Tap Changers helps us to regulate the output of a transformer by changing the turns ratio. We can change the turns ration by changing the tapping of a transformer.
There are two different methods to change the tapping of a transformer, those are Open Circuit Tap Changer (OCTC) and On Load Tap Changer (OLTC).
Open Circuit Tap Changer (OCTC): To change the tapping of a transformer, we have to first disconnect the transformer from the circuit/grid and then we can change the tap manually. In this manner, the load gets disconnected for some time.
On Load Tap Changer (OLTC): In this method, a close loop mechanism is connected to the tapping. The input voltage is sensed by using a feedback system and according to it, the tapping are changed (to keep the output constant) by using a motor without disconnecting the load. All these mechanisms are fully automatic. But the tapping are changed when the transformer is online so there will be sparking during the change. So to quench the spark we have to use some medium. We use the same transformer oil for this. That is why the oil tank of a power transformer is divided into two parts one for Core Coil Assembly (CCA) and one for On Load Tap Changer (OLTC).
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