Starting-methods race

DOL, star-delta, autotransformer, soft starter and VFD on the same motor and load.

Lesson: Starting methods

Try it: the starting-methods race

Load torque at full speed60 N·m

Inertia J0.40 kg·m²

Autotransformer tap65 %

Soft-starter initial voltage40 %

Direct on line
Star-delta
Autotransformer
Soft starter
VFD

Direct on line: 5.4× · 0.48 s
Star-delta: 3.7× · 1.66 s
Autotransformer: 3.7× · 1.22 s
Soft starter: 3.0× · 1.92 s
VFD: 0.9× · 4.63 s

Each value: peak line current as a multiple of full-load current (I_n = 19.3 A), then time to reach 90 % speed. Star-delta and autotransformer change over at 80 % speed, or after 6 s at the latest. Soft starter ramps from its initial voltage to 100 % in 4 s; VFD ramps 0 to 50 Hz in 5 s.