AUTO TRANSFORMER
Auto transformer
Auto transformer
An auto transformer has
one winding that is tapped at some point along the winding. Voltage is applied
across a portion of the winding, and a higher (or lower) voltage is produced
across another portion of the same winding. The equivalent power rating of the
auto transformer is lower than the actual load power rating. It is calculated by:
load VA × (|Vin – Vout|)/Vin. For
example, an auto transformer that adapts a 1000 VA load rated at
120 Volts to a 240 Volt supply has an equivalent rating of at least:
1,000VA × (240V – 120V) / 240V = 500VA.
However, the actual rating (shown on the tally plate) must be at least
1000 VA.
For voltage ratios that don't exceed about 3:1, an
auto transformer is cheaper, lighter, smaller, and more efficient than an
isolating (two-winding) transformer of the same rating.[2] Large
three-phase auto transformers are used in electric power distribution systems,
for example, to interconnect 33 kV and 66 kV sub-transmission
networks.