Briefly introduce the grades and connections of dry-type transformers

There are various connection levels for dry-type transformers, and the structures and connection methods employed differ as well. So, what are the different levels of dry-type transformers? And how are they connected? Perhaps a brief introduction from the editor of a dry-type transformer manufacturer would be helpful.   

dry-type transformer

The connection symbol for the dry-type transformer indicates the wiring method as follows: an uppercase English letter denotes the wiring method of the primary side (or primary winding), while a lowercase English letter indicates the wiring method of the secondary side (or secondary winding). Y (or y) denotes star wiring, and D (or d) denotes delta wiring.   

The data information is presented in a clock-like format to illustrate the phase angle relationship between the primary and secondary side operating standard voltages. The primary side operating standard voltage phasor is used as the hour hand, fixed at the 12 o’clock position on the clock, while the secondary side DC voltage phasor serves as the second hand.   

“Yn, d11” indicates that when the primary side operates at the standard voltage phasor, which is represented by the hour hand pointing to 12 o’clock on a clock, the secondary side’s DC voltage phasor is at the 11 o’clock position on the alarm clock. In other words, the secondary side’s DC voltage Uab lags behind the primary side’s operating standard voltage UAB by 30 degrees (or is 30 degrees ahead).   

The two windings of a dry-type transformer constitute four wiring levels: “Y, y”, “D, y”, “Y, d”, and “D, d”. In China, only “Y, y” and “Y, d” are used. When Y is connected, there are two types: with and without a neutral point. If there is no neutral point, no additional identification is provided. If there is a neutral point, an “n” is added after the English letter Y to indicate it. “n” represents that the neutral point has a transformer wire connection. For the Yn0 wiring level, when UAB and uab coincide, both the hour and minute hands point to 12. In the new wiring level, “12” is indicated by “0”