What is tap Changer in transformers. What is an on-load tap changer and why is OLTC installed on the high voltage side of the transformer? ~~~A tap changer is a device fitted to transformers to allow for variable turns ratios to be selected in steps. This enables voltage regulation and control of the transformer output. Tap changers can be manual or automatic, and they adjust the transformer's turns ratio to either step up or step down the voltage as needed. Manual tap changer is called offload