Understanding Tap Changers: Enhancing Transformer Performance

In the world of electrical engineering, tap changers play a crucial role in optimizing the operation of transformers. Tap changers allow for adjustments to the transformation ratio of a transformer, thereby regulating voltage levels. This adjustment can be categorized as either de-energized or on-load tap changing, each with its own design considerations and operational implications.

De-energized tap changers require the transformer to be switched off before adjustments can be made. Typically, these tap changers feature a regulation range of ±5% across two steps. The placement of tap sections is strategic, often situated at the midpoints or quarter heights of the high voltage winding to minimize transient voltages in the tapping zone. However, when taps are off-circuited, the current flow in the connected winding portion ceases, potentially leading to imbalances in ampere-turns and higher axial forces during short-circuit conditions.

On-load tap changers, in contrast, allow for adjustments without interrupting the power supply. This is particularly advantageous in applications requiring continuous voltage regulation. The regulation range for on-load tap changers is broader, often reaching ±10 to 20% with multiple taps, making them suitable for larger transformers. To optimize design and economic factors, it's advisable to position the tap winding near the neutral point in wye-connected systems, where insulation levels can be minimized.

Design considerations for tap changers extend beyond placement. For both wye and delta-connected windings, ensuring that tap windings experience less transient voltage is essential to reduce short-circuit forces and potential heating. Engineers often select between two types of tap windings: a single winding offering multiple voltages or a combination of coarse and fine tap windings, catering to varying transformer sizes and voltage levels.

Despite these advancements, voltage deviations are still a possibility, necessitating increased excitation to achieve required voltage levels at high voltage terminals. This involves raising the core's flux density, a factor that should be assessed during the design phase. Understanding the calculations and influences on voltage regulation is critical for engineers working with transformers, ensuring optimal functionality and safety in electrical systems.