There are two types of the transformer tap changer which are listed below.
- No-Load Tap Changer (NLTC)
- On-Load Tap Changer (OLTC)
No-load Tap Changer (NLTC)
No-load tap changer (NLTC) is also known as off-circuit tap changer (OCTC) or De-energized Tap Changer (DETC). It does not operate when the transformer is connected to the load. Transformer must have to be disconnected from the load before it is operated to change the turn ratio to make voltage adjustment. It is operated manually using a rotary or slider switch.
It usually provided in small, low voltage power transformer and used for seasonal voltage regulation. It is cheapest tap changer. It is used where voltage adjustments are infrequent and the cost-effectiveness of the mechanism is a priority (i.e. smaller distribution transformers, pad-mounted transformers, and dry-type transformers).
On-load Tap Changer (OLTC)
On-load tap changer (OLTC) is also known as on-circuit tap changer (OCTC). It can operate when the transformer is connected to the supply and load i.e transformer is energized. Transformer is not needed to disconnect from the load when it is operated to change the turns ratio. It can regulate the supplied voltage of the load without any interruption of the power supply.
It uses the concept to make before break contact using bridging mechanism with a resistance and reactor to limit circulating current during switching. It's contact is made with two taps. An adjacent tap is bridged before breaking contact with the load carrying tap for transferring the load from one tap to another tap without interrupting the load current.
It is almost provided in all large, high voltage power transformer and can be used for daily and short period voltage regulation. It is more expensive and complex. It's tap can be placed either internally in the main tank or separately sealed in a oil-filled compartment.
It provides continuity to the system and reduces power outage during the voltage adjustment. It is operated either with a motor, manually or remote control. It has provided with a handle for manual operation for the emergency.