ELECTRICAL ENGINEERING
Star-delta starting
A suitable three-phase motor starts with a lower winding voltage in star and then switches to delta.
INTERACTIVE EXAMPLESIMULATION
The principle
In star, each winding on a balanced three-phase supply receives the line voltage divided by √3. Following a switching pause, delta applies the full line voltage to each winding. Starting torque in star is roughly one third of direct delta starting under comparable conditions.
An example
With 400 V line voltage, each winding receives about 231 V in star and 400 V in delta. Step through the sequence.
Important
This requires six accessible motor terminals and a motor rated for delta operation at the supply voltage. Star and delta contactors must never close together; interlocking and proper protection are essential.