Transformers 67
Low-voltage
output
High-voltage
input
Core
High-voltage
winding
Low-voltage
winding
Figure 5.6
secondary wires would not receive an electric shock since there is
nowhere for currents which would flow through the body to return
to.
4 Electric arc welding. The primary is often connected across
two lines of a three-phase supply and so is at 415 V. The secondary
provides an output at between 90 V and 110 V when no welding is
taking place. This falls to about 25 V once the arc is struck. The use
of two lines for the input spreads the load over two phases of the
supply. Where several welders are used they should not all be con-
nected to the same two lines.
THE THREE-PHASE
TRANSFORMER
Three-phase transformers are essentially three single-phase trans-
formers wound on a single core. The windings are of concentric or
pancake type. The windings are arranged on a laminated iron