Why power transformer's oil tank has sections?

The oil tank of a power transformer is divided into two parts i.e. one part is of 70% of the whole capacity and the other part is of 30% of the whole capacity. The 70% part is for the transformer winding and core, and the 30% part is for On Load Tap Changer (OLTC). As the OLTC works by moving the connections when is transformer is on load, so it will create spark and probably will heat up. So there is dedicated section in the oil tank specially for OLTCs.

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