Definition
A dry-type transformer uses air, and often cast-resin or varnish-impregnated solid insulation, as its cooling and insulating medium instead of liquid. With no flammable oil inside, it carries far lower fire and spill risk, which makes it the default choice for indoor and occupied spaces. Building and fire codes frequently require dry-type units inside structures where an oil fire would endanger people or property.
Trade-offs versus liquid-filled units
Air is a far poorer conductor of heat than insulating oil, so dry-type transformers shed heat less efficiently and are generally limited to lower voltage classes, typically up to around 35 kV, and somewhat lower power ratings than comparable liquid units. In exchange they need minimal maintenance: there is no oil to sample, filter, or test for dissolved gas, and there is no containment berm or fire wall to build. They tolerate dusty, humid, or chemically aggressive environments well when properly enclosed, and they pose no soil or water contamination risk if damaged.
Where they fit in mining
For a containerized or in-building hashcenter, a dry-type unit stepping medium voltage down to the 415V or 600V three-phase used by mining PDUs keeps the fire load low and simplifies permitting in occupied or tightly spaced sites. Larger outdoor sites often still favor liquid units for their thermal headroom.
Compare the higher-capacity, fire-hazard alternative in oil-filled transformer, and note that either type may carry an on-load tap changer for voltage regulation.
In Simple Terms
A dry-type transformer uses air, and often cast-resin or varnish-impregnated solid insulation, as its cooling and insulating medium instead of liquid. With no flammable oil…