Definition
An on-load tap changer (OLTC) is a switching device built into a power transformer that adjusts the transformer's turns ratio in discrete steps while the unit stays energized and carrying load. By adding or removing winding turns, usually on the high-voltage side, the OLTC changes the output voltage without ever interrupting power flow, acting as a built-in automatic voltage regulator.
How it differs from off-circuit taps
Smaller transformers use off-circuit (de-energized) tap changers that require a shutdown to adjust. An OLTC instead uses a diverter switch and transition impedance so it can move between taps without open-circuiting the winding or short-circuiting adjacent taps, all under load. Control is typically automatic: an automatic voltage control relay senses output voltage and drives the mechanism up or down to hold a target. A typical OLTC offers a regulation range on the order of plus or minus 10 to 16 percent, divided into roughly 16 to 32 steps.
Relevance to large mining sites
A high-density hashcenter is a heavy, sometimes variable load fed from a medium-voltage service. As miners switch on in blocks, feeder voltage sags; an OLTC on the site transformer holds the secondary voltage in band so ASIC power supplies stay within spec and efficiency does not drift. The trade-off is mechanical: tap changers have moving contacts that wear and need periodic maintenance, and they are a leading source of transformer faults.
The OLTC lives inside the site step-down unit, see oil-filled transformer for the large outdoor units that usually carry one, and dry-type transformer for the indoor alternative.
In Simple Terms
An on-load tap changer (OLTC) is a switching device built into a power transformer that adjusts the transformer’s turns ratio in discrete steps while the…