The transformer does not itself perform the complete AC-to-DC conversion. Instead, it acts as the essential AC power source for the rectifier equipment. In a typical installation, electrical power enters the primary side of the transformer at a medium- or high-voltage level. The transformer reduces the voltage to a suitable level for the rectifier. The rectifier then processes the secondary-side AC power and produces DC power for the connected industrial load. This arrangement allows the voltage, current, isolation, and phase relationships to be engineered according to the requirements of the complete electrical system.
Rectifier transformers are available in several configurations depending on the rectifier technology and application. Some designs have a single secondary winding, while others contain multiple secondary windings. Multiple secondary windings can provide phase-shifted supplies to multipulse rectifier circuits. These configurations can help reduce Single Phase Pole Mounted Transformer harmonic components in the input current and improve the overall performance of the electrical installation. The number of phases, pulse arrangement, voltage level, current rating, and required phase displacement are therefore important considerations during transformer specification.
A six-pulse rectifier is one of the common configurations supplied by rectifier transformers. In this arrangement, three-phase AC power is transformed and supplied to a six-pulse rectifier bridge. The resulting DC output is suitable for many industrial applications. However, six-pulse systems can generate significant characteristic harmonics on the AC side. Where harmonic performance is especially important, engineers may use twelve-pulse, twenty-four-pulse, or other multipulse arrangements. These systems typically require specially designed transformer secondary windings with appropriate phase shifts.
A twelve-pulse rectifier transformer configuration generally uses two secondary supplies with a suitable phase displacement. The outputs are connected to two six-pulse rectifier bridges, creating a combined twelve-pulse rectification system. This arrangement can significantly reduce certain lower-order harmonics compared with a basic six-pulse system. The transformer therefore plays an important role in the harmonic performance of the complete electrical installation. Correct winding design and phase displacement are essential for achieving the intended rectifier characteristics.