OLTC (On-Load Tap Changer) — Transformer Glossary

Mechanical device that adjusts the transformer's turns ratio while energised and under load, allowing voltage regulation without interrupting supply.

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OLTC (On-Load Tap Changer)

Mechanical device that adjusts the transformer's turns ratio while energised and under load, allowing voltage regulation without interrupting supply.

OLTCs typically provide ±10% voltage adjustment in 16–32 steps. Major manufacturers include MR (Maschinenfabrik Reinhausen), ABB, and Huaming. The OLTC operates by making a new tap connection before breaking the existing one, using resistive or reactive transition elements to limit circulating current. Modern OLTCs in vacuum technology require less maintenance. OLTCs have a defined number of operations (typically 300,000–500,000) before overhaul. Oil contamination from OLTC switching is managed by a separate oil compartment.

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Where this term matters in the ETS portfolio.

transformersEHV Power TransformersExtra high voltage power transformers for transmission grids, generation step-up, and interconnection applications at 220–400 kV.

transformersMedium Power TransformersMedium power transformers for sub-transmission, industrial, and generation applications.

transformersGenerator Step-Up TransformersGenerator step-up transformers for power plants, connecting generators to the transmission grid at elevated voltage levels.

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Voltage RegulationThe percentage change in secondary voltage from no-load to full-load, expressed as a percentage of the rated secondary voltage.

Nominal VoltageThe designated voltage of a power system or equipment, used as a reference value for the system's operating voltage.