Autotransformer - tanmakihenatsuki (English spelling) autotransformer

Japanese: 単巻変圧器 - たんまきへんあつき（英語表記）autotransformer

A transformer with only one winding wound around an iron core. It is also called an autotransformer. One terminal on the low voltage side is connected to one terminal on the high voltage side and is integrated, and the other terminal is pulled out from the middle of the high voltage winding. If the number of turns on the high voltage winding _is n1 and the number _of turns on the low voltage winding is n2 (ignoring slight errors), the relationship between the high voltage side voltage V1 _and the low voltage side voltage V2 is _as follows:

A part of the high-voltage winding is shared with the low-voltage winding, but the current in this part is smaller than the low-voltage side current because the high-voltage side current and the low-voltage side current cancel each other out. For this reason, it requires less material and is smaller than a normal two-winding transformer for the same capacity. However, it is not generally used because there is a risk that abnormally high voltage from the high-voltage side will directly penetrate into _the low-voltage side. The closer n1 and n2 are to _each other, the less of a problem this abnormally high voltage is, and the effect of miniaturization due to the cancellation of the currents on the high-voltage and low-voltage sides is also greater. For this reason, it is often used in voltage regulating transformers. It is also used as an interconnection transformer between directly grounded systems with different voltages, and is widely used in compensating current transformers for adjusting the turn ratio of current transformers and in transformers in television and radio receivers.

[Masami Okamura and Yoshifumi Oura]

[Reference item] | Transformer

Circuit diagram of an autotransformer
©Shogakukan ">

Circuit diagram of an autotransformer

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

鉄心に巻かれた巻線が1個だけの変圧器。オートトランスともいう。低圧側の1端子は高圧側の1端子と接続されて一体となっており、他の端子は高圧巻線の途中から引き出されている。高圧巻線の巻回数をn₁、低圧巻線の巻回数をn₂とすれば（若干の誤差を無視すれば）、高圧側電圧V₁と低圧側電圧V₂の関係は、

となる。高圧巻線の一部は低圧巻線に共用されているが、この部分の電流は高圧側電流と低圧側電流が打ち消しあうので低圧側電流より小さくなる。このため二巻線の普通の変圧器よりも、同じ容量に対して材料も少なく、小型ですむ。しかし、高圧側からの異常高電圧が直接低圧側に侵入するおそれがあるため、一般的には使用されない。n₁とn₂が接近するほどこの異常高電圧の問題が少なくなるし、高圧側と低圧側の電流の打ち消しによる小型化の効果も大きくなる。このため電圧調整変圧器には多く採用される。また、電圧を異にする直接接地系統間の連系変圧器としても使用されるほか、変流器巻数比を調整するための補償変流器およびテレビジョンやラジオ受信器内の変圧器などに広く採用されている。