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Power transformers tap changers are used to adjust the transformer's voltage ratio. They enable fine-tuning of the output voltage to match the required level, compensating for fluctuations in the power system or varying load conditions. There are two primary types of tap changers: on-load tap changers (OLTC) and No-load tap changers (NLTC).

On-Load Tap Changers (OLTC): 

These tap changers allow the adjustment of transformer taps while the transformer is still energized and supplying power to the load. OLTCs are further classified into:

1. Oil-Immersed Type: The mechanism is submerged in the transformer's insulating oil, which helps with cooling and arc extinction during tap changes.

2. Vacuum-Type: Uses vacuum interrupters to extinguish the arc when changing taps, providing a cleaner and more reliable operation with less wear and tear.

No-Load Tap Changers: 

No-load tap changers (NLTC), also known as de-energized tap changers (DETC), and off-load tap changers, off-circuit tap changers (OCTC), employ manually operated switching equipment that changes the transformer turns ratio of the three phases simultaneously and by the same amount. The tap changers can only be operated when the transformer is not under load or has been disconnected from the power source. They are simpler in design and less expensive than OLTCs but require the transformer to be out of service during the adjustment, making them less flexible for continuous voltage regulation needs.

The primary function of tap changers is to maintain the desired voltage levels in the power grid, ensuring efficient power transmission and distribution. This is particularly important because voltage fluctuations can cause problems for sensitive equipment, reduce power quality, and lead to energy losses. By adjusting the transformer's turns ratio, tap changers help keep the voltage within acceptable limits, thereby improving overall system stability and efficiency.

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