There are fans rotating at very high speed near to fins (used to increase the surface area). Tap changing mechanism is provided for maintaining the secondary voltage constant with varying primary voltage. Tap changing causes change in leakage reactance, core loss, 12R loss etc. the tap changing means changing the turns ratio. The tapings are provided on the HV side so that it carries minimum current. Tank is welded construction. It is stiffened by structured steel.
It is provided with 2F earth terminals. HV and LV bushings are transported in crates. Conservator is a cylindrical tank divided into 2 chambers -one for the main tank and other for OLTC. The function of the main conservator is to keep the main tank completely filled with oil. OLTC is fitted with an oil sight window. Explosion vent has a bursting plate and is used as a safety device. When the internal pressure of transformer increases by abnormal phenomenon the diaphragm bursts. In latest models this is replaced by a pressure release valve.
Breather: When transformer becomes warm, the oil and gas expands. The gases at the top of the oil expel out and air is drawn into the ransformer. This process is called breathing. The air entering is made moisture free by letting it to pass through the breather. It consists of a small container with silica gel crystal. The material is blue when dry and whitish when damp. At the bottom of the container some oil is present along with aluminum silicate in order to absorb dust particles. There are 2 breathers, one for the main conservator tank and the other for OLTC.