y connection method, and the connection of the medium-voltage windings and the low-voltage windings is determined depending on the system conditions. The so-called system condition refers to the relationship between the voltage phasor of a high-voltage transmission system and the voltage phasor of a medium-voltage or low-voltage transmission system. For example, a low-voltage distribution system can be determined according to standard regulations. The high voltage winding is often connected to the Y connection because the phase voltage can be equal to 57.7% of the line voltage, and the voltage per volt of the AC transformer can be lower.

1). The voltage phasors of domestic 500, 330, 220 and 110kV transmission systems are all in phase, so for the three-phase three-winding or three-phase autotransformer of the following voltage ratio, the high voltage and medium voltage windings must be Use star connection. When the three-phase three-iron core structure is used, the low-voltage winding can also adopt the star connection method or the angle connection method, which determines that the voltage phasor of the low-voltage transmission system is in phase or lag with the voltage phasor of the medium-voltage and high-voltage transmission systems. 30° electrical angle.

500/220/LVkV-YN, yn0, yn0 or YN, yn0, d11

220/110/LVkV-YN, yn0, yn0 or YN, yn0, d11

330/220/LVkV-YN, yn0, yn0 or YN, yn0, d11

330/110/LVkV-YN, yn0, yn0 or YN, yn0, d11

2). There are two different phase angles for the domestic 60 and 35kV transmission system voltages.

For example, the 220/60kV transformer adopts the YNd11 connection method, and the 220/69/10kV transformer uses the YN, yn0, and d11 connections. The two 60kV transmission systems differ by 30° electrical angle.

When the 220/110/35kV transformer adopts YN, yn0, and d11 connection, the 110/35/10kV transformer adopts YN, yn0, and d11 connection methods. The voltage phasors of the above two 35kV transmission systems are also 30° electrical angle.

Therefore, it is necessary to be cautious when deciding the connection of 60 and 35kV windings. The connection must meet the requirements of the voltage phasor of the transmission system. The connection between the 60 and 35kV windings is determined by the relative relationship of the voltage phasors. Otherwise, even if the capacity is correct, the voltage ratio is correct, the transformer cannot be used, the connection is incorrect, and the transformer cannot be connected to the transmission system.

3). Domestic 10, 6, 3 and 0.4kV transmission and distribution system phasors also have two phases. In Shanghai, there is a 10kV and 110kV transmission system voltage phase difference of 60 ° electrical angle, this time can use 110 / 35/10kV voltage ratio and YN, yn0, y10 connection three-phase three-winding power transformer, but limited Three-phase three iron core column core.

4). However, it should be noted that when the single-phase transformer is connected to the three-phase combination method, the three-phase group of the YNy0 connection cannot be used. Three-phase shell transformers cannot also use the YNy0 connection.

The three-phase five-column core transformer must adopt YN, yn0, yn0 connection method, there must be a fourth winding connected to the angle connection in the transformer, and its output is not led out (the structure is not in the electrical test. This example).

5). When the transformers of different junction groups are operated in parallel, the general rule is that the linkage group labels must be the same.

6). When the distribution transformer is used in the multi-mine area, the Yzn11 connection method can be used. When the z-connection method is adopted, the impedance voltage algorithm is different from the Yyn0 connection method, and the z-connection winding has more copper consumption. The lightning protection performance of the low-voltage transformer Yzn11 connection distribution transformer is better.

7). When the three-phase transformer adopts four coil core frames, the YNy0 connection cannot be used.

8). All of the above are used for the connection of domestic transformers. For export, the appropriate connection and connection group labels should be supplied as required.

9). Generally, there are taps in the high voltage winding connected to the tap changer. Therefore, when selecting the tap changer (including the on-load tap-changer and the off-circuit tap-changer), it must be noted that the transformer connection is matched with the tap-changer connection (including connection, test voltage, rated current, per Stage voltage, voltage regulation range, etc.).